AlllOO T=lB73b

BUILDING SCIENCE SERIES 49

|.U52

t.Z

U.S.

)EPARTMENT

OF

COMMERCE

National

Bureau

of

Standards

Laboratory Studies

of the

Hydraulic Performance of

One-Story and Split-Level

Residential Plumbing Systems

With Reduced-Size Vents

I
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building materials, components, systems and whole structures. The Series presents research results, test methods and per- formance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

are directed toward the manufacturing, design, construction and research segments of the building industry, stand- ards organizations and officials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute for Applied Technology. The publications are divided in to three general groups: Building Systems and Processes; Health, Safety and Comfort; and Structures and Materials. Listed below are other publications in the category of

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Laboratory Studies of the Hydraulic

Performance of One-Story and Split-Level

Residential Plumbing Systems

With Reduced-Size Vents

"IjuitiiAO 6ciei\ce ^i\-es

Robert S. Wyly, Grover C. Sherlin,

and Robert W. Beausoliel

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Natipiial Bureau pi Sxanciarcls

MAY 6 1974

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued March 1 974
Library of Congress Catalog Number: 73-600336

National Bureau of Standards Building Science Series 49

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser 49, 53 pages (Mar. 1974) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. C13. 29/2:49). Price 95 cents. Stock Number 0303-01220
Foreword

Housing has concerned mankind throughout history, and continues to occupy the talents of people

in many professions. This is certainly true at the National Bureau of Standards, where a tradition of housing research stretches unbroken from the early 1900's to the present. Today, the Center for Build- ing Technology is involved with a broad range of housing problems. For example, an extensive series of experiments, using an advanced plumbing tower that provides great flexibility of operation, has

shown that in many cases plumbing vents of reduced size perform quite well. In these tests, drainage systems simulating those of one-story and split-level dwellings produced

satisfactory performance with vents smaller than those specified by building codes. Use of reducedsize vents would help conserve copper and iron, and could reduce the plumbing costs of one-family

units by $40 to $80. Such information will be useful to regulatory authorities when considering code

changes, and should also be of interest to the plumbing engineering profession.

Richard W. Roberts

Director

III

Contents

P«ge Foreword HI

1. Introduction 1

1.1. Background 1

1.2. Principal objectives 1

1.3. Scope 1

1.4. Performance criteria 2

2. Venting studies conducted on a test setup representing a complete DWV system for a one-story, single-bath,

slab-on-grade house 3

2.1. Purpose and scope 3

2.2. Description of DW\^ system 4

Z3. Approach to measurement and to test control 5

2.3.1. Measurement 5

2.3.2. Test load selection, designation, and application 7

2.4. Findings 8

2.4.1. Fixture calibrations 8

2.4.2. Tests with all vents either open or closed 9

2.4.3. Tests with some vents closed 11

2.4.4. Tests with reduced-size vents and manifold-type vent terminal 19

2.5. Summary 23

3. Venting studies conducted on a test setup representing a complete DWV system for a three-level (two stories and basement) , three-bath house 23

3.1. Purpose and scope 23

3.2. Description of DW\' system 24

3.3. Approach to measurement and to test control 25

3.3.1. Measurement 25

3.3.2. Test load selection, designation, and application 25

3.4. Test procedure 27

3.5. Results and discussion 28

3.5.1. Fixture calibrations 28

3.5.2. Travel times and apparent velocities for hydraulic loads 28

3.5.3. Transportability of solids 31

3.5.4. Trap performance with various loads and venting ajrrangements 33

3.6. Summary 38 4 Development of a table for sizing vents based on functional requirements 39

5. Conclusions and recommendations ^

6. References '^2

7. Appendix 42

7.1. Definitions 42

7.2. Units of measure and SI conversion factors 44

7.3. Discussion of field tests conducted by the NAHB Research Foundation 45

V

Laboratory Studies of the Hydraulic Performance of One-Story and

Split-Level Residential Plumbing Systems With Reduced-Size Vents*

Robert S. Wyly, Grover C. Sherlin, and Robert W. Beausoliel

A laboratory study of one-story and split-level experimental drainage systems where the vents

in some cases were varied from one to six pipe-sizes smaller than those presently specified by

codes showed satisfactory hydraulic and pneumatic performance under various loading conditions. The research was originally sponsored by the National Association of Home Builders and the National Bureau of Standards and more recently by a program of the Department of Defense through the Tri-Services Investigational Committee on Building Materials. This paper presents

criteria recommended for the design and evaluation of systems using reduced-sized vents and a

sizing table for one- and two-story systems. The laboratory work also contributed to the develop- ment of analytical and test procedures needed for evaluating the application of reduced-size venting

to a broad range of innovative drain-waste-vent designs for buildings of any height. This work indicates that, in some circumstances, reduced-size venting might be a good

alternative to other types of drainage systems for multi-story buildings which use conventional

or innovative venting concepts. Because this study involved only a limited number of drainage

system designs, it is recommended that ongoing field and laboratory studies be explored if code changes are contemplated to permit the use of smaller vents. Key words: Hydraulic criteria for plumbing; hydraulic test loads; plumbing-vent sizing; reducedsize vents ; sanitary DWV systems ; secondary ventilation ; testing plumbing systems ; vents for plumbing.

1. Introduction

1.1. Background

The work described in this paper was initiated under a Grant-in-Aid Program with support from the National Association of Home Builders (NAHB). The

NAHB requested that the generally accepted criteria for venting be reexamined and proposed specifically that the hypothesis be tested that vent sizes may safely

be reduced appreciably in size below those presently

allowed by codes. Recommendations for the scope of and approach to the work were furnished by an eightmember technical advisory committee including representatives from Federal agencies having responsibility for housing construction and for health and safety,

from the housing construction industry, and from the engineering profession.

The committee first reviewed relevant aspects of the

fluid dynamics of plumbing systems such as those

installed in one-story and split-level residences. Many

problems were identified, but the recommendation was made that the research be restricted to problems for which meaningful laboratory measurements could be

obtained with resources available to the program, and

that study of other problems be deferred, e.g., those dealing with the development of fouling, scaling, or corrosion over a period of time under service condi-

*A number of terms have been defined in section 7.1.

tions; those dealing with the performance of different piping materials or with the hydraulics of fixtures; or those concerned with water conservation.

1.2. Principal Objectives

The main objectives were to examine the hydraulic

and pneumatic performance of selected sanitary

DWV ^ systems utilizing vents smaller than generally

allowed by codes, and from this information, to present recommended criteria for the guidance of plumbing system designers and regulatory authorities. In the process of achieving these objectives it was antici- pated that progress would be made in the development

of relevant performance criteria and of a methodology

for testing plumbing systems.

1.3. Scope

The laboratory work consisted mainly of a considerable number of tests made on two test setups repre- senting complete sanitary plumbing drainage systems. In addition, several important tests were made on

simple "components," some of which were conducted on selected parts of the complete plumbing systems.

^ Signifies "drain-waste-vent."

1
This paper describes in detail the venting tests on

the two laboratory test setups representing complete

DWV plumbing systems. One of these wa^ patterned

after the plans for a one-story, single-bath, slab-on- grade house, as specified for a housing project that had been constructed by one of the member companies

of the NAHB. The other test setup was constructed

from a plan for a three-level, two-stories and base- ment, three-bath house developed jointly by the project staff and a representative of NAHB, specifically for experimentation.

The work on simple components provided signifi- cant hydraulic and pneumatic functional performance

data that helped explain the performance observed

with the complete DWV systems. Three publications

have been issued describing portions of the research on the complete systems and the components [1, 2, 3].^

1.4. Performance Criteria

The fundamental, qualitative performance require- ments for sanitary DWY systems are that (1) the waste water must be conveyed to a public sewer or

other acceptable point of disposal without nuisance or health hazard, and (2) the essential functional per- formance must not deteriorate too rapidly nor require

excessive maintenance under a normal service environ- ment. A more detailed breakdown of the requirements was presented in the National Plumbing Code [4].

Experience has shown that conformance to these re- quirements is facilitated for conventional gravity sys- tems by consideration of the following general principles at the stages of design and evaluation.

a. A gas barrier (trap) should be used for each

plumbing fixture to prevent passage of sewer gases or vermin into the house. A water-sealed trap with a seal depth of at least 2 inches has generally been found

adequate; however, deeper trap seals may be desirable under some circumstances, e.g., they increase resist- ance to siphonage and afford extended protection

against evaporation. Trap geometry and symmetry can

substantially affect trap-seal response under dynamic

loading. Other types of gas barriers would be neces- sary for drainage systems utilizing pressure or vac- uum.

b. Pneumatic-pressure fluctuations (excursions) in- side each fixture drain should be limited to a level that will prevent excessive depletion or disturbance of the trap seal and that will not cause annoying drain- age noises. Traps-seal retention ^ of at least 1 inch or one half of the full trap seal, whichever is greater as determined by realistic test procedures, should be generally adequate. Rather than this, however, most

plumbing codes actually require that acceptable de- signs provide for the maintenance of a pneumatic

pressure range throughout the system of ±1 in of water column, under normal loads. Further, many

^ Figures in brackets indicate the literature references in sec. 6. ' Trap seal retention is that depth of water remaining in the trap after the trap has been affected by passage of fluid through the trap or by action

of suction or back-pressure in the DWV system.

codes proceed to specify the sizes, lengths, and configuration categories that are required. Thus, the de- signer is inhibited from proposing designs based on

the trap-seal retention criterion, since such designs

may conflict with code specifications on dimensions,

configuration, or vent pressure excursion.

c. Peak hydrostatic and hydrodynamic pressures in the drainage piping should be limited to a level where

waste water originating from other fixtures will not back up into any particular fixture or into its trap. Generally accepted practice tends to recognize this need and provides for the control of these pressures by sizing all nominally horizontal drains having two

or more inputs so that they will flow significantly less than full (e.g., at l^ full depth) under design load

conditions. Codes generally take this approach in pre- scribing sizes for horizontal fixture branches to which

two or more fixtures are connected, as well as for primary and secondary branches of the building drain

and for the building sewer. Thus, a designer is effec- tively inhibited from proposing a design in which a hydrostatic head above the drain would exist under

design load conditions, even when the pipe line being

considered (e.g., building drain or building sewer)

would have no floor drain or fixture connections for many feet above its invert. Although pressure drain- age in this sense was proposed in 1940 by a govern- mental committee on housing research [5], the idea

has not been incorporated in codes.

It should be understood, however, that if the overall design depends on pressure or vacuum relief (venting

action) through the air space over the water in a horizontal drain, the drain cannot be allowed to flow

full. Thus, in considering full-pipe or pressure drain- age in a gravity system utilizing water-sealed traps, it may be appropriate to consider trade-off values be- tween drain and vent piping under some circumstances.

Of the several considerations listed above, trap-seal

retention is usually considered to be of the greatest

importance. In early investigations of stack venting, wet venting, self siphonage, and the hydraulics of plumbing fixtures and drainage stacks [6, 7, 8, 9]

important determinations were made utilizing measures similar to the criteria discussed above. For example, the study on self siphonage [8] utilized trap-seal

reduction as the principal measure of adequacy of performance, and the study on stack venting [6] rec- ognized blow-back as one of the measures of perform- ance of DWV systems. In figure 1 the result of moderate vacuum or suc- tion on trap seals is shown in illustration A-3 and the

result of excessive suction is shown in A-5. These

effects may be brought about by water flowing in other parts of the system (induced siphonage) or they

may be caused by the action of water discharged from

the fixture served by the trap being considered (self- siphonag;e). In this example, the suction is assumed to be relatively slowly applied and released. If a cyclic

(fluctuating) suction is applied at a critical frequency,

effects may be worsened due to rocking action, as explained below for back pressure.

2
A. EFFECT OF VACUUM OR SUCTION

B. EFFECT OF BACK PRESSURE

lETURN TO

ATMOSPHERIC

RP<;(niiAi ^P&i ' 0

RESIDUAL SEAL

TOO SMALL

Figure 1. Illustration of the effects of vacuum and back pressure on idle trap seals.

Illustrations B-1 through B-3 show how a moderate

positive (back) pressure fluctuation in a trap arm may

cause fluid in the trap to first rise toward the fixture and upon a sudden release of the pressure create a rocking action in the trap that results in some loss of

trap-seal fluid into the drainage stack. This rocking

action may be particularly effective in reducing the trap seal of an idle trap subjected to pressures fluc- tuating at a frequency approximating the natural fre- quency of the trap seal. Excessive back pressure, shown in B-4, can eject sewage from the system into the fixture, or in extreme cases into a living area. Both the rocking action, and the ejection phenomenon

sometimes associated with excessive back pressure, can

result in excessive depletion of trap seal, as shown in B-5.The criterion adopted for defining satisfactory trapseal performance in this study was a trap-seal reduction not exceeding one inch. This would be equivalent

to a trap-seal retention of 50 percent, in a trap having

a full seal depth of two inches. Plumbing codes generally require that traps have seal depths of at least two

inches, but limit greater seal depth in traps to four

inches unless special approval is granted by the cognizant authorities. The primary objectives of studying the two particular DWV systems described herein were (1) to obtain

performance data that could serve as the basis for design procedures for sizing the dry vents of systems

using the RSV principle and (2) to develop experi- ence in test-load selection, measurement techniques,

and test procedures generally that could be utilized in the definition and standardization of a methodology

for evaluating hydraulic and pneumatic performance

of any DWV system.

Fixtures in the two systems were not varied as part

of the study, but selected wet ' and dry ^ portions of the DWV system were changed during the study. The

lengths and diameters of the vents were varied, and

with each variation some selections in fixture-dis- charge loadings were made. Under each set of conditions, measurements were made of trap-seal reductions, particularly for the trap seals of idle fixtures.

* Signifies "reduced-size venting.**

^ A "wet" pipe conveys waste water intermittently.

^ A **dry" pipe carries air only.

2. Venting Studies Conducted on a Test Setup Representing a Complete DWV System for a One-Story, Single-Bath Slab-on-Grade House

2.1. Purpose and Scope

A DWV design for a one-story slab-on-grade house was selected for the initial studies for the sake of simplicity and because it was understood that at the time the study was undertaken, single-family-detached,

slab-on-grade houses comprised the majority of living units under construction. The plumbing system included the five fixtures usually considered to be a desirable minimum, even for low-cost housing. By

observation of the effects upon trap seals, caused by

the introduction of selected hydraulic loads into the plumbing system, it was anticipated that a rating of

satisfactory or of unsatisfactory operation of the sys- tem could be obtained. Test plans included measure- ments of air flow in vents, water depths and velocities

3
in drains, and air pressures in stacks or trap arms for possible correlation with the effects of the hydraulic

loads on the trap seals. As the study progressed, when test loads were ap- plied to the system, modifications were made in the system piping as follows:

1. Vents and drains sized as shown on builder's

plans, see figure 2. (a) All vents were open.

(b) All vents were closed.'

(c) All vents were open except for bathtub and

lavatory.

(d) One vent was open with four closed and two

vents were open with three closed (15 variations).

2. The two-inch cast iron building-drain branch

that served the clothes washer and kitchen-sink for the

tests in (1) was replaced by a three-inch cast-iron drain, as indicated in figure 3. fa) All vents were closed. (b) One-half-inch inside diameter (i.d.) flexible plastic tubing vents, each 20 feet long, were connected

to a 2-inch copper-tube manifold which was closed.

fc) Same as (b) except that manifold was open

to the atmosphere.

3. Same as (2) except final 14.7 feet of building

drain was replaced with 3-inch transparent rigid

acrylic plastic pipe.

(a) One-half-inch tubing vents, each 20 feet long, were connected to a 2-inch manifold which was closed. (b) Same as (a) except manifold was open.

(c) Individual vents were closed off 5 feet above

floor level.

open

1/2" tubing vents-^

2" vent manifold (4 ft length)

] closed

clothes washer

2" —

2'L 2"

, kitchen

73"

water

bathtub

w li"

'1/2" tubing vents

lavatory

clos|t

-2

By use of valves and blind flange plates (see fig. 2) .

Figure 3. Schematic representation of one-story, slab-on-grade

DWV test system, showing reduced-size vents and manifold

vent terminal.

4. Same as 3(b) except the one-half-inch vents were

successively 50 feet, 40 feet, 25 feet, 10 feet, and 1 foot in length.

2,2. Description of DWV System

The plumbing system was derived from the plans

for a simple single-bath, slab-on-grade residence with

kitchen and laundry facilities. For the bathroom the

fixtures consisted of a 20" x 18" ledge-back lavatory,

a 5-foot recessed bathtub, and a siphon-jet-type water

closet. For the kitchen the fixtures were a 32" x 21"

two-compartment, flat-rim kitchen sink, and an auto- matic clothes washer. Figures 2 and 3 are schematic

4
ABC

REDUCING BRANCH FITTING REDUCING CLjOSET BEND REDUCING CLOSET FLANGE

Figure 4. Several methods for connecting a floor-outlet water-closet bowl to a 3-in soil stack.

representations of the DWV system. Figure 4 shows

the method used to connect the water closet to the soil stack, and indicates other methods that are often used. The water closet was connected to the soil stack by

use of a 4" x 6" x 16" closet bend connected into a 3" X 4" Washington reducing combination wye-andeighth bend, as in figure 4(A)

The main building drain, soil stack, and soil vent

(stack vent) were constructed of service-weight nominal 3-in cast iron hub-and-spigot soil pipe. The branch

of the building drain serving both the kitchen sink

and the automatic clothes washer was constructed of service-weight nominal 2-in cast iron soil pipe for the

initial tests, but was later increased to 3-in size as described herein. A slope of l/4-in/ft was established

for the drains. All the soil pipe joints were made with

neoprene rubber gaskets with the exception of the

joint to the water closet fitting and the connections to galvanized steel pipe. Except for the soil stack, the

vertical cast iron drains for the individual fixtures terminated with 2-in cast iron hubs extending 4 inches

above the floor to simulate slab-on-grade construction. Schedule 40 galvanized steel pipe was caulked into these hubs and extended vertically to serve as waste

stacks and vents for the individual fixtures. The steel portions of the waste stack were 1%-in diam for the

lavatory, sink and bathtub, and 2-in for the clothes washer. In the initial tests, all of the vent piping

except for the soil vent was constructed of ll/2-in diam schedule 40 steel pipe. In later tests provisions were made for the use of %-in (i.d.) flexible plastic

tubing for all of the dry vents beginning about 5 ft above floor level, as shown in figure 3. Combination wye-and-eighth bends and long-sweep

quarter bends were used elsewhere in the drainage

piping with the exception that the 11/2-1" trap arm of the bathtub was connected to the bathtub vertical waste pipe below the floor level through a 2" x 1%"

tapped sanitary tee. The roughed-in drain piping was subjected to a 15-

ft head of water with no evidence of leaks. The completed system was subjected to air pressure equivalent

to a 2-in water column for a period of one-half hour.

Since the indicated pneumatic pressure remained es- sentially constant a tight system was confirmed.

