AlllDD

NATL INST OF STANDARDS & TECH R.I.C.

A1 11 00992752

loski, M. J/Hydraullc performance of a 435 .U58 NO. 60 V1974;C.2 0.1 NBS-PUB- C

/

BUILDING SCIENCE SERIES 60

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards^

HYDRAULIC

PERFORMANC

of a

FULL-SCALE

TOWNHOUSE

ORAIN-WASTE-VE

SYSTEM

with

REDUCED-SIZE

VENTS
The Building Science Series , Vjr 0

I'hc Building Sciciuo Series tlisscmiiiates technical information developed at the National Bureau of Standards on

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

arc directed toward the manufacturing, design, construction, and research segments of the building industry, standards 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 into three general groups: Building Systems and Processes;

Health, Safety and Comfort; and Structures and Materials. For further information regarding these publications

please contact the Scientific and Professional Liaison Section, Center for Building Technology, Institute for Applied Technology, National Bureau of Standards, Washington, D.C. 20234.

fSee mailing list announcement on last pagej
tatkinal Sureau of Stafidajsi

SEP 2 2 1975

Hydraulic Performance of a Full-Scale

Townhouse Drain- Waste- Vent System

With Reduced-Size Vents

ne5 %\^\m Saerce

(7

M. J. Orloski and R. S. Wyly

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by:

Tri-Services Investigational

Committee on Building Materials Department of Defense

Washington, D.C. 20330

U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued August 1975
Library of Congress Cataloging in Publication Data

Orloski. M J Hydraulic performance of a full-scale townhouse drain-waste- ven: system with reduced-size vents. (NBS Building Science Series; 60)

Supt. of Doc. No.: C 13.29:2/60

1. Drainage, House. 2. Plumbing—Testing. 3. Row houses. I. Wyly. Robert S.. joint author. H. United States. Tri-services In- vestigational Committee on Building Materials. HI. Title. IV. Series: United States. National Bureau of Standards. Building

Science Scries * 60 TA435.U58 No'. 6o' [TH6668] 690'.08s |696'.ll 74-28135

National Bureau of Standards Building Science Series

Nat. Bur. Stand. (U.S.). Bldg. Sci. Ser. 60, 43 pages (Aug. 1975) CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $1.05 Stock Number 030S-01352 Catalog No. C 13.29:2/60
Foreword

Housing research has been a major concern at NBS since its estabUshment in the early IQOO's.

Today, our modern research facihties include a plumbing laboratory that provides both great

flexibility of measurement and a basis for improving the evaluation methodology in this field. For example, recent measurements made with this facility have related the present design

criteria for vent sizing to performance criteria for the first time under representative dynamic

conditions. This work has shown that in many cases plumbing vents of reduced size perform quite

well, providing a basis for resource conservation by use of smaller vent pipes. Such information will be useful to regulatory authorities when considering code changes, and to the plumbing engineering

profession.

Ernest Ambler, Acting Director

I

1

iii

Contents

page Forev,'ord iii

1. Introduction 1

1.1. General 1

1.2. Background of present study 2

1.3. Objective, approach, and scope 2

2. Plan of experimental work 3

3. Component stack 9

3.1. Procedure 9

3.2. Results 9

3.3. Discussion 14

4. Townhouse 15

4.1. Procedure 15

4.2. Results 15

4.3. Discussion 24

5. Summary and conclusions 25

6. References 29

Appendix A. Sizing reduced-size vents, procedure and examples 30

Appendix B. Installation recommendations for reduced-size venting in 1-2 story drain- waste-vent systems 32

Appendix C. Units of measure and SI conversion factors 32

Appendix D. Determination of time increment for data averaging 34

Appendix E. Definitions, acronyms, and symbols 35

List of Figures

Figure 1. Example of averaging period selections for water flow rate through a flushometer

valve to show data smoothing 4

Figure 2. Component stack schematic showing locations and types of measurements 4

v
Figure 3. Plan view of stack connections (by stack number designation) to building drain of Page townhouse system 5 Figure 4. Standard vent sizes originally specified for townhouse before vent size reductions . . 6

Figure 5. Schematic showing townhouse system as built in NBS Plumbing Research Laboratory, with reduced-sized vents 7 Figure 6. Townhouse schematic showing locations and types of measurements 8

Figure 7. Relationship between vent pressure and air demand rate, comparing results of

two component stack investigations with one WC discharged 14

Figure 8. Relationship between dP (peak 0.2 s suction), dH (trap-seal reduction) in the

idle water closet trap, and^a (peak 0.2 s air demand) for single-fixture flush tests

in the component stack investigation 14

Figure 9. Relationship between dP (peak 0.2 s suction) and dH (trap-seal reduction) in

idle P-traps in the townhouse DWV system, with closed vent terminals 25

List of Tables

Table 1. Instruments and utilization in full-scale townhouse (TH) system and/or component

stack (CS) 3 Table 2. Discharge characteristics of the fixtures in the townhouse system (4-run average) . . 5 Table 3. Principal rationale for selection of test loads in townhouse system 9 Table 4. Component Stack, Single-fixture and back-to-back flush tests: peak air de- mand, peak vent suction and single run idle trap-seal reduction for conditions

of vent open, 3 degrees* of vent restriction and vent closed (idle trap not

plugged). Supply pressure was 30 psi 10

Table 5. Component Stack, Single-fixture and back-to-back flush tests: peak air demand, peak vent suction and single run idle trap-seal reduction for conditions

of vent open, 3 degrees* of vent restriction and vent closed (idle trap not

plugged). Supply pressure was 50 psi 11 Table 6. Component Stack, Single-fixture and back-to-back flush tests: peak air demand, peak vent suction and idle trap-seal reduction for conditions of vent

open, 3 degrees* of vent restriction and vent closed (idle trap not plugged).

Supply pressure was 70 psi 12 Table 7. Component Stack, Single-fixture flush tests: peak air demand and peak vent

suction for conditions of vent open, 3 degrees* of vent restriction and vent closed

(idle trap plugged). Supply pressure was 50 psi 13

Table 8. Component Stack, Single-fixture flush tests: peak air demand, peak vent

suction and cumulative trap-seal reduction for conditions of vent open and 2 degrees* of vent restriction up to onset of aspiration of air through idle trap.

Supply pressure was 50 psi 13

Table 9. Tabulation of Series I tests showing air flow rates, vent pressures, trap-seal reductions, and water depth in the building drain, for various test conditions applied

to the townhouse DWV system 16

Table 10. Tabulation of Series II tests showing cumulative idle trap-seal reductions for various test conditions applied to the townhouse DW\ system 22

Table 11. Summary Table (compiled from tables 9 and 10): Trap-seal performance as affected by various degrees of loading and other test conditions in the Series

1 and II townhouse tests 23

Table 12. Recommended criteria for selecting dry-vent sizes for 1-2 story sanitary drainage

systems 26

*Degrees of vent restriction were not necessarily the same (setting of the butterfly valve) in tables 4-8.

vi
Hydraulic Performance of a Full-Scale Townhouse

Drain-Waste-Vent System With Reduced-Size Vents**

M. J. Orloski and R. S. Wyly

This report describes the experimental findings of tests on a full-scale two-story plumbing

system with reduced-size vents under a range of operating conditions including tests with (he vent terminals closed and the building drain submerged. Kesults indicate that dry vent piping

in 1-2 story housing units can safely be smaller than presently allowed by design without jeopardizing the trap seals. On the basis of the current investigation and from earlier work on full-scale systems of substantially different geometry, criteria for sizing reduced-size vents arc given for general application to conventional 1-2 story housing units. In addition to the practical evidence

in terms of acceptable trap performance, the current study provided fundamental evidence of the

excessive present design criteria. For the first time measurements were obtained which relate traditional design criteria (air flow and vent pressure) to presently recommended performance

criteria (trap-seal retention) under dynamic conditions. These findings indicate that the vents can

be sized on the basis of 1.5 in water gage (equals 372.2 pascals) suction in the vent rather than

the 1.0 in W.G. (equals 248.8 Pa) presently specified in the plumbing codes. Also air demands

measured were significantly less than assumed in current practice for short stacks and for systems

with vent networks. Key words: DWV; performance testing; reduced-size vents; trap-seal retention; venting; venting

criteria; vents, reduced size.

1. Introduction

1.1. General

Gravity sanitary drain-waste-vent (DWV)^ sys- tems in buildings utilize water-filled traps to prevent sewer gas, fumes, or foul odors from escaping into

occupied spaces. Venting of the traps prevents the

hydraulic action of the discharging fixtures from

generating pneumatic pressures that would either cause excessive reductions of the trap seals or that

would produce ejection of waste water, suds, etc., into idle fixtures. Optimum vent length or diameter

(one of these must be assumed to find the other) is computed by means of an equation relating air demand, vent pressure excursion, and a materialdependent roughness factor [1].^ Vent sizing tables

in current plumbing codes are based on this computation.

Air demand estimates which are utilized for sizing

main vents in the current plumbing codes are based on limited data from studies of components of plumbing systems. For example. National Bureau of Standards Monograph 31 [1] presents data for air flow in simple stacks of multi-story height with the water

all being introduced at the top in most of the tests. Also, air demand estimates drawn from these data were based on the simplified assumption that air and water fall down a stack at the same mean

velocity, and did not adequately account for reduced

**This study is one element of a current program on RSV supported by the

Tri-Services Investigational Committee on Buildint; Materials of the Depart- ment of Defense, and by the Directorate of Civil Engineering, HQIJSAF.

^ Definitions, acronyms, and symbols used in this paper e.g. additives,

pascal, (IH, P-traps are given in appendix E.

air demand rates at vent pressures below atmospheric

or for air circulation in a typical vent network

as a source of air for venting. Moreover, because of

the absence of adequate data or mathematical

models for venting systems, branch vents of a vent

network and individual vents have been traditionally

sized by rule-of-thumb with respect to air demand.

In the case of vent pressure excursion, a 1-in W.G. (248.8 Pa) ^ value has been specified over the years in plumbing codes as the value to be used in the design computation [2]. Under service conditions

however, a 1-in reduction in trap seal of a trap with

a full-seal depth of 2-in has traditionally been

considered the basic criterion of performance [3, 4]. In other words, limiting the maximum pressure excursion in the vent by design is intended to assure that in actual performance no trap seal will be

reduced by more than 50 percent of its full depth

from representative fixture operation and from

evaporation. It is widely believed that the design

criterion of 1-in W.G. pressure excursion (along

with the conservatively determined air demands

described in the preceding paragraph) results in vent pipe sizes larger than needed for 50 percent

trap-seal retention. However, the relationship between

air demand rate, vent pressure excursion, and

trap-seal reduction has not previously been demonstrated by laboratory studies of full-scale systems

under representative dynamic conditions.

2 Figures in brackets indicate literature references on page 29

' U.S. customary units are used throughout this paper since these are

the units most frequently used in plumbing design work in the U.S. Conversions to SI units can be found in appendix C.

1
1.2 Background of Present Study

In the mid 1960's, a laboratory investigation of

reduced-size vents, conducted under joint sponsorship of the National Association of Home Builders

(NAHB) and NBS, was carried out on two full-scale systems (one a slab-on-grade and the other a split- level having three levels) and several partial DWV

systems [5]. The principal measurement on the full- scale systems was trap-seal retention. Principal

measurements in tests on the partial DWV system

were peak air flow rate and the corresponding pneumatic pressure in the vent. The data from the partial systems showed air de- mand rate to be affected by the (water) fall distance

and by small deviation of the vent pressure from

atmospheric (within the 1-in W.G. specified in the

codes) [6]. Air demand rate in a test stack with a fall distance of about Sji ft was significantly less than

that from a stack with a fall distance of 20 ft, which

in turn was less than that predicted by NBS Monograph 31 for tall stacks (having a fall distance of 30-40 ft). In addition, a significant finding was that

a slight reduction from atmospheric pressure substantially reduced the air demand in short stacks

(fall distance up to 20 ft) such as those tested. These

findings from tests on partial DWV systems helped

to explain the surprisingly good performance of full- scale DWV systems with reduced-size vents (RSV).

