NATIONAL BUREAU OF STANDARDS REPORT

8006

PROGRESS REPORT NO. 2

ON

FLUID DYNAMICS OF PLUMBING

by

R. W. Beausoliel

For Use Approved for public release by the

Director of the National Institute of

w Standards and Technology (NIST) on October 9, 2015.

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U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress,

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Published in Outside Journals 1950 to 1959) ($2.25); available from the Superintendent of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1005-12-10615 June 14, 1963

NBS REPORT

8006

PROGRESS REPORT NO, 2

ON

FLUID DYNAMICS OF PLUMBING

by

R. W, Beausoliel

for

The National Association of Home Builders

For Use of Sponsor, Project Advisory Committee,

and Project Staff Only,

Not for Publication or Distribution

IMPORTANT NOTICE NATIONAL BUREAU OF STANDARDS REPORTS are usually preliminary or progress accounting documents intended

for use within the Government. Before material in the reports is formally published it is subjected to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or open-literature listing of this Report, either in whole or in part, is not authorized unless permission is obtained in writing from the Office of the Director, National Bureau of Standards, Washington 25, D.C. Such permission is not needed, however, by the Government agency for which

the Report has been specifically prepared if that agency wishes to reproduce additional copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL DUREAU OF STANDARDS

ABSTRACT

This progress report, the second in a series, presents a physical

description of a test plumbing system constructed at the National Hydraulics

Laboratory. It represents a type that might be used in a one-story single

bath, slab on grade house. The report contains air rates in individual

fixture vents, water depths and average velocities in the drain, trap seal

losses, and pneumatic pressures occurring on the drain side of traps subjected to induced siphonage. Test loads comprised single fixture discharge, simultaneous discharge of two or more fixtures, and discharge of

selected combinations of fixtures in sequence. A number of test results

were compared for individual fixture vents open and closed.

1. INTRODUCTION

1 . 1 Purpose of Investigation

The general purpose of the investigation is to study aspects of the

fluid dynamics of plumbing systems such as installed in one- and twostory houses which have not been covered adequately by previous research.

Some phases of previous research done in the past which seemed particularly

difficult to instrument at the time may be investigated again in a more

efficient manner through the use of newly developed instrumentation

techniques

.

The main purpose of this report is to give an insight into the operation of a simulated plumbing system with various conditions of venting

and hydraulic loading.

At this time it seems reasonable to focus attention on the two ex- treme conditions which are defined as operation with maximum venting and

operation with minimum venting. The sequence of hydraulic loading was held constant during both extremes; therefore, the effects of venting can readily be compared to the effects of no venting in terms of trap seal

losses, water depth in the drain, etc. A test with some degree of venting between these extremes was also included.

Another purpose of this report is to present further information on

the relationship between air flow, water flow, and air pressures in a test

stack designed so that independent variables can be changed in a systematic

fashion

.

1.2 Authorization

The project was approved by the National Bureau of Standards under

the Grants-In-Aid program on December 21, 1962 as outlined in a letter

from Dr. R. D. Huntoon, Deputy Director of the National Bureau of Standards,

to Mr. John R. Dickerman, Executive Vice President, National Association of

Home Builders. Financial support in the amount of $25,000 was provided by

NAHB on May 10, 1962 and acknowledged by NBS in a letter dated May 28, 1962

from Mr. D. E. Parsons, then Chief, Building Research Division, to Mr.

Dickerman. It was understood that the cost of the work would not exceed

$25,000 per year over a period of two years.
2

2. PRELIMINARY ACTIVITY

An advisory committee was organized for the purpose of reviewing the

work at appropriate stages, making recommendations, and furnishing advice

on questions raised by the project staff. The functions of the committee

are advisory only. The committee comprises the following persons:

Mr. Ralph Johnson

Technical Director

National Association of Home Builders

Mr. Robert Schmidtt

Chairman, NAHB Research Committee

Mr. James Simpson, Chief

Standards and Technical Studies Section

Architectural Standards Division

Federal Housing Administration

Mr. Malcolm Hope

Assistant Chief

Division of Environmental Engineering

Department of Health, Education, & Welfare

Mr. D. E. Parsons

Consultant to the Director

National Bureau of Standards

Mr. John French, Hydraulic Engineer

Fluid Mechanics Section

Mechanics Division

National Bureau of Standards

Mr. Robert Wyly, Hydraulics Engineer

Codes and Safety Standards Section

Building Research Division

National Bureau of Standards

3 . ACCOMPLISHMENTS

3 . 1 Construction of the Test Plumbing System (See Fig. 1)