2.3. Approach to Measurement and

Test Control

2.3.1. Measurement

Instrumentation was provided for the indication

and recording of numerical values for parameters that described the hydraulic and pneumatic performance

characteristics of the plumbing system, e.g., trap-seal

retention, pneumatic pressures, water depth, etc. Residual trap seals in the P-traps of the lavatory, the sink, and the clothes washer were measured with

piezometers fabricated from glass tubing with attached graduated scales. The residual seals of the water closet and the bathtub were measured with electric point

gages. These methods are illustrated in figure 5. Fluctuating or rapidly changing pneumatic pres- sures and also the water depths were measured with

strain-gage bridge-type pressure transducers and re- corded on a multichannel recording oscillograph. Miniature pitot tubes were used to sense the air movement

in the vents. Pressures in pipes were transmitted to the transducers or indicating devices through short lengths of plastic tubing leading from %-in NPT

fittings screwed into tapped openings in the pipe

walls. Figure 6 shows the locations of the stations at which these measurements were made.

Dry air at atmospheric pressure (14.7 psia) and a temperature of 60 ° F was assumed in computing air velocities from measurements with the pitot tubes lo- cated in the vents. The effects of humidity and temperature under operating conditions were considered negligible for the purposes of this work. Mean velocity was assumed to be 80 percent of the indicated centerline velocity. The error introduced by this assumption

is probably the largest source of error in the measure- ment of air rates in the vents. The greatest uncertainty

in this experimentation was lack of information on the

5
HANDWHEEL 1

THREADED BRACKET3/8" ROD THREADED

16 PER INCH

MOUNTED SCALE

(TAPERED DISC FIXED TO ROD

FULL TRAP SEAL

WIRE CONNECTED TO CLAMP

ON TRAP

GLASS TUBING

A. FOR BATHTUB TRAP-. PIEZOMETER-ELECTRIC GAGE

FULL TRAP SEAL

P TRAP WITH CLEANOUT

-PLASTIC TUBE

B. FOR ABOVE-FLOOR TRAP: PIEZOMETER-SCALE

16 THREADS PER INCH

FULL TRAP SEAL.

C. FOR WATER CLOSET: ELECTRIC GAGE

Figure 5. Two methods for measuring trap-seal reduction/retention {one-story, slab-on-grade system).

^blind flange for closing vent- SYMBOLS

-o pitot tube in vent f pressure sensor on

trap arm p piezometer on trap

cleanout depth gauge in building drain

Figure 6. Locations of measurement stations on one-story, slab-on-grade DWV test system.

velocity profiles at the sections where the pitot tubes were placed. The velocity coefficients (i.e., the ratio of mean velocity to centerline velocity) determined by

Other experimenters range from 0.75 to 0.90, depending on a number of factors [10]. Thus, indicated air flow rates obtained by the procedure used could be in error by perhaps as much as ±10 percent. The antici- pated application of such data would not require

greater precision.

Information on the velocity of water flow in the building drain was obtained in two different ways. To

obtain an estimate of average velocities between se- lected measurement stations (D and E, and E and F),

the time intervals between the initial impact of the water at the upstream and downstream stations were

determined from the multichannel oscillograph record

of the outputs of the pressure transducers that monitored the depth of water during selected fixture load6
Figure 7. Method for measurement of varying water depth in building drain

{one-story, slab-on-grade system).

ings. The average velocity was computed as the dis- tance between stations divided by the time interval obtained as described. To obtain an estimate of the peak velocity as a function of distance above the

invert of the building drain, a vertical traverse with a

pitot tube was made with a selected hydraulic loading.

It was necessary to repeat the loading at each setting of the pitot tube on its traverse. In retrospect some

doubt exists about the significance of the pitot tube

measurements for two reasons: (1) the response time

of the pitot-tube measuring system was not determined

and (2) the measurement procedure did not prevent

air from entering the pitot tube. Because of these

uncertainties the measurements are not included in

this paper. The lavatory, bathtub, and sinks were calibrated to determine the average rate of discharge and duration

of discharge for selected water depths above the rim

of the outlet fitting. The water closet was calibrated on

a mechanical integrating device ^ which provided data

for computing average discharge rates over successive short time intervals during fixture operation. The au- tomatic clothes washer discharges were collected in a

calibrated container to obtain the measurements

needed for flow rate computations. More recently, the same clothes washer has been calibrated using a modern electronic load-cell weighing system as indicated

in section 2.4.1. Except where stated otherwise, the pressure of the water supply for the fixtures on the test system was

maintained at approximately 50 psig (estimated toler- ance 3 psi) by means of an adjustable pressure regulator. The source of supply was a 100 psig high- pressure water line.

'Shown on page 19 of NBS Monograph 86 [11].

The clothes washer had two distinct successive

events: a drain event followed by a spin-spray event. The sprays comprised 4 discharges of 7 s duration

each over a period of 2 min. The drain event dis- charged 16.4 gal of water during 60 s. The sprays discharged 4%-gal during 120 s. The method used for determining water depth in the building drain utilized a pressure transducer as shown

in figure 7. Comparison of peak-depth values, ob- tained from an oscillograph record of the pressure transducer output, with visual determinations using a

sight glass and scale indicated agreement within about

±5 percent, based on a number of comparisons with

individual fixture discharges

2.3.2. Test-Load Selection, Designation, and Application

2.3.2.1 Test-Load Selection The combinations of fixture discharges used cov- ered a wide range of loads, from single-fixture loads

to all fixtures discharged. Many loads used were probably much more severe than representative service

loads. For comparison, it may be of interest to note that a guide for selecting fixture loads for testing singlebranch-interval systems recently suggested by Wyly

and Sherlin [12] indicates that in a system comprising five fixtures the discharge of three fixtures to- gether would be a reasonable test load. Many of the

test loads employed comprised the discharge of three or more fixtures together.

2.3.2.2. Test-Load Designation

To simplify and shorten the descriptions of fixture loadings, a code has been devised that identifies the

7
fixtures, comprising the load, as well as the loading

sequence. For the fixtures shown in figures 2, 3, and

6, the individual fixtures are coded B = bathtub, C = automatic clothes washer, J and K = the two

individual compartments of the kitchen sink (J -(- K

if discharged together), L = the lavatory, and W =

the water closet. A time delay between the initiation of discharges from different fixtures is indicated by a numeral. For example W, 2. (B+J) = the washing

machine followed 2 seconds later by the simultaneous

discharge of the bathtub and the J-compartment of the kitchen sink; C, 4, W, 2, (B-j-J) = the clothes washer

followed 4 seconds later by the water closet, and then an additional 2 seconds later by the simultaneous

discharge of the bathtub and the J-compartment of the kitchen sink; All=all fixtures discharged simultaneously; and All —L=all fixtures except lavatory dis- charged simultaneously. This code has been used in presenting arid discussing the test results from the one-story system.

2.3.2.3. Test-Load Application

The discharging of fixtures was accomplished by means of electric solenoids which in the case of all fixtures other than the water closet and the automatic

clothes washer pulled the drain plugs completely out

of the water in the fixtures to eliminate interference to the flow. The water closet was actuated by a solenoid

acting through the flush-tank linkages. Each of the solenoids was controlled by a single-pole, single-throw

toggle switch. A toggle switch was used to operate the automatic clothes washer which was prefilled and

preset on the drain event. By using a digital seconds

counter (timer) a predetermined schedule of se- quenced discharges could be imposed on the system by

a single operator manipulating the switches while

watching the timer.

2.4. Findings

The tests on the one-story, slab-on-grade system

provided significant information on trap-seal retention

as affected by the following test conditions

1. All vents open (sized according to original de- sign as shown in fig. 2)

2. Complete closure of all the vents.

3. Complete closure of some of the vents, with all others completely open

4. Size-reduction of all the vents and the use of a manifold vent terminal which was either open or

closed. For clarity, the findings are presented separately

under each of the above categories. This is necessary because there were significant differences in the test system and in the test procedure that require separate

presentation.

2.4.1. Fixture Calibrations

Data obtained from the calibration of the fixtures are shown as figures 8, 9, 10, and 11. In figure 8 the

10 psi

SUPPLY PRESSURE VOLUME PERIOD RATE AFTERFLOW

psi e qal s qpm

• qal

10 14.4 3.80 15.0 15,20 045

50 15.9 4.20 165 15.3 0,76

TIME FOR DISCHARGE OF FULL TANK THROUGH BOWL OUTLET, S

Figure 8. Hydraulic calibration data for water closet.

5 on

FIXTURE VOLUME PERIOD RATE

i qal s qpm

B 150 39,6 2DI 11.8 C 620 164 60 16.4

50 100 i55~ TIME FOR DISCHARGE FROM 39.6 GAL. LEVEL, SECONI

10 20 30 40 TIME FOR DISCHARGE FROM FULL WASHER, SECONDS

Figure 9. Hydraulic calibration data for bathtub and

clothes washer.

FIXTURE VOLUME PERIOD RATE

e gal s gpm

J 15 3.96 14.2 167

K 15 396 221 10,8 J*K 30 7.92 206 23.1

5 10 15 TIME FOR DISCHARGE FROM FULL BOWL, SECONDS

Figure 10. Hydraulic calibration data for two-compartment

kitchen sink.

8
FIXTURE VOLUME PERIOD RATE

e qal s gpm

L 7 1,85 10.7 10,4 01 23456789 10 II TIME FOR DISCHARGE FROM FULL BOWL. SECONDS

Figure 11. Hydraulic calibration data for lavatory.

water closet data depicts the discharge characteristic for operating pressures of 50 psi and 10 psi. The

volume was measured in liters in graduated cylinders.

Through use of conversion factors the volume has

been converted to U.S. gallons in the tabulated computation. The average tabulated flow rate was calculated by using the time interval measured from beginning of discharge to the last trickle prior to the afterflow. Over the straighter portion of the calibration curve spanning the 5- to 10-second interval, a higher flow

rate may be calculated to be 26.8 gpm. Calibration curves for the bathtub and for the clothes washer are shown in figure 9. The calibration data were obtained

for volumes in the tub of 39.6 gal (9.05 in of depth)

and for 26.4 gal (6.75 in of depth)

At 39.6 gal of initial volume the average flow rate was 11.8 gpm and at 26.4 gal it was 10.9 gpm. A

simple extrapolation from these two values of flow rate gives a value of 10.8 gpm at 23.8 gal of volume (5.75

in of depth). An initial volume of 23.8 gal was agreed

upon for the purpose of standardizing the contribution of the bathtub to the test loads. In figure 10 calibration curves are shown for compartments (J) and (K) of the sink separately and for

the two compartments (J-j-K) discharged simultaneously. Each compartment was filled with 15 liters of water. A pronounced difference existed in the flow

rate of the two compartments. The reader is cautioned

to note that the curve for (J-f-K) is plotted against an ordinate of double the size for (J) and for (K)

The difference in flow rates for the two compart- ments may be explained as a phenomenon associated

with the arrangement of the drain piping. For compartment (K) the water discharged vertically downward through a tee into the trap whereas for compartment (J) the water would discharge vertically

downward to an elbow and then horizontally to the tee

at (K). When compartment (K) was discharged and

compartment (J) was empty, the pneumatic effect of

(J) on (K) was similar to that caused by the overflow

feature of a lavatory. In work done at NBS in 1939,

and confirmed by later studies reported in Housing

Research Paper 31 [9], it was established that when

the entrance to the lavatory overflow was sealed the time required to empty the fixture could be substantially reduced. When compartment (J) is discharged it may be that

as the water enters the tee beneath (K), a portion of the water is directed upward to seal off the drain from

the atmosphere as a "standing plug." Thus, essentially, compartment (J) discharges similarly to a lava- tory with a closed overflow and compartment (K)

discharges similarly to a lavatory with an open overflow. In figure 11a typical calibration curve is shown for the lavatory that was used in the one-story study.

The calibration curves are typical of others ob- tained for these fixtures. One of the causes for varia- tion between replicate curves obtained for bathtub,

sink or lavatory is the occasional formation of a vortex " .a allows venting. Such venting will usually

slow *m the flow; however, if the fixture and fitting so designed as to permit an occasional air lock to form, then a vortex may vent the air lock and speed

up the flow.

2.4.2. Tests With All Vents Either Open or Closed

2.4.2.1. Test Procedure

With all vents open, each fixture was discharged

individually. Water depths and average velocities were measured in the 3-in building drain, air flow rates in the vents were determined, and trap-seal reductions were measured. A velocity traverse was made at sta- tion "D" during the water closet discharge. Because representative loads for a 5-fixture system

probably should involve more than a single fixture, a

3-fixture load was next applied. This comprised the discharge of the water closet, followed two seconds

later by the simultaneous discharge of the bathtub and

the two compartment kitchen sink. A similar but still heavier load was next applied, comprising the abovedescribed load superimposed on the washing machine

discharge during the time the washing machine was

draining from full condition. The washer was started four seconds prior to the initiation of the water closet discharge. Finally, all fixtures were discharged simultaneously. For each of these three multi-fixture load- ings measurements were made similar to those de- scribed above for the individual fixtures. For the condition of all vents closed, fixtures in the system were operated as described for all vents open, and similar measurements were made, except that measurements of pneumatic pressures on the drain

sides of the idle traps were made instead of air flow

rates in the vents. With all vents closed, some of the loads resulted in excessive reduction in the trap seals of the sink and/

or the clothes washer. Evidently, substantial filling of the 2-in branch of the building drain serving the sink

and clothes washer sometimes resulted in induced si- phonage of one or more of these two traps. Had the branch of the building drain serving these two fix9
Table 1. Summary of results: ^ Comparison offunctional performance for all (customary size) vents either open or closed, with

various clean-water loads {one-story, slab-on-grade system *)

All vents open All vents closed

Description

of fixture discharge

load

Symbols

defining load ^ Average velocity

in drain, fps " Trap-seals

signifi- cantly

Average velocity

in drain, fps Trap-seals

significantly affected by

loading

Max trap- arm pressure

excursions,

J. 1 ClL/'Ov^Cll reductions, inches

(D-E) (E-F)

affected bv

loading

(D-E) (E-F) inches of water column 8

Bathtub B 2.6 2.9 None 2.9 2.6 None 0.00 0.0

Automatic clothes washer C 3.0 2.9 None 3.0 2.9 Sinkd Bathtub +0.3, -0.1

Slight ±

0.1 0.0

Kitchen sink, compartment not over

trap

J 2.9 2.9 None 3.4 2.9 Clothes washer

Sinkd Bathtub

-2.7

-0.1

2.0

0.9

Slight

Kitchen sink, compartment over trap K 2.6 2.9 None 2.6 2.9 Bathtub

Clothes washer

-0.1

-1.0

0.0

0.4

Kitchen sink, both compartments

J+K" 3.4 2.9 None 3.7 3.4 Bathtub

Clothes washer

Sinkd

-0.2

-2.4

Slight 1.8

1.1

Lavatory L 2.8 2.9 None 3.4 2.9 Sinkd -0.1 0.1 Water closet W 2,6 2.9 None 3.1 2.9 Bathtub +0.2 O.l" The water closet was discharged and followed two

seconds later by

the simultaneous

discharge of the bathtub and compartment (J) of the two compart- ment sink

W, 2, (B+J)

3.9 3.3 None 3.3 3.6 Clothes washer

Sinkd

-2.7 1.4

1.6

The clothes washer

was discharged and followed

four seconds later by the load de- scribed immediately above

C, 4, W, 2, (B+J)

3.4 2.9 None 2.9 o . o Lavatory

Sinkd

Clothes washer

-2.2 0.8

2.1 1.9'

All fixtures dis- charged simulta- neously

All 2.2 3.4 None 3.3 3.3 Sinkd Lavatory Water

closet

-3.6

0.8

1.8 0.5

* See figure 2 and 6. ^ These and similar symbols will be used thoroughout this paper to identify the fixtures that comprise a test load and also to define the intervals of time between the initiation of the segments or a sequential load.

" Travel distances are from: D-E 10 ft-3 in and from E-F 5 ft-9 in. ^ The two-compartment sink has a single trap under compartment K (does not have a food-waste disposal unit).

• Also observed at kitchen sink trap.

' Initial trap-seal depth of clothes washer is recovered when spray operates.

8 Where only a negative or only a positive value is listed, the value with the opposite sign was substantially lower in numerical

value, so was not recorded.

^ Calculated velocities have been rounded to the nearest tenth of a foot per second, and trap arm (vent) pressures and trap-seal reductions to the nearest tenth of an inch. Probably greater resolution was not possible with the instrumentation and procedures used.

10
tures been 3-in in diameter, effective air relief might

have been accomplished over the water in the building

drain, since the 3-in drain would not have been flow- ing fuU. Average velocities in the main building drain computed as described in section 2.3.1 and shown in table

1, do not appear to be significantly affected by closing

all the vents.

2.4.2.2. Results

Table 1 shows results of the initial tests on the onestory, single-bath system with code-size vents either all open or all closed. The tests with individual fixtures define the minimum loads utilized and provide a lower

reference for the comparison of effects of various

other loadings.

With all vents open, no significant trap-seal reductions were observed for any fixture loading applied, as indicated in table 1. The two columns at the right of

the table give the trap-seal reductions and associated vent pressure excursions for the trap most affected,

with all vents closed. The only traps losing in excess

of the inch of water seal were those serving the sink

and clothes washer.

2.4.2.3. Discnssion

With all vents open, no trap-seal reductions oc- curred with any of the fixture loadings; therefore it may be concluded that the venting was adequate to protect the trap seals even under severe loading conditions. Thus, the adequacy of the code-sized vents was

confirmed .

2.4.3. Tests With Some Vents Closed

2.4.3.1. Test Procedure

For these studies the experimental plumbing system was equipped with gate valves and removable blind

flange plates at the vent terminals (see figure 6). This

permitted each of the individual vents to be vented

directly to the atmosphere instead of through the main

stack vent when this was required. This arrangement was made to expedite the opening and closing of the various vents in different combinations of open and

closed vents. Preliminary tests with a given hydraulic

loading showed no detectable differences in trap-seal

reductions or in air-flow rates in the individual fixture vents that could be attributed to routing the bathtub

or lavatory vents directly to the atmosphere rather than through the stack vent. Two more water-depth measuring stations and pres- sure transducers fC and D') were added to the build- ing drain (see fig. 6)

A more-sensitive pressure transducer (full-scale range ±0.01 psid) was added to increase sensitivity in the measurement of air speed in the vents, using

pitot tubes, as described in section 2.3.1 and shown in figure 6. Previously the lowest-range transducer used was ±0.05 psid.

The effects of the selected loadings on trap-seal

reductions, air flow rates in the open vents, and water

depths in the building drain were investigated for all combinations of four vents closed and one vent open

and for three vents closed and two vents open. A number of fixture discharge patterns were uti- lized in these tests as indicated in table 2. These

discharges were picked by trial and error in an at- tempt to identify load patterns giving the greatest

trap-seal reduction for particular selections of open or closed vents. A number of the loads utilized were

three-fixture loads. A recently-published guide for se- lecting test loads for one-interval systems [5] gives three fixtures as a reasonable test load for such a system comprising five fixtures. Thus, the use of test loads comprising three fixtures in evaluating the per- formance of the complete system seems reasonable.

