An Engineer's Guide to Plumbing Cross- Connections · 2012. 5. 29. · PDHonline Course M108 (3 PDH) An Engineer's Guide to Plumbing Cross-Connections 2012 Instructor: Randall W

PDHonline Course M108 (3 PDH)

An Engineer's Guide to Plumbing Cross-Connections

2012

Instructor: Randall W. Whitesides, P.E.

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Cross-ConnectionControl Manual

Printed on Recycled Paper

Office of Water (4606M)EPA 816-R-03-002www.epa.gov/safewaterFebruary 2003

Cross-ConnectionControl Manual

United StatesEnvironmental Protection AgencyOffice of WaterOffice of Ground Water and Drinking Water

First Printing 1973Reprinted 1974, 1975Revised 1989Reprinted 1995Technical Corrections 2003

Preface

ii • CROSS-CONNECTION CONTROL MANUAL

Plumbing cross-connections,which are defined as actualor potential connectionsbetween a potable and non-potable water supply, constitutea serious public health hazard.There are numerous, well-documented cases where cross-connections have been respon-sible for contamination ofdrinking water, and haveresulted in the spread of disease.The problem is a dynamic one,because piping systems arecontinually being installed,altered, or extended.

Control of cross-connec-tions is possible, but onlythrough thorough knowledgeand vigilance. Education isessential, for even those who areexperienced in piping installa-tions fail to recognize cross-connection possibilities anddangers. All municipalities withpublic water supply systemsshould have cross-connectioncontrol programs. Thoseresponsible for institutional orprivate water supplies shouldalso be familiar with thedangers of cross-connectionsand should exercise carefulsurveillance of their systems.

This Cross-Connection ControlManual has been designed as atool for health officials, water-works personnel, plumbers, andany others involved directly or

indirectly in water supplydistribution systems. It isintended to be used for educa-tional, administrative, andtechnical reference in conduct-ing cross-connection controlprograms. This manual is arevision of an earlier bookentitled Water Supply andPlumbing Cross-Connections (PHSPublication Number 957),which was produced under thedirection of Floyd B. Taylor byMarvin T. Skodje, who wrotethe text and designed theillustrations.

Many of the originalillustrations and text have beenretained in this edition. Previ-ous revisions were done byPeter C. Karalekas, Jr. withguidance from Roger D. Leeincorporating suggestions madeby the staff of the EPA WaterSupply Division, other govern-mental agencies, and interestedindividuals.

This 3rd edition wasproduced as a result of anupdated need for cross-connection control referencematerial reflecting an increasein cross-connection controlactivity throughout the UnitedStates. It has been revised andre-issued reflecting a demandfor its use, together withrequests for a document thatcovers the broad spectrum of

cross-connection control fromboth the basic hydraulicconcepts through the inclusionof a sample program that canbe a guide for a program at themunicipal level. New backflowdevices have been included inthis revision that are now beingproduced by manufacturersreflecting the needs of themarket. Updated actual cross-connection case histories havebeen added containing graphicschematic illustrations showinghow the incidents occurred andhow cross-connection controlpractices could be applied toeliminate future re-occurrence.A more detailed explanation ofcross-connection control“containment” practice hasbeen included together with theuse for “internal backflowprotective devices” and “fixtureoutlet protection”.

This 1989 edition wasprepared by Howard D.Hendrickson, PE, vice presidentof Water Service Consultants,with assistance from Peter C.Karalekas, Jr. of Region 1, EPA,Boston.

This latest (2003) editionhas technical correctionsprovided by Howard D.Hendrickson, P.E., showingupdates on pages iv, 18, 23, 30,31, and 32.