The main building drain, soil stack, and stack vent were constructed

of standard weight nominal 3 inch cast iron soil pipe. The branch of the
3

building drain serving the kitchen sink and washine machine drains was constructed of standard weight nominal 2 inch cast iron soil pipe. A

slope of 1/4 inch per foot was maintained for these drains. All the

soil pipe utilized neoprene sealed joints with the exception of the water

closet fitting and the connections to galvanized iron pipe. Vertical cast

iron drains for the individual fixtures terminated with 2 inch cast iron

hubs extending 4 inches above the floor to simulate slab on grade con- struction. Nominal, standard weight, galvanized 1 1/2 inch pipe was caulked into these hubs and extended vertically to connect with the individual fixture vents and drains. The washing machine drain was of nominal

2 inch standard weight galvanized pipe from the 2 inch "P" trap to the 2 inch cast iron hub. The washing machine vent was of nominal 1 1/2 inch

galvanized iron pipe, standard weight.

The water closet was connected to the soil stack by way of a 4 x 6 x

16 closet bend which in turn connected to a 3 x 4 Washington reducing com- bination Y and eighth bend.

Combination Y and eighth bends and long sweep quarter bends were used

elsewhere in the system with the exception that the 1 1/2 cast iron bath

tub "P" trap connected to the bath tub drain below the floor level through

a 2 x 1 1/2 sanitary tapped tee.

The roughed-in drain was subjected to a 15 foot head of water to

detect any leaks. The completed system was subjected to air pressure equivalent to 2 inches of water. The pneumatic pressure head remained quite

constant for a period of one half hour, thus indicating a tight system.

The fixtures used are as follows:

Lavatory, ledge back, white, 20" x 18"

Water Closet, siphon jet type

Two Compartment Flat Rim Kitchen Sink, 32 x 21

Bath Tub, 5 ft recessed type

Washing Machine, automatic

3 . 2 Instrumentation

Residual trap seals were measured with glass piezometers in combination with short graduated scales. The water closet seal was measured with

an electric point gage.

Fluctuating or rapidly changing pneumatic pressures and water depths were measured with the aid of strain gage bridge type pressure transducers

and a multichannel recording oscillograph. Miniature pitot-static tubes
- 4 -

were used to sense air movement in the stack vent and individual fixture

vents. Static air pressures and water heads were transmitted to the transducers or indicating devices through short lengths of plastic tubing leading from tubing connectors located in the pipe walls. These connectors

are standard 1/8 national pipe thread fittings. See Figure 2 for measurement locations and symbol designations.

The lavatory, bath tub, and sinks were calibrated to determine the

average rate of discharge and duration of discharge for any given initial

water depth above the outlet orifice rim. 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 washing machine discharges were collected against

time in a container for which the relation between depth and volume was established. The machine has two distinct successive events: a drain

event followed by a spin-spray event. The sprays comprise 4 discharges

of 7 seconds each over a period of 2 minutes. The drain event discharges

16.4 gallons of water during 60 seconds. The spray discharges a total of

4 3/4 gallons of water during 120 seconds. All fixtures were supplied with

a constant water pressure of 50 psig (constant within ±3 psig). The calibration curves for these fixtures are shown in Figures 3-8.

The fixture discharges were actuated by means of a battery of solenoids

which in the case of all fixtures other than the water closet and washing

machine pulled the drain plugs completely clear of the fixtures; consequently, there was no interference to flow introduced by the drain plugs.

The water closet was actuated by a solenoid and the flush tank linkages.

All of the solenoids were controlled by a group of single-pole, singlethrow toggle switches. A toggle switch was used to operate the washing

machine which was prefilled and preset on the drain event. By using an accumulative seconds counter a predetermined schedule of discharges could

be imposed on the system by a single operator.

3 . 3 Test Procedure

A . All Vents Open

1. Water depths, and average velocities in the 3 inch building drain,

and air rates in the individual fixture vents and stack vent were

determined for each fixture discharged individually. Residual

trap seals were measured. A velocity traverse was made at depth

H D" (see Figures 1 and 2) during the water closet discharge.
5

2, The fixtures were discharged in combination. The water closet was discharged; two seconds later the bath tub and the two compartment

kitchen sink were discharged simultaneously. For a mode of comparison, these fixtures were again discharged as indicated, but

the discharge was superimposed on the washing machine discharge

during the time the washing machine was draining from full condition. The washer was started 4 seconds prior to the water closet

discharge. The same variables were measured as indicated under

(1) above.