2.4.3.2. Results

In table 2 the test data have been organized around

the column that shows which vents were closed in the

tests that produced the data. For each combination of open and closed vents, one of the hydraulic loadings

consisted of the water closet discharge followed two

seconds later by the simultaneous discharge of the bathtub and one compartment of the kitchen sink

(W,2,(B +J)). The other fixture discharge loadings were those picked by trial and error in an attempt to explore the effects of a broad range of potential loads. Table 2 categorizes for each test loading the trap-seal

reductions as being excessive or a 'failure (F), or

satisfactory (S) and identifies the fixtures where ex- cessive trap-seal reductions occurred, based on the

criterion that reductions exceeding 1 in are excessive. Peak air flow rates were measured only for the load

(W,2,(B +J)).

Water depths were measured at four places (D, D', E, F) along the length of building drain (see fig. 6).

The maximum value of the water depths has been

recorded in table 2 as a percentage of the drain

diameter. The corresponding depths expressed in inches may be obtained by multiplying the represented

percentages by the factor 0.03. Figure 12 consists of a family of curves showing peak water depth in the building drain at several stations along the length of the building drain. Each curve is identified by ^ a fixture discharge or the combination of fixture dis- charges that created the peak water depth.

Average flow rates were assigned to the several combinations of fixture discharges by adding the rates for the individual fixtures involved in the combination

loading (see calibration data, section 2.4.1 and figs 8-

11). It is recognized that the time delays between

individual fixture discharges as well as other factors undoubtedly affected the discharge rate at any given

station along the building drain. The assigned vahies. therefore, are to be taken only as approximations of the true discharge rates within the drain and as providing a simplified means of characterizing: the magnitude of the loadings, in the absence of more

precise data.

11
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13
FIXTURES DISCHARGED

TIME MEASURED FROM START OF FIRST FIXTURE DISCHARGE, SECONDS

Figure 13. Relative water depths in building drain produced during selected fixture discharges

at station F (one-story, slab-on-grade system)

14
Figure 13 shows measurements of relative water

depth made at station F during the passage of several

fixture loadings.

2.4.3.3. Discussion

The data given in table 2 for the tests with some or

all vents closed show that none of the loadings pro- duced a failure of the water closet or bathtub trap

seals, and that only the discharge of all fixtures to- gether produced a failure of the lavatory trap seal. The data also show that all failures of the sink and/or

clothes washer trap seals occurred when one or both

of these two fixtures were discharged to comprise all or part of the hydraulic loading. This indicates that reductions in the trap seals of the clothes washer and

the sink may have been caused by temporary complete

filling of some part of the 2-in branch of the building

drain serving these two fixtures, when one or both of

the vents serving these fixtures were closed. If this were the case, venting through the air space over the water would have been inhibited. Either phenomenon or a combination of the two

seems possible since a 2-in drain with n = 0.015 and

a slope of % in/ft has a capacity of only about 17

gpm flowing full as computed by the Manning formula

[13]. Because of the rougher-than-usual appearance

of the soil pipe used in this study, and because of configuration effects that might have reduced computed capacities it is reasonable to suppose that the 2-

in branch of the building drain was flowing full over

a portion of its length during the discharge of the sink

(J = 16.4 gpm, J -[- K = 23.1 gpm) or the clothes washer (16.4 gpm)

Further analysis of the pattern of the failures of the sink and clothes washer trap seals shows that failure of both occurred only when both vents were closed,

and that failure of either trap seal occurred only when

its vent was closed. It was surmised that improved

performance, especially with either the sink or clothes washer vent closed, might be achieved by enlarging

the building drain branch to 3-in diam.

A matrix arrangement of the data shown in tables 1 and 2 has been made in table 3, showing the effects of the various loads on the trap seals of the system when

operated with no vents (all vents closed) or with

combinations of one, two, or three vents open. The

loadings are broadly grouped and listed progressively

by the number of active traps contributing to the load. Within each such group the simultaneous loadings

such as (C-|-L-|-W) precede sequential loadings such

as C,2,(J +L)- Also, sequential loadings involving two pause=i are grouped after loadings that involve

only one pause. Within each strata of the tabulations resulting from

the arrangement described above, the loadings are

listed in alphabetical order according to the first letter in the coded descriptor. Further separation and order- ing are based on the second, third, or fourth letter of the code. Within a strata of sequential loadings the duration of the first pause is next considered such that

(C-f J+W),2,B would precede (C +J+W),4,B. For

a contrasting example, (C +J+L),4,B would precede

(C +J +W),2,B. Finally, C,2,(J+K),2,W would pre- cede C,2,( J +K),4,W.

The matrix demonstrates the value of hindsight and

serendipity. For example, a loading thought to be

reasonable (W,2,(B4-J)) was selected and used for

the particular combination of three vents open with

the bathtub and lavatory vents closed, for all combinations with two open vents, for all combinations with one open vent, and for the condition of all vents

closed. The location of the resulting trap-seal reduction data within the matrix, as in items 29, 31, and 35,

clearly shows a progression of effects on the trap seals by degree of venting.

For items 29 and 31 the use of a single vent, such

as the clothes washer vent or the kitchen sink vent, corrected the overload effect on the trap seals. In item

35 the use of the water closet vent only was not enough, but the combined vents of water closet and

clothes washer were adequate to protect the trap seals. For item 27, the single vent at the bathtub was

inadequate but the addition of the clothes washer vent

corrected the problem. At item 33, neither the single vent at the lavatory nor the combined effect of vents

at lavatory and bathtub was sufficient. Data on the combinations of vents (B;C;L), (B;J;L), or (B;L;W) were not obtained, but since (B;C), (B;J)

and (L;W) provided adequate venting, these three- vent combinations, created by adding the lavatory vent for two of the combinations and a bathtub vent

for the other, probably would have resulted in satis- factory trap performance had they been tested. For all of loadings tried when using the combination of three-vents, (C;J;W), adequate ventilation was

obtained; however, in the 59 items listed in the table, only 20 represented tests with this combination.

For items 33, 37, 38, and 39, data were sought on

the effect of varying the length of pause in the similar

sequential loadings. For each of the tests there were

one or more runs involving excess trap-seal reduction,

but there was no general trend with the progressive

change in the length of pause in these tests. The results obtained with the very heavy loading (s) of items 48 through 56 showed that the particular

combination of vents (C;J;W) provided adequate

venting for the system under all combinations of load- ing resulting from simultaneously discharging any

four fixtures in any combination. The results given by

other items in the table suggest that this probably

could be said also for any sequential discharge of two,

three, or four fixtures. Items 57, 58, 59 represent data for five fixtures discharged simultaneously. Item 59 shows that the vent combination (C;J;W) provided satisfactory vent- ing with this load also. The method of grouping the data by magnitude of loading and by degree of venting is useful in inter- preting data from venting tests, would be purposeful

in defining a systematic test progression at the stage

when test plans are being made, and would provide a guide to aid in decisions on the need for continuing

15
Table 3. Matrix of data from tables 1 and 2, arranged progressively by magnitude of loading and degree of venting

tjXces- rjXces- hixces- Exces- Item Fixtures that Number of No sive One sive Two sive Three sive comprise the traps open trap- open trap- open trap- open traptest loading vents seal vent seal vents seal vents seal reduc- reduc- reduc- reduc- Active Idle tion tion tion tion

1i R K" T nr W 1 4 (IN one; AT-, IN one (C; J; W) None

2 c 1 4 (i>ione

p ( w; /R. \y/\

(£), VV ) t, (L; J; W) None

3 J 1 4 (iNone; p (a. wi p

4 (J+K) 1 4 (iNonej r T Li, J (L; J; W) AT-, ^ INone

o 2 3 i\ one

f.o B 10 W 2 3 (C; J; W) ATNone

7 c' 2 B 2 3 (C; J; W) None

0o c' 2', J 2 3 (C; J; W) None

Q c' 2' L 2 3 (C; J; W) None

Wj10 c' 2 W 2 3 (C; J; W) None

1

11 r'

9' 2 3 (L; W) C, J None

IZ1 9 2 3 (C; J; W) None

10 C 3 B 2 3 (L; L) T\T INone

l^' 2 3 (C; W) INone

10 2 3 (B; J)

TVT INone 10 2 3 (C;J) C

1

1 i 2 3

/T. T \ (J; L) L

lo 2 3 (J; W) C

1lyQ 2 3 (C; J; W) None

on 3 2 (B; L) C

91 3 2 (C; J; W) None

99 3 2 (B; C) ATINone ZD9^ 3 2 (C; J; W) None

Z't 9A 3 2 ( VV)

/-I L

9'^ ZO J , Z, ^1-1 " / 3 2 J)

AT ^ INone ZO9fi 3 2 (B; j)

ATNone

Z971 W , Z, 1 J ^ 3 2 (None) T

J (d) L, J /R . r'^ (B; L) AT„ INone ZO9J1 W , Z, ^JJ ~J;' 3 2

/TJ . T\ (B; J)

ATINone zy90 W , Z, ^1J r J } 3 2 (None) C, J (C) T\T INone (C; J)

ATINone (C; J; W) None

oU W , Z, r7j

/

3 2 (L; L) ATNone

31 W, 2, (B+J) 3 2 (None) C, J (J) None (J; W) None (C; J; W) None

32 W, 2, (B+J) 3 2 (J; L) None

oa W 9 ^R-l-T^ 3 2

/AT \ W

(None) L, J C (B; L) C, J W 9 /R-J_T\

, Z, (D J

3 2 (L; W) None WW 9 /R-1_T\

, Z, (D "Tj ^ 3 2

/TVT \ (None) C, J (W) J (C; W) None (C; J; W) None

oo W 9 /R-LI\ W , Z, ^13 r J

3 2 (B; W) C, J ^7 W Q /R -H^ 3 2 (B; L) C

oo 3 2 (B;L) c

oy W , 0, (ti i" J j 3 2 (B; L) c WW 9 CR-l-T-HC^ , Z, ^D-rJ T^^/ 3 2

TJ W 9 ^RJ_T4-1<'^ 3 2 (<-)

TVT IN one W 9 /R _L T 4- 1<'\ 3 2 (J)

AT-, INone (J;L) ATNone PIT! Vj, 1, J, 1, WW 3 2 (0)

A A L, Z, (J -\- Jv), 1, B 3 2 (L; W) C, J

L., Z, (J T-K), 1, VV 3 2 (C; L)

T

J Aft rL., z,9 ^i_i_Ti^\

(J -rjv), 1,1 ww 3 2 (C; W) TJ AH L,, 0, i" K), 0, VV 3 2 (C; J; W) None

/I Q All P All — L. 4 (J) None

AO All T 4 1 (IN one) T C, J (L) C, J DU All T All —

4 1 (B; J) c

OX All AH — TL 4

\ (C; W) AT« INone 52 All -(J+K) 4 (B; C) None

53 L, 2, (B+J+K+W) 4 (J;L) None

OH! ^R4-r\ ^Dn^u), 4,/I n-4-T<'i (Jn^Jx^, d.4, wVV 4 (L; J; W) ATNone

(DT^L.), 0, (JT^IS.), 0, VV 4 (C; J; W) ATINone 56 C, 4, W, 2, (B+J) 4 (None) C, L, W

(C; J; W) None

57 All 5 0 (None) C, L (B) c (B; W) C

58 All 5 0 (None) C, L (C) L (C:L) J 59 All 5 0 (None) C, L (J) C, L (C; J) L (C; J; W) None

16
DURATION OF DISCHARGE OF LOAD W, 2, (B + J) AT STATION F, SECONDS

Figure 14. Repeatability of depth measurements in building drain in successive tests with and without venting {one-story, slab-on-grade system)

tests in a loading or venting progression after some

measurements are completed.

The data of table 2 and figure 12 on maximum

water depths in the main, 3-in building drain shows

that none of the loads, including the discharge of all fixtures together, caused the drain to flow completely

full. It is reasonable to suppose that with some vents

closed or omitted, or with sizes reduced appreciably

below usual values, critical demands for air may occur when horizontal drains flow full at some section (s), because under such conditions air relief through the

air space over the water in the horizontal drain cannot

be relied on to aid in the control of trap-arm pressure

excursions. As expected, the maximum depths were

generally associated with the greater rates of dis- charge into the system; however, the spatial distribu- tion of the input points for a multi-fixture load ap- peared to influence the maximum depths.

The data of figure 12 show that for all of the six loadings, the maximum depths occurred at the station

farthest down stream. This suggests that "cresting" of the intermittent hydraulic loads introduced into build- ing drains may well occur at considerable distances downstream of the points at which they enter the building drain. This phenomenon was investigated ex- perimentally in an earlier study of surge flow at NBS

[11] and the findings in that study showed that the distance of travel in the building drain before "crest- ing" was influenced by drain slope, hydraulic roughness, type of stack-base fitting, drain diameter, and

other factors. Distances of 15 to 66 ft were obtained

with a 3-in drain in the earlier study. This contrasts with the belief expressed by the proponents of one

single-stack system that the point of maximum depth

occurs within four or five feet of the point of connection of a drainage stack with the building drain [14].

Whether the indicated difference in cresting distance

in the building drain is a result of the differences in hydraulic design has not been determined.

The flow-profile data for several fixture loadings

shown in figure 13 is important in that it suggests that

it may be possible to infer which fixture or fixture combination produces a drain load by the analysis of the indicated water depth-time profile. This seems feasible for two reasons:

1. Repetitive discharges of selected fixtures or combinations, even with substantial variations in venting,

yielded almost identical profiles (see fig. 14).

2. The characteristic profiles of individual fixtures appear to be distinguishable to a considerable degree even when two or more fixtures are discharged to- gether or in sequence. The possibilities for a successful application of this technique as a research tool in obtaining load data in occupied buildings depend on the ability to precali- brate the fixture loadings against their flow profiles

and on the ability to utilize computer technology in the analysis of the profile data. The measurements of peak air-flow rates in the vent« produced values far below the values predicted

from direct application of the theory presented in NBS Mono 31 [15], which is widely utilized in the

17
Table 4. Summary of results: Comparison of trap performance for different combinations of open and closed }4-inX20-ft vents and 2-in manifold terminal, with various clean-water loads (one-story, slab-on-grade system

Individual Manifold Material comprising lower 15 ft of

Trap-seals reduced by more than 1 in » vents terminal

Test load: building; dram ° Trap

fixture combi- perfor- nations/ mance ^*

A 11 AllAll All Open Closed

sequences''

a

Cast iron Plastic"* i)

1^ a

Water

closet

0 open

1 J closed Clotl wash Kitcl sink Bath

Laval

vA X W, 2, (B+J) X S A A W, 2, (B+J) X s A

v"A All T All —

"VA F VA

VA"V" A All T All —

X S X All T All —

X F A YA

A AV All T All —

X S AV A All T All— JL VA s VA AV All W7" All — W X b VA

VA All-W X S X All WT" All — W X F YA

A A All W/" All — W X b VA A

All "WT All — W vX s A A All T All—

X F YA

A

AY

YA All -J

All T All—

AY

AY

S

s A YA All T All—

AY s YA YA All T All —J AY s YA YA All All —VA, YA t YA

YA

AY

AY All All —VJa. All All —K"XV AY

X

rc YA vA A All All — K"JV YX

vA X All All — XVK X

vA XAll n-\-V\h All — (J T^JV^" X S VA

VA All /T4-li'\ All — (J n^is.) X S X ~~' All /T 1 T/'\ All — (J+K) X F X

X X

All /T_LV\ AH — (J+K) X S VA X

All /T 1 t/'\ Ail — (J +K) X s X X

All t} All —rJ X F X X

X X All D All —Jti X S X All T> All —

X F X

X X

All TJ All—

X S X X All-B X S X X All-C X F X

X X All-C X S X All-C X F X

X X All-C X S X X All-C X s

' See figure 3. B= bathtub, C=automatic clothes washer, J = compartment of the kitchen sink not over trap and (K) = compartment of sink over trap, (J+K) indicates that the two compartments were discharged simultaneously acting as a single fixture. L = lavatory, W =

water closet. Three types of symbols are used to designate the fixtures discharged to comprise a test load: (a) simultaneous discharge of group such as All =B+C + (J+K) +L+W, (b) partial simultaneous; All — (J+K) =all fixtures except the two-compartment kitchen

sink, (c) sequential; W, 2, (B+J) = water closet followed by a 2-second pause followed by simultaneous discharge of the bathtub and compartment J of the kitchen sink.

^ Building drain was nominal 3-in diam throughout, including the branch serving the sink and the clothes washer.

" Methyl methacrylate transparent plastic.

' F=Failed (at least one trap seal reduced by more than one inch). S = Satisfactory, (no trap seal was reduced by more than one inch).

8 Occurring in at least one of three successive trials. Water seals were replenished manually between trials. A single trap served the two-compartment sink (J+K).

18
Table 5. Detailed results: Comparison of trap performance for different lengths of Min vents, with various clean-water loads

{one-slory, slah-on-grade system ")

Vent

length

(h)

Load''

appli- cation code

Maximum trap seal reductions''

Test load: Combinations/sequences

° s u ?

c

J= C

-a

m

o

«J

50 1 All-W; All-L; All-B; All-J; All-K;

A11-(J+K); All-C

0.62 0.50 0.50 0.06 0.62

50

50

2

3 (J+K);fC; W;L;B;A11

All-W; All-L; All-B; A11-(J+K);

All-C; B, 2, W; C, 2, (J+K)

.38

.75 .50.62

.12 .56

.06

.16 .50

.62

40 1 All-W; All-L; All-B; All-J; All-K; All -(J+K); All-C

.50 .50 .50 .03 .38

40

40

2

3 (J+K); C; W; L; B; All All-W; All-L; All-B; A11-(J+K);

All-C; B, 2, W; C, 2, (J+K)

.25 .09. 12

.75

. 12

.53

. 19

.12 .38

.50

25 1 All-W; All-L; All-B; AIl-J; All-K; A11-(J+K); All-C

.31 .62 .31 .00 .25

25252

3

(J +K); C; W; L; B; All All-W; All-L; All-B; All -(J+K);

All-C; B, 2, W; C, 2, (J+K)

.25

.38

.25 .50

. 12

.38 .06.06

.25

.38

10 1 All-W; All-L; All-B; All-J; All-K; All -(J+K); All-C

.12 .12 .00 .00 ,00

1010

2

3 (J+K); C; W; L; B; All; C, 2, (J+K)

All-W; All-L; All-B; A11-(J+K);

All-C; B, 2, W

.25 .25 .00

.19

.06

.25 .00 .09

.06

.19

i

1IA 1 1 W- All T.All P.Alt T. All — W; All —L.; All — r>; All —J

All-K; All -(J+K); All-C

r\r\ .00 .00 .00 r\r\

1

1 23 (J+K); C; W; L; B; All All-W; All-L; All-B; A11-(J+K);

All-C; B, 2, W; C, 2, (J +K)

.12 .06 .00

.00 .00.12 .00 .06

.00

.06

* See figure 3. Nominal 3-in diam building drain throughout, including the branch serving the sink and clothes washer.

'' The load applications/types of obervations are coded as follows:

(1) Three successive applications of load: trap seals replenished manually before each application; seal losses observed after each application.

(2) Four successive applications of load: beginning with full trap seals for first application, seals were not replenished between

applications; seal losses observed after each application.

(3) A sufficient number of successive applications of load so as to yield for each trap at least four successive seal-loss values not greater than the first in this series of four: beginning with full trap seals for first application, seals were not re- plenished between applications; seal losses observed after each application.