TABLE OF CONTENTS • iii

Contents

American Water Works Association Policy on Cross-Connections . . . . . . . iv

Chapter1. Purpose & Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. Public Health Significance of Cross-Connections . . . . . . . . . . . . . . . . . 23. Theory of Backflow and Backsiphonage . . . . . . . . . . . . . . . . . . . . . . . 124. Methods and Devices for the Prevention of Backflow and

Backsiphonage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165. Testing Procedures for Backflow Preventers . . . . . . . . . . . . . . . . . . . 256. Administration of a Cross-Connection Control Program . . . . . . . . . . 307. Cross-Connection Control Ordinance Provisions . . . . . . . . . . . . . . . . 33

AppendixesA. Partial list of plumbing hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38B. Illustrations of backsiphonage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38C. Illustrations of backflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40D. Illustrations of air gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41E. Illustrations of vacuum breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41F. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42G. Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43H. Sample cross-connection survey form . . . . . . . . . . . . . . . . . . . . . . . . . 44I. Sample cross-connection test form . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

IllustrationsHuman blood in the water system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Burned in the shower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Heating system anti-freeze into potable water . . . . . . . . . . . . . . . . . . . . . . . 3Salty drinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Paraquat in the water system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Propane gas in the water mains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Chlordane and heptachlor at the Housing Authority . . . . . . . . . . . . . . . . . . 5Boiler water enters high school drinking water . . . . . . . . . . . . . . . . . . . . . . . 6Pesticide in drinking water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Car wash water in the water main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Shipyard backflow contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Chlordane in the water main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Hexavalent chromium in drinking water . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Employee health problems due to cross-connection . . . . . . . . . . . . . . . . . . . 9Dialysis machine contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Creosote in the water mains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Kool aid laced with chlordane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure1 Pressure exerted by one foot of water at sea level . . . . . . . . . . . . . . . . 122 Pressure exerted by two feet of water at sea level . . . . . . . . . . . . . . . . 133 Pressure on the free surface of a liquid at sea level . . . . . . . . . . . . . . . 134 Effect of evacuating air from a column . . . . . . . . . . . . . . . . . . . . . . . . 135 Pressure relationships in a continuous fluid system at

the same elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Pressure relationships in a continuous fluid system at

different elevations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Backsiphonage in a plumbing system . . . . . . . . . . . . . . . . . . . . . . . . . 148 Negative pressure created by constricted flow . . . . . . . . . . . . . . . . . . 149 Dynamically reduced pipe pressure(s) . . . . . . . . . . . . . . . . . . . . . . . . . 1410 Valved connection between potable water and nonpotable fluid . . . . 15

11 Valved connection between potable water and sanitary sewer . . . . . . 1512 Air gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1613 Air gap in a piping system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1614 Barometric loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1715 Atmospheric vacuum breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1716 Atmospheric vacuum breaker typical installation . . . . . . . . . . . . . . . . 1717 Atmospheric vacuum breaker in plumbing supply system . . . . . . . . . 1718 Hose bibb vacuum breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1819 Typical installation of hose bibb vacuum breaker . . . . . . . . . . . . . . . . 1820 Pressure vacuum breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1821 Typical agricultural and industrial application of

pressure vacuum breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1922 Double check valve with atmospheric vent . . . . . . . . . . . . . . . . . . . . . 1923 Residential use of double check with atmospheric vent . . . . . . . . . . . 1924 Double check valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1925 Double check valve detector check . . . . . . . . . . . . . . . . . . . . . . . . . . . 2026 Residential dual check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2027 Residential installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2028 Copper horn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2029a Reduced pressure zone backflow preventer . . . . . . . . . . . . . . . . . . . . . 2129b Reduced pressure zone backflow preventer . . . . . . . . . . . . . . . . . . . . . 2130 Reduced pressure zone backflow preventer principle of operation . . . 2231 Plating plant installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2232 Car wash installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2233 Typical by-pass configuration, reduced pressure principle devices . . . 2334 Typical installation, reduced pressure principle device,

horizontal illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2335 Typical installation, reduced pressure principle device,

vertical installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2336 Typical installation, double check valve, horizontal and vertical

installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2437 Typical installation, residential dual check with straight