3. All fixtures were discharged simultaneously. The same variables

were measured as indicated in (1) above.

B • Ml Vents Closed

The above procedure was repeated except that in place of air rate trap

seal pressure readings on the drain side of the trap were taken when

a seal loss was detected.

C . All Vents Open Except Those for the Lavatory and Bath Tub

Residual trap seals ware measured after the fixtures ware discharged

in the following manner: individual fixture discharges, the washing

machine followed by sink No. 1, 2 seconds later, washing machine

followed 2 seconds later by the bath tub and both sink compartments

simultaneously, and all fixtures simultaneously. During these discharges, trap seal pressures ware taken on the drain side of the trap

for all fixtures not in operation.

4.

RESULTS

4 . 1 All Vents Open With Individual Fixture Discharges

Air rates in the stack vent and individual vents, and water depths

in the building drain for individual fixture discharges were the first

dependent variables studied through the use of the experimental plumbing

system. This information suffices as a foundation upon which to build more complicated modes of system loading, and it can be looked upon as minimum loading or a lower reference for the comparison of effects of

various loading modes. The peak water depths in the drain measured at

the stations shown in Figures 1 and 2 for each fixture discharge are given

in Figure 9. These peak water depths are accurate to within ±5% of the
6

actual depths viewed by means of visual inspection. To perform this inspection, glass tubes and scales were connected externally in place of the

transducers to form a closed loop from top to bottom of the drain and the

maximum rise of water observed for a given fixture discharge was recorded

and compared with the value obtained by the transducer for the same discharge. The peak depths measured at stations D, E, and F are not necessarily the maximum depths anywhere in the drain - if this be the case it

is purely coincidental. It is obvious, however, that the measurement

points chosen span the point of maximum depth in the drain. Depth D as a general rule is less than depth E and depth F is less than depth E but

greater than depth D. The average velocities between D-E and E-F in the

3-inch drain are shown in Table 1 for the operation of each fixture. The

velocities at D and E and F are somewhat higher than this average. Taking

into account the extra time necessary to obtain all of the velocities, at

each station, the decision was made to take velocities at station D as an indication of the magnitude of the discrepancy between the averages and, the

actual values at each station. To obtain the average velocities the time

intervals between the initial impact of water at stations D and E and stations E and F were obtained from the oscillograph record. Knowing the

distance between these positions on the drain, it was a simple matter to

obtain the average velocities over these legnths of the drain. The velocity at station D was obtained with a static pitot tube. The velocity decreased as the tube was lowered into the stream and increased as the tube was moved upward. In other words, it was found that the velocity at the

bottom of the pipe was less than the velocity at the crest of the surge.

This variation of velocity with depth appears to be small. The plot of

the pitot tube traverse is shown in Table 1. This velocity traverse was obtained only for the water closet discharge with all vents open.

Air rates were obtained using small pitot tubes located in the stack

vent and individual fixture vents. The effects of small changes in specific weight, relative humidity, and of inaccuracies in the instrumentation

were considered negligible. For analysis of computation, incompressible

flow of dry air at a constant pressure of 14.7 psia and a temperature of

60°F was assumed.

The error introduced by assuming the average velocity to be 0.80

times the indicated centerline velocity is probably the largest source of error in the measurement of air rates in the vents. The velocity factors

determined by other experimenters range from 0.75 to 0.90, depending on a number of factors.—/ Thus, indicated air flow rates obtained by the procedure used in this investigation could be in error by perhaps as much as

± 10%.

_1/ Fluid Meters "Their Theory and Application" Report of ASME research

committee on fluid meters fifth edition, 1959, page 182, paragraph 317.
7

Another factor of unknown magnitude may be introduced by turbulence

and non- symmetrical distortion of velocity profile. This could be cor- rected by increasing a straight pipe upstream from the pitot tube by say

50 to 100 pipe diameters or by installing straightening vanes, but these measures appear to be beyond the scope of the present investigation for

practical reasons.

The trap seals were checked after each fixture operation and no losses were indicated for any individual fixture operation.

