BH13

UNITED STATES DEPARTMENT OF COMMERCE

ELIMINATION OF WASTE SERIES

RECOMMENDED

MUM REQUIREMENTS

FOR PLUMBING

REPORT OF

SUBCOMMITTEE ON PLUMBING OF THE

BUILDING CODE COMMITTEE

BUREAU OF STANDARDS

UNITED STATES. GOVERNMENT PRINTING OFFICE

WASHINGTON

- , 1923

UNITED STATES DEPARTMENT OF COMMERCE

WILLIAM F. WHITING, SECRETARY ELIMINATION OF WASTE SERIES

RECOMMENDED

MINIMUM REQUIREMENTS

FOR PLUMBING

REPORT OF

SUBCOMMITTEE ON PLUMBING OF THE

BUILDING CODE COMMITTEE

REVISED AUGUST 30, 1928 GEORGE C. WHIPPLE, Chairman

HARRY Y. CARSON AUGUST E. HANSEN

WILLIAM C. GROENIGER J. L. MURPHY

JOHN M. GRIES, Chief Division of Building and Housing

GEORGE N. THOMFSON, Secretary R. B. HUNTER, In Charge of Tests

BUREAU OF STANDARDS

PRICE 35 CENTS

Sold only by the Superintendent of Documents, U. S. Government Printing Office Washington, D. C.

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON

3929
PREFACE

This report is a revision of a former report dated July 3, 1923,

entitled “ Recommended Minimum Requirements for Plumbing in

Dwellings and Similar Buildings.” The basic principles of the

former report are retained, but their application is extended to all types of buildings, n
CONTENTS

PART I—INTRODUCTION—GENERAL CONSIDERATIONS

Page Mode of procedure 2 Tentative report 3 Revision of final report 4 Local conditions 4 Acknowledgment 4 Chapter 1.—Regulation of plumbing 5 Definition of plumbing 5 Relation of plumbing to health 5 Public control of plumbing justifiable 7 Legal principles 8 Chapter 2.—Present status of plumbing regulations _ 11 Supervision of plumbing inspection 12 Conclusions based on scientific procedure 12 Chapter 3.—Basic plumbing principles 13 PART II. CHAPTER 4—RECOMMENDED PLUMBING CODE

Article I.—Definitions of terms 18

Sec. 1. Plumbing 18

Sec. 2. Plumbing system 18

Sec. 3. Water-service pipe 18

Sec. 4. Water-distribution pipes 18

Sec. 5. Plumbing fixtures 18

Sec. 6. Trap 18

Sec. 7. Trap seal 18

Sec. 8. Vent pipe 18

Sec. 9. Local ventilating pipe 18

Sec. 10. Soil pipe 18

Sec. 11. Waste pipe and special waste 18

Sec. 12. Main 19

Sec. 13. Branch 19

Sec. 14. Stack 19

Sec. 15. House drain 19

Sec. 16. House sewer 19

Sec. 17. Size and length 19

Sec. 18. Dead end 19

Article II.—General regulations 20

Sec. 19. Grades of horizontal piping_ 20

Sec. 20. Change in direction 20

Sec. 21. Prohibited fittings 20

Sec. 22. Dead ends 20

Sec. 23. Protection of material 20

Sec. 24. Workmanship 20

Sec. 25. Installation of plumbing by owner 20 in
IV CONTENTS

Page

Article III.—Quality and weights of materials 21

Sec. 26. Materials, quality of 21

Sec. 27. Label, cast or stamped- 21

Sec. 28. Vitrified clay pipe 21

Sec. 29. Cast-iron pipe 21

Sec. 30. Wrought-iron pipe 21

Sec. 31. Mild-steel pipe 21

Sec. 32. Brass and copper pipe * 21

Sec. 33. Lead pipe, diameter, weights 21

Sec. 34. Sheet lead 22

Sec. 35. Sheet copper or brass 22

Sec. 36. Galvanized sheet iron 22

Sec. 37. Threaded fittings 22

Sec. 38. Calking ferrules 22

Sec. 39. Soldering nipples and bushings 23

Sec. 40. Floor flanges for water-closets 23

Article IV.—Joints and connections 24

Sec. 41. Water and air-tight joints 24

Sec. 42. Vitrified pipe 24

Sec. 43. Calked joints 24

Sec. 44. Screw joints 24

Sec. 45. Cast iron 24

Sec. 46. Wrought iron, steel, or brass to cast iron 24

Sec. 47. Lead pipe 24

Sec. 48. Lead to cast iron, steel, or wrought iron 24

Sec. 49. Slip joints and unions 24

Sec. 50. Roof joints 24

Sec. 51. Closet, pedestal urinal and trap standard slop sink, floor connections 24

Sec. 52. Increasers and reducers 25

Sec. 53. Prohibited joints and connections 25

Sec. 54. Expansion bolts 25

Sec. 55. New materials 25

Article V.—Traps and clean outs 26

Sec. 56. Traps, kind and minimum size 26

Sec. 57. Traps, prohibited 26

Sec. 58. Traps, where required 26

Sec. 59. Water seal 26

Sec. 60. Trap clean outs 26

Sec. 61. Trap levels and protection 27

Sec. 62. Pipe clean outs 27

Sec. 63. Pipe clean outs, where required 27

Sec. 64. Manholes 27

Sec. 65. Clean outs; equivalents 27

Sec. 66. Grease traps 27

Sec. 67. Sand traps 27

Sec. 68. Basement floor drains 27

Sec. 69. Back-water valves 27

Article VI.—Water supply and distribution 28

Sec. 70. Quality of water 28

Sec. 71. Distribution 28

Sec. 72. Water service 28

Sec. 73. Water supply to fixtures 28
CONTENTS V

Article VI.—Water supply and distribution—Continued. Page

Sec. 74. Size of water-supply pipes 28

Sec. 75. Water-supply control 28

Sec. 76. Water-supply pipes and fittings—material 29

Sec. 77. Water-supply protection 29

Sec. 78. Relief valves 29

Sec. 79. Pumps and hydrants 29

Article VII.—Plumbing fixtures 30

Sec. 80. Materials 30

Sec. 81. How installed 30

Sec. 82. Water-closet bowls 30

Sec. 83. Frost-proof closets—where permitted 30

Sec. 84. Fixtures prohibited 30

Sec. 85. Floor drains and shower drains 30

Sec. 86. Fixture strainers 30

Sec. 87. Fixture overflow 30

Article VIII.—Ventilation of rooms and fixtures 31

Sec. 88. Location of fixtures 31

Sec. 89. Ventilating pipe, how connected 31

Article IX.—Soil, waste, and vent pipes 32

Sec. 90. Material 32

Sec. 91. Fixture unit 32

Sec. 92. Soil and waste stacks 32

Sec. 93. Soil and waste stacks, fixture connections 33

Sec. 94. Changing soil and vent pipes 33

Sec. 95. Prohibited connections 33

Sec. 96. Soil and waste pipe protected 33

Sec. 97. Roof extensions 33

Sec. 98. Terminals 33

Sec. 99. Terminals adjoining high buildings 33

Sec. 100. Traps protected, vents 33

Sec. 101. Distance of vent from trap seal 34

Sec. 102. Main vents, to connect at base 34

Sec. 103. Vents, required sizes 34

Sec. 104. Branch and individual vents 35

Sec. 105. Vent-pipe grades and connections 35

Sec. 106. Circuit and loop vents 35

Sec. 107. Vents not required 35

Article X.—House drains and sewers 36

Sec. 108. Independent system 36

Sec. 109. Old house sewers and drains 36

Sec. 110. Connections with cesspools 36

Sec. 111. Excavations 36

Sec. 112. House drains underground 36

Sec. 113. Material 37

Sec. 114. Depth of drains and sewers 37

Sec. 115. Size of drains, sewers, and horizontal branches 37

Sec. 116. Combined storm and sanitary sewer systems 38

Sec. 117. Plouse sewer in made ground 38

Sec. 118. Drainage below sewer level 38

Sec. 119. Sumps and receiving tanks 38

Sec. 120. Ejectors, vented 38

Sec. 121. Motors, compressors, etc 39

Sec. 122. Ejectors for subsoil drainage 39
VI CONTENTS

Page

Article XI.—Storm-water drains 40

Sec. 123. Drainage of yards, areas, and roofs 40

Sec. 124. Size of gutters and leaders ^ 40

Sec. 125. Inside conductors 40

Sec. 126. Outside conductors 40

Sec. 127. Defective conductor pipes 41

Sec. 128. Vent connections with conductors prohibited 41

Sec. 129. Overflows 41

Sec. 130. Subsoil, foundation, clear water, and absorption tile drains. 41

Sec. 131. Subsoil drains below sewer level 41

Article XII.—Refrigerator, safe, and special wastes 42

Sec. 132. Fixtures permitted to connect 42

Sec. 133. Refrigerator wastes 42

Sec. 134. Overflow pipes and motor exhausts 42

Article XIII.—Maintenance 43

Sec. 135. Defective fixtures 43

Sec. 136. Temporary toilet facilities 43

Article XIV.—Inspections and tests 44

Sec. 137. Inspections 44

Sec. 138. Notification 44

Sec. 139. Material and labor for tests 44

Sec. 140. System tests 44

Sec. 141. Methods of testing 44 () Water test 44 () Air test 45

(c) Final air test 45

Sec. 142. Order of tests 45

Sec. 143. Covering of work 45

Sec. 144. Uncovering of work 45

Sec. 145. Defective work 46

Sec. 146. House sewer and house drain tests ^ 46

Sec. 147. Conductor pipes 46

Sec. 148. Stable and stable-yard drain test 46

Sec. 149. Garage and drainage system 46

Sec. 150. Test of water distribution system 46

Sec. 151. Certificate of approval 46

Sec. 152. Air test of defective plumbing 46

Sec. 153. Inspections and tests not required 46 PART HI.—EXPERIMENTAL INVESTIGATIONS, STANDARDIZATION, AD- MINISTRATION AND COMMENTS

Chapter 5.—Experimental investigations 47 Unit of fixture discharge 48 Water-closets 48 Peak loads in house drainage systems 49

Capacities of house drains 50

Capacities of soil stacks 50

Characteristics of fail of water in partially filled stacks 51 Vent requirements 52 Admission of storm water 52

Running trap 53

Effect of wind blowing over stack tops 54
CONTENTS VII Chapter 5.—Experimental investigations—Continued. Page Frost closure of the stack tops 54 Siphonage of fixture traps 54

Resealing or antisiphon traps 55 Unvented horizontal branch waste pipes 56 Venting of branch wastes 57 Separate trap venting not necessary 57 The 3-inch soil stack 58

Concrete examples of vent requirements 58

Factors of safety 59 Planning for simplicity 59 Chapter 6.—Physics of plumbing systems. Report of experimental and

theoretical investigations 60 Purpose and method of investigations 60 Rates of discharge from plumbing fixtures 63 Apparatus employed 63

Water-closets 73

Interpretation and discussion of results 79

Fixtures, other than water-closets 85 Determination of the peak load in any plumbing system 91 Method of probabilities 91 Overlapping discharges 92 Mixed systems 94

Time factors •_ 94

Capacities of stacks and drains 99 Drains . 99 Stacks 101 Base fittings 103

Characteristics of flow of water in partially filled vertical pipes 104

Spiral flow 105

Velocity of flow 1 105 Vent requirements 109

Pressure effects 110 Pressure effects in a stack-vented system 114

Partial vacuums and vent requirements 115 Back pressures and vent requirements 120

Self-siphonage and vent requirements 122 Modifying conditions 124 Heavy rains 124 Submerged drains 126 House traps 126

Offsets in stacks 127 Winds 127

Frost closure 129

Floor drains 129 Siphonage of fixture traps 129

Self-siphonage 130

Permissible length of unvented horizontal branch waste

pipes 138

Resealing traps 141 Back venting 142 Recommendations „ 146
VIII CONTENTS

Chapter 6.—Physics of plumbing systems—Continued. Page

The factor of safety in a plumbing system and determination of the upper limit of service for a 3-inch soil stack 146 Establishment of a factor of safety 147 Functional factor of safet}^ distinguished from structural 147 Limits of service for a 3-inch soil stack 148

Increased by methods of construction 148

Simplification of plumbing construction 151 Separate floor layouts tested 152

Tests of complete plumbing installations 159

Critical tests 159 Test conditions 161 Notation 163 Test installation No. 1 164

Conclusions 167 Test installation No. 2 168

Test installation No. 3 173

General conclusions 176 Recommended construction details 177 Chapter 7.—Sizes of soil, waste, and vent pipes in plumbing systems 188

Introduction 188 Carrying capacities of vertical cast-iron pipes 188 Estimated peak load in plumbing stacks 191

Permissible number of fixtures on soil and waste stacks 193

Sizes of horizontal drains 194

Sizes of vent pipes 198 Chapter 8.—Standardization of plumbing materials 206

Chapter 9.—Administration 208

The plumbing business 208

Enforcement of plumbing regulations 209

The owner and his agents 209

The plumber 209

Proper administrative authority 209

State plumbing laws 210

Licenses v. certificates of competency 211 Chapter 10.—Explanatory notes and comments 212 Note 1. Data obtained by questionnaire 212 Note 2. Purity of water supply 212 Note 3. Dual sources of water supply 212

Note 4. Adequacy of water supply 213 Note 5. Pressure relief for water-heating apparatus 214 Note 6. Desirability of sewer connections 214 Note 7. Provision of water-closets 214 Note 8. Fixture design 214 Note 9. Velocity of waste water in drainage systems 216 Note 10. Useful life of system 216

Note 11. Limitations to the use of clean outs 217 Note 12. Trapping of fixtures 217 Note 13. Grease-trap requirements 217 Note 14. Air circulation in plumbing 218 Note 15. Simultaneous discharges 218 Note 16. Admission of destructive substances 219 Note 17. Lighting and ventilation of water-closet compartments. A _ 219
CONTENTS IX Chapter 10.—Explanatory notes and comments—Continued. Page Note 18. Sewage disposal 219

Note 19. Omission of the main house trap _ 220 Note 20. Plumbing as related to building design 221 Note 21. Three-inch soil stacks 221 Note 22. Vitrified clay pipe 222 Note 23. Sizes of distribution pipe 222 Note 24. Cast-iron pipe 223 Note 25. Simplification and cost reduction 223

PART IV.—APPENDICES

Appendix A.—Minority report 225

Reply to minority report 226

Appendix B.—Corrosion of metals in plumbing systems 228

1. The rusting of pure iron in pure water 228

2. The effect of nonferrous constituents in the iron 230

3. The effect of substances dissolved in water 231

4. Various conditions affecting the corrosion of iron 233

5. The corrosion of nonferrous metals in water 234

6. The corrosion of different metals in contact 236

7. The corrosion of iron in air 237

Practical considerations 238

Bibliography of corrosion 240

Appendix C.—A study of air currents in a horizontal waste pipe 241

Description of apparatus 242 Eddy currents! 243

Diffusion 244

Carbon dioxide experiments 245 Evaporation of water 249

Convection currents 249

Diffusion of gases through water-seal traps 249

Appendix D.—Standard specifications of the American Society for Testing Materials 253

Clay sewer pipe 253

Cast-iron soil pipe and fittings 263

Welded wrought-iron pipe 266

Welded and seamless steel pipe 270

Brass pipe, standard sizes 274

Copper pipe, standard sizes 277 TABLES

1. Rates of discharge from plumbing fixtures 91

2. Probabilities of overlapping, etc., 1, 2, and 3 hour periods 97

3. Probabilities of overlapping, etc., 2, 3, and 10 hour periods 98

4. Capacities of cast-iron drains, etc 100

5. Capacities of stacks, with fixtures connected direct 103

6. Volume of air transmitted, etc 120

7. Equivalent lengths of pipe in venting capacity, etc 120

8. Length of straight pipe equivalent in resistance to one elbow or tee

of equal diameter 120

9. Lengths of nominally horizontal unvented waste pipes believed

safe, etc - 141
X CONTENTS

Page

10. Assumed simultaneous discharges compared with possible maximum

discharges in typical installations illustrated, etc 160

11. Possible combinations of natural conditions affecting each plumbing

installation, etc 161

12. Approximate capacities of vertical cast-iron pipes 190

13. Stack capacities for one floor or level 191

14. Sizes of soil and waste stacks 194

15. Capacities of horizontal drains in fixture units 198

16. Heights of stack systems 201

17. Length of vent for soil and waste stacks 204

FIGURES

1. Photograph of fixture-rating apparatus facing 62

2. Detailed section of fixture-rating apparatus 63

3. Typical record of discharge-time curve from fixture-rating apparatus facing 63

4. Plotted reproduction of discharge-time curve 64

5. Typical derivative curve for fixture discharge (rate of discharge against

time) 65

6. Experimental system for rating water-closet discharges 67

7-18. Discharge curves for typical water-closet installations 67-73

19. Experimental supply and discharge systems for rating water-closets. _ 74

20-25. Discharge curves for typical water-closet installations 75-77

26. Supply line used for flush valves in rating water-closet discharges 77

27-38. Discharge curves for typical water-closet installations 78-88

39. Supply tanks at top of stack for determining the capacity of fittings

and stack 102

40. Pitot tube for measuring velocity of water at base of stack 107

41. Curve showing velocity of fall in a 3-inch stack 108

42. Pressure curves near base of a 3-inch stack with house drain, volume

rate of water 66 gallons per minute 111

43. Pressure curves near base of a 3-inch stack, volume rate of water 108

gallons per minute 111

44. Recording pressure gauge 112

45. Maximum and minimum pressure gauge 113

46. Experimental stack and vent system for determining air movements

in a plumbing system 115

47. Pressure curve for a 3-inch stack, water introduced at rate of 200 gal- lons per minute 116

48. Pressure curve for a 2-inch stack, water introduced at rate of 90 gal- lons per minute 117

49. Pressure curve for a 2-inch stack, water introduced at rate of 45 gal- lons per minute 118

50. Chart for determining permissible length of main vent for a 3-inch soil or waste stacks of known capacity 123

51. Experimental rain leader system 125

52. Submerged outfall of house sewer 127

53. Vented running trap 127

54. Apparatus for producing air current over stack top 128

55. Illustration of trail discharge from a flat bottom fixture 131

56. Arrangement of waste pipe to produce self-siphonage of a fixture trap.

57. Fixture and waste pipe to study effect of length of horizontal pipe on 131 self-siphonage 132
CONTENTS XI

Pago

58. Fixture and waste pipe to study effect of inclined waste pipe on self- siphonage 135

59. Fixture and waste pipe to study effect of combined horizontal and

inclined waste pipes 138

60. Diagram to illustrate the effect of horizontal waste pipe on velocity

and scour 139

61. Diagram to illustrate the effect of a vertical section of waste pipe on

velocity and scour. 140

62. Diagram to illustrate type of venting liable to clog 142

63. Diagram to illustrate type of venting least liable to clog 143

64. Diagram to illustrate type of venting liable to clog 143

65. Diagram to illustrate type of group venting in which vent is protected

from clogging 144

66. Diagram to illustrate type of group venting in which the vent is pro- tected. _ 145

67. Diagram to illustrate type of yoke venting tending to increase the

capacity of a system 149

68. Diagram to illustrate type of yoke venting applied to larger toilet rooms 150

69. Arrangement of bathroom group of fixtures tested 153

70. Illustration, crowfoot fittings 154

71. Arrangement of bathroom and kitchen-sink group tested 155

72. Arrangement of stack-vented bathroom group tested 156

73. Alternate arrangement of bathroom and kitchen-sink group tested 157

74. Arrangement of stack-vented bathroom and kitchen-sink group tested. 158

75. Experimental plumbing system showing arrangement of pipes and

location of fixtures 165

76. Return bend used in house sewer 166

77. Trap fitted with window and scale as used in tests 166

78. Experimental plumbing system showing arrangement of pipes and

location of fixtures 169

79. Change in arrangement of basement fixtures of Figure 78 172

80. Experimental plumbing system erected for demonstration purposes. _ 174

81. Approved design for a stack-vented bathroom group of fixtures (the

highest group of fixtures on the stack) 177

82. Approved design for stack and group vented fixtures 178

83. Approved design showing one alternative arrangement of waste pipes

for Figure 82 179

84. Approved design for stack-vented and group-vented fixtures 180

85. Approved design for lower floor 181

86. Approved design for lower floor bathroom group 181

87. Approved design for duplex bathroom group 182

88. Approved venting for lavatory and water-closet 183

89. Approved forms of venting single fixtures.. 184

90. Types of one-story one-family houses showing required venting 185

91. Types of two-story one-family houses showing required venting 186

92. Types of two-story two-family houses showing required venting 187

93. Relation of peak load to total number of fixture units 192

94. Relation between soil and vent stack 200

95. Vent chart for 3-inch soil stack 202

96. Vent chart for 4-inch soil stack 202

97. Vent chart for 5-inch soil stack — 203

98. Vent chart for 6-inch soil stack 203
XII CONTENTS

Page

99. Vent chart for 8-inch soil stack 204

100. Arrangement of piping for the study of air currents in horizontal waste pipes 242

101. Experiment A. Diffusion of carbon dioxide in a 1%-inch horizontal branch connected with a vertical stack. (Time, 20J4 hours; no

forced draft.) 246

102. Experiment B. Diffusion of carbon dioxide in a 1%-inch horizontal branch connected with a vertical stack. (Time, 48 hours; draft

in stack, 180 ft. /min.) 246

103. Experiment C. Diffusion of carbon dioxide in a l)4-inch horizontal branch connected with a vertical stack. (Time, 44 hours; no

forced draft.) 247

104. Experiments D and E. Diffusion of carbon dioxide in a 2-inch hori- zontal branch connected with a vertical stack. (Time, 48 hours; no forced draft.) 247

105. Experiment F. Evaporation of water in a 1%-inch horizontal branch

connected with a vertical stack. (Time, 46 hours; no forced draft.) . 250

106. Experiment G. Evaporation of water in a l)4-inch horizontal branch

connected with a vertical stack. (Time, 48 hours; forced draft, lOOft./min.) 250

107. Experiment H. Diffusion of carbon dioxide in 1%, l/4> and 2 inch

horizontal branches connected with vertical stacks 251
LETTERS OF SUBMITTAL

Washington, October 10, 1923.

Mr. Ira H. Woolson,

Chairman, Building Code Committee,

Department of Commerce, Washington, D. C. Dear Sir: We, the undersigned, members of the subcommittee on plumbing, submit the following final report covering our investigations of plumbing in dwelling houses.

Certain important matters not within the scope of our instructions were considered by the committee but were not brought to a

conclusion, namely, tests of materials, standardization of dimensions, and plumbing administration.

It is our opinion that simplified practice and standardization of plumbing should be brought about by mutual agreement of interested

parties rather than by detailed legislation, but without uniform

basic regulation standardization of plumbing is impossible. We

have, therefore, given our chief attention to this part of the problem

and have embodied the results of our studies in a recommended

Code of Plumbing Rules.

It is our opinion that important changes in present methods of

governmental control of plumbing are needed but that these should

not be attempted until the parties most interested have had an

opportunity to discuss thoroughly not only the legal but the business

and labor problems which are involved.

In our investigations we have necessarily been obliged to consider

the subject from the point of view of sanitarian, manufacturer,

plumber, and inspector, but in formulating the code we have endeavored to keep first in our minds the interests of the people whose

health may be endangered by faulty plumbing and whose comfort

will be increased by living in houses well supplied with means for

using water and for disposing of liquid wastes. Respectfully yours,

, George C. Whipple, Chairman. H. Y. Carson,

William C. Groeniger,

Thomas F. Hanley,

A. E. Hansen.

XIII
XIV LETTERS OF SUBMITTAL

Washington, December 15, 1923.

Mr. George C. Whipple,

Chairman of the Subcommittee on Plumbing of the Department of Commerce.

Dear Sir: The report of your committee transmitted with your

letter of July 3, 1923, has been received and has been given careful

consideration by the individual members of the Building Code

Committee, and it is my pleasure to inform you that we are a unit

in expressing our admiration of the exhaustive treatment your committee has given to the subject assigned.

There is abundant evidence of the thorough study given to each

phase of the subject and the earnest effort made to base your recom- mendations upon demonstrated physical facts, unbiased by personal

opinion or the rules of existing practice. It is recognized that the

judgment and experience of your committee members has been

freely exercised in analyzing the evidence produced in order to interpret its full significance and determine its value.

My committee was particularly impressed with the thorough and

comprehensive character of the original research conducted by the

Bureau of Standards under your committee’s direction. Such

investigations are of great value not only for the information developed for your report, but also for the accumulation of data useful

for comparison with subsequent similar studies.

The Building Code Committee has instructed me to express to your committee its sincere appreciation of the excellent service

rendered.

The report more than fulfills our expectations, and we believe it will prove a very valuable public document, helpful alike to individuals and municipalities in simplifying the operations and reducing

the cost of plumbing installations, particularly in dwelling-house

construction.

The report will be duly transmitted to Secretary Hoover, with an expression of my committee’s approval, and recommendation

that it be printed for distribution.

Yours very truly,

Ira H. Woolson,

Chairman, Building Code Committee,

Department of Commerce.

Washington, December 15, 1923. Hon. Herbert Hoover,

Secretary of Commerce, Washington, D. C. My Dear Mr. Secretary: I have the honor to transmit herewith the report of the subcommittee on plumbing appointed by you

to cooperate with the Building Code Committee. The report bears

evidence of its thorough and conscientious preparation.
LETTERS OF SUBMITTAL XV

It is a valuable document. The views of my committee upon the

merits of the report are briefly expressed in our letter of acknowledgment to the chairman of the subcommittee, copy of which is attached hereto and hence need not be repeated.

The Building Code Committee respectfully recommends that

this report be approved and printed for public distribution as a document of the Department of Commerce.

Yours very truly,

Ira H. Woolsox,

Chairman, Building Code Committee,

Department of Commerce.
LETTER OF ACCEPTANCE

Department of Commerce,

Office of the Secretary,

Washington, February 11, 1924,

Mr. Ira H. Woolson,

Chairman, Building Code Committee,

Department of Commerce, Washington, D. C. Dear Mr. Woolson: I am indeed well pleased with the completion of the Recommended Minimum Requirements for Plumbing

in Dwellings and Similar Buildings. The members of the subcommittee and of the Bureau of Standards staff deserve the greatest

credit for their unselfish and public-spirited devotion to the work.

Economical and sanitary plumbing systems are a vital necessity

for health in all settled communities and are hardly less essential in

rural households. Although the American people have expended

hundreds of millions of dollars for plumbing installations, the principles of their general layout have never been thoroughly understood.

Actual practice has been governed by opinions and guesswork, often

involving needless costly precautions which many families could ill afford. The lack of generally recognized principles is responsible to a certain extent for the contradictory plumbing regulations in differ- ent localities. Thanks to the work of the subcommittee and of the Bureau* of

Standards, the whole situation is altered, and there is now a scientific basis upon which State and local codes and small-dwelling in- stallations may be based.

The way is opened for effective standardization of plumbing supplies, with reduced costs to the industry and savings to the consumer. The subcommittee achieved these fine results by enlisting the aid

of the voluntary professional and commercial associations to which

its members are attached and of public officials, engineers, manufacturers, and representatives of workers, who willingly gave their

time and services in helping to arrive at conclusions in accordance

with the most varied experience. The experimental work necessary was performed with the utmost economy on account of the ability

of the Bureau of Standards staff, the contributions of materials

by manufacturers and the assistance given by members of the

subcommittee.

The report stands as a credit to leading men in the industry and

in public regulation. Prompt recognition of its principles by local authorities and by the plumbing industry generally is forecast by

advices that have reached this department, and such action will mean cheaper and better sanitation for the American people.

Yours faithfully,

Herbert Hoover,

XVI
RECOMMENDED MINIMUM REQUIREMENTS FOR PLUMBING

*

Report of Subcommittee on Plumbing of the Building Code Committee

PART I.—INTRODUCTION—GENERAL CONSIDERATIONS

In May, 1921, there was organized in the Department of Commerce a group of architects and engineers experienced in matters of building regulation, to be known as the Department of Commerce

Building Code Committee. Investigations by several agencies, and

particularly by the Senate Committee on Reconstruction and Production, had disclosed that prevailing inactivity in the building in- dustries was due in part to unnecessarily restrictive building code

requirements, and that under normal conditions great economic loss resulted from lack of uniformity and justice in such regulations.

The Building Code Committee proceeded to gather information

upon which minimum code requirements governing the various

phases of building construction might be based. These are being

issued in the form of ordinances recommended for adoption by those

writing or revising building codes.

Early in its work the committee undertook as a part of its program the formulation of rules for the plumbing of small dwelling

houses. Data regarding present practice were secured, and, in re- sponse to a questionnaire, the opinions of plumbers, sanitary engineers, and others in regard to some of the mooted questions were

obtained. It soon became evident that the problem could not be

solved satisfactorily by the questionnaire method, and that instead

of mere opinions there should be conclusions deduced logically from

scientific evidence obtained by experiment and experience. The

committee therefore decided to have the Bureau of Standards investigate the underlying principles of house drainage under the general supervision of a subcommittee of experienced sanitary engineers

and plumbers. This subcommittee was appointed by Secretary

Hoover in September, 1921, as follows:

George C. Whipple, 1 chairman, professor of sanitary engineering in Harvard

University, Cambridge, Mass. American Society of Civil Engineers.

American Public Health Association (fellow). American Water Works Association. New England Water Works Association. American Academy of Arts and Sciences. American Chemical Society.

Royal Sanitary Institute (honorary fellow).

1 Professor Whipple died Nov. 27, 1924. The first edition of the report was completed under his leader- ship. The report in its present form preserves all the basic principles established at that time but differs in the extension of those principles to larger structures. 20141°—29- •2 1
2 RECOMMENDED PLUMBING REQUIREMENTS

Harry Y. Carson,3 research engineer, American Cast Iron Pipe Co., Birmingham, Ala. American Society of Civil Engineers. Iron and Steel Institute. American Society for Testing Materials. American Foundrymen’s Association. National Research Council. William C. Groeniger, consulting sanitary engineer, Columbus, Ohio. American Public Health Association (fellow). American Society of Sanitary Engineering.

American Water Works Association. Society of American Military Engineers.

United States Naval Institute. Thomas F. Hanley, Hanley & Co., mechanical engineers and contractors, Chicago, 111. American Society of Sanitary Engineering.

National Association of Master Plumbers (chairman of standardization committee)

Western Society of Engineers. A. E. Hansen, hydraulic and sanitary engineer, New York, N. Y. American Society of Sanitary Engineering.

American Public Health Association. American Water Works Association. James A. Messer,3 president of the James A. Messer Co., Washington, D. C. William J. Spencer,3 secretary-treasurer of building trades department, American Federation of Labor, Washington, D. C. United Association of Journeymen Plumbers.

Albert L. Webster,3 consulting engineer, New York, N. Y. American Society of Civil Engineers.

American Public Health Association. New England Water Works Association. Franklin Institute. In September, 1928, Secretary Whiting appointed the following member:

J. L. Murphy, plumbing contractor, New York, N. Y.

National Association of Master Plumbers.

MODE OF PROCEDURE

Several meetings were held for planning and discussion of the tests which were carried on at the Bureau of Standards. At the first meeting Secretary Hoover received the members of the subcommittee

and explained in a general way his hopes in regard to the solution of the problem, emphasizing especially the benefits which should result from simplified practice in plumbing as well as in other branches of industry. John M. Gries, chief of the division of building and

housing; Ira H. Woolson, chairman of the Building Code Committee;

and Frank P. Cartwright, technical secretary of the Building Code

Committee, all met the subcommittee from time to time and discussed

2 Now consulting research engineer, National Cast Iron Pipe Co., Birmingham, Ala.

3 Circumstances not related to the work of the subcommittee compelled the resignation of Mr. Messer

on Jan. 5, 1922, of Mr. Spencer and Mr. Webster during October, 1922, and of Mr. Hanley in July, 1928. Their colleagues wish to express sincere appreciation of their valued services during their connection with

the work.
RECOMMENDED PLUMBING CODE 3

methods of procedure. Conferences were held with Dr. S. W.

Stratton, then Director of the Bureau of Standards; Dr. L. J. Briggs,

then chief of the engineering physics division and now assistant

director in charge of tests; and Dr. R. B. Hunter, then associate

physicist of the Bureau of Standards, now physicist in that bureau, to whom was delegated the task of conducting the experimental work.

TENTATIVE REPORT

On June 17, 1922, a preliminary report was submitted to the

chairman of the Building Code Committee, stating the tentative

conclusions of the committee at that time and briefly describing

the experimental work at the Bureau of Standards. This tentative

report was signed by all of the members of the committee except

William J. Spencer, who presented a minority report favoring individual venting for traps but concurred in the rest of the tentative report.

(See p. 225.)

One thousand copies of the tentative report were distributed in

all parts of the country among sanitary engineers, plumbers, architects, manufacturers, plumbing inspectors, and others whose experi- ence qualified them to discuss plumbing matters with authority, with

a request for critical discussion of the proposed requirements. In

response nearly 200 communications were received, discussing the

subject from all points of view and bringing to bear a vast amount of practical experience and operating data. The discussions and criti- cisms thus* obtained were found much more valuable than usually

result from the ordinary questionnaire method of obtaining information. The tentative report afforded a focus for criticisms and suggestions, and the recommendations of the committee have been revised

in the light of the information thus received. It is worthy of note

that approval of the majority report on the part of those who dis- cussed its provisions was quite general. More than half of the

respondents approved the tentative findings unconditionally, and

many more had only minor criticisms or suggestions to make. Very

few of the correspondents supported the contention of the minority

report.

The letters received indicated that some matters had not been

made sufficiently clear, and the committee took pains in preparing

the final report to clarify these doubtful points. Where the treat- ment of any particular question evoked considerable criticism, the reasons for the final conclusions of the committee were stated in a

series of notes to be found in chapter 10. The final report also was

influenced by the results of much additional experimental work at the United States Bureau of Standards, completed since the tentative

report was distributed,
4 INTRODUCTION GENERAL CONSIDERATIONS

REVISION OF FINAL REPORT

The committee reassembled in the spring of 1928 to review the

effect of its recommendations during the past five years and to consider whether any changes seemed to be indicated. In a very

extensive use that had developed, the only major need for revision

seemed to be with respect to the sizes of drains, stacks, and vents in

high buildings. Its original work had been concentrated on problems arising in dwellings and similar buildings, and the recommendations for other structures had been quite incidental. In response to a well-defined demand for the most economical requirements possible

in the case of high buildings, the members reviewed all available

information both on the side of theoretical calculations and on installations that had given no trouble in actual use. As a result, it has

felt warranted in giving requirements somewhat modified from those

mentioned in the previous report. The committee feels that these

requirements are the best that can be arrived at in the present state

of knowledge of the subject, but that a comprehensive program of experimentation should be undertaken as soon as possible to determine whether even more economical installations are practicable.

It has recommended that such a program be undertaken by the Bureau

of Standards.

LOCAL CONDITIONS

Although the findings of this report are believed to be based on sound general principles, nevertheless the committee • recognizes

that in a large country like the United States, which includes wide

differences of climate and living conditions, situations will occasionally

be found which will justify modification of the practices recommended.

No attempt has been made to outline these special situations.

ACKNOWLEDGMENT

The committee wishes to express its sincere appreciation of the

cooperation extended by the Bureau of Standards under direction

of Dr. S. W. Stratton and Dr. George K. Burgess. Measures for

the furtherance of its investigations have been prompt and adequate. Especial commendation should be given to Dr. R. B. Hunter

for his ingenious and accurate physical investigations of the hydraulics

and pneumatics of drainage systems under various conditions of

use. Acknowledgment is made of the valuable cooperation extended

by the great number of engineers, plumbing inspectors and plumbers,

architects, and others who have furnished data, reviewed the tentative recommendations, and have otherwise exhibited interest in the

work.
CHAPTER 1.—REGULATION OF PLUMBING

DEFINITION OF PLUMBING

The “ plumbing” of a building, as the term is commonly used,

includes the pipes for distributing the water supply, the fixtures for

using water, and drainage pipes for removing waste water and

sewage, together with fittings and appurtenances of various kinds,

all within or adjacent to the building. The “ service pipe/’ which

forms the connection between the water main and the building, and

the “house sewer,” which conveys the waste water and sewage from

the building to the street sewer or other point of disposal, are included

in the “plumbing system” of a building, using the term in a broader

sense. Connections for rain water are also included if the water is discharged through a house sewer or a house drain. The water

supply and drainage system are mutually dependent. Drains are needed to carry away the used water; water is needed to cleanse the

fixtures and transport solid wastes. The work of the committee has emphasized the necessity of considering the plumbing systems of buildings as intimately related to and forming an integral part of public water-supply and sewerage

systems. The number and character of plumbing fixtures in a

building are largely matters of individual choice, and owners have

not sufficiently considered their relation to features of public service.

Plumbing fixtures are the terminals of water-supply systems, and,

to a large extent, control the quantity of water used. At the same

time they are the beginnings of the sewerage system. The aggregate

discharges from plumbing fixtures determine the flow in sewers and

the volume of sewage reaching the outfall, this volume materially

affecting the cost of any pumping or treatment of the sewage. It is evident, therefore, that the public interest may well justify a certain

degree of governmental control over plumbing fixtures as affecting

both the quantity of water available for public use and the economical

operation of the sewerage system.

RELATION OF PLUMBING TO HEALTH

An important function of the house-drainage system is to carry

away from plumbing fixtures human excreta and wastes which may

contain disease-producing bacteria. Because of the possible presence

of such organisms sewage may be dangerous and must be disposed of

in such a manner that there will be no chance of disease transmission.

Sanitarians to-day place great emphasis on the importance of sewage

treatment and safe methods of ultimate sewage disposal.

5
6 RECOMMENDED PLUMBING REQUIREMENTS

The leakage of polluted water from the house-drainage system is insanitary and dangerous. Leakage "within the house may pollute

the habitation and permit food infection through the medium of

insects. Leakage in the ground outside the house may pollute

water supplies taken from neighboring wells or find its way into or under the building. The maintenance of water seals between fix- tures and drains and the permanent tightness of plumbing systems

arc important not only because they prevent the passage of air, but

because they prevent the access of insects to the interior of the

drains and sewers. If cockroaches, water bugs, and other vermin

can pass from drains to food, they may transport disease germs, and

thus be a bacteriological menace to health. It is therefore important

that the drainage system be tight and without danger of leakage.

L. O. Howard, chief of the Bureau of Entomology of the United

States Department of Agriculture, and C. W. Stiles, United States

Public Health Service, in personal conversation with the late chairman

of the committee, are authority for the statement that insects can and

do pass from the interior of leaking drainage systems to living quarters. Several other observers also report such occurrences. Another danger to be guarded against is the use of fixtures in

which the "water supply and waste connections are so arranged that

polluted waste water from the fixtures may, under certain circumstances, return into the water-supply pipes.

The line where the safe water supply ends and sewage begins is sometimes very finely drawn. If faucets with open spouts discharge over plumbing fixtures and if there is a break between the water supply and the waste pipe, self-protection exists against possible pollution

of the water-supply distributing system by the back flow of waste

water into it. Plumbing fixtures such as water-closets, urinals, bidets,

bathtubs, and lavatories with direct connections, secret wastes and

overflows, and combination cocks offer possible sources of pollution.

The air in sewers and drains often contains gases resulting from

the decomposition of excreta, soap, fats, and other wastes, together

with gases from mineral oils which may come from garages, streets, and industrial establishments. Illuminating gas may also find its way into sewers through leakage. Among these gases may be found

methane, sulphuretted hydrogen, and carbonic oxide. In large

amounts those gases are poisonous to the human system, and there are physiological objections to breathing them even in small quantities. Hence, the air of sewers or drains should be kept from enter- ing buildings intended for human habitation or occupancy by the use of proper plumbing installations and by suitable ventilation of

the rooms or compartments in which the plumbing fixtures are located.

The smell of these gases and other emanations from decomposing

organic matter is naturally repugnant to human beings. It not only
REGULATION OF PLUMBING 7

offends the sensibilities, but may produce shallow breathing, headache, and even nausea. In addition to the above facts, it is important to consider the

bacteriological aspects of sewer and drain air, a subject upon which

there has been some misunderstanding. In recent years bacteriologists have made studies which have thrown light upon this

subject. They have shown by experiment that while sewage often

contains disease-producing bacteria derived from human excreta and body wastes these bacteria are rarely found in the air which

escapes from sewers and drains. Hence, it has been argued by some

that escaping sewer air has no influence on health. The committee

does not agree with this conclusion. Health may be influenced by

factors which do not cause specific diseases, for there are chemical

and physiological as well as bacteriological factors involved. The

investigations thus far made by bacteriologists should be considered

to be merely a beginning of larger and more complete investigations

which will doubtless be made as the science of bacteriology ad- vances. The committee is of the opinion, therefore, that until

further light on this somewhat obscure subject has been obtained

the escape of sewer air from the house-drainage system, at frequent

intervals or in considerable quantities, threatens the health of the

building’s occupants.

This whole matter has a quantitative as well as a qualitative aspect.

The temporary losses of water seal in traps, which rarely occur and

which are immediately replaced, do not involve any great danger to the health of the occupants, for in many cases the final drainage from

the fixture will renew the seal within a short time, but where a loss of seal is likely to be of frequent occurrence and not readily replaced, or where breaks in the system admit sewer air continually to a building, the health of the occupants is subject to the dangers heretofore

described.

PUBLIC CONTROL OF PLUMBING JUSTIFIABLE

For the above-mentioned reasons regulations governing the installation of plumbing have been established by law in many places.

These regulations have been potent in improving living conditions

throughout the country; in fact, they have even set the standards

for those places where plumbing is not under public control. The

knowledge now in possession of sanitarians in regard to the lessened

bacteriological dangers of sewer air leads logically to some simplification in plumbing design, but it should not lead to an abandonment of practices necessary to protect buildings against the air of drains, which, in addition to its possible danger, is offensive to the

smell. The committee believes that good plumbing is a matter which

concerns health. Government has the right to protect the people’s
8 RECOMMENDED PLUMBING REQUIREMENTS

health, blit people also have rights, and plumbing regulations car- ried too far are unjust. Regulations which will not be supported by

the courts fully and without question under a liberal interpretation

of the police power may be regarded as unjust. Sanitary science,

however, must be the guide to justice in this matter. The principles

of science change as knowledge advances, and it is proper, therefore,

that plumbing regulations be reviewed from time to time and, if necessary, revised.

LEGAL PRINCIPLES

It is impossible to study the subject of plumbing regulation without having a proper conception of the common-law principle known

as upolice power,” for, though a part of the common law and without

absolutely definite limits, it can and must control court decisions,

without which plumbing regulations would be futile. Attention

should be called to the fact that this legal term “ police power” does

not mean the power of a policeman. It is true that the policeman,

with his uniform and his stick, is one agency for enforcing the “ police

power,” but plumbing inspectors, building inspectors, fire marshals,

and health officers also act under the same “ police power.” Police

power is that inherent power of government which protects the

people against harmful acts of individuals, in so far as matters of safety, health, morals, or the like are concerned. “ Police power” is “ community power.” Injuries against health come within the

proper scope of the police power; but acts of government to enhance

or promote health above normal, while laudable and often justifiable, do not fall within the scope of the police power.

There is a difference between conferring a benefit and preventing an injury, which, though difficult to define, is nevertheless real. Some of the requirements now generally included in plumbing codes

represent a failure to make this distinction properly and can not be

justified as essential to the protection of the public health from injury.

When there is difficulty in enforcing such regulations and the cases

are brought into court, it often happens that the code requirements

are not supported. In this way well-meaning citizens comply with

regulations which can not be enforced upon the unwilling citizen, and

injustice results. Unfortunately, this situation exists to-day. Plumbing regulations, therefore, should be carefully examined in the light

of modern sanitary science and accepted legal principles to determine

their legality, keeping in mind that in so far as they protect the

human health against injury they are justifiable, but no farther. It should be observed also that legally the police power has to do

with “health,” not merely the “ public health.” This is a distinction

which even a health officer often fails to make.

The following principles may be considered as safe guides in the

matter of governmental control:
REGULATION OF PLUMBING 9

1. The control of plumbing by government is distinctly an act done under the police power, because it has to do with protection of the health of the people against injury, using this term in its broad

and popular sense.

2. This use of the police power resides fundamentally in the State

governments, but may be and often is delegated to cities, towns, or other subdivisions of States.

3. The police power has not been delegated to the Federal Government, except so far as needed to cany out certain delegated powers

(as, for example, quarantine); hence, the Federal Government has

only advisory powers regarding its employment by States.

4. The use of the police power in plumbing regulations is justified on the theory, supported by scientific evidence, that the passage of

rats, cockroaches, water bugs, and other vermin in and out of drains, or the escape of sewage or of air from drains or sewers into occupied

human dwellings, are menaces to health, using this term in its broad

and popular sense.

5. Plumbing regulations can not legally contain requirements

which do not, either directly or indirectly, prevent injury to health,

safety, morals, or the like. No requirements can legally be made

which have to do merely with economies of construction, with

benefits to the house owner or occupants, or with benefits to manufacturers, traders, or laborers, for the right and only legal use of the

police power is to protect against injury.

6. The design of plumbing systems is properly within the scope of

legal regulation in so far as it has to do with the escape of solids,

liquids, or gases from, or the access of vermin and insects to drains and

sewers, in such a way as to endanger health, and in so far as a safe

and adequate supply of water to the fixtures is concerned.

7. Plumbing materials are properly subject to legal regulation in so far as their reliability in preventing dangers to health is concerned,

looking ahead to a reasonable life of the building.

8. Methods of plumbing construction are properly subject to

legal regulation in so far as they may be necessary to guard against

danger to health through faulty workmanship.

9. The control of plumbing by the system of permit and inspection

and test is a logical and apparently a satisfactory way of guarding

against injury to health through faulty plumbing; but in view of different conditions existing in large and small communities the

States should delegate to local communities the manner of administrating this control.

10. The system of examining plumbers is for the public benefit and

should be continued, but it might be better for the examining authorities to issue certificates of competency rather than “licenses.”

11. The requirement that plumbing work, subject to permit and

inspection, be done by licensed plumbers is justifiable under the

police power.
10 RECOMMENDED PLUMBING REQUIREMENTS

12. Uniformity in methods of plumbing control is desirable, as

it makes for convenience and economy. Uniformity can be secured

by following models set up by Federal or State governments.

13. Standardization of plumbing designs, so far as dimensioning

is concerned, standardization of plumbing materials, and even standardization of code requirements are for the public benefit, rather

than for protection against injury, and should be brought about by

agreement and concerted action. They can not be required legally

under the police power.

14. As the police power resides in State governments and as uniformity in plumbing regulation is for the public benefit, it is well for

all States to have simple, uniform, State-wide plumbing regulations

alike in essential respects, limited to matters which properly come

within the scope of the police power under a wide range of conditions,

with provision for permitting local communities to regulate installation and inspection by such methods as they see fit to adopt. These

may be appropriately called “ basic plumbing principles.”

15. The residence or dwelling is the basis for plumbing codes, be- cause the majority of all buildings are of this type. A code applicable to dwellings is also applicable, although not necessarily sufficient, for other classes of buildings. Buildings differ as to plumbing conditions, so that different regulations for different classes of buildings are fully justified under the police power. In fact, to apply

the same regulations to different conditions; that is, to require

practices necessary in one case for another case where they are not

necessary, is an improper use of the police power. The fourteenth

amendment to the Constitution of the United States provides for “ equal protection of the law,” but equal protection means under

like circumstances.

16. In addition to the basic plumbing principles, it is well for each

State to adopt a code of plumbing rules conforming substantially to that hereinafter recommended, which has been so drawn that compli- ance therewith will practically assure compliance with the basic

plumbing principles.

17. It is a well-established principle in drawing specifications for

works which involve operation that guaranteed results and detailed

methods of construction should not both be specified at the same

time. If certain guaranteed results are demanded, the contractor should be allowed some latitude in construction, and if detailed

methods of construction are specified, it should be expected that the

desired results will follow as a matter of course. Similarly, if reli- ance is placed on a general code of basic plumbing principles, there

should obviously be freedom of choice as to many details; whereas

if cities or towns choose to adopt a more rigid and detailed set of re- quirements compliance with them should be regarded as prima

facie evidence that the desired results will be obtained.
CHAPTER 2.—PRESENT STATUS OF PLUMBING

REGULATIONS

The committee has collected a large number of plumbing codes,

State laws, and local ordinances and given them careful study.

The situation may be described as chaotic.

1

Some States have no laws which regulate plumbing other than

local enactments. A few States have Xnandatory plumbing laws

state-wide in scope. Some have laws mandatory for cities of a

certain size or for cities and towns having public water supplies.

Others require cities to adopt ordinances regulating plumbing.

Still others have permissive acts. There is an utter lack of uniformity in legal procedure governing these matters. In the matter of administration some cities and some States

require master plumbers and journeymen to be licensed, but some

cities do not require licenses even though there are plumbing ordi- nances. The method of permit and inspection is almost universal,

where there is any regulation at all, but sometimes the inspection is under a board of health, sometimes under a building department,

occasionally under a special plumbing inspector, and, in a few

instances, under a water department.

In the matter of codes the lack of uniformity is even greater.

Some State codes are simple in their provisions; others set forth

rules of plumbing practice in great detail. In many States the

different cities have different codes. In one State there is a per- missive State code, as well as many city codes resulting from local enactments.

Going further into detail, it is found that there are unaccountable

differences in the regulations. Thus, in one State, where the whole

subject of plumbing has recently been under investigation, some

cities require the use of the running trap, other near-by cities prohibit its use, and some allow its use to be optional with the owner. Minor differences in regulations in different parts of the country

may sometimes be justified on account of different climatic or local

conditions, but the many radical differences found in the cities of a

single State are unjustifiable.

Nearly all of the present plumbing codes are applied in their

entirety to all of the buildings within the limits of their jurisdiction.

Compiled originally for dwellings, they have been extended to other

types of buildings, but proper discrimination has not always been

made between high and low buildings, single or multiple, public or

private, or between buildings used for different purposes. It is

1 The situation outlined in chapter 2 was that existing at the time of the committee’s first report in 1923, Considerable improvement has been effected, but to a large extent the description is still applicable to-day. 11
12 RECOMMENDED PLUMBING REQUIREMENTS

natural, perhaps, that codes should have developed in a rigid way,

because the first code drawn was based on the requirements of a

single city. Subsequent codes have been influenced by precedent,

local pride, and selfish prejudice. Many codes have been established

by copying other codes. Prejudice in favor of this or that method

of construction has brought about unnecessary differences.

SUPERVISION OF PLUMBING INSPECTION

There is frequently a lack of coordination between the different

municipal departments which, in one way or another, are concerned

with plumbing, namely, the departments of health, fire, water, sewers,

buildings, and streets. Under prevailing arrangements the owner or plumbing contractor must often obtain several permits from different

city authorities and arrange for inspection by several men in order to comply fully with the regulations. For example, he may be obliged

to go to the department of public works for permission to cut the

pavement and for an inspector to see that the fill is property made,

to the city engineer for line and grade of the sewer, to the city engi- neer and health officer for permission to make connections with the

sewer, to the division of water supply for permission to make water

connection, and to the plumbing inspector for approval of his plumbing installation.

CONCLUSIONS BASED ON SCIENTIFIC PROCEDURE

Because of the irregularities and incongruities in plumbing codes

the committee has not attempted to formulate minimum plumbing

requirements by any method of selection or by any averaging process

based on existing codes. Instead, the committee has studied the

entire problem anew and has based its conclusions for buildings on

legal principles and the applications of modern science, but has kept

in mind existing conditions in order that suggested changes may not

be great enough to cause serious inconvenience.
CHAPTER 3.—BASIC PLUMBING PRINCIPLES

The committee has given consideration to the formulation of a set of basic plumbing principles so general in scope and so fundamental

in character as to be worthy of adoption by State, city, or town as a

basis for its sanitary law. These have been drawn on the principle

of specifying the results desired, making provision for testing the

plumbing work to ascertain if the results are likely to be secured, but

not attempting to specify details of construction.

These requirements are not regarded as sufficient for all cities, but

the committee is of the opinion that States should adopt them on a state-wide mandatory basis or should give to cities, towns, or other

subdivisions the power to choose between them and the more detailed

plumbing code hereinafter recommended.

These principles were adopted by the committee early in its work

as embodying the fundamental sanitary considerations which successful plumbing systems must satisfy. They have been utilized as a guide, both in directing the investigational work and in formulating

recommendations.

In adopting these basic plumbing principles the committee has

endeavored to keep in mind differences in climate in different parts

of the country, differences in buildings, in methods of sewerage and

sewage disposal, in disposal of rain water, and other differences.

Some of the details of plumbing construction must vary with these

conditions, but the basic sanitary principles are the same and the

results desired and necessary to protect the health of the people are the same everywhere.

These principles are stated in the following pages. Explanations

of the reasons for their adoption and of their application to conditions

met with in practice are given in the notes in chapter 10. In making

these explanatory notes the committee has given careful consideration to the questions raised by those who have reviewed the tentative

report and has attempted to deal with the considerations naturally

arising when the adoption of such basic principles is under discussion.

1. All premises intended for human habitation or occupancy shall be provided with a supply of pure and wholesome water, neither con- nected with unsafe water supplies nor cross connected through

plumbing fixtures to the drainage system.

2. Buildings in which water-closets and other plumbing fixtures

exist shall be provided with a supply of water adequate in volume and

pressure for flushing purposes.

3. The pipes conveying water to water-closets shall be of sufficient

size to supply the water at a rate required for adequate flushing

without unduly reducing the pressure at other fixtures.

13
14 RECOMMENDED PLUMBING REQUIREMENTS

4. Devices for heating water and storing it in “boilers,” or hotwater tanks, shall be so designed and installed as to prevent all dangers from explosion and also prevent a back flow of hot water

through a meter connected with a public water supply.

5. Every building intended for human habitation or occupancy on premises abutting on a street in which there is a public sewer

shall have a connection with the sewer, and, if possible, a separate

connection.

6. In multiple dwellings provided with a house drainage system

there shall be for each family at least one private water-closet.

7. Plumbing fixtures shall be made of smooth nonabsorbent material, shall be free from concealed fouling surfaces, and shall be

set free of inclosures.

8. The entire house drainage system shall be so designed, constructed, and maintained as to conduct the waste water or sewage

quickly from the fixture to the place of disposal with velocities

which will guard against fouling and the deposit of solids and will prevent clogging.

9. The drainage pipes shall be so designed and constructed as to be proof for a reasonable life of the building against leakage of water

or drain air due to defective materials, imperfect connections, corrosion, settlements or vibrations of the ground or building, temperature

changes, freezing, or other causes.

10. The drainage system shall be provided with an adequate

number of cleanouts so arranged that in case of stoppage the pipes

may be readily accessible.

11. Each fixture or combination fixture shall be provided with a

separate, accessible, seK-scouring, reliable water-seal trap placed as near to the fixture as possible.

12. The house-drainage system shall be so designed that there will be an adequate circulation of air in all pipes and no danger of siphonage, aspiration, or forcing of trap seals under conditions of ordinary

use.

13. The soil stack shall extend full size upward through the roof

and have a free opening, the roof terminal being so located that

there will be no danger of air passing from it to any window and no

danger of clogging of the pipe by frost or by articles being thrown

into it or of roof water draining into it. 14. The plumbing system shall be subjected to a water or air pressure test and to a final air-pressure test in such a manner as to disclose all leaks and imperfections in the work.

15. No substances which will clog the pipes, produce explosive

mixtures, or destroy the pipes or their joints shall be allowed to enter the house-drainage system.
BASIC PLUMBING PRINCIPLES 15

16. Refrigerators, ice boxes, or receptacles for storing food shall not be connected directly with the drainage system.

17. No water-closet shall be located in a room or compartment

which is not properly lighted and ventilated to the outer air. 18. If water-closets or other plumbing fixtures exist in buildings

where there is no sewer within reasonable distance, suitable provision

shall be made for disposing of the house sewage by some method of sewage treatment and disposal satisfactory to the health authority

having jurisdiction.

19. Where a house-drainage system may be subjected to back

flow of sewage, suitable provision shall be made to prevent its over- flow in the building.

20. Plumbing systems shall be maintained in a sanitary condition.

PART II.-—CHAPTER 4—RECOMMENDED PLUMBING CODE

As a result of its investigations the committee has drafted the

following code of minimum requirements for plumbing.

Starting with the fundamental principle that plumbing regulations

are applications of the police power in the interest of health, two

ideas have been kept steadily in mind—simplification and standardization. Early studies showed the futility of attempting to bring

about complete standardization by law. Apart from questionable

legality was the insuperable difficulty of including in a code the in- numerable items that w*ouid be necessary. The committee’s attitude

in regard to the subject of standardization is set forth in chapter 8. On the other hand, an attempt to simplify plumbing regulations by

eliminating all items which are in the nature of specifications would

reduce them practically to the list of basic principles given in chapter

3. The code recommended is a compromise between the two extreme

ideas. It is shorter than some of the codes now being used, curtailments having been made in the interest of simplicity; it is longer than

some, details having been included with a view to bringing to pass a

certain amount of standardization. It is hoped that its requirements

of design, coupled with its detailed structural requirements, will result

not only in cheaper and better plumbing, but in a fairer and more uniform administration. A study of the recommended code will show

that its length is due quite as much to its detailed classification as to

its subject matter, brevity being sacrificed for the sake of clearness.

Attention should be called to the fact that the code, as originally

presented, was drawn primarily for dwelling houses, although most

of its provisions applied to any sort of building. With slight modifications required to adapt it to local administrative conditions,

the committee believes that its adoption in its present form by States

and municipalities will tend to bring order out of the chaos still existing.

In Article III, which covers the subject of quality and weight of

plumbing materials, references are made to standard specifications

adopted by the American Society for Testing Materials, instead of

writing these detailed requirements into the code, but for the in- formation of persons studying this report the specifications referred

to are given in Appendix D. In the case of lead pipe, no specifications have yet been adopted by the American Society for Testing

Materials, and, therefore, detailed weights are inserted in the code.

The idea of the committee is that codes adopted throughout the

country shall require that plumbing materials conform to prevailing

standards of good practice, and that an association of technical

experts is better qualified to establish such standards and revise them

as manufacturing arts progress than the State or municipal legislative authorities responsible for the plumbing code.

20141°—29 3 17
PLUMBING CODE

Recommended by the Subcommittee on Plumbing of the

Department of Commerce Building Code Committee

ARTICLE I.—DEFINITIONS OF TERMS

Section 1. Plumbing.—Plumbing is the art of installing in

buildings the pipes, fixtures, and other apparatus for bringing in the water supply and removing liquid and water-carried wastes. Sec. 2. Plumbing System.—The plumbing system of a building

includes the water supply distributing pipes; the fixtures and fixture

traps; the soil, waste, and vent pipes; the house drain and house

sewer; the storm-water drainage; with their devices, appurtenances,

and connections all within or adjacent to the building.

Sec. 3. Water-Service Pipe.—The water-service pipe is the pipe

from the water main to the building served.

Sec. 4. Water-Distribution Pipes.—The water-distribution pipes

are those which convey water from the service pipe to the plumbing

fixtures.

Sec. 5. Plumbing Fixtures.—Plumbing fixtures are receptacles

intended to receive and discharge water, liquid, or water-carried

wastes into a drainage system with which they are connected.

Sec. 6. Trap.—

A

trap is a fitting or device so constructed as to prevent the passage of air or gas through a pipe without materially

affecting the flow of sewage or waste water through it. Sec. 7. Trap Seal.—The trap seal is the vertical distance between

the crown weir and the dip of the trap.

Sec. 8. Vent Pipe.—A vent pipe is any pipe provided to ventilate a house-drainage system and to prevent trap siphonage and back

pressure. Sec. 9. Local Ventilating Pipe.—A local ventilating pipe is a pipe through which foul air is removed from a room or fixture. Sec. 10. Soil Pipe.—A soil pipe is any pipe which conveys the

discharge of water-closets, with or without the discharges from

other fixtures, to the house drain.

Sec. 11. Waste Pipe and Special Waste.—A waste pipe is any

pipe which receives the discharge of any fixture, except water18
RECOMMENDED PLUMBING CODE 19

closets, and conveys the same to the house drain, soil, or waste

stacks. When such pipe does not connect directly with a house

drain or soil stack, it is termed a special waste. Sec. 12. Main—The main of any system of horizontal, vertical, or continuous piping is that part of such system which receives the

wastes, vent or back vents, from fixture outlets or traps, direct or through branch pipes.

Sec. 13. Branch.—The branch of any system of piping is that

part of the system which extends horizontally at a slight grade, with

or without lateral or vertical extensions or vertical arms, from the

main to receive fixture outlets not directly connected to the main.

Sec. 14. Stack.—Stack is a general term for any vertical line of

soil, waste, or vent piping.

Sec. 15. House Drain.—The house drain is that part of the lowest horizontal piping of a house drainage system which receives the

discharge from soil, waste, and other drainage pipes inside the walls

of any building and conveys the same to the house sewer beginning

5 feet outside of the inner face of the building wall.

Sec. 16. House Sewer.—The house sewer is that part of the

horizontal piping of a house drainage system extending from the

house drain 5 feet outside of the inner face of the building wall to

its connection with the main sewer or cesspool and conveying the

drainage of but one building site. Sec. 17. Size and Length.—The given caliber or size of pipe is for a nominal internal diameter, except that other than iron pipe

size, brass pipe is measured by its outside diameter. The developed

length of a pipe is its length along the center line of pipe and fittings.

Sec. 18. Dead End.—A dead end is a branch leading from a

soil, waste, vent, house drain, or house sewer, which is terminated at a developed distance of 2 feet or more by means of a cap, plug, or other fitting not used for admitting water to the pipe.
ARTICLE II.—GENERAL REGULATIONS

Sec. 19. Grades of Horizontal Piping.—All horizontal piping

shall be run in practical alignment and at a uniform grade of not less than one-eighth of an inch per foot, and shall be supported or anchored

at intervals not to exceed 10 feet. All stacks shall be supported at

their bases, and all pipes shall be rigidly secured.

Sec. 20. Change in Direction.—All changes in direction shall be made by the appropriate use of 45° wyes, half wyes, long sweep

quarter bends, sixth, eighth, or sixteenth bends, except that single

sanitary tees may be used on vertical stacks, and short quarter bends

may be used in soil and waste lines where the change in direction of flow is from the horizontal to the vertical. Tees and crosses may

be used in vent pipes.

Sec. 21. Prohibited Fittings.—No double hub, double T, or double sanitary T branch shall be used on soil or waste lines. The

drilling and tapping of house drains, soil, waste, or vent pipes, and

the use of saddle hubs and bands are prohibited.

Sec. 22. Dead Ends.—In the installation of any drainage system

dead ends shall be avoided.

Sec. 23. Protection of Material.—All pipes passing under or through walls shall be protected from breakage. All pipes passing

through or under cinder concrete or other corrbsive material shall be

protected against external corrosion.

Sec. 24. Workmanship.—Workmanship shall be of such character

as fully to secure the results sought to be obtained in all of the sections

of this code.

Sec. 25. Installation of Plumbing by Owner.—All plumbing

installed by the owner shall comply with the requirements of this code and in such event the word “owner” shall be substituted for

the word “plumber” throughout this code.

20
ARTICLE III.—QUALITY AND WEIGHTS OF MATERIALS

Sec. 26. Materials, Quality of.—All materials used in any

drainage or plumbing system, or part thereof, shall be free from

defects. Sec. 27. Label, Cast or Stamped.—Each length of pipe, fitting,

trap, fixture, and device used in a plumbing or drainage system shall be stamped or indelibly marked with the weight or quality thereof and

the maker’s mark or name.

Sec. 28. Vitrified Clay Pipe.—Ail vitrified clay pipe shall con- form to the A. S. T. M.1 “ Standard Specifications for Clay Sewer

Pipe” (serial designation, C 13-24).

Sec. 29. Cast-Iron Pipe.—(a) Quality. —All cast-iron pipe and

fittings shall conform to the A. S. T. M. “Standard Specifications

for Cast-iron Soil Pipe and Fittings” (serial designation, A 74-18).

(See note 24, p. 223.)

(b) Coating . —All cast-iron pipe and fittings for underground use

shall be coated with asphaltum or coal-tar pitch.

Sec. 30. Wrought-Iron Pipe.—All wrought-iron pipe shall con- form to the A. S. T. M. “Standard Specifications for Welded Wroughtiron Pipe” (serial designation, A 72-27), and shall be galvanized.

Sec. 31. Mild-Steel Pipe.—All steel pipe shall conform to the

A. S. T. M. “Standard Specifications for Welded and Seamless Steel

Pipe” (serial designation, A 53-27), and shall be galvanized.

Sec. 32. Brass and Copper Pipe.—Brass and copper pipe shall conform, respectively, to the standard specifications of the A. S. T. M. for “Brass Pipe, Standard Sizes,” and for “Copper Pipe, Standard

Sizes” (serial numbers B 43-24 and B 42-24, respectively).

Sec. 33. Lead Pipe, Diameter, Weights.—All lead pipe shall be

of best quality of drawn pipe, of not less weight per linear foot than

shown below.

(a) Lead soil, waste, vent, or flush pipes, including bends and traps (extra

light):

Internal diameter Weights per foot Internal diameter Weights per foot Inches Lbs. Ozs. Inches Lbs. Ozs.

1 2 __ 2 4

1 % 2 8 3 4 12 iy2 3 8 4 6

1 American Society for Testing Materials, ning on page 253 of this report. These specifications are given in full in Appendix D, begin- 21
22 RECOMMENDED PLUMBING REQUIREMENTS

(6) Lead water-supply pipe above ground (strong)

Internal diameter

Inches K —

Weights per foot Lbs. Ozs. 22 8

34

Inches £

Internal diameter

Lbs. Os 8

Weights per foot Lbs. Ozs. 2

___ 3

___ 3

___ 4

Internal diameter Weights per foot Inches Lbs. Ozs. U 4 12

1 2 6

if 6 8

2 7 und (extra strong)

Internal diameter Weights per foot Inches Lbs. Ozs. li 6 11 7 8

If 8 Sec. 34. Sheet Lead.

Sheet lead shall weigh not less than 4

pounds per square foot. Sec. 35. Sheet Copper or Brass.—Sheet copper or brass shall be not lighter than No. 18 B. and S. gauge, except that for local and interior ventilating pipe it shall be not lighter than No. 26 B.

and S. gauge.

Sec. 36. Galvanized Sheet Iron.—Galvanized sheet iron shall be not lighter than the following B. and S. gauge:

No. 26 for 2 to 12 inch pipe.

No. 24 for 13 to 20 inch pipe.

No. 22 for 21 to 26 inch pipe.

Sec. 37. Threaded Fittings.—(a) Plain screwed fittings shall be

of cast iron, malleable iron, or brass of standard weight and dimensions. ( b

)

Drainage fittings shall be of cast iron, malleable iron, or

brass, with smooth interior waterway, with threads tapped out of

solid metal. (c

)

All cast-iron fittings used for water-supply distri- bution shall be galvanized, (d) All malleable iron fittings shall be

galvanized.