They were tested in the NBS laboratory and in a

field test program subsequently carried out by

NAHB involving DWV systems of 10 single-family

housing units. The NBS-NAHB investigation provided an empirical basis for broadening the vent-sizing criteria to include individual and branch vents, and a dis- tinction between 1-2 story systems. As a result of

these findings, in 1970 NAHB proposed to the three

model code bodies, Building Officials Conference of

America (BOCA), International Association of

Plumbing and Mechanical Officials (lAPMO), and

the Southern Building Code Congress (SBCC), to allow RSV in 1-2 story houses, and offered the

sizing table developed from the laboratory tests at NBS [5]. For several years, these regulatory

groups have been studying proposals to incorporate

provisions on reduced-size venting in the codes. Some

of the groups have indicated that they need further

research data, particularly with respect to the details of the experimentation, and to the consideration

given to some of the service parameters not adequately covered in the early work.

This need provided a basis for the present study.

The purpose of the present study is to confirm and

expand the RSV criteria developed in the earlier study with primary emphasis on their applicability to 1—2 story housing systems under service conditions. The current overall program, supported by

Tri-Services, includes a comprehensive analysis of

the early data, published separately [7], as well as laboratory tests on the system described in this

report, and on a 10-story high-rise RSV system

reported separately [8]. The current program is one interim step towards

the long-range goal for development and application

of a general computational method to the design

of plumbing systems. The continuing work on

venting criteria represents one portion of NBS's

broad long-range program on hydraulic design

criteria, intended to furnish a mathematical model

on which the general computational method for venting could ultimately be based.

1.3. Objective, Approach, and Scope

The present laboratory investigation, utilizing new capability for dynamic measurement and in- corporating new tests believed representative of the

service environment, is an extension of the earlier laboratory work at NBS on 1-2 story RSV systems.

The primary objectives in the current laboratory

study were twofold. The first was to provide the

sponsor with needed data regarding the practicability of building 1-2 story RSV systems, and the

second to study the performance characteristics of

the system in terms of the test conditions and measurable parameters, particularly at failure (1-in

trap-seal reduction in any trap). These objectives were also important to confirm and expand the

criteria developed earlier, from systems of very

different geometric configuration, for general application to 1—2 story housing units. For these reasons, the tests selected covered a wide range of operating

conditions, from normal to severe loadings, including some tests with the vent terminals closed and a few

tests with the building drain submerged. (Tests with

the building drain submerged and an adequate range

of tests with additives were not included in the

NBS-NAHB program.) In gravity drainage systems with water-sealed

traps, satisfactory trap-seal retention and unre- tarded fixture drainage along with the absence of

blowback and crossflow are the fundamental measures of perfoimance. Recently acoustical criteria have

been proposed as an addititional consideration [9]. The experimental approach in this investigation was

to evaluate the performance of the full-scale system

principally on the basis of trap-seal retention.

Audiovisual observations for blowback and fixture operation, particularly air aspiration through idle traps, were made in a number of instances. Due to the geometry of the full-scale system, crossflow and

retarded fixture drainage were not considered likely.

(Flow from only one branch interval was introduced on any one stack and individual fixture drains were

neither back-to-back nor joined together.)

A secondary objective of the present investigation was to compare the present design criteria (1-in W.G.

pressure excursion and air flow rates predicted in Monograph 31) with the fundamental criterion of

performance intended in service (minimum 50%

trap-seal retention) by means of an in-depth study of a simple one-stack system. The earlier work [7]

2
examined air demand rate and vent suction in some

of the tests and trap-seal retention in other tests. How ever, a better understanding of the simultaneous

dynamic relationship between the three parameters:

air flow rate, vent suction, and trap-seal retention is an important aspect of the development of a rational

basis for a general computational method for venting. In the present study, dynamic measurements of

air demand and vent pressure were made on a

selective basis in the full-scale system and for all the

work on the component system. Key to the capability for making a wide range of dynamic air demand

and vent pressure measurements was the programmable data acquisition system (DAS). The DAS can

average readings of rapidly changing phenomena for a preselected time period aud report one value,

presently for up to 64 channels simultaneously. This

system is an integral part of the NBS facility and

replaced the need for manual examination and

interpretation of dynamic curves for each measure- ment made—a very time consuming process. The

data are stored on magnetic tape, indexed, and can

be systematically retrieved by means of a data

analysis program.

2. Plan of Experimental Work

The simple one-stack system was studied first; then

the tests on the full-scale two-story DWV system were carried out. A list of instruments used and their

utilization in the experimental work is given in

table 1. An averaging period of 0.2 s (for the DAS)

was selected for transducers measuring air flow rate and pneumatic pressure in all tests, based on a

calculation (given in Appendix D) of % the frequency

Table 1. Instruments and utilization in full-scale townhouse {TH) system and/or component stack (CS)

Utilization

Air flow rate in stack vent, CS . . .

Vent pressure, CS

Pressure drop across Venturi in water supply line, CS. W ater supply flow rate CS

Trap reduction, CS

Spent water weight, CS, and

calibration of fixtures, CS.

Air flow rate in main vent terminal, TH.

Air flow rate in sink vent terminal,

TH.

Pressure drop across Venturi in main vent terminal, TH.

Pressure drop across loop meter

in sink vent terminal, TH.

Vent pressure except sink vent, TH.

Vent pressure, sink vent, TH

Building drain water depth, TH.

Trap seal reduction, TH

Trap seal reduction, TH .

Transducer calibration, CS and

TH.

Instrument description

Mass flowmeter hot wire type.

Strain-gage, bidirectional, wet -dry transducer (gage).

Strain-gage, bidirectional wet-wet

transducer (difl^erential).

Venturi

Strain-gage, unidirectional wet -dry transducer (gage). Load cell, strain-gage type with

indicator.

Venturi

Loop centrifugal meter, air

.

V ariable-range capacitance-type

\ transducers bidirectional drydry (differential/gage).

(Four ranges used)

Strain -gage, bidirectional wet-dry

transducer (gage).

Piezometers for LI, Bl, L2, S3, C4, L5.

Rulers for Wl, W2, W5

Range or size of instrument

Water manometer (6/2 in diam.) with Digital voltmeter

2.3 Ib/min full scale + 5 to -5 in W.G

+ 5 to -5 in W.G . .

1>2 in, (3=563

0 to +5 in W.G

(four) 500-lbf capacity. . .

iVi in, ^=427

1 in, |3 = 698

Range 1, ±0.5 in W.G. . . Range 2, ±1.6 in W.G, . . Range 3, ±5.3 in W.G. . . Range 4, ±16.05 in W.G.

±5 to -5 in W.G

6 in

12 in ± 10 in W.G . 10 V

Engineering variable

resolution of system "

0.23 gpm.

0.01 in W.G.

0.1 in W.G.

1-3 gpm.

0.01 in.

5 Ibf.b

1-3 gpm.

1-3 gpm.

0.00005 in W.G.

0.00016 in W.G.

0.0005 in W.G.

0.0016 in W.G.

0.01 in.

>i6 in.

Vw in.

0.001 in W.G.

0.001 V.

" "System" includes computer if computer was used. computer. The resolution of the indicator, which was used

Amplified transducer output would improve resolution by to calibrate the fixtures, was 0.1 Ibf.

3
Figure 1. Example of averaging period selections for water flow rate through a

flushometer valve to show data smoothing.

of "slosh" in a trap. An example of the data smoothing achieved by selection of a suitable averaging

period is shown in figure 1. Smoothing the data to some degree permits meaningful comparison of

maximum and minimum values (which can systematically be retrieved from the magnetic tape by means

of an analysis program).

Strictly interpreted, a 50 percent trap-seal reduction varies from 1 in for 2 -in-depth seals of P-traps,

found on fixtures such as lavatories, to 1^2 in for 3-in-depth seals, characteristic of water closets. In

the present investigation, a 1-in reduction in the

depth of any trap was assumed a failure for the

experimental work on both systems.

The simple one -stack system, or component stack,

designed for this study consisted of an 18-ft length

of 3-in PVC with two back-to-back flushometer type

water closets at the top, as shown in figure 2. Both

water closets were calibrated before the tests to

deliver 4 gal per flush in accordance with Federal

Specification WW-P-541b [10]. For the experimental work on the component

stack, measurements taken on pneumatic pressure in the vent stack, air flow rate, water flow rate, and

trap-seal reduction were made by means of the pro- grammable DAS. The computer flushed the w^ater

closet(s) by means of a solenoid actuator immediately after a start value ("zero") was recorded by

the DAS for all the transducers. Measurement loca- tions on the simple system are shown in figure 2. A strain-gage type pressure transducer was used

to sense the pneumatic pressure in the stack vent. Trap-seal reduction measurements were made by means of strain-gage pressure transducers (tapped

into the bottom of the trapways to measure the head

of water). Water flow rate was measured by means of

differential strain -gage type pressure transducers

used in conjunction with l}2-in Venturi meters in the water supply lines. An air mass flowmeter was

located at the top of the stack vent. By means of dif- ferent settings, a butterfly valve in the vent was

(l) load 01 butterfly valve gate valve

Figure 2.

® VENT AIR FLOW ® FLUSH VALVE WATER FLOW TRAP DEPTH SENSOR ® VENT PRESSURE

Component stack schematic showing locations and

types of measurements. (See Section 2 for discussion of the instrumentation.)

4
used to simulate varying air demand/restriction of

different sizes of vent pipes. Load cells situated under

the tank, >\here the spent water v/as collected, were

used to monitor the weight of water in the tank

which was periodically emptied, and to check that

the volume (by weight) of water delivered from each

flush was close to the 4 gal per water closet deter- mined by the calibration. The full-scale townhouse system constructed in the laboratory was selected from several family

housing plans submitted by the sponsor. The system

had nine fixtures distributed among: one full bath,

two half baths, a kitchen equipped with a two-compartment sink (food-waste-disposal-unit in one compartment), and a laundry area equipped with an

automatic clothes washer. The system had five drain- age stacks with four tied together in a common vent

header. The fifth stack (kitchen sink) was vented

individually. Discharge characteristics of the fix- tures in the townhouse system are given in table 2.

Table 2. Discharge characteristics of the fixtures in tin townhouse system {4-run average)

Volume Duration Average

Fixture discharged of discharge

discharge rate

(gal) is) igpm)

Bl 22. 2 158 8.4 LI 1.6 12 7.9 Wl ^ 4. 5 11 24.6 L2 1.6 12 7.7 W2 » 4. 5 11 24. 6 S3 w/fwdu operating. . 3.6 6 35. 5 C4 14. 8 53 16.9 L5 1. 6 12 7.9 W5 » 4. 5 11 24. 6

* From a caUbration of the same model tank/type water

closet. 1-s peak rate = 32 gpm.

The building drain w as turned 90 degrees from the

original design, as shown in figure 3, to permit the

system to fit into the laboratory. The sizes of the vents in the original design are shown in figure 4. The reduced-size vents were sized according to the

criteria from the earlier study [7]. The vent header was sized by an arbitrary square root relationship

(see appendix A). A schematic of the townhouse

system as constructed in the laboratory is shown in figure 5. The townhouse system was instrumented with

transducers compatible (putting out a voltage between ± lOV dc to the computer) with the DAS for measurement of vent pressure in the stacks, air flow

in the main terminal and the sink vent terminal, and

the depth (static head) of the water in the building

drain. Measurement locations in the townhouse

system are shown in figure 6. Three variablecapacitance type pressure transducers were used for

/3in -W5

'4in

,3in W5

Townhouse as built

in NBS Plumbing Research

Laboratory

Original design of townhouse

Figure 3. Plan view of stack connections {by slack number

designation) to building drain of townhouse system.

measurement of vent pressure in four of the five stacks: one each for stacks 1 and 2 separately, and

the third for stacks 4 and 5 together. In each case, the pressure to be measured, as shown in figure 6, was selected by means of a manifold with valveselect pneumatic connections to the stack. A strain- gage type transducer was used to sense the pressure

in stack 3. Air flow rates in the main vent terminal

and in the sink vent terminal were each measured

by means of a variable-capacitance type pressure transducer. In the main vent terminal, a l}2-in

Venturi meter was used as the differential-pressure

sensing element; in the sink vent terminal, a Yo-in loop (centrifugal) meter was used as the differential- pressure sensing element. The depth of the building

drain flow was monitored by means of a strain -gage type transducer (one side tapped into the bottom of

the drain to sense the head of water and the other

side tapped into the top to sense the air pressure).