" B= bathtub, C= automatic clothes washer, J = compartment of kitchen sink not over trap and K = compartment of sink over

trap, (J+K) indicates that the two compartments were discharged simultaneously acting as a single fixture. L=lavatory, W = water

closet. Three types of symbols are used to designate the fixtures discharged to comprise a test load: (a) simultaneous discharge of group such as All =B+C+ (J +K) +L+W, (b) partial simultaneous; All — (J+K) =all fixtures except the two-compartment kitchen

sink, (c) sequential; W, 2, (B+j) = water closet followed by a 2-second pause followed by simultaneous discharge of the bathtub and compartment J of the kitchen sink.

^ Maximum occurring in one or more of the various listed loadings.

' A single trap served the two-compartment sink (J+K).

sizing of dry vents by plumbing codes. This can be failures were observed for many loads with only one

explained on the basis that the vertical distances avail- or two vents open.

able for the water to fall before entering the building 2.4.4. Tests With Reduced-Size Vents and Manifold-Type

drain were so small in the one-story DWV system as Vent Terminal

2.4.4.1. Test Procedure to preclude the development of maximum water velocities and frictional drag, hence allowing substantial "slippage" between the water and the air in the verti- Figure 3 shows in schematic form the one-story

cal drains. This helps to explain why no trap-seal DWV system utilized for the tests described in sec19
BATHTUB TRAP IDLE

EFFECT OF VARIOUS LOADS

ON BATHTUB TRAP

CLOTHES WASHER TRAP IDLE

EFFECT OF VARIOUS LOADS

ON CLOTHES WASHER TRAP

•'(0,a,<3,v,»,»)""^(o,v,«,B) ^(,o,vrfi) KITCHEN SINK, LAVATORY, OR

/ WATER CLOSET TRAP IDLE

ao,»,«) '--Co,*,") EFFECT OF VARIOUS LOADS

° ON KITCHEN SINK TRAP

••(0,A,n,o,»,B) (A,n,^,m,m}

CO

o

ho

IDQ

LJ

or<

LU

CL

<

l.75 hSYMB0L TEST LOAD: FIXTURE COMBINATIONS

o ALL EXCEPT

1.50

1.25

1.00

0.75

050

025h

0

ALL EXCEPT

ALL EXCEPT

ALL EXCEPT

ALL EXCEPT

ALL EXCEPT

ALL EXCEPT

BATHTUB

CLOTHES WASHER

SINK COMPARTMENT (J) SINK COMPARTMENT (K) COMPARTMENTS (J*K)

LAVATORY

WATER CLOSET

CODE

(ALL-B)

(ALL-C)

(ALL-J)

(ALL-K)

(ALL-CJ+K])

(ALL-L)

(ALL-W)

-LAVATORY, BATHTUB, OR

SINK TRAP IDLE

EFFECT OF VARIOUS LOADS

ON LAVATORY TRAP

0.250

EFFECT OF VARIOUS LOADS

ON WATER CLOSET TRAP

/WATER CLOSET OR LAVATORY

TRAP IDLE

0

''*(0,A,0,o,V,*)'10 20 40 50 60

LENGTH OF REDUCED -SIZE VENT. FEET

Figure 15. Trap-seal reductions of all fixtures for various loads and for various lengths of V^-in vents {one-story, slab-on-grade system)

tions 2.4.1 and 2.4.2, as modified to accommodate the

tests with the reduced-size individual vents joined to a manifold vent terminal. The principal changes made in the test system were as follows:

1. The building drain branch serving the sink and

clothes washer was increased to 3-in diam.

2. The individual vents were decreased to V2-iri i.d. well above the flood-level rims of the fixtures served,

20
about 5 ft above floor level. The small-size flexible vent tubing used for these tests was coiled to accom- modate the excess over that required to reach to the manifold vent terminal, as described later in section 3. The test loads applied in these tests involved var- ious combinations of fixtures discharged. One type of load comprised the simultaneous discharge of all fix- tures except the particular one the trap seal of which was to be observed. These loads are indicated in tables 4 and 5 which also give the test results. The

load code follows the same format as explained in section 2.3. Three types of load effects were studied in these

tests, as follows

1. Single-run effect. Three successive applications of

load, with replenishment of depleted trap seals before

each application of the load. Trap-seal reductions were

recorded after each application.

2. Four-run cumulative effect. Four successive applications of load, beginning with all trap seals full but

without replenishment for the four runs. Cumulative

trap-seal reductions were recorded after each application.

3. Stabilized cumulative effect. A sufficient number

of successive applications of load, beginning with all trap seals full but without replenishment, so as to yield for all traps at least four successive trap-seal

reduction values not greater than the first in this series of four. Stabilized cumulative trap-seal reductions were recorded at the end of the series of runs. Some tests were run with the vent manifold closed

to simulate effects of complete closure by frost or

other environmental conditions, while at the same time

slightly restricting the flow in the building drain to cause it to flow at increased depth, as might occur in service due to an obstruction or gradual fouling.

Other tests were run with the lower 15 ft of the

cast-iron building drain replaced with smooth, trans- parent plastic of the same nominal 3-in diam. These

tests were intended to show possible effects of using a building drain material smoother than cast iron. These

tests were run first with the individual vents closed off and then with the vents and manifold terminal open.

2.4.4.2 Results

The principal results obtained with the tests on the

one-story, slab-on-grade DWV system with various

lengths of V2-in i-d. tubing instead of the usual code

sizes of vents are summarized in tables 4 and 5. It is important to remember that the results shown in table 5 are the most severe results observed with the several indicated loads with the entire building drain 3 inches

in diameter; actually the seal reductions for most of

the idle traps and for many of the loads were less than

the maximum value listed for the most-severely af- fected trap for each group of tests involving several

different loads. Figure 15 shows the results of the observations of trap-seal changes for all the fixtures as affected by length of l/2-in vents, for various loads comparing the simultaneous discharcge of all fixtures

COuiX

o

LENGTH OF VENT- FEET

Figure 16. Cumulative reductions of idle water closet or

lavatory trap seals, for various lengths of Vs-in vents

(one'Story, slab-on-grade system, all vents open)

except one. The data are the averages of trap-seal

reductions for three runs where traps were replenished

after each run. An upper-envelope curve encompasses

the plotted points representing the idle trap. Figure 16

shows cumulative trap-seal reduction for the water

closet and lavatory traps with all other fixtures dis- charged in each case. The data of tables 4 and 5, and

of figures 15 and 16, show no trap-seal failures with

any of the loads applied with the reduced-size vents and vent manifold open.

In table 4, satisfactory trap performance was ob- served in nine of fifteen tests with the manifold terminal closed, and in three of seven tests with all the vents individually closed. In all the tests with the reduced-size vents open and the manifold terminal

open, satisfactory trap performance was observed. Load W,2,(B +J) with 1/2 in diam vents 20 ft long

produced the following data:

Conditions

Stabilized cumulative trapseal reduction, maximum in any trap

Building drain 3-in diam cast iron throughout, manifold

vent terminal closed Lower 15 ft of building drain replaced with transparent

plastic, manifold vent terminal open to atmos- phere

0.4 in (clothes washer trap)

0.2 in (clothes washer trap)

These data show that the 3-fixture load used did not produce trap-seal failure, even with the vent terminal

closed. Comparison of the trap-seal reduction of 0.4 in

21
shown above for the closed-terminal condition with

the data of table 4, for somewhat similar loads with I/2- in vents 25-ft long and open terminal, suggests that closing the terminal probably had a relatively minor

ejSect.

Table 6. Effect of size of building drain branch serving

clothes washer and sink, with all vents closed (one-story, slab- on-grade system ")

Trap-seal reduction

Fixtures Trap observed comprising

load 2-in drain 3-in drain

in in

C Sink 0.16 0.00

J Clothes washer 2.00 0.19 K Clothes washer 0.44 .06 J+K Clothes washer 1.75 .62

* See figures 2 and 3 showing test system.

The data of table 6 for all vents closed shows the advantages of increasing to 3 in the size of the build- ing drain branch serving the sink and clothes washer.

For the test shown, the air relief with the 3-in drain

apparently occurred via the air space over the water on the 3-in building drain system.

The results of tests made with the lower 15-ft sec- tion of the 3-in cast iron main building drain replaced

with 3-in plastic pipe showed a striking improvement

over the results with the entire building drain of 3-in

cast iron. In both cases the test system utilized Vs-in vents connecting to the manifold terminal, but the terminal was closed. The comparison is presented for the case of the closed terminal rather than with it open, because any effects of the building drain on

effectiveness of the venting are more likely to be

detected with the vents closed or restricted than with

them fully open. So these comparisons are made using

data from test conditions not recommended as operating conditions, i.e., vent terminal closed—a very criti- cal test of the functional capability of any DWV

system. The concept of reduced-size venting is based on the premise that each DWV system will be vented

to the atmosphere through one or more adequately

sized terminal (s). Hence, in the comparison presented

here, some failures would be expected regardless of

the condition of the building drain. Twenty-one tests were conducted for each condition

involving seven different loads. Even though the vent manifold terminal was completely closed, trap-seal re- ductions did not exceed 1 inch in six of the tests with

the cast-iron reach, and did not exceed 1 inch in twenty of the tests with the plastic reach. Probably

this is attributable to the fact that the lesser hydraulic

resistance of the plastic reach might have been ex- pected to have reduced the peak depth of water in that section of the drain, thus allowing more effective pneumatic relief over the water surface than when the

cast-iron reach was employed.

Comparisons of trap-seal reductions with the plastic

drain, with the individual vents closed off and with ^2-

in vents 20-ft long connected to the manifold terminal

open to the atmosphere showed trap-seal reductions of one inch or less in fourteen of twenty-one tests involv- ing seven loading with all of the vents individually

closed, and no reductions exceeding one inch for the same tests with the 1/2-in x 20-ft individual vents open

and connected to the manifold terminal which was

open to the atmosphere.

Comparable data with the entire building drain of

3-in cast iron, obtained from the same tests and load- ings as above, showed trap-seal reductions of 1 inch

or less in five of the twenty-one tests with the terminal

closed, and no reductions exceeding 1 inch with it open. A pass-fail summary of the test results with the

entire building drain 3-in diam (either all cast iron or part plastic), taking into account open or closed condition for the individual ^-in diam x 20-ft long vents and the 2-in manifold vent terminal, is shown in table

4.

2.4.4.3. Discussion The most important findings are shown in table 5. These data show that there was not a single trap-seal failure in the many tests summarized in the table, with

the %-in diam individual vents as long as 50 ft. Figures 15 and 16 show that vent length affected idle trap-seal reductions, as was expected. No attempt was made to define equations for these curves. Figure 15 shows that although two or more traps

suffered some degree of seal reduction in some of the loads comprising the discharge of all fixtures except

one, the idle trap was affected the most, as had been

expected for the particular DWV system used for these tests. However, had the design utilized long trap arms or steeply sloped trap arms, self-siphonage might

have been expected and this could have produced

trap-seal reductions in active traps exceeding those in the idle traps. Possibly other conditions in complex

systems comprising some poorly designed components

could exhibit induced siphonage in active traps ex- ceeding that in the idle traps. This suggests that the organization of data in a format similar to figure 15

would be helpful in interpreting the data. The particular form of the envelope curves shown in figure 15 is empirical; however, experimentation and analysis de- signed to study this factor might provide a mathematical model to define curves of this type.

Review of the data of tables 4, 5, and 6 indicates the following:

1. The use of smooth materials in combination with

adequately sized building-drain system components

tended to prevent excessive water depths in the build- ing drain, and hence contributed to the maintenance

of a continuous air space and pressure relief above

the water during peak-loading periods.

2. Adequate venting was accomplished with a number of loads even when the individual vents or the common vent terminal were closed, with a 3-in build- ing drain beginning at the fixture farthest upstream,

especially when a part of the drain was comprised of smooth material.

22
RESISTANCE OF VENT TO AIR FLOW, APPROPRIATE UNITS

Figure 17. Conceptual illustration of relative trap-seal reductions as affected by resistance of vent and magnitude

of load.

2.5. Summary

The tests made utilizing several variations of the one-bath, slab-on-grade DWV system provided strong

support for the hypothesis that with competent engineering design and evaluation, many DWV systems in one-story houses could be adequately vented with re- duced-size vents. This was evidenced by the fact that

sufficient air relief occurred to protect trap seals with

vents much smaller in diameter than customarily used. Evidence was obtained that a considerable amount of

air exchange occurred within the DWV network when

the vents were connected to a manifold that was closed

to the atmosphere at its terminal. The results of tests made with loads that produced a

full or nearly full condition in the main building

drain or in the branch serving the kitchen/laundry

areas showed that complete closure of some or all of

the vents tended to produce significantly greater trapseal reductions than if the drains flowed less full with

the same loads (e.g., a smoother pipe or a larger-size

pipe).

The data showing apparent water depth in the building drain as a function of time provided signifi- cant support to the hypothesis that the monitoring of water depth in a horizontal drain serving a number of

fixtures may provide an economical way of identifying

load patterns in terms of composition and time distri- bution while at the same time determining drain ca- pacities with intermittent, short duration flow. The data with successive loads without refilling idle traps showed that generally maximum seal reduction

in the idle traps was closely approached in three or four occurrences of the load.

Little evidence of a meaningful relationship between

trap-seal reduction or retention and vent pressure ex- cursion was found, other than that large trap-seal

reductions were generally associated with large pres- sure excursions.

Review of the various data obtained provided a basis for figure 17, a conceptual illustration of the

effects of vent resistance and magnitude of load on

trap performance.

The forms of the curves have not been precisely

defined, but the broad trends and effects observed can ^e related to this illustration. Vent resistance is a function of diameter, length, roughness, and configuration. Load is a function largely of hydraulic dis- charge rate, DWV system dimensions and configuration, and time and spatial distribution of the elements

of the hydraulic discharge.

Various views have been expressed as to the upper

limit for relative trap-seal reduction, AH/H, that should be accepted. A relative reduction of 0.50 has

been shown here for illustrative purposes. The nature

of the function in the zone between "trap seal reduced

to zero" and "complete removal of water in trap" were

not studied in this investigation, and it does not seem

purposeful to perform research in this area (zone)

that has little practical significance.

Although the results obtained were significant, the

characteristics of the simple one-story system used for the first part of the investigation severely limited the application of the results in predicting performance in other types of systems. For example, how would trap

performance be affected by the greater stack heights

in systems with two, three, or more branch intervals? Would trap performance with a reduced-size vent be

significantly different with common venting or with wet venting instead of individual venting? How mierht the results be extrapolated to predict performance

with more complex configurations of DWV pipine and more and different types of fixtures? Consideration of these questions led to the decision to undertake a second series of tests with a split-level system with

fourteen fixtures, including three additional fixture types of fixtures or appliances.

3. Venting Studies Conducted on a Test Set-up Representing a Complete DWV System for a Three-Level (Two Stories and

Basement), Three-Batli House

3.1. Purpose and Scope interval of connected plumbing fixtures. It was ex- pected that the greater height and complexity of such

The test plan adopted for the study required trials a system might impose greater air demands and offer with a DWV system having more than one branch more opportunity for air recirculation within the sys23
reduced-size vents connected to standardsize vent stubs above

flood level of fixtures

served.

location of

station for obser

vation of travel

Figure 18. Split-level DWV test system, showing plumbing dimensions and

locations of measurement stations.

tern than the one-story, slab-on-grade system first studied, and hence, would be purposeful for testing the hypothesis that reduced-size vents might be successfully used in multi-story systems.

Other reasons for selecting the particular system

used included

(a) A greater number of fixtures and fixture types were used than for the one-story system.

(b) The utilization of common vents instead of individual venting provided the opportunity for examining the performance of this popular type of venting

with reduced sizes. These characteristics, typical of modern homes, were expected to place greater demands on the vents than in the case of the one-story system. The system

used for the tests, as shown in figure 18, was selected

in consultation with the NAHB staff. Three important types of measurements were made.

Fixtures not calibrated for hydraulic characteristics in connection with the tests on the one-story system were

calibrated, measurements were made of travel times

and apparent velocities in the building drain resulting

from several fixture loadings, and trap performance

(trap-seal retention and detergent blow-back) was

studied with various test loads, dimensions and ar- rangements of vents. 3.2 Description of DWV System

The test system, representing a complete DWV sys- tem for a three-level (two stories and basement)

,

24
three-bath house, is shown in schematic form in figure

18.To simplify the experimental work the vents were

not interconnected as would normally be done in the

field, but were terminated separately. This condition

may have provided a somewhat greater degree of venting than if they had been interconnected.

All drain piping which would normally be below

grade was fabricated of service weight cast-iron pipe, as were also the 3-in soil stacks and 3-in soil vents. The cast-iron soil piping and fittings were of hub type

joined with neoprene gaskets; however, in some in- stances where special fittings were not available,

oakum-pitch joints were made. All of the and 2-in vents and all of the drain branches that were installed in an above-grade location were fabricated of Schedule 40, galvanized steel pipe and appropriate recessed,

screwed, cast-iron drainage fittings. For most of the work the building drain was 3-in diam from its origin

downstream to the point of connection to the basement

laundry group, and beyond this point it was enlarged

to 4 in. Near the end of the program, the 4-in reach was extended upstream to the basement bathroom

group. This short reach of building drain between the basement bathroom group and the basement laundry

group served three water closets in addition to other

fixtures as shown in figure 18. The system was designed to discharge into the labo- ratory building drain through an air gap. Such sepa- ration assured atmospheric pressure at the end of the experimental drain. The two showers (R and S) were simulated by means of 2-in cast-iron soil pipe "P" traps. The floor drain (F) was represented by a 3-in cast-iron soil pipe "P" trap. A means was provided for introducing water to replenish any trap-seal reduction in these

traps, none of which were involved in creating any of

the test loads. The two back-to-back water closets (U and V) were

joined to the 3-in soil stack by 4" x 6" x 16" closet bends and 3" x 4" double Washington combination

wye-and-eighth bends. The water closet on the lower

level fW) was joined to the 3-in soil stack by a 4" x 3" reducing closet bend and a 3-in combination wyeand-eighth bend. As shown in figure 18, the other

fixtures included a bathtub (B) installed back-to-back

with a shower (R) ; two back-to-back lavatories (L

and M) on the upper level and one on the basement

level (N) ; and a two-compartment kitchen sink (J and

K) with food-waste disposal unit, and a dishwasher

(D) on the intermediate level. The dishwasher was

installed with its own trap and vent. The laundry

fixtures consisted of a concrete laundry tub (T) and

automatic clothes washer (C), each installed with a separate trap and vent. The clothes washer discharged

first into a 2-in standpipe, then through a screwed,

CEist-iron drainage "P" trap into a 2-in vertical waste

pipe. The water supply for the test system consisted of lengths of i-d. rubber garden hose terminating at the fixtures at one end and at a pressure-reducing

station manifold at the other end, adjusted to maintain

a supply pressure of approx 50 psi.

The complete DWV system was air tested with a positive pressure of 2-in of water column to assure a tight system.