Sec. 38. Calking Ferrules.—Brass calking ferrules shall be of the best quality red cast brass, with weights and dimensions in accord- ance with the following table:

Pipe size, (inches) Actual

inside diameter Length Weight

2.

Inches

213r

InchesH4iLbs. Ozs.

1 3 1 12 4 2 8
RECOMMENDED PLUMBING CODE 23

Sec. 39. Soldering Nipples and Bushings.—(a) Soldering nipples shall be of brass pipe, iron-pipe size, or of heavy, cast red brass

not less than the following weights

Diameters

Inches If

1 2 2

Weights

Ozs.

_ 6

_ 8

_ 14

Diameters

Inches 2*

3

4

Weights Lbs. Ozs. 1 6 2 0

3 8

(b) Soldering bushings shall be of brass pipe, iron-pipe size, or of heavy, cast red brass.

Sec. 40. Floor Flanges for Water-Closets.—Floor flanges for

water-closets shall be not less than three-sixteenths of an inch thick,

and of brass or cast iron.
ARTICLE IV.—JOINTS AND CONNECTIONS

Sec. 41. Water and Air Tight Joints.—All joints and connections mentioned under this article shall be made permanently gas

and water tight.

Sec. 42. Vitrified Pipe.—All joints in vitrified clay pipes, or between vitrified clay pipe and metals, shall be poured joints.

Sec. 43. Calked Joints.—All calked joints shall be firmly packed

with oakum or hemp, and shall be secured only with pure lead, not

less than 1 inch deep, well calked, and no paint, varnish, or putty

will be permitted until after the joint is tested. Sec. 44. Screw Joints.—All screw joints shall be American

standard screw joints, and all burrs or cuttings shall be removed.

Sec. 45. Cast Iron.—Cast-iron joints may be either calked or screw joints made in the approved manner.

Sec. 46. Wrought Iron, Steel, or Brass to Cast Iron.

The joints may be either screwed or calked joints made in the

approved manner.

Sec. 47. Lead pipe.—Joints in lead pipe or between lead pipe

and brass or copper pipes, ferrules, soldering nipples, bushings, or

traps, in all cases on the sewer side of the trap and in concealed

joints on the inlet side of the trap, shall be full-wiped joints, with an

exposed surface of the solder to each side of the joint of not less than

three-quarters of an inch and a minimum thickness at the thickest

part of the joint of not less than three-eighths of an inch.

Sec. 48. Lead to Cast Iron, Steel, or Wrought Iron.—The

joints shall be made by means of a calking ferrule, soldering nipple, or bushing.

Sec. 49. Slip Joints and Unions.—Slip joints will be permitted

only in trap seals or on the inlet side of the trap. Unions on the sewer side of the trap shall be ground faced, and shall not be concealed or inclosed.

Sec. 50. Roof Joints.—The joint at the roof shall be made watertight by use of copper, lead, or iron plates or flashings.

Sec. 51 . Closet, Pedestal Urinal and Trap Standard Slop

Sink, Floor Connections.—A brass floor connection shall be wiped

or soldered to lead pipe, an iron floor connection shall be calked to cast-iron pipe, or an iron floor connection calked or screwed to

24
RECOMMENDED PLUMBING CODE 25

wrought-iron pipe, and the floor connection bolted to an earthenware

trap flange. A metal to earthenware, a metal to metal union, or a

lead or asbestos gasket or washer shall be used to make a tight joint.

Sec. 52. Increasers and Reducers.—Where different sizes of

pipes or pipes and fittings are to be connected, proper size increasers or reducers, pitched at an angle of 45° between the two sizes, shall be

used.

Sec. 53. Prohibited Joints and Connections.—Any fitting or connection which has an enlargement, chamber, or recess with a ledge

shoulder or reduction of the pipe area in the direction of the flow on

the outlet or drain side of any trap is prohibited.

Sec. 54. Expansion Bolts.—Connections of wall hangers, pipe

supports, or fixture settings with the masonry, stone, or concrete

backing shall be made with expansion bolts without the use of

wooden plugs.

Sec. 55. New Materials.—Any other material than that specified in this code, which the proper administrative authority approves

as being equally efficient, may be permitted.
ARTICLE V.—TRAPS AND CLEAN OUTS

Sec. 56. Traps, Kind, and Minimum Size.—Every trap shall be

self-cleaning. Traps for bathtubs, lavatories, sinks, and other similar

fixtures shall be of lead, brass, cast iron, or of malleable iron galvanized

or porcelain enameled inside. Galvanized or porcelain-enameled traps

shall be extra heavy and shall have a full-bore smooth-interior waterway, with threads tapped out of solid metal.

The minimum size (nominal inside diameter) of trap and waste

branch for a given fixture shall not be less than that shown in the

following table:

Kind of fixture Size (in inches), trap and

branch Kind of fixture Size (in inches), trap and

branch

Bathtubs 1 1)4 Sinks, hotel or public. . 2 Bath, shower, stall 1 2 Sinks, large hotel or public.. 2 Bath, sitz. 1 J4 Sinks, small, pantry or bar.. 1)4 Bath, foot 1H Sinks, dishwasher .. 1)4 Sinks, slop, with trap combined 3 Bidets 1)4 Sinks, slop sink, ordinary 1 2 Combination fixture 1)4 Urinals, lip .. 1)4 Drinking fountains 1)4 Urinals, troughs 2 Fountain cuspidors 1H Urinals, pedestal 3 Urinals, stall 2 Floor drains.. 2 Washbasin 1 1)4 Laundry trays 1)4 Water-closet 3 Sinks, kitchen, residence ... 1)4

1 The present tendency is toward an increase in the size of trap and waste pipe for this fixture, in order

to reduce the time required for emptying it. Sec. 57. Traps, Prohibited.—No form of trap which depends for

its seal upon the action of movable parts or concealed interior partitions shall be used for fixtures. Sec. 58. Traps, Where Required.—Each fixture shall be separately trapped by a water-seal trap placed as near to the fixture as

possible, except that a set of not more than 3 laundry trays or lavatories or a set of 2 laundry trays and 1 sink may connect with a single

trap, provided the trap is placed centrally and the branches connect

into the trap seal at an angle of not more than 60° to the vertical arm. In no case shall the waste from a bathtub or other fixture dis- charge into a water-closet trap. No fixture shall be double trapped.

Sec. 59. Water Seal.—Each fixture trap shall have a water seal of not less than 2 inches and not more than 4 inches.

Sec. 60. Trap Clean Outs.—Each trap, except those in combination with fixtures in which the trap seal is plainly visible and accessible, shall be provided with an accessible brass trap screw of ample size,

protected by the water seal, 26
RECOMMENDED PLUMBING CODE 27

Sec. 61. Trap Levels and Protection.—All traps shall be set true with respect to their water seals and protected from frost and

evaporation.

Sec. 62. Pipe Clean Outs.—The bodies of clean-out ferrules shall be made of standard pipe sizes, conform in thickness to that required

for pipe and fittings of the same metal, and extend not less than one- quarter inch above the hub. The clean-out cap or plug shall be of heavy red brass not less than one-eighth inch thick and be provided

with raised nut or recessed socket for removal.

Sec. 63. Pipe Clean Outs—Where Required.—A clean out

easily accessible shall be provided at the foot of each vertical waste

or soil stack. There shall be at least two clean outs in the house

drain—one at or near the base of the stack and the other, with full- size Y branch, inside the wall near the connection between the house

drain and house sewer. Except for the latter, clean outs shall be of the same nominal size as the pipes up to 4 inches and not less than

4 inches for larger pipes. The distance between clean outs in horizontal soil lines shall not exceed 50 feet. Sec. 64. Manholes.—All underground traps and clean outs of a building, except where clean outs are flush with the floor, and all exterior underground traps shall be made accessible by manholes with

proper covers. Sec. 65. Clean Outs—Equivalents.—-Any floor or wall con- nection of fixture traps when bolted or screwed to the floor or wall

shall be regarded as a clean out. Sec. 66. Grease Traps.—When a grease trap is installed, it shall be placed as near as possible to the fixture from which it receives the

discharge and should have twice the capacity of the discharge.

Sec. 67. Sand Traps.—Sand traps when installed should be so designed and placed as to be readily accessible for cleaning.

Sec. 68. Basement Floor Drains.—Cellar or basement floor drains shall connect into a trap so constructed that it can be readily

cleaned and of a size to serve efficiently the purpose for which it is intended. The drain inlet shall be so located that it is at all times in

full view. When subject to back flow or back pressure, such drains

shall be equipped with an adequate back-water valve.

Sec. 69. Back-Water Valves.—Back-water valves shall have all bearing parts or balls of noncorrodible metal and so constructed as to insure a positive mechanical seal and remain closed except when

discharging wastes.
ARTICLE VI.—WATER SUPPLY AND DISTRIBUTION

Sec. 70. Quality of Water.—The quality of the water supply

shall meet accepted standards of purit}^.

Sec. 71. Distribution.—-The water supply shall be distributed

through a piping system entirely independent of any piping system

conveying another water supply.

Sec. 72. Water Service.—The Water-service pipe of any building

shall be of sufficient size to permit a continuous ample flow of water on all floors at a given time.

Sec. 73. Water Supply to Fixtures.—All plumbing fixtures

shall be provided with a sufficient supply of Water for flushing to keep them in a sanitary condition. Every water-closet or pedestal

urinal shall be flushed by means of an approved tank or flush valve

of at least 4 gallons flushing capacity for water-closets and at least 2 gallons for urinals, and shall be adjusted to prevent the waste of water. The flush pipe for water-closet flush tanks shall be not less than 134 inches in diameter, and the water from flush tanks shall be used for no other purpose.

No water-closet or urinal bowl shall be supplied directly from a water-supply system through a flushometer or other valve unless

such valve is set above the water-closet or urinal in a manner such

as to prevent any possibility of polluting the water supply.

No plumbing fixture, device, or construction shall be installed

which will provide a cross connection between a distributing system

of water for drinking and domestic purposes and a drainage system,

soil, or waste pipe so as to permit or make possible the back flow of

sewage or waste into the water-supply system.

Sec. 74. Size of Water-Supply Pipes.—The minimum size of water-service pipes from the curb to the dwelling shall be one-half

inch, and to fixtures as follows:

Sill cocks Hot-water boilers. Laundry trays

Sinks

Inch

F2

F2

Viy2

Lavatories

Bathtubs

Water-closet tanks.

Inch

3/sH

3/s Sec. 75. Water-supply Control.—A main shut-off on the Watersupply line shall be provided near the curb. Accessible shut-offs

shall be provided on the main supply line just inside the foundation

wall for each flat or apartment of a building, for each lawn sprinkler,

for supply to each hot water tank, and for each water-closet.

28
RECOMMENDED PLUMBING CODE 29

Sec. 76. Water-supply Pipes and Fittings—Material.—All water-supply pipes for a plumbing system shall be of lead, galvanized wrought iron or steel, brass, or cast iron, with brass or galvanized cast-iron or galvanized malleable-iron fittings. No pipe or

fittings that have been used for other purposes shall be used for dis- tributing water. Sec. 77. Water Supply, Protection.—All concealed water pipes,

storage tanks, flushing cisterns, and all exposed pipes or tanks subject

to freezing temperatures shall be efficiently protected against freezing.

Sec. 78. Relief Valves.—Wherever a check valve is installed on

the cold-water supply pipe between the street main and the hotwater tank there shall be installed on the hot-water distributing

system a suitable relief valve.

Sec. 79. Pumps and Hydrants.—All pumps and hydrants shall be protected from surface water and contamination.
ARTICLE VII.—PLUMBING FIXTURES

Sec. 80. Materials.—All receptacles used as water-closets, uri- nals, or otherwise for the disposal of human excreta, shall be vitrified earthenware, hard natural stone, or cast iron white enameled on the

inside.

Sec. 81. How Installed.—All plumbing fixtures shall be installed

free and open in a manner to afford access for cleaning. Where

practical all pipes from fixtures shall be run to the wall, and no lead

trap or pipe shall extend nearer to the floor than 12 inches unless

protected by casing.

Sec. 82. Water-Closet Bowls.—Water-closet bowls and traps

shall be made in one piece and of such form as to hold sufficient

quantity of water, when filled to the trap overflow, to prevent fouling

of surfaces, and shall be provided with integral flushing rims constructed so as to flush the entire interior of the bowl.

Sec. 83. Frost-Proof Closets—Where Permitted.—Frost- proof closets may be installed only in compartments which have no di- rect connection with a building used for human habitation or occu- pancy. The soil pipe between the hopper and the trap shall be 3

inches in diameter and shall be of lead, or cast iron enameled on the

inside.

Sec. 84. Fixtures Prohibited.—Fixed wooden wash trays or sinks shall not be installed in any building designed or used for human

habitation. No new copper lined wooden bathtubs shall be installed,

and an old fixture of this class taken out shall not be reconnected.

Pan and valve plunger, offset washout and other water-closets having

invisible seals or unventilated space, or walls not thoroughly washed

at each flush shall not be used. Long hopper closets or similar

appliances shall not hereafter be installed. No dry closet or chemical

closet shall be installed in a dwelling.

Sec. 85. Floor Drains and Shower Drains.—A floor drain or a shower drain shall be considered a fixture and provided with a strainer.

Sec. 86. Fixture Strainers.—All fixtures other than waterclosets and pedestal urinals shall be provided with fixed strong

metallic strainers with outlet areas not less than that of the interior

of the trap and waste pipe.

Sec. 87. Fixture Overflow.—The overflow pipe from a fixture

shall be connected on the house or inlet side of the trap and be so arranged that it may be readily and effectively cleaned.

30
ARTICLE VIII.—VENTILATION OF ROOMS AND FIXTURES

Sec. 88. Location of Fixtures.—No trapped plumbing fixtures

shall be located in any room or apartment which does not contain

a window placed in an external wall or is not otherwise provided

with proper ventilation.

Sec. 89. Ventilating Pipe, How Connected.—Ventilation

pipes from fixtures and toilet rooms shall be separate and distinct

and have no connection whatever with the other ventilating ducts

or pipes in the building.

31
ARTICLE IX.—SOIL, WASTE, AND VENT PIPES

Sec. 90. Material.—All main or branch soil, waste, and vent

pipes within tne building shall be of cast iron, galvanized steel or wrought iron, lead, brass, or copper, except that no galvanized steel or wrought iron pipe shall be used for underground soil or waste

pipes.

Sec. 91. Fixture Unit.—The following table, based on the rate

of discharge from a lavatory as the unit, shall be employed to determine fixture equivalents:

Fixture

units One lavatory or washbasin 1 One kitchen sink 1 y2 One bathtub 2 One laundry tray 3 One combination fixture 3 One urinal 3 One shower bath 3 One floor drain 3 One slop sink 4 One water-closet 6 One bathroom group consisting of 1 water-closet, 1 lavatory, and 1 bathtub

and overhead shower; or of 1 water-closet, 1 lavatory, and 1 shower

compartment 8 One hundred and eighty square feet of roof or drained area in horizontal projection shall count as one fixture unit.

Sec. 92. Soil and Waste Stacks.—Every building in which

plumbing fixtures are installed shall have a soil or waste stack, or

stacks, extending full size through the roof. Soil and waste stacks

shall be as direct as possible and free from sharp bends and turns. The required size of a soil or waste stack shall be determined from the

distribution and total of all fixture units connected to the stack in

accordance with the following table, except that no water-closets

shall discharge into a stack less than 3 inches in diameter:

Maximum fixture units on one stack

Diameter (inches)

With “sanitary T

”

inlets With all 45° Y or “combination Y and

one-eighth bend ” inlets Maximum

length, in- cluding

extension

as vent

In one branch

interval 1 On any

one stack In one branch

interval 1 On any

one stack m . 1 1 1 1 Feet

50

V/i 2 8 4 12 65

2 9 16 15 36 85

3 24 48 45 72 212

4 144 256 240 384 300

5 324 680 540 1, 020 390

6 672 1, 380 1, 122 2, 070 510

8 2,088 3, 600 3,480 5, 400 750

1 The term “branch interval” shall be interpreted to mean a vertical length of stack, not less than 8 feet, within which a branch or branches are connected, and the total fixture units on all branches connected

to a stack within any 8-foot length shall not exceed the maximum permitted by the table in one “branch

interval.”32
RECOMMENDED PLUMBING CODE 33

Sec. 93. Soil and Waste Stacks, Fixture Connections.—All

soil and waste stacks and branches shall be provided with correctly

faced inlets for fixture connections.

Sec. 94. Changing Soil and Vent Pipes.—In existing buildings

where the soil or waste vent pipe is not extended undiminished

through or above the roof, or where there is a sheet-metal soil or waste vent pipe, and the fixture is changed in style or location or is replaced, a soil or waste vent pipe of the size and material prescribed

for new work shall be installed.

Sec. 95. Prohibited Connections.—No fixture connection shall be made to a lead bend or branch of a water-closet or similar fixture. No soil or waste vent, circuit or loop vent above the highest installed

fixture on the branch or main shall thereafter be used as a soil or waste pipe.

Sec. 96. Soil and Waste Pipe Protected.—No soil or waste

stack shall be installed or permitted outside a building unless adequate

provision is made to protect it from frost. Sec. 97. Roof Extensions.—All roof extensions of soil and waste

stacks shall be run full size at least 1 loot above the roof, and when

the roof is used for other purposes than weather protection such

extension shall not be less than 5 feet above the roof. When there is danger of frost closure, no roof extension shall be

less than 4 inches in diameter. Change in diameter shall be made

by use of a long increaser at least 1 foot below the roof, and where

access to the roof is difficult a test opening shall be provided at this point.

Sec. 98. Terminals.—The roof terminal of any stack or vent, if within 12 feet of any door, window, scuttle, or air shaft, shall extend

at least 3 feet above the same.

Sec. 99. Terminals Adjoining High Buildings.—No soil, waste,

or vent pipe extension of any new or existing building shall be run or placed on the outside of a wall, but shall be carried up in the inside

of the roof. In the event that a new building is built higher than an existing

building, the owner of the new building shall not locate windows

within 12 feet of any existing vent stack on the lower building unless

the owner of such new building shall defray the expenses or shall himself make such alteration to conform with section 98 of this article. It shall be the duty of the owner of the lower or existing building

to make such alteration therein upon the receipt in advance of money

or security therefor, sufficient for the purpose, from the owner of the

new or higher building or to permit, at the election of the owner of

the new or higher building, the making of such alteration by the owner of said new or higher building.

Sec. 100. Traps Protected, Vents.—Every fixture trap shall be

protected against siphonage and back pressure, and air circulation

20141 °—29- 4
34 RECOMMENDED PLUMBING REQUIREMENTS

assured by means of a soil or waste stack vent, a continuous waste or

soil vent, or a loop or circuit vent. No crown vent shall be installed.

Sec. 101. Distance of Vent from Trap Seal.—No trap shall be

placed more than 5 feet, horizontal developed length, from its vent. The distance shall be measured along the central line of the waste or

soil pipe from the vertical inlet of the trap to the vent opening. The

vent opening from the soil or waste pipe, except for water-closets

and similar fixtures, shall not be below the dip of the trap.

Sec. 102. Main Vents to Connect at Base.—All main vents or vent stacks shall connect full size at their base to the main soil or waste pipe at or below the lowest fixture branch and shall extend

undiminished in size above the roof or shall be reconnected with the

main soil or waste vent at least 3 feet above the highest fixture branch.

Sec. 103. Vents, Required Sizes.—The required size of main vents

or vent stacks shall be determined from the size of the soil or waste

stack vented, the total number of fixture units drained into it, and the

developed length of the vent, in accordance with the following table,

interpolating when necessary between permissible lengths of vent

given in the table:

Maximum permissible length of vents (in feet) for soil and waste stacks

Diameters of soil or waste Number of Diameter of vent (in inches) stack (inches) units 1H 1H 2 2

1 <2 3 4 5 6 8 10

114 1 45 m Up to 8 35 60

2 Up to 18 30 50 90 24 Up to 36 25 45 75 105

3 12 34 120 180 212

3 . 18 18 70 180 212

3 24 12 50 130 212

3 . 36 8 35 93 212

3 _ 48 7 32 80 212

3 72 6 25 65 212

4 24 25 110 200 300 340

4 48 16 65 115 300 340

4 96 12 45 84 300 340

4 144 9 36 72 300 340

4_ 192 8 30 64 282 340

4 264 7 20 56 245 340

4 384 5 18 47 206 340

5 72 40 65 250 390 440

5 _ 144 30 47 180 390 440

5 __ 288 20 32 124 390 440

5 432 16 24 94 320 440

5 720 10 16 70 225 440

5 1 , 020 8 13 58 180 440

6 144 27 108 340 510

6. 288 15 70 220 510 630

6 576 10 43 150 425 630 6-.. 864 7 33 125 320 630

6 1, 296 6 25 92 240 630

6 2, 070 4 21 75 186 630

8 320 42 144 400 750 900

8 640 30 86 260 750 900

8 960 22 60 190 750 900

8 1, 600 16 40 120 525 900 8 2, 500 12 28 90 370 900

8. 4, 160 7 22 62 252 840

8 5,400 5 17 52 212 705
RECOMMENDED PLUMBING CODE 35

Sec. 104. Branch and Individual Vents.—No vents shall be

less than V/i inches in diameter. For V/i and inch wastes the

vent shall be of the same diameter as the waste pipe, and in no case

shall a branch or main vent have a diameter less than one-half that of

the soil or waste pipe served, and in no case shall the length of a branch vent of given diameter exceed the maximum length permitted

for the main vent serving the same size soil or vent stack.

Sec. 105. Vent-Pipe Grades and Connections.—All vent and

branch vent pipes shall be free from drops or sags and be so graded

and connected as to drip back to the soil or waste pipe by gravity.

Where vent pipes connect to a horizontal soil or waste pipe, the vent

branch shall be taken off above the center line of the pipe, and the

vent pipe must rise vertically or at an angle of 45° to the vertical

to a point 6 inches above the fixture it is venting before offsetting

horizontally or connecting to the branch, main waste, or soil vent. Sec. 106. Circuit and Loop Vents.—A circuit or loop vent will be permitted as follows: A branch soil or waste pipe to which two

and not more than eight water-closets, pedestal urinals, trap standard

slop sinks, or shower stalls are connected in the series may be vented

by a circuit or loop vent, which shall be taken off in front of the last fixture connection. Where fixtures discharge above such branch,

each branch shall be provided with a relief one-half the diameter

of the soil or waste stack, taken off in front of the first fixture connection.

Sec. 107. Vents not Required.—No vents will be required on

a down spout or rain leader trap, a back-water trap, a subsoil catch

basin trap, or on a cellar floor drain, provided the cellar floor drain

branches into the house drain on the sewer side at a distance of 5

feet or more from the base of the stack.

Where bathrooms or water-closets or other fixtures are located on

opposite sides of a wall or partition or directly adjacent to each other

within the prescribed distance, such fixtures may have a common

soil or waste pipe and common vent.
ARTICLE X.—HOUSE DRAINS AND SEWERS

Sec. 108. Independent System.—The drainage and plumbing

system of each new building and of new work installed in an existing

building shall be separate from and independent of that of any other

building, except as provided below, and every building shall have an

independent connection with a public or private sewer when available.

Exception. —Where one building stands in the rear of another building on an interior lot and no private sewer is available or can be

constructed to the rear building through adjoining alley, court, yard,

or driveway, the house drain from the front building may be extended

to the rear building and the whole will be considered as one house

drain.

Sec. 109. Old House Sewers and Drains.—Old house sewers and drains may be used in connection with new buildings or new

plumbing only when they are found, on examination and test, to conform in all respects to the requirements governing new sewers or

drains, as prescribed in this code. If the old work is found defective,

the proper administrative authority shall notify the owner to make

the necessary changes to conform with this code.

Sec. 110. Connections with Cesspools.—When a sewer is not

available, drain pipes from buildings shall be connected with approved

private sewage disposal works.

Sec. 111. Excavations.—Each system of piping shall be laid in a separate trench, provided that drainage trenches may be benched not

less than 18 inches for lighter piping, if not in violation of any city

regulation prescribed for their installation. Where a double system

of drainage is installed, the sanitary and surface house sewers or

drains may be laid side by side in one trench.

Tunneling for distances not greater than 6 feet is permissible in

yards, courts, or driveways of any building site. When pipes are

driven, the drive pipe shall be at least one size larger than pipe to be

laid. All excavations required to be made for the installation of a housedrainage system, or any part thereof within the walls of a building,

shall be open trench work. All such trenches and tunnels shall be

kept open until the piping has been inspected, tested, and approved.

Sec. 112. House Drains Underground.—Whenever possible all house drains shall be brought into the building below the basement or

cellar floor. 36
RECOMMENDING PLUMBING CODE 37

Sec. 113. Material.—(a) The house sewer beginning 5 feet outside of the inner face of the building wall shall be of cast iron or of

vitrified clay pipe; (b) the house drain when underground shall be of lead, brass, or cast iron; (c) the house drain when above ground shall be of cast iron, galvanized wrought iron or steel, lead or brass,

approved standards. (See Art. Ill, secs. 26 to 33, inclusive.)

Sec. 114. Depth of Drains and Sewers.—No house sewer or underground house drain shall be laid parallel to or within 3 feet of any bearing wall, which might be thereby weakened. The house

sewer and drains shall be laid at sufficient depth to protect them

from frost. Sec. 115. Size of Drains, Sewers, and Horizontal Branches.

The required size of sanitary house drains, sanitary house sewers, and horizontal branches shall be determined on the basis of the total

number of fixture units drained by them in accordance with the fol- lowing table:

Sanitary system only

Maximum number of fixture units Maximum number of fixture units Diameter of pipe

(inches) Slope,

14 inch

fall to

1 foot

Slope,

14 inch

fall to

1 foot

Slope,

Y>, inch

fall to

1 foot

Diameter of pipe

(inches) Slope,

14 inch

fall to

1 foot

Slope,

14 inch

fall to

1 foot

Slope,

14 inch

fall to

1 foot

114 1 1 1 5 162 216 264

134... 2 2 3 6 300 450 600

2 5 i 6 1 8 8 990 1, 392 2,520

4, 320

2, 220

3, 900 6,912

3

2 15 2 18 2 21 10 1, 800

4 84 96 114 12 3,084

1 No water-closet shall discharge into a drainpipe less than 3 inches in diameter.

2 Not more than two water-closets shall discharge into any 3-inch horizontal branch, house drain, or house sewer. The required sizes of storm-water house drains and house sewers and other lateral storm drains shall be determined on the basis of the

total drained area in horizontal projection in accordance with the

following table: Storm systems only

/ Diameter of pipe

(inches)

Maximum drained roof area (square feet) 1 Diameter of pipe

(inches)

Maximum drained roof area (square feet) 1

Slope,

14-inch

fall to 1 foot

Slope,

14-inch

fall to 1 foot

Slope,

14-inch fall to 1 foot

Slope,

14-inch

fall to 1 foot

Slope,

14-inch

fall to 1 foot

Slope,

14-inch

fall to 1 foot

3 865

1, 860

3, 325

5,315

1, 230

2, 610

4, 715

7, 515

1,825

4, 170

7, 465

11, 875

8 11, 115

19, 530

31, 200

42, 600

15, 745

27, 575

44, 115 60,000

24, 890

43, 625

69, 720 95,000

4 10 ....

5 12

6 ‘14

1 The calculations in this table are based on a rate of rainfall of 4 inches per hour.
38 RECOMMENDED PLUMBING REQUIREMENTS

Sec. 116. Combined Storm and Sanitary Sewer Systems.

Whenever a combined sewer system is employed, the required size of the house drain or house sewer shall be determined by multiplying

the total number of fixture units carried by the drain or sewer by

the conversion factor corresponding to the drained area and total fixture units, adding the product to the drained area and applying

the sum to the preceding table for storm-water sewers section 115. No combined house drain or house sewer shall be less than 4 inches

in diameter, and no combined house drain or house sewer shall be

smaller in size than that required for the same number of fixture units or for the same roof area in separate systems.

Conversion factors for combined storm and sanitary system

Number of fixture units on sanitary system

Drained roof

area, in square

feet Up

to

6

7to

18

19to3637

to60

61to96

97

to

144

145 to

216

217

to 324

325

to 486

487

to 732

' 733

to

1,098

1,099

to 1,644

1,645

to 2,466

2,467

to 3,702

3,703

to 5,556 Over

5,556 Up to 120 180 105 60 45 30 22 18 15 12 10 9.2 8.4 8.2 8.0 7.9 7.8

121 to 240 160 98 57 43 29 21 17.6 14.7 11.8 9.9 9.

1

8.3 8.1 8.0 7.9 7.8

241 to 480 120 75 50 39 27 20 16.9 14.3 11.5 9.7 8.8 8.2 8.0 7.9 7.8 7.7

481 to 720 75 62 42 35 24 18 15.4 13.2 10.8 9.2 8.6 8.1 7.9 7.9 7.8 7.7

721 to 1,080 54 42 33 29 20 15 13.6 12.1 10.1 8.7 8.3 8.0 7.8 7.8 7.7 7.6

1,081 to 1,620 30 18 16 15 12 11.5 11.

1

10.4 9.8 8.4 8.1 7.9 7.7 7.7 7.6 7.5

1,621 to 2,430 15 12 11 10.5 9.1 8.8 8.6 8.3 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.4

2,431 to 3,645 7.5 7.2 7.0 6.9 6.6 6.5 6.4 6.3 6.2 6.3 6.4 6.4 6.8 7.0 7.1 7.2

3,646 to 5,460 2.0 2.4 3 3.3 4.1 4.2 4.3 4.4 4.5 4.7 5.0 5.1 6.1 6.4 6.9 6.9

5,461 to 8,190 0 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.8 3.2 3.7 4.6 5.0 5.6 6.2 6.4

8,191 to 12,285 0 0 2.0 2.1 2.

1

2.2 2.3 2.3 2.4 2.5 2.6 2.7 3.5 4.5 5.2 5.6

12,286 to 18,420... 0 0 0 2.0 2.1 2.1 2.2 2.2 2.3 2.3 2.4 2.4 2.6 3.2 4.2 4.7

18,421 to 27,630... 0 0 0 0 2.0 2.1 2.2 2.2 2.2 2.3 2.3 2.3 2.4 2.5 2.8 3. 1 27,631 to 40,945... 0 0 0 0 0 2.0 2.1 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.3 2.4

40,946 to 61,520... 0 0 0 0 0 0 2.0 2.

1

2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Over 61,520 0 0 0 0 0 0 0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

Sec. 117. House Sewer in Made Ground.—The house sewer when laid in made or filled-in ground shall be of vitrified clay pipe,

laid on bed of approved grillage or concrete, or of cast-iron pipe,

A. S. T. M. approved standards.

Sec. 118. Drainage Below Sewer Level.—In all buildings in

which the whole or part of the house drainage and plumbing system

thereof lies below the crown level of the main sewer, sewage or house

wastes shall be lifted by approved artificial means and discharged

into the house sewer. Sec. 119. Sumps and Receiving Tanks.—All subhouse drains

shall discharge into an air-tight sump or receiving tank so located as to receive the sewage by gravity, from which sump or receiving tank

the sewage shall be lifted and discharged into the house sewer by

pumps, ejectors, or any equally efficient method. Such sumps

shall be either automatically discharged or be of sufficient capacity

to receive the house sewage and wastes for not less than 24 hours.

Sec. 120. Ejectors, Vented.—The soil or vent pipe leading to an ejector or other appliance for raising sewage or other waste
RECOMMENDED PLUMBING CODE 39

matter to the street sewer shall, where a water-closet or closets are

installed, be provided with a vent pipe not less than 4 inches in

diameter, and where fixtures other than water-closets are installed

the waste vent pipe shall be the same diameter as the waste pipe.

Sec. 121. Motors, Compressors, etc.—All motors, air compressors, and air tanks shall be located where they are open for inspection

and repair at all times. The air tanks shall be so proportioned as

to be of equal cubical capacity to the ejectors connected therewith,

in which there shall be maintained an air pressure of not less than

2 pounds for each foot of height the sewage is to be raised.

Sec. 122. Ejectors for Subsoil Drainage.—When subsoil catch

basins are installed below the sewer level, automatic water ejectors

provided with a ball float attached to the main water supply shall be

used. Such ejectors or any device raising subsoil water shall dis- charge into a properly trapped fixture or into a storm-water drain.
ARTICLE XI.—STORM-WATER DRAINS

Sec. 123. Drainage of Yards, Areas, and Roofs.—All roofs

and paved areas, yards, courts, and courtyards shall be drained into

the storm-water sewerage system or the combined sewerage systems,

but not into sewers intended for sewage only. When drains used

for this purpose are connected with the combined sewerage systems,

they shall be effectually trapped, except roof leaders and conductors,

where the roof or gutter opening is located not less than 12 feet from

a door, window scuttle, or air shaft. One trap may serve for all such

connections, but traps must be set below the frost line or on the

inside of the building. Where there is no sewer accessible, such connections shall be discharged into the public gutter, unless otherwise

permitted by the proper authorities, and in such case need not be

trapped.

Sec. 124. Size of Gutters and Leaders.—No gutter or inside

leader shall be of less size than the following:

Area of roof (in square feet) Gutter Leader

Up to 90

Indies

3 Indies

91 to 270 4 l*

271 to 810 4 3 811 to 1,800 5 3

1,801 to 3, 600 6 4

3,601 to 6, 500 8 6

5,501 to 9,600 10 6 Outside leaders to the frost line shall be one size larger than

required in the above table. Gutters 8 inches or over in width on new buildings shall be hung

with wrought-iron hangers of approved type.

The above sizes of rain leaders are based on diameter of circular

rain leaders, and gutters based on semicircular sheet-metal gutters

with the top dimension given and other shapes shall have the same

sectional area. Sec. 125. Inside Conductors.—When placed within the walls of any building or run in an inner or interior court or ventilating pipe

shaft, all conductors or roof leaders shall be constructed of cast iron or of galvanized wrought non or steel pipe.

Sec. 126. Outside Conductors.—When outside conductors or down spouts of sheet metal are connected with the house drain, they

40
RECOMMENDED PLUMBING CODE 41

shall be so connected by means of not less than one length of cast- iron pipe extending vertically at least 1 foot above the grade line. Along public driveways without sidewalks they shall be placed

in niches in the walls, protected by wheel guards, or enter the building through the wall at a 45° slope at least 12 feet above the grade.

Sec. 127. Defective Conductor Pipes.—When an existing

sheet-metal conductor pipe within the walls of any building becomes

defective, such conductor shall be replaced by one which conforms

to this code.

Sec. 128. Vent Connections with Conductors Prohibited.

Conductor pipes shall not be used as soil, waste, or vent pipes, nor

shall any soil, waste, or vent pipes be used as conductors.

Sec. 129. Overflows.—Overflow pipes from cisterns, supply

tanks, expansion tanks, and drip pans shall connect only indirectly

with any house sewer, house drain, soil, waste, or vent pipe.

Sec. 130. Subsoil, Foundation, Clear Water, and Absorption

Tile Drains.—Where subsoil drains are placed under the cellar floor or used to encircle the outer walls of a building, the same shall be

made of open-jointed drain tile or earthenware pipe, not less than 4

inches in diameter, and shall be properly trapped and protected

against back pressure by an automatic back-pressure valve accessibly

located before entering the house sewer or drain. They may dis- charge through a cellar drain.

Sec. 131. Subsoil Drains Below Sewer Level.—Subsoil drains

below the main sewer level shall discharge into a sump or receiving

tank, the contents of which shall be automatically lifted and dis- charged into the drainage system above the cellar through some

properly trapped fixture or drain.
ARTICLE XII.—REFRIGERATOR, SAFE, AND SPECIAL

WASTES

Sec. 132. Fixtures Permitted to Connect.—No waste pipe

from a refrigerator or ice box floor drain, or any other receptacle

where food is stored shall connect directly with any house drain,

soil, or waste pipe. Such waste pipes shall in all cases empty into an open sink that is properly supplied with water, connected, trapped,

and vented, the same as other fixtures, or they may discharge into a down spout or rain leader trap located inside the building or into a

cellar floor drain, but their ends must be left open. Such waste

connections shall not be located in inaccessible or unventilated cellars. Sec. 133. Refrigerator Wastes.—Refrigerator-waste pipes shall be not less than 1 J inches for 1 opening, 1 \ inches for 3 openings, and

for 4 to 12 openings must be not less than 2 inches, and shall have at each opening a trap, and clean-out at angles, so arranged as properly

to flush and clean pipe. Such waste pipes shall be continued not

less than full size through the roof, except where such fixtures are located in the basement or first floor. Sec. 134. Overflow Pipes and Motor Exhausts.—Pipes from

a water-supply tank or exhaust from a water lift shall not be directly

connected with any house drain, soil, or waste pipe. Such pipe shall discharge upon the roof or be trapped into an open fixture or dis- charge as for refrigerator wastes.

42
ARTICLE XIII.—MAINTENANCE

Sec. 135. Defective Fixtures.—All installed fixtures found

defective or in an insanitary condition shall be repaired, renovated,

replaced, or removed within 30 days upon written notice from the

proper administrative authorities.

Sec. 136. Temporary Toilet Facilities.—Suitable toilet facili- ties shall be provided for the use of workmen during the construction

of any building. These toilet facilities shall be maintained in a

sanitary condition.
ARTICLE XIV.—INSPECTIONS AND TESTS

Sec. 137. Inspections.—All piping, traps, and fixtures of a plumbing system shall be inspected by the proper administrative

authority to insure compliance with all the requirements of this code and the installation and construction of the system in accord- ance with the approved plans and the permit.

Sec. 138. Notification.—(a) It shall be the duty of the plumber

to notify the proper administrative authority and the owner, or

his authorized agent orally, by telephone, or in writing, not less than eight working hours between the hours of 8 a. m. and 4 p. m.

before the work is to be inspected or tested.

(b) It shall be the duty of the plumber to make sure that the work

will stand the test prescribed before giving the above notification.

(c) If the proper administrative authority finds that the work will not stand the test, the plumber shall be required to renotify as above

and to pay the sum of dollars for each renotification.

(d) If the proper administrative authority fails to appear within

24 hours of the time set for each inspection or test, the inspection or

test shall be deemed to have been made, and the plumber required

to file an affidavit with the proper administrative authority that the

work was installed in accordance with the code, the approved plans

and permit, and that it was free from defects and that the required

tests had been made and the system found free from leaks; also

whether the owner or his authorized agent was present when such

inspection or test was made, or was duly notified.

(e) At the time the permit is taken out a written waiver by the owner of notification may be filed with the proper administrative

authority.

Sec. 139. Material and Labor for Tests.—The equipment,

material, power, and labor necessary for the inspection and test shall be furnished by the plumber.

Sec. 140. System Tests.—All the piping of a plumbing system

shall be tested with water or air. After the plumbing fixtures have

been set and their traps filled with water the entire drainage system

shall be submitted to a final air-pressure test. The proper administrative authority may require the removal of any clean-outs to ascer- tain if the pressure has reached all parts of the system.

Sec. 141. Methods of Testing.—(a) Water test . —The water

test may be applied to the drainage system in its entirety or in sections. If applied to the entire system, all openings in the piping

44
RECOMMENDED PLUMBING REQUIREMENTS 45

shall be tightly closed, except the highest opening above the roof and

the system filled with water to the point of overflow above the roof.

If the system is tested in sections, each opening shall be tightly

plugged, except the highest opening of the section under test, and

each section shall be filled with water; but no section shall be tested

with less than a 10-foot head of water or a 5-pound pressure of air. In testing successive sections at least the upper 10 feet of the next

preceding section shall be retested, so that no joint or pipe in the

building shall have been submitted to a test of less than a 10-foot

head of water or a 5-pound pressure of air. Under any test the water or air pressure shall remain constant for

not less than 15 minutes without any further addition of water or air.

(ib) Air test. —The air test shall be made by attaching the air compressor or test apparatus to any suitable opening and closing all other inlets and outlets to the system, then forcing air into the sys- tem until there is a uniform pressure sufficient to balance a column

of mercury 10 inches in height or 5 pounds per square inch on the

entire system. This pressure shall be maintained for 15 minutes.

(c) Final air test —The air machine shall be connected to any

suitable opening or outlet and an air pressure equivalent to 1 inch

water column shall be applied and left standing at least 15 minutes.

If there is no leakage or forcing of trap seals indicated by the fluctu- ation of the drum, float,, or water column, the system shall be deemed

air-tight.

Sec. 142. Order of Tests.—The tests may be made separately,

as follows

(a) The house sewer and all its branches from the property line to the house drain.

(b) The house drain and yard drains, including all piping to the

height of 10 feet above the highest point on the house drain, except

the exposed connections to fixtures.

(c) The soil, waste, vent, inside conductor, and drainage pipes

which would be covered up before the building is inclosed or ready

for completion. The tests required for (b) and (c) may be combined.

0d) The final test of the whole system.

(e) After each of the above tests has been made and proved ac- ceptable the proper administrative authority shall issue a written

approval.

Sec. 143. Covering of Work.—No drainage or plumbing sys- tem or part thereof shall be covered until it has been inspected,

tested, and approved as herein prescribed.

Sec. 144. Uncovering of Work.—If any house drainage or plumbing system or part thereof is covered before being regularly

inspected, tested, and approved, as herein prescribed, it shall be uncovered upon the direction of the proper administrative authority.
46 RECOMMENDED PLUMBING REQUIREMENTS

Sec. 145. Defective Work.—If inspection or test shows defects,

such defective work or material shall be replaced within three days

and inspection and test repeated.

Sec. 146. House Sewer and House Drain Tests.—The house

sewer and house drain shall be tested with water or air. The water

test shall have not less than a 10-foot head of water and the air test not less than a 5-pound pressure. All alterations, repairs,, or extensions, which shall include more than 10 feet, shall be inspected and

tested. Sec. 147. Conductor Pipes.—Conductor pipes and their roof

connections within the walls of buildings, or conductor branches on

the outside system where such branches connect with the house drain

or are less than 3 feet from the wall of the building, shall be tested

by the water or air test. Conductor branches on the outside system

may be tested in connection with the house drain.

Sec. 148. Stable and Stable-Yard Drain Test.—If a stable or any part of a stable be used for human habitation, the same inspections and tests of plumbing and drainage systems thereof shall be

made as in the case of an ordinary dwelling. Otherwise, all stable

and stable-yard drains shall be inspected, but need not be tested. Sec. 149. Garage and Drainage System.—For a garage or any

part of a garage the same tests and inspection of the plumbing and

drainage system thereof shall be made as in the case of an ordinary

dwelling.

Sec. 150. Test of Water-Distribution System.—Upon the

completion of the entire water-distribution system, it shall be tested

and proved tight under a water pressure not less than the maximum

working pressure under which it is to be used.

Sec. 151. Certificate of Approval.—Upon the satisfactory

completion and final test of the plumbing system a certificate of approval shall be issued by the proper administrative authority to the

plumber to be delivered to the owner.

Sec. 152. Air Test of Defective Plumbing.—The air test shall be used in testing the sanitary condition of the drainage or plumbing

system of all buildings where there is reason to believe that it has

become defective. In buildings condemned by the proper administrative authority because of insanitary conditions of the plumbing

system the alterations in such system shall not be considered as

repairs, but as new plumbing.

Sec. 153. Inspections and Tests not Required.—No tests or inspections shall be required where a plumbing system or part thereof

is set up for exhibition purposes and is not used for toilet purposes and

not directly connected to a sewerage system; nor after the repairing

or replacing of an old fixture, faucet, or valve by a new one (to be used

for the same purpose) ; nor after forcing out stoppages and repairing

leaks.
PART III.—EXPERIMENTAL INVESTIGATIONS, STANDARD*

IZATION, ADMINISTRATION, AND COMMENTS

CHAPTER 5.—EXPERIMENTAL INVESTIGATIONS

One of the chief reasons for appointing the committee on plumbing was the manifest need of a carefully planned investigation of the

scientific principles of plumbing systems. In spite of many experimental investigations which have been made in England, Germany,

and the United States, some of the latter being of recent date, there

is a widespread feeling that the subject is still imperfectly understood, and that some of the present-day plumbing regulations are without an adequate scientific foundation. The committee, therefore,

welcomed the opportunity of having a scientific study of housedrainage systems made under its direction by the Bureau of Standards. The results have thoroughly justified this course. Through the courtesy of Dr. S. W. Stratton, then Director of the

Bureau of Standards, and Dr. L. J. Briggs, chief of the engineering

physics division, accommodations were provided at the laboratories

of the Bureau of Standards in Washington, and Dr. R. B. Hunter

and L. W. Snyder were assigned to the work. The investigations were begun in November, 1921, and were pursued continuously

imtil January, 1923.

The original intention of the committee was to begin with vertical

stacks and the simple elements of plumbing, combine these in an

orderly and progressive way, and study the hydraulic and pneumatic principles, proceeding from simple low systems to higher and more complex layouts. Necessity for haste in the solution of certain

problems applicable to the types of small dwellings under consideration by the Building Code Committee caused this plan to be deferred

and led to tests of certain concrete examples of plumbing installation

suitable for one-story one-family dwellings, and for two-story one- family and two-family dwellings. Wherever possible the work was

extended so that the results could be applied to plumbing in larger

buildings.

In view of the extensive nature of the series of experiments described, the systematic manner in which the subject was approached,

the extreme care with which the measurements and observations were made and recorded, the generous facilities afforded and the

disinterested attitude of the investigators, the committee is of the

opinion that the results of the experimental work performed at the

Bureau of Standards are by far the most important of any yet

obtained.

47
48 RECOMMENDED PLUMBING REQUIREMENTS

In view of the importance of corrosion as an element in the longevity of plumbing systems, one of the members of the committee

has prepared a memorandum on this subject, which will be found in

the appendix. Another experimental study bearing on the subject

of corrosion was made in the Sanitary Engineering Laboratory of Harvard University, under the direction of the chairman of the committee, by Dana E. Kepner and Warren E. Howland. It concerned

the movements of air and gases in horizontal branch waste-pipes,

especially long branches. Mr. Howland’s memorandum, to be

found in the appendix, describes only a few of the many experiments

conducted during a period of about six months.

Doctor Hunter’s original report (see ch. 6) will speak for itself, but because of its length and its technical character the committee

wishes to call attention to some of its salient features and to express

its own views on certain matters pertinent to the investigation.

UNIT OF FIXTURE DISCHARGE

In order to study the capacity of house drainage systems, it was

found desirable to establish a unit of fixture discharge—a unit in- volving both volume and time; that is, rate. The rate of discharge

of an ordinary washbasin having a nominal 1 J-mch outlet, trap, and

waste was found to be about 7.5 gallons per minute, a figure so near

to 1 cubic foot per minute that the latter was taken as the definition

of one fixture unit. The maximum rate of discharge of other fixtures

may be expressed in terms of this unit* For example, it will be seen from Table 1 that a sink with a l^-inch outlet is equivalent to 1J

units; a bathtub with a 1 J-inch outlet, to 2 units; and a watercloset, to 6 units. Fixtures differ a great deal, however, and minor

details of design may considerably affect the rate of discharge. It would be useful in designing plumbing systems to know the unit

value of each of the common fixtures on the market. No attempt was made to collect this information, although a dozen or more

fixtures were studied with reference to their rates of discharge.

WATER-CLOSETS

Doctor Hunter devised an ingenious apparatus for determining

the rates of discharge of water-closets by means of an autographic

record. This showed the advantage of siphonic action in flushing.

While no attempt was made to set definite limits for the rate of flush or for the volume of water required, it may be said that for “ washdown closets” efficient flushing was obtained by using rates of 27 to 33 gallons per minute, or 3.6 to 4.4 units; for siphon-jet closets, 3.2 to 4.8 units, the average value being about 30 gallons per minute,

or 4 fixture units. If the rate of discharge is too low, the closet may

not be properly cleansed; if it is too high, flushing will be less efficient
EXPERIMENTAL INVESTIGATIONS 49

and there will be a waste of water. There seems to be good reason

for limiting the volume of water to 5 gallons per flush and the rate

of discharge to 5 units. The maximum rate of discharge of a closet

may for an instant be as high as 45 gallons per minute; hence in

Table 1 the water-closet was rated as 6 units.

The committee is of the opinion that it is possible to design waterclosets which, while preserving the necessary rate of discharge, will

give a satisfactory flush with less than 5 gallons of water, perhaps

with half this amount. It must not be forgotten, however, that the

flow must be large enough to carry the solid matter into the street sewer. If this change were brought about, savings of water con- sumption of 5 to 10 gallons per capita daily might be effected. Future conservation of water resources will demand this saving.

A few studies of pressure flushing as compared with tank flushing were made, but were not followed up. From the standpoint of dis- charge, the two systems are not materially different. Flush valves

make a more severe draft on the house water supply and demand

supply pipes of larger diameter than do the water-closet tanks,

which fill slowly after the closet has been used. A tank may be used

in connection with a flush valve, and the necessity for using water

pipes of a larger size somewhat obviated. Flush valves on a small

house service interfere with the proper operation of the ordinary

five-eighths inch water meter. A larger meter is undesirable not

only because of added cost, but because larger volumes of water

might pass without registration. The committee is of the opinion

that the use of flush valves without tanks in small dwelling houses is undesirable, although they should not be debarred.

PEAK LOADS IN HOUSE DRAINAGE SYSTEMS

Most house drainage systems are designed to carry away the water

from more than one fixture, and obviously the pipes must be large

enough to carry the total volume of simultaneous or overlapping

discharges. In a small dwelling, where the fixtures are so installed

that all might be used and discharged at the same time, the house

drain must have a capacity equal to the total number of fixture

units. In larger buildings, where there are many fixtures of the same

kind, the capacity of the house drain need not be equal to the total

number of fixture units but must take into account the probable

frequency of coincident discharges. Up to the present time this has

been estimated by a rule-of-thumb procedure, which in the case of

many fixtures has given too large a total and in the case of few

fixtures too small a total. Doctor Hunter has submitted this problem

to a mathematical analysis, applying the principles of probability to certain facts and observations secured by members of the committee

in regard to the use of water-closets in public places. His computa20141°—29 5
50 RECOMMENDED PLUMBING REQUIREMENTS

tions, set forth in pages 91 to 98 of his report (see ch. 6), give some

interesting results, of which the following is a typical instance.

If, in a group of four water-closets, it be assumed that each flush

lasts 10 seconds, and that the interval between flushes is 5 minutes

during a rush period of 2 hours, the frequency of occurrence of 3

closets being discharged so that the flushes would overlap is once in

52 days, and the frequency of occurrence of all 4 overlapping is once in 28 years. In such a case it is sufficient to provide for a peak load of 3 times 6 fixture units; that is, 18 units, and not 4 times

6 units, or 24 units. Thus, even in such a commonplace subject as plumbing the so-called higher mathematics may be used to show

what capacities are necessary and sufficient. In the case of small

dwellings less dependence has been placed on mathematics, and

required capacities have been established by the common judgment

of the committee.

Doctor Hunter has contributed further calculations, giving what

are believed to be more precise results than heretofore available in

the case of tall buildings, in his supplementary paper on stacks,

drains, and vents, pages 188-205.

CAPACITIES OF HOUSE DRAINS

In designing a drainage system the house drain should be considered first and its capacity determined on the basis of the greatest

number of fixture units likely to be frequently discharged together

or so as to overlap, including rain water if discharged into it. The

house drain should be able to take away the water as fast as received

without backing up into the soil or waste stacks and at a velocity

sufficient to prevent the deposit of solids; that is, a velocity of about

2 feet or more per second. A table (Table 4) based upon Darcy’s

formula has been prepared which shows for different sizes and slopes

the volume of water in gallons per minute and the number of fixture

units which can be safely delivered to the house drain. For example,

a 4-inch pipe with a grade of one-fourth inch per foot will accommodate

14 fixture units, or practically one water-closet (6), one washbasin (1), one bathtub (2), one kitchen sink (li), and two combined laundry

trays (3), all discharged at once, which would seldom be the case. The figures in this table have been checked with Williams and Hazen’s

hydraulic tables. For small dwelling houses the common sizes and

grades for house drains appear to be reasonable.

At this point attention is called to the fact that street sewers not

infrequently become overloaded because of the growth of the city,

the substitution of apartment houses for single-family dwellings, and

skyscrapers for low buildings. This may cause sewage to back up

in the house drain.

CAPACITIES OF SOIL STACKS

There has been a tendency to use soil stacks and waste stacks which

are too large. Starting with the assumption that no static head

should be developed in the stack and considering that the place
EXPERIMENTAL INVESTIGATIONS 51

where the stack would he first likely to run full would be immediately

below the fitting through which the water entered, it was reasoned

that the capacity of the stack should be determined by the capacity

of the inlet fitting. Experiments were, therefore, made to determine the capacity of inlet fittings and, with these as a basis, the

capacities of stacks of different sizes were found by experiments and

computations. Doctor Hunter deduced a mathematical formula

for stack capacities. The following figures will show the capacities

of certain commonly used stacks and inlet fittings:

Capacity of stack in

fixture units

Diameter of stack in inches Single or double

sanitary T

fittings

Single or double Y, combination Y, and

one-eighth bend

fittings

2 6 12

3 13.5 27

4 24 48

It will be observed that the sanitary T is much less satisfactory

than a Y or a combination Y and one-eighth bend as an inlet fitting, as it limits the stack capacity. Or, to put the matter in another

way, a 3-inch stack with proper inlet fittings has almost as large a capacity as a 4-inch stack with sanitary T inlet fittings.

Another critical point in the design is the turn where the vertical

stack enters the horizontal house drain. In systems where the

stack and house drain have the same- diameter no special provision

need be made beyond providing a turn of sufficient radius to make

an easy bend. In systems where the house drain is one or more

sizes larger than the stack the bend should have a diameter at least one size larger than that of the stack.

CHARACTERISTICS OF FALL OF WATER IN PARTIALLY FILLED STACKS

Small flows of water down a stack tend to adhere to the sides and

to follow a spiral course. In the case of larger flows frictional

resistance of the air causes the water to form diaphragms across the pipe which persist temporarily and then break through. With

still larger flows the diaphragms become slugs and do not break

through. Solids tend to encourage the formation of slugs.

The studies of velocities in partially filled pipes were interesting

and instructive. The acceleration of falling water under the influ- ence of gravity and the friction of the water on the sides of the pipe,

which increases approximately as the square of the velocity, unite

to produce a velocity which, after it attains a certain maximum,

remains practically constant. This maximum is reached in a com-
52 RECOMMENDED PLUMBING REQUIREMENTS

paratively short fall and increases as the volume of flow increases.

This whole subject of vertical velocity is a matter of importance in

the design of tall stacks, and the studies indicate that the height of stacks need not be limited because of the fear of excessive downward

velocities. For example, in a 3-inch stack open at both ends the

velocity attained after a fall of 20 feet is 29 feet per second and

after 100 feet 34.2 feet per second, a relatively small increase. Doctor

Hunter’s experiments and computations are a valuable contribution

to hydraulic science in this field. VENT REQUIREMENTS

The subject of venting is complicated and can not be discussed in a few words. The committee has given attention to the necessity of relieving back pressure, partial vacuum, and self-siphonage of traps

in order that a plumbing system may function efficiently. It has

also made studies of air circulation and diffusion. The experiments

have been very numerous, and the results can be understood only

by giving careful study to the particular arrangement of pipes in

each case. The committee suggested as a criterion of satisfactory

trappage that the 2-inch seal of a trap should not be reduced to less than 1 inch. Stacks of 3 and 2 inches were chiefly used.

Speaking in general terms, it may be said that the size of the vent

stack depends upon three principal factors—the diameter of the soil pipe, the maximum volume of water discharged, and the length of the soil and vent stacks. Specifically, it was found that for a 3-inch

stack carrying its capacity load of 26 fixture units a 2-inch vent 36

feet long or a l|-inch vent 15 feet long gave satisfactory results. The flow of air in pipes is the controlling factor in vent requirements. Use was made of well-known pneumatic laws for air flow,

and these laws, together with the experiments themselves, gave the

basis for some important generalizations in regard to the design of vent stacks. Given the discharge and the developed length of vent

stack, the diameter required for a given soil stack can be determined.

Increasing the diameter of a soil stack requires greater proportional

increase in the diameter of the vent stack because of the increased

volume of air to be moved. On the other hand, decreasing the diameter of a soil stack permits a greater proportional decrease in the

diameter of the vent stack, but there are objections to using a vent

stack less than 1 \ inches in diameter.

ADMISSION OF STORM WATER

There are advantages in not admitting roof water to an interior

house drainage system. If the city has a “separate” system oi

sewers—that is, domestic sewage and rain water kept apart—the

admission of roof water to the house sanitary sewer would not be
EXPERIMENTAL INVESTIGATIONS 53

allowed. If the city has the “combined” system, the storm water

should be carried separately to the house sewer. There is a ten- dency to change from the combined to the separate system, and if this were done the cost of alterations in the plumbing required to bring about the separation would be much greater if the roof water

entered the house drain than if it entered the house sewer outside the

building.

The admission of roof water to a house drain increases the danger

of back pressure near the base of the stack, this danger increasing

rapidly with the rainfall. In its computations the committee considered that a rainfall rate of 4 inches per hour was a reasonable

allowance, and hence it was decided that 180 square feet of drained

area in horizontal projection should be considered as equivalent to one fixture unit. The method of applying this figure to the table

given in the code (see ch. 4, sec. 116) allows a large factor of safety.

This figure was reached after a careful study of the frequency of occurrence of different rates of rainfall in different parts of the

United States as published by the Weather Bureau of the United

States Department of Agriculture. At New York a rainfall rate

of 4 inches per hour occurs once in about two years; at New Orleans,

every year; and at St. Paul, Minn., once in three years. Where

large systems are being designed the committee’s reasonable allow- ance should not be used, but some other figure based on a careful

study of local rainfall intensity should be substituted for it. In computing the capacity of a house drain this rain allowance

should be added to the other requirements, for, although the chance

of such a rainfall as that assumed occurring at the time of the peak

load from the fixtures is small, the factor of safety thus provided is none too large.

Storm water, a high tide, or sewer stoppage may cause the house

sewer or even the house drain to be submerged, giving back-pressure

effects similar to those produced by admitting roof water to the sys- tem. Where such complications as this are likely to occur the committee favors a distance of at least 3 feet between the lowest fixture

inlet to the stack and the house drain.

RUNNING TRAP

Whatever be the supposed advantages of the house trap, or run- ning trap, as a protection of the house drainage system against the air of street sewers, the experiments made by Doctor Hunter indicate

that this device produces an effect similar to a partially submerged

drain. Whether vented or not, it decreases the capacity of the house

drain. Other reasons against using the house trap are given in note

19, chapter 10.
54 RECOMMENDED PLUMBING REQUIREMENTS

EFFECT OF WIND BLOWING OVER STACK TOPS

Studies of the effect of winds blowing over the tops of stacks were

included in the experiments. These effects were measurable, hut

too small to be of practical importance in the case of small dwellings.

FROST CLOSURE OF THE STACK TOPS

The closure of the top of the stack by frost or other cause was

studied. Complete closure caused some of the traps to be siphoned

by the discharge of a single water-closet, and this occurred whether

or not the traps were individually vented. Incomplete closures gave

less noticeable effects. It is., a matter to be guarded against as well

as possible, but can not be controlled by modifications of the venting

system.

SIPHONAGE OF FIXTURE TRAPS

Careful study has been made of the action of plain traps; that is, the ordinary S, | S, and § S (or P) traps, under different conditions.

The efficiency of a trap is sometimes thought to mean its resistance

to loss of seal, but the real efficiency is resistance to alternate suction

and back pressure. Loss of seal does not concern the trap alone.

The fixture itself is an element when self-siphonage is being considered. A trailing discharge, such as occurs in a bathtub, kitchen

sink, or laundry tray, is almost invariably sufficient to refill an

ordinary trap; but with an oval basin, where the discharge ends

suddenly, greater care must be taken to prevent self-siphonage.

The diameter of the tailpiece relative to that of the trap is an element.

There are advantages in having the tailpiece one nominal size smaller

than the trap. The length of the waste pipe and its inclination to the horizontal are also elements, as well as the presence of elbows

in the wastepipes. Hence, it is more logical to consider the efficiency of the trap and waste pipes as a whole than that of the trap alone

using the changes in trap seal as a measure of the efficiency of the

system.

With this idea in mind extensive studies were made to ascertain

the effects of pressure, aspiration, and self-siphonage on the seal of

traps and the best arrangement of designing waste pipes to secure an efficient system in the simplest way. The possible situations are

so numerous that the reader is referred to the detailed statements

and diagrams in Dr. Hunter’s report. The committee, reached the

conclusion that the minimum seal for a plain trap should be 2 inches,

and that a loss of seal greater than 1 inch in such a trap should be

regarded as unsatisfactory. While it is true that a seal is not actually

broken unless the water in the trap falls below the “dip,” some

factor of safety must be allowed to provide for unexpected shocks,

for evaporation, capillary loss, and for oscillations due to wind pressure, while a lowering of the seal exposes a foul surface on the house

side of the trap.
EXPERIMENTAL INVESTIGATIONS 55

A fixture trap is almost sure to foul to some extent; sediment may

collect at the bottom, grease may adhere to the sides, and growth of fungi may develop. The deeper the trap seal the greater the extent

of the fouling. While deep seal traps can withstand siphonage better

than traps of shallow seal, these other practical considerations combine to make it advisable to place a maximum limit upon trap seals,

and the committee has placed this at 4 inches. Experiments and

computations made by Mr. Howland (Appendix C) have shown that

the danger of gases in the drainage system diffusing through the trap

seal is negligible for water seals between 2 and 4 inches; that the

liability of odors from deposits in the trap is also negligible; but that

the possibility of odors from deposits on the pipe between the fixture

and the trap in the overflow waste pipe, and in the trap itself when

its seal is lowered below normal, is more important. While it is true that many traps which have seals as deep as 6 or 7 inches are in use, and while such deep-seal traps can not be said to be injurious to health the committee is of the opinion that the establishment of a minimum limit of 2 inches and a maximum limit of 4 inches for plain

traps is desirable, and gives a basis for standardization.

RESEALING OR ANTISIPHON TRAPS

The committee has given attention to the subject of antisiphon,

nonsiphon, or resealing traps, as they are called. Practically all traps, except the plain traps already mentioned, may be included in

this class. There are many different kinds, many of them patented

and more expensive than plain traps. They are supposed to resist siphonage better than plain traps by reason of having a deep seal, a greater area or volume, tortuous passages for the water, projecting

lips, partitions, or, in some cases, moving parts. The best of the

resealing traps when clean resist siphonage more than a plain trap

of 2 to 4 inch seal, and this may be the case even when slightly fouled.

When more completely fouled, this resistance to siphonage rapidly

lessens. Properly designed resealing traps unvented and clean

resist back pressure somewhat more than unvented plain traps of

the same depth of seal, but the difference is not sufficient to justify

their general use without vents. Their greater complexity causes them to clog more quickly than plain traps, and, if clogged, they are

less easily cleaned by the householder and can not be thoroughly

cleaned by the usual method of using a force pump or plunger.

Lack of standardization of these traps makes replacement more

troublesome and expensive. The supposed advantages of a resealing

trap lie in the fact that greater resistance to siphonage makes it possible to omit some of the vent pipes commonly installed and to use longer horizontal unvented waste-pipes and thus secure greater

freedom in the location of fixtures. Long unvented horizontal runs, however, are in themselves objectionable.
56 RECOMMENDED PLUMBING REQUIREMENTS

As before stated, the efficiency of traps should not be considered

alone; plain traps should not be compared with “resealing traps’ ’; the true comparison is between a drainage system including plain

traps and a drainage system including resealing traps. The experiments made by the Bureau of Standards have indicated that simplifications in venting are possible even when plain traps are used.

Plain traps have the advantages of economy, simplicity, greater

freedom from fouling, and greater ease of cleaning. For these reasons

the committee favors having drainage systems designed on the basis

of plain traps rather than on the basis of resealing traps and is of the opinion that the plain-trap system, with simplified venting,

affords ample range in the location of fixtures. Resealing traps

should not be accorded any special privilege with respect to venting over plain traps, but their use can not be prevented by regulation.

In short, plain trapping with vents should be the prescribed rule,

with resealing traps without vents permitted only under very

restricted conditions.

UNVENTED HORIZONTAL BRANCH WASTE PIPES

Directly involved with the question of resealing traps is that of the allowable length of unvented horizontal branch waste pipes,

because it is chiefly in connection with long branches that resealing

traps have an advantage over plain traps.

Long branches have a number of practical disadvantages. There

is a tendency to give them too little slope. Long straight runs are

likely to interfere with framing timbers and encourage unnecessary

cutting. If the fixture discharge is small and only partially fills the

pipe, deposits may occur, and if the discharge is so large as to completely fill the pipe, self-siphonage of the trap may occur. It .is this last danger that the resealing trap is supposed to prevent. If a long branch becomes stopped, it is more difficult to clean than a

short branch.

If long branches are unvented, there is danger of corrosion. While

this is well known by experience, especially where wrought iron or

steel is the metal used, the committee thought it worth while to have

this subject studied. The results of the experiments show that in

unvented horizontal branches connected to a stack the movements

of air in the stack produce eddy currents in the branch to a distance

of only 1 or 2 feet; that temperature changes may cause slight air movements in the branch; that diffusion of gases throughout the

length of the branch occurs; that if such a gas as carbon dioxide is produced from deposits of organic matter uniformly along the branch

the maximum concentration of this gas will increase as the square of the length of the branch; that deposits of moisture occur on the inner

walls of a pipe, especially along the top; that iron rust absorbs

moisture; that moisture thus collected absorbs carbonic acid, which
EXPERIMENTAL INVESTIGATIONS 57

tends to stimulate the corrosion of iron. In other words, the danger

of corrosion in an unvented branch 10 feet long is about four times

as great as in a branch 5 feet long. In the case of exposed horizontal

pipes leakage from corrosion might be detected and the pipe could

be readily replaced, but waste pipes are usually concealed, where

leakage might go undetected and replacement would be costly.

From the standpoint of self-siphonage the slope should lie between

one-eighth and one-half inch per foot and the outlet should not be

below the dip of the trap. Doctor Hunter’s experiments show that

in the case of wash basins plain traps of 2 to 4 inch seal, connected to horizontal wastes of 4 to 8 feet, would be safe against siphonage,

and in the case of wide bottom fixtures the lengths might be about

twice as long, with one 90° elbow not more than 18 inches from the

trap. But on the basis of all the evidence at hand the committee

decided that 5 feet should be established as a reasonable limit for

the* length of an unvented horizontal waste, measured horizontally

from the vertical inlet of the trap to the vent opening.

VENTING OF BRANCH WASTES

A clogged vent pipe is useless, just as useless as if no vent pipe had

been installed. If waste pipes are so arranged that the waste water

may rise into the vent pipe at times of discharge, the latter is very

liable to become clogged. If the connection of the vent pipe and

waste pipe lies below the hydraulic grade—that is, below a line

which connects the high-water line of the fixture and the point where

the waste pipe enters the stack—water is likely to rise into the vent

pipe. The crown vent is an example of this condition, and the fre- quent clogging of this vent has caused this arrangement to be looked

upon with disfavor and even to be prohibited by regulation, but

almost any vent which rises from a horizontal branch may act in

the same way if the discharge fills the waste pipe. If the vent forms

a continuation of the vertical leg of the waste pipe and if this connection is above the hydraulic grade, there will be no danger of the

vent becoming clogged. This is a reason for limiting the length of

all horizontal waste pipes, whether vented or not. Doctor Hunter’s

explanations of this subject are clear and illuminating.