The traps of all the fixtures except the water closets were equipped with piezometers connected to (the

cleanout plugs of) the P-traps equipped with scales graduated in the U.S. customary and SI units. Rulers

graduated in U.S. customary units were installed in the traps of idle water closets before a test. For all runs, fixtures were discharged manually at a verbal

signal given immediately after a run was initiated on

the DAS. Trap-seal depths were read manually at the end of a run. The fixture-discharge loads for the townhouse

tests were based on guidelines recommended for single-branch-interval systems, using table lA of BSS 41 [11]. Reasons for selection of the test loads

are summarized briefly in table 3. For the experimental work described in subsequent sections of

this report, a "test" was defined to consist of four

successive runs under conditions as identical as

possible. Additives (e.g. paper diapers, bubble bath)

used in some of the tests on the townhouse. were

introduced on the first and third runs of a test.

5
SECOND FLOOR FIXTURES

j STACK NUMBER

Bl BATHTUB

L I LAVATORY

Wl WATER CLOSET

L2 LAVATORY

WZ WATER CLOSET

FIRST FLOOR FIXTURES

STACK NUMBER

S3 SINK (A AND B

COMPARTMENTS)

C4 CLOTHES WASHING

MACHINE

L5 LAVATORY

W5 WATER CLOSET

Figure 4. Standard vent sizes originally specified for toivnhouse before vent size reductions.

6
Figure 5. Schematic showing townhouse system as built in NBS Plumbing Research Laboratory, ivith reduced-size vents.

7
(a) air flow

(?) vent pressure (pi , p2, p3, valve select)

(d) drain depth monitor

(t) trap ruler

(z) PIEZOMETER

Figure 6. Townhouse schematic showing locations and types of measurements. (See section 2 for discussion of the instrumentation.)

8
Table 3. Principal rationale for selection of test loads in townhousc system

Stacks

considered

(by number

designation)

Total

fixtures available to discharge

Number of concurrently

operating

fixtures to comprise

test load"

Fixture load selected

1 1 So

2 1 (or 2) W2 (second floor)

2 1 (or 2) Wo (nrst Hoor)

3 2 Wl + Bl

TVr I 1 T 1 Wi + Ll

Bl + Ll

3 2 W5 + C4

5 3 Wl + \v2-|-Jt>l

6 3 W1 + W2 + S3

6 3 W1 +W2 + C4

B1 +W2 + C4

9 4 W1+W2+W5+ S3 W1 +W2 +W5+ C4

Principal rationale

3

2

5

1

4 and 5

1 and 2

1, 2, and 3

1, 2, and 4

1,2,3,4, and 5.

To examine self-siphonage and pneumatic effects. To examine effect of height of water fall. To examine effect of height of water fall. To observe in a group of 3 fixtures the discharge of

2 at a time to determine greatest loading effect.

To observe interaction between 2 drainage stacks taking fixtures expected to produce greatest loading

effect. To observe interaction between 2 soil stacks taking

fixtures expected to produce greatest loading effect. To observe interaction between 3 drainage stacks taking fixtures expected to produce greatest loading

effect. To observe interaction between 3 drainage stacks taking fixtures expected to produce greatest loading

effect. To observe interaction between 4 drainage stacks taking fixtures expected to produce greatest loading

effect.

These numbers of fixtures to be discharged together are taken from Table lA of BSS41 [11].

3. Component Stack

3.1. Procedure

Tests were run with a water supply static pressure

of 30, 50, and 70 psi while varying air demand (by means of five settings of the butterfly valve in the

vent from open to closed) for flushes of each of the

two water closets in turn (single -fixture flushes) and

for both water closets together (back-to-back

flushes). Initial level of trap-seal surface was that

furnished by the automatic refill of the flushometer

valve. Maximum drop in the line pressure during a

flush was about 10 psi measured 2 ft upstream from

the flushometer stop. When tests were run with the

butterfly valve closed, the gate valve was closed also. The idle trap was not plugged in the tests, thus air was sucked through the idle trap in runs that pro- duced high levels of vent suction.

Next tests were run at a water supply static pres- sure of 50 psi for varying air demand for single flushes of each of the two water closets in turn with

the idle trap plugged with rags so that no air could be

pulled through the idle trap. The purpose of these

tests was to determine if appreciably more air flow- occurred in the vent when air could not enter the

system through the idle trap.

Then some series of runs were carried out at three

settings of the vent valve (open and two different

partially closed settings) up until the sound of air was heard being pulled through the idle trap during some runs. The purpose of these runs was to study

experimentally the relationship between vent suction

(dP), air demand rate in the vent {Qa)-, and trap-seal

reduction {dH) at the point of vent restriction when

the sound of air being sucked through the idle trap was just audible during a flush of the active fixture. It was felt this might provide a basis for relating

acoustical performance criteria to the traditional

hydraulic and pneumatic criteria for plumbing

systems [9]. 3.2. Results

Values of peak air flow rate, peak vent suction and

idle trap-seal reduction for tests at a supply static pressure of 30 psi are given in table 4, 50 psi in table 5, and 70 psi in table 6. Data obtained at 50

psi for peak air flow rate and suction in the vent with

the idle trap plugged are given in table 7. Data for peak air flow, vent suction and trap-seal reduction

with increasing restriction of the vent valve up to the sound of air being sucked through the idle trap

at a supply pressure of 50 psi are given in table 8.

9
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12
Table 7. Component stack, single-fixture flush tests: peak air demand and peak vent suction for conditions of vent open, 3 degrees of

vent restriction and vent closed {idle trap plugged)

Supply PresBure was SO psi

Single-fixture flush (North)

Run No.

(Vent open) (Nominal % open) (Nominal open) (Nominal Yi open) (Vent closed)

Qa dP Qa dP Qa dP Qa dP Qa dP

1234

Average

gpm

148.5 134.0

132.0

128.0

in W.G. 2.02

1.64

1.56

1.52

gpm 89.5

98.5 96.0

101.0

in W.G. 2.68

2. 98

2.84

3. 13

gpm

63.5 59.0

66.0

64.5

in W.G. 4.21

3. 53

4. 26

4. 05

gpm

38. 5 38.0

37.5

40.0

in W.G.

4. 79 4.51

4. 29

4. 85

gpm

4.

0.

0.

0.

in W.G.

5. 05

5. 62

5. 06

5. 05

136 1.69 96 2.91 63 4.01 39 4.61 1 5. 20

Single-fixture flush (South)

Run No. dP Qa dP Qa dP Qa dP Qa dP

12

34

Average

gpm 121.0

125.5

128. 5 136.0

in W.G. 1.33 1.46

1. 52 1.80

gpm

89. 5 96.5

98.5

96. 0

in W.G. 2.52

2. 88 2.92 2.83

gpm 60.5

60.0 60.0

58.5

in W.G.

3. 87

3. 44

3. 62 3.46

gpm

35. 5 34.0

36.0

34.0

in W.G.

3. 63

3. 36 3.61

3. 36

gpm

3.0.0.

6.

in W.G.

4. 18 4.43

4. 49

4. 22

128 1.53 95 2. 79 60 3. 60 35 3. 49 2 4. 33

TABLE 8. Component stack, single-fixture flush tests: peak air demand, peak vent suction and cumulative trap-seal reduction of conditions of vent open and 2 degrees of vent restriction up to onset of aspiration of air through idle trap

Supply Pressure was 50 psi.

Single-fixture flush (North)

(Vent open)

Qa dP

gpm

129.5

140. 0

129. 0 139.5

143. 0 127.5

138. 0 128.5

W.G.

I.2.

1.1.2.

1.1.88

1. 60

,66

,04

72

.961463

dH

0. 38

.03

.01 .04

.02 .00 .00

.00

Cum.

dH

0. 38

.41

.42 .46

.48 .48

.48

.48

(Partial flow restriction, level one)

Qa

gpm

135. 0

131. 0

136. 0 134.5

dP

in W.G. 2.05

1.96

2. 16

2. 10

dH

0. 60 .00

. 00

.00

Cum. dH

0. 60 .60

.60

.60

(Partial flow restriction, level two)

Qa dP dH

Cum. dH

gpm in W.G. in in 128. 5 2.41 0. 69 0. 69 127.5 2.47 .00 .69

129. 5 2. 51 .00 .69

127. 0 2.34 .00 .69

130. 0 2. 52 .00 .69

129. 0 2. 34 .00 .69

125. 5 2.37 .00 .69

119. 0 2. 03 .00 .69

''127. 0 2. 45 .80 .80

^118. 5 2. 13 .01 .81

''121.5 2.21 .02 .83

''126. 5 2. 36 .76 . 76

''132. 5 2.56 . 76 .76

Both traps filled for first run to trap weir. '' Air was heard sucked through the idle trap in these runs.

13
3.3. Discussion

Although prevaihng code language limits the

pneumatic pressure excursion in the vent to ±l-in

W.G., data in tables 4, 5, and 6 indicate that trapseal reductions in the idle water closet trap did not

exceed the 1-in reduction permitted in present

practice until beyond a peak (0.2 s) suction in the

vent of 3 in W.G. For a dH of I in, peak (0.2 s) dP

was 3 in W.G. for 4-run cumulative dH (determined

by extrapolation) and 4 in W.G. for single run dH.

Although the greatest trap-seal reduction occurs in the first run of a four-run set, cumulative dH is also of interest as an example of the effect on an idle trap

(as in a multi-family living unit where occupants are away but next-door neighbors are not) when the

active trap is flushed again and again

Air demand rates measured, whether or not the

idle trap was plugged, were well below the theoretical

prediction of NBS Monograph 31 for a one-stack

system with all the air being pulled in from the top.

For example, equation (56) in NBS Monograph 31

[1] predicts air demand rates (at atmospheric pres- sure) of the order of 200 to 250 gpm for a 3-in plastic

drainage stack, depending on the magnitude of the

hydraulic load. In tests on the component stack

with the vent open (minimum diameter of 1.05 in at the smallest part of the passageway through the air flowmeter), air demand rate ranged from a low of

111 gpm (single-fixture flush) to a high of 167 gpm

(back-to-back flush). These lower values are partly

attributable to the occurrence of vent suction

greater than 1 in W.G., as measured in these tests. The data for the idle trap plugged given in table 7, are plotted in figure 7, along with comparable data

obtained from a similar RSV system, with one water

closet, studied earlier at NBS [6]. The present data

are in good agreement with the earlier work with the

exception of the point with the vent closed. The more

primitive instrumentation used in the earlier study

may have been a factor in the difference between the

two values. (Data reported herein do not contain

measurements in the low dP-high Qa range because

of the relatively high resistance to flow through the

small air flowmeter available when the measurements

were made.)

Direct correlation of peak pneumatic pressure in the vent and its associated trap -seal reduction, made

possible by the laboratory capability for dynamic

measurement, is shown in figure 8. The data, taken

from table 5, are for single-fixture flush tests of each

of two water closets at a static supply pressure of

260

240

220

200-

180

160 -

140

120

100

80

60

- o

40

20

2 I H I

1

-theoretical peak

Qa, plastic stack

(nbs mono 31) at dP=0

20 J

• PRESENT WORK O EARLIER WORK

(Multiple run values)

o

0 12 3 4 5 6 7

dP, PEAK PRESSURE DROP IN VENT, IN W.G.

uj m

IE CE

or 3i

• 2

r Q.

3 PVC 18i

9o'

-"9

Ob

dH

e ' g h

140 120 100 80 60 40 20

DESCENDING SCALE —

OA, PEAK AIR FLOW SUPPLY. GPM (FOUR-RUN AVERAGE)

VENT

CLOSED

Figure 7. Relationship betiveen vent pressure and air demand

rate, comparing results of two component stack

investigations with one WC discharges. {Data for

' present study is from single-fixture flush tests in

•- table 7.)

Figure 8. Relationship betiveen dP (peak 0.2 s suction), dH

(trap-seal reduction) in the idle water closet trap, and Qa (peak 0.2 s air demand) for single-fixture flush tests in the component stack investigation. (Data is from table 5 for single-fixture flush tests.)