4 . 2 All Vents Open with Combinations of Fixture Discharges

The combination of fixture discharges chosen seem to include some loadings which might be encountered in the actual system and were heavy

enough to cause trap seal losses, but it cannot be said that the heaviest

possible fixture loading was included. Perhaps a combination with a different time sequence would create a loading condition worse than this or worse than all fixtures discharged simultaneously. The possibilities are many and varied. In any case, the loadings selected were applied throughout the experiment. These loadings were used for the two extreme conditions

of venting so that the full effect of venting on the water depths, trap seal

losses, and pressures in the system could be observed. One load combination

chosen comprised the discharge of the water closet, then, two seconds later,

the simultaneous discharge of sink number one and the bath tub. For com- parison, another combination was used as follows: the washing machine was

set on the drain event and the water closet discharged four seconds later,

followed by the discharge of the bath tub and sink number one as described

before. A third combination comprised the simultaneous discharge of all

fixtures. The peak water depths in the drain are shown in Figure 11 for

the loadings indicated above. No trap seal losses were detected during

any of these loadings.

4 . 3 All Vents Closed with Individual Fixture Discharges

The maximum or worst loading conditions are obviously approached when

all of the vents are closed. All phases of the test with vents open as described under section 4.1 were repeated with vents closed.

Referring to Figure 12, a comparison of water depths in the building

drain for a lavatory discharge of 1.8 gallons of water is presented for

the system with vents and without vents. There was a tendency to lose some of the sink trap seal during the second run without vents. About

1/16 inch of seal was lost. The rest of the seal depths remained un- changed, daring the second run.
8

Figure 13 shows the comparison of water depths for a water closet discharge during complete venting and without venting. During the first of

three runs without venting the following trap seals experienced slight

losses: the sink - 1/8", the bath tub - 1/8", and the washing machine - 1/16".

Figure 14 shows the comparison of water depths for the kitchen sink

draining one and two compartments at a time for the vented system and the

unvented system. The following trap seal losses were observed with vents

closed: the discharge of sink number one caused 15/16" loss of the water

closet seal, 1/16" of the bath tub seal, and 2" of the washing machine trap

seal. The discharge of sink number two caused 1/16" loss of the bath tub

trap seal, and 9/16" of the washing machine trap seal. The discharge of

both sink number one and sink number two caused 13/16" loss of the water

closet trap seal, and 1 15/16" loss of the washing machine trap seal.

Figure 15 shows a comparison of water depths for the discharge of the

washing machine during the drain event with venting and without venting.

There was a loss of 1/8" from the water closet seal with the vents closed.

No other seal losses were observed during the three runs taken.

Figure 16 shows a comparison of water depths for the discharge of the

bath tub with venting and without venting. No seal losses were observed.

Referring to Table 1, a comparison of the average velocities in the

drain lengths D-E and E-F is shown for the conditions of all vents open

and all vents closed off during the discharge of individual fixtures. No

trap seal losses were detected either with or without venting.

4.4 All Vents Closed and Combinations of Fixture Discharges

The same combinations of fixture discharges were used for this con- dition of all vents closed as were used during the tests with all vents

open, as described under section 4.2.

Figure 17 gives a comparison of the water depths in the 3-inch drain

with vents open and without vents for the simultaneous discharge of the

bath tub and compartment number one of the two compartment kitchen sink

two seconds after the initiation of the water closet discharge. With no venting the following trap seals were lost: the kitchen sink lost 1 9/16"

of trap seal and the washing machine lost 1 7/16" of trap seal.

Figure 18 gives a comparison of the water depths in the 3" drain with

vents open and without vents similar to that shown in Figure 17 except that

in this case the washer had been operating for 4 seconds prior to the water

closet discharge. With no venting the following trap seals were lost: the
the kitchen sink lost 2 1/16" o£ trap seal and the lavatory lost 11/16" of

trap seal depth.

Figure 19 gives a comparison of the water depths in the 3" drain with

vents open and without vents for all fixtures discharged simultaneously.

The following fixtures experienced seal losses during simultaneous discharge

of all fixtures. The lavatory consistently lost 1 3/4 inches of seal during

each of the three runs. The water closet lost an average of 1/2 inch of

seal. The bath tub and washer replenished their own seals due to trailing

discharge occurring after the sink, water closet, and lavatory had completed

their discharges.