3.3. Approach to Measurement and Test Control

3.3.1. Measurement

The hydraulic calibrations of the fixtures deter- mined as described in section 2.3.1 for the one-story

system were assumed valid for the split-level system in

all instances where the same fixture-drain fittings and

trap-arm configurations were used. The laundry tub and the dishwasher had not been used in the one-story

system. Neither had the food-waste disposal unit been

used with the sink. Two of these three fixtures were

calibrated in a simple fashion as stated in section

3.5.1. The approach to measurement of the time for water

discharged from the fixtures to reach particular sta- tions in the building drain (see fig. 18) was through

the use of stop watch and electric probes inserted through the crown of the drain and extending nearly

to the invert. The probes were connected to a power

supply, a microammeter, and a hand-operated multistation switch. This principle is illustrated in figure 5 (A and B), as used for detection of water level in the bathtub trap in the one-story system.

The approach to detection of trap-seal reduction in the split-level system also utilized the electric probe

technique. In order to facilitate the display of results

at a central station, an indicator system was fabricated

to permit advancing or retracting the probes so as to determine contact with the water surface, and to per- mit reading the reductions on an appropriate scale, all from the central station. This is shown schematically

in figure 19.

3.3.2. Test-Load Selection, Designation, and Application

3.3.2.1. Test-Load Selection

Test loads were selected to yield a range of composite discharge rates. This approach, a somewhat arbi- trary one, was similar to that described in section

2.3.2 for the one-story system. The general idea was to consider the DWV system in successively more complex assemblies, starting with individual fixtures, pro- ceeding then to consider the two or more fixtures served by common fixture branches or vertical waste

pipes, then to consider the group of fixtures in a particular room arrangement and the back-to-back

combinations of two room-groups, and finally to consider all the fixtures on a particular stack and on the system as a whole as a composite group. The intention was to select, in this way. a reasonable test load for

testing the drains and vents of each particular group

being considered. Reference to mathematical guides

presented recently [12] indicates that a number of the loads used in these tests were greater than might be

expected under normal service conditions for a DWV

system like the one represented by the split-level test system.

25
FRONT VIEW

TYPICAL INDICATOR PANEL FOR TRAP-SEAL RETENTION

/C.W

0 0 o 0

e C 0 F B

i i

Q

T U V w

CLOTHES WASHER (7\

I CONTROL

VIEW OF MANIFOLD USED TO FILL FIXTURES OR TRAPS

1/2" GARDEN HOSESIDE CONTROL PANEL FOR VERI- VIEW FYING DEPTHS IN FIXTURES a

(I^FOR DISCHARGING FIXTURES

COUNTER WEIGHT (CW)

WATER LEVEL DETECTION PROBE

SOLENOID a LIFT CRANK

PLUMBING FIXTURE

Figure 19. Method for filling and discharging fixtures, and for detecting trap-seal reductions

(split-level system)

Because of the lack of load data for plumbing,

particularly as to distribution of fixture operation by

time and fixture type, test load selection is likely to remain somewhat arbitrary. Better load data is needed

to provide the basis for the kind of mathematical

guides required to standardize the selection of loads

for testing DWV and water supply systems, following

the qualitative approach described above.

3.3.2.2. Test-Load Designation

To simplify and shorten the descriptions of fixture loadings, a code similar to that used with the onestory, slab-on-grade system has been used in presenting and discussing the findings. The letter symbols

used are defined in the footnotes to the tables of

results, and are shown on figure 18.

3.3.2.3. Test-Load Application In order to minimize the amount of manual work

required to fill and discharge fixtures, various electri- cal controls were added. This provided the means by

which all fixtures involved in creating the test loads

could be filled and discharged remotely from a central

station by one operator.

Figure 19 indicates schematically the methods used. Switches were provided on the control panel to per- form the following functions:

1. Selection of fi.xtures to be filled. 2. Starting and stopping of the filling operation.

3. Selection of fixtures to be discharged.

4. Initiation of discharges from fixtures accord- ing to predetermined, simultaneous or time-sequence

program.

Electric solenoids were utilized to pull the drain

plugs and flush the water closets in the same manner

as described in section 2.3.2.3 for the one-story sys- tem. Also, the initiation of the clothes washer dis- charge was accomplished as described in section

2.3.2.3. A light indicator was provided, on the control panel

for each fixture involved in the test load, that sig- nalled when the fixture was filled to a predetermined

depth. A timer was provided as an aid in the manual

operation of the fixture discharge switches according

to a time-sequence loading program.

26
^3 CAST IRON SOIL PIPE

J 7 1 1/2 PIPE NIPPLE 2

' LONG

STEEL PIPE \-Ui' OR 2'^

"*S' 7" IN ONE-STORY AND 4' 3"

IN SPUTLEVEL

1 ^XTURE TRAP FUMR

PLASTIC TUBING USED TO VENT WATER CLOSET FOR FIXTURES OTHER THAN WATER CLOSETS— ONE STORY AND SPLIT LEVEL

J,.

I GALVANIZED STEEL PIPE

1-1/4 STEEL PIPE

T \~\^t CAST IRON SOIL PIPE 3" CAST IRON SOIL PIPE\^^ '

LENGTH OF STEEL PIPE FOR MAIN VENT SPLTT-LEVEL SYSTEM l' LENGTH OF STEEL PIPE FOR MAIN VENT —SPLIT LEVEL SYSTEM

Figure 20. Methods for reducing vent sizes above fixture flood-level rim.

Table 7. Venting arrangements used in tests on split-level 3-bath system

Main vent All other vents Code

Diam Length Open Closed Diam Length Open Closed

in in ft

1 18 X VA ^ 5 X

2 IH 18 X Yi 25 X

3 1 1 X Yi 1 X 4 1 1 X Yi 25 X 5» Vi 1 X Yi 1 X 5^ 1 X

" Y2 1 X

= 6 y2 25 X Yi 25 X

7 50 X Y2 50 X

8 Yi 50 X

b Y2 50

* Vent to W was 3-in diam X approx 4-ft long, reduced to 2M-in diam at terminal by orifice. Closed by sealing terminals. Internal volume of each vent was approx Yi gal.

" Vents to kitchen sink and dishwashing machine closed.

With these provisions for remote application of se- lected hydraulic loads by a single operator at a central

station, the testing was greatly facilitated.

3.4. Test Procedure

The procedure for determination of times for the water discharged from the fixtures to reach selected

stations involved use of the electric-probe approach

described in section 3.3.1. Loads were repeated as determinations were made at the several stations in the building drain shown in figure 18. The procedure for studying trap performance in- volved the application of a variety of test loads, some

of which included detergents with either hot or cold

water. The quantities and types of detergents used, as

well as other details, are shown with the test results. For the purpose of comparing trap performance

with clean water and with included solids, cellulose sponge pieces were used. A sponge brick was cut into thirds so that each piece was approximately 4%-in

long and 1^/4- x 1%-in in cross section. Tests were made utilizing one, two, or three pieces in one toilet, flushed alone or with other fixtures. The water closet did not flush effectively with more than three pieces of sponge. This is a convenient way to simulate human

feces for the purpose of hydraulic tests, but because

they do not disintegrate under the action of the water

they may represent a more severe load than human

feces. Tests were made with several different venting

27
arrangements in which the standard-size vent stubs shown in figure 18 were extended with pipe or tubing

in the manner shown in figure 20. The various combinations of sizes and lengths of vents either open or closed are designated by code

number as shown in table 7. Trap-seal reductions were

determined using the approach described in section

3.3.1. For the test loads involving unusually severe

loads, visual observations of the lower fixtures were made for evidence of blow-back.

As to test statistics, the general procedure was to obtain all measurements in triplicate, with trap seals

refilled before each run. In the process of reducing

the volume of the data for compact presentation in

this paper, some of the measurements were classified as S (satisfactory) or F (fail), corresponding to a trap-seal reduction of 1.0 in or less or of more than

1.0 in, respectively. For the purposes of this classifica- tion the replicate measurements were reviewed and the

classification S or F made on the basis of the greatest

single trap-seal reduction recorded in the three runs.

It is believed this approach with the data obtained

tends to provide interpretations comparable to those with data on cumulative trap-seal reductions, with

traps not refilled before each run, as described in section 2.4 for the one-story, slab-on-grade system.

The method used pertaining to each specific group of data is indicated on the appropriate table or figure.

3.5. Result and Discussion

3.5.1. Fixture Calibrations

The active fixtures for the three level system consisted of three water closets (U,V,W), three lavatories (L,M,N), one two-compartment kitchen sink (J,K), one bathtub (B), one automatic clothes washer (C), one automatic dishwasher (D), and one laundry tub

(T).

The floor drain (F) and the two showers (R,S) were roughed-in for drainage but not for water supply. Water to refill the trap seals was supplied as needed. The food waste disposal unit (G) was at- tached to the kitchen sink and carried the same dis- charge load as the sink compartment.

Only the dishwasher and laundry tub were cali- brated since the two additional water closets and lavatories were identical with the ones used in the onestory facility. By observing the level to which the automatic operation of the dishwasher would fill the machine, with a supply pressure of 50 psi, it was

established that 2.38 gal of water was used in both the wash and the rinse cycles. The time required to dis- charge 2.38 gal was 50.2 s ±0.6 resulting in a rate of discharge of 2.85 gpm.

The laundry tub when filled to 7^/2 in above the discharge orifice contained 11.2 gal. It was deter- mined that the average flow rate during the discharge

period was 14.0 gpm.

The effect on the flow rate from the kitchen sink

compartment with the food waste disposal unit in- stalled was not determined.

3.5.2. Travel Times and Apparent Velocities for Hydraulic Loads

Table 8 and figures 21 and 22 show the results of measurements of the travel time for the flow of water

in the DWV system from the time of discharge to the time of arrival at the measuring station following the procedure described in section 3.4 and illustrated in figure 16.

0 10 20 30 40 50 60 70 DISTANCE FROM FIXTURE TO OBSERVATION STATION, FEET

Figure 21. Travel times for ivater to reach measurement

stations in building drain: effect of increasing discharge rate

(split-level system)

Load Key

Symbols Fixture (s) discharged

J+K Both compartments of kitchen sink K Sink compartment No. 2 (directly over food- waste disposal unit) L Top-story lavatory

L+M Top-story lavatories back to back

In figure 21 the pair of solid curves compare the

travel time for the discharge from the lavatory (L)

with that for the simultaneous discharge of the backto-back lavatories (L-(-M). This comparison is purposeful since the two lavatories have essentially identi- cal and/or common drain piping. The curves drawn

with dashes compare the travel time for one compartment (K) of the kitchen sink with the travel time of

the di<^charge from both compartments (J-(-K). The

drains from the two compartments have a common

trap.Doubling the discharge rate by simultaneously dis- charging both of the back-to-back lavatories resulted

in a reduction of travel time for the lavatories of 24

percent. An approximate doubling of the rate dis- charged through the sink trap (by discharging J-|-K

instead of K) reduced travel time by 20 percent. In figure 22 a comparison is made of the travel times for the discharge from the water closet (U) with

that for the simultaneous discharge of the back-to- back water closets (U-|-V). Here also the results showed that doubling the discharge rate reduced the

travel time substantially (27%).

28
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29
Comparison of these reductions in travel time with

predictions from continuous-flow theory, i.e., the Manning formula and the basic hydraulic elements for

circular sewers flowing partially filled [16], indicates

that the values obtained, although greater than predicted, are explainable on the basis of the attenuation

of short duration and/or "peaky" profile discharges.

Assuming a value of 0.013 for "n," a 3-in drain at a slope of 14-in/ft has a full-flow capacity of approx 56

gpm, according to Manas and Eaton [13]. Utilizing the values of average discharge rates for the fixtures involved (see figs. 8, 10, and 11), assuming no atten- uation of the discharge profile, and computing the

effect on travel time caused by relative difference in velocity for a given rate of discharge as a function of flow depths, due to added discharge rate, the follow- ing values are obtained

Fixture (s) contributing

load

Avg

discharge

rate Ratio h/dTheoretical reduction

in travel

time''

Measured

reduction

in travel time

gpm % %

L 10.4 0.29 L+M 20.8 .42 17 24 K 10.8 .30 J+K 23.1 .45 18 20 U 15.3 .36 u+v 30.6 .53 17 27

Assuming "n" constant with flow depth, (d) is the diameter of the pipe and (A) is the depth of flow in the pipe. ^ Due to increased discharge rate.

The discrepancy between the theoretical and measured values is explainable on the basis of attenuation

of flow depth as the discharges move through the building drain. Such attenuation elfects have been

shown and discussed by Wyly [11] in a study of hydraulics of horizontal drains. The two principal

factors are probably (1) the "peakiness" of the profile, e.g., the ratio of peak to average discharge rate from the fixture, and (2) the duration of the fixture discharge. For example, the discharge from a water

closet with a short, peaky profile would be expected to attenuate at a high rate due to the relatively high

gravitational forces tending to cause the "slug" to "slough off" at the ends, or to "flatten." By contrast, the discharge from a bathtub (or clothes washer) is characterized as relatively long-duration and nonpeaky, and this would be expected to produce conditions approaching those to which the Manning for- mula applies. Therefore, in actuality the flow depths

for water closet discharges would be expected to atten- uate to magnitudes appreciably less than predicted

from theory, and for bathtub discharges to be nearly

in agreement with theory. Following this reasoning,

the flow depth from a lavatory or sink would be

expected to attenuate somewhat less than for the water

closet, but more than for the bathtub. Examination of the curves representing the basic hydraulic elements

of circular sewers [fig. 15—1, ref. 16] shows that the

rate of reduction of velocity with reduction in flow depth is increasingly greater as flow depth is reduced.

Therefore, the greatest discrepancy between computed and actual reductions in travel time in the data

shown here should be for the water closet, and the

least for the kitchen sink. The data support this expectation; see preceeding tabulation. Curves for four other fixtures are shown in figure

22. The bathtub curve (B) implies a very slight slow- ing down of the water with the distance traveled. This

characteristic may be accounted for by the explanation offered above concerning attenuation of flow

depth. The same explanation together with the long

duration and essentially constant rate output of the dishwasher pump accounts for the nearly linear curve

for the dishwasher.

Data were taken at only one station for the laundry

tub and for the automatic clothes washer, but it is reasonable to suppose that had the additional data

been taken the curves would have resembled the bath- tub and the dishwasher curves, respectively.

For the fixture discharges (J*) and (J-f-K)* the food-waste-disposal unit was operating. From table 8, in a comparison with (J) and (J-j-K), respectively,

0 10 20 30 40 50 60 70 DISTANCE FROM FIXTURE TO OBSERVATION STATION, FEET

Figure 22. Tmvel-times for water to reach measurement

stations in building drain: comparison of various fixtures

{split-level system)

Load Key

Symbols Fixture (s) discharged

B Bathtub C Clothes washer D Dishwasher

T Laundry tub U Top-story water closet U+V Top-story water closets back to back

30
Table 9. Detailed results: Comparisons of trap performance for several test loads'" with main vent IH in X 18 fl and all others H i/t X 25 ft •> (split-level test system)

Fixture loadings with and without additives ° Trap-seal reductions, in inches, for fixtures identified by code

B C D F J L M N R S T U V W

(L+M) 0,02 0.02 0.02 0.54 (L+M) with 8 ml

detergent in each

of L and M .12 0.02 1.0 .20 0,66 0,12 .18 (J+K) .13 .02 ,03 ,02 (C+N+T+W) .06 0.33

(U) .30 .43 .35 0.06 0.04 ,24 (B+U) .56 .50 .31 .50 .16 ,50 (B+U) with 16 ml

detergent in (B) .16 1.07 (B+U) with 48 ml

detergent in (B) .07 .04 .05 0.04 .07 2.50 (B+L+U), 5, (C+W) .60 .70 .50 .36 .94 .29 .50 0.16 (B+L+U), 5, (C +W)

with 200 ml

detergent in (C)

.48 .60 .68 .50 .52 .25 .38 .50 ,12

(U, 3, V) .79 .96 .70 .58 .83 .29 .48 .08

(U, 5, V) 1.28 .80 1.00 .78 1.00 .42 .80

(U, 7, V) 0.88 ,77 1.00 .64 0.70 .48 .52

" See figure 18 for test syst

*> Vent arrangement code 2

" See footnotes to tables 10

as described in table 7. and 11 for explanation of load symbols.

without food-waste-disposal unit operating, the data

indicate that the operation of the unit caused a defi- nite slowing down of the water through the drainage

system. Possibly the additional turbulence, vorticity or

swirl could have accounted for this effect. Additional

data for simultaneous and sequential discharges of

fixtures are shown in table 8 together with their travel times and indicated rates of travel between measuring

stations.

It should be realized that a portion of the travel time for the discharges of any of the fixtures on the second and third levels of the system was used up in the passage of the water down the soil stack at the

velocity considerably in excess of the velocity that could be maintained in the building drain. This helps

explain the relatively high velocities indicated for some fixtures in the first reach from the fixture to station No. 1 (see data for B,L,L + M). This explanation, however, does not account for the data for the water closets, probably because of the delay due to

initiation of flushing action (and to collision of the streams in the stack for load U+V)

The data in table 8 provided guidance in the selec- tion of load sequences intended to concentrate the discharges within particular reaches of the drainage

system, and offered further support for the general

hypothesis that accurate measurements of velocities,

depths, and discharge profiles in a horizontal drain

serving multiple fixtures may provide a convenient

and economical way to obtain needed load data, pro- viding that the system can be precalibrated to correlate the measured parameters with known fixture load- ings and that computer processing of the data is systematically planned for.

3.5.3. Transportability of Solids

In tests made with pieces of sponge flushed through one of the top-story water closets (see sec. 3.4 for description), it was found that with a flush of one

piece, the specimen passed completely through the system in successive trials. When flushing two or three

pieces, one or more of the specimens usually stayed in

31
Table 10. Summary of results: Comparison of trap performance for different venting arrangements with various clean-water loads''

(split-level test system ^)

Listing

Number

Vent

arrange- ment

code =

Main vent All other vents

Test load'

fixture combinations/se- quences

Number

of fixtures discharged

Number

of trap

seals reduced by more

than 1 Inch

Diam Length

Condition Diam Length

Condition

Inches Feet Inches Feet

1 1 IH 18 Open 5 Open (U+V), 5, W 3 None'' 2 2 VA 18 Open Vi 25 Open U; (J+K); L + 1; 1; 2; 2; None

T T T* 1 T T" T» 1 U; B+U; B + 3; 4; 3; 4;

T ITT i~l 1 TIT ( L+U; C+N + 5 T+W; (U+V),

3, W; (B+L +

U), 5, W; (B-1- L+U), 5, (C +

W)

3 2 VA 18 Open Vi 25 Open TT 1 XT /TT 1 "trv U +V; (U +V), 2; 3 3

5, W

4 2 lA 18 Open 25 Open (U+V), 7, W; 3; 6 2 (B+L-rU+V),

5, (C+W)

5 3 1 1 Open 1 Open U; L+U 1; 2 None

6 4 1 1 Open y2 25 Open U; (J +K); L + 1; 1; 2; 4 None

U; C + N+T

-^W

7 5a 'A 1 Open y 1 Open U; (J+K); 1; 1; 2; 4 None L+U; C+N +

T +W

8 5b 1 Open " 1 Open ' U 1 1 9 6 Vi 25 Open 25 Open C+N+T+W 4 None

10 6 H 25 Open 25 Open U 1 3

11 6 'A 25 Open Vi 25 Open U+V 2 4

12 6 A 25 Open 25 Open L+U 2 5 13 7 A. 50 Open 50 Open u 1 5 14 7 A 50 Open K2 50 Open U +V 2 2

15 7 Ai 50 Open 50 Open B+L+M+U+

V

5 6

16 8 A2 50 Closed ' 50 Closed ' W; L; M; N; 1; 1; 1; 1; 1; None

B; J; J*i; K; K*; 1; 1; 1; 1; 1; D; C; T; D+T 1; 1; 2 17 8 A2 50 Closed ' 50 Closed ' T T *^ 1 HT 1 Tl U; C+N+T 1; 4 4 + W

18 8 Vi 50 Closed ' y2 50 Closed ' V; B +C+D + 1; 11; 7 2 J+K+L+M+ JVT 1 1 T T \ IT 1 N+T+U+V+

W; (D+J+K),

2, (B+L +M-l- U + V)

19 8 A2 50 Closed ' 50 Closed ' (J + K); 1; 1 1

(J JS.; 20 8 A 50 Closed ' 50 Closed ' U+V; L+U; 2; 2; 2; 2 5 B +V; L+M

21 8 Ai 50 Closed ' 50 Closed ' B+'L+M+U 5 3 +V

» Water at ambient cold temperature.