14
50 psi. Each data point in the figure represents a 4-run average vahie plotted against the corresponding 4-run average peak air flow rate. More exactly,

each lettered pair is a 4-run average of dP and

(single run) dH, and the pair is plotted on the

intercept (x axis) of the Q,, (average) for the same

4 runs—to show a three-way correlation between

Qa, dP, and dH. The data show that the idle trapseal reductions did not exceed 1 in at a peak (0.2 s) vent suction close to 4 in W.G. (pairs e, /, g, and h).

Another important finding, illustrated in figure 8, is that the rate of increase in trap-seal reduction, as the

air flow was reduced by restricting the vent butterfly

valve, was much less than the accompanying rate of

increase in the vent suction. With an excessive peak

(0.2 s) vent suction of 6.3 in W.G., obtained with

the vent completely closed, the trap-seal reduction

in the idle trap was only 1.1 in (pairs i andj).

Tlius adequate trap-seal retention in the idle water

closet traps for peak (0.2 s) vent suction exceeding

3 in W.G. and the small air demand required relative to the traditional theoretical predictions clearly

indicate that vent piping in 1-2 story housing units can safely be smaller than presently allowed by

design without jeopardizing tlic integrity of the trap

seals in service performance. On the basis of these

findings, vents for water closets with full trap-seal

depths of not less than 3 in can be sized for 2.0 in W.G. vent suction rather than the 1.0 in W.G.

suction presently allowed in the plumbing codes.

Criteria for back-pressure (positive pressure in the vent) were not studied in the component stack tests.

4. Townhouse

4.1. Procedure

Two series of tests were run in the experimental

work on the townhouse. In the first, Series I, a total of seven fixture-discharge loads were tested and in the second. Series II, six additional fixture-discharge

loads were tested along with two repeated from

Series I. In the Series II tests, a few tests were made

with the building drain submerged.

As in the procedure for the experimental work on

the component stack, data in the townhouse work

were taken in 4-run sets. Some tests (sets) were

repeated to include additives on the 1st and 3rd runs

or to compare the results of idle traps being filled or not filled between runs. The additives used were

paper diapers, detergent, and bubble bath; operation

of the food-waste-disposal-unit was also considered an additive in the tabulation of the data. In Series I, each discharge combination was applied both with

the main vent terminal open and closed. In both

series, all fixtures were manually discharged simultaneously at the beginning of a run just as (after)

the computer recorded an initial value from all the

transducers. JNo time sequencing of loads was used4.2. Results

Results of all measurements taken in Series I are given in table 9. These results show corresponding

peak air demand rate ()„, peak vent suction ofP, and

trap-seal reduction dH for the first time in a full- scale system (see tests 17-22, 28-30, 33, 37-40 in table 9). Results of the trap-seal reduction measure- ments for Series II are given in table 10. The largest

idle trap-seal reduction with the vents open and the

drain not submerged was 0.4 in (for C4 in test 37

and L5 in tests 34 and 38 of table 9 for a discharge of

S3+W1+W2+W5, and S3 in test 16 of table 10 for a discharge of C4 +W1 +W2 +W5). Discharge of

C4 +W1 +W2 (test 18 of table 9) produced the

largest values of peak (0.2 s) suction in the (Stack 4) vent, 0.56 in W.G. (2-run average) and of peak air demand rate, 83 gpm (2-run average) that were measured with the vent terminals and the building

drain open. The largest idle trap-seal reduction with

the vent terminal open and the drain submerged was

0.4 in (for W5 in test 9 of table 10) which occurred

for a discharge of B1 +W1 +W2.

A short description of the loads, conditions of test, and number of trap-seal failures for both Series I and II is given in table 11. Data in this table show

that in all the tests run, trap failure (s) occurred

only when main or both vent terminals were closed

and at least three fixtures were discharged. In one

case, a discharge of three fixtures with the vent

terminals closed did not produce a trap failure (test

30 of table 9), but did produce trap-seal failures when

the drain was submerged in addition (test 15 of

table 10). There were no trap-seal failures with the

building drain submerged and the vent terminals open. For a discharge of B1+W1+W2 with the vents

closed, tests made without refilling the traps between

runs produced a 4-run cumulative dH about twice

the magnitude of the single run dH, where the traps were filled between runs, but still less than 1 in (see tests 30 and 33 in table 9 and also figure 9). Lack of

significant difference between single run dH and

cumulative dH for a discharge of Bl+Wl with the

vent terminals open (tests 8-11 in table 9) is attrib- uted to the inability to detect very small changes by means of manual measurement of trap-seal depth

with a ruler. Table 9 also gives water depth measurements in the building drain (peak 0.2-s value) for Series I tests of 3 or more fixtures discharged, indicating that

the depth did not exceed 2.4 in in the 4-in drain for any of the loads (see tests 37-39 in table 9).

15
Table 9. Tabulation of Series I tests showing airflow rates, trap seal reductions, vent pressures and water depths in building drain, for various test conditions applied to the townhouse DWV system

Test conditions

Fixture

discharge

loads "

dS3A

« W5

d W5

W5

d W2

W2

= Bl +Wl. .

Bl +Wl .

.

Bl + Wl. . .

Bl + Wl. . .

^ Bl +Wl. .

d Bl + Wl. .

Bl +Wl . . .

Additives Vent terminals "

Air flow,

(0.2-s)

Main

vent

Sink vent

Vent pressures, dP

(0.2.S)

Stack 1

DET/fwdu in S3A.

fwdu

fwdu.

none.

PD in W5

.

none

PD in W2

.

PD in Wl

.

none

BB in Bl. none

both closed

.

both closed

.

main closed.

both closed

.

2725X

44

44

40

45

4144

4229

26

27

X

in W.G.

none main closed

-0. 20

-0. 21

-0. 20

-0. 22

-0. 19 -0. 25

-0.21

-0. 12

-0. 39

16
Table 9. Tabulation of Series I tests showing air flow rates, trap seal reductions, vent pressures and water depths in building drain, for various test conditions applied to the townhouse DWV system—Continued

Vent pressures, dP

(0.2-s)

Stack 3

in W.G. -1.56

-1.45

-5. 95 -0. 14

Stack 4

W.G.

Stack 5

W.G.

-0. 05

-0. 04 -0. 03

-0. 02

Cumulative idle trap seal reductions, dH

Bl LI

=0.0

0. 1

0. 1

Wl

= 0.0

0.

1

0.0

0. 0

0.0

0.0

A 0. 1 A 0.

1

L2

= 0.0

0.0

0.0

0.

1

W2 S3

"A

C4 L5 W5

Water depth

in open bldg. drain (0.2-s)

= 0.0

0.0

0.0

0.0

0.

1

0.2

A

A

17
Table 9. Tabulation of Series I tests showing airfloiv rates, trap seal reductions, vent pressures and water depths in building drain, for various test conditions applied to the toivnhouse DWV system—Continued

Test No.

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

Test conditions

Fixture

discharge

loads "

dC4+Wl+W2

C4+W1 +W2

C4+W1 +W2

<iC4+Wl +W2

f C4+W1 +W2

C4 +W1+W2

' C4+W1 +W2

^C4+W1+W2

dBl +Wl+W2

<1B1+W1+W2

dBH-Wl+ W2

dBl+Wl+ W2

d B1 + W1 + W2

B1 + W1+ W2

d B1 + W1 + W2

B1 + W1+ W2

B1 +W1 +W2

B1 + W1 + W2

<=B1 + W1+ W2

Additives ^

DET in C4. none

DET in C4. none

PD in Wl

.

none PD in Wl

.

none

BB in Bl. none

BB in Bl. none

BB in Bl. none

BB in Bl. none

Vent terminals "

both closed

.

both closed

.

sink closed.

.

main closed.

both closed

.

both closed

.

both closed

.

both closed

.

both closed

18

Air flow, Qa

(0.2.S)

Main

vent

66

65X

79

76

83

79X

68

67

7269

64

51

70

70

64

57

72

65

61X

X

X

X

Sink vent

Vent pressures, dP

(0.2-s)

Stack 1

in W.G.

-0. 43

-0. 43

-0. 45

-2. 92

-0. 95

-0. 40

-2. 34

-1.62

-2. 10

-0. 54

-0. 33

-0.31

-0. 24

-0. 35

-0. 28

-0. 25

-1.41

0. 35

-1.32
Table 9. Tabulation of Series I tests showing air flow rates, trap seal reductions, vent pressures and water depths in building drain, for various test conditions applied to the townhouse DfVV system—Continued

Vent pressures, dP

(0.2-s)

Stack 3

-0. 15

tOSC

-0.31

-0. 25

"OSC

-0. 55 -0. 48

Stack 4

^ osc

t osc

-0. 85

-0. 87

in W.G.

-0. 48

-0. 49 -0. 56

-3. 01

-0. 96

-0. 47

-2.49

-1. 65

-2. 12

-0. 30

t osc

-0. 95

-0. 83

Stack 5

m W.G. -0. 36 -0. 44

-0.21

-0. 19

-0. 28

-0. 28

-0. 75

Bl

0.0

0.0

0.2

0.2

1.9 0.0

0.3

1.2

0.

1

= 0.9

Cumulative idle trap seal reductions, dH

LI

0.

1

1.

1

0.

0.

1.0 0.0

0.

1.0. 1

=0. 7

0.

1

0.

1

0. 1

0. 1

0. 1

0.0

0. 1

0.6

0. 6

0.4

«=0.3

Wl L2

0. 3

1.3

0.2

0.3

2.

1

0.4

0.3

1.3 1.0

a. 0

0.

1

0.2

0.3

0. 1

0.

1

0. 1

0.

0.8

0. 8

0.6

•'O. 5

W2 S3

0. 1

0. 1

0.

1

0.

0.0

0.

0.

0.0.2

^0.

0.

1

0.

0. 1

0. 1

0.0

0. 1

0.2

0.4

0.3

0.3

= 0.2

C4

0. 1

0. 2

0.6

0.3

0.0

=0.3

L5

0. 3

1.

1

0.2

0.2

0.9

0.0

0.2

0. 9

0. 1

= 0.8

0.3

0.3

0.6

0.4

0. 5

= 0. 3

W5

0. 1

0. 1

0.

1

0.6

0.3

= 0. 5

0.

1

0.

0.4

= 0. 2

Water depth

in open bidg. drain (0.2-s;

1.9

d2. 1 2.0

1.8

1.9

1. 7

1.7

1.7

1.6

1. 5

19
Table 9. Tabulation of Series I tests showing air flow rates, trap seal reductions, vent pressures and water depths in building drain, for various test conditions applied to the townhouse DWV system—Continued

Test conditions

Test No.

Fixture

discharge

loads " Additives ^ Vent terminals

Air flow, Qa

(0.2-s)

Main

vent Sink

vent

Vent ressures, dP

(0.2.S)

Stack 1 Stack 2

34

35

36

37

38

39

40

dS3A+Wl + W2+W5

'S3A + W1 + W2+ W5

dS3A+Wl + W2+W5

dS3A+Wl + W2+W5

dS3A+Wl

+ W2+W5

'S3A+W1 +W2+W5

= S3A+W1

+W2+W5

DET/fwdu in S3A.

fwdu

DET/fwdu in S3A. fwdu

fwdu in S3A

.

DET/fwdu in S3A

and PD in Wl . . . fwdu

both closed

.

both closed

.

both closed

.

74

76

77

X

2325

X

X

W.G.

-0. 47

-0. 41

-0. 50

-2.84

-1.02

-2. 69

* Fixtures are identified by a letter and a number: Bl =

bathtub on Stack 1, C4 is the clothes washer on Stack 4. Likewise, there are lavatories LI, L2, and L5; water closets Wl, W2, and W5; and a 2-Corapartment sink, S3, with S3A

the compartment having the food-waste-disposal-unit and

S3B the other compartment.

^ Additives are identified by:

fwdu = food-waste-disposal-unit operating, an early model

having a shut-off pressure of 20 psi. PD =paper diaper, a commercially available "paper"

diaper made of an absorbent pad adhering to a porous inner liner and covered on the outside with a waterproof plastic sheet. The absorbent pad was

sloshed in the water closet to free it from the inner

liner which was not flushed, in accordance with the manufacturer's recommendation. The size was

identified by the manufacturer as for overnight use by babies over 11 lb. DET = granulated detergent, a commercially available product containing 8.7 percent phosphorus in the form of phosphates. The surfactants in the products

are reported to be biodegradable. When used in the

sink, /4 c. was stirred into the water, and for the

clothes washer, 1 c. was stirred into the water.