SEPARATE TRAP VENTING NOT NECESSARY

Every trap seal of a plumbing system should be adequately

protected against failure, but to accomplish this it is not necessary

that each particular trap have an individual vent pipe. For example,

stack venting appropriate for the highest fixtures is the most efficient and certain of all forms of venting. Venting requirements relate

to the drainage system as a whole. Wet vents—that is, portions of

the waste pipe which are used alternately for the discharge of water

and for venting purposes—are unobjectionable if installed with

regard to the principles already set forth.
58 RECOMMENDED PLUMBING REQUIREMENTS

The committee is strongly of the opinion that if due thought is given to the design of the drainage system vent pipes may be reduced

in size and number, plain traps may be used, and the whole system

made simpler and cheaper than is often the case to-day. To do

this, however, generally requires that fixtures be located relatively near a stack, and architects are urged to design buildings so that

this can be done.

THE 3-INCH SOIL STACK

An important conclusion reached by the committee after a thorough discussion of the experimental data was that a 3-inch soil stack has a greater capacity than has often been thought, provided

that the house drain is of adequate size, that the points of inlet are well chosen, and the inlet fittings of proper type. While admitting

that a larger size has a greater capacity and may under some conditions be desirable, a 3-inch soil stack is deemed sufficient for any

ordinary dwelling. The economies resulting from using a 3-inch

instead of a 4-inch size are material. Less metal is required, trans- portation and construction costs are less. The 3-inch pipe can be

placed in an ordinary frame dwelling wall, thus saving cost and room

space. A 3-inch soil pipe can be placed in a partition having 4-inch

studding, and a 3-inch bend can be housed in the flooring better

*than a 4-inch bend. A 3-inch soil stack may be satisfactorily used

for a high building, if the necessary conditions are complied with.

The reader is referred to Doctor Hunter’s report for information on

this point.

CONCRETE EXAMPLES OF VENT REQUIREMENTS

It is quite difficult to set forth vent requirements in words, and for

that reason it is difficult to frame regulations which will be adequate

and never unreasonable. Even Doctor Hunter’s conclusions, set forth on page 176 of his report, are difficult to visualize. The committee, therefore, asked him to arrange a series of plumbing layouts,

which should set forth in a concrete way the venting which the

experiments indicated to be desirable, assuming that plain traps are used and that the simultaneous discharges of fixtures are those

reasonably to be expected. These are shown in Figures 90, 91, and

92. It will be seen that in houses of the single, low bungalow type

very little individual venting is required; that with fixtures on two

stories an additional vent stack is needed, but few if any vents for

waste branches; that with fixtures on three stories venting of branch

waste pipes becomes necessary, but that even here group vents

rather than individual vents for each fixture suffice. These figures do not, of course, represent all possible layouts, but

they may be taken as types and deserve careful study. Attention is
EXPERIMENTAL INVESTIGATIONS 59

called also to some of the more detailed layouts shown on Figures

81 to 89, which will give a better idea of the situation than can be

told in words.

FACTORS OF SAFETY

The committee has given much attention to the factors of safety

needed in plumbing systems. That some margin should exist is obvious, for unforeseen conditions may arise, partial or complete

stoppages of portions of a drainage system may occur, fixtures may

remain out of use for long periods, workmanship is never perfect.

On the other hand, the occasional failure of a trap seal does not injure

the structure of the plumbing system, and in this instance the committee has decided that in the case of a trap having a water seal of 2 inches, two is a sufficient factor; that is, a 2-inch seal should never be reduced to less than 1 inch. In structural work factors of safety

of four or five are properly required.

With the best of intentions, factors of safety have sometimes been

multiplied, one upon another, until the system was overburdened

with precautions and expense. Yet even where this has occurred

there have been examples of unimportant matters being stressed

while vital requirements were neglected. The committee is of the

opinion that a careful study of Doctor Hunter’s report will clarify

many ideas in regard to plumbing design.

PLANNING FOR SIMPLICITY

The committee has less faith in plumbing regulations than in the

education of plumbers and the cooperation between sanitary engineers, plumbers, and architects. The plumbing system is an integral part of a modern dwelling. Structurally it must interlock with

other parts of the building. It should be given serious thought when

the building is planned. Simple plumbing can be obtained if it is planned for, but if the plumbmg is made the last element of the design complications are sure to arise. The committee is of the opinion that the principles of plumbing

and house drainage are not being given sufficient attention in schools

of engineering and architecture; that present-day textbooks of

plumbing give too much attention to fixture details and not enough

to the governing hydraulic and pneumatic principles of house drainage,

and that in many ways the whole matter of plumbing has been put on a commercial rather than on an engineering plane. The committee hopes that the report of the experiments made under its direction by the Bureau of Standards will mark a turning point in the

popular attitude toward plumbing and the plumber. Simplifying

regulations should not be a matter of “ letting down the bars” to encourage simpler designs; but better and simpler designs, resulting

from scientific work, should make simple regulations sufficient.
CHAPTER 6.—PHYSICS OF PLUMBING SYSTEMS. REPORT

OF EXPERIMENTAL AND THEORETICAL INVESTIGATIONS

By R. B. Hunter and L. W. Snyder

Bureau of Standards

PURPOSE AND METHOD OF INVESTIGATIONS

The purpose of these investigations was to supply data to aid the

subcommittee on plumbing in the formulation of essential regulations

and sound rules of practice applicable to small dwelling-house construction with the view of securing simplification of plumbing design

and uniformity of requirements and practice through the general

adoption of these rules. This report is a consolidation of the oral and written reports made

to the committee at various times during the progress of the work.

These partial or progress reports have been rearranged and abridged,

retaining only the more essential data and applications.

The series of experiments outlined by the committee, including

tests of several concrete examples of plumbing installation, covering one story, one story and basement, and two story and basement, one- family houses; one story and basement duplex, and two story and

basement, two-family houses, has not been completed in all parts.

However, the investigations have advanced to the point where conclusions and generalizations, in so far as they affect small dwelling

construction, are justified.

Certain phases of the investigation, the results of which may be

applied to the general problem of house drainage, have been carried

beyond the requirements for the small dwelling and are reported.

It seems impractical to attempt to divorce entirely the requirements

for dwellings from those of other types of buildings, since many of the principles involved are applicable, without modification or with

only slight modification, to all classes of plumbing construction.

This led to a number of independent experimental and theoretical

investigations related to the general problem of house drainage.

The nature of the problem as presented and the manner in which

the experimental work developed make it impractical to report the

investigations in the order in which they were conducted. Therefore, the separate fields of investigation have been arranged in as logical an order as possible leading to final conclusions.

The fact that a plumbing system consists of many parts—the

sewer, the house drain, the vertical stacks, the connections between

the stacks and the house drain, lateral branch drains of various sizes,

lengths and forms, the vent system, and the water-supply system

60
PHYSICS OF PLUMBING SYSTEMS 61

each of which may be varied independently and which are certain to be varied in practice, coupled with the fact that, in general, the pipes

are only partially filled and that both water and air movements must

be accounted for, make it impractical, if not impossible, to develop

an}^ single mathematical expression for general application. The

problem of developing even a series of formulas is rendered more

difficult by the failure of certain types of results to duplicate when

the experiment is repeated. For example, with the simplest system,

consisting of a washbasin fitted with a plain P trap and short waste

open at the end there is a wide difference in results produced on the

final seal of the trap when the basin is repeatedly discharged with

the same quantity of water and as nearly as possible in the same

manner. Some other types of experiments duplicate results with

unfailing accuracy. For the most part conclusions have been drawn

from the latter type of experiments and results of the former type

have been applied with extreme caution. Therefore, because of these complications the different parts of the problem have been

taken up separately for experimentation and discussion, and the

results combined for application to the complete system and finally

tested in a number of complete test installations. The results as applied are approximations, though based whenever possible on

experimental values.

Many simple experiments in which the general result could have

been foretold from theoretical considerations or experience have

been performed merely to obtain numerical values to aid in tying

the different parts together, and for the same reason some simple

principles are treated at some length.

Experimental work and tables on hydraulics and flow of gases

have been freely consulted and used whenever possible in checking our own experimental results and in extending them to a wider

application. Many of the tables represent such a combination of existing tables and the results of these investigations.

The growing belief that the 3-inch stack is adaptable to a much

wider use than found in present practice has given it a prominent

place in these investigations from the beginning. The modifying

effects of external conditions, frost closure, strong winds, heavy

rainfall in case of combined sewer systems, house trap in main house

drain, and submerged outfall of house drain have been considered in

connection with the proportioning of soil, waste, and vent pipes, and

have been made the subjects of special experimentation.

In passing we wish to state that available reports of other experimental work on plumbing have been examined with considerable

care, and that we have observed, as have others, contradictory

conclusions reached from experiments apparently conducted with

similar apparatus and under similar conditions. Some of these
62 RECOMMENDED PLUMBING REQUIREMENTS

stand out from the others as conducted by men of high standing in

their professions, and we venture the opinion that at least in these

instances the work was honestly conducted and honestly reported,

and that the charges of self-interest found in some of the later reviews

of such experiments were unwarranted. Further, it is our opinion

that the disagreements were due rather to what we may call small

differences in the apparatus employed, to limited facilities, and to the viewpoint that experiments on a single system are conclusive.

Certain criticism of the committee’s tentative report that has

appeared, arising in part at least from misinterpretation due to lax

reading, leads us to caution the reader against what seems to have

been one of the most common forms of misinterpretation—namely,

the extension of specific statements and conclusions to a general

application—and to caution against drawing general conclusions

from a single phase of the experimental work unless the results are

clearly of such character as will not be modified when the part is included in a complete system or will be modified in such a manner

as to increase the efficiency of the system. A superficial reading can be of little value, and a careful reading of the report as a whole,

with a clear understanding of the application of the principles in- volved, will be found necessary to afford an intelligent, independent

interpretation.

There is also a tendency on the part of some to discount experimental evidence supporting established physical principles on the

grounds that it is not in accord with experience. In most cases such

criticism is founded on impressions or prejudices rather than on a knowledge of the facts of the case. The fact that we get opposite opinions relative to the same point, both based on the so-called experience,

indicates that little weight should be attached to them unless the

opinions are backed by very specific data, gathered under accurately

known conditions. It is true that the solution of certain points in

the problem is offered only through experience, and that the final test of the whole problem is its working under service conditions.

For that reason we have drawn freely on the knowledge of experienced

engineers and plumbers and have kept in close touch with the plumbing committee and opinions obtained through their correspondence.

No claim is made that these investigations have been exhaustive

in every detail or that the conclusions may not be modified or ex- tended by improvement in materials or design. It is fully recognized that in the matter of venting it would be possible in some

cases to omit some of the vents recommended for general application were it possible to have each system designed by a man familiar

with all the principles involved and with all the conditions to be

encountered where the system is to be installed. The judicious use

of special fittings and traps would further modify the general con-
Minimum

Plumbing

Requirements

Fig.

1.—

Fixture-rating

apparatus
Minimum

Plumbing

Requirements

.—Typical

record

of

discharge-time

curve

(full

size

photographic

reproduction)
PHYSICS OP PLUMBING SYSTEMS 63

elusions for special cases. Stock materials not covered by patents

have been used almost entirely.

We believe that our conclusions as far as they go are sound, offer- ing a common ground on which all interests may safely unite, and

a foundation on which the work may be extended to cover buildings other than the small house.

The Bureau of Standards desires to acknowledge and express its appreciation of the valuable material assistance rendered by the

committee as individuals and as a body and by various private

parties and firms in presenting problems, in offering suggestions,

and in supplying equipment without which assistance the accomplishment of the results obtained within the time allotted would

have been impossible.

RATES OF DISCHARGE FROM PLUMBING FIXTURES

In order to obtain data for the determination of the strain on any

plumbing installation and for establishing a serviceable unit of measure for such strain, the rates of discharge from the various

types of plumbing fixtures ordinarily installed in dwellings were

determined as a preliminary to other experiments. To this end

fixtures, flush tanks, flush valves, traps, and fittings, believed to be

representative in kind and number, were secured.

' APPARATUS EMPLOYED

The apparatus employed is shown in Figure 1 and in detailed

section in Figure 2. It consists of a beam balance 10 feet 6 inches

Fig. 2.—Detailed section of fixture-rating apparatus. A, ball-bearing fulcrum; B, weighing tank; C, spring

balance; D, counterweight; E, tracing stylus; F, dash pot; G, fixed stylus tracing X-axis; II, sheet-iron pipe carrying baffle plate; 7, baffle plate to take impact

long supported on a ball-bearing fulcrum, A, a suspended tank, B,

for catching the discharge, a spring or spring balance, C, attached

to the end of the beam to bring the recording stylus, E, to the zero
64 RECOMMENDED PLUMBING REQUIREMENT'S

oil the recording device, and a dash pot, F, for damping out vibrations of the beam. The recording device consists of a small motor

geared to draw a specially prepared wax paper from a drum across a smooth plane at a uniform rate. A fixed stylus, G, traces the

zero line, or X axis, and the recording stylus, E, rising with the

beam under the weight of the discharge, traces a smooth curve on

the waxed paper. The discharge pipes from the fixture to the

weighing tank were varied to meet the demands of each purpose.

The sketch (fig. 2) represents a water-closet operating on a low

tank supply and discharging through a 3-inch cast iron closet bend

into a section of vertical 3-inch stack. The part below the fitting is a glass section 3 inches by 2 feet. Around this is a moveable pipe,

H, carrying a baffle plate, /, to take the impact of the discharge.

During the operation the baffle plate, suspended with a moveable

section of pipe from the platform above, is kept level with the sur- face of water in the tank and the discharge thrown horizontally to the walls of the tank. The impact of the discharge is thus taken

by the platform and resultant vibrations reduced to a minimum.

A baffle plate serving the same purpose was arranged for each fix- ture rated. Any lag produced either by the baffle plate or dash

pot is imperceptible in the general form of the record curve. The apparatus was accurately calibrated, so that the discharge

in gallons at one second intervals may be obtained from an accurate measurement of the record curve. Figure 3 is a full-size photographic reproduction of a typical record and Figure 4 the same

curve plotted to a convenient scale.
PHYSICS OP PLUMBING SYSTEMS 65

Data determined from Figure 3, and plotted in Figures 4 and 5

1.2.

3.4.

5.6 . 7.8.

9. 10. 11 .

Time in seconds Deflection Total

discharge mm Gallons

4 0. 43

11 1. 18 18.3 1.97 25.1 2.71

28. 5 3. 07

31.

3. 35 34.4 3. 71 38.8 4. 19 41.5 4.48

43.0 4. 64

43. 1 4.65

Mean rate of dis- charge for each second

Gals, per Gals, per

sec. min.

0.43 25.8

.75 45.0

.79 47.4 .74 44.4

.36 19.8 .28 16.8 .36 21.6 .48 28.8 .29 17.4 .16 9.6

.01 .6 The slight waves observed in the record curve do not materially

affect the accuracy and are entirely eliminated in the plotted curve. Figure 5 is the derivative curve of the same discharge plotted with

Pig. 5.—Derivative curve (rate of discharge against time) plotted from Figure 3. Total discharge 4.7 gal- lons, peak discharge 45.8 gallons per minute, mean rate of discharge 30.0 gallons per minute rates of discharge in gallons per minute as ordinates and time in

seconds as abscissa. The data for this last form of curve are obtained

by reducing the mean rate of discharge for each second of the total

time of discharge to rate of discharge in gallons per minute. The

exact maximum at a point is in some cases slightly higher than the

maximum obtained in the above manner. This difference is partially corrected by the method of drawing a smooth curve through

the plotted points of the derivative curve, thus giving in many cases 20141°—29 6
66 RECOMMENDED PLUMBING REQUIREMENTS

a slightly higher maximum than any plotted point on the curve and

one corresponding to the maximum slope of the original curve. The

difference, however, is unimportant, since a maximum that does not

last for more than one second can have little effect on the combined

maximum rate of discharge from two or more water-closets. In

this connection we have considered a mean maximum rate of dis- charge over a two-second interval, which we refer to as the peak dis- charge. This is believed to be a more representative value than the

simple maximum for two reasons, first in all efficient flushes the

approximate maximum was sustained for periods of from two to three seconds, and, second, any swell in the discharge of shorter

duration has but slight bearing on the problem. It will be noticed

that for all high rates of supply the “peak discharge” and maximum

rate of discharge approach the same value. The mean rate of dis- charge recorded is the mean for the whole time neglecting the trail discharge at the end. This is approximately the same as the mean

rate of supply to the water-closet. The reader is cautioned against

confusing the rate of supply and rate of discharge in later discussions.

A number of derivative curves plotted as in Figure 5, with descriptive details of the conditions under which each was determined,

follow. These are believed to be sufficiently representative of the

characteristics and rates of discharge from water-closets under

different conditions for our purpose. It should be kept in mind that

the detailed results herein recorded represent a small part of the

total work done on the subject. Duplicate records of most determinations were made. The method is sufficiently accurate that, in

general, duplicates superimposed show no difference to the eye. The slight differences that do appear are evidently due to variations

in the operation of the supply devices rather than to inaccuracies in

the weighing and recording apparatus. No attempt has been made

to average duplicate records, since such averages tend to obscure the

true characteristics of the discharge.

In order to give the reader a conception of the extent of the work

and the quantity of data obtained the following table is added:

Fixture Number

of differ- ent types employed

i

Number

of varia- tions in

discharge

pipes

Number

of varia- tions in supply i

Approximate

total number

of records

Water-closet . _ 6 3 3 to 5.... 150 Bathtub 2 4 None 16 Washbasin. 2 6 None 24 Kitchen sink.. 2 4 None 16 Laundry tray 2 6 None 24 Grand total. 230

1 “Standing fixtures,” bathtubs, washbasins, kitchen sinks, and laundry trays were rated with vessels

filled to the overflow or to fixed depths and were discharged by lifting the plug.
PHYSICS OF PLUMBING SYSTEMS 67

Fig. 6.—Experimental system for rating water-closet discharges

TIME m SECONDS

Fig. 7 —Rate of discharge curve for a Maddox wash-down bowl, 6-gallon low tank with 2-inch elbow flush

pipe, discharged through a straight unvented glass tube 2| inches diameter by 2 feet 8 inches long. (See

fig. 6.) Total discharge 4.6 gallons, peak discharge 40.5 gallons per minute, mean rate of discharge 34.2

gallons per minute
68 RECOMMENDED PLUMBING REQUIREMENTS

T!ME IN SECONDS

Fig. 8—Rate of discharge curve for the Maddox wash-down bowl, 8-gallon low tank with 2-inch elbow

flush pipe, discharged through the straight glass tube. Total discharge 5.3 gallons, peak discharge 45.0 gallons per minute, mean rate of discharge 37.6 gallons per minute

TIME IN SECONDS

Fig. 9.—Rate of discharge curve for the Maddox wash-down bowl, 8-gallon low tank with 2-inch elbow

flush pipe, discharged through a straight unvented brass tube 4 inches diameter by 2 feet 5 inches long. Total discharge 5.1 gallons, peak discharge 46.1 gallons per minute, mean rate of discharge 40.2 gallons per minute
PHYSICS OF PLUMBING SYSTEMS 69

TIME IN SECONDS

Fig. 10—Rate of discharge curve for the same set-up as Figure 9, with the tank valve held open until the tank was nearly empty, then allowed to close automatically. Total discharge 6.0 gallons, peak discharge

44.3 gallons per minute, mean rate of discharge 36.6 gallons per minute

TIME IN SECONDS

Fig. 11.—Rate of discharge curve for a Maddox siphon jet bowl, 6-gallon high tank with straight flush pipe

1£ inches diameter by 4 feet 6 inches long, discharged through the straight 4-inch brass tube. Total dis- charge 3.8 gallons, peak discharge 40.2 gallons per minute, mean rate of discharge 34.0 gallons per minute
70 RECOMMENDED PLUMBING REQUIREMENTS

Fig. 12.—Rate of discharge curve for the same set-up as Figure 11, with the tank valve held open 5 seconds, then allowed to close automatically. Total discharge 4.5 gallons, peak discharge 48.0 gallons per minute, mean rate o discharge 40.5 gallons per minute

Fig. 13.—Rate of discharge curve for the Maddox siphon jet bowl, 6-gallon high tank, with straight lj-inch

flush pipe, discharged through the 2|-inch glass tube. Total discharge 4.2 gallons, peak discharge 41.7 gallons per minute, mean rate of discharge 27.6 gallons per minute
PHYSIC'S OF PLUMBING SYSTEMS 71

TIME IN SECONDS

Fig, 14.—Rate of discharge curve for the same set-up as Figure 13, with the tank valve held open for 5 seconds, then allowed to close automatically. Total discharge 4.7 galtyns, peak discharge 47.7 gallons per minute, mean rate of discharge 38.1 gallons per minute

Fig. 15.—Rate of discharge curve for the Maddox siphon jet bowl, 8-gallon low tank with straight 2-inch

flush pipe, discharged through the 2f-inch glass tube. Total discharge 55 gallons, peak discharge 45.? gallons per minute, mean rate of discharge 33.6 gallons per minute
72 RECOMMENDED PLUMBING REQUIREMENTS

Fig. 16.—Rate of discharge curve for the same set-up as Figure 15, with the tank valve held open until the tank was nearly empty, then allowed to close automatically. Total discharge 6.6 gallons, peak discharge

44.2 gallons per minute, mean rate of discharge 31.2 gallons per minute

Fig. 17. Rate of discharge curve for the Maddox siphon jet bowl, 8-gallon low tank with straight 2-inch

flush pipe, discharged through the 4-inch brass tube. Total discharge 5.2 gallons, peak discharge 41.0 gallons per minute, mean rate of discharge 33.4 gallons per minute
PHYSICS OF PLUMBING SYSTEMS 73

WATER-CLOSETS

The water-closet supply tanks used in the plotted determinations were filled automatically through the supply valve furnished with the

tank, operating on a supply with pressure varying from 50 to 60

pounds per square inch. The floats were adjusted to allow the tanks

to fill approximately to the overflow, thus giving a greater total volume and slightly greater rate of supply than the same tanks would

give in service where they are usually adjusted to give a margin of safety in the overflow. The water-closets were flushed by fully

opening the tank valve, then allowing it to close automatically under

Fig. 18 —Rate of discharge curve for the same set-up as Figure 17, with the tank valve held open until the tank was nearly empty, then allowed to close automatically. Total discharge 6.3 gallons, peak discharge

42.7 gallons per minute, mean rate of discharge 30.0 gallons per minute the tank refill, except in a few instances specifically noted in the

legend of the figure when the valve was held open for a period.

The maximum rate of discharge may he read from the graph. The

total discharge, “peak discharge/’ and mean rate of discharge (mean

rate of supply) are recorded with each graph.

The curves shown in Figures 20 to 38 were obtained by discharging

the water-closets through a 3-inch cast-iron closet bend “sanitary

T” and short section of glass pipe, more nearly representing service

conditions than the preceding determinations. The upper end of the “sanitary T” was left open, venting the discharge system at this point. The glass section extended 20 inches below the “ sanitary

T ” fitting (fig. 19).
74 RECOMMENDED PLUMBING REQUIREMENTS

Figure 19 also shows a water-supply line, not drawn to scale,

which was used for flush yalves in a few experiments. The supply

line consisted of a three-fourth-inch section about 30 feet long leading from a 2-inch main in which the static pressure varied between

50 and 60 pounds per square inch, and a 1-inch section connecting

from the three-fourth-inch section to the flush valve, with gate

valves and one-fourth bends as indicated. The three-fourth-inch

supply line was old and gave inadequate supply, so was discarded

for the new supply line run later. Two curves (figs. 24 and 25) are shown to illustrate the characteristics with low rates of supply yet

sufficient to induce siphon action in the closet bowl. It should be

noted that the rate of supply for these two curves is limited by the

supply line, and only slight change was produced by adjustments

in the flush valve.

To give adequate supply and allow adjustment in the rate of supply, a new supply line, not drawn to scale (fig. 26), was installed. It consisted of a lj-inch section about 16 feet long leading from the

2-inch main and a section of 1 inch about 9| feet long from the 1Jinch section to the flush valve, with gate valve, pressure gauge, and

elbows in positions shown in the figures. The gate valve was installed to throttle the line and control the maximum rate of supply and in a measure controlled the operating pressure in the 1-inch section
PHYSICS OF PLUMBHSTG SYSTEMS 75

TIME m SECOND $

Fig. 20—Rate of discharge curve for the Maddox siphon jet bowl, 6-gallon high tank with straight l§-inch

flush pipe, discharged through 3-inch cast-iron closet bend. (See fig. 19.) Total discharge 5.1 gallons, peak discharge 43.6 gallons per minute, mean rate of discharge 28.8 gallons per minute

Fig. 21.—Rate of discharge curve for the same set-up as Figure 20, with the tank valve held open 5 seconds, then allowed to close automatically. Total discharge 5.2 gallons, peak discharge 49.7 gallons per minute, mean rate of discharge 40.8 gallons per minute
76 RECOMMENDED PLUMBING REQUIREMENTS

TIME \t4 SECONDS

Fig. 22. —Rate of discharge curve for the Maddox siphon jet bowl, 8-gallon low tank with straight 2-inch

flush pipe, discharged through the 3-inch closet bend. Total discharge 5.2 gallons, peak discharge 43.5 gallons per minute, mean rate of discharge 35.5 gallons per minute

TIME m SECONDS

Fig. 23.—Rate of discharge curve for the same set-up as Figure 22 with toilet paper and semisolid matter added to represent soil. Total discharge 5.6 gallons, peak discharge 41.0 gallons per minute, mean

rate of discharge 31.8 gallons per minute
PHYSICS OF PLUMBING SYSTEMS 77

Fig. 24:—Rate of discharge curve for the Maddox siphon jet bowl, supplied by a Sloan flush valve operat- ing on a 1-inch supply line (see fig. 19) discharged through the 3-inch closet bend. Total discharge 5.5 gallons, peak discharge 33.1 gallons per minute, mean rate of discharge 19.8 gallons per minute

Fig. 25.—Rate of discharge curve for the same set-up as Figure 24 except a special high-rate guide was used on the valve seat. Total discharge 5.2 gallons, peak discharge 32.5 gallons per minute, mean rate of discharge 20.4 gallons per minute
78 RECOMMENDED PLUMBING REQUIREMENTS

of the supply line. The pressure gauge enabled us to read the static

pressure in the supply line and the minimum pressure to which the

pressure dropped in the 1-inch section of the line during operation.

The static pressure in the line at the time is recorded as the maximum

pressure and varied between 44 and 60 pounds per square inch. The

minimum pressure is also recorded for each figure given and represents

the lowest operating pressure for the 1-inch section in that particular

experiment. The valves opened and closed under the maximum

Fig. 27.—Rate of discharge curve for the Maddox siphon jet bowl supplied by Sloan flush valve operat- ing on 1-inch supply line (fig. 26) under 57 pounds maximum and 26 pounds minimum pressure. Total

discharge 4.2 gallons, peak discharge 50.7 gallons per minute, mean rate of discharge 39.6 gallons per minute pressure. The operating pressure quickly dropped to the minimum

when the flush valve was opened, and gradually approached the

maximum as the valve closed. This variation in operating pressure

is similar to the variation that occurs in service lines during use. When supply lines give unnecessarily high rates under the service

pressure, the rate of supply may be reduced to the desired value by

partially closing the shut-off valve usually installed with flush valves.

The general effect is similar to that produced by partially closing the

gate valve in the experimental supply line used.
PHYSICS OF PLUMBING SYSTEMS 79

It is recognized that had the testing of flush valves been our

purpose the work would be incomplete without a more accurate control

of the operating pressure by means of pressure regulators or other

devices. The variations secured were sufficient for our immediate

purpose, namely, the determination of rates and characteristics of the

discharge from water-closets relative to the rate of supply.

In this connection we wish to state that we have made no tests on

flush valves, and that their use has been incidental to the other experiments. It is true we have gained some information on the relative

merits of the flush valves used, which we withhold from this report.

Fig. 28—Rate of discharge curve for the same set-up as Figure 27, flush valve operating under 55 pounds

maximum and 5 pounds minimum pressure. Total discharge 4.6 gallons, peak discharge 35.9 gallons per minute, mean rate of discharge 22.8 gallons per minute It would be unfair to the manufacturers to publish incomplete data on the subject.

Interpretation and Discussion of Results.—In the interpretation of the preceding rate-of-discharge curves it is essential that the

characteristics of the discharge producing the best results be kept in

mind. The most certain and efficient cleansing of the water-closet

bowl occurs when there is a strong siphon action in the first two or

three seconds, followed by a period of weak or broken siphon action,

during which the bowl is practically empty, and this in turn followed

by a second siphon action. These characteristics appear in the rate curves as a maximum point on from the second to the fourth second,

-followed by a minimum or decided tendency toward a minimum point,

in turn followed by a second maximum point lower than the first. The curves showing these maxima and minima points as described are

indicative of strong efficient flushes.
80 RECOMMENDED PLUMBING REQUIREMENTS

If the rate of supply is too low, a complete break in the siphon

action occurs, and in extreme cases the minimum point approaches

zero while the bowl is refilling following the first siphon action. (See

figs. 24 and 25.) The result is a sluggish and uncertain flush. If the

rate of suppty is too high, the siphon action becomes continuous with

the bowl partially filled until the end of the flush. This may result in

paper and fecal matter being floated in the bowl to settle to the bottom,

Fig. 29—Rate of discharge curve for a Mott siphon jet bowl supplied by Sloan flush valve operating under

50 pounds maximum and 25 pounds minimum pressure. Total discharge 4.0 gallons, peak discharge

46.6 gallons per minute, mean rate of discharge 37.2 gallons per minute or at best to be drawn into the trap at the end of the flush, and in an

incomplete refill, due to the flush ending with a strong siphon action.

The curves showing a single maximum with no tendency toward a minimum point are indicative of rates of supply too high for the best

results. The dividing line appears to be that which permits the

discharge to drop from a maximum to an approximately constant rate

of flow. (See figs. 10, 31, and 36.) A rate lower than this permits the

formation of a minimum (figs. 11, 14, and 17). A rate higher than
PHYSICS OF PLUMBING SYSTEMS 81

this gives a continuous rate of discharge approximately equal to the

maximum, which drops abruptly at the end of the discharge (figs. 9, 12, and 21). The conclusion, therefore, is that a rate of supply that

does not permit the formation of a minimum is unnecessarily high.

The siphon jet bowl, due to the jet action, has a somewhat wider

range of serviceable supply than the wash-down bowl, and for the same reason the upper limit of the most serviceable rates is not as sharply marked as for the wash-down bowl.

Fig. 30.—Rate of discharge curve for the same set-up as Figure 29, the flush valve operating under 44 pounds maximum and 14 pounds minimum pressure. Total discharge 4.3 gallons, peak discharge 40.8

gallons per minute, mean rate of discharge 30.4 gallons per minute It is impossible to fix a definite value for either the rate of supply

or the total quantity of water required which will give the best

results for all water-closets. These will vary with different bowls

and conditions. There are, however, pretty definite limits within

which the serviceable rates for all water-closets employed in these

tests, and we believe all water-closets that should be approved for

general use, fall. A study of the curves of discharge given will show that for wash-down closets the curves indicating a strong

efficient flush were obtained when the mean rate of discharge and

approximately the mean rate of supply was between 27 and 33 gallons

per minute. For siphon-jet closets the range is between 24 and 36

gallons per minute. This gives a mean value of approximately 30

20141°—29 7
82 RECOMMENDED PLUMBING REQUIREMENTS

gallons per minute as a rate of supply that, in general, will prove

satisfactory for either type of closet bowl. The quantity of water

required depends on the duration of the flush. The time varies from

6 to 10 seconds, the lower rate of supply, in general, requiring the

longer time. Considering this in connection with the curves of discharge indicates a range of from 3 to 5 gallons as a serviceable quantity. No doubt there are many closets on the market which a

Fig. 31.—Rate of discharge curve for a Trenton Potteries “Speedway” siphon jet howl supplied by

Sloan valve operating under 55 pounds maximum and 28 pounds minimum pressure. Total discharge

4.1 gallons, peak discharge 48.2 gallons per minute, mean rate of discharge 40.2 gallons per minute smaller quantity would serve satisfactorily under certain conditions.

The approximate mean values are, therefore, 4 gallons supplied at the average rate of 30 gallons per minute for eight seconds.

If the mean rate of supply exceeds 36 gallons per minute, in general, not only does a less efficient flush result, but there is an unnecessary waste of water and an unnecessary strain placed on the drainage and sewage-disposal systems. It is believed these are sufficient reasons for prohibiting for general use any flushing device that deliv-
PHYSICS OF PLUMBING SYSTEMS 83

ers more than 5 gallons or at a mean rate greater than 36 gallons

per minute and for prohibiting for general use any water-closet that

requires a greater quantity or greater rate than this. This leads to

slight, if any, change in existing materials or practice, since practically all flushing devices, with minor adjustments possible and

desirable at the time of installation, as well as the requirements of most water-closets, fall within these limits. The details of these

restrictions apply more particularly to the water-supply system than

to the drainage system, which is the particular field of this investigation and which is concerned only with the limits.

If the above restriction, which is believed justifiable, is granted,

we may proceed at once to determine the maximum rate of discharge

Fig. 32—Rate of discharge curve for the same set-up as Figure 31, the flush valve operating under 50 pounds maximum and 15 pounds minimum pressure. Total discharge 4.3 gallons, peak discharge 36.0 gallons per minute, mean rate of discharge 28.2 gallons per minute from water-closets. A further reference to the curves will show

that in one case only, in which the mean rate of supply does not

exceed 36 gallons per minute, does the “peak discharge” rise above

45 gallons per minute.

There are several reasons for selecting and applying the “peak

discharge’ 7 (see p. 66) as determined rather than the maximum

discharge at a point or for periods as low as 1 second. First, the

application will have a particular bearing on the subject only when

the peak load is approaching the limiting capacity of the stack or

drain. This will be the combined discharge of four or more waterclosets for stacks and possibly three or more water-closets for lateral branch drains. Second, the combined discharge from several waterclosets in coincidence or overlapping will, in general, be more uniform than the discharge from any single one of the group. This
84 RECOMMENDED PLUMBING REQUIREMENTS

combined discharge will become more uniform as the number of

water-closets is increased. Third, in general, not more than two

water-closets will discharge at the same point in a system and the

effect, barring stoppage or overcharging, will tend to make combined

discharges when overlapping occurs more uniform and tend toward

a mean value. And, finally, there is ordinarily but slight difference

Fig. 33.—Rate of discharge curve for a Trenton Potteries siphon jet bowl supplied by Sloan valve operat- ing under 55 pounds maximum and 33 pounds minimum pressure. Total discharge 3.9 gallons, peak

discharge 50.8 gallons per minute, mean rate of discharge 43.2 gallons per minute between the “peak discharge” and maximum when the rates are high enough to produce a “peak discharge” of 45 gallons per minute.

It therefore seems reasonable to assume a maximum rate of dis- charge from water-closets to be allowed for of 45 gallons per minute.

This is a value that, in general, will not be exceeded and seldom

reached if the former reasonable restriction in the rate of supply is adhered to. The rate may be criticized by some as too high, but it should be kept in mind that it is our purpose to fix minimum re-
PHYSICS OF PLUMBING SYSTEMS 85

quirements on the basis of maximum effects; that the employment

of this rate will be relative to the rate of discharge of other plumbing

fixtures ; and that due to the nature of the material and more thorough

scouring the rate will decrease less than that of other fixtures.

FIXTURES OTHER THAN WATER-CLOSETS

The curves of discharge obtained from plumbing fixtures other

than water-closets show no characteristic that may not readily be

predicted from the conditions involved.

Fig. 34.—Rate of discharge curve for the same set-up as Figure 33, the flush valve operating under 55 pounds maximum and 21 pounds minimum pressure. Total discharge 4.2 gallons, peak discharge 45.5 gallons per minute, mean rate of discharge 36.6 gallons per minute The rate of discharge from these fixtures, which we hereafter refer to collectively as “ standing fixtures,” is evidently dependent on

the head of water in the fixture itself, on the developed head in the

unvented portion of the waste, on the area of the cross sections of the outlet orifices, tailpiece, trap, and waste, with modifying effects produced by strainer, bends, etc. The curves of discharge for “standing fixtures” are smooth curves showing a uniformly decreasing rate of discharge with decrease in

head in the fixture, the rate of decrease being dependent on the area of horizontal cross section of the fixture. The rate for a given
86 RECOMMENDED PLUMBING REQUIREMENTS

Fig. 35.—Rate of discharge curve for the same set-up as Figures 33 and 34, the flush valve operating under 59 pounds maximum and 12 pounds minimum pressure. Total discharge 4.6 gallons, peak dis- charge 44.1 gallons per minute, mean rate of discharge 33.6 gallons per minute

Fig. 36.—Rate of discharge curve for a Trenton Potteries siphon jet howl supplied by Kenney flush valve

operating under 60 pounds maximum and 29 pounds minimum pressure. Total discharge 5.5 gallons, peak discharge 44.6 gallons per minute, mean rate of discharge 34.8 gallons per minute
PHYSICS OF PLUMBING SYSTEMS 87

head is independent of the area of the cross section and the shape

of the fixture.

These points are not of sufficient importance to justify the use of the space necessary for a detailed description and illustration. We

therefore omit these curves and data and confine the discussion to results based more on data obtained from fixtures set in place on

the stacks of the test installations. After a few determinations

Fig. 37—Rate of discharge curve for a Trenton Potteries siphon jet bowl supplied by Mott flush valve

operating under 60 pounds maximum and 21 pounds minimum pressure. Total discharge 5.0 gallons, peak discharge 52.2 gallons per minute, mean rate of discharge 46.2 gallons per minute which verify certain of these points it became evident that data for

11 standing fixtures” more applicable to our purpose could readily

be obtained from time and volume measurements with the fixtures

set in place on the stacks of the test installations.

It is impossible with the greeot variety of fittings now7- in use to

establish a single common unit of measure applicable to all. Even

by restricting the application to one size of outlet orifice., trap, and
88 RECOMMENDED PLUMBING REQUIREMENTS

waste, a unit that will serve to express relative rates of discharge

must at best be a rough approximation. Evidently such a unit

should represent highest mean rates of discharge.

The fixtures were fitted with plain P traps and wastes running

from the traps to the stacks or vented wastes with one-fourth inch

fall to the foot; hence, the rates of discharge are strictly applicable

only when this condition is approximated. Any change in the form

of installation, such as the use of an unvented S trap and waste to the floor, that tends to develop a greater head, increases the rate of

Fig. 38.—Rate of discharge curve for a Trenton Potteries wash-down bowl supplied by Sloan flush valve

operating under 55 pounds maximum and 30 pounds minimum pressure. Total discharge 4.0 gallons, peak discharge 44.1 gallons per minute, mean rate of discharge 37.2 gallons per minute discharge from that fixture. Ordinarily the application of the same

value for either condition in the case of a small fixture would lead

to no difficulties and would avoid complicated tables. Based on all the data at hand from both sources, we propose the

following rates of discharge for “ standing fixtures’ 7 applicable when

the specifications are approximately adhered to

For washbasins fitted with 1 J-inch P traps and wastes, with nominal

lj-inch tailpieces and strainers giving equal cross-sectional areas of

orifices, the highest mean rate of discharge is approximately 7.5 gallons (1 cubic foot) per minute.
PHYSICS OP PLUMBING SYSTEMS 89

For bathtubs fitted with IJ-inch outlet and wastes, and nominal

H-inch outlet connections with strainer giving equal cross-sectional areas of orifices, the highest mean rate is approximately 15 gallons

per minute.

For kitchen sinks fitted with IJ-inch P traps and wastes, and

nominal lj-inch tailpieces with strainers giving equal cross-sectional areas of orifices, the highest mean rate is approximately 11.3 gallons

per minute. This refers to the normal use of sinks wuth the outlet

orifice continually open. If the sink is used with a plug and dis- charged by filling and lifting the plug, the rate of discharge approaches

that given for laundry trays.

For laundry trays fitted with IJ-inch tailpieces, with strainers

giving equal cross-sectional areas of orifices, the highest mean rate

is approximately 22.5 gallons per minute.

For a combination fixture of one kitchen sink and one or two

laundry trays, or of two or three laundry trays, fitted with one

1 1-inch P trap and waste and nominal lj-inch tailpieces, the maximum

rate of discharge when two or more are discharging simultaneously

is not greater, and, in general, is less, than the maximum rate of the one of the group giving the highest rate when discharging alone.

This conclusion has been questioned, and in its support we offer the

following data obtained from two combinations of laundry trays of

two each.

Two single laundry trays practically identical and without strainers were set end to end on the same level and fitted with a l|-inch lead

P trap with nominal 2-inch seal depth and short lj-inch wrought-iron

waste and nominal IJ-inch tailpieces and connection. The tailpiece of one tray, A, was connected vertically into the P trap, the tail- piece of the other tray, B, was connected vertically into the short arm of a l§-inch lead one-fourth bend, and the long arm of the lead

bend was wiped into the side of the trap inlet above the water seal,

forming a T union. (See fig. 80.) They were filled with the same

volume each time and were discharged separately and also together

by lifting the plugs simultaneously. The time was taken from lifting

the plugs to the beginning of the swirl and trail discharge at the end.

The experiment was also repeated using trays A' and B' of smaller

capacity, with strainers.

Combination 1, without strainers

Volume discharged Depth

in

fixture

Time to empty

single

fixture Rate per minute

Time to empty

each tray both

flowing

A, 9 gallons __ .. . Inches

8

8

Seconds

21.4

24. 0

Gallons 25.2

22.4

Seconds

41.9 B, 9 gallons _ . 48.3 Mean rate of discharge with both laundry trays flowing, 22.3 gallons per minute.
90 RECOMMENDED PLUMBING REQUIREMENTS

Combination 2, with strainers

Volume discharged Depth

in fixture

Time to empty

singlo

fixture Rate per minute

Time to empty

each tray both

flowing

A', 9 gallons. Inches8J

8*

Seconds

22.4

23.6

Gallons

24.3

22.8

Seconds

38.

1

B', 9 gallons 46.8 Mean rate of discharge with both laundry trays flowing, 22.9 gallons per minute. These results are as were anticipated and are fully explained by the

fact that the resistance at the point of junction of two streams from

different directions more than balances the decreases in resistance,

due to the two outlets to the point of junction, the head being the same in both cases. The above is true in case there is no material

change in sizes of waste. If the trap and waste were increased in

size at and beyond the point of junction over that of the waste pipes

to the point of junction, the combined rate of discharge would be

greater than the rate of a single fixture of the combination, but in no case would it be double that of the one giving the highest rate of discharge. It may be anything between these values, depending on

the relative lengths and cross-sectional areas of the portions of the

combination waste pipes. The combination rate in most cases is nearer that of a single fixture than double the rate and frequently

falls below the rate of a single fixture. It therefore seems reasonable

to treat combination fixtures as one fixture and groups of fixtures

with separate traps as separate fixtures. The normal use of combination fixtures would be separate discharging, so that generally the

single-fixture rating would apply directly. The variation in combination rate of discharge from the single-fixture rate of discharge is, in general, so small that no material error would be introduced by

treating the combination as one fixture and the discharge rate the same as for a single fixture of the same kind. Any attempt to allow

for possible variation in combination fixtures leads to complications

that destroy any value attached to a table of relative rates of dis- charge. Such a table to be of service must necessarily be as simple

as possible.

The following table, based on all determinations and observations

made, is offered as approximately representing the rates of discharge

of the common plumbing fixtures under conditions specified with

relative values expressed in fixture units as well as rates of discharge.
PHYSICS OF PLUMBING SYSTEMS 91

Table 1 . —Rates of discharge from 'plumbing fixtures

Fixture

Basin... Sink Bathtub Laundry tub Common fixture with one trap

Water-closets

Outlet, nominal di- ameter 1

Trap

and

waste Rate

g. p. m.

Fixture

units,

or cubic

feet per minute

Velocity

in drain per second Time required to empty 2

Inches Inches Feet H H 7.5 1 1.9+ 12 seconds.

If li 11.3 n 2.0 30 seconds.

/ n If 15.0 2 2.7+ If to 2 minutes.

\

3 2 2 26.3 H 2. 0+ 1 to If minutes.

If if 22.5 3 4.0 20 seconds.

If ii 22.5 3 4.0 20 seconds up for one. 40 seconds for two.

3 3 45.1 6 2.0+ 6 to 10 seconds.

1 Outlets from fixtures are commonly made one nominal size smaller than the trap for convenience in making slip-union joints, a practice that offers other advantages; hence the actual diameter is less than

stated nominal values, varying from one-eighth to one-fourth inch.

2 Time for emptying the basin and sink are given for the full fixture If and 6 gallons capacity, respectively. The time given for other fixtures gives a range that will vary with the capacity of the fixture and extent of filling.

3 No determinations were made with 2-inch bathtub outlets, and the values given represent an esti- mate to the nearest one-half fixture unit. It will be observed that the fixture unit adopted, 7.5 gallons per

minute, is approximately 1 cubic foot per minute. It may be found more convenient to express rates of flow in cubic feet per unit time

than in gallons per minute as has been done in later tables. DETERMINATION OF THE PEAK LOAD IN ANY PLUMBING SYSTEM

In fixing the limits of use of soil stacks and drains it seems to have

been the custom to establish arbitrarily a given fraction of the

combined discharge of all the fixtures on a plumbing system as representing the probable peak load to be provided for. It is generally recognized that it is unnecessary to provide for the total

simultaneous discharge of all the fixtures. While the arbitrary

fixing of the peak load is supported to some extent by experience,

this only shows that the estimates have been liberal on the side of safety.

METHOD OF PROBABILITIES From the standpoint of economy in the installation of plumbing

systems it is obviously desirable to secure a closer approximation of the peak load and the frequency of its occurrence based logically

upon data representing the conditions involved. This can be done

by determining the probability of coincident discharge of the various

fixtures based upon the observed frequency of use, the duration of the individual discharge, and the predetermined rates of discharge

of the various fixtures.

The application of the method of probabilities to such a problem

is not precise, since it is based upon variable and somewhat indeterminate time factors. The results are, therefore, to be regarded as approximations and applicable to large systems more closely than
92 RECOMMENDED PLUMBING REQUIREMENT'S

to small ones. The method will, however, be found helpful in the

analysis of small systems.

To illustrate the method, let us suppose a system composed of

five water-closets and assume (1) that each water-closet requires

10 seconds to flush, and (2) that each water-closet is flushed at ran- dom once during a 10-minute, or 600-second, interval. Let us assume also that the flushing of two water-closets is coincident if the flush periods overlap nine seconds or more.

Probability may be defined as the ratio of the favorable ways in

which an event may occur to the total number of ways, favorable

and unfavorable, in which the same event may occur. On the

assumption of random flushing, any one of the 5 water-closets

may begin its flush during any of the 600 seconds in the 10-minute

interval. Therefore, the total number of ways in which the event

may occur is 600 5

. Suppose we wish to determine the probability

of 3 of the 5 water-closets being flushed together. The number

of different combinations of 5 objects taken 3 at a time Cl is 5X4X3

3X2X1 = 10. The 3 water-closets of any of these combinations

may begin their flushes during any one of the 600 seconds, and

either of the 2 remaining water-closets may begin its flush during any

of the remaining 599 seconds. The number of ways in which the

event may occur favorable to the coincidence of 3 water-closets only,

is, therefore, (7|X 600x599x599 = 10x600x599 2. Therefore, the

probability of 3 only of the 5 water-closets flushing in coincidence is = 3

6

~ Ti 5

’ approximately, or once in 36,115 times or 10 X 600 X 5992 1 6005 cycles.

A close approximation simplifying the computation may be made

as follows: In general, if n is the number of water-closets on the

system and r the number flushing in coincidence, and C

n

r the combination of n things r at a time, the probability of coincidence of r only out of n water-closets, provided r is equal to or greater than n . X 600 X 599w_r ^ C? 600n~r+1 C

n

r T, 2

18 6W ’ whlcl1 18 l6SS than 600^~=600^- If r

is less than the probability of coincidence of r only is also less than

C

n The approximation in both cases is close and in reality

includes all coincidences from r to n water-closets.

Overlapping Discharges.—It is evident that the chance of actual coincidence is so remote as not to require serious consideration.

There is, however, a greater chance for overlapping discharges which

may produce effects in a plumbing system quite as great as actual

coincidence. It is necessary, therefore, to extend the method to
PHYSICS OF PLUMBING SYSTEMS 93

include overlapping. The process of transforming the equation to include overlapping is tedious and somewhat complicated. The

final form, however, is fully as simple as the original approximation

for probability of actual coincidence.

In overlapping both the duration of flush and period of overlap come into the full equation. If we take into account all overlapping

of 4 seconds or more in flushes of 10 seconds duration, we shall have

included all except trail discharges at the beginning and end of the

flush.

If the results determined on the basis of 10 seconds duration of

flush and an overlap of 4 secbnds or more are applied to a system in

which the duration of flush is only 6 seconds, all overlapping will be

included. A study of the discharge curves of water-closets in this

connection shows that if we allow for an overlap of 4 seconds or more, few, if any, of the overlapping coincidences will give a combined maximum rate of discharge equal to the sum of the maximum

rates of the individual water-closets.

Briefly, the inclusion of all overlapping of from 4 to 10 seconds is equivalent to reducing the interval between flushes by the ratio

10 — 4 = 6. The probability of overlapping flushes then becomes

(7?/100r_1

, and also includes the probability of from r to n waterclosets overlapping. This is evidently fixing sufficiently wide ranges

to include all variations that might produce detrimental effects. The probability of 3 or more out of 5 water-closets overlapping 4 sec- onds or more, then, is Of/1002 = qqq = Tfipp * Put ^le resu^s int«

o

a more tangible form and allow for rush periods and periods of infre- quent use, they have been reduced to occurrence of once in a period

of days or years as follows : If we assume a rush period of two hours

daily during which all fixtures on the system are in constant use, and

assume that, at other times only a small part of the fixtures are in use, then, there will be 12 flushes of each closet, or 12 complete cycles

within the two hours rush period in which coincidences may occur, 60 2= 12. Then the probability of once in 1,000 times or cycles

,

. 1,000 00 . .83

becomes once m ^

~ = 33 days, or once m years.

If it were possible to deal with accurately determined time intervals throughout, the results by this method might be directly applied

with perfect safety. In practice all the factors will vary according

to conditions, the duration of the flush with the kind and condition

of supply apparatus, the interval between flushes with the number of people using the system and their habits, and the length of the rush

period with the type of installation and its location. The effect of
94 RECOMMENDED PLUMBING REQUIREMENTS

each of these time factors on the results should be considered in con- nection with any data on which it is based before passing judgment

on the selection of the factor.

The longer the duration of the flush the greater is the probability

of overlapping discharges. In selecting this factor we have chosen

10 seconds as the maximum duration of flush which we believe should

be permitted for general use and a value that represents an approximate maximum as water-closets are installed at present. The same

value would apply in all types of installation.

Mixed Systems.—Up to this point we have considered systems

composed of water-closets alone. While it is possible by a similar

method to calculate probabilities for mixed systems of water-closets

and other smaller fixtures, all the time factors vary with the kind of

fixture and are more indeterminate for the small fixtures than for

water-closets. It may be shown, however, that for two systems both

having the same total combined rate of discharge, one composed

entirely of water-closets and the other a mixed system of waterclosets and smaller fixtures, the probability of a given volume dis- charge is greater for the system composed of water-closets than for

the mixed system. We therefore propose the extension of the tables

for water-closets to include water-closets or equivalents, translating

in terms of fixture units. Any error thus introduced will be on the

safe side and simplifies the application by reducing the number of tables necessary.

Time Factors.—Before considering the other two time factors,

the interval between flushes and the length of the rush period, we

would divide installations into at least two classes—private and

public. The first class includes homes, private baths in hotels, and

such installations, in which a number of fixtures are inclosed in the same room or compartment and are ordinarily not accessible to more than one person at a time. The second class includes publiccomfort stations, railway toilets, factory and office building toilets,

schools, etc., in which each fixture is inclosed in a separate compartment or is open and accessible for use at all times. Other classi- fications might be made if found desirable.

We have prepared Table 2 to apply to the private class of installation and Table 3 to apply to public installations. Table 2 is based on the average interval of 10 minutes between flushes and rush

periods of one, two and three hours daily. Table 3 is based on the

average interval of five minutes between flushes and rush periods of

2, 3, and 10 hours daily. These two time factors are the most

difficult to determine with any degree of accuracy and are the most

variable. Both the interval between flushes during the rush period

and the length of the rush period should be taken as the averages over the whole period of years considered. It will be observed that

the shorter the interval between flushes the greater the probability
PHYSICS OF PLUMBING SYSTEMS 95

of coincidence or overlapping and the longer the rush period the

greater the probability.

We have based the interval between flushes for Table 3 on the

data following, supported by our own observations, and by physical

limitations as to possible frequency of use.' It is physically impossible for a number of people normally to use water-closets at a much

higher average rate except as urinals. Table 3 is merely a suggestion of possible application to larger structures and has no application to our immediate problem, the small dwelling house plumbing.

Data furnished to the plumbing committee by C. T. Coley from observation on the Equitable Building, New York, N. Y

.

Male population 400

Number of toilets in group 10 Time of observation, 8.30 a. m. to 5 p. m hours. _ 8|

Total number of uses 328

Average time in toilet per person minutes. _ 7. 1 Maximum time in toilet per person do 37 Minimum time in toilet per person do 3 Apparently, though not stated, there were separate urinals in the

toilet room in this instance. Data furnished to the plumbing committee by Charles F. Horan from observations made at the factory of the Hood Rubber Co., Watertown, Mass.

Number of minutes in toilet Number of persons Mal8 Female Under 1 4 11

1 to 2 . 36 23

2 to 3 _ 49 39

3 to 4 _ 29 23

4 to 5 . 52 29

5 to 6 36 45

6 to 7 23 10

7 to 8 9 4

8 to 9. 6 4

9 to 10 6 4

10 to 11 4 0 Total 254 192 Average time in toilet per person .minutes.. 4. 25 3. 97 Evidently, though not stated, these observations included use as

urinals. Both the very short periods of use and the manner in which

the number of persons for different periods vary indicate this. The

highest number of uses by males was for between 4 and 5 minutes

and the highest number of females between 5 and 6 minutes, indicating an average of approximately 5 minutes when not used as urinals.

However, taking the mean of the two sets of data regardless of the

kind of use, it is 5.11 minutes per person. The mean, weighted ac- cording to number of users, is 5.4 minutes per person.
96 RECOMMENDED PLUMBING REQUIREMENTS

The five-minute interval made the basis of Table 3 is close enough

to indicate the possibilities of the method as a means of approximation. It would be desirable and perhaps necessary, to secure more

data on the subject before making an extended application. The

method might also be applied with some modification to the proportioning of water-supply pipes for large buildings.

Table 2 applicable to private systems, though carried beyond the

requirements of separate dwelling houses, has some application in

this field. The basic difference between the two classes is the

inclosure of several fixtures in one room or compartment in the

private system. This at once restricts the possible use if privacy is maintained. The time intervals for Table 2 are not based on any

specific data, but rather on the extent of use they allow. It is to be

kept in mind that the rush period is not only an average over a long

period of time, but is independent of the number or duration of the

short rush periods into which the assumed daily rush period may be

broken. The real consideration is the number of cycles that occur

at the rush rate in the entire period of years considered. A rush

period of two hours on alternate with none on intervening days will have exactly the same effect in the long run as a rush period of one hour daily.

On this basis consider the extent of service a flushing interval or frequency of use of 10 minutes and a daily rush period of one hour

will permit in the case of a mixed system. It will allow an average

of six persons to the bath for an average time of 10 minutes each,

each person flushing the water-closet, the bathtub, and the basin, or

it will allow half the number of persons for double the time each

flushing the fixtures twice. If the same number of persons use the

bath to the same extent in a two-hour period instead of one hour,

the probability of overlapping is decreased. Again, it should be

remembered that the method will apply, in general, to systems

composed of several bathrooms and that six persons per bath is a

high, and 10 minutes per person to use all three fixtures a low,

average for these conditions. The liberal allowance here will amply

take care of cases of the same person flushing one or more of the

fixtures twice in one use of the bathroom. In addition to the use

of the bath as described, the assumptions would allow kitchen sinks,

laundry trays, and any other separate fixture on the system each to

flush 6 times within the one-hour rush period. This is a very

liberal allowance for these fixtures. Not only will any rush period

for these, in general, be at a different time in the day, but weekly

rather than daily for laundry trays. Laundry trays and even

kitchen sinks might well be neglected so far as their presence affects the required sizes for main stack and house drain. They have not

been disregarded but have been rated at full value throughout. We
PHYSICS OF PLUMBING SYSTEMS 97

have discussed this subject at length merely to show that any conceivable normal variation in service from the conditions assumed

tends to decrease the probability of coincident or of overlapping

discharges.

Table 2.—Probabilities of overlapping coincidence assuming 10 seconds' duration

of flush and 10 minutes interval between flushes with rush periods of 1, 2, and

3 hours daily

Number of water-closets on system Equivalent fix- ture units Rush

period

Discharges overlapping 4 seconds or more Number

of waterclosets

Equivalent fix- ture units Occurs

once in

Occurs

once in—

Hours per day Days Years

3. 18 1 2 12 5. 6

3. 18 2 2 12 2. 8

3 18 3 2 12 1. 8

3. 18 1 3 18 1,666 4.5

3 18 2 3 18 833 2 3.. 18 3 3 18 555 1.5

4 24 1 3 18 416 1.1

4 24 2 3 18 208

4.... 24 3 3 18 138

4__ 24 1 4 24 456

4 24 2 4 24 228

4 24 3 4 24 152

5 30 1 3 18 166

6 30 2 3 18 83

5 30 3 3 18 55

5. 30 1 4 24 90

5. 30 2 4 24 45

5 30 3 4 24 30

5.. 30 1 5 30 45, 600

5 30 2 5 30 22, 800

5 30 3 5 30 15, 200

6 . 36 1 4 24 30

6. 36 2 4 24 15

6.. 36 3 4 24 10

6 36 1 5 30 7, 600

6 36 2 5 30 3, 800

6. 36 3 5 30 2, 520

8 48 1 4 24 6 8. 48 2 4 24 3 8 48 3 . 4 24 2 8 48 1 5 30 816

8.... 48 2 5 30 408

8 48 3 5 30 272

10. 60 1 4 24 792 2

10 60 2 4 24 396 1 10 60 3 4 24 264

10 60 1 5 30 180

10 60 2 5 30 90

10 60 3 5 30 60

12 72 1 4 24 336

12 72 2 4 24 168 12 72 3 4 24 112

12 72 1 5 30 56

12. 72 2 5 30 28

12.. . . 72 3 5 30 19 25 150 1 6 36 25

25 150 1 7 42 949 60 300 1 8 48 95 50 300 1 9 64 1, 822

120.... 720 1 11 66 39

120 720 1 12 72 424 20141°—29 8
98 RECOMMENDED PLUMBING REQUIREMENTS

Table 3.—Probabilities of overlapping coincidence , assuming 10 seconds duration

of flushes and a 5-minute interval between flushes, with rush periods of 2, 8, and, 10 hours daily

Equivalent fix- ture units

Discharges overlapping 4 seconds or more Number of water-closets on system Rush

period Number

of waterclosets

Equivalent fix- ture units Occurs

once in

Occurs

once in—

3 18

Hours per day

2 2 12 Days

1.4 Years

3 _ 18 3 2 12 1. 0

3 18 10 2 12 .3

3 18 2 3 18 208

3. 18 3 3 18 139

3 18 10 3 18 41

4 24 2 3 18 52

4 24 3 3 18 35

4 24 10 3 18 10

4. 24 2 4 24 28

4 24 3 4 24 19 4 24 10 4 24 6

5 30 2 4 24 6

5 30 3 4 24 4 5 30 10 4 24 1 5 30 2 5 30 1, 427

5... 30 3 5 30 950

5 30 10 5 30 285

6 36 2 4 24 1. 9

6 36 3 4 24 1. 2 6 36 10 4 24 . 4

6 ... 38 2 5 30 1, 020

6. 36 3 5 30 680

6 36 10 5 30 204

8 48 2 4 24 140

8 ... 48 3 4 24 93

8 48 10 4 24 28

8 48 2 5 30 23

8 48 3 5 30 15 8 48 10 5 30 5 10.. 60 2 5 30 6

10. 60 3 5 30 4 10 60 10 5 30 1 10 60 2 6 36 339 10 60 3 6 36 226

10 60 10 6 36 67

12 72 2 5 30 658 1.9

12 72 3 5 30 438

12. 1 72 10 5 30 131

12 72 2 6 36 77

12 72 3 6 36 51

12 72 10 6 36 15 25 150 2 7 42 7.4 50 300 2 9 54 3. 5 120 720 2 13 78 1 180 1,080 2 18 108 76 These tables have been placed early in the report for the purposes

of reference in later chapters. The question of what frequency of occurrence should be provided for in an installation is one closely

connected with establishing a reasonable factor of safety, and the

dividing line should vary with the size and character of the installation. We, therefore, leave this question and the details of application for amplification in the chapter dealing with factors of safety

in plumbing systems.
99 PHYSICS OF PLUMBING SYSTEMS

CAPACITIES OF STACKS AND DRAINS

The problem of accurately determining the carrying capacity of a system of drainage pipes composed of vertical and horizontal sections

of varying diameters in which, in general, the vertical sections are only partially filled is difficult in comparison with the determination

of the carrying capacity of the same system flowing full under a known head. The problem is further complicated in the plumbing

system by the fact that both water and air movements must be taken

into account. Apparently, in view of the varying degrees to which the system or parts of the system may be filled, a very rough approximation of the maximum carrying capacity is all that may be hoped for. The

fact that an appreciable head of water developed in any portion of a plumbing system into which branches are discharging tends to impair the efficiency of the drainage indicates a limiting condition on which to base determinations of capacities. While the development

of a head of water in certain portions of a given system—namely,

in unvented small waste branches—may produce no detrimental

effects, the assumption of a condition under which no head can

develop in any portion of the stacks or house drain is certainly a

safe procedure and apparently the only one that will permit a general

application of results. The determinations following have, therefore,

been based on this assumption.

With a system composed of vertical and horizontal sections of the same diameter throughout it is evident that on the assumption that no static head may develop the limit of carrying capacity will first be reached in the horizontal sections of the systems. This at once

suggests the separate consideration of vertical and horizontal sections. The economical use of material would be that gradation of diameters which gave the same carrying capacities in ah sections.

The limitations in number of pipe sizes available and the nature of

demands from certain fixtures both render such close approximation

impractical and again lead to rough approximation by selection of the nearest size above actual requirements.

The plumbing

1 system naturally divides into distinct sections—

the house drain, the vertical stack or stacks, the lateral horizontal

branch drains, and the bends or turns connecting the stacks and vertical branches to horizontal sections. The house drain and large

lateral branch drains, which we have referred to as horizontal sections, in reality sections of low hydraulic gradient, may be considered

together since either may run full without head. By the expression

“without head” we mean flowing under its own head, that is, without developing a static head above the highest point in the horizontal

section.

DRAIXS

Existing hydraulic formulas offer means for fairly close approximations under these conditions. Kutter’s formula is generally
100 RECOMMENDED PLUMBING REQUIREMENTS

accepted as the most applicable to large sizes (14 inches in diameter

and over). Darcy’s formula is generally considered more accurate

for smaller sizes (under 14 inches in diameter), being based on data

obtained from pipes in this region while Kutter’s formula was based on data obtained from large pipes and open conduits.

Results calculated by Kutter’s formula with n = 0.015 and by

Darcy’s formula agree for a pipe of 14 inches diameter and show

increasing divergence on either side of this diameter, Darcy’s formula

giving higher values for smaller sized pipes and lower values for large

sized pipes than Kutter’s formula.

We therefore submit the following table of capacities for pipes

flowing full under their own head, based on Darcy’s formula for old

cast-iron pipes lined with deposit, which is offered for approximating

required sizes of lateral drains in which a static head is undesirable or detrimental.

Table 4.—Capacities of cast-iron drains, in gallons per minute and fixture units

or cubic feet per minute

Diameter in inches Fall

Capacities Velocity

full or one-half

full Gallons per minute

Fixture

units

Inch per Feet per

foot second

11.. - - 1 3. 6 0. 48 0. 92

11 1 5.

1

.63 1. 31

11 A 8.0 1.07 2. 07

11 1* 11.2 1.50 2. 93

11 5.8 .78 1.05

]| 1 8. 2 1. 10 1. 48

l| A 13.0 1. 70 2. 34

l| 1 18.4 2. 40 3. 31

2 1 12.6 1.68 1. 28 2 1 17. 6 2. 25 1.80

2 27.8 2.70 2. 85 2 1 40.0 5.20 4. 00

3 j 1 36. 2 4. 86 1. 65

3 1 51. 3 6. 80 2. 34

3 A 80. 3 10.07 3. 70

3 1 113.8 15.20 5. 24 4

1§ 77. 4 10.3 1. 97

4

1 109. 6 14. 6 2. 79 4 173. 6 23. 1 4. 42

4 1 245.4 32.7 6. 25

5 138. 6 18. 5 2. 25

5 1 196. 5 26. 0 3. 19 5. A 311. 0 41.4 5. 05

5 1 439.2 58.5 7. 13 6 1 221. 4 29. 5 2.51

6. _ I 313. 1 41. 7 3. 55

6 |

494. 8 65. 9 5. 61

6 1 699.4 93.2 7. 93

7 1 328. 5 42.8 2. 73

7 1 465. 6 62.0 3. 87

7. . . \ 735. 1 98. 0 6. 11 7. 1 1, 040. 7 137. 7 8. 65

8. 1 463.0 61.8 2. 94 8 1 656. 0 87.4 4. 16 8 A 1, 037. 0 138.3 6. 58

8 1 1, 468. 0 195.6 9. 31

10 i 814.0 108. 6 3. 33

10 i1, 149. 0 153. 2 4. 70

10 \ 1, 819. 0 242. 5 7.44

10 1 2, 572. 0 343.0 10.52

12 1, 300. 0 173.4 3.68

12 i

1, 838. 0 245.0 5.20

12 A 2, 905. 0 387.3 8.22

12 1 4. 034. 0 537.8 11. 62
PHYSICS OF PLUMBING SYSTEMS 101

Tables for steady flow are not strictly applicable to the conditions

of intermittent flow encountered in house drains. However, the

component of the entrance velocity from the stacks in the direction

of flow in the house drain is invariably greater than the velocity for

steady flow, hence the tendency is toward a greater capacity than

that given in the tables. Any increase in capacity due to an entrance

velocity operates as a factor of safety.

The necessity of a house drain of ample capacity can not be over- emphasized. The development of a head that extends up into the

vertical stacks produces detrimental effects difficult to prevent, and

in extreme cases even impossible to prevent by any system of venting.