^ See figure 18 showing test system. Building drain 3-in diam upstream of laundry group, 4-in downstream.

" See table 7 for explanation of Code.

•* Vent to (W) was nominal 3-in diam X approx. 4-ft long, reduced to 2}/^-in diam at terminal by orifice.

' Vents to kitchen sink and dishwashing machine closed.

' Closed by sealing terminals. Internal volume of each vent was approx. J/^ gal.

K B = bathtub, C= automatic clothes washer, D = dishwasher, J = compartment of the kitchen sink not over trap and K= compartment of sink over trap, (J+K) indicates that the two compartments were discharged simultaneously acting as a single fixture. L and M are back-to-back lavatories on the top level, N is a lavatory on the bottom level, T = concrete laundry tub, U and V are backto-back water closets on the top level and W is a water closet on the bottom level.

•> Three types of symbols are used to designate the fixtures discharged to compromise a test load: (a) simultaneous discharge of group such as All = B +C+D + (J +K) +L+M+N+T+U+V+W, (b) partial simultaneous; All - (J+K) =all fixtures except the two-compartment kitchen sink, (c) sequential; W, 2, (B+J) =water closet W followed by a 2-second pause followed by simultaneous

discharge of the bathtub and compartment J of the kitchen sink.

' A sing;le trap served the two-compartment sink (J +K).

' For the J* K* and (J+K)* loads the food-waste disposal unit was operated during the discharge of the sink compartment (s). ^ Similar results with nominal 3" diam. building drain upstream of lowest-level bathroom group and nominal 4" diam downstream of bathroom group, see figure 18.

32
Table 11. Summary of results: Comparison of trap performance for clean water loads and similar loads containing detergent or

solids additives^, with three venting arrangements

(split-level test system ^)

Main vent All other vents Number

Vent Test load: Number of trapar- fixture combi- of fix- seals range- Diam Length Con- Diam Length Con- nation/se- Additives tures reduced ment di- di- quences'* " dis- by more

code " Inches Feet tion Inches Feet tion charged than

1 inch

1 VA 18 Open VA 5 Open U+V, 5, W Clean water 3 None

2 IH 18 Open Vi 25 Open U+V, 5, W Clean water' 3 3 2 VA 18 Open Vt. 25 Open U+V, 7, W Clean water' 3 1 2 VA 18 Open Vi 25 Open L+M Clean water' 2 None

2 VA 18 Open Vi 25 Open L+M Clean water' 2 None

2 VA 18 Open Vi 25 Open L+M 8 ml of liquid detergent in 2 1 each lavatory' 2 VA 18 Open Vi 25 Open B+U Clean water' 2 None

2 VA 18 Open Vi 25 Open B+U 16 ml /of liquid detergent 2 1 in each bathtub 2 VA 18 Open Vi 25 Open B+L+U, 5, 200 ml of detergent 5 None C+W powder in clothes washer

2 VA 18 Open Vi 25 Open B +L+U, 5, Clean water' 5 None C+W

5a 'A 1 Open V2 1 Open J+K Clean water' 1' None

5a 'A 1 Open Vi 1 Open J+K 16 ml of liquid detergent

in each compartment of

sink

1' None

5a 1 Open Vi 1 Open (J+K)*- 16 ml of liquid detergent 1 None

in each compartment of

sink. System not purged

of suds between suc- cessive test runs

5a 1 Open V2 1 Open U 3 solids in water closet U 1 None

* Some loads involved hot water, others cold.

^ See figure 18 showing test system.

" See table 7 for explanation of code.

^ B = bathtub, C = automatic clothes washer, J = compartment of kitchen sink not over trap and K = compartment of the sink over

trap, (J+K) indicates that the two compartments were discharged simultaneously acting as a single fixture. L and M are back-to-back

lavatories on top level, U and V are back-to-back water closets on top level and W is a water closet on bottom level.

° Groups of symbols are used to designate the fixtures discharged to comprise a test load: (a) simultaneous discharge of group

such as B +U, (b) sequential; B+L+U, 5, C+W, simultaneous discharge of bathtub, lavatory L and water closet U followed 5 seconds

later by simultaneous discharge of the automatic clothes washer and water closet W.

' See figure 18, nominal 3-in diam building drain upstream of laundry group. Nominal 4-in diam building drain downstream of laundry group.

8 Similar results with nominal 3" diam building drain upstream of basement bathroom group, and nominal 4" diam downstream

of basement bathroom group; see figure 18. Vent to (W) was nominal 3-in diam X approx 4-ft long, reduced to 2V-in diam at terminal by orifice. Cold water as drawn from supply piping (approx 25 deg C).

' Hot water in range of 46 deg C to 56 deg C. Hot water in range of 58 deg C to 64 deg C

' A single trap served the two-compartment sink (J+K)

TM For the J*, K* and (J+K)* loads the food-waste disposal unit was operated during the discharge of the sink compartment (s).

the system (probably within the building drain) until washed through with a second or third flush with

clean water. The water closet did not flush effectively

with four or more pieces of sponge, hence no more

than three pieces were used in the subsequent trap

performance test made with the sponge pieces in the

load.

3.5.4. Trap Performance With Various Loads and

Venting Arrangements

Tables 9, 10, and 11 summarize the measurements

of trap performance with various loads and venting

arrangements, obtained by the procedure described in section 3.4. Some of the results are illustrated by

graphs in figures 23 through 34. Table 9 compares trap-seal reductions for several

test loads with venting arrangement 2 as described in table 7 (main vent Wi-in x 18-ft, all others 1/2-1" x

25-ft). These data provide the basis for the following

observations:

33
W 1-8 UJ^

1.6 ~ 1.4 I'

a 1.0

ill °^ 08

_1a 06 w

0.04 <

g 02 i

FAILED SATISFACTORY

UV LMRB J DWN SFCT

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

z

zo

I-o

a

_J<

05-

04-

03-

02-

01 -UVLMRBJDWNSFC FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 23. Effect of vent resistance on trap performance

for cold, clean-water load U

(split-level system, averages for measurements in triplicate)

Figure 24. Effect of vent size on trap performance for cold, clean-water load L + U

(split-level system, averages for measurements in triplicate)

Symbol

Main vent All vents other than main

vent code

Symbol

Main vent All vents other than main

Vent

code Diam

In LengthFt Diam

In Length

Ft Diam

In LengthFt DiamIn LengthFt

1 Vi 25 Vi 25 6 1 Vi 1 1 5a

2 1 1 25 4 2 1 1 1 3

3 VA 18 25 2

0.8-

07-

0.6-

05-

04-

03-

0.2-

Ol -

0. I

12

3 UVLMRBJ DWNSFC

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

2*O

I-o

Q Q2|-

tiJ a.

11 UVLMRBJDWNSFC

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 25. Effect of vent resistance on trap performance

for cold, clean-water load /+a

(split-level system, averages for measurements in triplicate)

Figure 26. Effect of vent resistance on trap performance

for cold, clean-water load C-\-N-hT-\-Jr

(split-level system, averages for measurements in triplicate)

Symbol

Main vent All vents other than main

Vent

code Symbol

Main vent All vents other than main

Vent

code Diam

In Length

Ft DiamIn Length

Ft Diam

In Length

Ft Diam

In LengthFt

1 Vi 25 Vi 25 6 1 H 25 Vi 25 6

2 1 1 Vi 25 4 2 1 1 Yi 25 4

3 VA. 18 Vi 25 2 3 VA 18 Vi 25 2

4 Vi 1 Vi 1 5a 4 Vz 1 1 5a

34
5

z

15

tFAILED i

SATISFACTORY UVLMRBJDWNSFCT FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

09

08

111 X 07 o

zz

06

TIO 05 o

0,4

tc. _l 03

<I

tlJ V) 02

a.< 0.1

0

Figure 27. Effect of vent resistance {including all vents

closed) on trap performance for cold, clean-ivater load U

(split-level system, averages for measurements in triplicate)

UVLMRB J DWNSFC' FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 28. Effect of closing sink and dishwasher vents on

trap performance for cold, clean-water load U

{split-level system, averages for measurements in triplicate)

Condi- Main vent All vents other Condi- Main vent All vents other

Symbol

tion of all than main

Vent Symbol

tion of

sink than main

Vent

vents Diam

In LengthFt DiamIn LengthFt

code and

and

dish washer Diam

In Length

Ft Diam

In Length

Ft

code

1 Closed H 50 50 8

vents

2

34

Open

Open

Open

ViVi

Vt.

50

25

1

Vt. Vi

50

25

1

76

5a

12 Open

Closed

1

1 Yi

1

1 5a5b

\A

12

I0--

0.8-

06-

0.4-

02-

t FAILED SATISFACTORY

UVLMRBJDWNSFCT

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 29. Effect of time sequence on trap performance for

cold, clean-water multi-fixture load U+V, t, W with vents in accordance with vent code 2

{split-level system, averages for measurements in triplicate)

Symbol Time delay, t s

1 3 2 5 3 7

3 2, m_ UVLMRBJDWNSFCT

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 30. Effect of solids on trap performance for cold water load U, with vents in accordance with vent code 5a

{split-level system, averages for measurements in triplicate)

Symbol Number of sponge pieces flushed

1 None

2 1 3 2 4 3

35
VLMRBJDWNSFC FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

UVLMRB J OWN SFC FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 31. Effect of 16 ml liquid detergent in each sink com- partment on trap performance for cold-water loads J-\-K and

{J-\-K)*, ivith vents in accordance with vent code 5a

(split-level system, averages for measurements in triplicate)

Symbol Detergent Fwdu operating System purged between runs

1 No No

2 Yes No No

3 Yes Yes No

4 Yes Yes Yes

Figure 32. Effect of 8 ml liquid detergent in back-to-back

lavatories on trap performance for cold-water load L+M,

with vents in accordance with vent code 2

{split-level system, averages for measurements in triplicate)

Symbol Condition

1 Clean water in L and M

2 8 ml liquid detergent in each of L and M

* Food-waste disposal unit operating.

0.9-

0.8-

0.7-

0.6- 05-

0,4-

0.3- 02-

Ql -

0 _

12 12

VLMRBJ DWNSFC

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Xo

z

o

l-o

a

Ui t FAILED

1.3 0

J

^ 3

3

n

L

3 1 i_P eJJ

SATISFACTORY

3

n UVLMRB JDWNSFCT

FIXTURE TRAPS OF SPLIT-LEVEL SYSTEM

Figure 33. Effect or 200 ml granulated detergent in clothes- washing machine on trap performance for cold-water load

B-\-L-\-U, 5, C-\-W, with vents in accordance ivith vent code 2

(split-level system, averages for measurements in triplicate)

Figure 34. Effect of two different concentrations of liquid detergent in bathtub on trap performance for cold-water load

B-\-U, with vents in accordance with vent code 2

(split-level system, averages for measurements in triplicate)

Symbol Condition Symbol Quantity of detergent in B

1 Clean water in each fixture 1 None

2 200 ml granulated detergent 2 16 ml

in C 3 48 ml

36
1. The discharge of the two top-story lavatories together with detergent produced a near-failure of the trap seal in the dishwasher (1.0-in reduction).

Subsequent investigation using other load patterns

with detergents showed that where several successive

test runs were made without alternating with clean- water jflushes, as was the case for figure 30, there was

a tendency to excessive detergent buildup, to the extent that the system could be shown to fail with

standard-size vents. Evidently the particular test shown in figure 30 was not repeated using alternating clean-water flushes.

2. When one of the water closets and the bathtub in the top-story group were discharged together with

detergent in the bathtub, failure of the basement

water-closet-trap seal occurred (1.07 in) and the fail- ure was worsened when the detergent concentration was tripled (2.50 in) , as shown in figure 34.

3. Based on the data from a five-fixture time-se- quence load that included the clothes washer, comparison of results with and without detergent in the clothes- washer did not show a significant effect attributable

to the detergent. This is illustrated in figure 33. The

reasoning in selecting the particular time sequence in

this load was that calculations derived from the travel time data illustrated in figures 21 and 22 indicated

that such a delay would tend to concentrate the dis- charge of all the fixtures in the building drain during

the same period of time. It was presumed this would

produce the worst condition with detergents in the

load.

4. Table 9 shows the results of experimentation with

the simultaneous discharge of the two top-story water

closets, with a time delay between the discharge of the

first and second fixtures. These data show that all the

idle traps on the top floor were affected most by a 5-s delay, next most by a 7-s delay, and least of all by a 3-

s delay. Any relationship between trap-seal reduction

and time delay that might have existed for the inter- mediate and lower floor traps was obscure. A failure occurred in one of the seven idle traps for which data were obtained and borderline performance occurred

in two additional ones, with the 5-s delay. Borderline

performance in one trap occurred with the 7-s delay

(no failures), and the least trap-seal reductions oc- curred with a 3-s delay (max trap-seal reduction 0.96

in).

Table 10 compares trap-seal reductions for different venting arrangements with various loads. One or more

vents were of smaller size than customary, in each test, and in some of the tests some or all of the vents were

closed. When all vents were closed, the loads comprising two or more fixtures caused failure of one or more

traps. Although no tests were made on the split-level

system with a common manifold terminal for the var- ious vents, consideration of the results of the tests on

the slab-on-grade system in the context of the recirculation hypothesis indicates that trap-seal failures may

not have occurred with at least some multi-fixture loads had a manifold terminal been closed rather than

the individual vents.

With y2-in x 50-ft or 1/2-in x 25-ft tubing for all vents, the loads involving one or both of the top-story water closets produced failure of one or more trap

seals. With l/4-in x 25-ft tubing for all vents except the main vent, which was l^/^-in x 18-ft, only loads that included the discharge of both top-floor water closets produced trap-seal failures. With all vents 1%-in x 5-

ft except the main vent, which was ll^-in x 18-ft, a three-fixture load involving both top-story water closets did not produce any trap-seal failures. Table 11 compares trap-seal reductions for clean- water loads and similar loads containing detergent or

solids additives, with three venting arrangements.

One or more vents were of smaller size than customary in each test. All vents were open in all the tests for the results given in table 11. With vent arrangement 1 (main vent ll4-in x 18-ft and all others lV2-in x 5-ft), a three-fixture clean- water load made up of all three water closets was

applied, first with the 4-in building drain beginning at the connection of the laundry group, and then with it beginning at the connection of the basement bath- room. No significant difference was observed in trap

performance.

The following observations are offered, based on

examination of the data in table 11

1. With vent arrangement 2 (main vent ll4:-in x 18-

ft and all others V2-in ^ 25-ft), clean-water loads that included the simultaneous discharge of both top-story water closets produced failure of one or more trap

seals.

2. With vent arrangement 2, simultaneous discharge

of the two back-to-back top-story lavatories containing

hot water and liquid detergent caused the failure of one trap seal. By comparison, the same load without

the detergent caused no trap-seal failure. A similar

result occurred with the simultaneous discharge of one

of the water closets and one of the bathtubs on the top

story, using clean cold water in the bathtub in comparison with hot water and detergent.

3. With vent arrangement 2, a five-fixture load was

applied that included the discharge of three of the six

fixtures in the two top-floor back-to-back bathrooms as

well as the clothes washer and the basement water

closet, first with clean water in the clothes washer and

then with a representative amount of powdered deter- gent in the clothes washer. The use of detergent powder in the clothes washer did not produce a trap-seal

failure.

4. With vent arrangement 5a (all vents ^-in x 1-ft) the two sink compartments were discharged first with

clean water, then with liquid detergent, and finally

with liquid detergent while operating the food-wastedisposal unit without alternating flushing with clean water between test runs. No trap-seal failures Avere produced with either of the three types of load. Figures 23 through 28 compare trap-seal reductions

for different degrees of vent resistance (e.g., size, length, closure). These figures show that in general:

37
1. The closure of all vents caused the failure of several trap seals for a load consisting of one topstory water closet.

2. The use of y2-in tubing 50 ft or 25 ft long for all vents produced failure of some trap seals for a load

consisting of one top-story water closet.

3. The use of ^-in tubing 1 ft long for all vents did not produce failure of any trap seals for the following

loads : (a) Discharge of one top-floor water closet. (b) Simultaneous discharge of one top-floor water

closet and one top-floor lavatory.

(c) The discharge of both compartments of the sink

together.

(d) The simultaneous discharge of all lower-level

fixtures (four, omitting floor drain and shower)

4. The use of either a 1-in x 1-ft or 1^/4-in x 18-ft main vent, and l/^-in x 25-ft tubing for all others produced satisfactory trap-seal performance for all the loads indicated in items 3(a)—3(d) above.

Figure 28 shows that the discharge of one top-story water closet produced substantially greater trap-seal

reductions with the sink and dishwasher vents closed,

but did not cause failure. Figure 29 shows that more of the trap seals were

adversely affected more by a time delay of 5s than by

either 3s or 7s in a 3-water-closet load. This may have

been due in part to a critical concentration of water in the building drain. The trap performance was marginal, with some failures of top-story and kitghen-level

fixtures. This finding is similar to that for the 2-watercloset load discussed near the beginning of this sec- tion.Figure 30 compares trap-seal reductions caused by

the discharge of one top-story water closet with and

without solids (see section 3.4 for method). For these

tests, all vents above the fixture flood levels were

reduced to V2-in x 1-ft. In some cases the clean-water load produced the greatest trap-seal reductions, while

in other cases the greater reductions occurred when

flushing one or more of the pieces of sponge, repre- senting feces. Trap-seal reductions did not exceed %

in on the top floor and % in on the intermediate floor. Reductions were negligible on the bottom floor. Figure 31 compares trap-seal reductions caused by

the discharge of the kitchen sink with and without

detergent. The data also compare reductions with and

without the food-waste-disposal unit operating, and

with and without purging the system with clean water between the successive detergent runs. For these tests

all the vents above the fixture flood levels were re- duced to %-in X 1-ft. These data show that the greatest seal reductions in the idle trap seals on the lowest and intermediate

floors occurred when detergent was used, and that the

greatest reductions in those traps occurred when the food-waste-disposal unit was operated and the successive test runs were made without clean-water flushing

between runs. By contrast, such trap-seal reduction as occurred in the idle top-story traps were greatest

either with clean water or with detergent in conjunction with clean-water flushing between tests.