BB = Bubble bath, a granulated bubble bath preparation

stated by the manufacturer to be biodegradable

and to contain no phosphates. In the bathtub, a sudsy condition was created by adding to warm

water Yi c. of the bubble bath.

' Open unless otherwise indicated.

<^ Additives, when used, were added on the first and third runs of a test. (In tests 1, 34, 36, 37, and 38 the fwdu was

utilized in all 4 runs.) Where additives were used, the average peak air flow rate and vent pressure (and building drain depth in test 18) are tabulated for the first and third runs

in the upper position and the second and fourth runs in the lower position.

^ Before each of four successive runs, the traps were filled to the weir level. These trap seal reductions are single run dH

4-run average values.

' For these tests, the peak air demand rate, peak vent suction, and trap-seal reduction for the FIRST run is tabulated

in the upper position. The peak air demand rate and vent

pressure suction is averaged for runs 2, 3, and 4 and tabulated

in the lower position. Cumulative additional dH lot runs 2, 3, and 4 is tabulated in the lower position.

K Active trap. A; vent terminal closed, X.

20
Table 9. Tabulation of Series I tests showing air flow rates, trap seal reductions, vent pressures and water depths in building draii for various test conditions applied to the townhouse DWV system—Continued

Test No.

34

35

36

37

38

39

40

Vent pressures, dP

(0.2-8)

Stack 3

W.G.

t OSC

OSC

OSC

OSC

Stack 4

W.G.

OSC

^ OSC

-2. 75

-0. 87

-0. 89

Stack 5

W.G.

" OSC

-2.48

-1. 17

Cumulative idle trap seal reductions, dH

Bl

0.0

0.0

0. 0

0. 1

0.3

0.3

1.9

0.

1

LI

0. 1

1.3 0.0

0. 1

0. 1

0. 1

1. 1 0.0

= 1. 1

Wl L2

0. 1

2.3

0. 1

0.3

0. 2

0.3

2. 1 0.2

'2.2

W2 S3 C4

0.3

1. 1

0. 1

0. 1

0. 4

0.3

1. 1 0.0

L5

0. 4

1. 3

0. 0

0. 1

0.3

0.4

2. 1

0. 1

= 1.4

W5

Water depth

in open Indg. drain (0.2-8)

2.4

2. 4

2.3

^ Vent pressure excursion oscillating such that both positive and negative values were determined significant. These values

are tabled below:

Test No.

18

20

28

29

29

34

Stack No. Runs of

test

1 and 3

.

2 and 4. 1-4 ... . 1-4

1 and 3

.

2 and 4.

1 and 3

.

2 and 4. 1 and 3

.

2 and 4.

Positive and

negative peaks

+0, + 0, +0, +0, +0, + 0, + 0, +0. +0. +0.

in W.

.37 to

,10 to

,11 to

,09 to

,14 to

,35 to

,04 to 22 to 17 to 25 to

G.-0.09. -0.21.

-0.10.

-0.12.

-0.14.

-0.12.

-0.30. -0.18.

-0.40.

-0.38.

Vent

terminals

Main Sink

X

Test No.

36

3737

38

38

39

Stack No. Runs of

test

1 and 3

2 and 4

1-4. .

.

1-4 ..

.

1 and 3

2 and 4

1 and 3

2 and 4

12,3, 4

Positive and

negative peaks

+0, + 0, +0, +0, +0, +0, +0, -fO,

-fo. +0.

in W.

,23 to

,23 to

,29 to

,22 to

,29 to 56 to 33 to

,26 to

,77 to 76 to

G. -0.46. -0.46.

-0.33.

-0.52.

-2.24.

-2.49.

-0.42.

-0.50. -0.48,

-0.55.

Vent

terminals

Main Sink

X

X

X

X

21
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22
Table 11. Summary table: {compiled from tables 9 and 10) Trap-seal performance as affected by various degrees of loading and

other test conditions in the Series I and II townhouse tests

Fixture

discharge load

d.eSSA

S3A

d S3B

S3B

W5

W5

W5

W2

W2

Ll +Wl

Ll + Wl

Bl + Ll

C4+W5

C4+W5

Bl + Wl

Bl +Wl

Bl +Wl

Bl +Wl

Bl + Wl

Bl + Wl

Bl + Wl

= S3A+W1 + W2

« S3A+W1 + W2

C4+W1 + W2

C4+W1 + W2

C4+W1+ W2

C4+W1+ W2

C4+W1 + W2

C4+W1+ W2

C4+W1 +W2

C4+W1 + W2

B1 +W1 +W2

B1 + W1 +W2

B1 + W1+W2

B1 +W1 + W2

B1 +W1 + W2

B1 +W1+W2

B1 +W1 +W2

B1 + W1+W2

B1 + W1+W2

B1 +W1+W2

B1 + W1 + W2

Bl + Wl-i W2

B1+W1+ W2

B1 + C4+W2

B1+C4 +W2

B1 + C4 + W2

B1 + C4+W2

= S3A+W1 + W2+ W5

S3A+W1 + W2+ W5.

.

" S3A+W1 + W2+ W5

» S3A+W1 + W2 + 5. . = S3A+W1 + W2 + W5

S3A+W1 + W2 + W5.

S3A+W1 + W2 + W5.

.

C4+W1 + W2+ W5...

No. of trap

seals failed "

0,

0,

0,

0.

0.

0.

0.

0.0.

0.

0.

0.0.

0.

0.0.

0.

0.

0.

0.

0.

0.

0.

0.

3.

0.

0.0.

0.2.

1.0.

0.0.

0.

0.0.

0.

0.

0.

0.

0.

2.

0.0.

0.0.

2.

0.4.

0.0.

0.

5.4.

0.

Severity

of loading

Normal

.

Unlikely.

Normal

.

Normal

.

Normal . . Normal

.

Unlikely.

Normal

.

Unlikely.

Normal

.

Unlikely.

Normal

.

Normal

.

Normal

.

Normal

,

Normal

.

Normal

Normal

Normal

.

Normal

.

Unlikely.

Unlikely. Unusual. Unusual.

Unlikely.

Unusual

.

Unusual

.

Unlikely.

Unlikely.

Unlikely.

Unlikely.

Unusual

.

Unusual.

Unusual.

Unusual.

Unusual.

Unusual.

Unusual.

Unlikely.

Unlikely.

Unlikely.

Unlikely.

Unlikely.

Unlikely

.

Unusual.

Unlikely

.

Unlikely.

Unlikely.

Unlikely

.

Unlikely.

Unlikely.

Unlikely.

Unlikely

.

Unlikely.

Unlikely.

Unlikely.

Test conditions

Vent terminals

Both closed.

Main closed

.

Both closed.

Main closed

.

Both closed.

Both closed. Sink closed. Main closed. Main closed.

Both closed. Both closed. Both closed. Both closed. Both closed.

Both closed.

Both closed.

Both closed. Both closed.

Building drain

Submerged 6 inches.

Submerged 2 inches

.

Submerged 2 inches. Submerged 2 inches.

Submerged 2 inches

.

Submerged 6 inches

.

Additives ' (first and third runs)

DET/fwdu in S3A. fwdu in S3A. DET in S3B. PD in W5.

PD in W2.

PD in Wl.

BB in Bl. PD in W5.

DET in C4.

PD in Wl.

BB in Bl.

DET/fwdu in S3A. DET/fwdu in S3A.

DET in C4.

PD in Wl.

PD in Wl.

BB in Bl. BB in Bl. BB in Bl. BB in Bl.

DET in C4. DET in C4. DET in C4. DET in C4. DET/fwdu in S3A. DET/fwdu in S3A. fwdu in S3A. DET/fwdu in S3A,

PD in Wl.

DET in C4, PD in Wl.

* Reduced by 1 in from full-seal depth.

Open unless otherwise noted,

fwdu = food-waste-disposal-unit.

DET= granulated detergent.

PD = paper diaper.

BB = bubble bath. S3A =fwdu compartment of double-bowl sink. S3B =non-fwdu compartment of double-bowl sink, fwdu utilized all four runs.

23
4.3. Discussion

Performance of the trap-seals with reduced-size vents and with both the main and sink vent ter- minals open was completely satisfactory. As mentioned in the last section and shown in tables 9 and

10, the trap-seal reduction did not exceed 1 in except

for loads of at least three fixtures with the vent ter- minals closed—a case of severe loading that would

be unlikely to occur under normal conditions. The

low air flow rates and associated mild suctions measured are further evidence that actual air demands in the various elements of the venting network were

less than commonly assumed, even for heavy loads. The highest (2 -run average) rate measured in the

main vent terminal in the present study was only 83

gpm (test 18 of table 9). Significant trap-seal reduction i.e., failures or near

failures, were observed only in the tests where both

vent terminals were closed. The data on failures,

when they occurred, show that the P-traps were more subject to failure than the water closet traps.

The direct correlation for peak (0.2 s) vent suction

and the trap-seal reduction dH is given in figure 9

for single-run and cumulative dH for P-traps. The

greater total effect for cumulative dH was expected.

The results show that peak (0.2 s) vent suction of about 1.8 in W.G. produced a cumulative dH of about 1 in. The data support the use of a design pres- sure drop in vents of 1.5 in W.G. for P-traps subject

to suction, rather than the 1.0 in W.G. suction specified in the current codes. The severity of the pneumatic effects in some

tests with the vent terminals closed was dependent

not only on the magnitude of the discharge rate of

water, but also on the number of potential air circulation paths (within the network comprised of

the various vents and the building drain) that were

restricted by the concurrent discharges of the

fixtures (see figure 9). For example, a discharge

of B1 +W1+W2 that had not produced a failure with the vent terminals closed or with the drain

submerged did produce a failure (see test 15 of table

10) when the drain was submerged and the vent

terminals were closed at the same time. This in- dicates that both the vents and the building drain of

this system were important elements of the air circulation network. Other tests indicated that

significant venting could have taken place through

the building drain. For a discharge of four fixtures,

the most fixtures used in a test, the measured water

depth in the building drain did not exceed 2.4 in

(see tests 37-39 in table 9). Most importantly, none

of the tests with the building drain submerged

produced a failure, showing that flooding the building drain in service to the level produced in these

tests, would not affect the satisfactory operation of

this particular system as long as the vent terminals were open. Height of water fall as a factor in air demand pro- duced by an operating fixture is shown by data (see tests 3, 4, 6 in table 9) where a second-story water

closet produced an air flow rate in the main vent

terminal of 26 gpm, but the first-story water closet

in a separate test produced only 8 gpm in the same

terminal. The effect of stack length (height of water

fall) on air demand has also been observed in other

studies [6, 12]. In the present investigation, air cir- culation within the vent-drain network, with the

main vent terminal closed, is thought to have fur- nished the air required by the operating fixture since

the suction in the vent was not significantly dif- ferent than that measured for the same fixture with

the vent terminal open (see tests 3-5, for a W5 first- story discharge, and 6 and 7 for a W2 second-story

discharge).

As expected, closing the individual vent terminal

serving the sink did not have an effect on the per- formance of the fixtures served by the main vent

network. This is shown by tests 18-21 in table 9

where closing only the main vent terminal produced

trap-seal failures whereas closing only the individual

vent terminal serving the sink did not. Although a high peak (0.2 s) value, 5.95 in W.G.

(2-run average) of vent suction was measured right

at the beginning of the run(s) in the individual sink

vent when the food-waste-disposal-unit was operated

with the terminal closed, trap-seal retention was

nevertheless adequate (see test 2 of table 9). This is attributable to the discharge from the relatively flat- bottomed sink which would have refilled the (active)

trap. Also, modern food-waste-disposal-units pro- duce lower discharge rates than the early-model one which was used, and hence the momentary peak

suction would be less. Thus, results on the two-story full-scale system

are a clear indication of the adequacy of trap

performance with reduced-size vents. The fact that

four of the discharge combinations of 1, 2, and in one case 3 fixtures, produced no excessive trap-seal

reduction even with the vent terminals closed

shows that there was sufficient air in the vent

network to satisfy operation of the fixtures as long as not more than two vents were blocked by

discharging fixtures. There were no failures among

the tests run with the building drain submerged

except for the case where both vent terminals were closed also. The results indicate that with

realistic loads, the system would have performed

adequately with even smaller vents except when

the vent terminals were closed.