set and copper horn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2438 Pressure vacuum breaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2639 Reduced pressure principle backflow preventer, Step 1 . . . . . . . . . . . 2740 Reduced pressure principle backflow preventer, Step 2 . . . . . . . . . . . 2741 Double check valve assemblies, Method 1 . . . . . . . . . . . . . . . . . . . . . 2842 Double check valve assemblies, Method 2 . . . . . . . . . . . . . . . . . . . . . 2943 Cross-connection protection, commercial, industrial and residential . 3044 Backsiphonage, Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3845 Backsiphonage, Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3846 Backsiphonage, Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3947 Backsiphonage, Case 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3948 Backsiphonage, Case 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3949 Backsiphonage, Case 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3950 Backflow Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4051 Backflow Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4052 Backflow Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4053 Backflow Case 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4054 Air gap to sewer subject to backpressure—force main . . . . . . . . . . . . 4155 Air gap to sewer subject to backpressure—gravity drain . . . . . . . . . . 4156 Fire system makeup tank for a dual water system . . . . . . . . . . . . . . . 4157 Vacuum breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4158 Vacuum breaker arrangement for an outside hose hydrant . . . . . . . . . 41

iv • CROSS-CONNECTION CONTROL MANUAL

An AWWAStatement of Policyon Public Water Supply Matters.

Cross Connections

Adopted by the Board ofDirectors Jan. 26, 1970,revised June 24, 1979, reaf-firmed June 10, 1984 andrevised Jan. 28, 1990 and Jan.21, 2001.

The American WaterWorks Association (AWWA)recognizes water purveyorshave the responsibility tosupply potable water to theircustomers. In the exercise ofthis responsibility, waterpurveyors or other respon-sible authorities mustimplement, administer, andmaintain ongoing backflowprevention and cross-connection control programsto protect public watersystems from the hazardsoriginating on the premisesof their customers and fromtemporary connections thatmay impair or alter the waterin the public water systems.The return of any water tothe public water system afterthe water has been used forany purpose on thecustomer’s premises orwithin the customer’s pipingsystem is unacceptable andopposed by AWWA.

The water purveyor shallassure that effective backflowprevention measures commen-surate with the degree ofhazard, are implemented toensure continual protection ofthe water in the public waterdistribution system. Customers,together with other authoritiesare responsible for preventingcontamination of the privateplumbing system under theircontrol and the associatedprotection of the public watersystem.

If appropriate back-flowprevention measures have notbeen taken, the water purveyorshall take or cause to be takennecessary measures to ensurethat the public water distribu-tion system is protected fromany actual or potentialbackflow hazard. Such actionwould include the testing,installation, and continualassurance of proper operationand installation of backflow-prevention assemblies, devices,and methods commensuratewith the degree of hazard at theservice connection or at thepoint of cross connection orboth. If these actions are nottaken, water service shallultimately be eliminated.

To reduce the risk privateplumbing systems pose to thepublic water distributionsystem, the water purveyor’sbackflow prevention programshould include public educationregarding the hazards backflowpresents to the safety ofdrinking water and shouldinclude coordination with thecross connection efforts of localauthorities, particularly healthand plumbing officials. In areaslacking a health or plumbingenforcement agency, the waterpurveyor should additionallypromote the health and safetyof private plumbing systems toprotect its customers from thehazards of backflow.

CHAPTER ONE • 1

Chapter One

Public health officials havelong been concernedabout cross-connections andbackflow connections inplumbing systems and in publicdrinking water supply distribu-tion systems. Such cross-connections, which makepossible the contamination ofpotable water, are ever-presentdangers. One example of whatcan happen is an epidemic thatoccurred in Chicago in 1933.Old, defective, and improperlydesigned plumbing and fixturespermitted the contamination ofdrinking water. As a result.1,409 persons contractedamebic dysentery; there were98 deaths. This epidemic, andothers resulting from contami-nation introduced into a watersupply through improperplumbing, made clear theresponsibility of public healthofficials and water purveyors forexercising control over publicwater distribution systems andall plumbing systems connectedto them. This responsibilityincludes advising and instruct-ing plumbing installers in therecognition and elimination ofcross-connections.

Cross-connections are thelinks through which it ispossible for contaminatingmaterials to enter a potablewater supply. The contaminantenters the potable water systemwhen the pressure of thepolluted source exceeds thepressure of the potable source.The action may be calledbacksiphonage or backflow.Essentially it is reversal of thehydraulic gradient that can beproduced by a variety ofcircumstances.

It might be assumed thatsteps for detecting and elimi-nating cross-connections wouldbe elementary and obvious.Actually, cross-connections mayappear in many subtle formsand in unsuspected places.Reversal of pressure in thewater may be freakish andunpredictable. The probabilityof contamination of drinkingwater through a cross-connection occurring within asingle plumbing system mayseem remote; but, consideringthe multitude of similarsystems, the probability isgreat.