STACKS

We have found no formula, tables, or data applying to the flow of water in partially filled vertical pipes. Therefore, independent determinations of stack capacities, based again on the assumption that no

static head is developed in the stack itself, have been made.

In vertical stacks a static head can develop only after the stack

has become filled at some point. With the water introduced at a given rate by volume, this will first occur at the point of lowest velocity, evidently at a point of entrance. Since the vertical component

of the entrance velocity is less than the maximum velocity attained

in the stack, the velocity increases from the point of entrance until

the maximum is reached. The vertical component of the entrance

velocity depends on the rate of flow by volume, the cross-sectional area of the inlet, and the angle of entrance. This points to the

capacity of the fitting as a measure of the “practical capacity” of the

stack.

We will define the capacity of the fitting as the rate of flow in

gallons per minute at which the water just begins to build up in the

vertical part of the fitting above the inlet branch of the fitting. This

is then taken as a measure of the practical capacity of the stack constructed with that fitting. With any rate of flow not exceeding this

value then the stack, barring stoppage or marked retardation, will not

be completely filled at any point.

Determinations were made with different fittings on both 2 and

3 inch stacks as follows : The fittings were set in the top of the stack

and water introduced at known rates through a trap and the fitting inlet (fig. 39), observation being made in the open upper end of the

fitting. So long as the water flowed freely with no appreciable retard

in the fitting, the rate was considered below that fitting capacity. The

rate at which the first tendency to back vertically into the fitting above

the level of the inlet appeared, was taken as the fitting capacity. When

the water stood above the level of the inlet, even temporarily during

the sustained rate of flow, it was considered that the capacity had
102 RECOMMENDED PLUMBING REQUIREMENTS

been exceeded. This last condition in the case of only one inlet to the stack would do no particular harm, and it should be noted that

the rate of flow that causes the water to stand in the fitting is greatly

in excess of the rate at which the tendency to build up first appears,

double the rate in some cases. The flow was maintained for from

15 to 30 seconds by means of the tanks, thus giving ample time for

observation and for any effect from lower portions of the stack to be

transmitted. Various lengths of stacks from 30 to 45 feet both with

and without house drains were employed, but as no modifying effect from the part of the system below the fitting was observed in any

case only the fitting and tank connections are illustrated in Figure 39,

showing a double Y fitting with water introduced simultaneously at both inlets.

Fig. 39—Supply tanks at top of stack for determining the capacity ox fittings and stack The preceding description applies to capacities with entrance at one level with either one or two inlets. For entrance at two levels two fittings of the kind under test were set at two points in the stack

approximately 11 feet apart, and a 1-inch glass tube bent in L shape was set in a side inlet in the lower of the two fittings and water in- troduced simultaneously at known rates through the main inlets of the two fittings as before. Any retard or interference in the lower

fitting sufficient to cause a slight back flow, neglecting splashes, into

the glass L tube was taken as exceeding the capacity of the fitting

under these conditions. As might be expected, the tendency is toward an increase in capacity with the water introduced at two

levels. This is essentially different from the effects in pipes flowing

full. It therefore seems safe to assume that the capacity of a given

stack with entrance points at more than one level is not less than the

capacity of the same stack with entrance points at one level only.
PHYSICS OF PLUMBING SYSTEMS 103

In fact, there is strong evidence that the capacity increases with the

increase in number of entrance points at different levels, tending

toward a maximum capacity measured by the stack flowing full with

the maximum velocity attained by water flowing in a vertical stack

of that diameter. What we have really determined is, therefore, the

maximum capacity of the stack for methods of construction that

give a relatively small maximum capacity compared to what might

be secured by other methods or design of construction. The experiments were based on the assumption that present methods of con- necting the fixtures directly to the stack through short waste or soil branches, especially for small house construction, would be continued.

The possibilities of extension of the serviceable limits to which the

smaller sizes of stacks might be used by some changes in the method

of construction will be pointed out later. Based on the observations described, the approximate ''practical

capacities’ 7 of 2 and 3 inch cast-iron stacks with entrance points at one or more levels is as follows:

Table 5.—Capacities of stacks, with fixtures connected direct

Practical carrying capacity of stack con- structed with single or double fit- tings

2 __ 3.. 4 i. 5.. 6 .. 8..

Diameter of stack in inches SanT Y or combination Y and £ bend

Gallons

per minute

Fixture

units Gallons per minute

Fixture

units

45

100

180 280

405

720

6.0

13.3 24.0

37.3 54.0 96.0

90

200

360 560

810

1, 440

12.0

26.7 48.0

74.7

108.0

192.0

1 Capacities for the 4, 5, 6, and 8 inch stacks were calculated from the equation. The capacity of a stack is approximately expressed by capacity = Ted2

, in which d is the diameter of the pipe in inches and Tc, a constant, is 22.5 for 45° Y inlets, 11.25 for San-T inlets. There are good

reasons for believing the same relation substantially holds for larger

sizes. BASE FITTINGS The remaining point for consideration in connection with capacities—namely, the bend or turn connecting between the stack and

house drain or a lateral branch to the house drain—is not readily

determined by experimentation. It is evident that insufficient

capacity in this part would produce effects very similar to those

produced by an insufficient house drain. Ample capacity may be

secured without material change in present methods. For small
104 RECOMMENDED PLUMBING REQUIREMENTS

systems no special provision as to sizes is necessary. For larger

systems, in which the probable peak load approaches the stack

capacity, it is necessary to specify the construction in order to insure a capacity in the stack base fitting at least equal to that of the stack.

In such cases the house drain will be one or more sizes larger than the

stack. A requirement that the increase be made at the union of the

stack and base fitting rather than at the union of the base fitting

and house drain would solve the problem. In case the house drain

is two sizes larger than the stack the base fitting might be the

intermediate size. For example, in a system that requires a

3-

inch stack and a 4-inch house drain the base fitting should

also be 4 inches, or in a system which requires a 3-inch stack and

a 5-inch house drain the base fitting should be at least 4 inches

in diameter. The specification might be simplified by the requirement that in all cases for soil stacks the base fitting between the

stack and house drain should be one size larger than the stack.

This last would work no particular hardship when the requirement

is not actually needed and would reduce the possibilities of detrimental back pressures around the base of the stack, which may occur under certain conditions even in very small installations. The same

requirement should be observed whether the turn is made by means

of a long sweep one-fourth bend, by means of the two Y fittings or by means of a Y fitting and one-eighth bend. In this connection

the long sweep one-fourth bend with reducing hub will give the

desired connections with one less fitting than if an ordinary long

sweep bend is used. We have used this bend with 3-inch stack and

4-

inch house drain in test installations with decidedly better results than were obtained with 3-inch stack, 3-inch base fitting, and 4-inch

house drain.

CHARACTERISTICS OF FLOW OF WATER IN PARTIALLY FILLED

VERTICAL PIPES

The character of the flow of water in a partially filled vertical pipe

varies with the extent to which the pipe is filled. Limited opportunity for direct observation of the flow was offered in the experimental work. Opportunity was given to observe the flow past glass

sections set near the point of entrance and near the base of the

stack, the flow from the open lower end of a vertical stack, and in a few cases through the stack itself. For small volumes of flow amounting to little more than a trickle the flow is entirely on the inner wall

of the stack. With increase in volume the adherence of the flow to the wall continues up to the point where the frictional resistance of

the air causes it to diaphragm across the pipe, temporarily forming

a short slug of water which descends as a slug filling the stack until

increased air pressure breaks through, the water forming the slug
PHYSICS OF PLUMBING SYSTEMS 105

either being thrown again to the wall or falling for a short distance

as separate streamlets in the center of the pipe. This diaphragming

and forming slugs probably first appears in a 3-inch stack when the

stack is from one-fourth to one-third full. As the volume of flow

increases, the slugs thus formed are more frequent and more persistent and in a stack open at the lower end may not be broken

through. This intermittent rate partially accounts for the rapid

erratic oscillations of pressure in a plumbing system.

SPIRAL FLOW

There is a decided tendency for the water to spiral with very

low volumes of flow, evidently due to the variable frictional resistance

encountered. The direction of the spiral motion is dependent on the

resistance of the uneven surface. With increased volume the spiral

motion is less evident and was not detected at all with volumes

sufficient to entirely cover the wall of the pipe. If such spiral motion

does occur, it is not sufficiently marked to justify its being taken into account.

VELOCITY OF FLOW

Investigation of the velocities attained by water falling in partially

filled vertical pipes leads to some interesting results that may be of considerable importance in their application. It is a well-known

fact that a body moving under a constant force against a resistance

that varies as the square of the velocity tends toward maximum

constant velocity as the resistance and the moving force approach

the same value. This is illustrated by bodies falling in the air and

is especially apparent with bodies of relatively low density. Wellestablished principles of hydraulics show that the frictional resistance

in water pipes increases approximately as the square of the velocity

and that it is independent of the pressure. In vertical pipes the re- sistance evidently varies in about the same manner, and in partially

filled vertical pipes the flow is mainly on the wall. The resistances

for the full and for the partially filled pipe are not materially different. Calculations made, assuming a full pipe and frictional resistance

given by the hydraulic formula for loss in head due to friction

flv2 =

D2g

§ave a maximum velocity for a 3-inch cast-iron pipe of 24.6 feet per second. Similar calculations for 2 and 4 inch pipes

gave, respectively, 16 and 29 feet per second. While these results are not dependable they indicate the magnitude of velocities to be

measured in experimental determinations. Such determinations were made for 2 and 3 inch vertical stacks, with open ends at the

top and bottom, flowing partially full with volumes equal to the

“practical capacities” and one-half the “practical capacities” as previously determined.
106 RECOMMENDED PLUMBING REQUIREMENTS

The differential equation for a falling body when the frictional

resistance varies as the square of velocity is

Substituting

-r. d

2s T orce = ma = m = m

ds 7jt 7 . dv d

2s -dv

vdt=ds and Trw

a)

and transforming, we get

vdv 7 , vdv j

dg =q-lctf or wzrj^= ds

Integrating (2) gives

-log (<g-Jcv2

)

g — lev2

27c =* + log C=s log e + log G

(2)

(3) Transforming (3) gives

g — lev2 = 0~2ke~2ks (4) When

s = o, v = v0 , then C~2k =*g — lev20 Substituting this value for C~2k in (4) g —lev2 = (g — 1ev20) e~2ks (5) or solving (5) for v («

the general equation for a falling body with the resistance varying

as the square of the velocity in which v is the velocity at any height, g, the acceleration of gravity, le , a constant depending on the resist- ance, v0) the vertical component of the entrance velocity, e, the base

of the Naperian system of logarithms, and s, the height of fall. To plot the velocity curve for any height of stack from this equation it is necessary only to determine the value of le and v0 for that

stack and volume of flow. Employing a vertical 3-inch cast-iron stack 45 feet in height, open

at top and bottom, water was introduced at the top through a 45°

double Y fitting as shown in Figure 39 and the velocities determined

by means of a Pitot tube (fig. 40) set in the stream at the open lower

end of the stack. The Pitot tube was kept full of water by means of the flask reservoir and correction made for rise of water in the flask under impact. The purpose of the air reservoir in the flask was to damp out rapid fluctuations and overthrows in the manometers,

enabling a more accurate reading. The flow was sustained for 17.5

seconds, allowing sufficient time for the manometer to reach and

stand at the maximum. The velocity was obtained from the equa-
PHYSICS tfF PLUMBING SYSTEMS 107

tion hdg = 1/2 dx V2

, in which h is the length of the supported column

of mercury, d, the density of mercury, g, the acceleration of gravity, d1} the density of water, and V, the velocity of impact of water. Velocity

curves, plotted from the equation with £ and V0 determined experimentally, for the 3-inch stack, with volumn-of-flow of 100 and 200

gallons per minute, and the velocity curve for a free fall with the constant acceleration, g, are shown in Figure 41.' Numerous other determinations of velocities with various heights

from 5 to 45 feet of 3-inch stack gave values that fell on the curve

plotted within the estimated errors of the determinations. Similar

less accurate determinations of velocities in a 2-inch cast-iron stack

up to 30 feet in length with volumes of flow of 90 and 45 gallons per

minute gave maximums of 24 and 18.5 feet per second, respectively,

attained in a fall of 20 feet. The work is still incomplete, but the

results are conclusive in some respects, namely, (1) that water falling

Fig. 40—Pitot tube for measuring velocity of water at base of stack in vertical stacks reaches an approximate maximum in a comparatively short fall; (2) that in a given stack the maximum increases

with increased volume of flow; (3) that in a given stack the approximate maximum is attained in a shorter fall with lower volumes of flow; (4) that with volumes of flow proportional to the areas of the

cross sections—that is, proportional to the u

practical capacities”

the maximum is smaller and is attained in a shorter fall in the smaller

of two given stacks; and (5) that with equal volumes of flow the

maximum is greater and a greater fail is required to attain the maximum in the smaller of two given stacks. The conclusions are all on

the assumption that while the stack is only partially filled the vol- umes of flow are sufficient to completely cover the walls of the stacks.

If the walls are not completely covered, the maximum velocity is practically independent of the size of the stack, is very small, and is attained in a very short fall. If the stacks are completely filled and

flowing under their own head, the maximum velocity and the height

in which it is attained increases with increased size of stack.
108 RECOMMENDED PLUMBING ' REQUIREMENTS

It should be noted that, with volumes of flow of 90 gallons per

minute in a 2-inch stack and 200 gallons per minute in a 3-inch

stack, slugs of water completely filling a short length of the stack are

occasionally formed and that the maximum velocity attained by

such slugs approaches the maximum velocity for a completely filled stack. As the maximum indicated by the manometer used with the

Pitot tube was used in the determinations the velocity curve for a completely filled 3-inch stack will not differ materially from the one

o

Li

iPi

tr. a

H

u,

>*h

o

o

Ju

> 10

5

0 10 ZO 30 AO SO GO 70 00 90 100 HEIGHT IH FEET

Fig. 41—Curves showing velocity of fall in a 3-inch stack plotted (fig. 41), for the 3-inch stack with volume of flow of 200

gallons per minute.

The fact that the air resistance encountered in an actual plumbing

installation, due to the influence of the horizontal house drain, was

not present in the determinations from which the curves were plotted,

should also be noted. Evidently the air resistance offered in a partially closed system, such as presented by a complete plumbing installation, increases more rapidly than the square of the velocity. Therefore, the velocity not only approaches the maximum more rapidly

than indicated by the curves, but probably reaches an absolute
PHYSICS OF PLUMBING SYSTEMS iod

maximum within the distances indicating approximate maximum

velocities in the curves. There have been some indications of a

slight decrease in velocity toward the base when measurements were made in the open end of a long sweep one-fourth bend set on the

lower end of the vertical stack. A marked decrease in velocity

could be produced only with the base of the system completely

closed to the passage of air. This is again getting away from practical conditions, for, if the house drain may become closed to the

passage of air, the fixture inlets and vents offer an outlet with a

relatively small increase in pressure. Even the small increase in

pressure necessary to produce circulation of air through vents will

have some effect on the kind described.

It therefore seems reasonable to assume that the approximate

maximum velocity of 32.8 feet per second attained in a 45-foot

length of 3-inch stack open at the top and bottom will not be ex- ceeded in a 3-inch soil or waste stack of any height in the partially

closed system presented by a complete plumbing installation.

The only apparent application of this data is on the point of limitation of height of stack of given diameter. For example, if a

3-inch stack in which a height to the highest group of fixtures of 20 feet is permitted, there is slight reason, on the grounds of increased

velocity, for placing any limitation on the height allowed. The

velocity attained in a fall of 20 feet in a 3-inch stack open at both

ends is 29 feet per second. That attained in a fall of 100 feet will be 34.2 feet per second.

The maximum velocity attained in a given vertical stack is apparently a linear function of the volume rate of flow; that is, the

maximum velocity is proportional to the volume rate of flow. Evidently this relation holds only with volume rates of flow between

that which will completely cover the wall of the pipe and that which

continuously completely fills the pipe. Below the former limit the

flow becomes a trickle on the wall of the pipe and the resistance is relatively greater. Above the latter limit a static head is developed

in the pipe and the equation no longer holds.

No doubt the velocities could be reduced by the introduction of

devices, such as spiral sections or fittings, that would hold the water on the wall of the pipe. There has been no time or opportunity

offered yet for investigation of such devices. The effects of such

fittings on the system in other respects are problematical, and we

offer no opinion as to general effects of special fittings without a thorough investigation by experiment and test. VENT REQUIREMENTS

There are three principal effects produced in a plumbing system

which must be relieved through venting in order to insure its efficient functioning, namely, back pressure, or increase above atmospheric
110 RECOMMENDED PLUMBING REQUIREMENTS

pressure, partial vacuum, or decrease below atmospheric pressure, and self-siphonage, a purely local phenomenon. To these may be

added the possible concentration of corrosive gases at certain points

in the system. In general, a relief of the first three conditions will largely prevent the last. In any event it should be treated as a

separate consideration.

The fact that back pressures and partial vacuums do not occur in

their maximum intensities in the same part of the system, and, in

general, where they do occur alternately are of relatively small in- tensity, suggests a separate consideration of the requirements to

relieve each.

PRESSURE EFFECTS

Numerous air-pressure measurements were made with sensitive

pressure gauges at various points from the base of the stack upward

in the plumbing test installations used. In ail cases back pressures

only were encountered at the base of the stack. The region of back

pressures extended upward as the volume of the discharge was in- creased. In the upper portions of the stack below the entrance

point of the discharge partial vacuums only were encountered.

Between these two is a region in which the pressure alternates

between positive and negative pressures measured from atmospheric

pressure as the zero. Figures 42 and 43 illustrate the pressure effects in a 3-inch stack,

unvented except by the open stack top. The stack connected into a 4-inch house drain, 38 feet developed length, consisting of two

straight sections connected by a return bend, inclined at an angle of 45°. The connection from the stack was made by a 3-inch Y set

in a 4 by 3 inch Y of the house drain. These pressures, especially

the partial vacuums, are not necessarily those in the center of the

stack, but rather the pressures that would be produced in an unvented

branch line connecting at that point. The two lower points were measured in 3-inch branches of fittings, the upper points by tapping

a one-fourth-inch gas cock in the pipe at that point. The small

orifice does not give the same results as the larger fitting opening,

the values being sometimes higher and at other times lower than

measurements taken in a 2 or 3 inch fitting inlet at the same level. However, they are sufficient to show the general characteristics, and

as no direct application was made of measurements taken through

small orifices the degree of accuracy is not important. In later

experiments where results have been applied all pressure measure- ments were made in or through branches of a fitting. In the figures

solid lines connect points for which actual records of maxima or minima were obtained and dotted lines, portions interpolated from

observations of fluctuations in the pressure gauges in reaching the

maximum or minimum.
PHYSICS OF PLUMBING SYSTEMS 111

h

hi

IU

a.b

x

o

atX

0 T a 3 4 5

PRESSURE IN INCHES OF WATER

Fig. 42.-Pressure curves near base of a 3-inch stack with house drain, volume rate of water 66 gallons per minute

Fig 43. Pressure curves near base of a 3-inch stack, volume rate of water 108 gallons per minute
112 RECOMMENDED PLUMBING REQUIREMENTS

Several types of pressure gauges were used, U-tube manometers,

both water and mercury, and a sensitive differential pressure gauge.

Figure 44 illustrates the principle of the last. It consists of two

shallow drums with flexible diaphragms attached to two light circular

plates of equal area connected at their centers by a small aluminum

rod. The mid-point of the connecting rod is attached to the end of a short lever balanced on a pivot. To the other end of the lever

two light coiled springs are attached. A light stylus attached to the pivot above the lever records the deflection on a drum rotated

by clockwork. The gauge was calibrated to 0.01 inch of water and

for small deflections is sensitive to that degree, being particularly

free from overthrows under rapidly fluctuating pressures.

Figure 45 shows an arrangement of water manometers giving a maximum and minimum pressure gauge. The valves in the bulbs were constructed of sheet rubber and automatically closed, stopping

the back flow from the highest point. The scale was graduated to

0.1 inch with the possibility of estimating 0.01 inch. The same

principle in a modified form was used with mercury manometers.

The operation of the valves was fairly dependable. By careful

observation any failure could be detected and the experiment

repeated. The records are given to the nearest 0.1 inch of water

and for the lower ranges are accurate to this degree. In the higher

ranges with the drum gauge the absolute accuracy decreases, while

the relative accuracy remains the same. In view of the characteristics of pressure fluctuations produced in a plumbing system and of the accuracy of established laws of flow of

gases in pipes under pressure, it is evidently possible to calculate the

requirements in sizes of vents necessary to relieve detrimental

conditions, provided a starting point for the calculation is given.
20141°—29 9 113
114 RECOMMENDED PLUMBING REQUIREMENTS

This starting point we have established on the following assumptions : (1) That the stack is carrying its full “ practical capacity,” 200

gallons per minute (26 fixture units) , for the 3-inch stack or a known

fraction of this; (2) that a vent which will relieve the pressure effect at the point of maximum effect is ample for all other points; and (3) that no positive or back pressure greater than 1 inch and no negative

pressure or partial vacuum less than 1 inch of water, measured from

atmospheric pressure as the zero, is to be developed in any branch

drain connecting to the stack above the house drain. It should be

kept in mind that pressure variations in the stack which can not

possibly be transmitted to a fixture trap have no bearing on the

problem. We are only concerned with the pressure effects in the

branches, whether vented or unvented.

The most widely distributed pressure effect is the production of partial vacuums, and it should receive first consideration. The partial vacuums are generally due to the aspirating effect of the stream

of water in the stack flowing past the opening of a branch waste or

soil pipe. The magnitude of the effect is evidently a function of the

volume of water per unit length and its velocity. However, the most

practical way, considering the many modifications of conditions to be

encountered, seems to b*e to work for the size of vent required to

relieve the effect for the conditions producing the maximum effect. Evidently, since the aspirating effect increases with increase in velocity, the maximum will be obtained with a vertical stack open at the bottom. With the stack closed at the top it is possible to produce vacuums limited only by the vapor tension of water. J. E.

Denton at Stevens Institute, about 1890, under these conditions

produced vacuums equivalent to 25.25 inches of mercury. Such

results have no application except to show the necessity of keeping

the stack top open. We have, therefore, experimented with the

stack top open or only partially closed to simulate frost closure.

. Pressure Effects in a Stack-Vented System.—With the 3-inch

stack 33 feet long (fig. 46) unvented except through the open top

water was introduced through a P trap and Y fitting at the rate of 200 gallons per minute and measurements taken in 3-inch Y fittings at intervals of 5 feet 10 inches, beginning at a point 10 inches

below the entrance point. The mean of two independent sets of measurements is plotted in Figure 47. The maximum of any

individual pressure reading was 31.3 inches of water vacuum at the

point 10 inches below the entrance point. Measurements taken in a

2-inch stack at a point 7 inches below the entrance gave a maximum

of 28.5 inches of water vacuum when water was flowing into the stack

at 90 gallons per minute, 12 fixture units. Other measurements in

Y and sanitary T branches indicate that there is slight difference in the aspirating effects produced at Y or sanitary T branch inlets with
PHYSICS OF PLUMBING SYSTEMS 115

branches either 2 or 3 inches diameter. Figure 48 shows the curve

of pressures obtained in the 2-inch stack 34 feet high open at both

ends and water introduced at one point 29 feet from the bottom at the rate of 90 gallons per minute. Figure 49 is the curve of pressures

for the same 2-inch stack with water introduced simultaneously at

Fig. 46.—Experimental stack and vent system for determining air movements in a plumbing system two points and P2 12 feet 4 inches apart, each at the rate of 45

gallons per minute. These determinations show conclusively that

the maximum aspirating effect under these conditions is below and

near a point of entrance and were made principally for the purpose

of verifying this fact. Partial Vacuums and Vent Requirements.—The next step

and the most important consideration in this connection is the deter-
116 RECOMMENDED PLUMBING REQUIREMENTS

mination of the minimum size vent of a given length required to hold the vacuum, produced in a branch waste connecting to the

stack at a point of maximum effect, below a given value fixed upon

as allowing a sufficient factor of safety, namely, 1 inch of water.

(See discussion of factor of safety in a later part of the report for

justification of this.)

PRESSURE IN INCHES OF WATER

Fig. 47.—Pressure curve for a 3-inch stack, water introduced at Pi at rate of 200 gallons per minute,

pressure measurements at P2 and P3 Numerous arrangements of vent pipes of various sizes and lengths were attached to the 2 and 3 inch stacks, with vents connecting at one or two levels, and water introduced at different rates at one or two levels. Pressure measurements were made in the vents near

their connections with the stack in each arrangement. Further

variations were made by partially closing the stack tops in imitation of frost closure and by adding short horizontals to the lower

end of the stack. An anemometer was set in the end of the vent

in each case to determine the velocity of air in the vent.
PHYSICS OF PLUMBIKG SYSTEMS 117

Figure 46 shows a typical arrangement for a 3-inch cast-iron

stack with 2-inch wrought-iron vent connected to stack at two

levels, with stack top closed to 1-inch diameter and 3-inch long

Fig. 48.—Pressure curve for a 2-inch stack, water introduced at Pi at rate of 90 gallons per minute, pres- sure measurements at P2, P3, P4, P5, and P6 sweep bend and 5-foot length of horizontal laid approximately 1 in

48. Following are the data for this arrangement:

Rate of flow of water in gallons per minute Maximum vacuum Maximum

velocity of

air in vent

1 Maximum

flow of air in vent

at P 1 at P2

Feet per Gallons per

Indies water Inches water second minute

200 0.5 1.0

.6 1.0 37.5 367

100 .25 .2

100.... _ - - .4 .3 32.2 315 2001. 1.7 1.8 130.5 1 300

1 With stack top open full 3 inches in diameter.
118 RECOMMENDED PIjUMBTNG REQUIREMENTS

Without going into details of other determinations we may summarize the results for 2 and 3 inch stacks as follows: A 2-inch vent

20 feet long with 3 elbows, equivalent to approximately 36 feet of straight pipe is sufficient to prevent a vacuum in a branch from

a 3-inch stack greater than 1 inch of water, with the stack carrying

200 gallons per minute. A lj-inch vent 14 feet long with 3 elbows

Fig. 49.—Pressure curve for a 2-inch stack, water introduced at rate of 45 gallons per minute each at Pi and P2 , pressure measurements at P3, P<, Ps, and Pe equivalent to 23 feet of straight pipe is sufficient to prevent a vacuum

in a branch from a 3-inch stack greater than 1.0 inch of water, with

the stack carrying 100 gallons per minute. A 1-inch pipe 22 feet long with 1 elbow, equivalent to 24 feet of straight pipe, is sufficient to prevent a vacuum in a branch from a 2-inch stack greater than

0.5 inch of water, with the stack carrying 90 gallons per minute.
PHYSICS OF PLUMBING SYSTEMS 119

The above values in connection with rates of air flow in the vents

measured simultaneously, and laws of flow of gases under pressure

enable a fairly close approximation of requirements for main vents to

relieve the aspirating effects in 2 and 3 inch stacks within the measured

limits of stack capacities. The laws of flow of gases referred to are expressed by the equation: WPIP

Id in which V is the velocity or volume per unit time, the value depending on the units employed, P

the drop in pressure, D the diameter of the pipe, l the length of the

pipe, d the density of the gas, and K a constant whose value depends on the units employed. Allowing the development of a vacuum equal

to 1 inch of water gives a drop in pressure through the vent of 1 inch

of water. Evidently the intensity of the vacuum produced is dependent on the intensity of the aspirating effect and on the rate at which the vent pipe will deliver air to the point of connection under

the drop in pressure thus created. Therefore, pipes that will deliver

air at the same rate under the same drop in pressure are equivalent

in venting effects. Calculations made from the preceding data and other data not

herein recorded indicate that a straight vent pipe 36 feet long 0.9 inch in diameter would prevent the production of a vacuum in a branch

from a 2-inch stack greater than 1 inch of water, with the stack carry- ing 90 gallons per minute. The result is believed to be dependable,

since similar calculations made for other sizes of pipes were checked

very closely by measurements of the kind employed.

A 0.9 inch vent, if available, is an impractical size to employ, and

the data are valuable only for purposes of calculation. There appear

to be good reasons for not employing any vent less than 1J inch in

diameter.

The following tables, adapted from tables for flow of gases under

low pressures, are presented as a basis for extension of the data obtained. The calculations for short lengths of pipe have been carried

through on the assumption that the short length in question is a

part of a longer pipe in which the pressure gradient is as indicated. In

other words, no correction has been made for the end effects observed

in fluid flow through short pipes which would decrease the rate of flow somewhat.
120 RECOMMENDED PLUMBING REQUIREMENTS

Table 6.—Volume of air transmitted by pipes of various lengths and diameters under a difference in pressure of 1 inch of water

Air flow (in gallons per minute) for various diameters (in inches)

pipe in feet i 1 U 11 2 21 3 31 4 5 6 8

1 181 236 520 805 1, 633 2,672 4, 866 7, 212 10, 187 18, 550 30, 225 61, 562

4 90 118 260 402 816 1,336 2, 433 3,606 5, 093 9, 275 15, 112 30, 781 9 60 78 173 268 544 890 1,622 2, 404 3, 395 6, 183 10, 075 20, 520

16 45 59 130 201 408 668 1,218 1,803 2, 546 4, 637 7, 556 15, 390

20J 41 52 115 179 362 638 1,081 1,603 2, 263 4, 190 6,869 13, 990

25 36 47 104 161 326 534 973 1, 442 2,037 3,710 6, 045 12, 312 30\ 33 43 94 144 297 485 884 1,311 1,852 3,315 5, 495 11, 192 36 30 39 86 134 272 445 811 1, 202 1,697 3,091 5,037 10, 260

49.... 26 33 74 115 223 381 695 1,030 1,455 2,650 4,317 8, 794

64 22 29 65 100 204 334 608 901 1,273 2,318 3, 525 7,695

81 20 26 57 89 181 296 540 801 1,132 2,061 3, 358 6, 840

100 18 23 52 80 163 267 486 721 1, 018 1, 855 3, 022 6, 156

144 15 19 43 67 136 222 405 601 848 1,545 2, 518 5, 130 169... 14 18 40 62 125 205 374 554 783 1,407 2,340 4, 735

196 13 16 37 57 116 190 347 515 727 1,325 2,158 4,397

225 12 15 34 54 108 178 324 482 679 1,236 2, 015 4, 104 400 9 11 25 40 81 133 243 361 509 927 1, 511 3, 078

625 7 8 20 32 65 107 194 288 407 742 1,209 2, 462 Table 7.—Equivalent lengths of pipe in venting capacity, under a pressure

difference of 1 inch of water

Equivalent lengths (in feet) for pipe of various diameters (in inches)—

l 1 n 2 2£ 3 CO 4 5 6 8

1 1.7 8 20 81 218 720

1 4.8 11 48 128 424

1 2.3 10 26 87 192 376 1, 220

1 4.

11 36 80 170 529

1 2.6 8.7 19 36 129 242 1, 465

1 3.3 7.3 14 46 128 529

1 2.2 4.4 14.5 38 160

1 2. 6.6 17.5 72

1 3.3 8. 7 36

1 2. 6 13

1 4.1 Table 8. —Length of straight pipe equivalent in resistance to one elbow or tee of equal diameter

Diameter (inches) 1 n n 2 2i 3 3£ 4 5 6 8

Length in straight pipe equivalent to one elbow or tee (feet).. 2 2.5 3 5 7 9 11 13 19 24 35

This last table is intended for use in determining the length of

straight pipe equivalent to a vent pipe made up of straight sections,

elbows, and tees. For example, a 2-inch vent pipe 30 feet long with

two elbows and one tee in that length is equivalent to 30 + (3 X 5) = 45

feet of straight pipe of the same diameter. The lengths given in the

other tables are lengths of straight pipes.

Back Pressures and Vent Requirements.

The maximum back

air pressures can not be readily determined by experiment due to
PHYSICS OF PLUMBING SYSTEMS 121

the tendency to develop a head of water in the lower part of the

stack as the conditions producing maximum air pressures are approached. However, it may be shown theoretically, that, in general, the vent required to relieve maximum aspirating effects is suffi- cient to prevent detrimental back pressures, provided the house

drain and stack base fitting have the proper capacity to prevent

back-water effects. Assuming a condition in which the house drain is closed to the

passage of air from the stack and an inflow of air, then the volume

rate at which air must be removed from the lower portions of the

stack, in order that the pressure may not rise above 1 inch of water

measured from atmospheric pressure, will be equal to the rate of displacement by the discharge into the &tack; that is, equal to the

rate of inflow into the stack. The “ practical capacity” (see p. 101)

determined for the type of construction under consideration, was

used as a basis for determining vent requirements for the relief of

maximum aspirating effects. On the same basis under the assumed

condition the vent required for a 3-inch stack to prevent the production of a back pressure greater than 1 inch of water must be capable

of carrying air under the difference of pressure at a volume rate equal

to the “ practical capacity” of the 3-inch stack, namely, 200 gallons

per minute. Reference to Table 6 shows that a lj-inch pipe 16

feet long, a 2-inch pipe 64 feet long, a 2i-inch pipe 169 feet long, or a

3-inch pipe 600 feet long have approximately that capacity.

It is conceivable that in rare instances a condition might occur

in which a piston effect would be produced, driving the total volume

of air in the stack through the vent. Under this condition the

volume of air passing through the vent would not be greater than

the difference between the total volume of air in the stack ahead of

the piston and the water content in the same portion of the stack.

Allowing a maximum velocity, 30 feet per second of fall to be attained

in a 3-inch stack in a two or three story building, the maximum rate

at which air would have to be removed would be 660 — 200 = 460

gallons per minute. Under a pressure difference of 1 inch of water

the lengths of 1J, 2, 2-J, and 3 inch pipe that will remove air at that

rate are 3, 12, 39, and 110 feet, respectively. In this connection it should be kept in mind that with vent connections at each floor level below the top floor the vent stack is not called upon to function

throughout its entire length as a relief to back pressure but only in

the first 10 or 20 feet at its base, since aspirating effects are produced

in the upper portions of the stack when back pressures are produced

at the base. The portion operating in relief to back pressure may

thus be under a greater difference in pressure than the 1 inch of water

allowed. To illustrate, suppose P2 in Figure 46 is near the base of

the stack, and that water is flowing in the stack at a rate sufficient
122 RECOMMENDED PLUMBING REQUIREMENTS

to produce back pressure, or a positive pressure measured from at- mospheric pressure as zero, equivalent to + 1 inch of water, at the same time Pv being higher on the stack and near the point of entrance

of water, will be under reduced pressure; that is, under a negative

pressure measured from atmospheric pressure as zero. Suppose

this negative pressure is equivalent to — 1 inch of water, then the

difference of pressure in the vent between P2 and P1 willbe + 1 — ( — 1) = +2 inches of water, and there will be a flow of air from P2 to P1 under a differential head of 2 inches of water. The effective pressure

in the vent is measured between the absolute pressure at P2 and

another absolute pressure somewhat lower than atmospheric. There

is thus produced, in systems in which both aspiration and back

pressure are present, a certain amount of recirculation of air in the

lower portions of the system giving greater relief in this region than

is obtained when the entire length of vent stack is functioning in one

direction only. It is impossible to assign any definite value to the

extent of the relief due to recirculation of air, since it will vary with

conditions of installation and volume of water discharged. However, the extent of recirculation of air without doubt increases as the intensity of back pressure increases with volume of discharge.

It is therefore concluded that the vent required to relieve maximum aspirating effects if extended down undiminished into the region

of back pressures is sufficient to relieve the latter effect, except under

conditions where a static head due to back water is developed in the

stack. This last condition is one that must be avoided by a proper

proportioning of the house drain and base fitting to the peak discharge

of the system.

Self-siphonage and Vent Requirements.—The vent required

to prevent self-siphonage may be considered on a similar basis.

Any vent that will supply air to the waste or soil line at a volume rate equal to that of the fixture discharging through the line will prevent

a siphon pull on the trap greater than the pressure difference neces- sary to produce this rate of flow in the vent line. Reference to the

table on flow of air in pipes shows that under a difference of pressure of

1 inch of water a 1-inch pipe 16 feet long will deliver air at the rate of 59 gallons per minute, a rate greater than the rate of discharge of any single fixture in a dwelling. In fact, with a vent of this size and

length the pull on the trap of such a fixture would be much less than

1 inch of water, since the vent pipe will begin to deliver air as soon as a difference in pressure begins to develop. It is evident then that the

vent of the size most practical to install will be ample to prevent any

loss in the trap seal of the fixture from self-siphonage.

For convenience we have plotted the results in Figure 50, giving

a chart from which the size of vent stack required for the 3-inch

soil stack may be read when the peak load or probable maximum dis-
PHYSICS OF PLUMBING SYSTEMS 123

charge and the total developed length of the vent stack are known.

For example, the coordinate point for an estimated peak load of 180 gallons per minute, 24 fixture units, and a developed length of

vent stack of 100 feet lies between the curves for a 2-inch and a

2J-inch vent, therefore, for such an installation a 2§-inch vent stack

is required for a 3-inch soil stack of this height and peak load.

The curves are plotted from results of rough measurements in

gome respects, but calculations made from these measurements

check measurements on rate of flow of air made at the same time so

closely, to the nearest unit in many cases, that the results are believed

to be more accurate than a casual review would imply. At any rate they are believed to be sufficiently accurate, in view of the rigid

Fig. 50.—Chart for determining the permissible length of main vent of a given diameter for a 3-inch soil or waste stack when the maximum discharge through it is known restriction imposed and the fact that only rough approximations are possible in the application.

The method may readily be extended to other and larger sizes of

soil stacks if the demand justifies, and certain refinements in

methods of measurements are also possible if closer approximations

are desired.

It is interesting to note the relation of vent requirements for the

2 and 3 inch stacks with volumes of flow equal to their rated capacities, 90 and 200 gallons per minute, respectively. For vents of the same developed total length the requirements are approximately ex-

^2 p4 ^ 2)2 pressed by = jjr or bi which d and dx are the diameters of required vents, respectively, for stacks of diameters I) and I)x

. There

are good reasons for believing that the same relation holds for largersized stacks.
124 RECOMMENDED PLUMBING REQUIREMENTS

The relation of rates at which air is moved through the vents

during the discharge is also interesting and may serve to answer some questions raised with reference to the use of the 3-inch soil stack. With equal volumes of flow in the 2 and 3 inch stack and

with vents that allowed approximately the same vacuum to be

produced at the point of connection of the vent to the stack, the

ratio of the rates by volume at which air was drawn through the

vents was found to be 1 to 5. The ratio of the fourth powers of the diameters of the stacks 2

4/34 = 16/81 = 1 to 5, approximately.

This not only checks the preceding equation for vent requirements

for 2 and 3 inch stacks carrying their full practical capacities (see p. 101), but also indicates the requirement of a larger vent for the

3-inch stack when the two stacks are carrying equal volumes, provided the volumes approach the practical capacity of the 2-inch

stack. A similar relation may be expected for 3 and 4 inch or 5

and 6 inch stacks, probably more marked than for the small stacks,

since with 1 inch difference in diameter the ratio of the smaller to the larger cross section of two pipes increases with increase in size. MODIFYING CONDITIONS

Numerous conditions are encountered in service which may produce

sufficient modifying effects on the functioning of a plumbing system

to justify special provisions. Among these the effects of heavy rains,

of submerged sewer outfall, of strong winds over the stack tops, and

of closure or partial closure of stack tops by frost or snow have

received special attention and have been made the subject of experiments to determine the magnitude of the effects and a means of pre- venting or alleviating them. These are grouped together here for

discussion and for convenience of reference.

All the experiments were made on complete plumbing test installations, and specific data for some will be found in the report on such

test, installations.

Heavy Rains.—The only direct effect of heavy rains on a plumbing system is encountered when a combined sewer system is employed.

There is no doubt that a complete separation of storm and sewage

mains greatly simplifies the problem of house drainage. When the

street mains are combined sewers, the problem would be simplified

to a lesser degree by separate connections to the street main.

Means of introducing water into the house drain at known rates was provided. Figure 51 shows a typical arrangement providing for

the introduction of the water through rain leader A ahead of the

stack, or through rain leader B, beyond the stack, or simultaneously

through both rain leaders. The worst conditions were encountered

with storm water introduced ahead of the stack discharge as through

A, Figure 51. The effects in the stack were only slightly less with
PHYSICS OF PLUMBING SYSTEMS 125

storm water at the same total rate equally divided between A and B.

The effects were appreciably less with storm water introduced at the same rate through B alone. Only one distance, approximately

6 feet between soil stack and rain leader B connection to the house

drain, was employed. It is evident that the farther from the soil stack the rain-leader connection on the sewer side is removed, the

less the effects of storm water will be felt in the plumbing stacks.

The effect of storm water in all cases is an increase in back pressures

around the base of the stack, the effects increasing rapidly with

increase in the rate of introduction of storm water. This is true even with a house drain of sufficient capacity to carry off the total

discharge from stack and rain leaders if it were introduced to the

house drain at one point only. The apparent decrease in carrying

capacity of the house drain is evidently due to two or more streams

entering it from different directions. If the combined discharge from

the stacks and rain leaders exceeds the carrying capacity of the house

drain under its own head, the result is backwater into the base of the stack. When the backwater extends upward into the stack

above the level of the lowest fixtures, it is impossible to protect the

traps of such fixtures completely by venting. It is necessary,

therefore, to look for the cure by insuring an ample capacity in the

house drain. Detrimental effects may be further reduced or rendered

less liable to occur by giving the greatest possible vertical distance

between the lowest level of fixture inlets and the house drain when

this distance is short. Whether the combined or separate sewer

systems are employed, there is a distinct advantage in having a

vertical distance of at least 3 feet between the lowest fixture inlet to the stack and the house drain, the distance increasing with the

height of the stack and volume of discharge through it.
126 RECOMMENDED PLUMBING REQUIREMENTS

The plumbing committee has agreed that an allowance for a

rainfall of 4 inches per hour is liberal, and that an allowance for

1,500 square feet of roof or drained area was sufficient to include

all types of the small dwelling house under consideration in its report. Before this agreement had been reached many tests had

been made allowing for a rainfall of 6 inches per hour over 1,200

square feet of roof area. If these rates seem too high to some, it should be remembered that a much lower rate of rainfall for an

extended period under certain conditions, in low-lying territory, etc., may prove as detrimental as the higher rate for a short period of time.

A rate of rainfall 4 inches per hour discharges water to the sewer

at the rate of approximately 1 gallon per minute for every 24 square

feet of drained area, which is equivalent to 1 fixture unit for every

180 square feet of drained area. The house drain should have suffi- cient capacity to carry off the combined estimated peak discharge

from the stacks and the discharge from the drained area. It is true

there is small chance of the two maximum discharges occurring

together, but the effects from the combined sewer are so detrimental

and the conditions encountered so varied that this allowance in

capacity will not give an unnecessarily large margin of safety in

low-lying territory and regions of frequent heavy rains.

Submerged Drains.—The effects arising from a submerged

house drain or submerged outfall of house drain are very similar to those produced by an overcharged house drain in the combined

sewer system. Tests were made with submerged outfall (fig. 52),

from 2 inches up to 3 feet depth, the latter giving backwater in the

house drain to the base of the soil stack. Increase in the size of the

house drain will afford slight, if any, relief to this latter condition.

The only complete protection seems to be to specify construction

that will insure the lowest fixtures being well above the level of

submergence, otherwise such fixtures will be forced out of service

during periods of submergence. The problem is not to be solved

by experimentation.

House Traps.—The effects of a house trap (fig. 53), or running

trap, in the house drain are similar to those arising from a partially

submerged drain. Whether the house trap is vented or unvented

the first effect is a decrease in the carrying capacity of the house

drain due to the added resistance. In the British il Report of the

Departmental Committee on the use of Intercepting Traps in

House Drains,” 1 following thorough investigation, both experimental and by observation on systems in use, the advantages and dis- advantages of intercepting traps are fully discussed.

1 This report was published in 1912 by H. M. Stationery Office, printed by J. Truson & Son

(Limited), London, Eng.
PHYSICS OP PLUMBING SYSTEMS 127

Our experiments have shown that the effect of an unvented trap

in the house drain is similar to that of partial submergence. For

heavy discharges with the trap either vented or unvented the effect

is similar to that of a considerable degree of submergence. With

the trap vented on the house side, for small discharges not sufficient to fill the house drain to the point of closing the vent, the effect is practically that of an open house drain. There seems to be no case

in which the house trap increases the capacity of the system.

Offsets in Stacks.—Many questions have been asked concerning

the effects of offsets in soil or waste stacks. We may answer these

questions as far as the data at hand and theoretical considerations

justify conclusions. If the offset is above the highest fixture con- nections to the stack, there can be but slight effect on the functioning

of the system. If the offset is below the lowest point of fixture

connections to the stack, the effect will be similar to that from a house drain at the same level as the offset. The longer the offset

Fig. 52.—Submerged outfall of house sewer Fig. 53.—Vented running trap the more nearly the effects will approach those of a house drain at the same level. The farther the offset is placed below the lowest

fixture connection the more nearly the effect will approach that of the straight stack. The effect of offsets in the stack between levels of fixture connections to the stack is problematical and will doubtless

be found to vary with different installations. This last is a condition

of construction which should be avoided when possible and which,

if impossible to avoid, should be safeguarded by additional vent

connections to the stack at the fixture levels on either side of the offset. Winds.^-The effect of winds was obtained by directing an air current over the stack tops by means of a motor-driven fan of the

propeller type (fig. 54). By means of rheostats the velocity could

be varied up to 45 miles per hour (55 miles per hour U. S. Weather

Bureau rating). The frame carrying the motor was constructed to permit adjustment directing the current horizontally or at an

inclination of 30° to the horizontal in either direction. The effect of air currents was studied in connection with complete plumbingtest installations. All of the tests involving wind effects were made
128 RECOMMENDED PLUMBING REQUIREMENTS

on systems with 3-inch soil stacks, 2-inch waste stacks, and 4-inch

house drains.

With the system idle, the 2-inch waste line closed and the end of the house drain open the maximum effect obtained by a 45-mile

per hour air current directed horizontally over the 3-inch stack top was a decrease in pressure in the system of 0.2 inch of Water. With

the end of the house drain submerged, giving a system closed at the

lower end, a decrease in pressure of 0.36 inch of water was produced

by a 45-mile per hour current directed horizontally and 0.4 inch

of water by a 45-mile per hour current directed upward at 30° to the horizontal.

With fixtures on the system discharging, the wind effect was generally masked or shut off from unvented fixture branches below the

e>J

Fig. 54.—Apparatus for producing air current over stack top point of discharge. In individually vented branches and unvented

branches above the point of discharge the combined effect was

the sum of the separate wind and fixture effects. In no case was a combined effect observed greater than that indicated by the additive relation.

There seems to be no ready means of protecting against wind

effects when the vent stack or vent lines are connected into the

soil stack before passing through the roof, since they are transmitted more readily to vented than to unvented fixtures during use and as readily during idle times. In view of the small effects encountered,

it seems reasonable to assume that in the small dwelling house they

will be taken care of by factors of safety referred to elsewhere.

A considerable degree of protection would be afforded in tall buildings or other buildings exposed to very high winds by running

the soil stacks and vent stacks separately through the roof and con-
PHYSICS OF PLUMBING SYSTEMS 129

necting them together above the highest fixture inlets and branchvent connections, thus giving an opportunity for relief of pressure

differences above the fixture connections. Then only when the

effect was of the same kind and intensity over both stacks would

the full intensity reach the fixture traps.

Frost Closure.—Frost closure was simulated by setting sections

of pipe of various diameters and length into the stack tops. No

measurable effect was produced by setting a li-inch pipe 20 inches

long into the tops of the 3-inch stacks of the different systems. A

1-inch pipe 12 inches long set in the 3-inch stack only slightly in- creased the vacuum produced by a heavy discharge from the fixtures. No doubt the effect would be felt more with an increase in the volume

of discharge. With a complete closure of the stack top the water was sucked from one or more traps by the discharge of a single

water-closet on the system. This occurs whether the traps are individually vented or not provided the stack tops are completely

closed. Floor Drains.—The floor drain, though not itself a modifying

condition, is considered in this connection because the type and

position in which it may be installed will be determined by such

modifying conditions. No tests were made with true floor drains.

However, tests were made with traps connected to the soil stack near

its base and connected into the house drain on the sewer side. There seems to be no reason why a floor drain might not be con- nected into a soil or waste stack when conditions permit, subject

to the same requirements in venting, etc., as a fixture connecting

into the stack at the same point. If the house drain is sufficient in

size for the system and located high enough to be free from backwater effects, a floor drain might connect directly to a nominally

horizontal house drain at a point 5 feet or more from the base of the

stack on the sewer side without danger from aspiration or back

pressure, and, hence, need not be separately vented unless its form

is such as to induce self-siphonage or for other good reasons. The

velocity of flow attained in a house drain is insufficient to produce

aspiration, and the head is not great enough at such a point to produce sufficient back pressure to endanger the trap seal. In all places

where there is any danger of backwater or overcharged sewers the

floor drain, if installed, should be fitted with a suitable backwater

valve.

SIPHONAGE OF FIXTURE TRAPS

The subject of trap siphonage is somewhat more complicated than

expected from a casual consideration. Whether the effect is due to self-siphonage or siphonage by aspiration or a vacuum transmitted

to the trap from some other part of the system, the extent of siphon20141 0 —29 10
130 RECOMMENDED PLUMBING REQUIREMENTS

age is evidently dependent on the intensity of the pull and a quantity factor or, in other words, the energy that may be expended on

the trap. In the case of aspirating effects the energy is great, and a

considerable volume of air must be moved into the system to protect

the trap when the intensity is equal to or greater than the pressure

represented by the seal depth of the trap. The venting of a branch

line on which a trap is placed prevents, by the introduction of air, the intensity of the vacuum produced from rising above a fixed

value. The problem of venting to protect against aspiration and

back pressure was taken up in an earlier section. These same considerations enter into the problem of self-siphonage.

Self-siphonage.—The intensity of the pull in self-siphonage is determined by two different causes which may be present at the same

time. The first is an unbalanced column of water as represented in

the common siphon. The second is the momentum pull exerted by

the moving column of water, which is present whether the pipe is horizontal, vertical, or inclined and its intensity is dependent on the

length of the column or length of filled pipe and its velocity. In

vertical pipes the former cause is predominant. In pipes approaching the horizontal the latter is predominant. The quantity factor

is dependent on the volume of the pipe, hence, on the length of the

pipe. The volume of pipe inducing the siphonage effect is in

small fixture traps relatively small, hence, a small volume of air introduced is sufficient to prevent the intensity from rising to a point

that endangers the seal of the trap.

Before taking up the discussion of self-siphonage in detail we desire to call attention to some very pertinent facts in connection with

wide-bottom fixtures, such as bathtubs, kitchen sinks, and laundry

trays. In the discharge from such fixtures a swirl is formed before

the fixture is empty which draws air through the trap, tending to reduce the intensity of the pull toward the end of the discharge.

There is a long trail discharge from such fixtures during which the

velocity in the waste pipes is reduced with a resultant reduction in

the pull due to velocity. Refer to Figure 55 for illustration of the

effects of swirl and trail discharges. In no case, using flat-bottom

fixtures, have we been able to reduce the final seal materially below

the normal full seal and in no case with such fixtures set in place on a test system have we detected any reduction in seal. With oval-bottom fixtures tending toward a funnel shape, as the

washbasin, it is essentially different. In such fixtures the discharge

ends abruptly with a very short swirl. Self-siphonage is almost

certain when an unvented waste has a vertical section greater in

length than the seal depth of the trap and followed by a horizontal

section of near the same diameter (fig. 56) . If the entire waste from

the trap is nominally horizontal (fig. 57) the momentum pull in its
PHYSICS OF PLUMBING SYSTEMS 131

Fig. 56 —Arrangement of waste pipe to produce self-siphonage of a fixture trap
132 RECOMMENDED PLUMBING REQUIREMENTS

full intensity is exerted at the end of the discharge. In a “P” trap

a part of the water invariably flows back from the horizontal part of the trap. At least a partial seal is always left. Any seal left is theoretically sufficient to prevent air circulation from the plumbing

system to the room, except where the waste connects low on the

stack within the region of back pressure. It of course may be completely destroyed by evaporation. The degree of protection of traps

connecting to the stack above the region of back pressures is therefore dependent on the frequency of use as well as on the seal depth.

Because of the differences in siphonage effects in wide and ovalbottom fixtures, except for a few independent tests to verify the facts

regarding wide-bottom fixtures, the laboratory tests were confined to self-siphonage in washbasins. Including a number of tests on fixFig. 57.—Fixture and waste pipe to study effect of length of horizontal pipe on self-siphonage tures set in place on the test installations, several hundred tests were made. Space will only permit detailed description of a few of the

most pertinent.

1. To determine the effect on self-siphonage of size of outlet orifice relative to size of waste pipe, an oval washbasin was arranged with

nominal lj-inch waste in a form to induce strong self-siphonage

(fig. 56), a = 9 inches, b = 17 inches, c = 26 inches, d= 26 inches,

e = l bend fitting, actual internal diameter of waste = 1 X

9X inches.

Capacity of basin=lj gallons, discharged each time by lifting plug

from outlet; trap lj-inch drawn brass with normal full seal of 3.2 inches.

Seal left

Internal diameter of outlet (inches) Mean of

five deter- minations Minimum

of five determinations

Velocity in waste pipe

1* Inches

1. 92 Inches

1.2 Ft. 'per sec. 4.2

If .96 .8 4. 5 !&__ .86 .7 4.9

i
PHYSICS OF PLUMBING SYSTEMS 133

The unbalanced column of water in the waste is the same in each

case. Evidently, then, the reduction in self-siphonage with reduction in size of outlet orifice is due to the slight reduction in velocity

thus produced. An outlet orifice and tailpiece slightly less in diameter than the trap and waste only slightly reduces the velocity in the

waste pipe, so does not materially affect the scouring effects. At the same time there is an increased velocity through the tailpiece itself, giving a better scouring in this part which is always exposed to the room. It therefore seems reasonable and offers many advantages

to allow the tailpiece of a fixture to be the nominal size smaller than

the trap, convenient for making a slip joint between the two.

2. To determine relative resistance to self-siphonage of unvented

plain P traps of various seal depths, tests were made with the fixtures

connected to a 3-inch stack plumbing test installation. The oval

washbasin and bathtub were served by a common waste, 1£ inches

from the bathtub and 1 J inches from the basin. The basin waste was

26 inches vertical from the outlet end of the trap to its connection

into a recessed combination Y and £ bend in the l|-inch bath waste

2 feet 6 inches from the stack. The horizontal distance from the

basin outlet to the trap connection with the vertical waste was 15

inches. The exact arrangement is unimportant, the point being to secure a strong siphonage effect on the basin trap. The data following represents the effect of the combined discharge of the washbasin

and bathtub, which is stronger than that of the basin alone. The

intensity and quantity pull were practically the same for each of

the traps. The tailpiece of the basin had an internal diameter of

1£ inches, the internal diameter of the traps and basin waste were

approximately the same, l-^ inches.

Nominal

seal

Seal left

Mean of

five deter- minations Minimum

of five determinations

Cast brass, lj-inch P trap..

Inches

2.6 4.0

7.0

Inches

0.88

1.56

2. 62

Inches

0.8

1.4

2.

1

Lead, 1 5-inch Ptrap.. __ __ - Do . These data, supported by other observations on seals retained by

traps of various seal depth of from 2 to 7 inches on different waste

lines, indicate a retained seal proportional to the depths of the normal

full seals. Other considerations enter into the question of permitted

depths of seal. The effect of seal depth on scouring properties has

not been specifically investigated. However, it is evident that the

scouring properties decrease with depth of seal, especially with refer- ence to heavy materials. The very shallow seal in addition to
134 RECOMMENDED PLUMBING REQUIREMENTS

offering less resistance to self-siphonage is less resistant, because of smaller volume of water, to loss of seal by evaporation. We therefore suggest a minimum normal seal of 2 inches and a maximum of 4

inches as serviceable limits. From a consideration of all tests our

personal inclination is toward a nominal seal depth of 3 inches for

washbasins not separately vented.

3. To determine effect of length of unvented waste on self-siphonage (fig. 57) : Oval basin capacity gallons discharged by lifting

plug from full basin. Diameter of outlet orifice and tailpiece =1£

inches, diameter of waste 1^ inches, a= 7 inches, c = J bend open

end turned down.

[Normal full seal of lj^-inch lead P trap=2.2 inches]

Seal left in

Length b Mean of Minimum

three of three determina- determinations tions

Fall A inch to the foot: Inches Inches

2 feet 8 inches 2. 2 2. 2

3 feet 2 inches _ 2.2 2. 2 3feet8inches 2. 2 2 2

4 feet 2 inches .. 2.2 2.2

Fall y2 inch to the foot: 3 feet 8 inches 1. 93 1. 6 4 feet 2 inches - 1. 26 i!o Diameter of outlet orifice and tailpiece =i* inches.

[Normal full seal of 1^-inch lead P trap =2.3 inches]

Length b

Seal left— Mean of three determinations

Minimum

of three determinations

Fall A inch to the foot: 2 feet 2 inchesInches

2. 13

1. 13 .87 .80

Inches

2.0

1.0

.8

.7

2 feet 8 inches

3 feet 2 inches __ 4 feet 2 inches One-fourth bend fitting set in horizontal section (fig. 58); diam-

' eter outlet orifice and tailpiece = 1^- inches, a = 7 inches, b = 12

inches, c = 2 feet 2 inches.

[Normal full seal lead P trap=2.2 inches]

Seal left—

Length b and c Mean of three determinationsMinimum

of three determinations

Fall A inch to the foot: 3 feet 2 inches

Inches

1.7 Inches

1.6
PHYSICS OF PLUMBING SYSTEMS 135

4. To determine effect of fall or inclination of waste on self- siphonage (fig. 58)

:

Fig. 58.—Fixture and waste pipe to study effect of inclined waste pipe on self-siphonage Diameter of outlet orifice and tailpiece = 1^- inches. 1 J^-inch lead

P trap, a = 9 inches, b = 13 inches, c = 5 feet 2 inches, diameter

c = l^g- inches.

[Normal seal=2.0 inches]

Seal left— Mean of two

determinations

Minimum

of two

determinations

Fall in section c:

x/i inch to the foot 1°+.

Indies

1.7.65

.75 .70

1. 10

1. 90

2.00

Indies

1.5.6

.7.7

1.0

1.8 2.0

1 inch to the foot 5°.. ___ 10° to horizontal

15° to horizontal _ . 20° to horizontal _ 25° to horizontal _ 30° to horizontal
136 RECOMMENDED PLUMBING REQUIREMENTS

With diameter of outlet orifice and tailpiece = 1 % inches, 1 J^-inch

cast brass P trap, 5 = 10 inches, c = 5 feet, diameter c = 1J4 inches.

[Normal seal depth =3.0 inches]

Seal left— Mean of three determinations

Minimum

of three determinations

Inclination of section c:

34. inch to the foot, 1°+

Inches

2. 93 Inches

2.9

y-i inch to the foot, 2%° 1. 57 1. 5 5° to horizontal _ 1.65 1.5

10° to horizontal— 2. 40 1. 2

15° to horizontal— 3.00 3. 0

20° to horizontal 3.00 3.0

30° to horizontal 3. 00 3.0

45° to horizontal 3.00 3.0

60° to horizontal. 3. 00 3. 0

Vertical 3.00 3.0

5. To determine the influence on self-siphonage of a 90° elbow in a nominally horizontal unvented waste (fig. 58) several independent

experiments were conducted. No more specific conclusions follow

from these data than may be drawn from other experiments in

which such an elbow was employed. It is sufficient to state that an elbow in a nominally horizontal waste at a horizontal distance

from the vertical inlet arm of the trap not greater than 18 to 20

inches reduces the self-siphonage effect. This means that from the

standpoint of self-siphonage alone a greater length of pipe may be

permitted when an elbow is placed within these limits than where

the waste pipe is straight from the trap to its connection with the

stack or a vented branch.

6. To determine the effect of fouled waste pipes on self-siphonage:

The experiments conducted for this purpose were not wholly satis- factory because of the difficulties of securing representative fouling

of the waste pipes. If extreme fouling is assumed, such as to re- duce the cross section of the waste materially below that of the

fixture outlet orifice and of the trap, the self-siphonage is much

greater than if we assume a slight degree of fouling in which the

cross section of the waste is not reduced below that of the fixture

outlet orifice. The whole question of degree of fouling that takes

place in traps and small waste pipes in service is one that must be

decided from extended observation and specific records under actual

service conditions. Time and facilities have not permitted such

observations. The alternative is to require construction that will tend to reduce fouling ol wastes to a minimum and assume that

under such conditions the fouling that takes place will not reduce

the cross-sectional area of the trap and waste below that of the
PHYSICS OF PLUMBING SYSTEMS 137

fixture outlet orifice and tailpiece. On this assumption the data

would permit an approximation of allowable length of horizontal

unvented waste. It is necessary further to arbitrarily assume some

permissible degree of self-siphonage. If no reduction of seal is per- mitted, it leads to one conclusion. If any other remaining seal depth is assumed, it leads to another conclusion. The plumbing

committee fixed on a minimum remaining seal of 1 inch as repre- senting the limit of satisfactory conditions in tests for traps with

nominal 2-inch full seals. Any reduction in seal below this value was considered unsatisfactory. In this connection we wish to say

that we believe this is a fair limit for a trap with a 2-inch normal

seal. In general, a remaining seal of not less than one-half the

normal full seal would more nearly represent the dividing line between safe and unsafe conditions than an arbitrarily fixed value

irrespective of normal seal. An S or a P trap seal may be drawn

to the point of breaking the seal with a loss of approximately onehalf its full seal, after which it may be subjected repeatedly to the same or a smaller strain with no further loss of seal. Reference to the data shows that with a fixture-outlet orifice equal to the cross section of the waste a clean straight waste laid

one-fourth inch fall to the foot and 2 feet 8 inches long measured

from the center of the inlet arm of the trap did not reduce the nominal

2-inch seal of trap below 1 inch; and that with a 90° elbow 13 inches

from the trap and 5 feet 2 inches of clean waste laid one-fourth inch

fall to the foot beyond the elbow did not reduce the nominal 2-inch

seal below 1.5 inches. It is a fact, although not shown in the data,

that an increase in the length of the section beyond the elbow produces slight, if any, increase in self-siphonage effect until the outlet

end of the waste falls below the dip of the trap.

No specific recommendations are made as to the allowable length

for an unvented horizontal waste from a washbasin. We desire,

however, to call attention again to certain modifying conditions:

A slight reduction in the size of the outlet orifice of a washbasin

appreciably decreases the self-siphonage; a decrease in the size of

the waste by fouling or other causes tends to increase self-siphonage.

In general, if a washbasin is placed in a region of no or slight back

pressure, there is no particular danger if the seal left is reduced below

1 inch, except as it may be affected by the factor of evaporation.

The washbasin is, in general, the most frequently used fixture of the

bathroom group and the factor of evaporation is usually negligible.

On the grounds of self-siphonage an increase in depth of normal

seal would permit a proportional increase in allowable length of

unvented waste. There is no necessity for limiting the length of an

unvented horizontal waste laid with a fall of cue-fourth inch to the
138 RECOMMENDED PLUMBING REQUIREMENTS

foot from a bathtub, kitchen sink, and laundry tray on the grounds

of sclf-siphonage, except as it is limited by the requirement that the

outfall end may not be below the dip of the trap. A long sloping

waste (fig. 59) with the sloping section of the same cross section aa the trap and horizontal section will not produce self-siphonage

when the angle of inclination from the horizontal is greater than

30°, provided the horizontal section is not in itself sufficient to induce self-siphonage. This is true in service only if the cross section

of the inclined part does not become materially reduced by fouling.

Whether it is a practical form of installation or not depends on its liability to foul to such an extent.

Permissible Length of Unvented Horizontal Branch Waste

Pipes.Four reasons for limiting the length of an unvented horizontal waste or soil branch have been advanced. These are increased

danger of self-siphonage, increased corrosion due to decreased cir- culation of air, increased liability to stoppage or fouling due to decreased velocity of flow and increased cooling and fouling area and

decreased facility of use of fixtures due to sluggish action in long horizontals. If the reasons advanced were all of the same weight and

supported by uncontrovertible evidence of the effects claimed, the

problem would be immediately limited to the one placing the greatest

restriction. As it stands there is some uncertainty, especially con- cerning the effect of long unvented branches on corrosion. There

are no data bearing directly on this effect available. The opinions

expressed by practical men are based for the most part on the fact
PHYSICS OF PLUMBING SYSTEMS 139

that long unvented branches have been found badly corroded in many

cases. There is no evidence at hand that a vented branch in the same

position and service would not have corroded to the same or greater

extent, or that the corrosion was due to lack of air circulation in the

branch. Experiments conducted at Harvard University during the

past year for the plumbing committee have shown that induced cir- culation of air in an unvented horizontal 1 £ inches in diameter takes

place up to a length of about 2 feet, due to the circulation of air in the stack to which the unvented branch is connected. The same and

other earlier experiments show a fairly rapid change of air by con- vection currents and diffusion up to a much greater length. It would seem, then, that if the contention that lack of air circulation

hastens corrosion were granted there would still be slight grounds for

Fig. 60.—Diagram to illustrate the effect of horizontal waste pipe on velocity and scour limiting the length of an unvented branch to less than 6 feet. The

same arguments might be applied to any unvented branch whether

horizontal or vertical. In any event, it is a question of the life of the pipe rather than one of functioning until the pipe has corroded

through or has corroded to the extent of materially reducing the

cross-sectional area. The questions of stoppage, fouling, decreased rate of flow apply

also to all horizontal wastes and drains whether they are vented or

not. In fact, the general effect of a vent in a branch waste is to decrease the rate of flow. Compare Figures 60 and 61 to the same

wastes unvented. With the vents shown in the waste lines the

effective head on the horizontal waste will be measured by b. In

the same systems unvented the effective head will be measured by a. It is evident, without experimentation to show the magnitude of the

effects, that from the standpoint of drainage alone long wastes leading
140 RECOMMENDED PLUMBING REQUIREMENTS

directly from the trap on the horizontal or with small gradient are bad practice and should he reduced to the minimum consistent with

other requirements.

As to self-siphonage and its relation to the limit of the allowable

length of an unvented horizontal waste pipe, our experiments indicate

that the slope should be confined between the limits of a fall of one- fourth inch to the foot and one-half inch to the foot, and that the outlet

end should not extend below the dip of the trap. It will be observed

that from a consideration of self-siphonage effects alone there are so

Fig. 61.—Diagram to illustrate the effect of a vertical section of waste pipe on velocity and scour many conflicting elements that any conclusion is largely a matter of judgment. For these reasons and because of the uncertainty of the

effect of long unvented branches on corrosion it is difficult to make

specific recommendations. However, the following table summarizes the results of the experiments, giving what are believed to be safe maximum lengths for nominally horizontal unvented wastes

from fixtures connected to a stack or vented branch at points where

they are free from detrimental aspirating or back-pressure effects. It is to be understood that they refer to self-siphonage only. Possible increase in self-siphonage due to fouling has been taken into account.
PHYSICS OF PLUMBING SYSTEMS 141'

Table 9.—Lengths of nominally horizontal unvented waste pipes believed to be safe against self-siphonage

Plain P traps, nominal depth, full seal

Safe lengths of waste pipes for

Washbasin

with fall not greater than £inch

to 1 foot or

less than * inch to 1 foot

Wide-bottom fixtures with fall—

| inch to 1 footI inch to 1 foot

2 inches

Feet

4

6

8

Feet

4

68

Feet 8

12

16

3 inches

4 inches. ... . These lengths are from the center of the trap to stack or larger

vented branch waste and would permit one 90° elbow in the waste

at a distance not greater than 18 inches from the inlet arm of the

trap. Elbows in other positions or added elbows should be counted

as equivalent lengths of pipe.