24
2.5 -n

2.C

1.5 -

1.0

0.5 -

0

KEY IDLE P-TRAP

TYPE OF dH LI L2 L5 Bl SINGLE RUN,

4-RUN AVERAGE

4-RUN CUMULATIVE • 0 + [D

X

CLOSED

/50 PERCENT RETENTION / PERFORMANCE CRITERION

0

0.5 1.0 L5 2.0

—\—

2.5 3.0

dF^ PEAK SUCTION IN VENT, IN W.G.

Figure 9. Relationship between dP {peak 0.2 s suction) and AYl {trap-seal reduction) in idle P-traps in the townhouse DWV sys- tem, with closed vent terminals. {Data is taken from table 9: tests 22, 30, 33, and 40.) The six dtl data points below dP = 7.5 in W. G. are results from two tests of a hydraulic load of Bl-\- Wl + W2 {involves two stacks) ; the four d H data points betiveen dP = 2.0 and 2.5 in W. G. are results from a test of a hydraulic load of C4+ Wl-\- W2 {involves three stacks) ; the four dH

data points above dP = 2.5 in W.G. are results from a test of a hydraulic load of S3 + TFl + JV2 + W5 {involves four stacks)

.

5. Summary and Conclusions

In this study, the hydraulic and pneumatic

performance of a two-story full-scale DWV system

with RSV has been evaluated utilizing modern

measurement techniques in a wide variety of tests. On the basis of this investigation and the earlier NBS work (see [13] and Section 4 of [7]), criteria for

sizing dry vents for general application in 1-2 story

housing systems are given in table 12. In the utiliza- tion of the recommended criteria, engineering

judgment may be required in some special instances

to carry out the intent of the criteria. Appendix A

should be reviewed, also. It describes the procedure

for application of table 12, and shows the results of

its utilization with the system studied in this investigation. In addition, the sizing criteria in table 12 are recommended for RSV installation under competent engineering direction. For a detailed discussion involving climate and important

details of installation, see Appendix B.

25
Table 12. Recommended criteria for selecting dry-vent sizes for 1-2 story sanitary drainage system *

SIZING

SEQUENCE

First

.

Next.

Last.

SELECTION CRITERIA

Function of vent

d FIXTURE VENTS:

Individual

(serves single trap).

Common

(serves two traps).

Stack vent (Main vent at top of a

soil or waste stack).

« CONFLUENT VENTS:

For two fixture vents . .

For three fixture vents .

For four or more fixture vents.

^ARTERIAL VENT:

Vent stack, 1 or Stack vent serving as a relief vent J

Elevation of trap

(determines distance

of water fall)

ft Up to 8 . . .

8 to 16

Up to 8 . .

.

8 to 16. . .

.

Up to 8 . . .

8 to 16

Not applicable

Not applicable

Not applicable

Not applicable

.

Maximum load

(served by vent)

FU

1 to 3. 4 to 6.

1 to 3. 4 to 6.

1 to 3. 4 to 6.

1 to 6.

1 to 6. .

.

7 to 15.. 16 to 30.

1 to 6..

.

7 to 15.. 16 to 30.

Not applicable

Not applicable

Not applicable

10.

10. 30.

30.

MINIMUM VENT SIZE

(nominal pipe diameter)

.1.

.1.

.1/4. m

.1%.

.P/2.

.2.

One pipe size larger than the

largest fixture vent served.

' In most cases, increase one

pipe size over largest fixture vent served.

« Area of pipe selected must

equal or exceed the value computed from:

AcONFLVENT = '\/Alaroest- ^Aserved

.lYi (36 ft max). .IH (120 ft max).

.iVi (30 ft max).

.1/2 (100 ft max).

26
Table 12, Footnotes

^ This table may also be applied to 3-level split configurations in which the total height of water fall between the highest

fixture and the main building drain does not exceed 16 ft. Elevation of trap above first lower (vented) horizontal

fixture branch, (vented) soil or waste stack offset, or building

drain branch that serves the trap.

Figure A

' Exceptions requiring two pipe size increas.'!

TRAP

DISCHARGE ELEVATION

Fixture unit values for usual plumbing fixtures found in

residences [2]. For consistency, these values should be used

for sizing the dry vents. The applicable code values, even if different from those given below, may be used for sizing the wet piping.

Common

symbol

P-1

P-2

P-3

P-4

P-5

P-6

F.D

Fixture

Tank WC

Lavatory

Bathtub

Shower

Sink w/fwdu and DWM

Clothes washer

Floor drain

Load

FU

4

12

23

3

3

^ Fixture vent: Any single vent that provides the sole or primary ventilation for a trap or group of traps located

at the base of the vent. These sizes are valid for vent lengths up to 25 ft. For longer lengths, increase by one pipe size.

" Confluent vent: A vent pipe that serves two or more

fixture vents.

(Three) fixture vents served Confluent vent

in in in in

1 1 1 1/2 IH VA 1/4 oZ % 1 I

A

2 % 1/ VA 2

1 1 I

A

2

1 VA I

A

2 IH 1/2 I

A

3

1/2 1/2 3

« Cross-sectional areas by which to calculate confluent vent

size using the square-root formula are as follows:

Nominal

diameter

pipe

Internal cross-sectional areas

Schedule 40 Copper tube M DWV

in in 2 in 2 in A 0. 304 0. 254 % 0. 533 0. 517

1 0. 864 0. 874

1/4 1.495 1.317

1/2 2.036 L 865

2 3.355 3.272

3 7. 393 7.235

These sizes (a one-pipe-size reduction derived from table 14 of [1]) are on the basis that significant pressure relief occurs through the building-drain and building-sewer route,

significant circulation occurs in the branches of the vent network, and air demand is minimal in short stacks. If flooded sewer conditions are anticipated, the arterial vent

size, obtained as indicated, should be increased one pipe size.

Because the sizing and installation procedures for reduced-size venting are unlike those now used for the venting of traditional DWV systems, the

procedures (see table 12, its footnotes, Appendix A,

and Appendix B) should be thoroughly understood by designers and installers responsible for applying the recommendations to a set of conventional specifications and drawings. The sizes of the

"dry" fixture and confluent vents obtained from

the recommended procedures are intended to apply

to either a wet vented, individually vented, or stack vented system, upward from an elevation

at least 6 in above the flood rim of the highest

fixture served by the vent. If analysis of the system

indicates significant potential for the rise of waste

water to a higher level in the event of drain-pipe

stoppage, then the vent should be standard size to this elevation (e.g. possibly in the case of a singlebowl kitchen sink with a food-waste-disposal -unit).

In the (table 12) sizing sequence, the primary

elements, or fixture vents, are sized first. A fixture vent provides the primary or sole ventilation for a trap or group of traps located at the base of the

vent. Where two or more fixture vents are connected,

the joint pipe is sized in the next step as a confluent

vent by means of a square -root formula which

relates the sum of the areas of the fixture vents

served to that of the confluent vent. Last in the

sizing sequence is a consideration of the air circula- tion in the system as a WHOLE. The arterial vent sizing criteria apply to DWV systems more than

one story and are intended to provide circulation

and back-pressure relief in multi-story systems.

The arterial vent may be one of the stack vents of

a system comprising two or more drainage stacks,

that is chosen to serve as a (building drain backpressure) relief vent; or it may be a separate vent

stack, depending on the particular overall configuration of the DWV piping.

27
It is recognized that further laboratory work on

air circulation patterns along with a better correla- tion of design air flow rates and pressure limits with system performance in terms of trap-seal

stability and system geometric variations (e.g. horizontal offsets in drainage stacks, fitting shapes,

and vent stack design) would result in further size definition of the various vent types addressed by

the table 12 criteria. This would broaden the criteria and contribute to the development of a rigorous,

generalized, mathematical model for reduced venting.

The current study has provided not only practical

evidoiice in terms of acceptable trap-seal performance

imder tests simulating adverse service conditions,

but also fundamental evidence of the excessive

present design criteria as the reason for the good

performance of the system under operating conditions. Present design criteria have been developed

principally from continuous flow experimentation

and the assumption of static relationships. It has

been shown experimentally in this study that, based on 0.2 s peak values, the widely held assumption

that a fluctuating suction of 1 in W.G. is roughly

equivalent to 1 in trap-seal reduction is erroneous. Data obtained using the new capability for dynamic measurement showed that trap seals were

safe under dynamic peak (0.2 s) suctions of 1.5 in W.G. Tolerance to high momentary suction values

is greater when the pressure is rapidly fluctuating. In addition, the high momentary (shorter than 1 s) suction values such as those reported here are believed representative of normally operating resi- dential plumbing fixtures. Different criteria may

prevail, however, for a load that produces "sus- tained" (over 1 s or longer) peak pressure levels. These criteria are under development as part of the

general computational method, referred to in section

1.2.In the current investigation, data have confirmed

and expanded the earlier findings with regard to the

reduced air demand in short stacks (versus air demand in tall stacks on which the estimates are

traditionally based). It is believed, furthermore,

that the additional benefits of reduced air demand

at slight suctions e.g. 1.0 or 1.5 in W.G. (versus air demand at atmospheric pressure) and of reduced

air demand in some elements of vent networks

attributable to circulation (versus air demand as- suming that the demands by multiple operating

fixtures are uni-directional and additive) which

contributed to the favorable performance of RSV in systems with short stacks, would contribute importantly to favorable performance of RSV in tall-stack (high-rise) systems. Delineation of these

criteria under dynamic conditions is an essential part of the development of the general computational method.

Although eliminating the air circulation path

through the building drain by submergence of the

drain in the system tested did not compromise

the performance of this system with the vent

terminals open, it is recommended that in the

utilization of RSV, the building drain (and building

sewer) should be large enough that it would not

completely fill with water under normal service

conditions. It is believed that building drains and

building sewers sized according to the codes would

provide this capacity. Because of limited knowledge

of the possible effects of submerged sewers on

various designs of RSV systems, RSV is not recom- mended where frequent occurrence of sewer backwater is anticipated. The present investigation has

indicated that the building drain is an important

element of the air circulation path within a vent

network system.

Field studies provide the opportunity, greatly

needed, to document plumbing loads and performance in real systems. It is anticipated that, in the

long-range program, field trials will be utilized. This could furnish a realistic basis for improved

selection of test loads in the laboratory and of

performance limits in design computations. For

RSV field trails, these should incorporate measure- ments of street sewer pressure to determine if any

criteria for this parameter will be needed should

RSV become extensively utilized in one community.

It has been assumed in this study that street sewer (pneumatic) pressures in residential communities

are usually sufficiently close to atmospheric so as to preclude adverse effects on fixture traps in RSV

systems.

The authors wish to acknowledge important

contributions made by the following persons:

John R. Schaefgen who helped with the instru- mentation and laboratory work on the component

stack and the programming needs of the tests; Daniel E. Rorrer who assisted in mapping out the

utilization of the data acquisition system; DeForest

Z. Rathbone for coordinating some of the test procedures in the townhouse tests to account for precision in terms of service conditions and construction parameters; Grover C. Sherlin who

helped with the organization and mode of presentation of the data; and Jack E. Snell for his many

helpful suggestions for clarity in the presentation

and interpretation of complex technical ideas in the context of the performance approach. In addition, we wish to thank Donald F. Dickerson, a professional plumbing engineer, Dickerson/Gladstone/Associates, Van Nuys, California, for consultation contributing to the clarity of the presentation

of the table 12 sizing criteria.

28
The present support, by the Directorate of Civil Engineering, Headquarters

U.S. Air Force, of a field application of the laboratory findings to design has re- sulted in improved usefulness of the criteria reported. The performance data to be

measured in this field study at Andrews Air Force Base, Maryland are to be the

subject of a later report.

6. References

[1] Wyly, R. S., and Eaton, H. N., Capacities of stacks in sanitary drainage systems in buildings, Nat. Bur. Stand. (U.S.) Monogr. 31. 52 pages (July 1961).

[2] National Standard Plunibin«; Code, National Association

of Plumbing-Heating-Cooling Contractors, and American Society of Plumbing Engineers (1973).

[3] Recommended Minimum Requirements for Plumbing

in Dwellings and Similar Buildings. Final Report

of Subcommittee on Plumbing of the Building Code

Committee, Nat. Bur. Stand. (U.S.), Elimination of Waste Series (July 3, 1923).