Why do suchcross-connectionsexist?

First, plumbing is frequentlyinstalled by persons who areunaware of the inherentdangers of cross-connections.Second, such connections aremade as a simple matter ofconvenience without regard tothe dangerous situation thatmight be created. And, third,they are made with reliance oninadequate protection such as asingle valve or other mechanicaldevice.

To combat the dangers ofcross-connections and backflowconnections, education in theirrecognition and prevention isneeded. First, plumbinginstallers must know thathydraulic and pollutionalfactors may combine to producea sanitary hazard if a cross-connection is present. Second,they must realize that there areavailable reliable and simple

standard backflow preventiondevices and methods that maybe substituted for the conve-nient but dangerous directconnection. And third, it shouldbe made clear to all that thehazards resulting from directconnections greatly outweighthe convenience gained. Thismanual does not describe all thecross-connections possible inpiping systems. It does attemptto reduce the subject to astatement of the principlesinvolved and to make it clear tothe reader that such installa-tions are potentially dangerous.The primary purpose is todefine, describe, and illustratetypical cross-connections and tosuggest simple methods anddevices by which they may beeliminated without interferingwith the functions of plumbingor water supply distributionsystems.

Purposeand Scope

Chapter Two

Public health officials havelong been aware of theimpact that cross-connectionsplay as a threat to the publichealth. Because plumbingdefects are so frequent andthe opportunity for contami-nants to invade the publicdrinking water through cross-connections are so general,enteric illnesses caused bydrinking water may occur atmost any location and at anytime.

The following documentedcases of cross-connectionproblems illustrate andemphasize how actual cross-connections have compromisedthe water quality and the publichealth.

Human Blood inthe Water System

Health Department officialscut off the water supply toa funeral home located in alarge southern city, after it wasdetermined that human bloodhad contaminated the freshwater supply. City water andplumbing officials said that theydid not think that the bloodcontamination had spreadbeyond the building, however,inspectors were sent into theneighborhood to check forpossible contamination. Thechief plumbing inspector hadreceived a telephone calladvising that blood was comingfrom drinking fountains withinthe building. Plumbing andcounty health departmentinspectors went to the sceneand found evidence that theblood had been circulating inthe water system within thebuilding. They immediatelyordered the building cut offfrom the water system at themeter.

Public HealthSignificance ofCross-Connections

Investigation revealed thatthe funeral home had beenusing a hydraulic aspirator todrain fluids from the bodies ofhuman “remains” as part of theembalming process. Theaspirator directly connected tothe water supply system at afaucet outlet located on a sinkin the “preparation” (embalm-ing) room. Water flow throughthe aspirator created suctionthat was utilized to draw bodyfluids through a hose andneedle attached to the suctionside of the aspirator.

The contamination of thefuneral home potable watersupply was caused by a combi-nation of low water pressure inconjunction with the simulta-neous use of the aspirator.Instead of the body fluidsflowing into the sanitary drain,they were drawn in the oppositedirection—into the potablewater supply of the funeralhome!

Reverse flow throughaspirator due toback siphonage

Body fluids

“Hydro”aspirator

Negative supply pressureOpen

Closed

Closed

Normal operationPositive supply pressure Potable water Open

2 • CROSS-CONNECTION CONTROL MANUAL

Burned in theShower

One neighbor’s head wascovered with blisters after shewashed her hair and otherscomplained of burned throatsor mouths after drinking thewater.

The incident began after an8-inch water main, that fed thetown, broke and was repaired.While repairing the watermain, one workman sufferedleg burns from a chemical inthe water and required medicaltreatment. Measurements of theph of the water were as high as13 in some sections of the pipe.

Investigation into the causeof the problem led to a possiblesource of the contaminationfrom a nearby chemicalcompany that distributeschemicals such as sodiumhydroxide. The sodium hydrox-ide is brought to the plant inliquid form in bulk tankertrucks and is transferred to aholding tank and then pumpedinto 55 gallon drums. Whenthe water main broke, a truckdriver was adding the waterfrom the bottom of the tanktruck instead of the top, andsodium hydroxide back-siphoned into the water main.