Resealing Traps.—It should be noted that the preceding

restrictions refer to the use of plain P traps. The experiments with

“reseating,” so-called “antisiphon” traps, owing to difficulties encountered in satisfactorily fouling the traps and in determining the

kind and degree of fouling to be expected in different kinds of service,

have not been completed.

The tests have shown that “resealing” traps when clean retain a

greater seal under a suction test and are more resistant to back

pressure with the seal left after the suction test than clean unvented

plain P traps of the same full seal depth when subjected to the same

suction and pressure tests. The same is true to a lesser degree for

resealing traps of the better types, fouled by artificial means. The tests so far indicate that there is a field in which a judicious use of the better types of resealing traps would be found a distinct

advantage, such as in places where there is danger of self-siphonage

or of aspiration and back pressure within certain limits and where

structural difficulties are encountered that make the venting of the

plain trap costly or impractical. The data are not yet at hand to determine to what extent “resealing” traps may be used with safety.

With data available it will be found difficult to state in a general way

the extent of their use without opening a way for misuse under

certain conditions. Where an unvented plain trap will serve there

is no special advantage gained in using a “resealing” trap at an added cost, and there is no advantage gained by the use of “resealing”

traps in places where it is necessary to vent individually regardless of the kind of trap used.

It is obvious that, tied up as the question of the use of “resealing”

traps is, with efficiency of functioning and economy of construction
142 RECOMMENDED PLUMBING REQUIREMENTS

and surrounded, as it is, by strong prejudices both for and against

their use, any general regulations must be administered with considerable latitude of discretionary powers if full advantageous use of

11 resealing ” traps is to be obtained and no abuse is to result. Such

discretionary powers would, of course, assume a complete knowledge

of the subject on the part of the administrative officer and might

easily lead to special privileges. It is unfortunate that the data are not available to enable us at least to state the limits beyond which

resealing traps may not be used with safety.

The same questions are bound to rise with respect to other usages

in plumbing work; for example, that of individual venting of fix- tures. With any rules that may be applied generally with safety

many places will be found where we could go beyond the limits stated

in the rules with perfect safety were there a competent authority

to prescribe the limits for the condition encountered.

Back Venting.—In connection with the employment of individual

or group vents as a protection against siphonage and pressure effects

Fig. 62.—Diagram to illustrate type of venting liable to clog or as a means of insuring air circulation, it is of extreme importance

that the position and manner of making the vent connection receive

special attention and be safeguarded by regulations. The experiments on fouling conducting at the Bureau of Standards and numerous instances cited for service installations indicate that there is a strong liability of a vent line becoming completely closed near its junction with the waste line when conditions for fouling are favorable.

It has been shown that vents are required at certain points in a complex plumbing installation of two or more floors in order to protect the trap seals. It is evident that a vent poorly installed has

not met the condition and that one that has become completely

stopped in service is as bad as if no vent had been installed. The

method of crown venting has been generally prohibited because of

liability of closure by fouling. Some forms of continuous waste

and vent may give rise to conditions quite as bad as crown venting.

The “ continuous waste and vent” has been favored by the plumbing committee. As “ continuous waste and vent” is defined it would
PHYSICS OF PLUMBING SYSTEMS 143

permit the vent being taken off the top of a horizontal waste or the

continuation of a horizontal waste as a vent. For illustration of three distinct effects, all of which fall within the definition of “continuous waste and vent/’ refer to Figures 62, 63, and 64. Figure

62 represents a nominally horizontal waste vented from the top of a combination Yand J bend in the horizontal waste line in which the waste

and vent are in the same vertical plane. Assuming the same cross

sections of trap and waste throughout x-aj represents the approximate

Fig. 64—Diagram to illustrate type of venting liable to clog hydraulic gradient when the waste line is flowing full under the head

in the fixture. Evidently in an arrangement of this kind there will be

periodic back flow into the vent and strong liability to stoppage in

the vent. Figure 63 represents a waste, with a corresponding hori-
144 RECOMMENDED PLUMBING REQUIREMENTS

zontal distance between the fixture and stack, in which there is a

vertical section, c, following the point of venting. Here the vent

connection lies above the hydraulic gradient, x-y, therefore the vent

line is protected against back flow and consequent stoppage. When

venting is necessary to protect trap seals, the type of venting repre- sented in Figure 63 is believed to be the best possible; that is, a “continuous waste and vent” in which the vent is a continuation of a vertical section of the waste. The restriction necessary to insure

protection against back flow into the vent or vent connection would

be that ~ is equal to or greater than g

«

Keferring again to Figure

63, a would represent the vertical distance from the level of the

fixture overflow to the level of the outlet of the first horizontal

section, b the horizontal distance from the fixture outlet to the first

1

Fig. 65.—Diagram to illustrate type of group venting in which vent is protected from clogging vertical section or to the vent connection, c the length of the vertical

section from the vent connection to the level of the outlet of the

second horizontal section, and d the length of the second horizontal

section. For small fixtures, a washbasin or kitchen sink, a might be

measured from the top of the fixture outlet with perfect safety, since

by the time the waste has become filled by the discharge the fixture

will have practically emptied. Call this new distance a

1 then the

new hydraulic gradient is x

xy. It will be observed that the direction at which b leads into c makes no difference. To apply concretely

to a practical case suppose a washbasin with trap set close to the

fixture and the waste from the trap leading directly into the wall,

thence vertically to the floor, and thence horizontally through the

floor to the stack. Suppose a

1 = 6 inches measured from the basin
PHYSIOS OF PLUMBING SYSTEMS 145

outlet, 5-12 inches, and c=17 inches, then to hold the relation-?a

is equal to or greater than g, d can not exceed 34 inches. It is recog- nized that in the case of bathtubs and other fixtures which set low on the floor it is impractical to attempt to hold any relation between

verticals and horizontals, such as suggested when a long waste leads

through the floor on which the fixture is set. Figures 62 and 64

show that in this case the vent connection is always below the hydraulic gradient for a full fixture and a full waste line. Figures 65

Fig. 66—Diagram to illustrate type of group venting in which the vent is protected and 66 represent types of 11 group venting” in which it would be

possible to hold the relation ^

so far as the dry vent is concerned. The wet vent portion would be kept open by the discharge

of the fixture that it serves as a waste. For this reason these types

of group venting are believed to be better than individual venting

when the one vent fully protects the traps of the two fixtures. The preceding discussion has been based on the assumption that

the trap and its waste would be of the same nominal cross section

throughout. If a gradation of sizes were employed in which the horizontal section beyond the point of vent connection were increased over that of the parts preceding, the results would be modified. The

purpose has been to emphasize the necessity of limiting permitted

lengths of vented horizontals if the vent is to be surrounded by condi20141°—29 11
146 RECOMMENDED PLUMBING REQUIREMENTS

tions favorable to its continuous operation in service and if the best

scouring effects in the waste lines are to be secured.

It is not to be inferred that the following opinions and recommendations are based entirely on the above theoretical reasoning. The

effects were observed in a general way during the experiments. There seems to be little chance of obtaining new data on the subject more

suitable for general application than the direct application of the

principles of hydraulics.

Recommendations.—From a consideration of the subject of limitation of length of small waste branches from all standpoints, facility of drainage, self-scouring of waste lines, circulation of air, self-siphonage, stoppage of vents, some of which are mutually conflicting in

their requirements, the following is suggested as a solution

:

1. That the developed length of an unvented horizontal waste be

limited to 6 feet.

2. That the developed length of an unvented horizontal waste from

a washbasin or other oval-bottomed fixture be limited to 4 feet for

traps with nominal 2-inch seals and 6 feet for nominal 3-inch, or more, seals.2 3. That a horizontal section of the vented portion of a waste be

limited to 6 feet, except when the vent is the continuation of a vertical

portion of the waste, in which case it may be extended to c (see

fig. 63), section b being in general the length necessary to make the

connection from the fixture to the vertical section, c, in the partition

or wall, limited always by the condition pertaining to an unvented

horizontal waste.

4. That whenever practical a vent be the continuation of a vertical

section of the waste. THE FACTOR OF SAFETY IN A PLUMBING SYSTEM AND DETERMINATION OF THE UPPER LIMIT OF SERVICE FOR A 3-INCH SOIL

STACK

The determination of the allowable upper limits of service of a given soil stack—that is, the determination of the number of fixtures

of different kinds or number of fixture units that may with safety be

drained into the stack—involves a consideration of all parts of the

plumbing system in their relation to each other and unless extreme

care is exercised may lead to inconsistencies. It is necessary to know the maximum carrying capacity of the stack under the conditions involved and the “peak load” determined or estimated from

the total number of fixtures of different kinds that are to be drained

into the stack. The former has been determined for certain con8 The plumbing committee later agreed on a maximum developed length of 5 feet permissible for horizontal unvented waste pipes for all fixtures.
PHYSICS OF PLUMBIHG SYSTEMS 147

ditions by observation of known rates of discharge into the stack. It is proposed to estimate the latter from predetermined maximum

rates of discharge from individual fixtures and probable coincident

discharge of these fixtures. Before combining these it is necessary

to establish a reasonable factor of safety and to determine some

boundary lines for frequencies of coincidence that need or need not

be accounted for in estimating the “peak load.”

ESTABLISHMENT OF A FACTOR OF SAFETY

The establishment of a factor of safety is difficult because in reality

not one, but many factors of safety are involved. With reference

to the pneumatics of the system the fixture traps are the weak points.

The variations in air pressure in the stacks themselves is of no importance, as this is not transmitted to the traps. In the determinations for vent requirements a factor of safety of 2 against aspirating

effects has been proposed by the plumbing committee and used for

traps of 2-inch normal seal depth. Recommended methods of construction by which branches would be connected to points of minimum aspirating effect, rather than at point of maximum effect, as was done in determining vent requirements; the method employed of always keeping the estimated peak discharge from a permitted in- stallation under the rated capacity for the stack; and the method of alw;ays employing a vent of the nearest size larger than the cal- culated required size to give this factor of safety, all operate to give a factor of safety greater than the assumed one of 2. The same

applies to back pressures, except that in regions where there is no

aspirating effect, as is generally the case where there are strong back

pressures, the initial assumed factor of safety becomes 4 instead of 2

with trap seals of 2 inches employed. In both aspects an increase

in normal seal depths of traps employed would increase the factor of safety proportionally.

FUNCTIONAL FACTOR OF SAFETY DISTINGUISHED FROM STRUCTURAL

It should be kept in mind that this is a factor of safety in functioning and that it materially differs from a structural factor of safety.

A strain on the system sufficient to use up the entire factor of safety can result in no more than a temporary decrease in efficiency of functioning and no structural depreciation, except in the matter of overflowing or flooding, which has no direct connection with the

matter of venting. It is evident from the maximum carrying

capacity of stacks, which is greatly in excess of the rated “practical

capacity” used in fixing the limits of service for a stack, that the

factor of safety would have to be greatly exceeded before any material

reduction of efficiency of functioning occurred. Apparently, then,

the only danger is from overflowing or flooding, and this only when

the estimated “peak load” for the system approaches the maximum
148 RECOMMENDED PLUMBING REQUIREMENTS

carrying capacity of the stack, which is three or more times the rated

practical capacity. The matter of local flooding of lateral branches

must be considered separately from the requirements for stack

vents and house drains. The greatest danger of overflowing or

flooding, except local, is from complete stoppage of the stack or house drain, which may occur even with any size of stacks and even

with small loads. In view of the preceding relations and in view of

certain relations of frequencies of occurrence in the probability

tables, it seems reasonable to assume that an estimated “peak load”

occurring once in the order of one year is ample allowance for fixing

the size of stacks, vents, and drains to the nearest size, and to assume

that a coincident discharge occurring once in the order of 10 or 100

years may be neglected. Referring to Table 2, it will be observed

for systems up to 12 water-closets that if the probability of coincidence of a given number of water-closets is of the order of once in one year the probability of coincidence of one more than this number

is of the order of once in 100 years. Also, from a consideration of

the equations from which the tables were computed, the chance that

if a given number of water-closets in coincidence is exceeded it will

be exceeded by one and not more than one is of the order of 100 to 1. A concrete illustration may be made for the 3-inch stack. Refer- ence to Table 2 shows that allowing for a rush period of one hour

daily the probability of overlapping coincidence of 4 out of 12 waterclosets on a system is once in 336 days, the probability of 5 out of 12 once in 56 years.

LIMITS OF SERVICE FOR A 3-INCH SOIL STACK

The rated “practical capacity” of the 3-inch stack for the type of construction in which a part, at least, of the waste pipes from the

small fixtures connect directly into the stack falls between the combined discharge of 4 water-closets and that of 5 water-closets. It is therefore concluded that a 3-inch soil stack with properly proportioned house drain, lateral branches, and vents will efficiently serve

in this type of construction for 12 water-closets or their equivalent.

The requirements in house drain and vents may be taken from the

tables or charts for this or any smaller number of water-closets or

their equivalent. This is far in excess of the requirements for any

separate dwelling and would permit its use to include a maximum

of 72 fixture units, or 8 complete bathroom groups of fixtures.

Increased by Methods of Construction.—We have previously

mentioned the possibility of extension of the limits of service of the

3-inch or other stacks by a slight change in methods of construction.

No doubt the limits could be extended without change in methods of construction by increasing the size and number of vents.
PHYSIOS OF PLUMBING ‘SYSTEMS 149

It will be remembered that the ''practical capacity” of the 3-inch

stack was rated on the assumption that the stack may not flow full at any point. If the construction is made such that no fixture is connected directly onto the stack, then there is no reason why the

stack may not be permitted to flow full and even under a slight head.

Experiments have shown that a velocity of 30 feet per second in a 3-inch stack is attained in a fall of between 25 and 30 feet with a

possible maximum velocity of about 35 feet per second. A 3-inch

stack flowing full with a velocity of 30 feet per second will carry

Fig. 67 —Diagram to illustrate type of yoke venting tending to increase the capacity of a system water at the rate of 660 gallons per minute, approximately equivalent

to the combined discharge of 15 water-closets. Reference to Table 2

shows that a carrying capacity of this amount would allow 100 waterclosets with an ample margin of protection against flooding or overflowing. It would seem, then, that the service to which the 3-inch

stack may be adopted for certain types of buildings is practically

unlimited.

Figures 67 and 68 illustrate a step in this direction, representing

single floors for two types of buildings which may be duplicated on any number of floors up to the limit of service of the 3-inch stack.

With such an arrangement the soil stack will serve only as a carrier
150 RECOMMENDED PLUMBING REQUIREMENTS

during heavy discharges, each floor approximating the effects in a separate small system. No specific tests have been made with such

construction, but the data at hand enables us to approximate the

limits to which the 3-inch vent may be employed by extension of the curves in Figure 50. With bathroom units in corresponding positions on successive floors in apartment houses or hotels the type of

construction represented in Figure 67 might be carried to any height

with a 3-inch soil stack, the only precaution necessary being that of

insuring sufficient capacity in the house drain and base of stack conFig. 68.—Diagram to illustrate type of yoke venting applied to larger toilet rooms nection to the drain, one that is necessary regardless of the size of

stack employed. There are limits to the height to which a 3-inch

vent stack might be employed. Estimates made on the basis of Table 2 for probable coincident discharge and an extension of the

3-inch vent curve in Figure 50 to include higher rates of discharge

give an approximate maximum length of 3-inch vent stack of 150

feet. Allowing for elbow or other reductions and for length of vent

above level of fixtures indicates a limitation of height for a 3-inch

vent to about 12 stories. Up to this height the construction might

be a 3-inch soil stack, a 3-inch vent stack, and 3-inch main vent con- nection on each floor. Above that height an increase in size of vent

stack only would be required. With lower structures on the same
PHYSICS OF PLUMBING SYSTEMS 151

plan both the vent stack and main vent connection might be reduced

below 3 inches. The construction would serve equally well in duplex,

as indicated by dotted branch of double Y and branch vent connection, with only a small reduction in limited heights. Figure 68 repre- sents the same method applied to office building toilet-room construction.

As indicated these are very rough estimates, based as they are on

the extension of data obtained for vent requirements with smaller

“peak loads” than would be encountered in these larger systems.

However, we have elaborated to a considerable extent merely to emphasize the possibilities of service of the 3-inch stack. Before

any definite recommendation can be made it will be necessary to make further determinations and test the results thoroughly.

It should be observed that there are limitations for the employment of 3-inch stacks imposed by 3-inch lateral branches leading to the stack for types of construction in which the number of fixtures

emptying into the stack on the same floor exceeds approximately

six water-closets, or their equivalent in fixture units, because of the

liability to local flooding. No such restriction need be placed on

the employment of 4-inch stacks and 4-inch lateral branches to the

stack in the same plan of construction (fig. 68). With a 4-inch

horizontal and water-closets set 30 inches apart the holding capacity

of the pipe and closet bends is approximately equal to the total discharge from all the water-closets thus placed on any 4-inch

horizontal. There is therefore no danger of flooding from local causes and the run-off during the discharge will practically insure

proper functioning with any possible combination of discharges of

water-closets on such a line, always assuming that it is properly

vented to protect it against pneumatic effects. It would seem,

therefore, that there is no necessity for using a soil stack larger than

4 inches in diameter for any building, provided the construction is such as to protect the fixture traps from the pneumatic effects produced in the stack itself. Here, again, definite recommendations

are dependent on further experiments and a complete testing of the

plan.

The size of main vents or vent stacks required by the proposed

plan would be about the same as now commonly employed with the

4-inch soil stack. The required size of the house drain would be

dependent on the total number of fixtures on the system and the

kind of use for which it is intended.

SIMPLIFICATION OF PLUMBING CONSTRUCTION

The degree to which plumbing construction may be simplified and

the resultant reduction in cost depend to a large extent on the planning for such simplification. The planning to secure the greatest
162 RECOMMENDED PLUMBING REQUIREMENTS

degree of simplification should begin with the architects design and

extend throughout to the completion of the plumbing work. It is not to be expected that the architect will plan the building around

the plumbing system. It is not, however, too much to expect that

he should he familiar with the plumbing requirements of the place

for which the building is designed and that he should keep in mind

(1) that the plumbing is an integral part of the completed building,

and (2) that the mere location of the position of the fixtures without

any consideration to the possible location of the stacks and branch

drains is not sufficient. It is a fact, so evident as to be almost an axiom, that the shorter

and more direct the drainage pipes in a plumbing system are, consistent with pneumatic effects produced, the more efficient the drainage will be. The most direct system of pipes will be secured by

grouping the fixtures closely around the stack serving them. In a few cases the necessity of venting against pneumatic effects may be

accentuated by the close grouping, but this will be more than balanced by a corresponding simplification of the vent system, by decrease in length of connecting vent pipes, etc. These points are

especially true of the small dwelling house, with only one bath, in

which it is possible by close grouping of the fixtures to install the

plumbing system with no venting except the soil stack and at the same time secure more efficient and safer drainage of the fixtures than

if they were individually back vented. The same principle applies

in a lessened degree to systems of two or more bathrooms and other

fixtures.

Minor considerations in the design of the building that will fre- quently serve the above ends may be here pointed out. Bathrooms

should be located, if possible, so that the soil stacks may be placed

in or adjacent to the walls of it. The fixtures should be located in

the bathroom so as to reduce the length of wastes and branch vents,

when required, to a minimum. Where such an arrangement is not

practical or desirable, an arrangement should be made that will

permit the installation of a simple system of wastes and branch

vents within the limits of length governing such installations. It is hardly necessary to add that the paths of wastes and vents through

the walls or floors from the fixtures to the stacks must be kept in

mind in the location of the fixtures.

SEPARATE FLOOR LAYOUTS TESTED

With these points on efficiency of drainage and simplicity of construction in mind several different arrangements and methods of connecting wastes to the soil stack were installed in complete plumbing test installations. These are considered separately from the rest

of the installation for purposes of illustration and discussion, and
PHYSICS OF PLUMBING SYSTEMS 153

the advantage and defects of each design are pointed out. The vent

lines shown in the sketches are not to be considered as required,

since gate valves were installed in the lines to enable cutting out

portions of the vent line not needed and the form of connecting the

vents to main vents or stacks is not always recommended as a desirable one. The point was to determine when individual vents were and were not needed. Specific data applicable to each sketch

will be found in connection with the tests on complete installations

in which the same design was used.

Figure 69 shows a design employed on the top floor in a one story

and basement construction with a water-closet and laundry trays

installed in the basement. It is shown here, as used, with double

branch fittings in the stack and waste lines, thus giving opportunity

to throw the same into a duplex system with two bathroom groups of fixtures set back to back. During the tests for a single system the

Y branches opposite the water-closet and bathtub were plugged and

a deep seal glass trap set in the fitting branch opposite the washbasin. With all valves in the vent closed, the discharge of the washbasin and bathtub together almost completely siphoned the washbasin

trap. With valves 3 and 4 only open there was no loss in either the

bath or basin traps by self-siphonage from the single or combined

discharge of the two. With all valves in the vents closed, one of the
154 RECOMMENDED PLUMBING REQUIREMENTS

traps would practically lose its seal from the discharge of the watercloset. This is due to aspirating effect of the water-closet discharge

flowing past the waste opening into the stack. With the vent valves

3 and 4 open no measurable loss of seal in either the basin or bath

trap was produced by any combination or order of discharge of the

three fixtures. At times a very slight back pressure was observed in

the bath trap when the basin was discharged.

With the duplex installation it was found necessary to vent each

pair of fixtures, the baths by the "common vent” (ft); the basins by

the common vent (3), the water-closets being “ stack vented.”

With a pair of fixtures thus placed back to back the valve in the

"common vent” for the pair closed the discharge of one of the pair

invariably pulled the seal from the other trap. The effect was not

90

6side outlet 45side outlet

Fig. 70.—Illustration, crowfoot fittings as great with the pair of bathtubs as with the pair of washbasins,

yet was sufficient to reduce the trap seal materially.

The plan of connecting the bath and basin common waste into a

fitting below the water-closet fitting was also tested with TJ-inch

waste from the bathtub with similar results. These results, verified

by later pressure measurements in similar positions on a straight 3- inch stack, indicate that the waste pipe connection to the stack was made near the point of maximum aspirating effect of the water-closet

discharge. One result is to require a larger vent to protect the traps

against the aspirating effect than would be required to protect against

self-siphonage alone. The employment of a side inlet termed a

u crowfoot” fitting was suggested by the plumbing committee as a

practical means of protecting fixture traps from the aspirating

effects produced by water-closets on the same floor. The “ crowfoot” fitting is illustrated in Figure 70, showing elevation and plan

views of these fittings with side inlets at 45, 90, and 135° to the main

inlet branch. The fitting may readily be made right and left for all
PHYSICS OF PLUMBING SYSTEMS 155

three types, as well as with two or more side inlets at different angles

if required.

The special advantages of the “crowfoot” fitting for small-house

construction will become evident from the applications made in the

tests. Pressure measurements made in the complete plumbing test installations and in straight 3-inch stacks at points on the stack

above the inlet through which water was introduced into the stack

showed no measurable effects when the stack top was open. At

the same level as the inflow only very slight suctions or back pressures were produced. The use of the “crowfoot” fitting affords almost

complete protection from aspirating effects produced by the dis- charge of fixtures on the same floor. The “ crowfoot” fitting, as described, is not a patented fitting. Its use somewhat simplifies

the venting necessary to protect from the aspirating effects of dis- charges from higher floors. Figure 71 shows an arrangement of fixtures similar to Figure 69

with a kitchen sink added. This was tested as the highest floor on

the system.
156 RECOMMENDED PLUMBING REQUIREMENTS

With valves (1) and (2) closed the arrangement illustrated in

Figure 71 showed no measurable loss of seal in any trap of the group

from aspirating effect, with fixtures discharged in any combination

and in any order when the group is the highest on the system. There was the usual loss of seal in the basin trap by siphonage when the

basin and bath were discharged together, and some loss in seal from

self-siphonage when the basin discharged alone. There was no

measurable loss of seal in any trap when valve (1 ) was opened.

Therefore, to completely protect the traps of the group from all local

effects a small vent from the basin branch is necessary.

The same arrangement of fixtures (fig. 71) was completely tested

as the first floor of a two story and basement structure with 10 feet 10 inches between first and second floors with the fixtures arranged

as shown in Figure 72 installed on the second floor. The discharge

Fig. 72—Arrangement of stack vented bathroom group tested from the water-closets was varied by adjustment of supply devices

up to a mean rate of discharge of 60 gallons per minute. The tests show that the venting with valves (1) and (2) open (fig. 71) is suffi- cient and needed to completely protect the bath, basin, and sink traps

in that particular layout' against the aspirating effects produced by

the combined discharge of a water-closet with paper and soil, a bathtub, a washbasin, and a kitchen sink from the floor above. Repeated

tests with a heavy discharge from the second-floor fixtures in conjunction with the discharge of the washbasin on the first floor in

various orders of sequence failed to produce any measurable loss of seal in the bath trap on the first floor. Apparently the interval

between the closing of vent ( 1 ) by the washbasin discharge and the

closing of the horizontal waste from the bath is too short to permit

the transmission of aspirating effects to the bath trap. Once the

horizontal waste is filled the bath trap is completely protected from

aspirating effects. With valve (2) closed a complete loss of seal was

produced in the sink trap by a heavy combined discharge or by the

repeated discharge of a single water-closet from the floor above.
PHYSICS OF PLUMBING SYSTEMS 157

The protection offered the water-closet trap by the venting with

valves ( 1 ) and (2) open is not complete. A heavy discharge from

the second floor, in conjunction with either or both the washbasin

and bathtub on the first floor discharging, produced a measurable

loss of seal in the water-closet trap on the first floor. A repeated

discharge of a water-closet with paper and soil, washbasin, bathtub

and kitchen sink from the top floor in conjunction with either or both

the basin and bathtub on the first floor left approximately 0.7 inch

seal in the closet trap on the first floor, starting with a normal full seal of 4 inches in the water-closet trap. A single discharge of the same fixtures did not reduce the water-closet seal on the first floor

Fig. 73—Alternate arrangement of bathroom and kitchen-sink group tested below 1 inch. The conclusions to be drawn with reference to layout

(fig. 71) with a bathroom group, or bathroom group and kitchen sink, on a floor above are: ( 1 ) That each small waste connecting independently into the stack must be vented; {2) that considering the

slight probability of all the fixtures of the group above discharging

at the same time as the basin or bathtub in the lower group, the

water-closet may be left without a separate vent with comparative

safety; and (3) that with possible heavier discharges from above than

described the water-closet should be separately vented.

Figure 73 represents a plan, of rearrangement of the fixtures of the group (fig. 71), interchanging the relative positions of the wash-
158 RECOMMENDED' PLUMBING REQUIREMENTS

basin and bathtub. It was tested in the same position on the 3-inch

stack and in the same manner as for layout (fig. 71). With valve (I) only open Ho loss of seal in any trap of the group was produced by

any combination or order of discharge of the fixtures within the group

itself. With valves (1) and (#) open and the discharge of a watercloset, washbasin, bathtub, and kitchen sink from the floor above in

conjunction with the washbasin of the lower group the seal of the

bathtub trap was materially reduced, leaving in one instance only

0.2-inch seal of a normal 2.0-inch full seal. The conclusions are:

(1) That for the highest group of fixtures on a stack a vent from the

basin waste is sufficient, and (2) that for a lower floor the vent requirements are the same as for the plan in Figure 71 with the addition

of a separate vent for the bathtub waste. To eliminate the necessity of any except stack venting for a singlefloor group or the highest group of fixtures on the stack, the arrangement of fixtures shown in Figure 74 was installed and tested. With

this layout no measurable loss of seal was produced in any trap of the group by any combination or order of discharge of the fixtures

of the group itself, or in conjunction with other fixtures lower on the

stack. The combined discharge from a washbasin and kitchen sink

into a 3-inch stack is not sufficient to produce aspirating effects great enough to cause measurable loss of seal in traps whose unvented

wastes connect to the stack at points below.

The conclusion is that within the limits of permitted length and

fall of unvented wastes it is unnecessary to individually vent any
PHYSICS OF PLUMBING SYSTEMS 159

fixture of a group installed on this plan (fig. 74). It will be observed

that with “crowfoot” fittings a great variety of arrangement and

spacing of fixtures within the limits of permitted lengths and fall of unvented wastes may be secured without in any way affecting the

general results indicated. The preceding layouts of construction

(figs. 69 and 74), though closely representing the installations as

tested, are not drawn to scale and are not to be considered as approved

in detail. A number of detailed drawings representing approved

application of the plans and principles involved are given later. TESTS OF COMPLETE PLUMBING INSTALLATIONS

As has been previously indicated, the final test of any plumbing

design or detail of plan of construction must be its satisfactory operation in service. While much of the preceding investigation has a wider application, a full knowledge of the principles thus disclosed

are believed essential for an intelligent interpretation of test results on small-house installations.

In order to hasten the work, the following tests of complete test plumbing installations, covering one story, one story and basement,

and two story and basement dwellings were carried on parallel to the general investigations of the hydraulics and pneumatics of a plumbing system. The result has been that many tests were made

which might well have been omitted as having no direct bearing on

small-house plumbing. In this report an attempt has been made to condense into small space the results of elaborate tests on plumbing

installations by omitting all data, except results of “critical tests” and a few additional tests which serve to emphazise the principles

disclosed in the general investigations or stated in that connection

from theoretical considerations.

CRITICAL TESTS

The term “critical test” may be defined as any combination or se- quence of discharge of fixtures on a given installation which may

occur frequently enough and which in conjunction with modifying

conditions may prove detrimental to the functioning of the plumbing

system. It is evident that there may be many “critical tests” for

the same system and that in this connection the discharge of a single

fixture may be of more importance in some cases than the combined

discharge of several fixtures on the same system.

Almost any plumbing installation, either test or service, may be

shown good or bad according to the severity of the modifying conditions imposed or assumed and according to the' severity of the

test in the matter of combined discharge from fixtures to which it is subjected. Just what constitutes a fair test in the way of combined

discharge and severity of imposed modifying conditions and what is
160 RECOMMENDED PLUMBING REQUIREMENTS

a fair measure of satisfactory results must be decided as matters of

judgment. Any decision reached by an individual or group of individuals readily lends itself to adverse criticism from unsympathetic

reviewers, who may be prejudiced by personal interest or a narrow

point of view.

For large installations the matter of coincxdent discharge constituting a maximum fair test might be determined from tables of probable coincident discharge similar to Tables 2 and 3. For small in- stallations consisting of two or three bathroom units and other

small fixtures the arbitrary method of selection (Table 10) adopted

by the plumbing committee is believed more applicable for the types

of buildings under consideration.

Table 10.—Assumed simultaneous discharges compared with possible maximum

discharges in typical installations illustrated in Figures 90 to 92

BUNGALOW TYPE, ONE-STORY, ONE-FAMILY

Total of all fix- tures discharged

together An assumed simultaneous discharge for deter- mining venting requirements and size of housedrain Type reference

to Figures 90

to 92 Number of stacks Gallons Equiv- Gallons

Total to house

drain per minute

alent units Fixtures per minute

Units

Gallons

per minute

Units

1 1 soil 90 12

fl W. C.„.

\l B. T

45

15

6

2 1 82. 5. 11

2. do 146.3 19*

ll Comb...

fl W. C____

fl B. T

22.5

45

15

3

6

2

1

[ 82.5 11

1 L. T 3

3 | do 67.5 9 /1W. c.___\1 B. T

45

15

62 }

60 8

(l water. 22.5 3 1 L. T 22.5 3 22.5 3 90 12 82.5 11

|l soil 112.5 15

fl W. C____

\1 B.T

45

15 6 \ 60 8

4.. 2 J |l water 33.8 4* 1 L. T 22.5 3 22.5 3 146.3 19* 82.5 11 TWO-STORY, ONE-FAMILY TYPE

5 1 soil 142.5 19

6 do 213.8 28*

7

[1 soil 187.5 25

1 1 waste 22.5 3

210. 0 28

8

fl soil 232.5 31

ll waste 33.8 4*

266.3 35*

1W. C____

1 B. T

1 W. B____

1 L. T-...

2 W. C_._. 1B.T

1W.B.... IK. S

1 W. C_„_

2 B. T

2 W. B_._. Comb

2 W. C..„

2B.T

2 W. B

1 K. S

45

157.5 22.5 90

157.5

11.3 45

30

1522.5

90

30

1511.3

1 90

1

| 123.8 16*

| 90 12 22.5 3 112.5 15

[ 135 18

i 11.3 11 146.3 19*
PHYSICS OF PLUMBING SYSTEMS 161

Table 10. —Assumed simultaneous discharges compared with possible maximum

discharges in typical installations illustrated in Figures 90 to 92—Continued.

TWO-STORY, TWO-FAMILY TYPE (SUPERIMPOSED)

Total of all fix- tures discharged

together Type reference

to Figures 90 Number of stacks

to 92 Gallons Equivper alent minute units

9 1 soil 180 24

10 do 292.6 39

11 jl soil 135 18 U waste.. 45 6 180 24

[l soil 225 30

12 \[1 waste 67.6 9 292.6 39

An assumed simultaneous discharge for deter- mining venting requirements and size of house

drain

Total to house

drain Fixtures Gallons

per minute

Units

Gallons

per minute

Units

f2 W. C„„ 90 12

) 2B.T 30 4 t 142.

19

ll Comb..

22.5 3

[2 W. C— 90 12 |2B. T___. 1 11 K. S

30

11.3

41£ \ 153.

20£

[l L. T 22.5 3 1 r2 w. c„„ 90 12

} [2B.T 120 16 30 4

1 Comb... 22.5 3 22.5 3

142.5 19

r 3 W. C„„ 135 18 } i2B.T 165 22 30 4

' 1 K. S

[1 L. T

11.3 22.5 ? } 33.8 4*

. 198.

26§ TEST CONDITIONS

To illustrate the number of variations of modifying conditions to be considered in connection with complete tests and to guide in

outlining and classifying tests, Table 11 was prepared by the plumbing

committee. It is not to be understood that all combinations given were tested with each installation or that the table represents all possible combinations of conditions. It is possible to strike out

many and reserve only certain ones which may be referred to as

critical test conditions, for example, the occurrence of a high wind,

frost closure, and a heavy rain at the same time is so unlikely that it need not be considered.

Table 11 . —Possible combinations of natural conditions affecting each plumbing

installation, which may vary independently in degree or intensity

[N =means normal full opening at stack tops; O =free and unobstructed discharge through the house drain; F=stack tops reduced to simulate frost closure; S=the discharge end of house drain submerged; T=a

running trap and fresh air inlet in the house drain; W=a current of air over stack tops to simulate winds; R=water discharged into the house drain through a rain leader ; (

) =combinations of conditions considered

unlikely to occur.]

Weather Combinations of weather conditions and status of plumbing system

tions N-0 F-0 NS FS NTO FTO NTS FTO

Wind

Rain. WNO

RNO

WFO

(RFO)

WNS

RNS

WFS

(RFS)

WNTO

RNTO

WFT

(RFT)

WNTS

RNTS

WFTO

RFTO

Wind and

rain WRNO (WRFO) WRNS (WRFS) WRNTO (WRFT) WRNTS (WRFTO)

20141°—29 12
162 RECOMMENDED PLUMBING REQUIREMENTS

The manner of making tests and interpreting the results of tests is another matter that is dependent on judgment. Assuming that the

condition in which the trap seals are left by the test is the best criterion

for determining satisfactory and unsatisfactory results, and that a minimum remaining seal representing satisfactory results has been

established, the question of repeating tests without restoring the

trap seals to normal is still undecided. It is evidently a fair test in

all respects to repeat the discharge of a single fixture on a system any

number of times without restoring the trap seals. It is manifestly an

unfair test of normal service to repeat the coincident discharge of

several fixtures, of which the chance of coincidence is very remote,

without between tests restoring the trap seals to normal or to the

seal left by some less severe test that is likely to occur frequently in

ordinary service.

The preceding points in reference to “ critical tests,” “ critical conditions,” and manner of making the tests should all be kept in

mind in the interpretation of results. The validity of results obtained from clear water tests is frequently

questioned. In this connection we wish to point out that these

tests have not been entirely clear-water tests. Many tests were made using toilet paper and imitation fecal matter, hereafter re- ferred to as “soil,” in the water-closet discharge. With this type

of discharge from a single water-closet a marked, though somewhat

erratic, effect was produced. With the discharge of two or more

water-closets with imitation “soil” in conjunction with other fix- tures on the system the added effect of “soil” became less marked

and was usually lost, evidently because in the latter case the imitation “soil” is at once separated and carried forward in small

separate units by the increased volume of discharge. The use of

foul water in a clean system could not possibly materially change

the results of clear-water tests. With reference to the effect of

fouled waste pipes, it should be remembered that, in general, the

first effect of such fouled waste pipes must necessarily be a decreased

rate of discharge from the fixtures served by them and that the

general requirements for venting would not be materially changed

thereby. It will be observed, too, that most fixtures used in the

tests were adjusted to give higher rates of discharge than the rates on which minimum requirements have been calculated. A test that holds under these rates would more surely hold under the

lower service rates of discharge. The matter of the effect of fouled

waste pipes on self-siphonage has been discussed in an earlier part

of the report and should be treated as a separate consideration.

As has been before stated the data which follow are a small part

of the total obtained from plumbing-test installations. An attempt

has been made to arrange the data given into a form rendering
PHYSICS OF PLUMBING SYSTEMS 163

interpretation more easy. From the nature of the case it will be

observed that there is a different “

critical test” for the highest

group, for the lowest group, and for a middle group of fixtures on

a system, and frequently a different “ critical test” for each fixture

within a group. For these reasons the data have been arranged in

series and groups, a series, in general, being all the tests on an installation, and a group, the “ critical tests/’ for each floor of the

installation. The data given are, in general, for the test showing

the greatest effect when there was a choice between several tests. To the “ critical tests,” which are intended to cover normal, heavy

service conditions, other tests giving heavier discharges have been

added to test for possibilities of flooding or overflowing. It is believed that the latter should not be considered in connection with

vent requirements but only in the connection stated.

NOTATION

The following notation will serve as a key to the illustrations of

test installations and tabulated data for tests on the same: B denotes a bathtub or bathtub trap; C denotes a water-closet or water-closet trap; L denotes a lavatory (washbasin) or lavatory

trap; S denotes a kitchen sink or kitchen-sink trap; T denotes a laundry tray or laundry-tray trap.

Subscripts are used with the above letters to designate the floor on which the fixture was installed; thus C0 denotes a water-closet

in the basement, Ct a water-closet on the first floor, and C2 a watercloset on the second floor. A prime denotes that the fixture was

installed on a waste stack; thus S'2 is a kitchen sink on the second

floor connected to a waste stack. Quotation marks are used to denote a second fixture of the same kind on the same floor; thus “ C0 ” denotes a second water-closet on the basement floor. R

denotes a trapped rain leader connected to the house drain at the

base of the stack, and with subscript the rate of rainfall used in the

test. R' denotes a trapped rain leader connected to the house drain on the sewer side, and with subscript the rate of rainfall used in the

test; thus in the tabulated data R\ denotes water introduced through

rain leader R' at a rate equivalent to a rainfall of 4 inches per hour

over a drained area of 1,500 square feet. D denotes submerged

outfall of house drain with subscript to denote extent of submergence

in inches. F denotes partial closure of stack tops simulating frost closure with subscript to denote the diameter of free opening in

inches. W denotes a wind current of 45 miles per hour over the

stack tops directed horizontally unless otherwise stated. Vv V2 , etc., denotes valves in vent lines numbered from left to right and

from the top floor down. Gt , G2 , etc., denotes gate valves in horizontal waste pipes or horizontal drains numbered from the highest
164 RECOMMENDED PLUMBING REQUIREMENTS

down and from right to left on each floor. “Soil” denotes toilet paper and imitation fecal matter added to the water-closet dis- charges.

TEST INSTALLATION NO. 1 Experimental plumbing installations with framework and platforms to carry the pipes and fixtures were installed in an 8 by 12 foot

elevator shaft. The different installations are described in considerable detail. The first installation for which data are recorded in

this report is shown in Figure 75. The house sewer of 4-inch cast- iron pipe was carried in line with the house drain, at a fall of one- fourth inch to the foot, to a return bend (fig. 76), 22 feet from the

base of the 3~inch soil stack and then back to the pit of the elevator

shaft with the same fall in the straight run, where it discharged

through an open or submerged end as the imposed conditions demanded. The return bend in the house sewer, composed of two 4- inch short sweep one-fourth bends, was set at an angle of 45°. The

total developed length of house drain and house sewer was 38 feet. The fittings taking the fixture discharge were double “sanitary tees”

of which one side was plugged flush with the inner wall of the fitting

when employed as a single house installation, with the exception of

the two deep seal glass traps shown. These were also plugged in the

trap during tests in which the pressure changes were great enough to break the trap seals. The valves in the vent lines were of the cockvalve type, giving cross-sectional openings equal in area to the pipes

in which they were installed. The valves in the branch horizontals

of the house drain were gate valves.

The traps of the individually trapped fixtures were lj-inch lead

P traps with nominal 2-inch seals except the lavatory, which was a

li-inch cast brass trap with a nominal 2.5-inch seal. The traps were

fitted with glass windows and scales (fig. 77) to enable the reading of the seal depth at any time.

Air-pressure measurements were made at various points in the

3-inch stack and in the vent lines during the tests. These pressure

measurements have but little value in judging the defects or advantages of a particular system, hence have been discussed elsewhere in

connection with the pneumatics of plumbing systems.

The data are to be considered typical of the type of tests made and

representative of maximum effects under the assumed “critical tests” and “critical conditions” imposed. Practically every group of tests, as well as individual tests, was repeated at least once. Other tests giving discharges near the assumed “ critical test” rate were made in

most cases. Many slight modifications were made in the different

installations, of which only those showing appreciable changes in

results of tests are recorded in detail.
PHYSICS OF PLUMBING SYSTEMS 165

pL'H
166 RECOMMENDED PLUMBING REQUIREMENTS

The data of series 1 were obtained with full free opening at stack

tops and open free discharge at the end of the house sewer beyond

the return bend. Column 1, giving the number of the test and successive discharges of the same fixtures or group of fixtures or of different groups of fixtures under one number, indicates that the

whole constituted one test and that the traps in question were not

refilled during the test unless they were automatically refilled by the

discharge of the fixture itself. Column 2 gives the fixtures dis- charged in each test, those in line being discharged together, with

repetitions in the same test in column. Conditions imposed when

not applying to the whole group are also given in column 2 in connection with the part to which they apply. Column 3 gives the

vent-line valves and drain-gate valves that were open, it being understood that all other valves on the system were closed for that test. The remaining columns give the condition in which the trap seals are

left after each test, showing also the cumulative effect when the test consisted of repeated discharges.
PHYSICS OF PLUMBING SYSTEMS 167

Series 1, group 1 , upper floor tests

Number Fixtures discharged Valves open

Trap JBi; seal 1.9 inches Trap L\\

seal 2.6 inches

Seal left— Seal left

1 (Ci None

Inches

0.

95

.7 1.2

1. 1 1.0.9

.7 1.3

1.1 1.0

.7 1.9

1.8 1.8

1.8

Inches

2.1 2.0

2.

1

2.0

1.9 1.9

1.9 2.6

2.6 2.2

2.2

2.6 2.6

2.6

2.6

\ do.. do

2

I Ci, “Soil” do. . ....do do

i ...do.. do

do.

l do do

[Li, Ci, Co . . do....

1. ...do... do

3

4.

| Cl, Co do

l do do

(Ci Vs and Vi

\ do .. ..do

5 Li, C\ do

6 Bi,Lu Ci do Group 2, basement tests

Number Fixtures discharged Valves open

Trap to

seal 2.0 inches Trap Co; seal 5.7 inches

Seal left— Seal

1 7?iy Tj\ J Cl _ _ _ _ Vi and Vi. Inches

1.8 Inches Steady.

2 j Cl j To do 2.0 Do.

3 S\ 9 Ci f Co do 1.75 Full seal. 4 7?i f Ci 9 Tot Rb - Vi, Vi, and Ci 1.8 Blown.

5 jBl y Cl y S'If R'fr Vs, Vi, Ci, and Gs 1.7 Do.

6 J3ly Cl y S'l y R§ Vs, V4 , Gs, and Gs 1.7 Do.

7 JBly L\y Cl y S'l y TQy R$ Vi, Vs, V4 , V5 , G2 , and Gs 2.0 Do.

8 do. Vi, Vs, V4 , Vo, Gs, and Gs 2.0 Steady. Note—The partial loss of seal in trap To in tests 3, 5, and 6 was evidently due to waving from back pres- sure. The term “blown” in column 5 indicates that water was thrown up into the closet bowl by back

pressure. The term “steady” indicates a steady, slight oscillation in the water-closet trap Co. In all cases even when “blown” there was only a slight loss of seal in trap Co. Conclusions.—1 . For the installation as represented (fig. 75)

with separate sewer system a single loop vent from the washbasin

branch is required and is sufficient to prevent a material loss in any

trap seal on the system. It should be noted, however, that the

horizontal branch from the laundry tray and water-closet in the

basement connect to the stack near the point of minimum pressure

variation, and that a connection either closer to or farther from the

house drain would be more in need of back venting. Therefore, in

many cases a back vent from the lowest horizontal branch would

be necessary for complete protection of trap seals, preferably in this case the vent represented by 7e from the water-closet O0

. 2. With a combined sewer system a vent line represented by line when 7e , 71; 7S , and 74 are open is required and is sufficient to protect the trap seals.
168 RECOMMENDED PLUMBING REQUIREMENTS

3. The different waste and soil stacks of a system may be considered independently so far as vent requirements are concerned, provided the house drain and house sewer are sufficient in capacity for

the system.

Tests were made on the same system with the stack tops partially

closed to represent frost closure, with a wind current over the stack

tops, with a vented running trap in the house drain, and with a submerged outfall of the house sewer. The general effects of a running

trap in the house drain have been described in connection with

modifying conditions. Data from later installations show the effects to be expected from partial frost closure, wind, and submerged outfall of house sewer to better advantage.

TEST INSTALLATION NO. 2 The installation (fig. 78) was constructed by remodeling the 3-inch

stack and vent system of the first installation (fig. 75), the house drain,

house sewer, 2-inch waste stack, and rain leader systems being left as before. The water-closets were connected to “ crowfoot ” fittings as shown, and small fixture waste lines were connected to side inlets or to fittings above the water-closet branch fittings. The waste and

vent lines were reduced to what was believed to be the smallest

convenient serviceable size from all considerations for general construction in dwelling houses. Flush valves were installed to supply

the water-closets and adjusted to give a mean rate of supply of approximately 60 gallons per minute for periods varying from 6 to 10 seconds.

Under these conditions the maximum rate of discharge from the

water-closet does not materially differ from the rate of supply (see curves of discharge and discussion in the first part of the report).

The kind of supply is not an essential factor in the test work, the

purpose of the high rates being to prove and emphasize the adequacy

of the pipe system as installed for the same fixtures with satisfactory

service rates of supply. The strainers were removed from all the

separately trapped smaller fixtures, hence the rates of discharge from

these were also slightly higher than those given in Table 4. Series 2, group 1, tests on the second floor

Number Fixtures discharged Valves open

Trap Bi)

seal 2.1 inches Trap Li\

seal 2.6 inches

Seal left—

1 S. None

Inches

2.

1

2.0 2.0

Inches

2.6

2.6

2.6

2 (USi . ..do.

\ do do Note—

T

he discharge of any single fixture on the floor produced no measurable loss of seal in the trap of that fixture. The discharge of the water-closet Ca produced a very slight oscillation in the trap of the bath

tub and no noticeable effect on any other trap in the group.
PHYSICS OF PLUMBING SYSTEMS 169

Z7'o'
170 RECOMMENDED PLUMBING REQUIREMENTS

Series 2, group 2, tests on the first or middle floor of the system for local effects with

the second floor and basement idle

Number Fixtures discharged Valves open

Trap Bi;

seal 2.2 inches Trap Li\

seal 2.6 inches

Seal left—

fii Ci

Inches

2.2

2.2

2.2

2. 2 VNot ob-

/ served. 2.2 Not

2ob- served. Not observed. 2.0

2.2

1. 95 2.2

2.2

2.2

2.2

Inches

2.5

2.5

2.6

2.6

} 1

2.6

2.6.9

.9

.9

.9

.9 2.6

2.6

2.6 2.6

1

\ do dodo 2

i do do /Mi— do 3

\ do do (C! 4

5

do ... . do (Bi,Llt Ci do..

B\, Ci, "Soil” do

Ci, Si, "Soil”.. do

B\, Ci, W45"Soil” do

Ci, Si, W45 " Soil” do Mi. — - Fiand Ci

6 ....do do

)li

7 .. \ do ..do Note—

he discharge of any single fixture on this floor produced no appreciable loss in the trap seal of the fixture itself, except the lavatory Lu Therefore, a continuous waste and vent from the lavatory is sufficient to protect completely the group installed in this manner when it is the highest group on the system.

Series 2, group S, tests on first or middle floor of the system with a full bathroom group and kitchen sink in use on the floor above V2 closed and sink S2 outlet plugged

[(-) denotes an interval of time between starting the fixture discharges. Fi denotes closure of 3-inch stack

to 1-inch diameter to a depth of 15 inches]

Number Fixtures discharged Valves open

Trap Si;

seal 2.2 inches Trap Ci; seal 4 inches

Seal left—

[L1-L2 , C2, Fi Fi and Gi Inches2.2

2.2

2.2 2.2

2.2

2.2 2.2

Inches

2. 0

1.2

1.2 1.0 4.0

3.6 3.0

1 do do..

1 . ...

2

1 Ij2) C2 , L\9 F\-~ do

\Li, Ci, Si,L\, Fi... do

Si9 -Kb - - Fi, Ci, and Cs.

3 _B2 j C2 , Lif Si9 ** Soil do. 1

- do do Note.—

rap Ci seal was temporarily broken by the last run of test 1. Series 2, group 4, test on first or middle floor of the system with sink and water-closet only connected, Gx being closed

Number Fixtures discharged Valves open

Trap Si; seal 2.2 inches

Trap Ci; partial 2.0-inches

seal

Seal left—

1 .. Cz None

Inches

0.3.0

Inches

1.5

2 Ci, Si do 1.0
PHYSICS OF PLUMBING SYSTEMS 171

It is apparently impossible to destroy permanently the seal of water-closet C1 by discharges from above, when the side inlet branch

waste is vented. With 10 feet or more of straight stack below the

water-closet there is slight danger of it being subjected to back

pressure from the stack. The only danger of air leakage through the

water-closet is therefore from complete loss of the trap seal by

evaporation. It is necessary to back vent each small waste branch

connected independently to the stack on a middle floor.

Series 2, group 5, tests on basement fixtures (fig. 78) with separate sewer system;

that isj Gz , G4, and G5 were closed

[Di recorded with fixtures discharged in column 2, indicates the end of the house sewer was submerged to a depth of 3 inches and Wu indicates that a 45-mile per hour wind current was directed horizontally over the stack top.]

Number Fixtures discharged Valves open

Trap To;

seal 1.8 inches Trap Co;

seal 4 inches

Seal left— Seal

1 [Bi, Cj, Li, “soil,” Di Vi, Vi, Vi, G and Gi do

Inches

1.6 1.5

1.4

1.4 1.8

Steady. Do.

Do.

Do.

Blown.

)Bi, Li, Si, “soil,” Di

1 Bi, Ci, S2, “soil,” Di do

2 ._

1 Bi, Clt Li, Si, “soil,” Di WiS do..

Bi, Ci, Lt, Si, To, “soil” do

Series 2, group 6, tests on the basement fixtures with combined sewer system

Number Fixtures discharged Valves open

Trap T0 ; seal 1.8 inches Trap Co; seal 4.0 inches

Seal left— Seal

1 Bi, Li, Ci, Si, Bi, Di Vi, Vi, and Gi

Inches

1.8 Blown.

2 Bi, Li, C2, Si, Ci, Bi, Di do 1. 8 Poor refill. 3 Lt, Ci, Si, Bi, Di do 1.8 Small bubble.

4 Li, Ci, Si, To, Bi, Di .. _ do 1.8 Large bubbles.

5 Bi, Li, Ci, Si, Bi, Di Vi, Vi, Vi, G1 , and Gi... 1.7 Small bubbles. Note.—The term “steady” means steady fluctuation in the trap seal under back pressure. “Blown”

means water thrown up from the closet bowl or out of the bowl by back pressure. “ Bubble” or “bubbles ” means a small quantity of air forced back through the trap by back pressure. Evidently much of the trouble from back pressures in test groups

5 and 6 is directly due to insufficient capacity of the house drain and

house sewer. The presence of the return bend in the house sewer and submerged outfall impose rather severe conditions and the

volume of water discharged is somewhat greater than the same fix- tures would give in ordinary service. Attention has been called to the

fact that the water-closet discharge approached or exceeded 60 gallons

per minute. The carrying capacity of the 4-inch drain has been

estimated at 108 gallons per minute when laid with a grade of one- fourth inch per foot and flowing full under its own head. The combined rate of discharge for most of the tests exceeds this value; for

example, No. 1, group 6 gives a combined rate of discharge to the

house drain, including that from the rain leader, of nearly 200 gal-
172 RECOMMENDED PLUMBING REQUIREMENTS

Ions per minute. In order to show the presence of backwater in

the stack the 2-inch combination Y and $ bend branch A in the

stack above the water-closet C0 was opened up, F3 closed, the watercloset C0 stopped in the trap and the following discharged into the

stack and drain, BzLz CzSiT0RbDz giving a total estimated discharge

of 215 gallons per minute. The water spurted from the branch of the

fitting to a distance of 3 or 4 feet, showing that the stack was flowing

under considerable head above that point. Therefore, the tests of

group 6 mean but little in connection with vent requirements and

serve only to emphasize the need of an adequate house drain. The

tests of group 6 do show the danger from back pressure when fixtures are connected near the base of the stack. In order further to test these effects, the basement fixtures of installation (fig. 78) were

lowered to a vertical height of 21 inches between the center of the

house drain and center of the combination Y and J bend branch

taking the basement water-closet. (See fig. 79.) A lj-inch vent was carried from the top of the closet bend as shown, the stack and

upper floor fixtures remaining as in Figure 78.

Series 2, group 7, tests of Figure 79 basement fixtures

Number Fixtures discharged Vents open Trap Co; seal 4 inches

1 7?2 Tj^ fTgiSfi To 7?4 T)4 Vi Vi ViGi and Gi Steady. Do.

Do.

Blown. Do

2. B\ L\ Ci S\ ToIfaDi Vi Vi ViG\Gi and Gi

3 . JO2 C% iS?2 Tj\ CiS i TqD\ Vi V3 ViGi and Gi

4 . 7?2 Tj2 C2S2-B1 Tj\ Ci Si ToDa. __ ..do

5 B2L2 C2 S\ ToItiDi- Vi Vi and Gi With the installation represented by Figure 78 and basement

installation (fig. 79) , the house drain was disconnected at rain leader
PHYSICS OF PLUMBING SYSTEMS 178

R' connection and discharged vertically at that point through a

one-fourth bend submerged to a depth of 6 inches in a tank. The

total horizontal distance from the center of the 3-inch stack to the

center of the vertical part of the one-fourth bend was 7 feet 3 inches.

Series 2, group 8, tests of basement fixtures (fig. 79) with submergence near the base of the stack Number Fixtures discharged Valves open Trap Co

1 Bii/iCiSiToDi V2 Vz Vi and Gz Small bubbles. Blown. Do.

Do.

Small bubbles.

2. . BiLzCzBiSiToDz __ do

3 B2 L2 C2 S1 T%D$ Vz Vz and Gz

4 B2 Cz ToDi do...

5 O2 TqDq .. ..do

Tests of groups 7 and 8 show that with fixtures connecting near

the base of the stack it is necessary to back vent each branch separately, and that with inadequate house drain or submergence near

the base of the stack it is difficult if not impossible in extreme cases to protect completely the trap seals of fixtures thus located.

TEST INSTALLATION NO. 3 The final tests on small-house plumbing systems were made on an

installation (fig. 80), erected for the purpose of permitting anyone

interested in the work to witness or make any test desired. In a measure it embodies the better features of the earlier installations.

The system as displayed consisted of a two story and basement

structure with a bathroom group of fixtures on the upper or second

floor, a bathroom group on the first or middle floor, and two waterclosets on the basement or lower floor, all connected to the 3-inch soil stack, and in addition two batteries of two laundry trays each on the

basement floor and one kitchen sink on each of the first and second

floors connected to a 2-inch waste stack. Gate valves were installed

in the vent lines so that the fixtures below the upper floor might be

back vented or not as desired.

Data for only a few representative “ critical tests” are given. The

construction and tests for the upper floor were so nearly the same as that in Figure 78 that no data are given. It was impossible to re- duce the seal of any trap on this floor materially by any combination or sequence of discharge of fixtures on the system. Likewise,

it is unnecessary to consider one stack in reference to the other for

floors above the basement. Basement floor fixtures on one stack

may be affected by discharge into the other stack. The water-closets

in the system (fig* 80) were installed with low-tank supply giving

rates of discharge approaching that given in Table 4. The strainers were removed from the separately trapped fixtures, hence the rates

of discharge were slightly higher than given for the same fixtures in

Table 4.
174 RECOMMENDED' PLUMBING REQUIREMENTS
PHYSICS OF PLUMBING SYSTEMS 175

Series 8, group 1 , tests on first or middle floor of the system for local effects

Number Fixtures discharged Valves open

Trap Bi;

seal 1.4 inches Trap Li;

. seal 2.5 inches

Seal left—

1 Li

Inches

1.4

1.4

1.4

1.4 1.4

1.4

Inches

2.5 2.5

1. 25

1. 25 2.5

2.5

2 do

3 BiLi _ dn

4

6 do V,

6 B\C\ “soil” Note—

T

here was no appreciable loss of seal in trap Cof the water-closet at any time. Series 8, group 2, tests on the first floor as the middle floor of a two story and base- ment structure

Number Fixtures discharged Valves open

Trap Bi;

seal 1.4 inches Trap Ci;

seal 4 inches

Seal left—

1 . None

Inches

1. 4 Inches Steady.

2 Bi CiLtSh -do 1. 4

3 __ _Z?2 C2L2L1 V2 and V4 - 1.4 2

f B2 C2 L2 B1 L1 do 1.4 1 4 XBiCiBi" soil” do 1.4 2 Note.—

T

here was no loss of seal in trap L\ in tests 2, 3, and 4. Series 8, group 8, tests on the basement or lower floor of the installation [Under columns trap Co and trap To effects given are for either of the pair of water-closets or either of the laundry tray traps]

Number Fixtures discharged Valves open Trap Co;

seal 4 inches Trap To;

seal 2.1 inches

1 B3 CtTjiS^iDi None Blown Blown.

2 Bi CiltiS^iDi Vi Steady Do.

3 BiCiLiS^iDt _ V] and Vi ...do Do.

4 BiCiLiS1! “soil" Bi ViViVt and V4 ...do Steady. Note—

T

he blowing of the seals of the laundry-tray traps in test No. 3 was evidently due in part to overcharging of the horizontal drain from the 2-inch stack. There was only slight permanent loss of seal in either laundry tray or water-closet traps in any of the tests of groups even when the seals were “blown" by back pressure. The tests of the installations represented by Figures 75 and 78

showed the deterimental effect to be expected in a combined sewer system when the house drain is insufficient in capacity to carry both

the storm water and discharge from the stacks. To test the effects with an adequate house drain, the 5-inch house drain and house sewer

represented at the bottom of Figure 80 were connected in place of the 4-inch drains shown connected in the drawing. The rain leader was 3-inch diameter, 22 feet long, with box arranged at the top as before described.

The tests on the upper floors did not differ in results from those

with 4-inch drains and separate sewer system, hence no data for

these are reported.
176 RECOMMENDED PLUMBING REQUIREMENTS

Series 3, group 4, tests on the basement or lower floor with combined sewer system Number Fixtures discharged Valves open Trap Co;

seal 4 inches Trap To;

seal 2.1 inches

1 J?2 C/%L% S*2 Tq T()* _ None "Blown Not observed. Do.

Do.

Steady. Not observed.

2 Bi CjLt-LiDi Vi.. Steady

3 _ R\~Bj CjLtS'i . . _do do

4 Ri~Bi CjLi S'i~Bi CiLi S' i D\ _ Vi V2 V3 and Vi . .do.

6

/ RrBi

C

2L1 S'2-Bi CilaS'i... \ do (See note)... \~Co “ Co” To“To” Lh---- / Note—Test No. 5 was made merely to determine whether or not the system would drain with the total possible discharge from the fixtures in combination with storm water. The dashes (-) inserted with fix- tures discharged indicates an interval of time between starting discharges on the different floors in order

to obtain a greater volume rate of discharge into the house drain. There was a poor flush in the basement

water-closets in No. 5, the water rising in the bowls to about 1 inch of the top then flowing out as the water

receded from the house drain. The test is abnormal, and, as stated, shows only the degree of safety against flooding or overflowing during any normal heavy use. The total rate of discharge into the house drain was slightly in excess of 300 gallons per minute. GENERAL CONCLUSIONS

The results of the preceding tests in connection with other experiments justify a number of general conclusions which may safely be

applied to all dwelling-house plumbing, namely:

1. The 3-inch stack is adequate for all separate dwelling house

plumbing.

2. It is possible by close grouping of the fixtures around the soil stack to obtain safe and efficient drainage for a single floor and for

the highest floor of a more complex system without back venting

any of the fixtures.

3. It is necessary to back vent individually or in groups all small

branch waste lines connecting directly into the stack below a watercloset on the same stack to protect fully the seals of traps on such

branches.

4. A back-vented side-inlet branch to a “crowfoot” fitting on a middle floor offers a degree of protection that makes it unnecessary

to back vent the water-closet individually, provided the possible

discharge does not exceed that from one bathroom group plus a kitchen sink or 10 J fixture units.

5. In cases where the possible discharge from floors above exceeds

10^ fixture units it is necessary to back vent each separate branch

individually, including water-closet branches, on a middle floor.

6. It is necessary to back vent each separate branch connection

individually on the lower floor including water-closet branches, unless there is 3 feet or more of straight stack below the fittings taking

such branches, in whicji case the rules for a middle floor may be

applied with safety.

7. In a combined sewer system it is necessary to make ample

provision in the size of house drain and house sewer in order to protect fixtures set low on the stack, even when such fixtures are individually back vented.

The above conclusions are based on the assumption of the use of plain traps and with the realization that in practice considerable

departure from any fixed conditions assumed for test purposes may
PHYSICS OF PLUMBING SYSTEMS 177

occur. The conclusions embodied in the recommended desings are

of construction which follow, Figures 81 to 89. RECOMMENDED CONSTRUCTION DETAILS

Figures 81 to 89 represent details of construction in which the

principles and requirements, as determined by the experimental

fixtures on the stack) work, are applied to the types of buildings under consideration,

namely, small dwelling houses. The layouts were originally prepared

by the plumbing committee, but have been modified and elaborated

with their full approval to bring out certain features in venting and

to illustrate possible variations that may be made by use of properly

designed “crowfoot ” fittings. They by no means show all the variations that may be made with the more elaborate systems composed

20141°—29 13
178 RECOMMENDED PLUMBING REQUIREMENTS

of two or more bathroom groups and other fixtures, but are believed

to be sufficient to indicate other variations that might be made to meet different structural conditions encountered without in any way

changing the general results or in any way lessening the efficiency of

the system.

1*3

location) We have pointed out that the most efficient drainage will be secured

with the most direct wastes consistent with the general requirements

to protect the trap seals. It follows that an individual vent installed

where one is not needed is not only an added expense but may prove

a detriment by reducing the velocity of flow and consequently the scour in the waste or soil pipe thus vented. For these reasons we

have given preference to the plan involving the simplest venting.

This, in general, involves a close grouping of fixtures about the stack,

assuming that the stack will be located so as to make possible such
PHYSICS OF PLUMBING SYSTEMS 179

grouping within the limits of allowable length of unvented wastes.

It is recognized that such grouping and arrangement will not always

be possible, and alternate plans in the order of preference are given

for each type of building represented. The types go from the

simplest to the more complex, and, in general, a plan for one type will serve equally well in the same position in a simpler type of building.

It will be observed that the plans (figs. 81 to 89) in connection with

Figures 90 to 92 graphically represent a summary of conclusions in so far as they apply to small dwelling-house construction. The

maximum developed length of all horizontal unvented waste branches

is limited to 5 feet with slopes of one-fourth to one-half inch per foot. In general, the drawings are shown for wrought-iron construction in

waste and vent pipes. Any approved material may be used within

the same limits. For the most part dimensions are omitted from the

drawings, since the same construction applies to any sized soil stack

and required vent and waste pipes.

Design A (fig. 81) is suitable for the highest group of fixtures on

the soil stack. A kitchen sink, with an independent waste branch
180 RECOMMENDED PLUMBING REQUIREMENTS

connecting to the stack above the water-closet branch, may be added

to the group without other change. It will be observed that the

design offers great flexibility in the matter of spacing and order of arrangement of fixtures by the selection of the proper “ crowfoot ”

fitting, the principal restriction being the limitation of unvented

horizontal waste branches to a maximum developed length of 5

feet. Still greater flexibility may be secured by a proper location of the stack relative to the desired fixture positions.

Fig. 84 (Design D).—Approved design for stack-vented and group-vented fixtures. (See text for restric- tions in location) Design B (fig. 82), design C (fig. 83), and design I) (fig. 84) are alternative layouts recommended for the highest group of fixtures

when the desired location of fixtures can not be secured with design A.

These are not adapted to as many variations in order of arrangement

as design A, but permit some which can not be secured in design A,

such as the location of the lavatory on the opposite side of the bath- room from the soil stack. A kitchen sink may be added to the group

with the same restrictions as before. Design B will also serve with

comparative safety on a lower floor when the possible discharge from

above does not exceed one bathroom group plus a kitchen sink or 10J fixture units. Design E (fig. 85) may be used on a lower floor under the same conditions. Design F (fig. 86) may be used on a lower floor when the possible discharge from above exceeds 10

J
PHYSICS OP PLUMBING SYSTEMS 181

85 (Design E).—Approved design for lower floor. (See text for restrictions in location)

Fig. 86 (Design F).—Approved design for lower-floor bathroom grour
182 RECOMMENDED PLUMBING REQUIREMENTS

fixture units. Design G (fig. 87) represents approved duplex arrangement for the highest group. Two kitchen sinks or two combination

fixtures with wastes connecting above the water-closet branches may

be added without other changes. Design H (fig. 88) shows approved

venting of a lavatory and water-closet group on a lower floor. Figure 89 represents approved forms of venting single fixtures,

with wastes connecting independently to the stack to be employed

when necessary to vent in any position and approved forms of venting

Fig. 87 (Design (?)—Approved design for duplex bathroom group water-closets when connected to the stack near the base and when

connected independently to the house drain.