4 . 5 All Vents Open Except the Bath Tub and the Lavatory Vents

No seal loss from the lavatory trap was detected as a result of individual fixture loadings with the exception that 1/16" was lost when the

water closet was discharged. The lavatory trap seal pressure varied by

±0.1 inch of water from atmospheric pressure.

The following combinations of fixture loadings were applied without a detectable lavatory seal loss: washing machine followed by sink No. 1 2 seconds later, washing machine followed 2 seconds later by simultaneous

discharge of the bath tub and both sink compartments, and all fixtures discharged simultaneously. The following combinations of fixture discharges

caused a loss of lavatory trap seal: (a) the washing machine discharged,

followed 2 seconds later by the water closet, causing a lavatory seal loss

of 1/16" with a peak seal pressure of +0.04 inches of water; (b) the washing machine discharged then 5 seconds later, the bath tub and two compartment sink discharged simultaneously, followed by the water closet 10 seconds

after the start of the washing machine, causing lavatory seal loss of 3/16".

The bath tub trap seal experienced no loss during individual fixture

loadings and during the discharge of all fixtures simultaneously. When both

sinks were discharged followed by the water closet 2 seconds later, the tub

trap seal loss amounted to 3/16" brought about by a positive seal pressure

of +2.0 inches of water. When the washing machine was discharged followed

by both sinks 5 seconds later and the water closet 10 seconds later, a seal

loss of 1/8" with a seal pressure of +2.5 inches of water was experienced

by the bath tub trap.
10

5. AIR DEMAND AS A FUNCTION OF STACK LENGTH AND INLET FITTING

TYPE FOR A 2 IN. TEST STACK

Ttiis work is a continuation of that reported in section 3.4 of Progress

Report No. 1. A complete description of the test setup was given in the

earlier report. In brief the test setup comprised an experimental 2 inch

stack 22 feet in length constructed of standard weight, galvanized iron

pipe assembled in such a way as to facilitate the shortening of the stack

length. Water was introduced into this stack from a branch through a re- cessed, cast iron, screwed 2x2 sanitary tee type drainage fitting. Air

was introduced through the stack vent extending upward from the fitting.

Water and air flow rates as well as air pressures were measured.

The long term objective is to obtain data on this stack with different

inlet fitting types, different stack lengths, and different diameters of

branch and stack. Information on air rate (or demand), stack length, fitting

type as affected by water rate, and other independent variables ifl needed in

order to provide a rational basis for vent pipe system design.

5 . 1 Results and Conclusions Pertaining to Air Demand Vs. Stack Length

and Inlet Fitting Type

Figure 21 shows a plot of air flow as a function of water flow. This

plot is similar to that shown in section 3.4 of report No. 1. The plot compares the effect on the system of changing the drainage fitting. From a practical point of view, it is significant that for a given water flow rate

the air flow associated with the use of the long-turn T-Y was greater than

that with the sanitary tee; consequently, the pressures, throughout the

length of the stack, were closer to atmospheric pressure when the long-turn

T-Y fitting was used than when the sanitary tee fitting was used. More

protection for trap seals against the effects of induced siphonage would

be maintained through use of the long-turn T-Y for introducing water to a stack.

At this time, little or no data is available on the change of air rate

with stack length variation under the condition of a constant water rate

input. This information is needed particularly for stacks one and two

stories in height. Earlier investigations have utilized stacks of the order

of 30 feet in height. In an initial attempt to explore the effect of stack

length on air rate, the length of the stack was increased from 22 feet to

35 feet. Figure 22 shows a plot of air rate as a function of water rate

for the two stack lengths. The effect of changing the drainage fitting

type is again seen in this plot.
11

It can be concluded from this plot that the amount of air that is re- quired by a system increases as the distance from the base of the soil stack

to the horizontal branch increases. This indicates that, in general, long

soil and waste stacks require more venting than short ones, and that stack

vents for short stacks need not be as large as for long stacks.

6. CONCLUSIONS PERTAINING TO THE VENTING STUDY

With all vents open, no trap seal losses were experienced during any of

the fixture loadings. From this it is concluded that the venting is adequate

to protect the trap seals even under the most severe loading condition.

With all vents closed off, no more than two fixtures experienced trap

seal losses at one time during the discharge of one fixture. (see Table 3).