Figure 32 compares trap-seal reductions caused by

the simultaneous discharge of both top-story lavatories, with and without detergent. For these tests, all vents above fixture flood levels were reduced to ^2-1" X 25-ft except the main vent, which was ll/4-in x 18-ft. For most of the idle traps the greatest trap-seal

reductions were associated with the detergent loadings. Although the converse is shown for the bottomstory water closet (W), this may have been affected by an excess of suds accumulated in the building

drain from previous testing with detergents before

starting the clean-water test runs. The greatest reduction occurred in the dishwasher

trap on the intermediate floor, but did not exceed 1-in with the detergent loading.

Figures 33 and 34 compare trap-seal reductions

with and without detergents for two different loads. For these tests, all vents were reduced as described

above for figure 32. In these tests, the greatest trapseal reductions on the top and intermediate stories occurred with the clean-water loads in most instances. As for the other detergent tests shown in figures 31

and 32, one or more of the trap seals on the bottom

story were adversely affected by the addition of the detergents in each test shown in figures 33 and 34. Only in figures 31 and 34 did the reductions exceed 1

in, and in both instances this occurred in the bottomstory water closet (W).

In reviewing the results of the detergent tests shown

in this paper it is important to recognize the complexity of the phenomena associated with detergent loading, and to remember that for most of the data shown

the tests were made without any systematic clean- water purging between detergent runs,

3.6. Summary

The tests made utilizing several variations of size and length of vents of the three-bath, split-level DWV

system provided further support for the hypothesis

that with competent engineering design and evaluation, two- and two-and-one-half story systems need not be provided with dry vents as large as presently specified by codes. However, the data obtained clearly

show that for equivalent trap-seal protection, the split- level system required vents capable of delivering significantly greater rates of air flow than were required

for the slab-on-grade system.

Trap performance with all vents of l/o-in diam x 25-

ft length was inadequate with a number of realistic loads, although it was marginal when the main vent was increased to a size giving approximately the re- sistance offered by a 1%-in steel pipe 18-ft long. The

nature of the trap performance with this arrangement

indicated that with a 11/4- or l^/o-in main vent and %-

or 1-in sizes for the other vents, performance might

well have been satisfactory with all realistic loads. Unfortunately, it was necessary to terminate the study

before such tests could be made.

The tests with detergents showed that some load

patterns with detergents produced greater trap-seal

reductions than similar clean-water loads, particularly

38
in the lowest branch interval. Test loads with deter- gents repeated several times in succession without al- ternating flushes with clean water produced results that suggested a build-up of suds concentration in the system as a leading cause of the trap-seal failures observed both with reduced-size and customary-size

vents. Thus, in testing with detergents, heavy concentrations and successive loading without alternating clean-water purges probably should be avoided, if realistic test results are to be obtained. In the absence

of appropriate field data, detergent load patterns suit- able for test purposes cannot be scientifically defined

(e.g., concentration, clean-water purging, temperature,

etc. ) . For the time being the choices should be deter- mined through a consensus of current experts in this

field. Tests with detergents in which the effect of water temperature was investigated showed that greater ef- fects occurred with hot water than with cold, other

factors being equal.

4. Development of a Table for Sizing Vents Based on Functional Requirements

For practical use by the designers of plumbing

systems and by approval authorities, it is important

that sizing rules be presented in a simple format and

in terms familiar to the plumbing trade, e.g., magnitude and distribution of fixture load, configuration,

and dimensions.

A review of the state of the art underlying the ventsizing rules presently contained in most plumbing

codes shows that large safety factors were used in applying the results of experimental studies. This con- servatism has long been considered necessary principally because of the following reasons:

1. The experimentation on which the sizing rules of codes are based was incomplete in scope, and was

necessarily conducted with instrumentation and data

analysis techniques considered primitive by today's

standards.

2. Wide variations in configuration and dimensional

detail occur at the installation state in traditional site- built systems, even for systems designed as identical,

and some of these variations may cause substantial

effects on air demand.

3. Wide variations in hydraulic load patterns probably occur for a variety of reasons, and such variations can substantially affect the functioning of venting sys- tems. In the code sizing rules, worst-case conditions

are assumed.

4. Environmental conditions such as temperature,

wind, local sewer flow, and gas-generating characteristics, etc., may affect the functioning of venting sys- tems. The scope of the early experimentation did not

fully cover all these points.

The work described herein is an extension of the work on venting begun at NBS after World War II. Some instrumentation capable of producing a record- ing of simultaneous dynamic phenomena at several

stations in the test setup was utilized. Also, the work

emphasized examination of the performance of potential solutions currently unacceptable under the contem- porary model codes. In much of the previous work,

the emphasis had been on supplying a scientific ra- tionale for the design specifications on pipe sizing

typically presented in codes, and on the development

of performance data for traditional solutions acceptable to codes through the test of experience.

The generally accepted theory underlying the sizing

of main vents [15] begins with these primary assumptions, in effect:

1. There is no "slippage" between the air and water

as the water falls down a drainage stack, i.e., the water falls at terminal velocity in an annulus in contact with the wall of the stack and drags the air in the inner "core" with it at a mean velocity equal to the computed mean terminal velocity of the water.

2. All the air dragged down the drainage stack of a

multi-story system by the falling water must be re- lieved upward through the vertt stack.

3. No pressure or vacuum relief occurs due to recirculation of air between the elements of a DWV

network (e.g., between active and idle elements).

4. It is necessary to size all vents to accommodate

computed peak air demand with a pressure drop limited to 1 in of water column.

5. No vent may be of a diameter less than ll/4-in (some codes specify a 1%-in minimum) or one-half

the diameter of the drain which it vents, whichever is greater.

6. Any structure in which a building drain is in- stalled must have at least one stack vent or vent stack extending to the atmosphere with a diameter of not

less than 3-in, or of not less than the size of the building drain if such building drain is less than 3-in

in diameter.

7. Where frost closure is likely, all vent terminals

must be at least 3 in in diameter. Where local experi- ence supports the need for a larger diameter, the change in diameter to an appropriate fitting must be

made at least 1 ft belov/ the roof. A realistic review of existing information shows

that a number of the foregoing assumpions are either unfounded, irrelevant, or only partially true in the context of modern plumbing design, particularly

where industrialized building methods are utilized. The concept of reduced-size venting was recognized

to some degree in 1940 by the Central Housing Committee on Research Design and Construction [5]. In

this concept, stack vents could be reduced to sizes less than those of the corresponding soil or waste stacks, if the connected fixture-unit load was less than one-half

the allowable load with full-size vents and the system

had horizontal branches in not more than two branch

intervals. The sizing table offered for this situation was the same as for sizing vent stacks or main vents

39
(see para. 1014 and table 1013, ref. 5). Taking a conservative interpretation of this rule, one could have

obtained a stack vent (main vent) size of lV2-in for

either of the two complete experimental DWV systems

described herein. By extrapolation of table 1013, still smaller sizes could have been inferred. Data on air demand in components [1, 2, 3] was

reviewed to obtain some idea of the relationship be- tween air demand, vent pressure, fall distance, and

rate of water input. Computations and inferences of minimum vent sizes from this approach were compared with the trap performance data obtained from

the two complete DWV test systems that were constructed with selected reduced-sizes. Also, the measured air-flow rates in vents obtained in the tests with

components and with the complete one-story test sys- tem were compared with the values computed from

generally accepted theory, and the minimum vent sizes indicated by the two different approaches were compared. This procedure showed the code-specified sizes

to be the largest, the sizes obtained from direct computation from Monogr. 31 theory [15] the next

smaller, and the sizes computed from measurements of

actual air demand or shown adequate by trap per- formance of the complete DWV systems the smallest. The data also showed it reasonable that for equal

performance, the vents for the split-level system had to be of greater diameters than for the one-story, slab-on- grade system.

Following the approach indicated, table 12 was pro- duced. It takes into account the important parameters

affecting air demand through system configuration

and vertical distribution of plumbing fixtures, the ef- fect on air demand due to position of the vent element

in the system, and the effect of magnitude of con- nected fixture load served by the vent. Connected

fixture load is frequently characterized in terms of

fixture units, a term which had been carefully ex- plained by Eaton and French [17].

Table 12. Guide for sizing reduced-size vents for one- and

two-story systems

J. ^ pc Ul SyciLCiIl 1 ype oi vent

„.

r ixture- unit load served by

vent ^'

Size of vent * (in)

.One-Story, slab-on Individual vent Up to 3 f u

grade or crawl 4-6 f u %

space (fixtures within one LiOmmon vent Up to O I U %

nranr*ri interval or branch 4-—0 t u 1

IvTfiin <;tfipL' ^cfM*l U p 10 U I u

1 or waste) vent ^ 7 1 ^ f 11

I —ID I U 174

Tw'o-sto ry (fixtures \ T\ f\^\71^\^'\ "i7*in+d XllUiVlUUaX VCIJI up 10 O I U /2

in not more 4-6 f U Va than 2 branch

intervals), or Common vent^ Tin tn ^ f 11 sp] it -level sys- \J I \JLCLll\jH 4—6 f u tem (fixtures vent 7-12 f u IM

distributed 13-20 f u IH

between not more than 3 Main stack (soil Up to 6 f u IH

levels over a or waste) 7-15 f

m vertical span of vent (o) or 16-30 f u 2 not more than vent stack

15 ft)

Dry vents only. Sizes estimated on the basis of research

data on two full-scale laboratory systems. Some adjustments in range limits may prove necessary for some systems, depending on configuration. Engineering judg- ment should be exercised in such instances.

" Assumed size of soil stack 3 in. It is assumed the soil vent may provide direct ventilation for two or more fixture traps on

the top floor. For the purpose of this table, it is assumed that these vents

are less than 25 ft in length, and that the water does not have an unbroken fall of more than 5 ft in the waste stack or vertical waste pipe to which the trap-arm connects and which is being

vented by the indicated vent.

5. Conclusions and Recommendations

The study showed that, within the scope of the

investigation, many DWV systems in one-story and

split-level houses can be designed to provide essential trap performance with vents much smaller than usually required by codes. The data presented herein, taken together with the data on the air demand-vent pressure relationship ob- tained on component systems, have provided the basis

for table 12 which can be looked upon as a guide. It does not take the place of engineering judgment and

experience by the plumbing designer, particularly

when systems differ substantially in configuration

from those so far studied. In the utilization of reduced-size venting for split level and one- and two-branch interval slab-on-grade or

traditional houses, it is important that several simple

rules be observed by designers and installers, that are not necessarily relevant to traditional DWV systems:

1. Reduced-sizes should not be installed below a point approximately 6 in above the flood rim of the

fixtures served. Vents for single-bowl sinks with food- waste disposal units should not be reduced below the

elevation corresponding to the shut-off head of the

unit. These measures are necessary to minimize the

fouling or clogging effects of intermittent deposits of

particulate matter in reduced-size vents over a period

of time in normal service.

2. Reduced sizes should be used for dry vents only.

Thus, wet vents or reaches of vents designed as dry

vents, but nevertheless likely to be intermittently sub- merged or subjected to wetting by aerosols or suds,

should be designed to conventional sizes.

3. The cross-sectional area of a manifold vent or vent header (a vent terminal to which two or more

smaller vents are connected) should be greater than

the largest of the vents connected to it, but if three or

40
more vents connect to the manifold, the manifold area need not equal the sum of the connected areas. Probably, a size of one commercial pipe size larger than the

largest connected vent should suffice for the DWV

system usually installed in housing construction.

4. In areas where frost closure may occur, vent terminals should be sized to account for the effects of

local weather as explained by Eaton and Wyly [18].

The use of vent piping that has low thermal conductivity, or the use of some other means for reducing or counteracting natural heat loss might be employed to reduce the likelihood of frost closure. Reduced-size

vents should not run through unheated spaces where

frost closure is likely.

5. Vent terminals serving reduced-size vents should

be fitted with durable, corrosion-resistant enlarged

caps of screen having open areas greater than the

cross-sectional area of the vent terminal, so as to provide an allowance for clogging of the screen and to prevent entrance of leaves and insects into the vent

system. Probably an open area 50 percent greater than

the area of the terminal is adequate.

6. All vent piping should be positioned, supported,

and continuously graded so that condensation or other moisture will drain by gravity to (a) a soil or waste

pipe, or (b) to an acceptable location outside the

structure, provided that this solution is not employed

in frost-closure-prone areas without suitable protection

against freezing

7. Reduced-size vents should be made of material

that does not contribute to substantial reduction in diameter from scale formation or other causes under

ordinary conditions of use. This study examined the performance of reducedsize venting as employed in full-scale laboratory sys- tems simulating sanitary DWY systems of one-story

and split-level houses. Various combinations of the plumbing fixtures were discharged to produce a range

of hydraulic loadings, and many different venting ar- rangements were utilized, for each system. Most of the

testing was done with clean-water loads, but some tests involved detergents or solids. The results suggest that reduced-size venting could

be successfully used for the venting of sanitary drain- age systems of greater heights, and to systems with more complex vent-system configurations. This is based on the fact that the vent rules specified in codes

do not satisfactorily account either for slippage be- tween air and water or for recirculation relief in vent networks. Both effects probably exist to an appreciable

degree in lightly to moderately loaded, branching sys- tems as used in multistory buildings of low to moderate height, and substantial recirculation relief un- doubtedly occurs in high-rise systems utilizing

individual venting, wet venting, or circuit-and-loop

venting.

Among additional investigations that could provide

better definition of the functional performance of reduced-size venting, and that could establish a broader

base for the application of reducedsize venting to various designs under the memy possible service conditions are the following:

1. Experimentation with reduced-size venting with

greater numbers of vent-system elements, greater

heights, and greater fixture-unit-loads than those rep- resented in the research reported herein. This would

be helpful both in perfecting and in expanding table 12 to make it applicable to a wider range of systems.

2. Determination of the dynamic relationships be- tween peak air demand rate, vent pressure, and trapseal retention over a wider range of pipe diameter, fall distance, fitting shape, pipe roughness, load distribution, etc., than was possible in the study reported

here.

3. Development of a rational method ^ for sizing of vent headers and manifold vent terminals, and the improvement of methods for selection of representative

hydraulic loads for laboratory tests. 4. Field verification of performance predicted from

laboratory tests. This type of feedfback from one or more systems previously tested in the laboratory

would serve to confirm and/ or improve criteria such

as table 12, and to improve test methodology so as to provide suitable agreement between the performance

in the laboratory and in the field. 5. Development of representative performance data

over a wider range of conditions, concerning possible

hydraulic and pneumatic effects of solids and deter- gents, for comparison with similar data with clean- water loads developed in the study described herein. Investigation of the relative effectiveness of various

methods for controlling the effects of detergents. In

the long run, trends in the detergent industry appear

to be headed toward reduced sudsing and this should

be encouraged.

6. Development of representative performance data

for vent reservoirs, vacuum relief valves, and un- vented vertical sections of soil and waste pipes, all of which received only limited attention within the scope

of the component tests referred to herein.

7. Development of appropriate environmental data

concerning the magnitude of pressures within sanitary

DWV systems that might be attributable to effects of wind pressures or of pressures generated within public sewers or individual sewage-disposal systems.

8. Development of appropriate data concerning the

likelihood of frost closure of vents in different geo- graphical locations of the United States. The development of a "frost closure map" or similar guide from

official weather records could remove some of the uncertainty in establishing realistic criteria for sizing vent terminals in cold climates.

B The empirical sizing methods currently used in experimentation performance of DWV systems with RSV and in sizing vent hes

generally accepted practice need verification and improvement thron measurements on systems in service.

41
6. References

[1] Beausoliel, R.W. and Wyly, R.S.; Minimum Venting for Plumbing Systems, Nat. Bur. Stand. (U.S.) Tech. News Bull. 50, No. 5, 75-77 (1966).

[2] Performance of Reduced-Sized Venting in Residential DWV Systems, NAHB Research Foundation, Inc., Rockville, Md., Report LR 210-17 (1971).

[3] Wyly, R.S., Venting; International Association of Plumbing and Mechanical Officials (lAPMO) "Official" Part 1, 14-19, Jan-Feb 1970; Part II 14-21 and 27, March-April 1970.

[4] American Standard National Plumbing Code, American

Society of Mechanical Engineers and American Public Health Assoc., ANSI A40.8-1955.

[5] Plumbing Manual, NBS Building and Structures Report

BMS 66 (1940).

[6] French, J.L., Stack Venting of Plumbing Fixtures, NBS

Building Materials and Structures Report BMS 118

(1950).

[7 J French, J.L.; Eaton, H.N.; and Wyly, R.S., Wet Venting

of Plumbing Fixtures, NBS Building Materials and

Structures Report BMS 119 (1950).

[8] French, J.L. and Eaton, H.N., Self-Siphonage of Fixture

Traps, NBS Building Materials and Structures Report

BMS 126 (1951).

[9] McGhan, F.W., Wyly, R.S. and Hintz, 0. ; Performance of Plumbing Fixtures and Drainage Stacks; Housing and Home Finance Agency, Housing Research Paper 31

(1954).

[10] Rouse, Hunter, Elementary Mechanics of Fluids (John

Wiley and Sons, Inc., 1946).

[11] Wyly, R.S., Investigation of hydraulics of horizontal drains in plumbing systems, Nat. Bur. Stand. (U.S.) Monograph 86 (1964).

[12] Wyly, R.S. and Sherlin, G.C., Performance of a single- stack DWV system utilizing low-angle stack-branch

confluence and bottom shunt venting, NBS Building

Science Series No. 41 (1972).

[13] Manas, V.T. and Eaton, H.N., National Plumbing Code

Handbook, (McGraw-Hill Book Co., New York, 1957).

[14] Copper Sovent Single-Stack Plumbing System, Design

Handbook, (Copper Development Association, Inc., New

York, 1970).

[15] Wyly, R.S. and Eaton, H.N., Capacities of stacks in sanitary drainage systems for buildings, Nat. Bur. of Stand. (U.S.) Monogr. 31 (1961).

[16] Fair, G.M. and Geyer, J.C.; Water Supply and Waste Water Disposal (John Wiley and Sons, New York,

1954)

[17] Eaton, H.N. and French, J.L., Fixture unit ratings as used in plumbing system design. Housing and Home

Finance Agency, Housing Research Paper No. 15 (1951).

[18] Eaton, H.N. and Wyly, R.S., Frost closure of roof vents in plumbing systems, NBS Building Materials and Struc- ture Report BMS 142 (1954).

7. Appendix

7.1. Definitions

For the purposes of this paper, a number of terms

are defined in the context of the work reported. In

general, the definitions are in accordance with the model plumbing codes, but where necessary to facili- tate comprehension, new terms have been defined and some standard definitions have been modified.

Active fixture—A fixture that is discharging for the purpose of creating or contributing to a hydraulic

test load, or that is discharging under service conditions.