Figures 90 to 92 represent types for small dwellings which we believe

to be sufficiently varied to illustrate all types within the scope of the

present report. Many variations of each type might be made

without in any way changing the principles or the requirements. In

general, a fixture or a group of fixtures may be omitted from a lower

floor of any type without changing the requirements in venting for

other fixtures on the same floor or floors above.

Types 1 and 3 may use any one of the designs A to E with variations within the limits prescribed elsewhere for installing the fixtures.
PHYSICS OF PLUMBING SYSTEMS 183

Types 2 and 4 may use any one of the same designs for the upper

floor, with the basement fixtures vented as indicated in any of the

approved methods of venting for the position.

Types 5 and 6 may use on the second floor any of the approved

designs for the highest floor of a system and designs B, E, or F, with

the sink or combination fixture vented in approved manner as indicated, and the basement fixture in type 6, vented in approved manner. Types 7 and 8 may use design G (fig. 86) or any equivalent variation for the upper floor within prescribed limits of permitted lengths

and design H (fig. 88) or an equivalent variation for the first floor with the basement water-closet type 8 vented in an approved manner. Types 9, 10, 11, and 12, two story and two story and basement

two-family houses, may use any one of the approved designs for the

second or top floor.
184 RECOMMENDED PLUMBING REQUIREMENTS

Types 9 and 10 may use any of designs B, E, or F on the first floor with the sink or combination fixture vented in an approved manner

as indicated.

Types 11 and 12 may use any designs B, E, or Fon the first floor for

the main stack, with fixtures on the waste stack vented in an approved manner.

It is impossible to describe or illustrate all possible variations in

design in which the same general characteristics can be maintained.

The preceding construction has been described in considerable detail to illustrate the flexibility of the designs given to meet different

conditions. It has been previously pointed out that there is considerable flexibility in the designs themselves. Figures 81 to 89 are limited always by the permitted lengths of wastes and by venting

requirements for the position in which the layout is to be histailed.
PHYSICS OF PLUMBING SYSTEMS 185

Preference has been given in all illustrations to the simplest form

of venting that we believe will be safe for general application because

(1) from the drainage standpoint it will, in general, be more efficient;

(2) there is less chance for depreciation in service in the simple

Type I Type 2

Symbols used in Types I To \Z loclustve

5=3- ^ C <=?

Both Basin Closet Sink L.TVoys Comb. ED.

I -x-x-x- ArTernafe bouse droso -—Required ver?T lines

Fig. 90.—Types of one-story one-family houses showing required venting system; and (3) the work can generally be installed with a saving in

material, labor, and space. The designs and requirements in venting are given for the 3-inch

soil stack. This is not to be interpreted as a requirement for the

use of a 3-inch soil stack. It has been found to be serviceable
186 RECOMMENDED PLUMBING REQUIREMENTS

beyond the requirements for any of the types of buildings within

the scope of the plumbing committee’s report, and its employment

in preference to a 4-inch soil stack introduces a saving in material,

labor, and space. It has been suggested that the employment of a

4-inch soil stack would permit a reduction in the venting required

|ff(p=7

V— <333-

* - .hsci::

J

Type 7

\—lM ^r7

vrH

•

•\ si - Cl

b

%ie 8

Fig. 91.—Types of two-story one-family houses showing required venting for a 3-inch stack. The experiments so far indicate that this would

not be true and that, in general, where vents are required for a 3-inch

stack they would also be required for a 4-inch stack. Theory indi- cates that in many cases larger vents would be required for a 4-inch

than for a 3-inch stack with the same fixtures installed on both.
PHYSICS OP PLUMBING SYSTEMS 187

The 3-inch soil stack offers distinct advantages over the 4-inch

stack, which have not yet been sufficiently emphasized in the matter

of saving space and in being more readily worked into walls or

Fig. 92.—Types of two-story two-family houses showing required venting partitions. The saving may be small in the single small dwelling,

but in the aggregate the saving in material and labor in these particulars will be very great.
CHAPTER 7.—SIZES OF SOIL, WASTE, AND VENT PIPES IN

PLUMBING SYSTEMS

By R. B. Hunter

Bureau of Standards (Supplementary paper prepared for the consideration of the committee, 1928)

INTRODUCTION

In the paper on the “ physics of plumbing systems/’ published in the final report of the subcommittee on plumbing/ certain tables were

included as applicable to large plumbing systems. With reference to these tables on which the tables of the Recommended Plumbing Code

were largely based, further study and experimentation have led to the

conclusion on the part of the writer that if safe and serviceable, and

at the same time the most economical, construction were to be

obtained with various sizes of soil and vent pipes, it would be neces- sary to differentiate in requirements regarding both the height of

the structure and the type of inlet fitting (sanitary T or 45° Y) used

in the construction. While attention was called to the effect of these

differences in construction on the capacity of soil and waste stacks, no differentiation in these respects was made in the tables referred to. It is the purpose of this paper, taking into account these differences, to develop tables and charts applying to all plumbing construction,

for the consideration of the committee in a contemplated revision of

the Recommended Plumbing Code. It will be understood that only

approximations are possible in tables for general application, since

the demands on plumbing systems even of the same size and general

layout differ greatly because the land and distribution of fixtures

and the occupancy and use of the buildings differ in the different

systems. An exact list of the requirements in pipe sizes for any one system can only approximately meet the demands of many others of

the same size and type.

CARRYING CAPACITIES OF VERTICAL CAST-IRON PIPES

Experiments reported in the former paper, pages 101-109, showed

that water introduced into a 3-inch cast-iron stack through a 45°

3-inch inlet at the volume rate of 200 gallons per minute attained a

velocity of 32.8 feet per second in a fall of 45 feet. The velocity-height curve obtained indicates that, given sufficient height, a maximum

velocity of about 34 feet per second would be attained in a pipe of

this size with this volume rate of flow.

Recommended Minimum Requirements for Plumbing in Dwellings and Similar Buildings, United

States Department of Commerce, Elimination of Waste Series, 1924. 188
SIZES OF SOIL, WASTE, AND VENT PIPES 189

The experiment referred to verified the assumption that, for water

flowing in a vertical pipe without external head, the frictional re- sistance (.F) varies as the square of the velocity ( V); that is, F=KV2

. The hydraulic formula,

, jLV2 T/r fV2 h=W>’ 0Th,L= kD (1)

applies to a sloping pipe without external head and expresses the same

relation, since for maximum velocity under this condition (Ji) is a measure of the frictional resistance and is a constant. In a full vertical pipe the hydraulic gradient h/L becomes unity, and we may

write the equation for that condition as jV2

, 2jD = l01 v=

'2jny>

(2) It is known that the frictional constant (/) decreases both with

increase in diameter of pipe and increase in velocity, and for the

present it will be treated as a variable.

From equation (2) we may obtain,

expressing the relation between the maximum velocities, V and Vh

obtained in full pipes of diameters, D and Zh, with frictional constants

/ and/i, respectively.

The carrying capacity (C) varies as V D2

, therefore

C:Ci=V D2

: Vx Dx 2 (4) Combining (3) and (4) and transforming

rt.ri ° •t'l - jtt (5) giving the relation between maximum carrying capacities for vertical

pipes flowing full wi thout external head.

For maximum velocity, the frictional resistance must equal the

force acting in the direction of flow, and in equation (1) is a measure of frictional resistance per unit length of pipe. Since in a

partially filled vertical pipe (mg) is the force, we may replace by

(mgc). This leads to the following relation between maximum velocities and masses of water per unit length of pipe.

m : mi=JV2 '.j

x V? or V : ( 6 )
190 RECOMMENDED PLUMBING REQUIREMENTS

Treating (/) as a constant in equations (5) and (6) gives,

C'.C^DK.DK (7) an approximate relation for maximum carrying capacities of vertical

pipes of different diameters when flowing full, and

V:Vt = (8) an approximate relation of maximum attainable velocities in the same

pipe filled to different degrees.

In the following table, obtained from the data for a 3-inch vertical

pipe with 200 gallons per minute flowing in the pipe, by applying

equations (7) and (8), the carrying capacities given are lower than

actually obtainable for the conditions stated. This follows from the

fact that we have started with the lowest (m) in equation (8) and with

the smallest diameter in equation (7) and have treated (/) as a constant whereas it actually decreases as the diameters and velocities

increase.

Table 12.—Approximate capacities of vertical cast-iron pipes

Flowing

Flowing one-third full Diameter in inches full, gallons per minute

Gallons

per minute

Fixture

units

3 1,415

2, 870

5, 010 8,000

16,300

272 36

4 550 73

5. 965 128

6 1, 535

3, 160

204

8 421 The carrying capacities for pipes flowing full are predicated on

conditions as regards number and distribution of inlets and as regards

volume rates of inflow at the different inlets such as to just keep the

pipe full as the velocity increases. Since in plumbing systems inlets are usually spaced a story height apart and the volume rates of inflow

at different inlets may vary from zero up to the peak load from the

branch drain or drains on one floor, the maximum carrying capacities

flowing full are evidently not safe values on which to base the maximum permissible number of fixtures unless a substantial factor of

safety is employed. They do, however, aid in interpolating for safe

values and in introducing a reasonable factor of safety.

The table for stack capacities in the earlier paper, page 103 of

the final report, though not so stated at the time, gives in reality the

fitting capacity or the stack capacity with inlets at one approximate

level.
SIZES OF SOIL, WASTE, AND VENT PIPES 191

This table is repeated here with some modification in the headings

for direct reference and for use in forming the tables to follow

Table 13. —Stack capacities for one floor or level

Diameter in inches With sanitary T inlet With 45° Y or combination Y and one- eighth bend inlets

Gallons

per minute

Fixture

units Gallons

per minute

Fixture

units

3 100 13.3 200 26.7

4 180 24.0 360 48.0

5 280 37.3 560 74. 7 6 405 54.0 810 108 0

8 720 96.0 1,440 192.0 ESTIMATED PEAK LOADS IN PLUMBING STACKS

An estimated peak load is an essential factor in fixing upper limits

of service for any plumbing stack in terms of fixture units. The

principle of probabilities as a means for making such estimates was

given in the former paper and its application described. It is obviously useless to attempt to make these estimates with any great

degree of accuracy, because of the variation in the kind and distri- bution of the fixtures as well as the variation in the frequency of use in different plumbing systems. A peak load curve drawn from

points calculated by the method of probabilities from assumed or predetermined factors does show the manner of the variation of the

peak load with the total number of fixtures, and if the factors are

carefully chosen, estimates may be safely made from such a curve. No claim is made further than that, with the frequency of use allowed

for, the peak load given by the curve for any number of fixture

units will probably not be reached oftener than once in the time

stated—10 years in the curve shown in Figure 93. It is simply a device by which we may make systematic estimates, with reasonable assurance that the factors of safety introduced will amply take care

of any excess above the estimated peak loads chus made.

Without going again into the details of the calculations, which

were fully explained in the former paper, curve 1, Figure 93, shows

the peak discharge that will probably occur on the average of once in

10 years, with an average use of fixtures of once each in five minutes

for three hours daily. These estimates are based on a peak discharge

of 45 gallons per minute for each water-closet, an average duration of 10 seconds per flush per water-closet, and an allowance for all over- lapping of flushes of 6 seconds or more as giving a peak load equal to the sum of the overlapping peak discharges of the water-closets. The

curve is based entirely on a system of water-closets, but it may be

shown that in a mixed system of water-closets and other fixtures
192 RECOMMENDED PLUMBING REQUIREMENTS

having the same number of fixture units the peak discharge will not

be greater.

Below curve 1, curve 2 shows the average or mean flow based on

the same frequency of use and allowing an average discharge of 5 gallons per water-closet per flush. It is evident that with only a few fixtures on the system the flow in

the drains will be intermittent, but that as the number increases a point will be reached where with the same frequency of use the flow

will be continuous but not regular. It is also evident that when the

peak discharges do occur they will occur during periods of heaviest

use, and the peak discharges will be added to the flow already in the

drain and, therefore, the peak load may approach the sum of the

continuous flow and peak discharge. Curve 3, which is proposed for estimating peak loads, is obtained by adding the ordinates of curve 1 to those of curve 2. Using this curve, the estimated peak loads, up

to about 12 fixture units, is the sum of the individual peak discharges

from all fixtures on the system, or 100 per cent of the total possible

discharge. As the number of fixtures on a system increases the esti- mated peak load as a percentage of the total gradually decreases in accordance with the law of probability until for 5,400 fixture units

it is less than 8 per cent of the total. There is another condition in practice partially controlling possible

peak loads and which operates as an additional factor of safety.

The water-suppty lines should be, and generally are, proportioned to
SIZES OF SOIL, WASTE, AND YENT PIPES 193

supply water at a normal rate to a fraction of the fixtures only. With

flush-valve supply this limits the possible discharge to the capacity of the water-supply system. There seems to be no reason why the house

drainage pipes and house water-supply pipes should not be based on

the same estimated peak loads. With tank supply to the waterclosets and with plug outlet fixtures, the connection between supply

and drainage is not so close as with flush-valve supply, but there is a

limit to the rate at which the tanks or the fixtures will refill after flushing, which also places a comparable limit on the possible peak

load.

The same peak-load curve could be used with fairly satisfactory

results for determining the required sizes of horizontal branches, house

drains, and house sewers, but since the holding or storage capacity,

as well as the run-off during the discharge, is a factor, it seems more

logical to base the sizes of these on a maximum mean rate of flow. This has been done, as described later in the paper.

PERMISSIBLE NUMBER OF FIXTURES ON SOIL AND WASTE STACKS

Table 12 gives approximations for the maximum carrying capacities

of stacks under gravity flow. While these are admittedly only

approximations, they indicate that a vertical pipe of sufficient height

in which to attain maximum velocity has from thirty-five to forty

times the carrying capacity of the same pipe laid with a fall of one- eighth inch per foot and from fifteen to eighteen times that of the same pipe laid with one-half inch fall per foot. It seems illogical and

unreasonable to permit the use of sloping pipes in plumbing systems

to almost full capacity and not permit something approaching the same relative use of vertical-pipe capacities. It is true that the

controlling of air pressures is a greater problem in vertical than in

horizontal or sloping pipes, because of the greater velocities of flow

attained in the former. The proposal made here to base estimates

for the maximum use of stacks on their capacities when flowing

one-third full and on peak loads, as given by curve 3, Figure 93,

makes ample allowance for the separation and circulation of air. All available data on the subject indicate that this proposal gives a low

estimate on actual capacities of the stacks under service conditions.

Likewise all available data indicate that peak loads estimated by

Figure 93 are greater than actually occur in plumbing systems. Together they form a large factor of safety. The proposal is a step in

the right direction at least and provides a table in advance of anything that has been offered up to* this time.

With this advance, however, it will be necessary to impose certain

restrictions regarding the distribution of fixtures and regarding the use of “ sanitary T” fittings in order to prevent local overloading of the

stack. This may be done either by limiting the number of branches

in a given height of stack, or by limiting the number of fixtures on

20141°—29 14
194 RECOMMENDED PLUMBING REQUIREMENTS

all branches to a stack in a given height. The latter serves the

purpose and is more flexible, as it imposes no direct restriction on the

size or number of branches to the stack and is therefore the method

chosen in building the table.

It has been found that a stack will take the capacity discharge

from two horizontal branches of the same diameter as the stack

through a double 45° fitting. We will introduce here the term

“branch interval” and define it as any section of the stack, at least 8 feet in length, within which one or more branches are connected.

In the proposed table, with all inlets 45°, the total number of fixtures on all branches connected within any 8-foot section of the stack will not exceed two and one-half times the permissible number on one branch of the same diameter as the stack and with a fall of one-fourth

inch per foot. A comparable limit when any “sanitary T” fittings are used in the stack is one and one-half times the number permitted on one branch with a fall of one-fourth inch per foot. Two “branch

intervals,” not less than 16 feet of stack, permits double the number

of fixture units on the stack, provided not more than one-half are on

branches connected to the stack within any 8-foot section. For

three or more “branch intervals” the total on one stack will be dis- tributed so that the restriction as to the “branch interval” or length

of stack is not violated.

Table 14.—Sizes of soil and waste stacks Maximum number of fixture units with

Diameter of stack (inches) Sanitary T inlets All inlets 45° Y or combination Y and

one-eighth bend

In one branch

interval On one

stack In one branch

interval On one

stack

3 . 24 48 45 72

4 144 256 240 384

5 324 680 540 1,020 2,070

5,400

6 672 1,380 3,600

1,122

8 2, 088 3,480 SIZES OF HORIZONTAL DRAINS

As previously stated, the tables for required sizes of horizontal

branches, house drains, and house sewers are to be based mainly on an estimated maximum mean rate of flow or discharge, with

certain modifications to be described, and not on a temporary peak

discharge produced by the coincident discharge of fixtures. The

reasons for this are: That the individual peaks are wiped out by

overlapping when we approach the capacity of the drain and are further smoothed out by the flow in the drain itself; and also that

the temporary peaks do not have an effect on venting requirements

for horizontal branches comparable to the effect of a corresponding
SIZES OE SOIL, WASTE, AND VENT PIPES 195

peak in a partially filled vertical stack. There are, however, two

factors that come into play when we approach the maximum capacity

of a horizontal drain. One is the holding or storage capacity of the

drain in its relation to peaks of short duration, which in the case of short drains of small diameter is the dominating factor; the other is the effect of head above the drain on its limiting or maximum capacity.

The storage capacity of a drain increases with increased diameter

in two respects—the increased capacity per unit length and the in- creased length of drain necessary to accomodate fixtures sufficient to give a capacity load in the larger drain. Evidently the condition

in which the temporary peak has the greatest opportunity to over- charge the drain is in the drain of comparatively small diameter to which water-closets are connected directly. Evidently, too, the

maximum congestion and, therefore, the worst condition to contend

with in this respect is produced by a double row of water-closets

connected to the drain by means of double fittings. If we estimate

the required size of branches to take care of this condition, it will be ample for all other conditions, including unobstructed house

drains and house sewers. Observations on toilet rooms, in public schools in Cleveland,

Ohio, indicate that, with full occupancy in girls’ toilets, the average

time of occupancy per person may be as low as one minute. There

is no record of a lower average period of occupancy. In boys’ toilets,

where separate urinals are installed, the average period of occupancy

for water-closets is much greater. Observations in office buildings

and large industrial plants (see data on p. 95) show average occupancies varying from 3.97 minutes per person for females to 7.1 minutes

per person for males. It would seem reasonable and wholly safe,

therefore, to estimate peak loads on frequencies of use varying from

once a minute for diameters in which the storage capacity is a limiting

factor and in which congestion is likely to occur to once in two minutes

for a 12-inch drain in which the run-off is the controlling factor and

in which congestion is improbable.

From these data and assumptions the following tentative table

for drains with a fall of one-fourth inch per foot is computed on the

basis of each water-closet discharging 5 gallons once a minute.

Tentative Table A

Diameter of drain

(inches)

Capacity, with one-fourth inch

fall per foot Diameter of drain

(inches)

Capacity, with one-fourth inch

fall per foot

Gallons

per minute

Waterclosets Fixture

units Gallons

per minute

Waterclosets Fixture

units

Q 51.3 10.5 63 8. - 656 131 786

4 109.6 22.0 132 10 1, 149 230 1, 380

K 196. 5 39 234 12- 1, 838 363 2, 208

6.. 313.1 63 378
196 RECOMMENDED PLUMBING REQUIREMENTS

An examination of this table in connection with experimental data

indicates that for the 3-inch drain the estimate is high. The assumption that an allowance for an average flushing rate of once in two

minutes is ample for a 12-inch drain indicates that for the larger sizes the estimates are low. It is proposed to correct these estimates by

grading between the test value for a 3-inch drain and an assumed

permissible rate of flushing for a 12-inch drain. Three water-closets

closely spaced on a 3-inch horizontal drain with one-fourth inch fall per foot have been shown by test at the Bureau of Standards to operate

successfully. That this is the approximate limit is shown by a sluggish flush when an additional laundry tray is added to the branch.

Comparing the test value with the tentative estimate indicates that

the estimate for the 3-inch drain should be reduced to about 0.3 of

its value to be certain of taking care of all conditions.

At the other extreme a flushing rate of once in two minutes would

permit the tentative estimate for a 12-inch drain to be increased to twice its value. It is evident that the reduction in the tentative esti- mate for the 3-inch drain is necessary because of the limited storage

capacity. It is also evident that the increase in the tentative estimate

for a 12-inch drain is permissible, not only because of increased storage

capacity but also because of the decreasing chance of a proportional

number of the fixtures being flushed at the same time and the practical

certainty that the high assumed average rate of flushing of once a minute per water-closet can not be maintained in a system large

enough to require a 12-inch drain. The 8 and 10 inch drains are almost on the same basis as the 12-inch drains in that it is almost

entirely a question of the run-off and the mean rate of discharge

during a period of full occupancy. Balancing all the factors—storage

capacity, run-off, probability of coincident discharge, and possible

frequency of use—the following modifying factors are proposed to give safe and comparable estimates for the different diameters: 0.3 for 3-inch, 0.75 for 4-inch, 0.9 for 5-inch, 1.2 for 6-inch, 1.85 for 8-inch,

1.9 for 10-inch, and 2.0 for 12-inch drains. These factors applied to the tentative estimates of Table A give what is believed to be a logical

and safe gradation for the different sizes as shown in Table B.

Second tentative Table B

Diameter of drains (inches) Maximum

permissible number of waterclosets

Carrying capacity in 10-second periods Capacity for coincident

discharge, including

storage

Waterclosets Per cent

of total Waterclosets Per cent

of total

3 3 1.75 55 2.50 83

4 16 3.7 23 6.25 40

6 36 6.5 18 15.5 45

6 75 11 14 37.5 50 8 216 22 10 177 76

10 420 39 9 458 109 12 720 62 8 1,098 150
SIZES OF SOIL, WASTE, AND VENT PIPES 197

A column giving the capacities of the drains in a 10-second interval, which is, in fact, the capacity for coincident discharge in run-off

alone, and one giving the capacity for coincident discharge, including

storage in the minimum length necessary to accommodate the number of water-closets, have been included in Table B. The percentages show a regular gradation except for the 3-inch diameter. As

previously stated, the higher factor of safety is necessary because of limited storage and greater possibility of congestion. It should be

noted that, except for the 3-inch drain, there is an increasing factor

of safety given by the storage capacity as indicated by the last percentage column.

If the estimates of tentative Table B are accepted for drains with

a fall of one-fourth inch per foot, the second factor, effect of added

head, should be considered in connection with other slopes. It is a

fact that a small head may develop above the sloping drain without

interfering with the operation of the fixtures. While such a head is in general not desirable, it is a fact also that the limiting or maximum

capacity of a drain is determined by the head that may develop without interfering with the operation of the fixtures. The experimental

determination for the 3-inch drain on which the estimates for the

smaller sizes were based evidently involved a slight head above the

sloping drain. It will require the same length of 3-inch pipe to accommodate

three water-closets whether the slope is y inch, % inch, or y inch

fall per foot. The run-off, by D’Arcy’s formula, will vary as the

square roots of the total heads. The actual heads for maximum

capacity will vary as ^+ a> .A + a, and i+ a, where L is the length

in feet and a the added head in inches, and not as the slopes %, y, and y. It is impossible to make a definite calculation of this effect except for special cases. Estimates for a 3-mch pipe with the close connection in question indicate that the maximum or limiting carry- ing capacities vary approximately as 5:6:7 for y, y, and y inch

falls, respectively, instead of 36:51:80 as given by D’Arcy’s formula.

Similarly, ratios of 4:5:6 for 4-inch, 3:4:5 for 5-inch, and 2:3:4 for 6-inch drains are indicated for the minimum length necessary to accommodate the permissible number of fixtures. For 8-inch and

larger diameters, because of the length required to accommodate the

number of fixtures necessary to give the estimated peak load, the

possible added head becomes negligible compared to the head in the

sloping drain, and D’Arcy’s formula, may be applied directly for all slopes.

These indicated ratios are of course not exact, but their application to the estimates for a slope of y inch fall per foot in estimating
198 RECOMMENDED PLUMBING REQUIREMENTS

for y2 inch fall per foot gives an added factor of safety and comes

nearer to the actual capacities for both the y8 and y2 inch fall than

a direct application of the formula. Therefore, these ratios have

been applied in forming the following complete table: Table 15.—Capacities of horizontal drains in fixture units

Diameter of drain

(inches)

Slope, J^-inch

fall per

foot

Slope,

lA- inch

fall per

foot

Slope, H-inch

fall per

foot Diameter of drain

(inches)

Slope, K-inch

fall per

foot

Slope, Ji-inch

fall per

foot

Slope, J4*inch

fall per

foot

3 15 18 21 8 990 1,392 2, 220

4 84 96 114 10 1,800 2, 520 3, 900

5 162 216 264 12 3,084 4,320 6,912

6 300 450 600 SIZES OF VENT PIPES

The proper proportioning of vent-pipe sizes to soil and waste pipe

sizes is important in securing economy in construction, together with

the proper functioning of a plumbing system.

The subcommittee on plumbing suggested, and used in examining

the data submitted to them, the assumption that a system in which

the peak load did not reduce the seal in any trap having a full seal depth of 2 inches to less than 1 inch was satisfactory. This is equivalent to a requirement that the pressure variation in the system shall not exceed ± 2-inch water column and is probably a fair criterion by

which to judge test results for a particular system. When the results are to be used in calculations, a factor of safety should be introduced to allow for variations from the conditions of the test or experimental results. The following calculations are based on a permissible variation of pressure in branches of ± 1-inch water column

which in a 2-inch trap would leave 1%-inch seal under suction and

approximately a full seal under back pressure and hence gives the

suggested factor of safety.

In our experiments (see p. 118) we showed that a reduction in pres- sure of approximately 1-inch water column was produced in a 3-inch

branch from a 3 -inch stack in which water was flowing at the volume

rate of 200 gallons per minute (26.7 fixture units) when the branch was vented by a 2-inch pipe 36 feet long, equivalent in venting

capacity to a 3-inch pipe 312 feet long. Also, with a flow of 100

gallons per minute (13.3 fixture units), a 1%-inch pipe 23 feet long

held the pressure variation to about the same value. This length of 1^-inch pipe is equivalent to about 825 feet of 3-inch pipe.

It was observed that the discharge from one water-closet (six

fixture units) produced about the same pressure variation in the branch

with no vent except the open upper end of the soil stack ; that is, an

infinite length of vent pipe to the branch will serve in this case. At the
SIZES OF SOIL, WASTE, AHD VENT PIPES 199

other extreme, the maximum discharge at maximum velocity will

evidently produce the greatest demand on the vent; that is, some

short length of 3 -inch vent pipe (b) will be required to hold the pres- sure variation within the prescribed limits when the peak load is flowing.

These data suggest a curve of the form (y — a) (x — b) = c as express- ing the relation, in which y is volume rate of flow in fixture units and x

the required length of vent and a, 6, and c constants. The curve is asymptotic to the lines y = a and x = b. As we have two points on the curve for a 3-inch soil stack, y = 13.3, £ = 825, and y = 26.7; £ = 312,

from these two points and the value of one constant a = 6we may determine the value of the constants b and c, giving the equation

(y — 6) (£ — 33) = 5,780, expressing the relation between volume rate

of flow in a 3-inch soil stack and length of 3-inch vent required to hold

the pressure variation in a branch to ± 1-inch water column. This

relation may be regarded as fairly accurate for the one combination for which we have data. In order to obtain a similar relation for combinations of other sizes of soil stacks and vents, it is necessary in the

absence of data for these to make certain assumptions:

1 . Since the flow in partially filled vertical pipes has been observed

to be mainly on the walls of the pipe and since in this discussion we

are considering only cast-iron soil pipes, it appears to be a reasonable

assumption that approximately the same maximum velocities will be

obtained in different pipes when the volume rates of flow are pro- portional to the wetted perimeters; that is, proportional to the

diameters of the pipes.

2. Since the difference between the pressure in the stack and atmospheric pressure is evidently a function of the velocity and depth of the stream of water on the wall of the pipe, we may assume that the

difference in pressure will be approximately the same when the volume

rates of water are proportional to the diameters, for by assumption

(1) the velocities are the same and for thin streams the depth on the

walls will be approximately the same when the volume rates are proportional to the diameters.

3. Since holding the difference in pressure in a branch to a given

value is evidently a question of the vent being of the size and length

necessary to change the air in the branch, under the pressure difference

created, at the rate it is taken from or driven into it by the action in

the stack, and since at times the entire air volume in the stack may be

carried or driven forward with a velocity equal to but not greater

than the velocity of the stream of water in the stack, we may assume that

with equal velocities of the water streams the maximum demands on

the vents will be proportional to the cross sections of the stacks; that

is, proportional to the squares of their diameters.
200 RECOMMENDED PLUMBING REQUIREMENTS

4. If we define the venting capacity of a pipe as the volume rate

at which it will deliver air under a given difference in pressure between

the ends, it follows that two pipes that will deliver the same volumes

of air under the same difference in pressure are equal in venting capacity for that difference in pressure. The laws of air flow in pipes under pressure in connection with the

preceding assumptions lead to the following equations expressing

the relation between volume rate of flow in soil stack and length of vent of the same diameter required to hold the pressure variation in branches to ± 1-inch water column, the curves of which are shown

in Figure 94 without further details regarding the computations:

3-

inch vent with 3-inch soil stack (y— 6) (x— 33)= 5,780.

4-

inch vent with 4-inch soil stack (y— 8) (x— 27) = 11,400.

5-

inch vent with 5-inch soil stack (y— 10) (x— 20) =20,280.

6-

inch vent with 6-inch soil stack (y— 12) (x— 16) =31,240.

8-inch vent with 8-inch soil stack (y— 16) (x— 12) =81,040.

Pig. 94.—Relation between soil and vent stack These equations are based on meager experimental data and on

assumptions, hence are offered as rough approximations only. However, in the curves obtained the factors, volume rate of flow and length

of vent, evidently vary with each other in the right order, and it is doubtful whether more accurate determinations for specific layouts

would be more serviceable in general application for the purpose

intended, which is to give systematic approximations for upper limits

of service. However exact the experimental data obtained for a few

specific layouts may be, the extension of these data to tables or charts

for general application must of necessity result in very rough approxi-
SIZES OF SOIL, WASTE, AND VENT PIPES 201

mations for the reason that one or more of the conditions assumed in obtaining the data will be at variance with those existing in almost

every practical case. The criterion by which their usefuless in practice is judged [should

be whether or not their application results in imposing reasonable

and safe limits in the use of vents of different sizes. Limits for maximum heights of soil stacks were recommended by

the subcommittee on plumbing on the assumption that a certain

amount of sewer ventilation through the stack is necessary. There

seems to be no Way of determining just how much is necessary for

this or whether it is necessary to set a limit in maximum height at all. The limits were set in the first recommended code on the basis of a

permissible height of 150 feet for a 3-inch soil stack. In this con- nection we wish to point out that two stacks, a vent and soil stack,

will generally be required before this height is reached, and that if arbitrary limits are set, they should be relative to the ventilating

capacities of the combination. The following table gives equivalent

heights of different combinations, starting with 150 feet for a 3-inch

soil stack with no separate vent stack. It will be observed by referring to the vent charts that these maximum limits in height will seldom

apply in practice, for the reason that lower limits in the permissible

length of vent stack will be set in particular cases by the vent charts or tables. Table 16.—Heights of stack systems {feet) giving equivalent sewer ventilation

Diameter of vent stack (inches) Diameter soil stack (inches)

3 4 5 6 8 No vent stack.. 150 215 285 335 530

1 y2 152 2 160 220 2Y2 - 180 240 290

3. . 212 265 305 340

4 265 300 340 364 538

5 340 390 440 570

6 440 510 630

8 630 750

10 900

12 1,200

Figures 95, 96,97, 98, and 99 for soil stacks 3,4,5, 6, and 8 inches in

diameter, respectively, were formed by combining the curve of Figure

93 with the curves of Figure 94, substituting for the flow in the soil stack (fig. 94) the number of fixture units (fig. 93) giving that flow as an estimated peak load, and plotting the curves to these new coordi- nates (number of fixture units—length of vent stack) and imposing

the maximum limits of Table 16. The curves for vents larger or smaller than the soil stack are extrapolated by applying assumption 4. These curves, Figures 95 to 99, inclusive, are proposed for determining
Total

fixture

units

on

system

Total

fixture

units

on

system

202 RECOMMENDED PLUMBING REQUIREMENTS

Fig. 96.—Vent chart for 4-inch soil stack
SIZES OF SOIL, WASTE, AND VENT PIPES 203

Fig. 97.—Vent chart for 5-inch soil stack

Fig. 98.—Vent chart for 6-inch soil stack
204 RECOMMENDED PLUMBING REQUIREMENTS

in connection with Table 14 the appropriate sizes and lengths of vent

stacks and branch vents necessary to insure the proper functioning

of any plumbing system.

If a table is found easier to apply and more serviceable than the

charts, the following table, taken directly from them with some

interpolation between the tabulated values, will give approximately

the same results: Table 17.—Length of vent (in feet) for soil and waste stacks

Number Diameter of vent (in inches) uiaineier oi son or waste

stack (inches)

fixture units 1M VA 2 2^ 3 4 5 6 8 10 iy 1 45 iy2 . Up to 8 35 60

2 Up to 18 30 50 90

2y2 Up to 36 25 45 75 105

3 12 34 120 180 212

3 18 18 70 180 212

24 12 50 130 212

3 36 8 35 93 212

3 48 7 32 80 212

3 72 6 25 65 212

4 . . 24 25 110 200 300 340

4 . 48 16 65 115 300 340

4 96 12 45 84 300 340

4 144 9 36 72 300 340

4 192 8 30 64 282 340

4 264 7 20 56 245 340

4 384 5 18 47 206 340

5 72 40 65 250 390 440

5 144 30 47 180 390 440

5 288 20 32 124 390 440

5 432 16 24 94 320 440

5 720 10 16 70 225 440

5 1.020 8 13 58 180 440
SIZES OF SOIL, WASTE, AND VENT PIPES 205

Table 17.—Length of vent ( in feet) for soil and waste stacks—Continued

6

6

6

6

6

6

Diameters of soil or waste

stack (inches) Number of fixture units

144 288

576 864

1,296

2, 070

8 . 8 . 8 . 8 . 8 . 8 . 8 .

320

640 960

1, 600

2, 500

4, 160

5, 400

Diameter of vent (in inches) m 1H 2 2 H 3

27

15

10

76

4

4 5

108 340

70 220

43 150

33 125 25 92

21 75 42 144 30 86

22 60

16 40

12 28

7 22

5 17

6 8 10

510

510 630

425 630

320 630

240 630

186 630 400 750 900

260 750 900

190 750 900

120 525 900

90 370 900

62 252 840

52 212 705 The preceding tables have been given with only a brief outline of the principles and calculations involved in their development. They

are built around test or experimental determinations extended mathematically into tables. Frequent mention has been made of factors

of safety, ranging in value from 2 to 10, added at different points in

making the approximations. It is futile, however, to attempt to assign a definite value to the factor of safety applying to the system

as a whole. The term “ factor of safety” as used here is essentially

different from a structural factor of safety in which strength of materials is involved. In a plumbing system, if the estimated peak load

is exceeded even to the extent of using up the factor of safety allowed;

the only result will be a temporary and slight decrease in the effi- ciency of operation, with no injury to the system itself. Tables 14, 15, and 17 for sizes of stacks, horizontal drains, and vents,

respectively, give in the opinion of the writer thoroughly safe limits

and are proposed for substitution for the corresponding tables of

the recommended code in its contemplated revision. They offer a

distinct advantage over the old tables in that they set variable limits for use of the different sizes of pipe, depending on the length of pipe

and number and distribution of fixtures on the system.

It is probable that a better knowledge of carrying capacities of

vertical and horizontal pipes, of peak loads actually occurring in

plumbing systems, and of vent requirements would, by making

closer approximations possible, permit a further extension of the

limits proposed in these tables. It is also probable that a knowledge

of the extent of recirculation of air in a plumbing system would also lead to a reduction of the sizes of vent pipes. They are not impossible fields of investigation and promise a considerable saving in

plumbing costs, especially in tall buildings, if tnoroughly reliable

data were obtained.
CHAPTER 8.—STANDARDIZATION OF PLUMBING

MATERIALS

The standardization of the various materials used in plumbing

and the elimination of many articles and devices infrequently used

should reduce the cost of plumbing. Even if standardization be

confined to dimensions and roughing-in measurements, much may

be accomplished; but matters of this sort do not directly affect the

public health. Standardization must be brought about by agree- ment between all the parties interested. Standardization is for the

public benefit, irrespective of the police power.

While admitting that there are some real, though minor, disadvantages in standardization, yet, if not carried to unreasonable

lengths, standardization should be a benefit to manufacturer, dis- tributor, sanitary engineer, architect, plumber, municipal authority,

and owner. It should, in the long run, reduce production costs; lessen the stock required to be transported, stored, and sold, thus

saving overhead expenses and increasing the turnover of stock;

lessen the time required to make plans and estimates of plumbing

work; facilitate installation and repairs; reduce the original cost of installation and the cost of maintenance and depreciation. At the

time when the first edition of this report was issued the Department

of Commerce was already making excellent progress in bringing

about simplification of practice in various lines of business, and it was the opinion of the committee that this work might be profitably

extended to the plumbing industry.

The committee stated that the basis of standardization must be

the “Standard Plumbing Rules/’ or the plumbing code, as it is com- monly called. While the Federal Government can not dominate

the States in the exercise of police power, it can give advice and it can set up model laws, the acceptance of which by States and cities will result in effective uniformity.

It seemed certain that the standardization of fixture dimensions

would result in material economies. The only way that this standardization could be brought about was by the concerted action of

manufacturers, distributors, sanitary engineers, plumbers, and

governmental authorities.

The committee took steps to ascertain what had already been

done in this matter. It found that many efforts had been made

by various associations connected with the plumbing industry, and

that, in general, there was a strong desire on the part of engineers,

architects, manufacturers of plumbing supplies, plumbers, builders,

and governmental authorities to have standardization brought about

in some way. Some, however, were indifferent and a few were

opposed.

206
STANDARDIZATION OF MATERIALS 207

The plumbing industry is highly differentiated. There are many

kinds and qualities of materials used in plumbing—cast-iron pipe,

steel and wrought-iron screw pipe, vitrified-clay pipe, brass pipe

and fittings; porcelain ware, enameled iron ware, Wooden ware, etc. Minor matters of standardization affect a single branch of the in- dustry, and much has already been accomplished by associations

representing the several industries. But there are items of standardization which affect moie than one branch of industry; hence,

there is need for a broader cooperation than has existed thus far. If there were no variance in plumbing rules, it would be a relatively

easy matter for the different associations representing the industries to get together and adopt standards, but in the face of rules which vary widely in different parts of the country it is well-nigh

impossible for the parties interested to agree.

It seemed evident to the committee that no satisfactory standardization or simplification could be effected unless the parties to the

agreement included not only manufacturers, but State and municipal authorities, architects, engineers, house builders, master

plumbers, journeymen, and others. Time did not permit the committee to undertake such an extended program, but it expressed the

hope that the Department of Commerce would arrange to have the

necessary conferences held in order that simplification in plumbing

practice might be established.

It was suggested that those interested in standardization might

well take advantage of the facilities extended by the United States

Department of Commerce for furtherance of such activities. There

had been organized in this department a division of simplified practice, which offered its services to the various industries in bringing

together those interested in standardization programs, in making

the necessary arrangements for cooperation of the various groups,

and in following up the projects agreed upon. Similar measures had been carried out by other industries through aid of the divi- sion of simplified practice with marked success, and it was felt that

the plumbing industry should also avail itself of the opportunity.

Considerable work along this line has been done since the publication of the first edition of this report. The results are embodied

in publications of the division of simplified practice, of which the

following are examples:

Simplified practice recommendations:

No. 8. Range boilers. No. 13. Structural slate for plumbing and sanitary purposes. No. 21. Brass lavatory and sink traps. No. 25. Hot-water storage tanks. No. 29. Eaves trough conductor pipe, conductor elbows, and fittings. No. 32. Staple vitreous china plumbing fixtures. No. 57. Wrought-iron and wrought-steel pipe, valves, and fittings.
CHAPTER 9.—ADMINISTRATION

The committee has considered the subject of plumbing administration and has studied the various laws by which plumbing regulations are now being put in force. The subject is so complex,

affects so many different interests and classes of people, involves so many legal matters which differ in different parts of the country and

in communities differently constituted that the committee has felt

itself incompetent to make definite recommendations. It presents

the following ideas as a basis of possible further investigation:

THE PLUMBING BUSINESS

Plumbing developed first as a craft. The early simple plumbing

codes were based on the idea of protecting health by assuring good

craftsmanship and were sufficient. Present conditions are different;

plumbing is more elaborate; factory-made plumbing supplies have

replaced those made in the shop and on the job; the business element

has increased; cities have increased in size and changed in character;

the relations between owner and plumber, between employer and

employed, between buyer and seller, are less personal and more

artificial than formerly; plumbing is still highly technical; knowledge

of plumbing design is even more important than in former days;

good workmanship is still necessary.

To-day the so-called “master plumber” may be both a business

man and a craftsman. As a business man he is related to the jobber

and the manufacturer from whom he obtains supplies; as a crafts- man he is related to the journeymen and apprentices whom he

employs. Competition is keen. Journeymen are continually rising

into competition with the master plumbers. In so far as they are

qualified this is desirable, but the incompetent journeymen are often

those most eager to force “themselves into the plumbing business.

Without a shop, without capital, without business responsibility,

men ill-fitted by experience are undertaking to do plumbing work

buying their supplies and installing them in such a way as to pass

inspection with the least margin. It is largely because of this

situation that present-day plumbing regulations need to be more

detailed than formerly. The people do not understand this situation and naturally look with disfavor on rules and regulations which seem to them to have only one purpose—that of making plumbing more expensive. This element of the problem needs to be more

thoroughly studied.

208
ADMINISTRATION OF CODE 209

ENFORCEMENT OF PLUMBING REGULATIONS

The enforcement of plumbing regulations affects three classes of people: {a) The owner and his agents, (b) the plumber, and (c) the

public official. The relations between these parties should be clearly

and definitely set forth in the laws and ordinances. Without at- tempting to formulate these in legal terms the committee is of the

opinion that the following items should be considered:

THE OWNER AND HIS AGENTS

1. The owner, or his agents—that is, architect, engineer, contractor and subcontractor, foreman, and employee—should be prohibited

from installing plumbing contrary to regulations, but the owner

should not be prevented from personally installing plumbing in

accordance with the code, provided this is done subject to permit

and inspection. Consideration should also be given to a plan for

having the owner file a bond at the time of taking out a permit.

2. Owner or agent (person, firm, or corporation) should be re- quired to have permit issued after (a) filing of application, with

plan and specification; (b) approval of plan and specification before

signing of contract; and (c) payment of fee.

3. Owner or agent (person, firm, or corporation) should be entitled to receive a certificate of approval of the plumbing work done after

(a) receipt of permit; (b) application for inspection; and (c) approval

by inspector.

4. Penalties should be provided for: (a) Failure to take out permit;

(b) failure to apply for inspection; and (c) noncompliance with

regulations and should result in refusal to issue certificate of approval

or in a fine in case plumbing is used without certificate of approval.

THE PLUMBER

1. The status of the plumber (master plumber, contracting

plumber, or employing plumber—all agents of the owner) should be

provided for by registration in one of the following three ways: (a) By certificate of competency; (b) by license; and (c) by bond.

2. Plumber should be prohibited from installing plumbing contrary to the regulations or without a permit for the work.

3. As agent of the owner, he should (a) file application for permit,

with plans and specifications; (b) pay fee; (c) receive permit; (d) install work in accordance with regulations; (e) apply for inspection

and test; and (/) deliver certificate of approval to owner.

4. Penalty for failure to comply with the law should be (a) loss of

certificate of competency or license or forfeiture oi bond, and (5) fine. PROPER ADMINISTRATIVE AUTHORITY

1. Jurisdiction in the enforcement of plumbing regulations should

be committed to the board of health, building department, or other

municipal department.

20141°—29 15
210 RECOMMENDED PLUMBING REQUIREMENTS

2. Under this jurisdiction a department or division of plumbing

should be organized to enforce the regulations, the official in charge

being called the plumbing inspector.

3. Duties of the plumbing inspector should be definitely assigned.

They should include such matters as (a) examination of application

for plumbing, examination and approval of plans and specifications

issuance of permits and collection of fees; ( b) inspection of plumbing

and conduct of tests; (c) issuance of certificates of approval; (d) ar- rest and prosecution of offenders; (e) office records and reports; and

(/) advisory service to the public in the matter of plumbing regulations.

4. Qualifications and status of plumbing inspector should include

such matters as (a

)

competency in plumbing; ( b) nonengagement in

the plumbing business or in the manufacture or sale of plumbing supplies; (c) bond; (d) compensation; and (e) authority to enter buildings.

5. A schedule of fees should be established, the total of which

should approximately pay for the enforcement service, the individual

fees being graded according to the magnitude of the work.

6. Provisions should be made for enforcing the penalties upon each

of the three clauses of persons referred to.

7. The penalties for failure of plumbing inspector to perform his

duties should be loss of position, fine, or other appropriate penalty.

8. Limitation of discretionary power should be provided.

STATE PLUMBING LAWS

While the methods for the local enforcement of plumbing regulations may be readily standardized and are, in fact, quite uniform at the present time, the present State laws in regard to plumbing vary

greatly. The committee is of the opinion that the following provisions should be included in the statutes

1. All plumbing throughout the State should conform to the basic

plumbing principles set forth in chapter 3. These state results, not

methods. They should be written into the statutes.

2. The State board (or department) of health should adopt a plumbing code in conformity with the basic plumbing principles and

revise the same when necessary.

3. Every city, town, or other subdivision of a State having a public water supply should be required to have a plumbing code and

should either accept the State code or adopt a code of its own, subject

to approval by the State board (or department) of health. In

places where there is no public water supply the acceptance or adoption of the code should be permissive.

4. In places where no code is accepted or adopted the basic plumbing principles of the statutes should be enforced by State, county,
ADMINISTRATION OF CODE 211

or local boards of health. If enforced by the State, the authority

should be vested in the division of sanitary engineering of the State

department of health.

5. Owners or plumbers doing plumbing work within the State should

be responsible for its compliance with the basic plumbing principles.

LICENSES v. CERTIFICATES OF COMPETENCY

The license is a crude governmental device for assuring the public

that plumbing work will be done satisfactorily and in accordance

with legal regulations. It was originally intended to guarantee

craftsmanship and knowledge of the regulations. It can do no

more, and it does not always do that. It does not always stimulate

a plumber to improve his knowledge after his license has been secured.

It was not intended and, indeed, can not assure business competency

or reliability, and to-day the business side of plumbing is important.

The distinction between journeymen’s license and master plumbers’

license is vague and differs in quantity rather than in kind.

Furthermore, the license, which debars the competent nonlicensed

man from doing plumbing work, is not for the interest of the country,

for desirable individual competition is prevented.

The committee is of the opinion that the time has come for a thorough study of the license system, with the idea of possibly substituting for it a system of certificates of competency—a system that

would tend to improve the status of the plumber by causing him to be stimulated by competition both in business and craftsmanship,

and that would give greater protection to the public against faulty

plumbing. Under a system of certificates of competency the owner would desire to choose a certified plumber, whereas under the license

system he would be compelled to choose a licensed plumber.

What is needed is some plan to give the public confidence in the

persons who are engaged in the plumbing business. If plumbers

will actively take up the problem of raising their own status on the

basis of competency, a great deal can be accomplished in establishing the confidence of the public in the plumbing industry.

The committee wishes to place on record its appreciation of what

the plumbing industry has done to improve the living conditions in

American homes. People generally do not appreciate the extent to which house plumbing has improved the public health. The in- fluence has often been indirect rather than direct, and for that reason

it has not always been easy to recognize. Public water supplies

would lose much of their value were it not for the opportunity to use water at convenient fixtures. The disposal of fecal matter, the

greatest sanitary problem in the world, is best solved by the introduction of the modern water-closet.
CHAPTER 10.—EXPLANATORY NOTES AND COMMENTS

In further explanation of various matters discussed in the report,

and in answer to questions which were raised by those who submitted comments on the tentative report of the first edition, the committee has prepared the following series of notes. NOTE 1. DATA OBTAINED BY QUESTIONNAIRE

The tentative report included a compilation of data relating to plumbing regulations in different cities and States and a statistical

analysis of various items found in 81 plumbing codes. The data were

secured as a result of a questionnaire sent out before the committee

began its work. Many correspondents criticized these data because

of their incompleteness and their nonrepresentative character. The

committee, therefore, decided not to publish these statistics with its final report. Only one conclusion could be drawn from the facts

collected, namely, that the present situation with reference to plumbing laws and codes was nothing less than chaotic.

# NOTE 2. PURITY OF WATER SUPPLY

If the water supply is from a public source, the individual householder has no responsibility except as a citizen. If the supply is from a local source, such as a well, the responsibility rests upon nim

to provide pure water, and the health department may exercise control, under the police power, if the supply is not safe. The plumber,

by using proper methods of sewage disposal, thereby preventing the

pollution of the soil, can do much to safeguard local water supplies.

There is no reason why rural dwellers should not enjoy safe and comfortable living conditions more nearly like those of the city dweller

than is now the case. Some of the committee’s correspondents have called attention to the possibilities of injury to health through the use of lead watersupply pipes or of lead joint compounds for the installation of pipes.

In this connection the nature of the local water supply should be

given careful consideration. The subject of corrosion, including the use of lead, is discussed at length in Appendix B. NOTE 3. DUAL SOURCES OF WATER SUPPLY

It sometimes happens that there are two or more supplies of water—a pure water for drinking and an impure or unsafe water for

flushing. This creates a dangerous condition, as an unsafe water, if 212
EXPLANATORY NOTES AND COMMENTS 213

available, is liable to be used through ignorauce or by mistake.

Cross connections between pure and impure systems under such cir- cumstances are always hazardous and should not be permitted except

under special conditions. Preferably all water supplied to buildings

should be pure.NOTE 4. ADEQUACY OF WATER SUPPLY

If the water supply in a building is not adequate, the fixtures will become foul, insanitary, and dangerous to health. The problem of insuring an adequate water supply for each building is not a simple

one. There are three major factors which affect the supply of water

available at fixtures, namely, the pressure in the mains, the size and

length of supply pipe, together with the number of changes in its course, and the number of fixtures which probably will be operated

simultaneously. There is much evidence that the rule-of-thumb

methods so often used by builders and plumbers have not resulted

satisfactorily.

The combination of small pipes and large faucets should be avoided.

Pipes of corrodible material, such as steel or wrought iron, should

be large enough to allow for the effects of interior rusting, especially

in localities where the water is known to be corrosive. Small-sized

pipes and interior corrosion reduce the water pressure available at

faucets, and householders frequently complain of low pressure in

the mains when the trouble is really with their own plumbing sys- tems. The custom in some places of using service pipes as small as one-half inch in diameter does not admit of adequate service to

several fixtures simultaneously. Use of the garden hose, for example, or the operation of a flush valve may, for the time being, absorb

all or nearly all the supply of a building, and lack of adequate flushing

water may set up insanitary conditions in water-closets. The

tendency of the day is to use larger service pipes than formerly.

In some places water-supply pressures are too great, resulting in water waste and in unnecessary wear of valve seats with resulting

continuous leakage. It is possible, however, to use pressure-reducing

valves.

Attention is called to the fact that flush valves if used without

supply tanks make greater demand on the system than do tank

closets because they use water at a higher rate. Where flush valves

are used without a tank the supply pipes in the building, and even

the service pipe in the street, should be of larger size than where

tank closets are used. It is possible, however, to use supply tanks

in connection with flush valves. The problem is one of balancing

the cost of larger pipes with the cost of a supply tank.
214 RECOMMENDED PLUMBING REQUIREMENTS

NOTE 5. PRESSURE RELIEF FOR WATER-HEATING APPARATUS

Serious results from the explosion of hot-water heaters or boilers are frequently reported and are foimd due in almost every case to stoppage of the hot-water pipes, overheating, or the lack of provision

for pressure relief. Overheating of the copper used for boilers

reduces its strength. Boilers should be provided with relief valves

or with one or more relief faucets which will automatically open

under high pressure. Under some circumstances hot water may be

forced hack into the cold-water supply pipe and service pipe, and, if there is a meter on the system, moving parts made of hard rubber

will be damaged thereby. To protect meters, check valves are sometimes placed on the supply line inside the meter, but this only

increases the danger of boiler explosion. When these check valves

are used the need for adequate relief valves becomes all the greater.

NOTE 6. DESIRABILITY OF SEWER CONNECTIONS

Privies, cesspools, and other means for the disposal of fecal matter

are so frequently the cause of insanitary conditions that they should

not be permitted to exist where public sewers are available. The

advisability of sewer connections wherever possible and the need

of a separate house sewer for each building have been strongly

emphasized by the committee’s correspondents.

NOTE 7. PROVISION OF WATER-CLOSETS

The reason for specifically requiring at least one water-closet for

each family is that if one closet is used by more than one family

lack of responsibility for its upkeep leads to uncleanliness and

indecency. The question has been raised by correspondents whether

this provision should not be included in a housing code rather than

as a part of the plumbing regulations. While from one point of view this may be logical, yet for administrative purposes better

results will be secured by making it a plumbing requirement.

NOTE 8. FIXTURE DESIGN

From a health point of view it is essential that plumbing fixtures

shall be of smooth, nonabsorbent material, as free as practicable

from concealed fouling surfaces, and set free of inclosures. They

should be suitably designed for their respective uses and for con- venience in cleaning. This will help greatly to avoid dirt accumulation and continual dampness, will prevent growth of insects and

fungi, and minimize odors due to existence of insanitary conditions.

A number of the committee’s correspondents have called attention

to the insanitary possibilities of the device known as the u

standing

waste and overflow.” This device is now made so that it is devoid

of its former objectionable features.
EXPLANATORY NOTES AND COMMENTS 215

Many plumbing fixtures now on the market exhibit inconsistencies

that do not seem to be justified. The clear area of opening in

strainers, plugs, fixture couplings, tailpieces, and traps is not such

as to insure equivalent flow at these points for any individual fixture. At present the relations of these elements of fixture design appear

to be illogical and open to improvement. The plumbing regulations

of many cities prescribe the size of traps required for different kinds

of fixtures without prescribing the sizes of fixture outlets or prohibiting constrictions between the trap and fixture. Some distinction

should be made between fixtures which drain rapidly and those which

drain slowly.

The rules for plumbing in many cities fix the sizes of drainage and

vent pipes required for the service of different kinds and numbers

of fixtures but do not prescribe the maximum permissible rate of flow or discharge from the fixtures, the only controlling feature fixed

by the rules being the size of the trap or waste. The discharge

through them may vary greatly with different types, design, and

method of installation.

There are believed to be possibilities of economy in use of water

by a more efficient design of water-closets. These have been

designed almost entirely from the manufacturers’ point of view, with

the object of insuring successful operation but with small regard for

the amount of water used. Users also have, in general, disregarded

this consideration. Through a mistaken idea that large quantities of water are necessary to clean the bowl thoroughly and operate the

system effectively, some codes have required fixtures to be designed

for comparatively large quantities of water. The fact should not be

lost sight of, however, that water is needed to transport solids to the sewer as well as to flush closets. The provision of an adequate water supply is in many cases difficult and in all cases a serious item of municipal expense and deserves

attention. The committee is of the opinion that by improvement of water-closet design the quantity of water necessary for satisfactory

operation of such fixtures may be materially reduced. It is recom- mended that as a matter of national economy a thorough investigation of these possibilities be undertaken by the manufacturers of water-closets.

Owing to the lack of time, the committee has not made a thorough

study of fixtures, but finds that many are not well designed. A

special study of fixture design could well be made by manufacturers

in order to determine the practical elements best adapted to secure sanitary and efficient fixtures of moderate cost.
216 RECOMMENDED PLUMBING REQUIREMENTS

NOTE 9. VELOCITY OF WASTE WATER IN DRAINAGE SYSTEMS

The dangers of clogging are serious, and a well-designed house

drainage system should remove from the building as quickly as

possible the waste water and all the materials it conveys without

unnecessary fouling of the pipes and appliances. The fouling of pipes may be caused by the adhesion of greasy and sticky materials

to the walls of the pipes, or by the deposit of material carried in sus- pension in the waste water, or by both of these causes. The results

of fouling are a decrease in the carrying capacities of the pipes,

stoppages either partial or complete in drainage and vent pipes,

which may impair the service or stop it altogether, the production of deleterious and corrosive gases through the decomposition of organic

matter, the development of bacterial and fungus growths on the

organic matter in the pipes, and the production of noxious odors.

A well-designed system of house drainage should aim to reduce these

ill effects to a minimum, but they can not be completely eliminated.

Furthermore, a slight coating on the interior of the pipes sometimes

offers some protection against corrosion.

It is realized that the subject is charged with variable and conflicting elements. If the pipes are of a size to scour under the dis- charge of a single fixture, they may be too small for proper service

under simultaneous discharge from several fixtures. If designed for

several coincident discharges, they may not scour under the discharge from a single fixture, and scour will occur only periodically

when favorable coincident discharges take place. If the waste pipes run full, the aspirating and self-siphonage effect on fixture traps will

be increased, and venting protective for partial flow will be inadequate for full flow. It is possible in this connection that more efficient fixture design

elsewhere suggested may render feasible reduction in size of branch

drain and vent pipes now generally specified without reducing their

convenient and useful service or increasing the danger of stoppage.

NOTE 10. USEFUL LIFE OF SYSTEM

Leakage is, perhaps, the greatest danger to be guarded against.

This is influenced by the kind and strength of materials, the nature

of joints, the method of attaching the pipes to the building, the depth

of pipes in the soil, air circulation and diffusion, methods of passing

pipes through building walls or foundations, etc. In view of the stress placed upon plumbing design and construction

as a matter affecting health, the committee thinks that it is only

logical to insure, so far as possible, the permanence of the protection

thus secured, and that such materials and workmanship should at all times be required as will produce a plumbing system as nearly as possible equal in life to that of the structure inclosing it. This is
EXPLANATORY NOTES AND COMMENTS 217

specially important in the case of pipes placed in walls or otherwise

not readily accessible for inspection or repair.

Aside from care in construction there are other factors affecting

the useful life of plumbing systems. Inadequate foundations and

unskillful framing of buildings sometimes cause settlement with

resulting structural failures in plumbing systems which no precautions as to design, materials, or workmanship would prevent. Igno- rance and carelessness as to the proper use of plumbing are often

responsible for corrosion or clogging of pipes and improper use of

fixtures. NOTE 11. LIMITATIONS TO THE USE OF CLEAN OUTS

Clean outs on plumbing systems are important and useful for

three purposes—to remove any stoppage of the pipes, to provide means for testing the separate parts of a drainage system by the use

of water or air, and to make it possible to give the system a final air-pressure test after the fixtures have been installed. Clean outs should be accessible and so made that the ordinary householder can open and replace them. They should be as few in number as is consistent with these requirements. Because of the danger that

clean-out caps will be removed and not replaced some cities have

discouraged and even prohibited their use. The committee does

not approve this prohibition.

NOTE 12. TRAPPING OF FIXTURES

The effectiveness of traps in preventing access of vermin to drains

and the escape of sewer air into rooms is partially sacrificed when

more than one fixture is connected to the same trap. There is generally a greater length of untrapped waste pipe exposed, and dirty

water is liable to flow from one fixture to another. Laundry trays or a sink and tray can safely be thus connected, but greater satis- faction will be obtained if each fixture is separately trapped.

NOTE 13. GREASE-TRAP REQUIREMENTS

Some cities require grease traps to be installed on kitchen sinks

in residences as well as in hotel and restaurant kitchens. While they

undoubtedly are desirable for these larger installations, the committee thinks that in private residences the danger of neglect offsets their beneficial qualities and recommends that they be omitted,

except where sewage is disposed of in small septic tanks or under

private auspices.

The operation of septic tanks, such as are commonly used with

rural homes, is seriously hindered by the presence of grease in quantity, and wherever possible in such cases the kitchen wastes should

be disposed of separately from fecal matter.
218 RECOMMENDED PLUMBING REQUIREMENT'S

The clogging of waste pipes with grease, hair, lint, or other matter

is generally due to improper sizes of piping and faulty construction

rather than carelessness of the housewife. The committee contends

that a plumbing system properly designed with pipes, fittings, and

connections that form a smooth interior waterway which gives

opportunity to carry off any solids or semisolids in suspension can

not and will not become clogged under ordinary usage. Wherever

a small horizontal waste pipe discharges into a pipe of considerably

larger area, which makes it impossible to secure the proper scouring

action, there is a likelihood of stoppage. The quick change in temperature and the greater area of the pipe forms a natural grease

receptacle. The use of caustic soda or soda lye in drains should be

discouraged, as it makes a hard soap and may increase the clogging.

There are several instances on record where workmen have been

burned and blinded due to ignorance and criminal carelessness in the use of this substance. Potash or potash lye is sometimes used advantageously prior to flushing with hot water as it makes a soft soap

which will not clog the pipes. Properly sized waste pipes will

minimize stoppages and the necessity of the use of any foreign

materials.

NOTE 14. AIR CIRCULATION IN PLUMBING

Fixture drains should be designed so as to prevent self-siphonage

of traps. Ventilation of drainage systems tends to prevent the

growth of the fungi which produce “slime” and to retard corrosion

by the evaporation of moisture.

Chief reliance for ventilation of the drainage system and for relief of pressure changes set up by fixture discharge is placed upon a free course of air from street sewer to roof terminal. Effects of frost closure as determined by experiments apparently are so slight as to be negligible if a clear opening is left at the top of the stack equal

in area to a circle 1J inches in diameter. A diameter of 4 inches at the roof line has been found adequate under most conditions, but

in some parts of the United States and in Canada severe climatic

conditions require increasers 2 inches wider than the pipe diameter

below the roof. Extension of such pipes above the elevation of possible snowdrifts has been found unnecessary, as the escaping air “honeycombs” the snow sufficiently to prevent obstruction. It also has been found that vent pipes which extend but a few inches above

the roof are less subject to frost closure than longer lengths. This,

however, sometimes increases the effect of wind pressure on the trap

seals. NOTE 15. SIMULTANEOUS DISCHARGES

The committee’s assumptions as to proportion of fixtures likely to be discharged simultaneously were presented in the tentative report

and were received without criticism. One or two reviewers pointed
EXPLANATORY NOTES AND COMMENTS 219

out that these assumptions erred on the side of safety, if at all. As

elsewhere stated, much thought was given to this subject and a valuable body of data and computations has been accumulated,

bearing on similar questions in large buildings.

NOTE 16. ADMISSION OF DESTRUCTIVE SUBSTANCES

Substances such as gasoline and oil from garages, acids, steam,

grease in large quantities, liquids containing silt, hairs, fibers, etc., ought not to be admitted to plumbing systems or to sewers. While

the abuse of plumbing systems can not, of course, always be pre- vented, connections plainly intended for the admission of such

substances can be forbidden.

NOTE 17. LIGHTING AND VENTILATION OF WATER-CLOSET COMPARTMENTS

The requirement that water-closet compartments be well lighted

and ventilated to the outer air, as submitted in the tentative report

of the first edition, was somewhat severely criticized. The committee

thinks, however, that at least for the small dwelling house the re- quirement involves no hardship to the owner.

It is the general observation, furthermore, that direct lighting and

ventilation tend to prevent carelessness in the use and maintenance

of fixtures in cases where living standards are not of the highest. If the compartments are dark, the fixtures are likely to become soiled

from neglect. Ventilation is important in order to prevent odors

and to dilute any air accidentally escaping through the fixtures. The provision of a window opening directly to the outer air is apt

to be omitted only in the case of speculative builders selling or renting a cheap type of house, and under such circumstances the improved

sanitary conditions resulting from direct lighting and ventilation are well worth while.

NOTE 18. SEWAGE DISPOSAL

Precautions should be taken to prevent the possible pollution of wells or other sources of water supply and the escape of sewage on

the surface of the ground. Local soil conditions are an important

factor, and so many conditions may exist that an inspection of each

situation is necessary. Eequirements must vary according to soil and climate. The committee has not felt called upon to discuss the

subject of local sewage disposal in detail, especially as the matter is now being considered by the board of excreta disposal of the United

States Public Health Service. The methods adopted must vary

according to local conditions. Many State departments of health,

the United States Public Health Service, and the United States

Department of Agriculture have issued bulletins giving information on this subject.
220 RECOMMENDED PLUMBING REQUIREMENTS

NOTE 19. OMISSION OF THE MAIN HOUSE TRAP

The committee finds that this trap and the fresh-air inlet are in

most cases a needless expense. Experiments under the committee’s

supervision have shown that the house trap interferes with the flow

of sewage and air movements in the house drain. It increases the

possibility of trouble from back pressure in the soil stack. Its omission gives opportunity of inoffensively ventilating the street sewers through a multiplicity of outlets. Where the sewage is discharged

into a septic tank, a trap and a foot vent on the house side of it is thought by some to he desirable in order to prevent the escape of

the tank air and to maintain a circulation of air in the house system,

but with the septic tank properly designed it is not necessary.

The recommendation in the tentative report of the first edition that

installation of the main or house trap and fresh-air inlet be discontinued aroused much discussion. Of the respondents who discussed

this matter in particular, the greatest number favor the omission of

the house trap, a few would retain it, and a few seem to think that it3 advantages and disadvantages are about equal. The committee’s

reasons for advocating its omission have already been given. The

chief arguments of those who would retain it are as follows

It is argued that fixture traps and floor-drain traps do occasionally

siphon in spite of all precautions and that leaks in the pipe system

occur because of structural failures and settlements, thermal expansion, and poor workmanship. In such cases the house trap affords an additional barrier against admission of sewer air, insects, etc. To this it may be said that conditions within the house system give

rise to emanations fully as objectionable as those from the sewer.

It has been shown conclusively that in very cold climates the

increased circulation of air through the house system results in clos- ing roof vents completely with hoar frost, and the use of house traps

has been found absolutely necessary.

It is argued that in cities where house traps are now generally in use the installation of systems not thus equipped exposes occupants

of neighboring buildings to concentrated fumes from sewer systems

otherwise unvented. This may, under certain circumstances, justify

the requirement of a house trap, but where a reasonable distance

intervenes between roof vent and neighboring windows the committee thinks that use of the house trap should be optional.