The washing machine received the largest trap seal losses during these discharges which indicates that a blockage of venting action through the piling

up of water occurred in this 2 inch drain. This drain diameter should

be increased. If the drain were larger, air would be able to flow above the

water from either the washing machine vent or the kitchen sink vent; therefore, the trap seals would be less subject to failure and perhaps one of

these vents might be eliminated.

It seems that both the bath tub and lavatory vents could possible be

removed. Referring to section 4.5, it will be seen that the lavatory lost

only 1/16 inch of seal during a peak seal pressure of ±

0 . 1 inch of water.

This was caused only by the water closet discharge. After the loss of an initial 0.1 inch of seal, no more seal should be lost from this fixture.

The water depths shown in the report are primarily presented at this

time to indicate the order and magnitude or change in the depths during the

extreme venting conditions. We intend to expand our depth sensing instrumentation through the installation of more pressure transducers on the drain.

When more water depth measurements are available in conjunction with degrees

of system venting, it is hoped that more can be said about the effect of

venting on these depths. Although none of these recorded depths indicate

a full drain, it is believed that at times a full drain does exist at the

junction of the 3 inch drain and the 2 inch branch. Positive pressures

on the drain side of the bath tub trap seem to indicate this. (see section

4.5).

The trap seal losses reported in sections 4.3 and 4.4 included both the case of induced siphonage; that is, the loss of the trap seal from a fixture

not in operation caused by the operation of another fixture or fixtures, and
12

the loss of trap seal from a fixture in operation. This latter case is not

necessarily self-siphonage , but may be a combination of siphonage and selfsiphonage. Self-siphonage is defined as the loss of trap seal from an operating fixture which is brought about as a result of its own discharge.

Seal pressures (on the drain side of the trap) were determined only for the case of trap seal loss from a fixture not in operation. These seal pressures and losses are shown in Tables 3 and 4. A third type of trap seal

loss was observed occasionally. This occurred after the passage of a positive trap seal pressure. The mechanism of loss consists primarily of the

seal surface being elevated above the initial full trap seal surface level on the fixture side of the trap. The instantaneous potential energy developed

at the instant of maximum positive seal pressure is transferred to kinetic

energy upon the reduction in positive seal pressure. The momentum of the

trap seal liquid may be sufficient to cause water to spill over the trap

weir as it overshoots the initial position. The amount of loss depends

upon the maximum positive seal pressure and upon the rate of reduction of

this pressure.

Occasionally a combination of both positive and negative pressures on

the seal occurred during one loading pattern. Figure 20 is a rather dramatic

example of this case. This graph shows the history of trap seal failures

for the washing machine and lavatory.

7. PROPOSED WORK FOR THE NEXT REPORTING PERIOD

One of the main purposes of this study is to determine the effectiveness

of different degrees and methods of venting in retention of trap seals and

maintenance of gravity flow. From the results, it is hoped that some indications will be available about what vents could be safely eliminated or if

not eliminated what minimum size of pipe will be adequate to protect the trap

seals and allow the system to function in a satisfactory manner as far as hydraulics and pneumatics are concerned. Of course, in order to learn something about the effects of venting, the degree of venting has to be the independent variable and all other possible variables held constant.

The two variables of importance that should be held constant are the

system configuration and at least one hydraulic loading. This particular

hydraulic loading will be the same as that used throughout this report and,

namely; the discharge of the water closet followed by the simultaneous discharge of compartment No. 1 of the kitchen sink and bath tub two seconds

later. By utilizing this loading consistently, the effect of degrees of

venting on water depths and average velocities in the drain may be seen.
13

It is expected that the instrumentation will be broadened to include more transducers on the building drain. This will give a more complete record

of the velocities and depth along the drain. Other fixture discharge com- binations will be used with each degree of venting including the one indicated above. These combinations of fixture discharges will be used to

determine the combinations if any that least affect the trap seals and the ones that cause the greatest trap seal loss.

The degree of venting can be varied through thirty possible arrangements

of the five vents open and closed. For instance, one vent may be closed off

and four remain open or four may be closed and one remain open. This approach

yields ten degrees of venting. Also, if two vents are shut off, three will

remain open. There are twenty possible degrees of venting between this mode

and the converse mode of three closed and two open. Also, degree of venting

can be changed by replacing the existing vents with smaller commercial sizes.

It is possible to vary the individual fixture vents through the following

nominal commercial pipe sizes: 1/8", 1/4", 3/8", 1/2", 3/4", 1", and 1 1/4".