Air demand—The quantity of air (usually ex- pressed as a volume- or mass-rate) required to be

moved through a vent in response to pneumatic

pressure differentials created by the movement of water from fixtures discharging into branch assemblies and drainage stacks. Back vent—A back vent is a branch vent installed primarily for the purpose of protecting fixture traps

from self-siphonage.

Blind flange—A blind flange is a cover plate bolted

or otherwise fastened across a pipe flange to seal the pipe.

Blow-back—Is the ejection of suds, air, or other

gases through the trap seal to the room side of a trap as a result of excessive pneumatic, hydrostatic.

or hydrodynamic pressure on the drain side of the

trap. Branch—Is any part of the piping system other than a main, riser, or stack. Branch vent—Is any vent pipe connecting from a branch of the drainage system to the vent stack. Building (house) drain, sanitary—The sanitary

building or house drain is that part of the lowest

horizontal piping of a sanitary building drainage

system which receives the discharge from soil, waste, and drainage pipes within the walls or foot- ings of any building and conveys the discharge to the sanitary building sewer. Code—The word code, as related to plumbing work,

usually means an ordinance, with any subsequent

amendment thereto, or any emergency rules or regulations which a city or a governing body may adopt

to control the plumbing work within its jurisdiction.

Combination wye-and-eighth bend—Is a fitting

which was originally made in cast iron to provide

the features of two separate fittings, a 45° wyebranch and a 45° bend which together accomplish

a 90° change in direction. In some of the newer

materials used for drainage fittings, the wye-andthe-eighth bend are assembled into one fitting by

the user. Common vent—Is a vent connecting at the junction

of two fixture drains and serving as a vent for both

fixtures.

42
Cross flow—Is the movement of waste water from

the trap of an operating (active) fixture to the trap

of a nonoperating (idle) fixture. [Could also be

defined to cover movement from active to idle branch drain, etc.]. Diameter—Unless specifically stated, the term diameter means the nominal diameter as designated commercially.

Dip of trap—The dip of the trap is so located as to be the highest point on the internal wall of the trap

at the cross section where the bend (inverted si- phon ) of the trap is at its lowest part. Drain—Is any pipe which carries waste water or water-borne wastes in a building drainage system.

Dual vent—(sometimes called a unit vent) Is a group vent connecting at the junction of two fixture branches and serving as a back vent for both fix- tures. DWV system—The drain-waste-vent system, in- cludes all the sanitary drainage and vent piping

inside the building or relevant portion thereof, and

includes the building drain to its point of connection with the building sewer.

Fixture drain (also called trap arm) —Is the drain

from the trap of a fixture to the junction of that drain with any other drain pipe.

Fixture load—The fixture load is the term used to indicate the types and sum total of fixtures con- nected to a plurribing system or portion thereof.

Fixture unit (drainage) —The term fixture unit

identifies a measure of the probable discharge into the drainage system by various types of plumbing

fixtures. The fixture unit value for a particular

fixture depends on its volume rate of drainage dis- charge, on the time duration of a single drainage

operation, and on the average time between successive operations during peak use periods.

Fixture unit load—Is the sum of the numerical

values of the fixture-unit ratings for all the fixtures connected to a plumbing system or portion thereof.

Fixtures or appliances, plumbing—Plumbing fix- tures or appliances are installed receptacles or de- vices which are supplied with water, or which re- ceive liquid and/or discharge liquids, or liquidborne wastes, either directly or indirectly into the drainage system.

Flood-level rim—Is the top edge of a receptacle or

fixture bowl from which water can overflow.

Frost closure—Is the partial or complete closure of a roof vent in cold weather by the formation of a layer of frost on the inner surface of the vent.

Group vent—Is a branch vent that performs its functions for two or more traps.

Group venting—is the arrangement of the drainage

piping such that a single vent may serve more than one fixture. Wet venting is one form of group

venting.

Horizontal branch—A horizontal branch is a drain

pipe extending laterally from a soil or waste stack or building drain with or without vertical sections or branches, which receives the discharge from one

or more fixture drains and conducts it to the soil or waste stack or to the building drain.

Idle fixture—A fixture that is not discharging dur- ing the imposition of a hydraulic test load by active

fixtures, or by natural use of the system in service. Individual vent—Is a pipe installed to vent a single

fixture trap and so connected with the vent system

or with the open air that free movement of air is possible at all times. Induced siphonage—Is the process whereby a re- duction in the surface level of a trap seal of a

fixture is caused by the discharge of other fixtures on the system, such discharge resulting in transient

local pressure fluctuations that siphon or otherwise remove water from the trap. Main vent—Is the principal artery of the venting

system to which vent branches may be connected.

Manifold—Is a pipe fitting with several outlets for connecting three or more pipes.

Nominal size—Is the approximate size of the pipe

or tube. The actual size within tolerances is defined

by standards established for various types of pipe

or tube. Performance criteria—Performance criteria are the

attributes or characteristics of a (plumbing) system,

or element of the system, which are measured or evaluated to determine on some quantitative scale whether the performance requirements (health and

safety, comfort, convenience, efficiency, durability,

etc.) have been met.

Piezometer—A piezometer is a device for the meas- urement of pressure in pipes or conduits consisting

of a vertical transparent tube which is connected at

its lower end to a piezometer orifice in the wall of the pipe or conduit and is open to atmosphere at its upper end. The height to which fluid rises in the transparent tube is a measure of the head or pres- sure in the pipe or conduit.

Piezometer Orifice—A piezometer orifice is a small hole through the wall of a pipe or conduit drilled at a 90° angle to the wall and carefully finished at the inner edge of the hole.

P-trap—The P-trap, resembling an inverted siphon,

is one of several designs of devices used in drains

to provide a water seal. Reach—A reach is one of the continuous sections of a pipe, e.g., a drain pipe located between inlets or between inlets and outlets.

43
Recirculation—Recirculation in a DWV system is the flow of air within the network comprised of interconnected vent piping, to meet the demand for

air in critical areas inside the system as water is discharged from the fixtures.

Reduced-size venting—A type of venting which uti- lizes dry vent sizes smaller than permitted by

plumbing codes. Such reduced-size vents are limited

to locations not lower than 6 in above effective flood level for the fixtures involved.

Roughing-in—Is a term indicating the installation of all parts of the plumbing system which can be

completed prior to the instaUation of the plumbing

fixtures. This includes drainage, water supply, vent piping and the necessary fixture backing/supports.

Run (test) —A complete hydraulic event, beginning

with the discharge of selected fixtures and ending

when the water so discharged has passed through

the DWV system.

Self-siphonage—Reduction in trap seal of a fixture

after completion of the fixture discharge, caused

solely by the discharge of that fixture.

Service Weight (soil pipe) —-The designation of a weight or thickness of cast-iron soil pipe. Soil pipe

is designated extra-heavy (XH) and service (SV).

Class (SV) has a wall thickness of approx 70 per- cent that of class (XH)

Slab-on-grade (slab on ground) —Is a term used to identify a concrete floor poured on the ground at grade level when necessary precautions have been

taken regarding ground water or unstable soils.

Slippage—The term used here to indicate the de- gree to which the mean velocity of the air is less than the mean velocity of the water at a particular

cross section in a soil or waste stack in which

falling water carries air with it.

Slope (grade) —Is the degree or extent of deviation

from the horizontal, usually expressed in in/ft for plumbing drains.

Stack—Is the vertical main of a system of soil, waste or vent piping.

Stack vent—(sometimes called a waste vent or soil vent) Is the extension of a soil or waste stack above

the highest horizontal drain connected to the stack.

Stack venting—Is a method of venting a fixture through the soil and waste stacks, without the use

of individual, branch, or relief vents. Trap—A fitting or device constructed so as to provide, when properly vented, a water seal for protection against the emission of noxious or explosive sewer gases, without significantly retarding the flow

of sewage or waste water through it. Trap arm—Is another name for fixture drain.

Trap seal—Is the vertical distance between the trap

weir and the dip of the trap.

Trap-seal retention—Is that depth of water remaining in the trap after the trap has been affected by

passage of fluid through the trap or by action of suction or back-pressure in the DWV system.

Trap weir (crown weir) —Is the lowest point in the

vertical cross-section of the horizontal waterway at the exit of the trap. Vent—Is a pipe installed to provide a flow of air to or from a drainage system or element thereof so as

to provide protection of trap seals from siphonage

and back pressure. Vent stack—A vertical vent pipe extending through

one or more stories, installed to provide circulation of air between different elements of the DWV sys- tem. Usually, the vent stack is the vertical main of

the vent system, to which branch vents are connected. Vent stub—Is the length of code-size vent that ex- tends at least six inches above the flood-level rim of the fixture, as employed in the research on reducedsize venting.

Vent terminal—Is that portion of the vent piping

extended outside the building and open to the at- mosphere.

Vertical pipe (soil, vent, or waste) —Is any pipe

which is installed in a vertical position or at an

angle with the vertical of not more than 45 degrees.

Waste stack—Is the vertical main of that portion of

a drainage system which carries no urine or feces,

its stack vent may extend independently through

the roof or it may connect to the stack vent of the

soil stack. Wet Venting—is the arrangement of the drainage

piping such that the venting of some fixtures is provided by pipes that also serve as drains for other fixtures.

7.2. Units of Measure and

SI Conversion Factors

The results of the investigation described herein are reported primarily in conventional U.S. units, for two

reasons: first, most of the instrumentation used was

calibrated and graduated in conventional units; sec- ond, the results of this research are directed to those groups who ordinarily use conventional units. However, in recognition of the increasing importance of international standards in foreign commerce

and of international technical committee activity in plumbing technology, it is recommended that those who utilize the results of this work assume the responsibility for appropriate conversion to International

Standard (SI) units, recognized by the USA in 1960

as a signatory to the General Conference of Weights

44
and Measures which gave official status to the metric

SI system of units. For this purpose, the following

conversion factors are given applicable to the conventional U.S. units used in this paper: Force

1 pound (lb) = 4.448 newtons (N)

Length

1 inch (in) = 0.0254* meter (m), or 25.4* milli- meters (mm)

1 foot (ft) = 0.3048* meter (m), or 30.48* centi- meters (cm)

Mass

1 pound [avoirdupois] (lb) = 4.536 kilograms

(kg)

Temperature

Degrees Celsius (°C) converts to (°C + 273.15)*

degrees Kelvin (°K or K)

Degrees Fahrenheit (°F) converts to 1.8 (°F — 32)

degrees Celsius (°C)

also converts to 1.8 (°F — 459.67) degrees

Kelvin (°K or K)

Time

1 minute [mean solar] = 60.0* seconds (s) Area

1 in2 = 6.4516* X 10-^ meter2 (m2), or 6.5416*

centimeter^ (cm^)

Volume

1 gallon [U.S. liquid] = 3.785 liters (1) = 3.785 X 10"^ meters^ (m^)

Volume/Time

1 gallon [U.S. liquid] per minute (gpm) = 6.309 X 10~2 liters per second (Ips) also = 3.785 liters per minute (1pm)

Velocity

1 foot per second (fps) = 3.048* x 10"^ meters

per second (m/s)

1 foot per minute (fpm) = 5.080* x 10^ meters

per second (m/s)

Pressure

1 psi = 6895 newtons per meter^ (N/m^)

1 inch of water column [at 39.2°F] = 249.1 newtons per meter- (N/m^)

1 inch of water column [at 60 °F] = 248.8 newtons per meter^ (N/m^)

7.3. Discussion of Field Tests Conducted

by the NAHB Research Foundation, Inc. A discussion of field tests conducted for the National Association of Home Builders (NAHB) is pre- sented here for the following reasons:

(a) The field program described represents the only

known planned study to verify the performance of reduced-size venting as designed on the basis of the NBS laboratory findings and as installed in actual houses.

(b) The work provides the basis for a comparison

of the vent sizes used for the service installations with

the minimum sizes indicated by table 12 of this paper.

(c) The results point out the importance of systematic test procedures and accurate measurement techniques, and demonstrate the need for field data on fi) plumbing loads to provide an improved basis for se- lection of laboratory test loads, and on (ii) hydraulic

performance with service loads to provide final confir- mation of the adequacy of an innovative design.

The NAHB Research Foundation (NAHB RF), a subsidiary of the National Association of Home Builders, cosponsor of the laboratory work described in section 1 through 6 of this publication conducted field tests on DWV systems with reduced-size vents in- stalled in test houses located in the following geo- graphical areas:

1. Camden, New Jersey (two houses). Both houses were one-story ranch style, slab-on-grade construction,

with 3 bedrooms and 2 bathrooms each;

2. Muncie, Indiana (one house). This house was

one-story ranch style, crawl-space construction, with 3 bedrooms and 2 bathrooms.

3. Fremont, California (one house). This house was

a one-story ranch style, crawl-space construction, with

3 bedrooms and 2 bathrooms.

4. Fairfax, Virginia (one house). This house was a

bilevel style, having two branch intervals of plumbing,

with 3 bedrooms and 2 bathrooms.

In addition, the NAHB Research Foundation stated that a builder in central Illinois has reported observations on seven units employing reduced-size venting in his own program. The houses were described as fol- lows:

1. One-story, ranch style, basement construction,

with 2 bathrooms (one house)

2. Split-level style with 3 bathrooms (two houses)

3. Split-foyer style with 3 bathrooms (three

houses)

4. Two-story, three family apartment building over basement, with one bathroom in each living unit

(three living units).

The principal aspects of the venting designs, of the

tests, and of the findings, that are of interest herein

are summarized as follows:

1. The systems in the NAHB RF program were

selected by the NAHB RF staff as modifications of designs acceptable under codes in the sense that the code-approved DWV configurations were not changed,

but the conventional sizes of some of the dry vents were reduced.

2. The NAHB RF utilized the early reports of the NBS on the laboratory study of RSV that had been

conducted by NBS, as an aid to down-sizing the con- ventional vents of selected conventional DWV designs. In several instances staff of the NAHB RF consulted with staff of the NBS in reviewing plans for the modified designs, and in planning site tests. 3. NBS staff did not conduct or direct the conduct

of site tests, nor prepare the test procedures actually

used by test personnel. An NBS staff member observed

the conduct of the tests of the system in the Muncie,

Indiana house that were made before occupancy.

4. All of the systems are shown as installed with

vents reduced in size to a substantial degree below the

sizes of those ordinarily permitted by codes. For details of the DWV piping configurations; pipe sizes;

45
and fixture types, numbers, and locations the reader is referred to NAHB RF Report LR 210-17, September

1971 [2].

5. The NAHB RF reported that before-occupancy

tests in five houses, and after-occupancy tests in two

of the houses made after periods ranging from 15 to 24 months, showed that trap-seal reductions did not exceed one inch or 50 percent of the initial full trap

seal in any test. The builder in Illinois who conducted

his own study in seven units is credited with reporting

"satisfactory performance."

The authors of the present paper have reviewed

the four sets of plans (Camden, Muncie, Fremont,

Fairfax) shown in NAHB RF Report LR210-17. This

review shows that a number of the vent pipes were

sized one to two pipe sizes smaller than might have

been obtained through the use of the sizing table shown although the magnitude of the discrepancy may

depend to some extent on the interpretations made of the table when applied to the particular DWV config- urations. It should be realized that the table was not completed, even in tentative form, when most of the

test houses were designed. Thus it is not surprising

that not all the sizes actually used can be obtained

from the table. The numbers of fixtures discharged together to cre- ate the test loads generally seem to be as great as or

greater than would be obtained by the use of table lA

of BSS 41 [12]; however, a review of the rationality of the particular choices used was not presented in the

report, nor has one been attempted by the authors of the present paper. Trap-seal reductions reported exceeded 1 in only

for the two-story system (Fairfax. Virginia), and that occurred only after multiple applications of the test loads without replenishing the idle trap seals. The

data show that even in these cases at least 50 percent

of the trap-seal depths were retained after four to six successive applications of the loads. The report does not describe or discuss the methods

of measurement used nor does it give any calibration data for the discharge characteristics of the fixtures. In some of the tests, measurements evidently could not be made on the bathtub traps, nor on traps connected

to food waste disposal units. A detailed presentation

and discussion of these items would have improved the

report.

With reference to the independent tests reported by

the Illinois builder (but for which measurements are not shown) the vent-size reductions seem rather ex- treme in view of the data shown for the houses tested by the NAHB RF. A further concern relates to the termination of the vents in the attic space. This might

contribute to excessive moisture and the accumulation

of foul and possibly hazardous gases within the structure.

It is unfortunate that it was not possible for the

field program to provide for measurements of per- formance with natural loading patterns, i.e. "people"

loadings. The field tests reported utilized "heavy"

loads chosen from a consideration of the state of the

art for DWV load-testing, but nonetheless, loads chosen by test engineers and applied by test engineers

not by the building occupants themselves as a natural

part of their daily living patterns. Until suitable up- dated data on load patterns generally are obtained,

purposeful evaluations of innovative plumbing systems

should provide for some measurements of the signifi- cant performance parameters in field trials with natural loadings, after laboratory tests have first shown

the system (s) to offer strong promise.

46

•tfr U.S. GOVERNMENT PRINTING OFFICE: 1974 0—528-427
FORM NBS.114A (1-71)

U.S.' DEPT. OF COMM. 1 . PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA NBS-BSS-49

SHEET

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Laboratory Studies of the Hydraulic Performance of One-Story

and Split-Level Residential Plumbing Systems with Reduced Size

Vents/Investigation of Reduced-Size Venting

5. Publication Date

\A-^-My^*U 107/1 JVLar on i V 1

4

6. Performing Organization Code

7. AUTHOR(S)

Robert S. Wyly, Grover C Sherlin and Robert W. Beau.<?o1ie]

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

IN A i HJiN A L DUKHAU \Jr oi AiNU AKUo

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4624191

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same as 9.

13. Type of Report & Period Covered

Fiaal Report 62-66

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Cataloge Number: 73-600336

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

A laboratory study of one- story and split-level experimental drainage systems where

uuc VC1.1U& ill buiiit; cases were variea rrom one to six pipe-sizes smaller than those

presently specified by codes showed satisfactory hydraulic and pneumatic performance

under various loading conditions. The research was originally sponsored by the National

Association of Home Builders and the National Bureau of Standards and more recently by

a program of the Department of Defense through the Tri-Services Investigational Committee

on Building Materials. This paper presents criteria recommended for the design and

evaluation of systems using reduced-sized vents and a sizing table for one- and two-story

systems. The laboratory work also contributed to the development of analytical and test

procedures needed for evaluating the application of reduced-size venting to a broad

range of innovative drain-waste-vent designs for buildings of any height.

This work indicates that, in some circumstances, reduced-size venting might be a good alternative to other types of drainage systems for multi-story buildings which use either conventional or innovative venting concepts. Because this study involved only a limited number of drainage system designs, it is recommended that ongoing field and

laboratory studies be explored if code changes are contemplated to permit the use of

smaller vents.

17. KEY WORDS (Alphabetical order, separated by semicolons) Hydraulic Criteria for plumbing; hydraulic

test loads; plumbing-vent sizing; reduced- size vents; sanitary DWV systems; secondary

ventilation; testing plumbing systems; vents for plumbing

18. AVAILABILITY STATEMENT

[Xl UNLIMITED.

1 1 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

53

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

95(?

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