Careful observations made in England have disclosed that sewer

systems are, in general, much more thoroughly ventilated through

manhole leakage, etc., than is popularly supposed, and that the pres- ence or omission of house traps has at most a minor influence on the

atmospheric conditions in sewers. In this connection it should also

be remembered that the fresh air inlet, as an indispensable adjunct
EXPLANATORY NOTES AND COMMENTS 221

to the house trap, may be a very real nuisance to those in its neighborhood.

It is argued that the main house trap prevents incursions of rats from the main sewer system. Observations both in this country and

in England show that rats can pass readily through large house traps,

and the usefulness of the traps in this respect, therefore, is questionable. The best protection against rats is the small fixture trap, and

since soil pipes are no longer customarily made of lead the danger

of rats passing from sewers to the house system is not as important

as formerly.

NOTE 20. PLUMBING AS RELATED TO BUILDING DESIGN

The practice of fixing the location of plumbing fixtures on the floor plans without taking into consideration the importance of supply and

drainage pipe construction very often results in poor, undesirable, and

costly installation. Whether in walls or partitions or beneath floors,

sufficient piping space must be provided to eliminate complicated

and undesirable construction and the use of unnecessary fittings,

which add to the cost of labor and material without increasing the

efficiency of the system.

In designing the plumbing and drainage system architects and engi- neers should bear in mind that adequate piping space must be provided in order that the system may be installed in an efficient and

economical manner. Type of building construction, fixtures to be served, and location

of supply and waste pipes are equally important and can not be

divorced. It must be remembered always that the highest type of plumbing fixtures will not function properly without efficient water

supply and drainage.

NOTE 21. THREE-INCH SOIL STACKS

The use of the 3-inch soil stack, recommended in the tentative report

preceding the first edition, was very thoroughly discussed in the letters received regarding that report. Nearly all respondents expressed unqualified. approval of 3-inch stacks for small dwellings, most of these

reporting satisfactory experience with such systems in practice. A few

opposed the use of 3-inch stacks on the grounds that they are more

likely to clog and that pressure disturbances are more serious, but

only two of these mention actual observation of the 3-inch systems in

use. Several raised the question as to whether lack of ventilation and

increased back pressure would occur with the smaller pipe. In answer

to these doubts it may be stated that experiments and computations have shown that the 3-inch stack is less subject to undesirable pneumatic conditions than the 4-inch stack, for the reason that
222 RECOMMENDED PLUMBING REQUIREMENTS

the quantity of air moved in a 3-inch is less than in a 4-inch

stack. There is less ventilation of the street-sewer system through

the 3-inch soil stack, hut this is a minor consideration in view of other

advantages.

NOTE 22. VITRIFIED CLAY PIPE

The committee decided that the use of vitrified clay pipe should

be prohibited for house drains—that is, for use inside of dwellings

on the basis of history, experience, and weight of authority. The

committee favors the idea of having arrangements made for a thorough study of its safety and fitness for use in house drains.

NOTE 23. SIZES OF DISTRIBUTION PIPE

The proper sizes for the water pipes leading to the various fixtures

depend upon several factors, such as the material of the pipe, the

water pressure, the length of the pipe, the size of the faucet, and the

rate at which water needs to be used. The figures given in the

recommended code as minimum sizes will ordinarily be sufficient

in dwelling houses where the service pressure is as high as 35 pounds

per square inch and when the pipes are unobstructed with rust. They are safe for use where brass pipe is used or for wrought iron or

steel pipe where the water is hard or noncorrosive. If the water is corrosive, wrought iron or steel pipes, even though galvanized, are

liable to rust and clog, so that their carrying capacity is diminished.

The rate at which rusting occurs depends upon the character of the

pipe, the corrosiveness of the water, the oxygen in the water, the

temperature, the quantity and velocity of water flowing through

the pipe, etc. Pipes carrying water which has been softened by the

use of lime often become incrusted, and some allowance needs to be

made for this factor.

The loss in capacity of iron or steel pipe through rusting is an

important consideration. Actual data are difficult to obtain hence

experiments on this subject would be useful. The following figures

show the approximate relative equivalents of pipe suitable for use under different conditions, but not all of the sizes given are commercially obtainable.

Nominal sizes

Brass or lead

pipe, any

water

Wrought-iron or steel pipe

Hard water Soft water

Corrosive water

or softened water

Inches Inches Inches Inches

Vs Vs Vi Vs

Y% b2 Vs M

Vs Vs H l

34 U l IX

1 l V4 i Yt
EXPLANATORY NOTES AND COMMENTS 223

NOTE 24. CAST-IRON PIPE

The committee has had no opportunity to investigate the quality

and weight of plumbing materials, and its recommendations are conventional, following the best average practice of the present time.

In the case of cast-iron pipe referred to in section 29 of Article III, reference is made to the American Society for Testing Materials

Standard Specifications for Cast-Iron Soil Pipe and Fittings. These

specifications call for the so-called extra heavy pipe, the dimensions

of which are based on a wall thickness of one-fourth inch, whereas

so-called standard pipe is based on a thickness of only one-eighth

inch. The committee is of the opinion that extra heavy pipe is unnecessarily heavy, but that standard pipe is too light for the

great majority of plumbing uses. The tonnage of iron which is used

in soil pipe is great enough to warrant a thorough scientific study of the whole subject in the interest of the best engineering practice and

the conservation of natural resources. The committee favors the

idea that the manufacturers of soil pipe, in cooperation with the

American Society for Testing Materials, should investigate the question of reducing the wall thickness of cast-iron soil pipe to some thick- ness between one-eighth and one-fourth inch, and if such reduction

is found desirable and practicable, to standardize the same and allow

cast-iron pipe of the new dimensions to take the place of the extra heavy and standard pipe now in common use. The committee also favors a careful study involving the manufacture of cast-iron soil pipe in lengths exceeding 5 feet. A thickness of three-sixteenths inch

for straight pipe has been suggested, but the committee is of the

opinion that the actual dimensions of both pipe and fittings should

be based on tests of strength and quality of metal and other involved

factors and should not be the result of compromise or off-hand opinion.

The committee recommends also that manufacturers of cast-iron

pipe continue to develop and market small sizes of pipe, namely,

1J and li inches in diameter.

NOTE 25. SIMPLIFICATION AND COST REDUCTION

The chief object of the simplifications and modifications of plumbing rules recommended by the committee has been to secure to the owner of a dwelling a better and more durable plumbing system and

to accomplish this, if possible, at a lessened first cost. It is believed

that if the recommended rules are generally applied both of these

objects will be secured, and that both of them will be of financial

value to the building owner. It would be interesting, if it were

possible, to express these benefits in dollars and cents, but because

of the widely varying plumbing regulations in different parts of the

country, because of different unit prices of materials, different

freight costs and labor costs, any attempted comparison would be far from accurate and would have only an illustrative value. In spite
224 RECOMMENDED PLUMBING REQUIREMENTS

of this fact, it seemed desirable to attempt a comparison to show the

effect of simplification on the first cost of plumbing.

Estimates were made of the probable number of dwellings likely

to be built during the 10 years following the first edition of the report

in order to replace old buildings, to make up for the lack of building

during the war, and provide for the increasing population.

The computations were interesting and suggestive. In many

localities the first cost of plumbing will be materially reduced if the

recommended code is adopted in place of those now in force. In

localities without plumbing codes the quality of plumbing will be

improved at a slightly increased cost. On the whole, the adoption

of the committee’s recommendation should save to the people who

build dwelling houses very large sums of money, the figures probably

amounting to several million dollars per annum. Furthermore, these

savings in first cost do not tell the whole story. Lessened bills for

maintenance and repairs and lower depreciation of the plumbing

systems are important matters to the householder, but there are no

data upon which to estimate them even approximately.

In this matter of cost the committee wishes to emphasize the fact

that good designing in plumbing will do as much, and, perhaps, more,

to save money to the house owner than simplified regulations. Plumbing systems should be made safe and permanent regardless of legal

requirements. The competent plumber can save money for the owner by advising him in the choice of fixtures and by laying out

the work carefully with full knowledge of the regulations. The

architect can save money by arranging rooms in which plumbing

fixtures are placed in such a way that fixtures are located near the

stacks and that the number of stacks is reduced to a minimum. In

order to have simple plumbing, the buildings themselves must be

simple.

The committee believes that uniformity in plumbing regulations

will tend to promote economy, as it will facilitate design, reduce

“ overhead” costs of plumber and architect, and lay the foundations

for standardization and simplified practice, and that the substitution

of the “ certificate of competency” for the “ license” will secure better

plumbing and ultimately reduce costs by developing greater competency in those who design and install plumbing.
PART IV.—APPENDICES

APPENDIX A.—MINORITY REPORT

When the tentative report of the first edition, to which reference

has been made, was prepared for distribution, one member of the

committee did not approve the stand taken by the rest in regard to the question of venting. His objections were presented in the form

of a minority report which was duly presented with the tentative

draft of the majority report for general discussion. His report is as follows

As a member of the subcommittee on plumbing of the Building

Code Committee, I regret to inform you that I find it necessary to express disagreement with the report of the committee only with

regard, however, to section 4 of the summary, which reads

4. Separate venting—that is, an individual vent for each trap—is not necessary. Group venting—that is, providing one vent for the group of fixtures—

is safe under certain conditions designated in the report. Adequate provision,

however, must be made for air circulation. I disagree with the committee in the first statement: “ Separate

venting—that is, an individual vent for each fixture—is not neces- sary.”

_ It therefore becomes necessary on my part to file a minority

report in connection with this matter.

As a journeyman plumber, with an experience upward of 35 years,

I feel free to say that I possess practical knowledge as to the utility

and necessity for direct or separate venting. My experience has

been such as to warrant an unshaken conviction in the popular

practice of modern high-grade plumbing for the employment of

direct or separate vent as a preventative against siphonic action.

It is freely admitted in the majority report that the official tests conclusively proved up the generally accepted theory on siphonage

that is to say, in a battery of fixtures the discharge of one was shown

to siphon the trap of another—and as a corrective, ventilation is recommended

It is further admitted that the tests were conducted with clear

water discharging through a clear system, and that resulted siphonage

might be intensified after constant household use, yet this actual

condition was given no consideration evidently in the expressed

opinion that direct or individual venting is not necessary. The experimental tests conducted by the committee were abnormal

in the sense that the bore of the traps and waste lines were perfectly

clear and, therefore, free of the fouling matter as found in the system

reduces the bore of the trap and , v the tests proved,

under certain conditions, that without vent a fixture filled to capacity

when discharged produced siphonic action in the trap.

A waste trap is in its final analysis a cesspool intended to arrest the

discharge of polluted air from the house dram into the room where the

fixture is installed. When the trap has siphoned either through the

20141°—29 16 225

MINORITY REPORT BY WILLIAM J. SPENCER

July 24, 1922.

subjected to use by occupants which naturally
226 RECOMMENDED PLUMBING REQUIREMENTS

force of the fixture it serves or that of another connected with the sys- tem, then it has ceased to function as a measure of protection against

the introduction of noxious gases. Under these circumstances it must be plain that we can not afford to take a chance with such a deli- cate and vital question as the public health, nor are we justified in

modifying a condition that has received popular approval for upward

of 40 years. Permit me to draw your attention to the fact that malignant epidemics have been practically eliminated in our country, and we stand

preeminently as the most healthful nation on the earth. Sanitation

lias played its part in not only banishing the terrors of plagues from

our country, but from those neighboring States over which we have

been privileged to exercise some measure of sanitary authority. For

nearly half a century the preponderating opinion of the thousands

upon thousands of those having to do with sanitation has favored

direct or separate vents as a means of preventing waste-trap siphonage.

Therefore, direct vents have been accepted as an integral part of a plumbing system. Those favoring high-grade plumbing have a right

to claim equal credit with all others whose efforts have been helpful in

producing the sanitary conditions herewith referred to. Loop venting as a substitute for the direct method is tantamount

to an acceptance of the minimum, and minimum rule is sometimes

dangerous. As an instance of proof, permit me to draw your attention to a certain theater 1 in this city that was erected under the minimum rule; that is, established conditions were not observed; cost, perhaps, was reduced by noncompliance with the building code,

without regard to the safety of patrons. You will recall that as a

result of failure to afford proper protection against accident nearly

100 lives were sacrificed.

This is one of hundreds of cases that might be cited where minimum

rule has exacted toll when chance was taken with human life, and yet

it is proposed in the majority report that a system of venting be

adopted likely to place in jeopardy the life of our entire urban population as against one which has assisted in the elimination of pestilential ravages.

In careful, orderly, well-kept homes loop or group venting may not

be considered dangerous, but in these hideous disease does not lurk. All homes, however, are not well kept; indeed, the contrary is the

case in many, while in many, many more filth abounds and pestilence

finds its origin in filth. For this reason the maximum rule has been

invoked in preference to the minimum, with credit to its sponsors.

Believing it to be unnecessary to further discuss my objection to

section 4 (mentioned above) contained in the summary of the majority report, I, therefore, feel called upon to submit to you this state- ment in the form of a minority report and protest to that filed by

Chairman George C. Whipple, under date of June 16, 1922, and beg

leave to add that in other respects the report of the subcommittee on plumbing meets with my approval.

(Signed) Wm. J. Spencer.

REPLY TO MINORITY REPORT

In replying to the minority report the committee wishes to explain

that when Mr. Spencer wrote his report the experiments made at the

1 The Knickerbocker Theater in Washington, D. C..
APPENDIX A MINORITY REPORT 227

Bureau of Standards had not been completed and bis resignation from the committee prevented him from having advantage of the

results subsequently obtained. Inasmuch as the recommendations

of the committee given in the tentative report remain practically un- changed in the final report as to the matter upon which he took

issue—namely, the necessity of venting every trap separately—and

as about half a dozen of those who commented on the tentative

report supported the minority report in its contention, the committee

thinks that a frank explanation of its position should be made.

The committee holds that every fixture trap should be protected

from siphonage and back pressure, and that air circulation be as- sured by means of a vent pipe. The committee is of the opinion

that complete venting of fixture traps is necessary, but that separate venting—that is, an individual vent for every trap—is unnecessary.

. The minority report held that an individual vent for each

trap is necessary. The issue is clear cut. In everyday practice, and that which has been approved for more

than 30 years, 2 sinks, 2 lavatories, 2 bathtubs, or 2 water-closets,

which are located on the same floor back to back on opposite sides

of partitions, have been served by a common waste and vent pipe.

Separate or individual venting of these fixture traps is not necessary. Adequate protection from self-siphonage and back pressure have been

afforded and air circulation assured. Again, it has been considered

good practice for years to stack-vent top fixture traps. This is sound

practice in which complete and adequate venting is provided, but

this could not be classed as separate or individual venting.

It is true that most of the experimental tests of the committee were abnormal in the sense that they were clear-water tests, but

there was consistency in the size of the fixture opening, the trap and

waste pipe in which scouring action was assured, and the probability

of fouling being reduced to a minimum. It should also be remembered that stoppages in the waste pipe of a fixture affect only that

part of the horizontal vent pipe above the fixture branch and below

its water level, and should stoppage occur in the waste or vent pipe

it would have the same effect on the separate or individual vent as on the common vent. The probability of a partially clogged branch

waste pipe serving a bathtub and a lavatory affecting the water seals of either trap would only occur on the coincident discharge of both

fixtures, with the result that the bathtub trap would be subject to siphonage. The length of time required to discharge a lavatory is so much shorter than that required to discharge a bathtub that the

possibility of the loss of trap seal in either fixture is almost negligible.

The partial stoppage of the horizontal waste pipe between the fix- ture trap and vent pipe will have a greater effect on the loss of trap

seal ’than individual or separate vents. If the fixture has a separate or individual vent, a partial stoppage in a long horizontal waste pipe

between the trap and its vent will be responsible for the loss ot the

trap seal. That part of the minority report which concerns the relation between plumbing and sewer air needs no comment, as the committee

expressed its view fully in chapter 1, to which Mr. Spencer agreed.

In fact, it should be noted that the minority report raised but one

controversial issue—the necessity of a separate vent for each trap.
APPENDIX B.—CORROSION OF METALS IN PLUMBING

SYSTEMS

[A memorandum prepared for the subcommittee on plumbing, by Prof. George C. Whipple]

The corrosion of metals is the greatest factor in shortening the life of plumbing systems. In spite of its importance and in spite of innumerable investigations and a vast amount of scientific study the

phenomena are still imperfectly understood, but out of the researches

conducted by physical chemists and engineers definite theories which

appear to be sound are taking shape. If these are substantiated

and further developed, they ought to he useful in many ways—in

improving the quality of materials, in helping to choose the best

metals for a given service, and in making better plumbing designs to avoid corrosive conditions. It is the purpose of this memorandum

to explain in as simple language as possible some of the newer theories as to how corrosion takes place.

Chemistry has greatly changed in recent years, and modern

scientific writers on the subject of corrosion employ terms which are not well understood by those who studied chemistry a generation ago. Only the fundamental conceptions will be described. No attempt

will be made to discuss the great variety of conditions under which

corrosion takes place. The following is a list of topics considered:

1. The rusting of pure iron in pure water.

2. The effect of nonferrous constituents of iron.

3. The effect of substances dissolved in water.

4. The corrosion of nonferrous metals.

5. Corrosion of different metals in contact.

6. The corrosion of iron in air.

1. THE RUSTING OF PURE IRON IN PURE WATER

Pure iron will rust in pure water exposed to the air. Water, as almost everyone knows, is composed of the elements hydrogen and

oxygen chemically combined. It used to be called H20, but there

are advantages in regarding it as H.OH. H. means an atom ofhydrogen, but if written H+

it means that the atom carries a charge of positive electricity and is called a hydrogen ion. In the same way Oil"

stands for what is called the hydroxyl ion, and the combination of these two atoms carries a negative electrical charge. When the two

ions join together, the positive and negative electrical charges neutralize each other, and the result is a molecule of water, H.OH, which

is electrically inert. But in water, even if it be distilled and redistilled, not all of the PI+ and OHions are united; some remain in the

water as free ions, which, because of their electrical charges, are in such a state of motion that they exert a pressure against the walls of the container, or against whatever is in the water, in a manner similar

to gas pressure. This separation of the ions is known as dissociation.

228
APPENDIX B—CORROSION Of METALS 229

It has been learned that pure distilled water contains something

like 1 gram H+ in 10,000,000 liters of water; hence, the amount of H+ m pure water resulting from dissociation is 0.0001 part per million

by weight. The number 10,000,000 may be written 107

; that is, 10

to the seventh power, 7 being the logarithm of 10,000,000. It will be

noticed that the power .7 is equal to the number of ciphers. Sorenson,. the Swedish chemist, first represented this hydrogen ion concentration by the letters Hp (hydrogen potential), but now it is usually

written pH; hence, the pH value for pure distilled water is 7. The

hydroxyl ion concentration of pure water is also 7, but in matters of

corrosion we are not so much interested in this as we are in FH, be- cause it is this little actively moving hydrogen ion which so aggressively attacks metals. Now, there may be hydrogen ions in water

derived from other sources, so that instead of 1 gram in every

10,000,000 liters there may be one in 100,000 liters, or one in 105

; that is, pH = 5 instead of 7. The more H+ there is the lower the

figure for pH.

Old time chemists used the words acid and alkaline very loosely.

The modern chemist is more exact. With him the “ hydrogen ion

concentration” stands for acidity and “ hydroxyl ion concentration”

stands for alkalinity. Pure water has a pH value of 7 (the hydroxyl

ion concentration also being 7) and is neutral. If the water contains

such substances that the pH is less than 7, the water is acid and the

lower the pH value the more acid it is. If the pH value is above 7, the water is alkaline and the higher the pH the greater the alkalinity.

The sum of the pH value and the pOH value is always 14. If the

pH value is 5.5, the pOH value is 8.5. Hence, modem chemists do

not use the expression pOH, but think of acidity and alkalinity both

in terms of pH, values lower than 7 indicating acidity, and values

higher indicating alkalinity. It will be noticed that water when it dissociates does not yield

atoms of oxygen and hydrogen but hydroxyl (OH-

) and hydrogen

(H+

) ions. When water is exposed to the air, it absorbs oxygen gas. Most natural waters contain “ dissolved oxygen.” Without it fish could not breathe. There are limits to the amounts of oxygen which

water can absorb. Water is said to be saturated with oxygen when it holds in solution all that it can hold at a given pressure and temperature. The higher the temperature the less oxygen it can hold in

solution and the higher the pressure the more it can hold. Books on

water chemistry give the saturation values for different temperatures

and pressures. Oxygen gas dissolved in water is invisible, but oxygen gas may be present in excess of the saturation point, in which

case it may appear as little bubbles of gas. The nitrogen of the air dissolves in water in the same way but not to the same extent. If cold water saturated with air is warmed, air bubbles will be driven

out. In a closed pipe or tank they may rise to the top as air. Let us now consider the phenomena involved in the rusting of pure

iron in contact with pure water. We have already been introduced

to the chief actors in the play—water (H.OH), the hydrogen ion

(H+

), and oxygen gas (02). Iron itself (called Fe, from the. Latin

word ferrum) needs no introduction, but let it be. said that just as the H+ has a pressure which pushes it against the iron, so Fe has a

solution pressure which makes it try to go into solution.
230 RECOMMENDED PLUMBING REQUIREMENTS

The action takes place as follows: Two aggressive little hydrogen

ions (H+

) move rapidly to the exposed metal and give their charges

to an atom of iron. This latter enters the water as a double-charged

iron ion (Fe++

), while the hydrogen atoms, their charges lost, remain

on, or are “plated out” on, the iron in a “nascent”; that is, a very

active chemical condition. The hydrogen thus plated out would

tend to protect the metal from further attacks of H+ were it not for the fact that dissolved oxygen (O) steps in, unites with the two hydrogen atoms forming water (H.OH) , and thus clears the metal for further

attacks. Meantime the iron ion (Fe++

) unites with two hydroxyl

ions (OH-

) to form the insoluble ferrous hydrate Fe (OH) 2

. As the

H+ attacks the iron, more water is dissociated, more H+ and OHare formed, and the corrosion proceeds. If the water is not exposed to the air and there is no other source of oxygen, the corrosion will stop

when the oxygen has been used up; but the oxygen does something

else. It, together with a molecule of water, unites with the ferrous

hydrate, Fe (OH) 2 , to form ferric hydrate, Fe2 (OH) 3 , a more thoroughly oxidized condition of the iron. It will be seen, therefore, that

the hydrogen ion and the dissolved oxygen are copartners in crime.

The hydrogen ion is the thief, the oxygen is the receiver of stolen

goods. It is not far from the truth to say that the hydrogen ion causes the corrosion, the oxygen causes the rusting. If the water

has little or no motion, most of the rust remains on the iron, covering

it with a yellowish-brown (partly ferrous) or reddish-brown (nearly

all ferric) coat of rust. If the water is in motion, some of the rust may be distributed through the water. There is an intermediate

oxide, magnetic oxide of iron, black in color. Different colors of

iron rust are due to the different mixtures of these oxides as well as

to various enmeshed impurities.

2. THE EFFECT OF NONFERROUS CONSTITUENTS IN THE IRON

In the foregoing paragraph it was said that the hydrogen ion was “plated out” on the iron, an expression often used in connection

with electric batteries. It is a fact generally known that if strips

of copper and zinc are put into a slightly acid water—that is, one

containing hydrogen ions—hydrogen ions will “plate out” on the

copper and zinc will be eaten away, the hydroxyl ion acting chemically on the zinc, forming zinc hydrate. This movement of the electrical

charges of the ions sets up a “current” of electricity. The metallic

elements may be arranged in a series, the higher in electromotive

properties at one end, the positive end, and the lower at the other, or negative end. If any two of the metals are put into water which

contains hydrogen ions, the latter will plate out on the metal lower

in the series, and the metal higher in the series will be corroded instead

of the other. The following is a list of the metals in the electromotive

series. The figures given in the last column are not very accurate,

and published lists do not agree exactly.
APPENDIX B CORROSION OF METALS 231

Potential series of metals

[Based on data given in “Electrolytic Dissociation Theory, ” by Talbot and Blanchard; 1907; and “Theoretical and Physical Chemistry,” by Bigelow; 1912]

Element

Positive end

Ion Potential Sodium .... . _ ... Na+

Ca++ Mg++

A1+++ Mn++

Zn++

Fe++ Ni+v

Sn++ Pb++

+2. 715 Calcium.. . .. .. .... Magnesium .. ... . .. . ... . .. +1. 550 +1. 276 +1. 075 + .770 + .340 + .228 + .192 + .148

Aluminum. . . _ Manganese..

Zinc .. .. . Iron. .. . ...

Nick6l . . .. . . ._ . .. Tin

Lead. .. . ... . Hydrogen. . . .. ... . .. _ -. ... ... H+ .000 Copper . .. ... . . _. Cu++ Hg+

Ag+ - .329 - .750 - .771 - .863 -1. 079

Mercury. . .. . . .. .. .. . _ Silver . . .... . . Platinum . ... ....

Gold Oxygen _ . __

Negative end

Note.—In the second column each cross after the chemical symbol stands for one “charge” of electricity on the ion. In the third column the + sign indicates that the solution is charged positively with respect to the metal. The potential of the hydrogen ion is taken as zero, and the potentials of the other metals are

referred to it. If referred to the “ calomel electrode ” the potential of hydrogen would be—0. 277 (though

—0.283 is, perhaps, more accurate)

.

The higher the potential the higher the solution pressure of the metal, and, in general, the greater the chemical activity.

Let us now suppose that there is a bit of zmc in the iron. The

hydrogen ions will plate out on the iron instead of on the zinc, because

the zinc is higher m the series. The zinc will be corroded and the

iron “protected.” This explains why a “zinc fish” used to be put

into a boiler to prevent corrosion, why zinc bars are attached to the

iron gates of the Panama Canal locks, and why pipe is galvanized

or otherwise coated with zinc. But suppose that the foreign substance in the iron is below iron

in the series, as, for example, a bit of mill scale. This time the

hydrogen plates out on the scale and the iron corrodes. Where such an impurity exists the action is more localized than elsewhere and the

corrosion extends deeper into the metal; a pit may be found in place

of a more general corrosion. Some kinds of organic matter also act

to produce local corrosion.

3. THE EFFECT OF SUBSTANCES DISSOLVED IN WATER

Pure water is not found in nature. If water is exposed to the air, it absorbs carbonic acid gas (C02). This gas reacts with the water

itself, forming carbonic acid (HCOs) and H+

, the hydrogen ion. Therefore, when C02 is dissolved the hydrogen ion concentration is increased; that is, the pH value is lessened. This increased hydiogen

ion concentration means that the force of the hydrogen ion attack on

iron is increased. Hence, it is said that C02 causes iron corrosion.

Just as before the H+ makes the attack, but this time the carbonic
232 RECOMMENDED PLUMBING REQUIREMENTS

acid (HCO~3) seizes the iron ion (Fe++

) and ferrous bicarbonate is formed, a substance soluble in water. In the absence of dissolved

oxygen this iron salt remains in solution, but oy^gen changes it to iron rust. Actually the chemistry of the process is somewhat more

complicated, but what has been said is typical of what usually occurs. In the same way hydrochloric acid (II Cl) added to water increases

the hydrogen ion concentration and so do all acids. In other words,

acids corrode iron because they yield H+ in water. If the hydrogen

ion attack is very severe, hydrogen may be plated out so fast that it leaves the iron as bubbles of gas without waiting for the depolarizing

action of dissolved oxygen. In other words, very acid waters may

corrode iron badly even if little or no dissolved oxygen is present.

This condition is seldom an important one in natural waters.

If lime (CaO) is added to water, the hydroxyl ions are increased,

the water is made alkaline, the hydrogen ions are decreased, (that is, the pH value increased) and the rusting action is checked. In a general way, therefore, alkalies tend to check rusting.

If an acid salt, such as aluminum sulphate or magnesium chloride

(found in sea water), is added to water it is dissociated and the hydrogen ion concentration of the water increased. Such solutions

increase corrosion.

Natural waters usually contain great varieties of chemical substances in varying proportions. There may be mineral and organic

substances which increase the hydrogen ion concentration ; there may

be substances which unite chemically with the iron. The matter is one

of great complexity. But from the standpoint of corrosion the

complex factors reduce themselves to the hydrogen ion concentration,

the dissolved oxygen, the hydroxyl ion, and the solubility of the iron

compounds produced by their action. It should be noted that both oxygen and carbonic acid are always

present in the atmosphere, that carbonic acid results from decomposition of organic matter and from the exhalations of animals, and

that both are lavishly distributed in nature. Most public water

supplies are saturated with oxygen or nearly so, and the hydrogen

ion concentration is the critical factor in corrosion. Thus soft waters

(pH values low) are more corrosive than hard waters (pH values

high), colored waters containing organic acids are corrosive, salty

waters are very corrosive, well waters which derive C02 from the

ground air are corrosive. On the other hand, oxygen is sometimes

the critical factor. If it is not present, rusting ceases ; as, for example,

in closed hot-water heating systems. Of two waters which have the same pH value one may be more corrosive than the other, for, as already stated, the dissolved mineral matter is an important factor,

but one which has not yet been sufficiently studied. From the

standpoint of water analysis the corrosiveness of water involves

chiefly the determinations of alkalinity, free C02 , the pH value,

dissolved oxygen, and the mineral constituents.

In most waters the determination of “alkalinity” gives a measure

of the carbonates and bicarbonates of calcium and magnesium.

The test is commonly made and is fairly accurate. The common test

for C02 is accurate in most cases, but sometimes far from accurate. The test for dissolved oxygen is quite accurate. The pH test is relatively new and fairly accurate. It is not often made but is coming

into use.
APPENDIX B CORROSION OF METALS 233

4. VARIOUS CONDITIONS AFFECTING THE CORROSION OF IRON

In general, heat increases the rate of corrosion of iron, because with

higher temperatures H+

is formed more rapidly and because the dif- fusion of oxygen in the water is increased. On the other hand, heating

water drives air (both oxygen and nitrogen) out of solution. In hot

water oxidation of ferrous iron takes place more rapidly. Rusty hot

water, sometimes called the red water plague, is due to the corrosion

of pipes. It is most likely to occur in soft waters, especially if colored or alum treated. It seldom occurs with hard waters, even though iron

pipes be used for water distribution.

An increased flow of water in a pipe increases rusting, provided there

is a sufficiency of H+

, because it brings larger volumes of dissolved

oxygen into contact with the iron. It follows from this that small

pipes will corrode and become filled with rust more rapidly than large

pipes. This is an argument for the liberal sizing of iron pipes in a plumbing system. Low velocities which allow the water to flow

quietly in parallel lines cause less rusting than higher velocities which

give a more turbulent flow, bring more oxygen in contact with the

sides of the pipe, and wash off the rust which is formed.

If metallic iron is fully protected from the water, corrosion will not

occur. Coating an iron pipe with coal tar, asphalt, or similar preparations is intended to do this and does so fairly well. In cast iron

the crystals of metallic iron are bound together by graphite and

cementite, which largely prevents rusting. In “genuine wrought

iron” the crystals of iron are protected somewhat better than in

steel, and hence the corrosion on the whole is less, but this is by no means always the case. Some steels resist corrosion better than some

genuine wrought irons, and the difference is probably not as great as

is commonly thought.

Service pipes are often protected from corrosion by lining them with

cement. This acts in two ways—first, by keeping the water away

from the metal; second, by reducing the hydrogen ions which reach

the metal, the cement being alkaline. It is an excellent method,

deserving further development.

Uniformity in the structure of the metal makes for uniformity in

corrosion. Impurities in the metal tend toward localized corrosion,

that is, pitting. Cast iron seldom pits. Genuine wrought iron and

steel both pit. The removal of mill scale from steel reduces pitting.

Pitting is worse than uniform rusting, because it causes leaks in pipes or holes in sheet iron.

Going back to the explanation of corrosion and rusting, let us

consider what happens to the rust formed. If the movement of water is rapid and turbulent, the iron rust may be carried along

with the water and, perhaps, deposited, somewhere. If the move- ment of the water is gentle, it may remain near the point of formation and form a sort of film or membrane. This membrane acts

as a sort of sieve. It allows the hydrogen ions and gases to pass

through but holds back iron rust. Consequently, iron rust accumulates back of the film. If a piece of iron pipe is placed in a trough

through which water is slowly flowing, this film forms quickly and

attains considerable size. It forms in the inside of a pipe as well

as on the outside. It may be easily ruptured by increasing the

flow of water beyond the critical velocity—that is, beyond the
234 RECOMMENDED PLUMBING REQUIREMENTS

point when flow in straight lines is changed to a turbulent flow. Even where the flow is rapid the film may form, but in this case

it holds close to the pipe or is localized. Iron rust deposited back

of such film accmnulates in “

tubercles.” After a time the “film”

becomes a substantial deposit of iron, but apparently continues to act as a sieve, letting aggressive hydrogen ions, oxygen, and water

pass to the iron pipe, but holding back the oxide of iron formed.

If water contains organic matter, it may be deposited on this film or precipitated by the sticky iron oxide on the walls of the pipe,

in either case tending to build up and hold together the deposit of iron oxide. The bacterial decomposition of organic matter yields

H+

, and hence tends to increase corrosion. Animal forms, such

as the fresh-water sponge or pipe moss found in large water mains,

also give off C02

. It is a well-known fact that the raw water pipes

of a nitration plant become more tuberculated than the pipes carry- ing filtered water, because in the latter case the pipes contain less organic matter and no pipe moss. On the other hand, some deposits

are thought to protect the metal against the action of the water.

5. THE CORROSION OF NQNFERROXJ3 METALS IN WATER

The principal nonferrous metals used by themselves in plumbing

systems are lead, zinc, tin, and copper, and they are obtainable in a

fairly pure state, while commercial iron always contains foreign

substances. In general, it may be said that pure metals resist corrosion better than two or more different metals mixed or alloyed

or in contact with each other. Reference to the potential series will show that zinc, lead, tin, and iron are higher in the series than

hydrogen. Their solution pressures are higher and they are more

susceptible to attack by the hydrogen iron. Copper, on the other

hand, is lower in the series than hydrogen and than most cf the

other metals used in plumbing work. Consequently, it is not

attacked by the hydrogen ion under ordinary conditions. Oxygen

is lower in the series than copper and therefore may attack it. Inas- much, however, as the copper oxide found is insoluble in water, it will protect the metal against further action unless it is physically

removed or dissolved by some acid or ammonia. The atmosphere

of a city usually contains carbonic acid and sulphurous or sulphuric

acid. These are absorbed by the rain and may thus play a part in

the corrosion of copper roofing. When copper is used in connection

with urinals, the ammonia will dissolve the copper oxide, exposing

the metal to further oxygen attack and thus contribute to its corrosion. In the same way the ammonia resulting from the droppings

of pigeons and other birds on roofs may contribute to the corrosion

of sheet copper. It is a well-known fact that copper is corroded

readily when ammonia is present. It will be noticed that zinc and

iron are much higher in the potential series than tin and lead. The

solution pressure of zinc and iron greatly overbalances the osmotic

pressure of their ions, a fact which adds to the facility with which

they are corroded; but there is another factor which has an important influence on corrosion, namely, the solubility of the substances

produced by corrosion. If the resulting salt is not readily soluble

in water, it is likely to be deposited upon the metal and will protect

it against further corrosion, while if the resulting salt is soluble in

water it will not be so deposited and the metal will be exposed to
APPENDIX B—CORROSION OF METALS 235

new attacks by the corroding forces. A few examples may serve to make this clear. When pure iron is put into water which contains free carbonic

acid gas but no dissolved oxygen, ferrous bicarbonate is formed and

this is soluble in water. This action may take place when an iron

pipe carries well water rich in C02 but poor in dissolved oxygen.

If oxygen is present in the water, the ferrous carbonate will be

oxidized to ferric hydrate (iron rust) and in so far as it deposits on

the metal it tends to protect against corrosion.

If the acid is hydrochloric instead of carbonic, ferrous chloride is formed and that, too, is soluble ; and in the same way sulphuric acid

may act on iron and form ferrous sulphate, also soluble. But in

the case of tin in water containing C02 the situation is different. There is no bicarbonate or even carbonate of tin formed. Any tin

salts formed are relatively insoluble. This is one of the reasons why

block tin is so commonly used in soda-water fountains to carry

water highly charged with carbonic acid.

The action of different waters on lead may be explained along

these lines. In soft waters, and especially soft colored waters, the

hydrogen ion content is large (that is, pH is well below 7). Lead

pipes exposed to such waters are attacked with the formation of lead

carbonate which is quite soluble. The result is that the metal is left bare for further attacks, while the water containing the dissolved

lead may cause lead poisoning if used for drinking. This is why

soft well waters high m C02 and poor in oxygen ought not to be

conveyed through lead pipes. If, however, the water has a high

alkalinity (high temporary hardness) and little carbonic acid, the

hydrogen ion content will be relatively low and the attack on the

lead will also be low. Under these conditions a basic lead carbonate

will be formed by the oxygen present. As this substance is insoluble,

it tends to coat the walls oi the pipe and protect the lead from

further corrosion. In such waters there may be deposits of calcium

carbonate which add to the protection. To some extent silicates in the water protect lead and also iron against corrosion.

Another example is worth mentioning because of its frequent

occurrence. When soft waters are treated with alum, as in the

process known as mechanical filtration and sometimes even with

slow sand filtration, their corrosive action on the seams of watercloset tanks has often been noticed. The addition of alum to water

changes calcium carbonate, an alkaline salt, to calcium sulphate

and also produces carbonic acid. The hydrogen ion concentration

is therefore increased (the pH value lowered) unless some alkali is also added. The soldered joints of copper-lined tanks are thus

likely to be more seriously attacked than by the same water without

alum treatment, zinc by virtue of its position in the potential series being dissolved. Zinc sulphate is more soluble in water than zinc

carbonate. If the latter is formed, as may be the case when the

calcium carbonate in the water is very large in proportion to the

calcium sulphate, it will not readily dissolve but remains on the

zinc as a protective coating. If, however, the calcium sulphate is large in proportion to the calcium carbonate, there would appear to be a greater tendency for zinc sulphate to be formed, which will dissolve in the water, leaving the metal free for further galvanic

action.
236 RECOMMENDED PLUMBING REQUIREMENTS

It is evident, therefore, that corrosion depends not only upon the

hydrogen ion alone, although that is the attacking agent, nor upon

the hydrogen ion and dissolved oxygen together, but also upon the

nature of the various acids, bases, and salts which may be present

in water in varying proportions. No wonder, then, that different

waters act differently upon different metals! No wonder that

experiments are conflicting! No wonder that plumbers are confused

in regard to a subject upon which even chemists themselves are confused

!

6. THE CORROSION OF DIFFERENT METALS IN CONTACT

It has already been explained that a bit of zinc in contact with

iron will cause the hydrogen to be plated out on the iron, the zinc

to be corroded, and the iron protected. In general, it may be said

that when any two metals are in contact in water containing hydrogen

ions, the one higher in the series will be the most corroded, while

the one lower in the series will be protected. Thus zinc protects

iron in a galvanized pipe, the zinc itself corroding. Thus also iron

protects lead in a lead-lined pipe, the iron itself corroding. Iron

protects tin; tin protects copper, the tin itself not being much

corroded, however, because the resulting salts of tin are rtdatively

insoluble. Even in such an alloy as brass the zinc protects the copper

and the larger the proportion of zinc the more the brass (really

the zinc in the brass) is corroded.

Another important principle is that a metal in the presence of water containing hydrogen ions will corrode more rapidly if in

contact with a metal lower in the series than if present in the water

alone. Thus, zinc will corrode more rapidly if in contact with iron;

iron will corrode more rapidly if in contact with lead; zinc will

corrode more rapidly if in contact with solder (tin and lead) than

if present alone. It is for these reasons that joints of different

metals are especially liable to be corroded. When two metals are thus brought into contact in acid water (one containing hydrogen

ions in excess of hydroxyl ions), the exchange of electric charges

of the ions causes an electric 11 current” (called m this case a galvanic

current), and it is sometimes said that the corrosion is due to galvanic action, a satisfactory explanation if one understands how the

galvanic action results from the potential differences of the elements

in the series. A few examples of this “ galvanic corrosion” may be cited. In

the case of a galvanized steel pipe, the protection of the iron would

be excellent if the zinc coating were perfect and entire. Actually

it is not perfect. For one reason or another the iron is exposed and

a contact of zinc and iron in water results. The zinc dissolves and

iron is left bare, and then corrodes as it would do if no zinc were

present. Galvanized pipes often have to be cut and threaded, and

where the cut is made the iron is laid bare. Water is carried by

capillarity into the threaded joint, a couple results, and corrosion

proceeds rapidly.

Tin plate, such as that used for roofing, is iron coated with tin. If the tin is removed at some spot the iron will rust faster than if it had not been tinned. If iron pipe is lined with lead and if a pinhole

exists in the lead coating, water may come in contact with both

metals, and if the water has a low pH value the iron will suffer a rapid local corrosion and a hole in the pipe may result. Similar
APPENDIX B CORROSION OF METALS 237

corrosion is likely to occur at the joints where it is difficult to secure a continuity of lead lining.

A brass coupling or a brass faucet attached to a piece of iron pipe

tends to increase the corrosion of the iron, and the effect is not limited

to the point of contact but may extend to a considerable distance

from the joint. In the case of brass piping, the fittings are of different

composition from that of the pipe itself; hence, brass piping not

infrequently gives out at the joints. It must not be forgotten that in most cases of galvanic corrosion

the action is greater in waters having a high hydrogen ion concentration (a low value of pH) . Thus, a water which has had its hydrogen ion concentration increased by the use of alum (sulphate of alumina) in connection with filtration may cause more severe cases

of galvanic corrosion than the same water before filtration. The

addition of liquid chlorine to water also tends to increase the hydrogen

ion concentration and hence to increase the galvanic corrosion, but

the quantity of chlorine added is usually very small.

7. THE CORROSION OF IRON IN AIR

Thus far only corrosion in water has been discussed. It remains

to consider the corrosion of metals in air, and as before iron may be

considered first. In perfectly dry air iron does not rust at all. Water is necessary. Air usually contains moisture, sometimes only a little, sometimes

enough to saturate or supersaturate it. Clean iron exposed to a

film of moisture rusts rapidly. An excellent example is the rust which appears on a bright iron rail of a railroad track a few hours

after a shower. The principles of rusting are the same as before, a

corrosive attack by and an oxidation by oxygen. Be it remembered that the air contains C02 and oxygen, that C02 is very soluble,

and that a thin film of water may dissolve oxygen from the air and

(although the rate of diffusion of oxygen in water is very slow)

transmit it quicldy to the metal because the film is thin. Thus,

although the C02 and oxygen in a drop of water may be small, the

drop may easily replenish its supply, if used up, from the atmosphere.

In a soil or drain-pipe deposits of organic matter decompose with

the formation of C02 , and this may be dissolved by a film of water

or drops of water attached to the pipe. Sulphur compounds may

also dissolve in drops and films of water on the interior of drain

pipes. Acid substances in the sewage or water discharged may

increase the hydrogen ion concentration of the water which remains

attached to the walls of the pipe. On the other hand, soap and grease

deposits may be alkaline and may protect against corrosion both

mechanically and chemically.

In horizontal waste pipes that are infrequent^ used drops of water

often collect near the top of the pipe, absorb C02 from the drain air, and cause vigorous corrosion in the upper half of the cross section.

If the drains are used frequently and are fully flushed, the collected

drops of water, rich in C02 , will be replaced by other drops lower in C02 , and rusting will be less rapid. When rust is once formed, its. porosity causes it to absorb moisture, so that rust on the interior of

drains is usually moist.

Vertical soil or drain stacks corrode less rapidly than horizontal

drains because moisture is less likely to collect upon them. Deposits;

of grease upon the inner walls of soil pipes tend to protect them from
238 RECOMMENDED PLUMBING REQUIREMENTS

corrosion by mechanically preventing water from reaching the metal.

Yet grease on decomposition yields organic acids, which like other

acids furnish hydrogen ions; and if, for any reason, the metal becomes

exposed, these hydrogen ions will attack it. Vent pipes are not

protected in this way hy grease deposits, and should small amounts

of grease reach them by accident corrosion would be stimulated

instead of being prevented. A small amount of grease may do a great amount of damage.

The air of cities contains more C02 than the air of the country.

City air also contains sulphurous acid gas (S02) from the burning

coal, and it seems probable that the use of oil instead of coal will

increase this still further. Mexican oil, at any rate, contains much

more sulphur than most of the American oils. Air near the seacoast

contains more salt than air farther inland, and so does rain near the

seacoast. The air of a seacoast city may be, therefore, much more

corrosive than that of an inland rural district. PRACTICAL CONSIDERATIONS

The above statement of the scientific theory of corrosion is by no means complete, no reference whatever being made to colloids and

surface phenomena; but even as it stands it might be regarded as too technical if it did not lead to certain practical results, which may

be stated as follows from the plumber’s standpoint

1. The plumber ordinarily has to take a public water supply as it is and adjust his choice of materials to it. In doing so, he should

remember that

(a) Acid waters are more corrosive than alkaline waters. The pH

value of a water is a measure of its acidity. If less than 7.0, the

water is acid; if more than 7.0, it is alkaline. Colored waters contain organic acids and usually carbonic acid.

(b) Soft waters are more corrosive than hard waters. Waters on

the Atlantic seacoast are generally softer and more corrosive than

the 'waters of the middle States.

(c) Well waters are usually harder than surface waters of the same

region, but they often contain carbonic acid. The corrosive powers

of well waters differ. If they are relatively soft and contain much

carbonic acid, they may attack iron or lead vigorously; but if they

are hard and the carbonic acid is low, the action may be slight or

negligible. If high in silicates, corrosion may be slight.

(d) There are two types of hardness in water—carbonate hardness

and sulphate hardness. The former tends to protect metal pipes

from corrosion, the latter does not.

( e) A water analysis is required to tell in advance whether or not

a water is corrosive. To-day the waters of most cities are analyzed

by State departments of health, but the analyses are made principally from a health point of view and do not always include the data

necessary to determine corrosiveness.

(j0 The rusting of iron by water requires both an acid and dis- solved oxygen. Most public water supplies are saturated with oxygen

and need the oxygen in order to be palatable.

2. The plumber should know the effect on the corrosiveness of water of certain processes commonly used for water purification.

(a) Aeration tends to remove carbonic acid, and thus reduces the

corrosiveness of water. On the other hand, it assures saturation

with oxygen, and if acids are present rusting will occur.
APPENDIX B CORROSION OF METALS 239

(b) The addition of whiting or lime neutralizes the carbonic acid

and reduces the corrosiveness of water.

(c) Softening water does not increase corrosiveness. Softening is never used unless the water is excessively hard.

id) The use of alum in connection with filtration tends to increase

corrosiveness. There are ways to counteract this to some extent,

but they are not always employed.

(e) The use of liquid chlorine as a disinfectant tends to increase

the corrosiveness of water, but the effect is usually unappreciable.

if) The process of “ deactivation” removes oxygen from water.

It tends to prevent rusting and corrosion. The addition of sodium

silicate to hot water is said to prevent the corrosion of pipes by

forming a film on the metal which prevents the attack of the hydrogen

ions.

3. Where the water is soft and contains much carbonic acid, or where for other reasons the water is corrosive, the choice of metals

is important.

id) For service pipes lead should be avoided because of the danger

of lead poisoning 1

; iron or steel should be galvanized or, what is better, protected by an inner cement lining.

(b) Iron or steel pipe used for distribution in the house should

be galvanized and made of ample size to allow for rusting. Lead

should not be used.

(c) Brass pipe used for hot-water distribution should contain

at least 67 per cent of copper. If it contains too large a percentage

of zinc, this metal is likely to be corroded in spots and at the joints,

causing the pipe to leak. As brass pipe does not clog with rust, smaller sizes may be used than with iron or steel.

( d) Cast-iron water backs rust badly, produce “red water,” and

may become clogged.

( e) Cast iron serves better for the drainage system than wrought

iron or steel.

4. Where the water is hard, the choice of metal is less important

and may depend upon other factors than corrosion. Even with

hard water cast iron serves best for drainage systems because of the

development of corrosive gases in the pipes.

5. In any water, but especially in soft corrosive water, two metals

when in contact are likely to be affected by galvanic action. The

metals are attacked in a definite order—zinc before iron, iron before

lead, lead before copper.

id) A brass which contains much zinc corrodes more than one which contains less. Bronze corrodes less than brass, and copper

corrodes less than bronze.

(b) Soldered seams in water-closet tanks are corroded by an

acid water. This is often noticed in an alum-treated water. Covering the seams with a wash or paste of tar or asphalt mixed with

cement should prove beneficial.

1 The committee, after careful consideration, learns that danger from lead poisoning generally exists only

in cases where the water is soft and is charged with “aggressive” carbon dioxide. The present tendency

is to free municipal water supplies of “aggressive” carbon dioxide, and where this is accomplished there is little danger from lead poisoning.
240 RECOMMENDED PLUMBING REQUIREMENTS

BIBLIOGRAPHY OF CORROSION

In 1909 the Carnegie Library, of Pittsburgh, published a Bibliography of Corrosion, and in 1915 a supplement to it was published

in the Proceedings of the Engineer’s Society of Western Pennsylvania. Recently (1923) a Bibliography of the Corrosion of Metals

and its Prevention was published by Nathan Van Patten, assistant

librarian, Massachusetts Institute of Technology, Cambridge, Mass.
APPENDIX C.—A STUDY OF AIR CURRENTS IN A HORIZONTAL WASTE PIPE

By Warren E. Howland

This memorandum covers a series of experiments made in the

laboratory of the department of sanitary engineering of Harvard

University as a part of a study of conditions which affect the corrosion

of metals used in plumbing systems. It relates to the movements of

air and gases in unvented horizontal waste pipes; that is, horizontal

waste pipes connected with a vertical stack at one end and having a

trap (or a plug) #at the other end. Four kinds of air movement may

occur in an unvented horizontal waste pipe. They are

:

1. Eddy currents induced by an upward draft in the vertical stack

to which the horizontal waste pipe is connected or by down rushes

of water in the stack.

2. Movements due to diffusion.

3. Convection currents in the pipe itself; that is, movements of the

air due to temperature differences.

4. Displacement of the air in the pipe by the discharge of the

fixture connected with it. . The experiments were not carried to such a point that definite

quantitative conclusions can be drawn, but the following inferences

appear to the writer to be sound: . . 1. Movements of air in the stack induce eddy currents of air m the

horizontal waste pipe for only a short distance from the stack, say, for 1 or 2 feet. . , 2. Diffusion is the most important factor in causing gases to spread

through or from the horizontal pipe. If gases, such as carbonic acid

gas or sulphuretted jryffrogen, are formed in a horizontal run, they

will become more concentrated in a long pipe than m a short pipe, the

maximum concentration varying approximately as the square of the

length of the pipe. In other words, gas will leave a short pipe more

quickly than a long pipe. On the other hand, oxygen from the stack

will diffuse into a long pipe with more difficulty than into a short

pipe. These statements are true regardless of the diameter of the ^ 3. Convection currents, caused by temperature

likely to be present throughout the whole length of the horizontal

waste pipe, but such currents are of small magnitude. ~

’ icement of the ah ^ * of water completely fills it ; but if the discharge

4. Displacement of the air in the pipe occurs whenever the discharge

water completely fills it; but if the discharge of water does not ffll the pipe, the displacement of air is also incomplete. (Ihis was not

s

‘"SgSSBySt’fo— m ih. of wjf.

ipes in plumbing systems are, first, the oxygen, nitrogen, and car- onfc acicl gas (present in small amounts) of the atmosphere; second

water vapor or humidity; third, carbonic acid gas, sulphuretted

hydrogenfan’d other gaseous products of the decomposition of organic

matter The experiments here described have involved measurements

showing the movement of several of these gases, namely, sulphuretted

hydrogen, carbon dioxide, and water vapor.

20141°—29 17 241
242 RECOMMENDED PLUMBING REQUIREMENTS

When the writer began his experiments in February, 1923, Dana E.

Kepner, then assistant in sanitary engineering in Harvard University,

had already done considerable work on the problem and had erected an experimental equipment which, with some additions, was used

throughout the experiments. Early attempts to study air movements by the use of sulphuretted hydrogen having proved unsuccessful, a method involving the absorption of carbonic acid from the

air b}^ solutions of lime water located at different places in the pipes was tried with good results. This method, together with the evaporation of water, formed the basis of the experiments described below.

Free use has been made of a report submitted by Mr. Kepner to Prof.

George C. Whipple, to both of whom acknowledgments are made.

DESCRIPTION OF APPARATUS

The first pipe used was of steel, inches in diameter and 25 feet long, closed at one end and connected at the other end by means of

Fig. 100.—Arrangement of piping for the study of air currents in horizontal waste pipes a sanitary tee with a 3-inch stack, 11 feet high. It had a slope of one-fourth inch to the foot. Crosses were placed at a point 1| feet from the vertical stack and thereafter at intervals of 3 feet to the

closed end. At first glass plates were placed over the ends of the

crosses and silk threads suspended in such a way that any large movements of air could be detected. All results were negative. The

glass plates at the tops of the crosses were, therefore, removed,

corks put in and sealed with paraffin. Screwed plugs were placed at the bottom of the crosses, so that glass cups of solutions could be

inserted. Figure 100 shows this arrangement. Afterwards two additional horizontal pipes, one 1J inches and one 2 inches in diameter and

26 feet long, were set up on either side of the original apparatus with

crosses at intervals of 3 feet. These pipes were connected to separate

stacks 11 feet long.
APPENDIX C AIR CURRENTS IN WASTE PIPES 243

EDDY CURRENTS

The rapid movement of air up the vertical stack produced eddy

currents for a short distance in the horizontal laterals. A glass tube

1 inch in diameter was placed in a nearly horizontal position, sloping

one-fourth inch to the foot, closed at the outer end and connected

with a 2-inch vertical stack. When air was moving up the stack,

movements could be detected by observing untwisted fine silk threads suspended from the top of the interior of the glass tube at distances not exceeding 7 inches from the vertical stack. Probably,

however, very slight movements of air extended farther in the pipe

than could be detected with the eye. This same apparatus was used for experiments with hydrogen sul- phide. Into the outer end was inserted a small porcelain boat of hydrochloric acid in which iron sulphide was dissolving and giving

off hydrogen sulphide. The tube was quickly stoppered. A draft was maintained in the vertical stack. ‘At the end of 15 minutes

moist lead acetate paper previously placed in the open end of the

pipe was examined for the metallic luster of lead sulphide. A similar

experiment was carried on simultaneously with another glass tube,

the open end of which was not exposed to a draft. The results showed that the draft in the stack hastened diffusion of the hydrogen

sulphide to the open end, but the difference between the two was not

great.

Indication of the presence of eddy currents was also given by the

evaporation of drops of water placed in rows on the interior of steel pipes and glass tubes. Two horizontal glass tubes closed at one end were filled with water and then emptied, leaving the interior wall

covered with drops. Over the end of one of these pipes a strong

draft of air was allowed to play. At the end of 24 hours the drops near the open end of the pipe and to a distance of 17 inches from the

end had evaporated. In the other pipe, over which no draft had

been allowed to play, the drops had disappeared to a distance of 10 inches.

This experiment was repeated with a 2-inch steel pipe, closed at one end with a water-sealed trap and connected to a 4-mch stack at the other end. A draft of 280 feet per minute was maintained in the

vertical stack. After 67 hours the drops in the horizontal pipe had

evaporated to a distance of 18 inches from the stack. In another

pipe similarly placed, but with no draft maintained in the vertical

stack, the drops had disappeared to a distance of 17 inches from the

stack. In this case not only was the pipe wet with drops of water,

but there was considerable water adhering to the rust particles on

the walls, as shown by their moist feeling when touched with the

finger. It may be concluded, therefore, that no appreciable drying

of the interior of the pipe took place beyond a distance of 2 feet when

the pipe was wet as often as once in 24 hours.

Experiments were made to discover whether or not minute particles in the air moving in the vertical stack would enter into the

horizontal branch and thus give evidence of air currents. Smoke

from smoky flames and smoke of ammonium chloride were used

both hot and cold. Particles of dust were also used and culture

plates for the detection of bacteria and molds were placed at intervals

in the horizontal branch. In the following case only was the presence
244 RECOMMENDED PLUMBING REQUIREMENTS

of particles which had come from the air in the vertical stack detected

in the horizontal pipe. Smoke from a smoky flame was allowed

to pass up the vertical stack for 24 hours. At the end of that time

white papers previously placed on the bottoms of the crosses as shown

on the before-mentioned sketch appeared as follows:

Paper in cross: 1? feet from vertical stack 100 per cent black.

3 feet from vertical stack 75 per cent black. 6 feet from vertical stack Trace of black.

All others No trace of black. This effect was undoubtedly due to the convection currents set up by the higher temperature of the ascending gases, which, being

lighter than the air in the horizontal pipe, tended to rise to the top

of the horizontal pipe and flow toward the dead end, depositing its smoke on the way. This condition would not, of course, exist in

actual plumbing systems.

It seems probable, therefore, that ^ddy currents are not present in

the horizontal pipe beyond a distance of about 2 feet from the vertical

stack. Such currents may cause a relatively complete displacement

of air in the first 1 £ feet of the pipe. This has the effect of reducing

by this amount that portion of the pipe within which diffusion and

convection are the chief causes of the movement of gases. Downrushes of water in the stack will produce suction or pressure

of the air in the horizontal pipe. The effect will be a movement of the

contained air, due to its change in volume and to the yielding of the

trap. Assuming that the drainage system is so designed that the

trap will not lose its seal, then the distance from the vertical stack

within which displacement mil take place may be expressed by the

following formula

Horizontal dis1 (yield of placement in the

[ =4 trap verair in inches j (tical, inches

[yield of trap

I 34

length of pipe in

feet. It has been computed that in the case of a horizontal pipe 15 feet long and with a 2-inch yield of the water in the trap only 3 horizontal

inches of air might be changed. Larger movements of water in the

trap and longer Horizontal runs might give proportionally larger dis- placements. This effect does not extend as far as the eddy currents before considered and is so small and infrequent that it may be entirely neglected.

DIFFUSION

Early experiments showed that diffusion is by far the most important factor in accounting for the movement of gases in horizontal

branches. The gases absorbed at various points in the horizontal

pipes were measured as described beyond. It was found that drafts

in the vertical stack had very little to do with this absorption. For

example, the placing of a fine wire screen at the end of the horizontal

pipe where it entered the vertical stack checked the eddy current but

did not prevent the absorption of gases by the various solutions placed

at intervals along the pipe. Other experiments confirmed the importance of diffusion.

Thirty-two experiments depending upon the absorption of carbon

dioxide—that is, carbonic acid gas—by water and five experiments

depending upon the evaporation of water were made. Only a few of
APPENDIX C—AIR CURRENTS IN WASTE PIPES 245

these experiments will be here reported. Following them the results of a mathematical analysis of the problem is given, but the computations themselves, being somewhat involved, will be omitted.

CARBON DIOXIDE EXPERIMENTS

Small cups, each containing 10 cubic centimeters of limewater, were placed at the crosses in the horizontal pipe, as shown by Figure

100. The absorption of carbon dioxide by these solutions was determined chemically. Allowance was made for the carbon dioxide originally present in the air.

. The diagrams (figs. 101 to 104, and 107)

show at each cross in the pipe the amounts of sulphuric acid which was

found by experiment to be equivalent to the carbon dioxide reaching

that point through the stack from the outside air. The amount of

carbon dioxide absorbed at each joint as shown is a measure of the

concentration of the gas at that point. The diagrams, therefore, show

the variation in concentration of carbon dioxide throughout the pipe.

The concentration of gases coming into the pipe diminishes rapidly on the way back from the open end and finally reaches a point beyond

which further change in concentration is not noticeable. This limit

of the noticeable effect of diffusion extends not much farther with a

higher concentration of gas in the vertical stack than with a lower

concentration. In experiment A (fig. 101) the air in the stack contained 7.6 parts per 10,000 of carbon dioxide. Absorption of this gas

by the limewater in the cups was noticeable for 9 feet in the pipe. In

experiment B (fig. 102), the air in the vertical stack contained 5.8 parts per 10,000 of carbon dioxide and the absorption was noticeable

for about the same distance. In other experiments with li-inch, 1 J- inch, and 2-inch pipes the distance within which absorption took

place varied from 3 to 9 feet and averaged about 6 feet. There was no

consistent relation between this distance and the diameter of the pipe.

The time allowed for absorption made very little difference with

the shape of the curve. It increased the absorption within the limits

of diffusion but did not increase the limits themselves. This is shown

by experiments A and C. The former had a duration of 20J hours

and the latter 44 hours, all the other conditions being practically the

same, yet the results were almost identical as to the distance within

which diffusion took place.

In order to show that diffusion was more active in the 6 (3 to 9) feet near the stack than at greater distances, an experiment was made (experiment D) in which the absorbing solutions near the stack

(at a and b) were omitted. Comparison was made with experiment

E (fig. 104) in which these cups were retained, other conditions remaining the same. If the absorption in cups c and d of experiment D had

given results like those of cups a and b of experiment E, the conclusion

would have disproved what has been said above. It will be observed,

however, that they did not do this, a fact which supports the contention that diffusion is limited to the distances mentioned.

Not content with the simple experiments above mentioned, even though they corroborated each other in a general way, a mathematical

analysis of the problem of diffusion in a closed pipe was made and its results compared with those of the experiments. This comparison

may be seen on the diagram which gives the results of experiment C. The agreement was striking and furnished additional proof of the

correctness of the deductions from the experiments.
246 RECOMMENDED PLUMBING REQUIREMENTS

>*

>v ^

* ^ a

,0 vj ,

i!

a

\b

i

£ &

A

0 -3 6 9. /a. /s /&. zr. a#

s$tock D/stance from the stock m feet Oosecf

£nd.

Fig. 101.—Experiment A. Diffusion of carbon dioxide in a 1^-inch horizontal branch connected with

vertical stack. Time, 20 1 hours. No forced draft

Stock D/stance from the stack m feet C/osed

fhct

Fig. 102.—Experiment B. Diffusion of carbon dioxide in a 1-Hnch horizontal branch connected with

vertical stack. Time, 48 hours. Draft in stack; 180 feet per minute
APPENDIX C—AIR CURRENTS IN WASTE PIPES 247

Fig. 103.—Experiment C. Diffusion of carbon dioxide in a 11-inch horizontal branch connected with a

vertical stack. Time, 44 hours. No forced draft

S'**

Is

a

**4

H

« « «

O & , t $

rth4 c \ d

e. g.

: i

o

*Stac/c

3 3

Distance

9. from

/2. fh&

is m

stack m feet

24

Closed

End

Pig 104 Experiments D and E. Diffusion of carbon dioxide in a 2-inch horizontal branch connected with a vertical stack. Time, 48 hours. No forced draft
248 RECOMMENDED PLUMBING REQUIREMENTS

A formula was set up showing the variation of the concentration of carbon dioxide throughout the pipe for a particular set of conditions.

x = distance from the closed end of the pipe.

K= diffusion constant for the gas in question.

A = area of cross section of the pipe.

Q = a constant expressing the rate of absorption of the gas. C= concentration of the gas at any point.

C0 = concentration of the gas at the point where x equals zero. There are two principal ways in which the length of the pipe

affects the concentration of the gas in the pipe. In the case of a

gas produced uniformly throughout the length of the pipe, the greater

the length of the pipe the greater will be the concentration of the

gas throughout the whole pipe. For any given pipe, whether absorbing or emitting a gas, the extent to which diffusion will equalize

the concentration within and without the pipe is much greater in the

section of the pipe near the open end than in other parts of the pipe.

For any particular case there is a limit beyond which diffusion can

not be relied upon to remove appreciable amounts of an evolved

gas or to convey into the pipe appreciable amounts of gases from the

stack. The factors which determine the concentration of gases in a horizontal pipe and which, therefore, will determine the limit of diffusion are the following:

1. Length of the pipe.

2. Ratio of the rate of evolution (or absorption) of the gas in the

pipe to the cross-sectional area.

3. The diffusion coefficient of the gas.

4. The concentration of the gas in the air of the stack.

The diffusion will depend largely upon the length of the pipe and

the ratio of the evolution of the gas in the pipe to the area of cross

section; that is, to the first two items mentioned above. The experiments made were confined to a particular value of this ratio; that is, the absorption of carbon dioxide by limewater in a cup of definite

size. If larger cups had been used, the limit of absorption would

theoretically have been less than was observed; if smaller cups

had been used, it would have been larger. If the ratio referred to could be actually determined in any case, an exact limit could be

computed; and if further experiments are made, they should be

devoted to a study of this ratio of gas evolution (or absorption)

to the cross section of the pipe.

Theory and experiment, therefore, agree in showing that diffusion

is the really important element in the movement of gases in a long,

horizontal pipe closed at one end. Theory also shows that if a gas

such as carbon dioxide is produced uniformly along the pipe, as may

be the case when deposits of organic matter decompose, the maximum

concentration of this gas in the pipe will vary as the square of the

length of the pipe; that is to say, in a pipe 20 feet long the maximum

concentration will be four times as great as in a pipe 10 feet long,

if the short length near the stack wherever eddy currents occur be

neglected.
249 APPENDIX C AIR CURRENTS IN WASTE PIPES

EVAPORATION OF WATER

The same cups that were used in the previous experiments were

filled with 10 cubic centimeters of distilled water and exposed to the air of the pipe as before. The cups of water were weighed

before and after exposure and the loss in weight, or evaporation,

recorded. Experiments F and G (figs. 105 and 106) represent

typical results obtained by this method.

Calculations revealed the fact that more water was evaporated

from the cups than the air in the pipe was able to retain in the form

of vapor. Either the moisture must, therefore, have been removed

from the air or the air itself must have been replaced by fresh air. According to the. other experiment made, it seems unlikely that

the air

_ of the pipe could have been thus replaced. Moreover,

calculations showed that diffusion could not have removed as much

water vapor as was produced. It is probable, therefore, that the

rust on the interior of the pipes absorbed some of the moisture from

the air after being evaporated from the cups. The absorption of moisture by the rust on the pipe would explain the absence of a

critical distance from the stack within which diffusion occurred.

CONVECTION CURRENTS

Under certain conditions temperature differences will cause convection currents in horizontal pipes. This has already been mentioned

in connection with the hot smoke experiments. When the air in

the stack is warmer than that in the horizontal branch, it will tend

to enter the branch and push inward along the top, displacing the

cooler air which will leave the branch along the bottom. In this way a convection current may be set up. Differences in temperatures

along the horizontal pipe, such as may occur when a pipe extends

through a warm room and the cooler atmosphere of a partition, may

also set up local convection currents. These would have much the same effect as diffusion currents. Some of the experiments made

show that this phenomenon occurs. The effect of convection currents is shown by experiment IT

(fig. 107) , which ran for five days. In this case there was a relatively

greater absorption of carbon dioxide at cups Ti and i because these

cups were getting the relatively fresher air (higher in carbon dioxide)

which had been passing along the top of the pipe for some distance.

In other words, the carbon dioxide w

r as kept away from the absorbing

solutions at the bottom of the pipe until it had reached the last cup, i. This same effect is shown to a less degree in experiments B and D.

These temperature effects, however, are slight and erratic and can

not be expected to play an important part in the movement of gases

to or from the pipe.