[4] French, J. L., Eaton, II. N., and Wyly, R. S., Wet

venting of plumbing fixtures, Nat. Bur. Stand. (U.S.), BMS 119 (December 1950).

[5] Performance of Reduced-Size Venting in Residential DWV Systems, a joint report by the National Bureau

of Standards and the NAHB Research Foundation,

Inc., 627 Southlawn Lane, RockviUe, Md. 20853 LR 210-17, (September 1971).

[6] Laboratory study (of) minimum venting for plumbing

systems, Nat. Bur. Stand. (U.S.) Tech. News Bull. 50, No. 5, p. 77 (May 1966).

[7] Wyly, Robert S., Sherlin, Grover C, and Beausoliel, Robert W., Laboratory studies of the hydraulic

performance of one-story and split-level residential plumbing systems with reduced-size vents, Nat. Bur.

Stand. (U.S.) BSS 49, 53 pages (March 1974).

[8] Jackson, T., and Konen, T. K., An Investigation of the Adequacy of Performance of Reduced-Size Vents

Installed on a Ten Story Drain, Waste and Vent

System, Stevens Institute of Technology (U.S.), Report SIT-DL-73-1708 (July 1973).

[9] Rosrud, Tore, Performance requircmcnls for plumliing

systems, Nat. Bur. Stand. -Spec. Publ. 361 Vol. 1: Performance concept in buildings. Proceedings of the Joint RILEM-ASTM-CIB Symposium held .\lay2-5,

1972, Phila. Pa., 819 pp. (March 1972).

[10] Federal Specification WW-P-541b, Plumbing Fixtures,

Land Use, Section 18.2.3.2, General Services Administration, (Sept. 20, 1954).

[11] Wyly, R. S. and Sherlin, G. C, Performance of a Single- Stack DWV System Utilizing Low-Angle Stack- Branch Confluence and Bottom-Shunt Venting, Nat.

Bur. Stand. (U.S.) BSS41, 24 pages (April 1972).

[12] Pink, B. J., The effect of stack length on the air flow in drainage stacks, from Drainage services in buildings.

Proceedings of the CIB Commission W62 Symposium

held at the National Swedish Institute for Building

Research, Stockholm, September 24 and 25, 1973, Document D14:1973, published by the National Swedish Institute for Building Research, Stockholm

(1974).

[13] Plumbing Manual, Report of Subcommittee on Plumbing—Central Housing Committee on Research, Design,

and Construction, Nat. Bur. Stand. (U.S.) BMS 66, Section 1014, (1940).

[14] Manas, V. T., and Eaton, H. N.. National Plumbing

Code Handbook, (McGraw-Hill Book Co., New York

1957).

[15] Eaton, H. N., and Wyly, R. S., Frost Closure of Roof

Vents in Plumbing Svstems. Nat. Bur. Stand. (U.S.), BMS 142 (1954).

[16] Freberg, C. R., and Kemler, E. N., Elements of Mechanical Vibration, (J. Wiley, 2nd edition, pp. 19-

20, 1949).

29
Appendix A. Sizing Reduced- Size Vents, Procedure and Examples

A. 1 . General Approach

It is recommended that the piping schematic first be marked with appUcable fixture unit ratings by

fixture. The sizing sequence, using table 12, is: STEP i—Fixture vents STEP 2—Confluent vents STEP 3—Arterial vent

It is important to identify on the DWV piping

schematic the various vent types given in table 12. A fixture vent is a vent pipe that provides the sole or primary ventilation for a trap or group of traps

located at the base of the vent. A confluent vent is a vent pipe that serves two or more fixture vents. The

fixture vents need not all join the confluent vent at a

single point. That is, confluent vents should be sized on the basis of the fixture vents served, not on the

basis of the branch vents that may connect directly to the confluent vent. For example, figure A.l

shows that Confluent Vent 2 serves Fixture Vents

1, 2, and 3 which do not all connect at the same point.

FIXTURE VENT I

_£qNFLUE_NT^ VENT I

IFIXTURE

I VENT 2

I

I

_CqNFLUENT VENT 2

FIXTURE VENT 3

Figure A.l Schematic showing fixture and confluent vents.

The arterial vent (applicable only to systems greater

than one story) may be recognized as the main artery

of the vent system serving other vents and as the

most direct route for the relief of potential back

pressure in the building drain.

A.2. Example of Use of Table 12 to Size RSV

Sample calculations of how the vents in the

townhouse system were sized, step-by -step, are as

follows: STEP 1 —Fixture vents. The appropriate fixture- unit loads for single fixtures were obtained from the

National Standard Plumbing Code [2], for the

fixtures in the townhouse system, as listed in foot- note c of table 12. From this, the connected fixture- unit load by stack was determined as listed in table A.l for the five stacks. From the geometry

of the system however, W5 was considered to be

vented equally through stacks 4 and 5. On this

basis, the FU loads vented by these two stacks were

recalculated as listed in table A.2. Table A.l. Connected fixture-unit load by stack

Stack

desig- nation

Fixtures Load

FU

1234

5

Ll +Wl+ Bl

L2 + W2

S3C4

L5+W5

7

5

3

3

5

Table A. 2. Estimated fixture-unit loads vented through stacks 4 and 5

Stack

desig- nationFixtures Load

FU

4

5 C4+KW5

>iW5+L5

53

The results of the determination of the FU loads

for the five stacks are shown in figure A.2. Fixture

-

unit loads considered to be vented through each stack

are shown, rather than the loads connected. The

DWV vent piping is standard size to 6 in above the

fixture flood-rim level. To complete STEP I, the early tentative criteria

[5,7] (now incorporated in table 12) were utilized to

size the fixture dry vents for stacks 1-5. This

produced the sizes shown in table A.3.

stack 2

Figure A.2 Schematic showing Fixture Unit loads vented through each stack.

30
'r.XBi.K A.3 Fixture diy vciit sizes for townhouse system

(Icsip- iiation

Selection Criteria Normal

pipe Fixture size vent type Elevation

of Irap(s) Load

f' FU in

1 Stack vent ... 8 to 16 7

Stack vent .... o to 10 r5 1/4

3 Individual .... Up to 8 3

4 Common Up to 8 5 1

5 Common ... . Up to 8 3

STEP 2—Confluent vents. As an aid to the

computation of sizes for confluent vents, figure A.

3

was prepared showing, not only the sizes for the

fixture dry vents, but also the unsized elements

X, Y, and Z, (the vent header). The sizes for these

elements were determined by computation using

the square-root relationsliip given in table 12, and

selecting the next larger pipe size from footnote g

of table 12. The relationship is:

^CONFLUENT — LARGEST -^SERVED (A.l)

where

^coA-FLc/^Arr =theoretical internal cross-sectional area required in the confluent vent

ALARGEST

SERVED

= actual internal cross-sectional area

for the largest fixture vent served

by the confluent vent

=sum of actual internal cross-sectional areas of all the fixture vents served

by the confluent vent

To C4

(5FU)

.•v 3/4-^

I<

To L5 a W5

(3 FU)

i/4'^-<b

I

I

J.

To L2 a W2

(5FU)

• V *

I 1/2'

To LI, Bl £

(7 FU)

Figure A.3 Schematic showing four fixture vents and three confluent vents (X, Y, and Z) for the townhouse system.

Sizing confluent vents by eq (A.l) results in a one-pipe-size increase for all cases where two fixture yenls (from to 2 in) are served. Wliere three

fixture vents (any combination of three of )^ to

2 in) are served, eq (A.l) produces eight exceptions

to a one -pipe-size increase. These require a twopipe-sizc increase over the largest fixture vent

served and are listed as footnote f of table 12.

I'or confluent vents serving four or more fixture vents, the confluent vent size should always be

calculated by use of eq (A.l).

Confluent vent sizing of X, Y, and Z, the elements

of the vent header of the townhouse system, is tabulated in table A.4. This completes STEP 2. Table A.4 Confluent vent sizes for townhouse system

Confluent vent

Nominal sizes of fixture vents served

X

Y

1, V4...

1,

1,1^4, %, \Vl.

Nominal size confluent vent

m

Increase one size V/'i

Increase two sizes 2

(see table 12, f) Use eq (A.l) area and

select nearest larger

commercial size 2

(See table 12, g)

STEP 3—Arterial vent. Utilization of these sizing

criteria to provide a pressure relief route for the

building drain may take precedence over the sizes calculated for this route in STEP 1 or STEP 2. For the NBS experimental townhouse system, the

arterial vent was chosen as Stack 1. The FU load on the system was 23 FU, and a flooded sewer was

not made a condition, thereby making the arterial vent size, V/i in. This size was already the size of Stack 1 by STEP 1; the vent terminal size was

2 in by STEP 2. Thus no size change was called

for to meet the IK size determined in STEP 3. When the final vent sizes are determined as just

described, a DWV piping schematic should be marked

to complete the procedure.

A. 3 Construction Note

Familiarity with the RSV sizing procedures and

the rationale behind them is needed when they are applied to the on-site as-built wet piping configuration. This can be particularly important because

construction constraints and other field conditions

may result in on-site changes in the planned wet

system that would require significant modifications

in the planned sizing of the reduced-size dry vents. Beyond the systematic sizing of RSV, special

details of their installation are covered in Appendix

B which follows at the top of the next page.

31
Appendix B. Installation Recommendations for Reduced- Size Venting in 1-2

Story Drain-Waste-Vent Systems

In the utilization of reduced-size venting for split level and one- and two-branch interval slab-on-grade

or basement 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 foodwaste-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

submerged or subjected to wetting by aerosols or

suds, should be designed to conventional sizes.

3. In areas where frost closure may occur, vent

terminals should be sized to account for the effects of

local weather as explained by Manas and Eaton [14] and Eaton and Wyly [15]. 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.

4. 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.

5. 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.

6. 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.

7. Use manufacturer's recommendations on fit- tings for making size changes, for the materials

selected for the pipes, fittings and joint systems, and

for installation procedures.

Appendix C. Units of IMeasure and SI Conversion Factors

The results of the investigation described herein

are reported primarily in U.S. customary units,

for two reasons: first, most of the instrumentation

used was calibrated and graduated in U.S. customary

units and, second, the results of this research are directed to those groups who ordinarily use these

units. However, in recognition of the increasing importance of international standards in foreign corrunerce 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 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 U.S. customary units

used in this paper:

Force

1 pound-force (lbf) =4.48 newtons (N)

Length

1 inch (in) =0.0254* meter (m), or 25.4*

millimeters (mm)

1 foot (ft) =0.3048* meter (m), or 30.48*

centimeters (cm)

Volume

1 gallon [U.S. liquid] (gal) =3.785 liters =

3.785X10-3 meters^ (m^)

1 cup [U.S. dry] (c.) =0.2753 liters

VolumeITime

1 gallon [U.S. liquid] per minute (gpm) =

6.309X10"^ liters per second

Pressure

1 newton per meter^ (N/m^) =l* pascal (Pa)

1 psi =l* (lbf/in2)=6895 pascal (Pa) =6.895k Pa

1 inch water gage (in W.G.) [at 60 ° F] =248.8

pascal (Pa)

Area

1 in2=6.4516*XlO-* meter^ (m^), or 6.5416*

centimeter^ (cm^).

Prefix

k =times 1000

*By definition. Conversion charts for units of air flow, and for pneumatic and hydraulic pressure used in this paper

are given in figure C.l, opposite, as a convenience to readers who may wish to convert between units

systems.

32
AIR FLOW

(US)gpm liters/s

200 —

180-

160-

140-

120-

100-

80-

60

40-

20-

0-

10

l(US)gpm= 6.309x10"^ liters/8

15.85 (US)gpm = I liter/8

PNEUMATIC PRESSURE

in. W.6. Pa

1000

900

800

700

600

500

400

300

200

100

lin.W.6.= 248.8 Pa

4.02 xlO"^in.W.G.= IPG

Figure C.l Conversion charts for air flow, pneumatic pi-essure and hydraulic pressure.