The stack vent may be varied through this size range plus 1 1/2", 2", and

2 1/2" sizes. Of course, it is understood that much of the work indicated

above may be undesirable from the standpoint of time required for its com- pletion, or may be unnecessary from obvious considerations, but in general

any particular system responds to the various degrees of venting that can be

produced between the two extremes of no venting and complete venting.

Table 1

AVERAGE VELOCITY IN 3"

(D-E = BUILDING DRAIN FOR

10 1/4 ft, E-F = 5 INDIVIDUAL FIXTURE3/4 ft)

USE

Vents Open

Average Velocity

fps

Vents Closed

. Average Velocity

fps

Fixture D-E E-F D-E E-F

Water closet 2.56 2.88 3.1 2.9

Lavatory 2.77 2.88 3.4 2.87

Bath tub 2.56 2.88 2.87 2.62

Washing machine 3.01 2.88 3.02 2.88

Sink Number 1 2.85 2.88 3.42 2.88

Sink Number 2 2.56 2.88 2.57 2.88

Sink Numbers 1 & 2 3.42 2.88 3.66 3.38
Table 2

AVERAGE VELOCITY IN 3" DRAIN FOR COMBINATION FIXTURE USE

Vents Open

Average Velocity

fps

Vents

Average

fp

Closed

Velocity

s Fixture Combinations D-E E-F D-E E-F

Washing machine on drain

event, 4 seconds later

water closet discharged,

then bath tub and com- partment No. 1 of the two

compartment sink 3.41 2.88 2.93 3.83

Same as above without

the washer 3.93 3.29 3.26 3.59

All fixtures simultaneously 2.19 3.38 3.31 3.31
Table 3

SEAL PRESSURES AND TRAP SEAL LOSSES FOR FIXTURES NOT IN USE

DURING THE USE OF INDIVIDUAL FIXTURES WITH ALL VENTS CLOSED

Fixture

In Use

Trap Seals

Affected

Sea 1 Pressures

,

Inches of

Water

Trap Seal

Losses

,

Inches of

Water

Lavatory Sink -0.06 0.06

Sink No. 1 Bath tub o o 0.03

Sink No. 1 Automatic washer -2 . 66 2.00

Sink No. 2 Automatic washer o o

s

—

!

0.44

Sink. No. 1 Bath tub -0.15 0.03

Sink No. 2 Automatic washer -2.36 1.75

Water closet Bath tub +0.22 0.125

Automatic washer Sink +0.27, -0.12 0.17

Bath tub No losses

(
Table 4

SEAL PRESSURES AND TRAP SEAL LOSSES FOR FIXTURES NOT IN USE

DURING COMBINATIONS OF FIXTURE DISCHARGES WITH ALL VENTS CLOSED

Fixtures

In Use

Trap Seals

Affected

Seal

Pressures

,

Inches of

Water

Trap Seal

Losses

,

Inches of

Water

Water closet

discharged, then

2 seconds later

sink No. 1 and

the bath tub

simultaneously

Automatic

washer 04

r^ i OJ 1.28

Same as above

except that the

automatic washer

was started on the

drain event 4

seconds prior to

the water closet

discharge Lavatory -2.2 * 1.75

G
Figure

1.

Dimensional

description

of

the

1

bath,

slab

on

grade

plumbing

system

(See

Figure

2

for

symbol

designations)
Figure

2.

Measurement

location

and

symbol

designation
VOLUME

RATE

OF

WATER

FLOW

GPM

SEC

Figure 3. Flushing characteristics of water closet
TIME

FOR

FIXTURE

TO

EMPTY

SEC.

DEPTH OF INITIAL FILL FROM WATER

SURFACE TO THE RIM OF THE OUTLET ORIFICE

INCHES

VOLUME RATE OF WATER FLOW

6PM

Figure 4. Drain characteristics of two -compartment kitchen sink,

both compartments draining simultaneously
TIME

FOR

FIXTURE

TO

EMPTY

SEC.

DEPTH OF INITIAL FILL FROM WATER

SURFACE TO THE RIM OF THE OUTLET ORIFICE

INCHES

VOLUME RATE OF WATER FLOW

GPM

Figure 5, Drain charac. -eristics r f. No. 1 compartment of

two compartment kitchen sink
TIME

FOR

FIXTURE

TO

EMPTY

SEC.