DIFFUSION OF GASES THROUGH WATER-SEAL TRAPS

The rate at which a gas such as hydrogen sulphide in a drain

below a trap will pass through the water seal into the atmosphere of a room depends upon four factors—the amount of gas in the drain, the

cross section of the trap, the developed length of the trap seal, and

the character of the gas with respect to its power of diffusion, tho-
250 BECOMMENDED PLUMBING BEQUIBEMENTS

Stock O/sfanee from the stock //? feet Cfaced

End.

Fig. 105.—Experiment F. Evaporation of water in a l|-inch horizontal branch connected with a vertical stack. Time, 46 hours. No forced draft

Stack Distance from the stock in feet Ctosed

End.

Fig. 106.—Experiment G. Evaporation of water in a 1^-inch horizontal branch connected with a vertical stack. Time, 48 hours. Forced draft; 100 feet per minute
APPENDIX C-AIR CURRENTS IN WASTE PIPES 251

latter being known to chemists. The deeper the seal the less gas

will pass; the greater the cross section of the trap and the larger

the amount of gas in the drain the more gas will pass through. There

is one other factor which may influence diffusion, namely, the time

the water remains in the trap. The longer the time, up to a certain

limit, the greater the amount of diffusion.

. Computations for hydrogen sulphide, based on theoretical considerations, showed that the danger of this gas diffusing through the

water from the drain to the room atmosphere is negligible. To make

this computation required some experimental work.

5f^sck Distance from the stack in feet Closed

End

Fig. 107.— Experiment H. Diffusion of carbon dioxide in If, If, and 2 inch horizontal branches connected with vertical stacks. Time, 120 hours. Forced draft; 180 feet per minute A 2-inch half S trap was tightly sealed on the side which would

ordinarily be toward the drain. Two rubber tubes were led into the

interior of the trap through its open end, their openings being very

near to the closed end of the trap. The trap was then mounted in a

horizontal position and water poured into it until there was a depth

of seal of about 2 inches. Hydrogen sulphide was then led into the

sealed arms through one of the rubber tubes, the other rubber tube

being used to relieve the pressure. After one and one-half hours a

distinct odor could be detected by placing the nose near to the water

in the open end of the trap. This indicated that the gas had diffused

through the water.
252 RECOMMENDED PLUMBING REQUIREMENTS

Probably the concentration of the gas in the sealed arm was not

far from 100 per cent. This condition would never occur in practice.

If the concentration of hydrogen sulphide in the sewer air were 1 part

per 10,000, an amount probably larger than ever occurs, the odor

from the water of the trap on the room side would be far too small to be detected and may be regarded as entirely negligible. It may be

safely said that the danger of odoriferous gases passing through a water seal trap by diffusion is negligible.

The generation of gases by the decomposition of organic material

collected in the trap itself would be of greater importance. These

would be proportional to the amount of decomposable matter caught

in the trap. The larger the volume of water in the trap the less would

be the concentration of the gas and the odor given off for a given

amount of material. A large, deep trap, however, would tend to retain more sediment and offer a larger interior surface for bacterial

growth. Such a trap, therefore, might slightly increase the odor on

the room side. More important than odors diffusing through the trap or being

generated in the trap are those due to the decomposition of organic

matter deposited on the walls of the pipe between the fixture and

the trap and on the walls of the trap itself which may be exposed

when the trap seal is reduced.
APPENDIX D—STANDARD SPECIFICATIONS OF THE AMERICAN SOCIETY FOR TESTING MATERIALS

[Affiliated with the International Association for Testing Materials]

CLAY SEWER PIPE ' Serial Designation, C 13-24

[Issued as tentative, 1917; adopted in amended form, 1920; revised, 1924] 1. These specifications cover clay products intended to be used

tor the conveyance of sewage, industrial wastes, and storm water

2 Sewer pipes furnished under these specifications shall be of a

single class to be designated “A. S. T. M. Clay Sewer Pipe.” MATERIAL AND MANUFACTURE

3* W Clay pipes shall be manufactured from surface clay, fire clay

or shale, or a combination of these materials.

(b) Surjace clay is an unconsolidated, unstratified clay,2 occurring on the surface.

(c) Fire clay is a sedimentary clay 2 of low flux content. Note.—It is usually associated with coal measures.

(d) Shale is a thinly stratified, consolidated sedimentary clay 2 with well-marked cleavage parallel to the bedding.

(e) The materials shall possess such physical and chemical properties that when molded into pipes and subjected to a suitable temperature the product will be strong, durable, and serviceable, free from

objectionable defects, and in compliance with these specifications

and tests. CHEMICAL TESTS AND REQUIREMENTS

4. The consumer or purchaser may prescribe in advance special

chemical requirements in cases where industrial Wastes have marked

acid or alkaline character, or are of abnormally high temperatures.

He may make use of chemical analysis of the pipe material to ascertain

whether these special requirements are met. The presence of visible grains or masses of caustic lime, iron pyrites, or any other materials

which cause slaking or disintegration shall be a cause for rejection.

PHYSICAL TESTS

5. The physical tests of pipes shall include crushing test, hydrostatic pressure test, and absorption test.

6. The specimens to be tested shall be selected by the purchaser

or his representative at the point or points designated by him when

placing the order. The manufacturer or seller shall furnish speci- mens for test, without separate charge, up to 1 per cent of the number

of pipes to be delivered or furnished in each size of pipe, except that in no case shall the number of representatives furnished be less than five.

7. (a) Failure of 20 per cent of the specimens to meet the requirements of any of the tests imposed shall result in rejection of all the

1 Under the standardization procedure of the society, these specifications are under the jurisdiction of the A. S. T. M. Committee C-4, on Clay and Cement-Concrete Pipe.

2 The definitions for the terms “surface clay,” “fire clay,” and “shale” are based upon the following

definition for the term “clay”: Clay—An earthy or stony mineral aggregate consisting essentially of hydrous silicates of alumina, plastic when sufficiently pulverized and wetted, rigid when dry, and vitreous when burned at a sufficiently high temperature. 253
254 RECOMMENDED PLUMBING REQUIREMENTS

pipe in the shipment or delivery, corresponding to the sizes thus

failing to comply; except that in the event of 20 per cent of theh

specimens in any size failing to meet the requirements, the manufacturer or seller may, with the consent of the consumer or purchaser,

furnish for test without charge additional specimens from the same

shipment to be selected as specified in section 6. In case more than

80 per cent of the specimens tested, including those first tested,

shall show substantial compliance for each of the various tests per- formed, then the entire shipment or delivery for this size shall be

accepted; otherwise it shall be rejected.

(6) In addition to the foregoing requirements, failure of individual

specimens to develop 75 per cent of the average crushing-strength

requirements shall be cause for rejection of the shipment, but the

seller may cull the pipe and submit the balance of the shipment for

retest, and, if the shipment then passes all the requirements of these

specifications, it shall be accepted.

8. The specimens of pipes shall be sound, full-size pipe. They

shall first be freed from all visible moisture. When dry, each specimen shall be weighed, measured, and inspected. The results of

these observations shall be recorded and preserved as shown in

Table 1. 9. Specimens which, when placed in a vertical position, do not

give a metallic ring when struck with a hammer, or are observed to have fire cracks or other defects in form or dimensions in excess of

the limits permitted in these specifications, shall be discarded and

replaced with additional specimens from the shipment.

(.4) Crushing tests 10. (a) Any prime mover or hand power which will apply the

load at a uniform rate of about 2,000 pounds per minute, or in increments of not more than 100 pounds at the same rate, may be used in

making the test.

(b) The pipe shall not be allowed to stand under load longer than

is required to apply the load and to observe and record it. 0c ) The testing machine shall be substantial and rigid throughout,

so that the distribution of the load will not be affected appreciably

by the deformation or yielding of any part.

(i) The bearings and the specimen shall be accurately centered so

as to secure a symmetrical distribution of the loading on each side

of the center of the pipe in every direction.

(e) The load shall be applied until the pipe yields by cracks passing

through the shell. 11. (See figs. 1, 2, and 3.) Except as otherwise hereinafter specified,

the pipe to be tested shall be supported by a metallic knife bearing

1 inch wide and extended from a point just back of the socket to the

spigot end of the pipe. Before the pipe is placed a fillet of plaster of Paris and sand 1 inch wide and thick enough to compensate for all the inequalities of the pipe barrel shall be cast on the surface of the

knife-edge bearing. The pipe shall be placed upon the fillet while the

plaster of Paris is still somewhat plastic. The load shall be applied

through an upper knife bearing of the same size and length as the

lower bearing. A plaster-of-Paris fillet, 1 inch wide, shall be cast along the length of the crown of the pipe to equalize the lower bearing

before the upper one is brought into contact.
Table

1

.

—

Dimensions

,

etc.,

of

clay

sewer

pipe f

urnished

as

test

specimens

APPENDIX D PLUMBING MATERIALS 255

Remarks

Internal

diameter

(inches)

Socket

jejnoz

-i joh

IB0IJJ9A

Back

of

socket pjuoz

-i joh

IT30TJJ8A

Spigot pqnoz -won

IBOXJJ0A

Thickness

of

socket

(inches)

9PIS

®PJS

U.AVOIQ

JJ8Anj

Thickness

of

spigot

(inches)

®PTS

9PTS tmoiQ

JJ8AUJ

(j98j) qjSnaq;

(spunod) iqStQAi

(saqom) azis fBunno^j

Aiojo,ej jo noij'eoo'T

jajnjo'ejmrejA

jeqnmu qof

o^CE jaqmnu nampadg

|
256 RECOMMENDED PLUMBING REQUIREMENTS

Both of the bearings shall be sufficiently rigid to transmit and re- ceive uniform loads throughout their lengths without deflection and

shaM be so attached to the machine as to transmit and receive the

maximum stresses produced by the tests without lost motion, vibration, or sudden shock.

At the option of the consumer or purchaser the crushing test may

be applied with sand bearings or with two or three edge bearings.

The crushing strength shall be calculated by dividing the total load required to break each pipe by the net inside length of the barrel

of the pipe, measuring from the bottom of the socket to the end of the spigot.

12. (See fig. 2.) When three-edge bearings are used, the ends of

each specimen of pipe shall be accurately marked in halves of the

circumference prior to the test. The two lower bearings shall consist of two wooden strips with

vertical sides, each strip having its interior top corner rounded to a radius of approximately one-half inch. They shall be straight and

shall be securely fastened to a rigid block with their interior vertical

sides 1 inch apart.

The upper bearing shall be a wooden block, straight and true from

end to end.

The test load shall be applied through the upper bearing block

in such a way as to leave the bearing free to move in a vertical plane

passing midway between the lower bearings.

In testing a pipe which is “out of straight,” the lines of the bearings

chosen shall be from those which appear to give most favorable conditions for fair bearings.

13. (See fig. 3.) When sand bearings are used, the ends of each

specimen of pipe shall be accurately marked prior to the test in

quarters of the circumference. -Specimens shall be carefully bedded,

above and below, in sand for one-fourth the circumference of the

pipe measured on the middle line of the barrel. The depth of bedding

above and below the pipe at the thinnest points shall be one-half the

radius of the middle line of the barrel. The sand used shall be clean and shall be such as will pass a No. 4

sieve. The top bearing frame shall not be allowed to come in contact with

the pipe nor with the top bearing plate. The upper surface of the

sand in the top bearing shall be struck level with a straightedge and

shall be covered with a rigid top bearing plate, with lower surface a

true plane, made of heavy timbers or other rigid material capable

of distributing the test load uniformly without appreciable bending.

The test load shall be applied at the exact center of this top bearing

plate in such a manner as to permit free motion of the plate in all directions. For this purpose a spherical bearing is preferred, but two

rollers at right angles may be used. The test may be made without

the use of a testing machine, by piling weights directly on a platform

resting on the top bearing plate, provided, however, that the weights

shall be piled symmetrically about a vertical line through the center

of the pipe, and that the platform shall not be allowed to touch the

top bearing frame.

The frames of the top and bottom bearings shall be made of timbers

so heavy as to avoid appreciable bending by the side pressure of
APPENDIX D- -PLUMBING MATERIALS 257

20141°—29 18

l-'-

'

i

i. I

Upper

Side

View.

Bearing

Frame.

Fig. 1

.—

Knife

or

two-edge

bearings

Fig.

2.—

Three-edge

bearings

Fig.

3.—

Sand

bearings
258 RECOMMENDED PLUMBING REQUIREMENTS

sand. The interior surfaces of the frames shall be dressed. No

frame shall come in. contact with the pipe during the test. A strip

of cloth may, if desired, be attached to the inside of the upper frame on each side, along the lower edge, to prevent the escape of sand

between the frame and the pipe.

14. The crushing test shall ordinarily be applied to not less than

75 per cent of the specimens received for testing purposes.

15. Pieces of the crushed pipe may be used as specimens in making

the absorption test.

( B) Hydrostatic test

16. Sound full-size pipe not exceeding about 25 per cent of the

specimens received for test in each size of pipe, shall be tested for

leakage under internal hydrostatic pressure. The ends of the pipe shall be tightly closed by wooden or metallic

bulkheads or covers faced with rubber or leather so that no leakage

shall occur through the covers at the test pressure. One cover shall be provided with a three-fourths inch wrought-iron nipple passing

through the cover and held securely in place and made water-tight by means of lock nuts and washers or gaskets. The outer end of the

nipple shall be connected with a pump discharge or water service

line.Water pressure, as measured by a standardized gauge attached

to the delivery pipe close to the specimen, shall be internally applied

to the specimen as follows

5 pounds per square inch for 5 minutes.

10 pounds per square inch for 10 minutes.

15 pounds per square inch for 15 minutes.

The specimens shall show no leakage under these pressures. Moisture appearing on the surface of the pipe in the form of patches or beads adhering to the surface shall not be considered leakage.

( C) Absorption test 17. The specimens shall be sound pieces, with all edges broken,

and may be from pipes broken in the crushing or other tests. They

shall be from 12 to 20 square inches in area and shall be as nearly

square as they can be readily prepared. They shall be free from

observable cracks, fissures, laminations, or shattered edges.

18. Preparatory to the absorption test, the specimen shall be first weighed and then dried in a drier or oven at a temperature of not

less than 110° C. (230° F.) for not less than three hours. After

removal from the drier the specimen shall be allowed to cool in dry

air to a temperature of20to25°C. (68to77°F.) and then reweighed.

If the specimen is comparatively dry when taken, and the second

weight closely agrees with the first, it shall be considered dry. If the specimen is wet when taken, it shall be placed in the drier for a drying treatment of two hours and reweighed. If the third weight

checks the second, the specimen shall be considered dry. In case of

any doubt, the specimen shall be redried for two-hour periods, until

check weights are obtained.
APPENDIX D PLUMBING MATERIALS 259

19. The balance used shall be sensitive to 0.5 g when loaded with

a kg, and weighings shall be read to the nearest gram. When other

than metiic weights are used, the same degree of accuracy shall be

obtained.

20. The specimen after final drying, cooling, and weighing shall be

placed with other similar specimens in a suitable wire receptacle,

packed tightly enough to prevent jostling, covered with distilled water or rain water, raised to the boiling point and boiled for five hours, and then cooled in water to a final temperature ofl0tol5°C

(50 to 59° F.). 21. The specimen shall be allowed to drain for one minute and,

the superficial moisture having been removed by towel or blotting

paper, placed upon the balance.

22. The test result shall be calculated as percentage of the initial dry weight.

23. One specimen shall be tested of each pipe broken in the crushing test. 24. The results shall be reported separately for each individual

specimen, together with the mean for all the specimens from the same shipment of pipe.

25. Each specimen shall be marked so that it may be identified

with the pipe used in the crushing test from which the specimen was

taken. The marking shall be applied so that the pigment used

shall not cover more than 1 per cent of the total superficial area of the specimen.

PHYSICAL TEST REQUIREMENTS

26. The test requirements of clay sewer pipe shall be as given in Table 2. The individual results of the various tests for each size of pipe and for each shipment, class, and mill shall be tabulated separately, so as to show the percentage which fails to comply with the

requirements of each test.

A. S. T. M. SIZES AND DIMENSIONS

27. Pipes shall be furnished of the sizes, internal diameter, and

with the dimensions given in Tables 3 and 4. Where several lengths

are mentioned in the table the consumer or purchaser shall indicate, at the time of purchase, which lengths shall be furnished, and unless

so indicated the manufacturer shall furnish such lengths as he may

elect. 28. The permissible variation from the dimensions given in Table 3

shall not exceed those stated in Table 4. Where the thickness of

barrel is increased beyond that given in Table 4 in order to meet

the specified requirements of strength, the diameter at inside of

socket shall be increased by double the increase in thickness of

barrel. Pipes intended to be straight shall not have variation in alignment of more than one-eighth inch per foot of length.

WORKMANSHIP AND FINISH

29. Pipes shall be substantially free from fractures, large or deep

cracks and blisters, laminations, and surface roughness.
260 RECOMMENDED PLUMBING REQUIREMENTS

Table 2.—Physical test requirements of clay sewer pipe

Average crushing

strength

Internal diameter Knife-edge 1 and three- edge 2 bearings Sand

bearings 3

Maximum

absorption

Inches Pounds pertin. ft. Pounds per

tin. ft. Per cent 4 1,000 1,430 8

6 1,000 1,430 8

8 1,000 1,430 8

10 1, 100 1,570 8

12 1,200 1,710 8

15 1,370 1,960 8

18 1,540 2,200 8

21 1, 810 2, 590 8

24 2,150 3, 070 8

27 2, 360 3, 370 8

30 2,580 3,690 8

33 2, 750 3,930 8

36 3,080 4, 400 8

39 3,300 4, 710 8 42 3, 520 5,030 8

1 See section 11. * See section 12. 3 See section 13. 30. The inner surface of the socket and the outer surface of the

spigot end shall be scored by triangular-shaped or semicircularshaped rings about one-eighth inch deep.

The number of scorings shall be as follows

For pipes 4 to 6 inches in internal diameter, inclusive None. For pipes 8 to 10 inches in internal diameter, inclusive 2 For pipes 12 to 21 inches in internal diameter, inclusive 3 For pipes 24 to 30 inches in internal diameter, inclusive 4 For pipes 33 to 42 inches in internal diameter, inclusive 5 31. The glaze shall consist of a continuous layer of bright or semibright glass substantially free from coarse blisters and pimples. If present, none of these shall project more than one-eighth inch above

the surrounding surface. Not more than 10 per cent of the inner

surface of any pipe barrel shall be bare of glaze except the socket,

where it may be entirely absent. Glazing will not be required on

the outer surface of the barrel at the spigot end for a distance from

the end equal to two-thirds the specified depth of socket for the

corresponding size of pipe. Where glazing is required, there shall be

absence of any well-defined network of crazing lines or hair cracks.

All glazing shall be equal to that produced by the best salt-glazing process.

32. The ends of the pipes shall be square with their longitudinal

axis, except as provided in Table 4. 33. (a) Special shapes shall have a plain spigot end and a socket

end corresponding in all respects with the dimensions specified for pipes of the corresponding internal diameter. Branch pipes shall be

furnished to lay the same lengths as straight pipe. All specials

shall conform in finish to the specifications for pipes given in sections

29, 30, 31, and 32.

(b) Slants shall have their spigot ends cut at an angle of approximately 45° with the longitudinal axis.
APPENDIX D—PLUMBING MATERIALS 261

(c) Curves shall be at angles of 90, 45, and 22^°, as required. They shall conform substantially to the curvature specified.

Table 3.—Dimensions of clay sewer pipe

Internal diameter

(D) Laying

length (L)

Inside diameter

at mouth

of socket (W

Depth of socket (Ls

)

Minimum

taper of socket ( H)

Thickness

of barrel (T) Thickness of socket (Ts)

Inches

4 Feet

2 Inches

6 Inches 1H 1:20 Inches He The thickness of the

6 2 8 H 2 1:20 H socket H inch from its 8 2, 2H, 3 10M 2H 1:20 H outer end shall not

10 2, 2fc,

3

13 2H 1:20 7A be less than three- 12 2, 2Yi, 3 15J4 2H 1:20 l fourths of the thick15 2, 2

3

im 2H 1:20 lU

ness of the barrel of pipe.

18 2, 2Vi, 3 22 n 3 1:20 m 21 2, 2y2, 3 26 3 1:20 m 24 2, 2J^, 3 29H 3 1:20 2 27 2H,3 33 J4 3H 1:20 2H

30 2^,3 37 3H 1:20 2H

33 2H,3 40H 4 1:20 2H

36 2^,3 44 4 1:20 2U

39 2H,3 47H 4 1:20 2K

42 2H,3 51 4 1:20 3

1 When pipes are furnished having an increase in thickness over that given in last column, the diameter

of socket shall be increased by an amount equal to twice the increase of thickness of barrel. (d) Branches shall be furnished with the connection or connections

of the size or sizes specified, securely and completely fastened by fusion

in the process of vitrification to the barrel of the pipe. T branches

and double T branches shall have their axes perpendicular to the

longitudinal axis of the pipe. Y branches, double Y branches, and

V branches shall have their axes approximately 45° from the longitudinal axis of the pipe measured from the socket end. All branches

shall terminate in sockets, and the barrel of the branch shall be of

sufficient length to permit making a proper joint when the connecting

pipe is inserted in the branch socket.

(ie ) Channel or split pipes, curves, and branches shall be accurate

half sections of the corresponding size of straight pipe and specials.

MARKINGS

34. Pipes shall bear the initials or name of the person, company, or corporation by whom they are manufactured, and the location of the

mill. The markings shall be indented on the exterior of the barrel near the socket and shall be plainly legible for purposes of identification.

INSPECTION

35. All pipes shall be subject to inspection at the factory, trench, or other point of delivery by a competent inspector employed by

the consumer or purchaser. The purposes of the inspection shall be

to cull and reject pipes which, independent of the physical tests herein specified, fail to comply with the requirements of these

specifications.
262 RECOMMENDED PLUMBING REQUIREMENTS

Table 4.—Permissible variation in dimensions of clay sewer pipe

Limits of permissible variation in—

Normal

size (inches) Internal diameter

Length, Lengths of (inches) Depth of Thickness of inches per two oppo- socket (—

)

barrel (—

)

foot (—). site sides Spigot (±) Socket (±)

Inches Inches Inches

4 X X X Me X Me

6 X X Me H X Me

8 X X X Me X. Me

10 X X H Me X Me

12 X X Me X X Me

15 X X Me X X X2

18 X •Me X Me X X2 21 X Me Me X X X

24 X H X Me X X

27 H X X 1 Me X X

30 X X X 1 Me X X

33 % J Mo X Me

36 X X X 13/l6 X Me

39 X X M 13/l6 X Me

42 X X H 1 Me X Me

Note.—

T

he minus sign (—) alone indicates that the plus variation is not limited; the plus and minus

sign (±) indicates variation in both excess and deficiency in dimension.

36. Pipes shall be subject to rejection on account of the following:

(a) Variations in any dimension exceeding the permissible variations given in Table 4.
APPENDIX D PLUMBING MATERIALS 263

(b) Fracture or cracks passing through the shell or socket, except

that a single crack at either end of a pipe not exceeding 2 inches in

length or a single fracture in the socket not exceeding 3 inches in

width nor 2 inches in length will not be deemed cause for rejection

unless these defects exist in more than 5 per cent of the entire shipment or delivery.

(c) Blisters where the glazing is broken or which exceed 3 inches

in diameter, or which project more than one-eighth inch above the

surface.

(d) Laminations which indicate extended voids in the pipe material.

(e) Fire cracks or hair cracks sufficient to impair the strength,

durability, or serviceability of the pipe.

(/) Variations of more than one-eighth inch per linear foot in alignment of a pipe intended to be straight.

(g) Glaze which does not fully cover and protect all parts of the

shell and ends except those exempted in section 31; also glaze which

is not equal to best salt glaze.

Qi) Failure to give a clear ringing sound when placed on end and

dry-tapped with a light hammer.

(i) Insecure attachment of branches on spurs.

37. All rejected pipes shall be plainly marked by the inspector and

shall be replaced by the manufacturer or seller with pipes which

meet the requirements of these specifications without additional cost

to the consumer or purchaser.

CAST-IRON SOIL PIPE AND FITTINGS

Serial Designation, A 74-18

[Issued as tentative, 1917; adopted 1918]

I. MANUFACTURE

1. The cast iron from which the pipe and fittings are made shall be of such composition and the conditions of manufacture so maintained that the castings will be of uniform physical character, close grain, and not hard, brittle, nor difficult to cut with file or chisel.

2. (a) When pipe or fittings are to be coated, coal-tar pitch shall be used, which shall contain sufficient oil to make a smooth coating.

The pitch shall be tough and tenacious when cold and not brittle nor having any tendency to scale.

(b) The varnish shall be heated to about 300° F. and shall re- main at this temperature during the time the casting is immersed.

(c) Each casting shall be heated to a uniform temperature of about

300° F. immediately before it is dipped and shall possess this temperature at the time it is put in the bath.

(id) Each casting shall remain in the bath at least two minutes.

(e) Fresh pitch and oil shall be added when necessary to keep the

mixture of the proper consistency, and the vat shall be emptied of

its contents and refilled with fresh pitch whenever the accumulation

of sand or carbonaceous mattar renders this desirable, as can be seen by the solids adhering to the underside or lower ends of the castings.

(j0 After being coated the pipe and fittings shall be carefully

drained of the surplus varnish.
264 RECOMMENDED PLUMBING REQUIREMENTS

CHEMICAL PROPERTIES AND TESTS

3. Drillings taken from the fractured end of the arbitration test bar shall not contain over 0.10 per cent of sulphur.

PHYSICAL PROPERTIES AND TESTS

4. The transverse test specimens (arbitration test bars) specified

in section 7, when placed horizontally upon supports 12 inches apart

and tested under a centrally applied load, shall conform to the fol- lowing minimum requirements:

Average load at center pounds, _ 2, 500

Average deflection at center inches. _ 0. 10

Fig 1.—Mold for arbitration test bar 5. All pipe shall be tested to a hydrostatic pressure of not less than

50 pounds per square inch before coating. Any casting showing

defects under this hydrostatic test shall be promptly broken and

returned to the cupola.

6. The form and dimensions of the mold for the arbitration test bar shall be in accordance with Figure 1. The bottom of the bar

shall be one-sixteenth inch smaller in diameter than the top to allow

for draft and for the strain of pouring. The pattern shall not be

rapped before withdrawing. The flask shall be rammed up with

green molding sand, a little damper than usual, well mixed and put
APPENDIX D—PLUMBING MATERIALS 265

through a No 8 sieve, with a mixture of 1 to 12 bituminous facing.

I he mold shall be rammed evenly and fairly bard, thoroughly dried and not cast until it is cold. The test bar shall not be removed from

the mold until cold enough to be handled. It shall not be rumbled

or otherwise treated, being simply brushed off before testing. 7 From each melt of metal not less than three test specimens

(arbitration test bars) shall be poured, the first of which shall be

poured within five minutes after the first ladle is tapped and the

remainder at intervals not exceeding one hour throughout the melt.

STANDARD SIZES AND WEIGHTS

8.

(a) The inside diameter of the barrel of any pipe or fittings or branch thereof shall not vary more than one-eighth inch under the

nominal size of pipe. r

(b) The outside diameter of the barrel of pipe and fittings shall be

one-half inch greater than its nominal inside diameter. A variation

in the outside diameter of one-eighth inch over or under these figures

will be permitted.

(c) All pipe and fittings shall be of uniform thickness of Wall and

present true circles at the hub and spigot ends. A variation of onesixteenth of an inch under the following dimensions will be permitted,

but only when the actual weight is not less than the variation of the

marked or estimated weight as given in Tables 1 and 2

:

Thickness of— Inch Barrel M

Body of hub ^ Bead of hub 3^ Bead of spigot end ^

9.

(a) Weights and measurements of pipe and fittings shall be taken

as those of plain uncoated pipe. All weights shall be given in pounds.

(b) Individual lengths of pipe and fittings may weigh 5 per cent

less than designated in Tables 1 and 2, but only when the average

weight of a given size and weight of pipe and fittings selected at random is not less than that shown in Tables 1 and 2.

(c ) The regular length of pipe shall be such as to lay 5 feet, including hub.

{d) The average weights of soil pipe and fittings shall not be less than those given in Tables 1 and 2. Table 1 . —Weights of soil pipe

Size (inches)

Single hub Double hub

Per 5-foot length Per foot in- cluding hub

Per 5-foot length

2__ . Pounds27Y

47}4

6585

100

Pounds5Hm13

1720

Pounds

27 Yi 47Yx

6585

100

3... . 4

5

6 WORKMANSHIP AND FINISH

10.

(a) All pipe and fittings shall be practically straight and

cylindrical and fittings true to pattern. The specified sizes shall be for the inside diameter and shall conform, within the allowable

variation, to the dimensions given in the tables.
266 RECOMMENDED PLUMBING REQUIREMENTS

(b) All pipe and fittings shall be carefully examined for defects and

sounded with a hammer before shipment. No fillings with metal,

cement, or other material, or so-called “ burning on” of iron will be

permitted. The castings shall be sound and free from cracks, sand

holes, blowholes, and cold shots.MARKING

11.

All pipe and fittings shall be marked with the name of the

manufacturer or appropriate initial. Each casting shall have cast upon it the minimum or estimated weight of same as shown in Tables

1 and 2. Table 2.—Weights of soil-pipe fittings [Only the staple fittings are shown. From the data herewith the weights of other fittings may be calculated. All values are in pounds]

Size of fittings (inches) Fittings 3 4 4 5 5 5 6 6 6 6

2 3 4 5 6 by by by by by by by by by by

2 2 3 2 3 4 2 3 4 5 % bends, regular 6

%

10)4 15 19 23)4 % bends, short sweep. 8H 12)4 17% 22)4 27)4 % bends, long sweep io % 15% 22 27)4 33)4 % bends. 6H 9% 13% 17)4 21)4 % bends 6 9 H 13 16)4 20 % bends 5% 8)4 12)4 15)4 18)4 %6 bends 5 7% 10% 13% 15%

Return bends 8 % 14 20)4 26)4 33)4 Tees... 10 % 15 % 21 26)4 32)4 13% 16)4 18% 19% 22 24% 22% 25 27% 30 Tapped tees (tapped up

to 2 inches) 8% 11% 15 17% 20%

Sanitary tees ... 11 16% 22)4 28 34)4 14 17% 19% 20 23 25% 23 26 29 31% Tapped sanitary tees (tapped up to 2inches)

.

9 12 15% 18 21% Y branch . . 11 17 24 31)4 39)4 14 17% 20% 20 23% 27% 23 27 31 35 % Y branch 10% 15)4 21)4 27)4 34 13)4 16% 19 19% 22 25 22% 25% 28% 31 Tapped inverted Y

branch (tapped up to

2 inches). 10% 13% 17)4 21 24 Inverted Y branch n% 18 25)4 33 41)4 15 18% 22 22 25% 29% 25% 29% 33 37 Combination Y and %

bend 12 18% 27 35 44)4 15 18% 22% 21 25% 30% 24 29 34 39 Upright Y branch 12)4 19)4 28 36)4 46 15% 18% 23 21% 26% 31% 24% 29% 35 40 INSPECTION AND REJECTION

12. The manufacturer shall afford the inspector representing the

purchaser, free of cost, all reasonable facilities to satisfy him that the

castings are being furnished in accordance with these specifications. All tests and inspection shall be so conducted as not to interfere

unnecessarily with the operation of the works and shall be made prior

to shipment unless otherwise specified.

13. All pipe and fittings which fail to conform to the provisions of these specifications shall be subject to rejection.

WELDED WROUGHT-IRON PIPE

Serial Designation, A 72-27

[Issued as tentative, 1917; adopted, 1918; revised, 1921, 1924, 1927] 1. These specifications cover “standard weight,” “extra strong,”

and “double extra strong” welded wrought-iron pipe.

2. All pipes to be used on locomotives and cars shall be of coiling or bending quality.

MANUFACTURE

3. (a) The iron shall be made from muck bars, made from pigpuddled iron, free from any admixture of iron scrap or steel.
APPENDIX D PLUMBING MATERIALS 267

(5) All pipe 3 inches or under in nominal diameter may be buttwelded, unless otherwise specified. All pipe over 3 inches in nominal

diameter shall be lap-welded.

4. Iron scrap. This term applies only to foreign or bought scrap and

does not include local mill products, free from foreign or bought scrap. PHYSICAL PROPERTIES AND TESTS

5. (a) The material shall conform to the following minimum

requirements as to tensile properties:

Tensile strength lb. per sq. in__ 40, 000

Yield point do 24,000

Elongation in 8 inches per cent__ 12

(b) The yield point shall be determined by the drop of the beam

of the testing machine. The speed of the crosshead of the machine

shall not exceed three-fourths inch per minute.

6. All pipe shall be tested at the mill to the hydrostatic pressures

specified in Table 1. Table 1 . —Hydrostatic pressures for welded wrought-iron pipe

[Pressures expressed in pounds per square inch]

Size (nominal inside diameter)

inches)

“Standard weight” pipe “Extra strong” pipe “Double extra strong” pipe Weight of pipe per

linear foot threaded and with

couplings

Butt weld Lap

weld

Weight of pipe per

linear foot plain ends

Butt

weld Lap

weld Buttweld Lap

weld

H..:

Pounds

700 700

700

700

700

700

700 700

700 800

800

Pounds

700

700

700

700 700

700

1,500

1, 500

1, 500

1, 500

1, 500

U.%

y2 700

700

700 2,200

2,200

2,200 2,200

2,200

%

im 1,000

1, 000

1,000

1,000 1,000

1,000 1,000

1, 000

1,000

800

1, 000

600

700 900

600 800

2, 500 2,500

2, 500 2,000

2, 000

2,000

2, 000

1, 800

1, 800

i y2 _... 3,000

3, 000

3, 000

3. 000

2, 500 2,500

2, 000

2. 000

2, 000

22H

33^__.

4

5

6

8 25.00

28. 81 32.00 35.00

41. 13

45. 00

50. 71

8 43. 39 1, 500

10. 10

10 54.74 1, 000

1212 65. 42 1,000 1 2St For pipes over 12 inches in inside diameter, the test pressure should be calculated by the formula P=—

in which P= pressure in pounds per square inch; S=fiber stress =12,000 pounds per square inch; ^thickness of wall in inches; D— outside diameter in inches. 7. A section of pipe 6 inches in length shall be flattened until

broken by repeated light blows of a hammer or by pressure; the

fracture developed shall have a fibrous appearance.

8. For pipe 2 inches or under in diameter a sufficient length of coiling or bending pipe shall stand being bent cold through 90°

around a cylindrical mandrel, the diameter of which is 15 times

the nominal diameter of the pipe, without developing cracks at any portion and without opening the weld.
268 RECOMMENDED PLUMBING REQUIREMENTS

9. In case of doubt as to the presence of steel, the purchaser may,

at his own expense, make micrographic examination and chemical

analysis to assist in determining whether the material meets the

requirements of section 3 (a). 10. (a) Test specimens shall consist of sections cut from a pipe.

They shall be smooth on the ends and free from burrs.

(b) Tension test specimens shall be longitudinal.

(c) All specimens shall be tested cold.

11. One of each of the tests specified in sections 5, 7, and 8 may

be made on a length in each lot of 500 or less of each size. Each

length shall be subjected to the hydrostatic test. 12. If the results of the physical tests of any lot do not conform to the requirements specified in sections 5, 7, and 8, retests of two

additional pipes shall be made, each of which shall conform to the

requirements specified.

STANDARD WEIGHTS

13.

(a) The standard weights for pipe of various inside diameters

are given in Table 2.

(b) Nipples shall be cut from pipe of the same weight and quality

as described in these specifications.

Table 2.—Standard weights and dimensions of welded wrought-iron pipe

Size (nominal inside diameter) (inches) Outside

diameter

“Standard weight’’ pipe “Extra strong”

pipe “Double extra strong” pipe

Number

of threads

per inch Thickness

Weight

of pipe

per

linear

foot, threaded and with

couplings

Thickness

Weight

of pipe

per

linear

foot, plain ends

Thickness

Weight

of pipe

per

linear

foot, plain ends

Inches Inch Pounds Inch Pounds Inch Pounds H - - 0. 405 27 0. 068 0. 25 0.095 0. 31 H- .540 18 .038 .43 .119 .54 H.... .675 18 .091 .57 .126 .74 H— - .840 14 .109 .85 .147 1.09 6. 294 1. 71 H- - 1. 050 14 .113 1.13 .154 1. 47 .308 2.44

1 1. 315 im .133 1.68 .179 2. 17 .358 3. 66 m 1. 660 UH .140 2.28 .191 3.00 .382 5. 21 m 1.900 ll H .145 2. 73 .200 3. 63 .400 6. 41

2 2.375 im .154 3. 68 .218 5.02 .436 9.03

2 }4 2. 875 8 .203 5. 82 .276 7.66 .552 13.70

3 3.500 8 .216 7. 62 .300 10.25 .600 18. 583 3H- 4.000 8 .226 9.20 .318 12. 51 .636 22. 85

4 4. 500 8 .237 10. 89 .337 14. 98 .674 27.54

5 5. 563 8 .258 14. 81 .375 20.78 .750 38. 55

6 6. 625 8 .280 19. 19 .432 28. 57 . 864 53. 16

8i 8. 625 g .277 25.00 .875 72.42

8 8. 625 8 .322 28.81 . 500 43. 39

10 1 10. 750 8 .279 32.00

101-.. 10. 750 8 .307 35.00

10 10. 750 8 .365 41. 13 . 500 54.74

12 1 12. 750 8 .330 45.00

12 12. 750 8 .375 50. 71 . 500 65. 42

1 Unless specifically stated on the order, the lighter weights will not be furnished. Weights given in the

table are for pipes up to and including 12 inches in nominal inside diameter, with threaded ends and couplings; sizes larger than those shown in the table are measured by the outside diameter and will be furnished with plain ends unless otherwise specified; for such sizes it will be necessary to accept manufacturers’ weights or calculate the weights on the basis of 1 cubic inch of steel weighing 0.2833 pound. Note.—By unanimous agreement of representatives of manufacturers, distributors, and users, made at a meeting May 28, 1926, under the auspices of the division of simplified practice, Department of Commerce,

agreement was reached that certain sizes and dimensions taken from this list would be regarded as regular production. The conclusions of this conference may be consulted in Simplified Practice Recommendation

No. 57 of the Department of Commerce.
APPENDIX D PLUMBING MATERIALS 269

14. The weight of the pipe shall not vary more than 5 per cent from that specified in Table 2. 15. Unless otherwise specified, pipe shall be furnished as to lengths

in accordance with the following regular practice:

(a) Standard weight pipe shall be in random lengths from 16 to 22

leet, but not more than 5 per cent of the total number of lengths may

be “jointers,” which are two pieces coupled together. When ordered

with plain ends, 5 per cent may be in lengths of 12 to 16 feet.

(b) Extra strong pipe shall be in random lengths of 12 to 22 feet and 5 per cent may be in lengths of 6 to 12 feet. WORKMANSHIP AND FINISH

16. For pipe \y2 inches or under in inside diameter the outside

diameter at any point shall not vary not more than one sixty-fourth

inch over nor more than one thirty-second inch under the standard

size. For pipe 2 inches or over in inside diameter, the outside diameter shall not vary more than 1 per cent over or under the standard

size.17. Unless otherwise specified, pipe shall conform to the following

regular practices:

(a) Each end of standard weight pipe shall be threaded.

(b) Extra strong pipe shall be furnished with plain ends.

(c) All threads shall be in accordance with the American standard 2 and cut so a,s to make a tight joint when the pipe is tested at the mill to the specified internal hydrostatic pressure. The variation from

the standard, when tested with the standard working gauge, shall not

exceed a maximum of one and one-half turns either way.

(d) Each length of threaded pipe shall be provided with one

coupling, having clean-cut threads of such a pitch diameter as to make a tight joint. Couplings shall be of wrought iron.

18. The finished pipe shall be reasonably straight and free from

injurious defects. All burrs at the ends of the pipe shall be removed.

INSPECTION AND REJECTION

19. The inspector representing the purchaser shall have free entry

at all times, while work on the contract of the purchaser is being per- formed, to all parts of the manufacturer’s works which concern the

manufacture of the pipe ordered. The manufacturer shall afford

the inspector, without charge, all reasonable facilities to satisfy him

that the pipe are being furnished in accordance with these specifications. All tests and inspection shall be made at the place of manufacture prior to shipment, unless otherwise specified, and shall be so conducted as not to interfere unnecessarily with the operation of the

works.

20. Each length of pipe which develops injurious defects in shop

working or application will be rejected, and the manufacturer shall be notified.

2 A complete description of the American Standard Pipe Thread is contained in the Pipe Thread Standard prepared under the sponsorship of the American Gas Association and the American Society of Mechanical Engineers and approved as American standard by the American Engineering Standards Committee.
270 RECOMMENDED PLUMBING Pr TV • WELDED AND SEAMLESS STEEL P'.TE

Serial Designation, A 53-27

[Adopted, 10 U; revised. 1918. 1021.. 1924, 1927] 1. These specifications cover “standard” weight, “extra strong”

and ' double - a strong” welded and seamless steel pipe. Pipe

ordered under these specifications is intended for coiling, bending,

flanging, and other special purposes. Butt-welded pipe is not in- tended for flanging. The purposes for which the pipe is intended

should be stated in the order.3 Where seamless pipe is ordered for

coiling, bending, or welding, the low-carbon grade should be specified.

MANUFACTURE

2. (a) The steel for welded pipe shall be soft weldable quality

made by the Bessemer or by the open-hearth process. The steel for seamless pipe shall be made by the open-hearth or electric-furnace

process.

(b) Welded pipe 3 inches or under in nominal diameter may be

butt-welded, unless otherwise specified. Welded pipe over 3 inches

in nominal diameter shall be lap-welded.

CHEMICAL PROPERTIES AND TESTS

3. (a) Ladle tests of open-hearth steel shall conform to the following requirement as to chemical composition:

Lapwelded Seamless Phosphorus, per cent _ Not over 0.06 Not over 0.045

( b ) Analysis may be made by the purchaser from each lot of 500

lengths or less of finished pipe. The phosphorus content thus determined shall not exceed that specified in paragraph (a) by more than

25 per cent. Drillings for analysis shall be taken from several points

around each pipe.

PHYSICAL PROPERTIES AND TESTS

4. (a) The material shall conform to the following minimum

requirements as to tensile properties:

(b) The yield point shall be determined by the drop of the beam

of the testing machine or other approved method.

Welded Seamless

Bessemer Open

hearth Open

hearth low

carbon

Open

hearth medium

carbon

Tensile strength pounds per square inch.. Yield point do ... Elongation in 8 inches per cent..

50.000 30.000

18

45.000

25.000

2030

48, 000

26,500

62,000

35,000 Elongation in 2 inches do 40 25

3 Double welding.—Unless double-welded pipe is specifically called for on the order, single-welded pipe may be furnished. When double-welded pipe is ordered, the flattening test on crop ends specified in section 9 shall be made with the weld on the side.
APPENDIX D PLUMBING MATERIALS 271

5. Pipe shall be tested at the mill to the hydrostatic pressures

specified in Table 1. Welded pipe 2 inches and larger shall be jarred near one end while under test pressure.

6. (a) For lap-welded pipe over 2 inches in nominal size, a section

of pipe 4 to 6 inches in length shall be flattened between parallel

plates until the distance between the plates is one-third the outside

diameter of the pipe without developing cracks. In this test the

weld shall be located 45° from the line of direction of the applied

force.

(b) For butt-welded pipe over 2 inches in nominal size, a section

of pipe 4 to 6 inches in length shall be flattened between parallel

plates until the distance between the plates is 60 per cent of the

outside diameter of the pipe without developing cracks. In this test the weld shall be located 45° from the line of direction of the applied

force.

(c) For low-carbon seamless pipe over 2 inches in nominal size, a section of pipe not less than 2 y2 inches in length shall be flattened

between parallel plates until the distance between the plates is onethird the outside diameter of the pipe without developing cracks.

In no case need the distance between the plates be less than five times the thickness of the pipe wall.

(d) For medium-carbon seamless pipe over 2 inches in nominal

size, a section of pipe not less than 2 % inches in length shall be flat- tened between parallel plates until the distance between the plates

is one-half the outside diameter of the pipe without developing

cracks. In no case need the distance between the plates be less than

seven times the thickness of the pipe wall.

(e) The flattening test will not be required on double extra strong

pipe.

7. For pipe 2 inches or under in nominal size, a sufficient length of pipe shall stand being bent cold through 90° around a cylindrical

mandrel, the diameter of which is 12 times the nominal diameter

of the pipe, without developing cracks at any portion and without

opening the weld. When ordered for close coiling, the pipe shall stand being bent cold through 180° around a mandrel, the diameter

of which is eight times the diameter of the pipe, without failure. The bend test will not be required on double extra strong pipe over 1% inches in diameter.

8. (a) Test specimens shall consist of sections cut from a pipe.

They shall be smooth on the ends and free from burrs, except when

made on crop ends taken from welded pipe.

(b) Tension test specimens shall be cut longitudinally from the

pipe and not flattened. The sides of specimens shall be parallel

between gauge marks. Pipe may be pulled in full section, if desired.

Where impractical to pull a test specimen in full thickness, the

A. S. T. M. standard K-inch test specimen may be used.

(c) All specimens shall be tested at room temperature.

9. One of each of the tests specified in sections 4, 6, and 7 shall be made on a length in each lot of 500 or less, of each size. Each

length shall be subjected to the hydrostatic test. In the case of welded pipe ordered for “flanging,” the crop ends cut from each

length shall withstand the flattening test specified in section 6 (a).
272 RECOMMENDED PLUMBING REQUIREMENTS

Table 1 . —Hydrostatic pressures for welded and seamless steel pipe

[Pressures expressed in pounds per square inch]

Standard weight pipe

Size (nominal inside diameter) (inches) Weight

of pipe

per lin- ear foot, threaded and with

couplings

Butt

weld Lap

weld and

seamless

Weight

of pipe

per lin- ear foot, plain ends

Butt

weld Lap

weld and

seamless Butt

weld Lap

weld and

seamless

H

Pounds

700

700

700

700 700

700

700

700

700 800

800

Pounds

700

700

700

700 700

700

1, 500

1,500

1, 500

1, 500

1, 500

H

?*H 700

700

700

2, 200

2, 200 2,200

2, 200 2,200

u

lm 1, 000

1,000

1, 000

1,000 1,000

1,000

1,000 1,000

1,000 800

1, 000 600

700 900

600

800

2,500

2,500 2,500

2,000 2,000

2,000 2,000

1,800

1,800

1H-- - 3,000

3, 000 3,000 3.000

2, 500 2,500

2.000

2,000

2,000

22H—

3.3W4

6

6

8. 25.00

28. 81

32. 00 35.00

41. 13

45. 00

50. 71

8. 43. 39 1,500

10

10

10 54.74 1,000

12. 12 .. . 65.42 1,000

Extra strong pipe Double extra strong pipe

For pipes over 12 inches in inside diameter the test pressures should be calculated by the formula P=2St/D, in which P=pressure in pounds per square inch; £=fiber stress, 12,000 pounds per square

inch; t =thickness of wall in inches; D=outside diameter in inches. Table 2.—Standard weights and dimensions of welded and seamless steel pipe

Size (nominal inside diameter), (inches) Outside

diameter

“Standard weight” pipe “Extra strong” pipe “Double extra strong” pipe

Number

of threads

per inch Thickness

Weight of pipe per

linear foot threaded and with

couplings

Thickness

Weight of pipe per

linear

foot, ' plain ends

Thickness

Weight of pipe per

linear

foot, plain ends

Inches Inch Pounds Inch Pounds Inch Pounds

0. 405 27 0. 068 0.25 0.095 0.31 U .540 18 .088 .43 . 119 .54 §6 .675 18 .091 .57 .126 .74

Vi .840 14 .109 .85 . 147 1.09 6.294 1. 71

3A —

1. 050 14 . 113 1. 13 .154 1.47 .308 2.44

l 1. 315 1VA .133 1.68 .179 2. 17 .358 3. 66 1H - 1.660 11 Vz . 140 2.28 . 191 3.00 .382 5.21 1M~~ 1.900 1VA . 145 2. 73 .200 3. 63 .400 6. 41 2 2.375 11 Yi . 154 3. 68 .218 5. 02 .436 9. 03 2H 2.875 8 .203 5. 82 .276 7. 66 .552 13. 70

3 3.500 8 .216 7. 62 .300 10. 25 .600 18. 583 3^ - —

_

4. 000 8 .226 9.20 .318 12. 51 .636 22. 85

4 4.500 8 .237 10.89 .337 14. 98 .674 27. 54 5 5,563 8 .258 14. 81 .375 20.78 .750 38. 55
APPENDIX D PLUMBING MATERIALS 273

Table 2.—Standard weights and dimensions of welded and seamless steel pipe—

Continued

‘ ! Standard weight ” pipe ‘ ‘ Extra strong ” pipe

‘

‘ Double extra strong” pipe

Size (nominal inside diameter), (inches) Outside diameter Number

of threads per inch

1 Thickness

Weight of pipe per

linear foot threaded and with

couplings

Thickness

Weight of pipe per

linear

foot, plain ends

Thickness

Weight of pipe per

linear

foot, plain ends

6 Inches6. 625 8 Inch

0.280 Pounds19. 19 Inch

0. 432 Pounds

28. 57 Inch

0. 864

.875 Pounds

53 16 8 i 8. 625 8 .277 25.00 72,42

8 8. 625 8 .322 28. 81 .500 43. 39 10 i 10. 750 8 .279 32.00

10 1 10. 750 8 .307 35.00 10 10. 750 8 .365 41. 13 .500 54.74

12 i 12. 75Q 8 .330 45.00

12 12. 750 8 .375 50. 71 .500 65. 42

1 Unless specifically stated on the order, the lighter weights will not be furnished. Weights given in the

table are for pipes up to and including 12 inches in nominal inside diameter, with threaded ends and couplings; sizes larger than those shown in the table are measured by the outside diameter and will be furnished with plain ends unless otherwise specified; for such sizes it will be necessary to accept manufacturers' weights or calculate the weights on the basis of 1 cubic inch of steel weighing 0.2833 pounds. Note.—

S

ee note below table for Welded wrought iron pipe, p. 268. 10. If the results of the physical tests of any lot do not conform

to the requirements specified in sections 4, 6, and 7, retests of two

additional pipes shall be made, each of which shall conform to the

requirements specified. In the case of flattening tests on the crop

ends of each length of welded pipe, if any section fails, other pieces

from the length may be cut until satisfactory tests are obtained;

otherwise the length shall be rejected.

STANDARD WEIGHTS

11. (a) The standard weights for pipe of various inside diameters

are given in Table 2. (b) Nipples shall be cut from pipe of the same weight and quality

as described in these specifications.

12. The weight of the pipe shall not vary more than 5 per cent for standard weight and extra strong pipe and not more than 10 per cent

for double extra strong pipe from that specified in Table 2. 13. Unless otherwise specified, pipe shall be furnished as to lengths

in accordance with the following regular practice:

(a) Standard weight pipe shall be in random lengths of 16 to 22

feet, but not more than 5 per cent of the total number of lengths may

be “ jointers,” which are two pieces coupled together. When ordered

with plain ends, 5 per cent may be in lengths of 12 to 16 feet.

(b) Extra strong and double extra strong pipe shall be in random

lengths of 12 to 22 feet. Five per cent may be in lengths of 6 to 12

feet. WORKMANSHIP AND FINISH

14. For pipe 1)4 inches or under in nominal size, the outside

diameter at any point shall not vary more than inch over nor more than ^ inch under the standard outside diameter. For pipe

2 inches or over in nominal size, the outside diameter shall not vary

20141 °—29 19
274 RECOMMENDED PLUMBING REQUIREMENTS

more than 1 per cent over or under the standard outside diameter.

The wall thickness shall not be more than 12.5 per cent under the

nominal wall thickness at any point.

WORKMANSHIP AND FINISH

15. Unless otherwise specified, pipe shall conform to the following

regular practice:

(a) Each end of standard weight welded pipe shall be threaded.

(b) Extra strong welded pipe and standard weight and extra strong

seamless pipe and all double extra strong pipe shall be furnished with

plain ends.

(c) All threads shall be in accordance with the American standard 1 and cut so as to make a tight joint when the pipe is tested at the mill to the specified internal hydrostatic pressure. The variation from

the standard, when tested with the standard working gauge, shall not exceed a maximum of one and one-half turns either way.

(d) Each length of threaded pipe shall be provided with one

coupling

. having clean-cut threads of such a pitch diameter as to make a tight joint. Couplings may be made of wrought iron or steel. 16. The finished pipe shall be reasonably straight and free from

injurious defects. All burrs at the ends of the pipe shall be removed.

INSPECTION AND REJECTION

17. The inspector representing the purchaser shall have free entry

at all times, while work on the contract of the purchaser is being

performed, to all parts of the manufacturer’s works which concern

the manufacture of the pipe ordered. The manufacturer shall afford

the inspector, without charge, all reasonable facilities to satisfy him

that the pipe are being furnished in accordance with these specifications. All tests and inspection shall be made at the place of manufacture prior to shipment, unless otherwise specified, and shall be so conducted as not to interfere unnecessarily with the operation of the works.

18. Each length of pipe which develops injurious defects in shop

working or application will be rejected, and the manufacturer shall be notified. BRASS PIPE, STANDARD SIZES

Serial Designation B 43-24

[Issued as tentative, 1922; adopted, 1923; revised, 1924] 1. These specifications cover seamless brass pipe suitable for use

in plumbing, boiler-feed lines, etc, MANUFACTURE

2. The pipe shall be cold-drawn to size.

3. (a) The pipe shall be annealed sufficiently to enable it to pass

the physical tests herein specified.

(jb) All pipe shall be annealed sufficiently to prevent cracking.

Semiannealed pipe, which is suitable for ordinary uses, shall be

furnished unless otherwise specified.

(c) When pipe is required for bending, the purchaser shall so

specify, in which case the pipe shall be furnished fully annealed.

See footnote 2, page 269.
APPENDIX D PLUMBING MATERIALS 275

CHEMICAL PROPERTIES AND TESTS

4. The brass shall conform to the following requirements as to chemical composition:

Hot pierced

process Cold

process Copper _ per cent .

.

Lead, maximum. . ...... ..do.. . Iron, maximum do

59. 00-63. 00 0.50

.07 Remainder.

65. 00-68. 00

0. 80 .07 Zinc. .... . . ... .... Remainder.

5. The sample for chemical analysis shall consist of drillings,

millings, or clippings taken from the pipes selected for testing purposes, as specified in section 12, equal quantities being taken from

each pipe and thoroughly mixed. Samples so prepared shall be

divided into three equal parts, each of which shall be placed in a sealed package, one for the seller, one for the purchaser, and one for an umpire, if necessary. PHYSICAL PROPERTIES AND TESTS

6. The pipe shall be capable of withstanding the following test without showing cracks or flaws : A piece cut from the ends of the pipe

shall be hammered flat on different elements throughout its length

so that a gauge set at three times the thickness of the metal shall pass over the pipe freely throughout the flattened part, except at such

points where changes in the elements of flattening take place.

7. A test specimen 3 inches in length when split shall withstand

opening out flat without showing cracks or flaws.

8. A test specimen 3 inches in length shall withstand an immersion

in an aqueous mercurous nitrate solution containing 100 g of mercurous nitrate and 13 cc of nitric acid (sp. gr. 1.42) per liter of solution

for 15 minutes, without cracking.

9. The pipe shall withstand threading in a satisfactory manner.

10. In the case of pipe for bending, annealed full sections of the

pipe shall withstand being bent cold through 180° without cracking on the outside of the bent portion around a pin, the dianieter of which

is one and one-half times the inside diameter of the pipe. This test shall be in addition to the tests specified in sections 6 to 9, inclusive.

11. Each pipe shall withstand, without showing weakness or

defects, an internal hydrostatic pressure sufficient to subject the material to a fiber stress of 7,000 pounds per square inch, determined by

the formula for thin hollow cylinders under tension:

in which P equals the pressure in pounds per square inch, i equals the

thickness of wall in inches, D equals the outside diameter of ohe pipe

in inches, and S equals the allowable unit stress of the material =

7,000 pounds per square inch. No pipe shall be tested beyond a

pressure of 1,000 pounds per square inch unless so specified.

12.

A sufficient number of pipe shall be taken at random to constitute 0.5 per cent of the shipment. One flattening, one strain, and

one threading test-shall be made on each pipe so selected.
276 RECOMMENDED PLUMBING REQUIREMENTS

DIMENSIONS AND PERMISSIBLE VARIATIONS

13. The standard weights and dimensions for pipe of various outside diameters are given in Table 1. Table 1 . —Standard weights and dimensions for brass pipe

Size of pipe (inches) Outside diameter

Standard pipe Extra strong pipe

Thickness Nominal

weight

(per foot

of length)

Thickness Nominal

weight

(per foot

of length)

• Inches Inch Pounds Inch Pounds

Ys 0. 405 0. 0620 0. 246 0. 100 0. 353 .540 .0825 .437 . 123 .593 % .675 .0905 .612 . 127 .805

Vl .840 . 1075 9.11 .149 1. 19 % 1. 050 . 1140 1.24 .157 1. 62

i... 1. 315 .1265 1.74 .182 2. 39 1M i 1.660 .1460 2.56 . 194 3.30

1.900 .1500 3.04 .203 3. 99

2 2. 375 .1565 4. 02 .221 5.51 2>X

1 2. 875 .1875 5.83 .280 8. 41

3 3. 500 .2190 8. 31 .304 11.24 3M 4.000 .2500 10. 85 .321 13. 67 4 | 4. 500 .2500 12. 29 .341 16.41 A'A 5.000 .2500 13. 74 .375 20. 07

5 5. 563 .2505 15. 40 .375 22.52 6 6. 625 .2500 18. 44 .437 31. 32 7 7.625 .2815 23. 92 .500 41. 23 8 8.625 .3125 30. 05 .500 47.02

9 9. 625 .3440 36. 94 .500 52.81

10 10. 750 .3655 43.91 .500 59. 32

14. (a) No single piece of pipe that exceeds the calculated weight by more than 5 per cent will be accepted. One cubic inch of the material

is assumed to weigh 0.307 pound.

(b) The weight of the pipe shall not vary more than the following

percentages from the weight specified in section 13 : Pipe 6 inches or

less in diameter, 5 per cent; pipe from 6 to 8 inches in diameter, 7 per

cent; pipe over 8 inches in diameter, 8 per cent. WORKMANSHIP AND FINISH

15. (a) The pipe shall be round and of uniform thickness throughout. They shall be free from cracks, seams, slivers, scale, and other

surface defects.

(b) The thickness at any point shall not be less than that specified

in section 13 by more than the following percentages: Pipe 6 inches or

less in diameter, 5 per cent; pipe from 6 to 8 inches in diameter, 7 per

cent; pipe over 8 inches in diameter, 8 per cent.

16. All pipes shall be acid-cleaned after the final annealing.

INSPECTION AND REJECTION

17. (a) When the pipe is finished and ready for shipment, the

inspector shall make the tests to govern the acceptance of the pipe.

If any specimen fails to meet the requirements of sections 6 to 11,

inclusive, two additional specimens may be taken, each of which shall conform to the requirements specified.
APPENDIX D PLUMBING MATERIALS 277

(&). Pipes that show nonuniform annealing under handling shall be rejected from the lot. 18. The manufacturer shall afford the inspector, without charge,

all reasonable facilities to satisfy him that the pipe is being furnished

in accordance with these specifications. All tests (except check

analyses) and inspection shall be made at the place of manufacture

prior to shipment, unless otherwise specified, and shall be so con- ducted as not to interfere unnecessarily with the operation of the

works.

COPPER PIPE, STANDARD SIZES

Serial Designation B 42-24

[Issued as tentative, 1922; adopted, 1923; revised, 1924] 1. These specifications cover seamless copper tubes and seamless

copper pipe suitable for use in plumbing, boiler-feed lines, etc. MANUFACTURE

2. (a) The pipe shall be cold-drawn to size.

(b) When pipe is required for bending, the purchaser shall so

specify, in which case the pipe shall be furnished with a proper

bending temper.

CHEMICAL PROPERTIES AND TESTS

3. The copper shall have a purity of at least 99.880 per cent as determined by electrolytic assay, silver being counted as copper.

4. The sample for chemical analysis shall consist of drillings,

millings, or clippings taken from the test specimens specified in

section 9, equal quantities being taken from each specimen and

thoroughly mixed. Samples so prepared shall be divided into three

equal parts, each of which shall be placed in a sealed package, one for the seller, one for the purchaser, and one for an umpire if necessary. PHYSICAL PROPERTIES AND TESTS

5. The material shall conform to the following minimum requirements as to tensile properties:

Tensile

strength Elongation

in 4 inches

Pipe less than 2 inches in outside diameter .

Lbs. per sq. inch 40.000

30. 000

Per cent10 Pipe 2 inches or over in outside diameter (after annealing). 25

6.

(a) The test specimen, after being annealed, shall withstand

being bent cold through 180°, without cracking on the outside of the

bent portion, as follows: For material less than one-half inch in

thickness, flat on itself; and for material one-half inch or over in thickness, around a pin, the diameter of which is twice the thickness

of the specimen.

(ib ) In the case of pipe for bending, annealed full sections of the

pipe shall withstand being bent cold through 180°, without cracking on the outside of the bent portion, around a pin, the diameter of which is one and one-half times the inside diameter of the pipe. This

test shall be in addition to the test specified in paragraph (a).
278 RECOMMENDED PLUMBING REQUIREMENTS 7. (a) An annealed test specimen not more than 4 inches in length

shall have a flange turned over at right angles to the body of the pipe

without showing cracks or flaws. The width of this flange, as measured from the outside of the pipe, shall be one-fourth of the

inside diameter of the pipe.

(b) In making the flange test it is recommended that the flaring tool and die block shown in Figure 1 be used.

A = Outs. Diam. of Flue less K £*> Outs. Diam, of,Flue iessii

Outs. Diam. ofFlue plusV.

Flaring Tqq|,

Position .Position afterUsing ( afterUsing

Har/ng Taol^ / Flatter. ~r

J

A* Outs. Diam, of.Flueplus

Die BIqqK.

Fig. 1

liners-’"*-

A

8.

Each pipe shall withstand, without showing weakness or

defects, an internal hydrostatic pressure sufficient to subject the

material to a fiber stress of 6,000 pounds per square inch, determined

by the formula for thin hollow cylinders under tension:

in which P equals the pressure in pounds per square inch, t equals the

thickness of wall in inches, D equals the outside diameter of the pipe

in inches, and 8 equals the allowable unit stress of the material =

6,000 pounds per square inch. No pipe shall be tested beyond a

pressure of 1,000 pounds per square inch unless so specified.

e»

i 1 /I

k

4- H

Fig. 2

9.

(a) Tension test specimens for pipe less than 2 inches in outside

diameter shall consist of a full section of the unannealed pipe; the

ends shall be plugged with metal plugs, which shall not extend within

the gauge marks.

(b) In the case of pipe 2 inches or over in outside diameter and

not exceeding 6 inches in outside diameter, the test specimen shall be cut longitudinally. In the case of pipe exceeding 6 inches in outside diameter, the test specimen shall be cut circumferentially.
APPENDIX D PLUMBING MATERIALS 279

(c) The test specimen taken as specified in paragraph ( b ) shall be heated to a cherry red and straightened while hot. It shall then

be machined to conform in shape to Figure 2. The width of the

specimen shown in Figure 2 shall be governed by the thickness of the

material. For material one-fourth inch or less in thickness, the

width of the narrow portion of the test specimen shall be approximately 1 inch; for material over one-fourth inch in thickness, the

width shall be such as to give a cross section of approximately one- fourth square inch in area, but in no case shall the width be less than

the thickness of the material. The drawn surfaces shall not be

machined, but be left in their original condition.

(d) The bend test specimen shall consist of a strip not over

inches in width cut longitudinally from the pipe.

10. One bend test shall be made for each 2,000 pounds or less of the finished product. For the remaining tests a sufficient number

of pipe shall be taken at random to constitute 0.5 per cent of the

shipment.

DIMENSIONS AND PERMISSIBLE VARIATIONS

11. The standard weights and dimensions for pipe of various outside diameters are given in Table 1

Table 1 . —Standard weights and dimensions for copper pipe

Size of pipe (inches) Outside diameter

Standard pipe Extra strong pipe

Thickness Nominalweight

per foot

of length

Thickness Nominalweight

per foot

of length

Inches Inch Pounds Inch Pounds

Vs 0.405 0. 0620 0. 259 0.100 0.371 K .540 .0825 .460 .123 .624 ^ .675 .0905 .643 .127 .847 M —

.840 .1075 .957 .149 1. 25 % 1.050 .1140 1. 30 .157 1.71

1 1. 315 .1265 1. 83 .182 2. 51 1M 1. 660 .1460 2. 69 .194 3. 46 iy2 1. 900 .1500 3! 20 .203 4. 19 2 2. 375 .1565 4.23 .221 5.79 2V2

2. 875 .1875 6.14 :280 8. 84 3 3. 500 .2190 8. 75 .304 11. 82 sy2 4. 000 .2500 11. 41 .321 14. 37 4 4.500 .2500 12.94 .341 17.25 4)4 5. 000 .2500 14. 46 .375 21. 10 5 5. 563 .2505 16. 21 .375 23. 67

6 6. 625 .2500 19. 41 .437 32. 93

7 7. 625 .2815 25. 17 .500 43. 34 8 8. 625 .3125 31. 63 .500 49. 42 9 , 9. 625 .3440 38. 83 .500 55. 56

10 10. 750 .3655 46. 22

1 .500 62. 40

12.

(a) No single piece of pipe that exceeds the calculated weight

by more than 5 per cent will be accepted. One cubic inch of the

material is assumed to weigh 0.323 pound.

(b) The weight of the pipe shall vary not more than the following

percentages from the weight specified in section 1 1 : Pipe 6 inches or less in diameter, 5 per cent; pipe from 6 to 8 inches in diameter,

7 per cent; pipe over 8 inches in diameter, 8 per cent.
280 RECOMMENDED PLUMBING REQUIREMENTS

WORKMANSHIP AND FINISH

13. (a) The pipe shall be round and of uniform thickness throughout. They shall be free from cracks, seams, slivers, scale, and other

surface defects.

(b) The thickness at any point shall not be less than that specified

in section 11 by more than the following percentages: Pipe 6 inches

or less in diameter, 5 per cent; pipe from 6 to 8 inches in diameter,

7 per cent; pipe over 8 inches in diameter, 8 per cent. INSPECTION AND REJECTION

14. When the pipe is finished and ready for shipment the inspector

shall make the tests to govern the acceptance of the pipe. If any

specimen fails to meet the requirements of sections 5 to 8, inclusive,

two additional specimens may be taken, each of which shall conform

to the requirements specified.

15. The manufacturer shall afford the inspector, without charge,

all reasonable facilities to satisfy him that the pipe is being furnished

in accordance with these specifications. All tests (except check

analyses) and inspection shall be made at the place of manufacture

prior to shipment, unless otherwise specified, and shall be so con- ducted as not to interfere unnecessarily with the operation of the

works.