HYDRAULIC PRESSURE

psi kPa

700

100-

90

80-

70-

60'

50"

40-

30-

20-

Ip8i = 6.895 kPa

O.I45p8i =1 kPa

33
Appendix D. Determination of Time Increment for Data Averaging

To take advantage of the capability of the DAS

for averaging rapidly changing phenomena, some

rationale was needed to select an appropriate

increment. As an aid to the selection of an appropriate value, it was decided to utilize the formula

for computing the undamped natural frequency of

oscillation of a liquid in a U-tube [16]. The phe- nomenon is similar to that in a plumbing fixture trap partially filled with water. An averaging period of }i the natural frequency was then chosen, arbitrarily, on the basis that the

trap seals could not readily respond to very short

transients because of inertia. Selection of too large an averaging period, on the other hand, would

result in misleadingly low values, much less than

those of the shortest transients to which the trap

seals could respond.

The same increment, 0.2 s, was used for all the

experimental v.ork. Considering the arbitrary choice

of a cycle, it was convenient to keep the increment

fixed to reduce variability in the data due to different

averaging periods.

Calculations of % the natural frequency for three

sizes of trao follow:

CALCULATIONS

For (i= IK in

S (assumed) =2 in

R (assumed) = (C—r) =2}^-%=!% in

Zi=(2+lK)-(l3^+^)=33^-2K =l in

2TrR

-2Zi =5.498+2=7.498 in

(C.l)

(C.2)

^=-.=^4^=0.620 s / 1.613

(C.3)

(C.4) =0.155 s

For d=2 in

S (assumed) =2 in

R (assumed) = (C—r) =3- 1=2 in

Zi = (2+2)-(2+l)=4-3 =l in

-r 2tR

(C.l)

2Li =6.283+2=8.283 in (C.2)

j 1.535

=0.651 s

(C.3)

(C.4)

=0.163 s

ASSUMED TRAP GEOMETRY

Figure D.l Assumed trap geometry.

FORMULAE

Lr={S+d)-(R +r) L^^-^+2U

(C.l)

(C.2)

For d=^ in

S (assumed) =3 in

R (assumed) = (C-r)=4K-lK =3 in

i, =(3+3)-(3 +lM)=6-4K=l3^in (C.l

^ 2TrR

-2Zi=9.425+3 =12.425 (C.2)

J-2^^ L

(C.3)

where (/=386 in/s^; Z=length of trap seal, in

t = l/f (C.4)

where /=natural "slosh" frequency, Hz; and

i=time for one cycle, s.

159^/?^^--= 1.253 (C.3)

12.425

7=0.199 s 4

(C.4)

34
Appendix E. Definitions, Acronyms, and Symbols

10.

11. 12.

13.

14.

15.

16.

17.

18.

19.

. Active trap—Trap of a fixture discharged at the

beginning of a run.

. Additives—Materials added in some of the townhouse tests including paper diapers, bubble bath,

and detergents; operation of the food-wastedisposal-unit in the sink.

. Averaging period—Time period selected for measurement for which the computer data

acquisition system will retain a single value

representing an average value of the many

values scanned for that period. The value

selected, 0.2 s in this work, was input to the

computer for each channel (for each transducer)

before taking data. (In this case the averaging

period used was the same for all the channels

but this is not required by the data acquisition

system.)

Bl— Bathtub on stack 1. Blowback—The ejection of suds, air, or other

gases through the trap-seal to the room side of

a trap as a result of excessive positive pressure on the drain side of the trap.

Branch—Any part of the piping system other

than a main, riser, or stack. (Usually branches

are horizontal.)

Branch interval—Distance between two branches,

usually about 10 feet, corresponding to the dis- tance between stories in a building.

Building (verb)— In the context of this report,

the word "building" refers to the process of

design and installation. Building drain—That part of the lowest piping

of a drainage system which receives the dis- charge from soil, waste, and other drainage

pipes inside the walls of the building and conveys

it to the building sewer beginning 3 ft outside

the building wall. Building sewer—That part of the drainage system

which extends from the end of the building drain

and conveys its discharge to a public sewer, private sewer, individual sewage disposal system,

or other point of disposal.

C4—Clothes washing machine on stack 4. CI—Cast iron. Cleanout plug—Screw plug in a fitting to facili- tate entry of mechanical cleaning tools. Common vent—A vent serving two fixtures. Component stack—Simple one-stack system of

this study (a partial DWV system).

Confluent vent—A vent pipe that serves two or more fixture vents.

Crossfloiv—The movement of waste water from

the trap of an active fixture to the trap of an idle

fixture. Cumulative dH—Trap-seal reduction after four runs under identical conditions without refilling

traps of fixtures between runs.

acquisition system.

28.

29.

20. dH—^The amount of decrease in trap-seal depth

from full-seal depth.

21. dP—^Maximum value of vent pressure suction

obtained during a run for a selected averaging

period (0.2 s in this study).

22. Drainage stack—A soil or waste stack.

23. Dry venting—The arrangement of drainage piping such that only air passes through the vents.

24. DWV—Drain-waste-vent.

25. Failure—Trap-seal reduction of at least 1 in. 26. Fixture-discharge load—The hydraulic load of (from one to four) active fixtures discharged at the beginning of a run.

27. Fixture vent—^Any single vent pipe that provides

the sole or primary ventilation for a trap or a group of traps located in the proximity of the

base of the vent. Flushometer valve—A device which by external

actuation discharges a predetermined quantity

of water to a fixture for flushing purposes and

which involves an internal automatic operating

cycle energized by direct water pressure. FU—Fixture unit. A number assigned to plumbing fixtures that is used as a measure of the probable peak demand on the water supply system or peak discharge into the drainage system.

30. fwdu—Food-waste-disposal-unit in one compartment of the double -compartment kitchen sink on stack 3. 31. Idle trap—Trap of a fixture not discharged

during a run. Individual vent—^A pipe installed to vent a

single fixture and so connected with the vent system or with the open air that free movement

of air is possible at all times (not part of a vent

header).

Induced siphonage—Phenomenon of the reduction in trap-seals of idle fixtures caused by the

discharge of active fixtures. 34. Ll—Lavatory on stack 1. 35. L2—Lavatory on stack 2. 36. L5—Lavatory on stack 5. 37. P trap—Descriptive term for type of trap which

resembles the letter P on its side and is found on

waste fixtures such as lavatories and sinks

(distinct from water closets which have integral

traps).

38. pascal—SI unit of pressure measurement that

equals 1 N/m^ by definition, equals also 4.02X10-2 in W.G. (see Appendix C).

39. Piezometei—A device for the measurement of pressure in pipes consisting of a vertical trans- parent tube which is connected at its lower end

to an orifice in the wall of the pipe (at 90 degrees

and carefully finished at the inner edge of the

hole) and is open to the atmosphere at its upper

end. The height to which the fluid rises in the

transparent tube is a measure of the head or pressure in the pipe.

32

33

35
40. PRL—^Plumbing Research Laboratory.

41. PVC—Polyvinyl chloride.

42. Qa—Maximum value of the air demand flow

rate obtained during a run for a selected averaging period (0.2 s in this study).

43. RSP— Reduced-size vents.

44. Run—A complete hydraulic event, e.g., a water

closet flush. 45. S3—Kitchen double-compartment sink on stack

3. 46. Self-siphonage—Phenomenon of reduction in trap seal in a fixture after discharge, caused

solely by operation of that fixture. 47. Service parameters—Factors intended to simulate

normal and severe in-service conditions: additives, closed vent terminals, flooded building

drain.

48. Short stack—A drainage stack in which the

maximum height of (water) fall does not exceed

20 ft measured with reference to the building

drain or a vented horizontal offset at the base

of the stack.

49. Single-fixture flush test—Flush of one water

closet four times (4 runs) in the work on the

component stack as distinct from a back-toback flush test in which both water closets were

flushed four times (4 runs).

50. Single run dH—Trap-seal reduction produced by

a single run (in a series of four) under identical

conditions, by filling the idle trap between runs.

51. Soil stack—A stack intended to convey sewage

containing fecal matter to the building drain.

52. Stack—General term for any vertical line of

soil, waste, vent, or inside conductor piping.

53. Stack 1 —Soil stack serving a second-floor water

closet, a bath, and a lavatory.

54. Stack 2—Soil stack serving second-floor water

closet and a lavatory.

55. Stack 3—Waste stack serving first-floor 2- compartment sink with a food-waste -disposalunit in one compartment.

56. Stack 4—Waste stack serving first-floor clothes washing machine.

57. Stack 5—Soil stack serving first-floor water

closet and a lavatory.

58. Stack vent—The extension of a soil or waste

stack above the highest horizontal drain con- nected to the stack.

59. Submerged building drain—A building drain in which a positive hydraulic head exists at the crown of the drain without the discharge of

plumbing fixtures or appliances.

60. Tall stack—A drainage stack in which the maximum height of (water) fall is greater than 20 ft measured with reference to the building drain

or a vented horizontal offset at the base of the

stack.

61. Test—^Four runs under identical conditions.

Additives when used are used on the first and

third runs of a test.

62. Trap-seal reduction—^Same as dH.

63. Trap-seal retention—The amount of a trap-seal

retained in relation to full-seal depth (commonly expressed as a percent).

64. Trap weir—^The lowest point in the vertical cross -section of the horizontal waterway at the exit of the trap.

65. Trapivay—Water passage way through a trap.

66. Vent header—A vent that joins together or

serves two or more vents with the principal

pipe being horizontal, see confluent vent.

67. Vent stack—^A vertical vent pipe installed to provide circulation of air to and from the

drainage system (usually the vertical main

of a vent system in a multi-story design).

68. Wl—Tank-type water closet on stack 1. 69. JV2—Tank-type water closet on stack 2. 70. W5—Tank-type water closet on stack 5. 71. W.G.—water gage. A measure of pressure, with

reference to atmospheric pressure, expressed

in terms of equivalent height of water column

(see Appendix C).

72. Waste—Liquid waste not including fecal matter.

73. Waste stack—A stack that conveys only waste.

74. Wet venting—The arrangement of the drainage

piping such that the venting of some fixtures

is provided by pipes that also serve inter- mittently as drains for other fixtures.

76.

77.

78.

79.

80.

81

©

©

©

©

®

©

-ixlAir flow demand sensing point.

Depth measurement sensing point.

Load cell.

Pressure measurement sensing point.

Water flow rate.

Trap ruler or piezometer location.

Butterfly valve.

Gate valve.

86

U.S. GOVERNMENT PRINTING OFFICE :1975 O—563-497
ANNOUNCEMENT OF NEW PUBLICATIONS IN

BUILDING SCIENCE SERIES

Superintendent of Documents,

Government Printing Office, Washington, D.C., 20402

Dear Sir:

Please add my name to ttie announcement list of new publications to be

issued in the series: National Bureau of Standards Building Science Series.

Name

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Address. _

City State Zip Code

(Notification key N-339)
NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS BSS-60

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Hydraulic Performance of a Full -Scale Townhouse

Drain-Waste-Vent System with Reduced-Size Vents

5. Publication Date August 1975

6. Performing Organization Code

7. AUTHOR(S)

M.J. Orloski and R.S, Wyly

8, Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proiect/Task/Work Unit No. 4624471

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Tri-Services Investigational

Committee on Building Materials

Department of Defense

13. Type of Report & Period Covered

Final Rppnrt 77-7

A

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74-28135

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.) This report describes the experimental findings of tests on a full-scale two-story

plumbing system with reduced-size vents under a range of operating conditions including tests with the vent terminals closed and the building drain submerged.

Results indicate that dry vent piping in 1-2 story housing units can safely be

smaller than presently allowed by design without jeopardizing the trap seals. On

the basis of the current investigation and from earlier work on full-scale systems

of substantially different geometry, criteria for sizing reduced-size vents are given for general application to conventional 1-2 story housing units. In addition

to the practical evidence in terms of acceptable trap performance, the current

study provided fundamental evidence of the excessive present design criteria. For

the first time measurements were obtained which relate traditional design criteria

(air flow and vent pressure) to presently recommended performance criteria (trapseal retention) under dynamic conditions. These findings indicate that the vents

can be sized on the basis of 1.5 in water gage (equals 372 pascals) suction in

the vent rather than the 1.0 in W.G. fequals 248.8 Pa) presently specified in the

plumbing codes. Also air demands measured were significantly less than assumed in

current practice for short stacks and for systems with vent networks.

17. KEY WORDS fsix to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

DWV; performance testing; reduced-size vents; trap-seal retention; venting criteria;

venting; vents, reduced-size

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