DEPTH OF INITIAL FILL FROM WATER

SURFACE TO THE RIM OF THE OUTLET ORFICE

INCHES

VOLUME RATE OF WATER FLOW

GPM

Figure 6. Drain characteristics of No. 2 compartment of

two compartment kitchen sink
DEPTH OF INITIAL FILL FROM WATER

SURFACE TO THE RIM OF THE OUTLET ORIFICE

INCHES

VOLUME RATE OF WATER FLOW

GPM

Figure 7. Drain characteristics of lavatory
DEPTH OF INITIAL FILL FROM WATER

SURFACE TO THE RIM OF THE OUTLET ORIFICE

INCHES

VOLUME RATE OF WATER FLOW

GPM

Figure 8. Drain characteristics of 5' recess-type bath tub
WATER

DEPTH

-IN

INCHES

LENGTH OF 3" DRAIN-FEET

Figure 9 . Water depths in 3” 6x a xn with all vents open

for individual fixture use
VELOCITY

VARIATION

WITH

DEPTH

-FPS.

0 O.l 0.2 0.3 0.4 0.5 0.6 0.7 0.8

DEPTH FROM THE DRAIN BOTTOM-INCHES

Figure 10. Variation of velocity with depth at "D" on the 3" drain

during a water closet discharge with all vents open
WATER

DEPTH

-IN

INCHES

Figure 11. Water depths in 3" drain for fixtures discharged in

combinations with vents open
WATER

DEPTH

-IN

INCHES

Figure 12. Water depths in the 3" drain for lavatory discharge

with vents closed and with vents open
WATER

DEPTH

-IN

INCHES

Figure 13. Water depths in the 3" drain for water closet

discharge with vents open and with vents closed

4
WATER

DEPTH

-IN

INCHES

Figure 14. Water depths in 3" drain during two compartments discharged

simultaneously and during the discharge of one compartment at

a time with vents open and with vents closed
WATER

DEPTH-IN

INCHES

1.0

0

I h ill L_i_L_ij-i_i i 0 5 10 15 20 25 30 35 40 45

LENGTH OF 3" DRAIN-FEET

Figure 15. Water depths in 3" drain for the washing machine discharging during

the drain event with all vents open and with all vents close
WATER

DEPTH

-IN

INCHES

Figure 16. Water depths in 3" drain for the bath tub discharging from

half full water level with vents open and with vents closed
WATER

DEPTH

-IN

INCHES

2.4

2.2 -

2.0 -

.8

0

I L i 1 1 i li lil i i 0 5 10 15 20 25 30 35 40 45

LENGTH OF 3" DRAIN-FEET

Figure 17. Water depths in 3" drain for the discharge of compartment No. 1 of the sink simultaneously with the bath tub 2 seconds after a water closet discharge with vents open and with vents closed
WATER

DEPTH

-IN

INCHES

Figure 18. Water depths in 3" drain for the washer discharging during the drain

event, the water closet discharged 4 seconds later then 2 seconds

after the water closet discharge, the simultaneous discharge of the

bath tub and compartment No. 1 of the two compartment kitchen sink

with vents open and vents closed
WATER

DEPTH

-IN

INCHES

Figure 19. Water depth in 3" drain for the discharge of all

fixtures simultaneously with and without vents
TRAP

SEAL

PRESSURE

-INCHES

OF

WATER

Figure 20. Lavatory and washing machine trap seal pressures versus the time

during the discharge of the water closet then two seconds later

the discharge of the two compartment kitchen sink and tub simultaneously with all system vents closed

I .
VOLUME

RATE

OF

AIR

FLOW

GPM

VOLUME RATE OF WATER FLOW

GPM

Figure 21. Air demand as a function of water flow rate and vent pressure, for

2" test stack. The following symbols indicate the air pressure in

the stack vent at a point located one foot above the water inlet:

0 indicates +1.0 inches of water

A indicates 0.0 inches of water

• indicates -1.0 inches of water
no

ICO

90

80

TO

60

50

40

30

20

10

0

FITTING. STACK DIAMETER -2.'

10 20 30 40 50 60 70 80 90 100 1 10 li WATER RATE- GALLONS PER MINUTE

re 22. Air rate versus water rate for a change in stack length and inlet

fitting type (The static pressure of the air flow was held at

atmospheric pressure at a point in the stack vent one foot above

the horizontal branch through which the water was introduced into

the system. Stack and stack vent were 2" diameter.)
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