Heating SystemAnti-Freeze intoPotable Water

A resident of a small town inAlabama, jumped in theshower at 5 a.m. one morningin October, 1986, and when hegot out his body was coveredwith tiny blisters. “The more Irubbed it, the worse it got,” the60 year old resident said. “Itlooked like someone took ablow torch and singed me.”

He and several otherresidents received medicaltreatment at the emergencyroom of the local hospital afterthe water system was contami-nated with sodium hydroxide, astrong caustic solution.

Other residents claimedthat, “It (the water) bubbled upand looked like Alka Seltzer. Istuck my hand under the faucetand some blisters came up.”

Chemical bulk storage and holding tanks

“Burned in the shower”

Water mainbreak andrepair

water service Hose with bottom fill

Automobile antifreezeadded to boiler water

Backsiphonage(reverse flow)

Normal flow

Curb stop with stopand waste drain

Water main

Bangor Maine WaterDepartment employeesdiscovered poisonous antifreezein a homeowner’s heatingsystem and water supply inNovember, 1981. The incidentoccurred when they shut off‘the service line to the home tomake repairs. With the flow ofwater to the house cut off,pressure in the lines in thehouse dropped and the anti-freeze, placed in the heatingsystem to prevent freeze-up ofan unused hot water heatingsystem, drained out of theheating system into housewater lines, and flowed out tothe street. If it had not beennoticed, it would have enteredthe homeowner’s drinkingwater when the water pressurewas restored.

CHAPTER TWO • 3

Salt water suction linefor fire protection

Main freshwater line

Pump prime line

High pressure fire lineSeawater

Backflow preventerreplaced by spool piece

Mixing Sink

Herbicide holding tank

Potable town water

Recommended installation ofbackflow preventer

Salty Drinks Paraquat in theWater System

water supply piping had beenleft open. A lethal cross-connection had been createdthat permitted the herbicide toflow into the potable watersupply system. Upon restora-tion of water pressure, theherbicides flowed into the manyfaucets and outlets on the townwater distribution system.

This cross-connectioncreated a needless and costlyevent that fortunately did notresult in serious illness or loss oflife. Door-to-door publicnotification, extensive flushing,water sample analysis, emer-gency arrangements to providetemporary potable water fromtanker trucks, all contributed toan expensive and unnecessarytown burden.

In January, 1981, a nationallyknown fast food restaurantlocated in southeastern UnitedStates, complained to the waterdepartment that all their softdrinks were being rejected bytheir customers as tasting“salty.” This included sodafountain beverages, coffee,orange juice, etc. An investiga-tion revealed that an adjacentwater customer complained ofsalty water occurring simulta-neously with the restaurantincident. This second complaintcame from a water front shiprepair facility that was alsobeing served by the same watermain lateral. The (investigationcentered on the ship repairfacility and revealed thefollowing:

• A backflow preventerthat had been installed on theservice line to the shipyard hadfrozen and had been replacedwith a spool piece sleeve.

• The shipyard fireprotection system utilized seawater that was pumped by bothelectric and diesel drivenpumps.

• The pumps were primedby potable city water.

With the potable primingline left open and the pumpsmaintaining pressure in the firelines, raw salt water waspumped through the priminglines, through the spool sleevepiece, to the ship repair facilityand the restaurant.

“Yellow gushy stuff ”poured from some ofthe faucets in a small town inMaryland, and the State ofMaryland placed a ban ondrinking the water supply.Residents were warned not touse the water for cooking,bathing, drinking or any otherpurpose except for flushingtoilets.

The incident drew wide-spread attention and made thelocal newspapers. In addition tobeing the lead story on theABC news affiliate in Washing-ton, D.C. and virtually all theWashington/Baltimore news-papers that evening. The newsmedia contended that lethalpesticides may have contami-nated the water supply andamong the contaminants wasparaquat, a powerful agricul-tural herbicide.

The investigation disclosedthat the water pressure in thetown water mains was tempo-rarily reduced due to a waterpump failure in the town watersupply pumping system.Coincidentally, a gate valvebetween a herbicide chemicalholding tank and the town


Recommended installationof hose bibb vacuum breakerbackflow preventer

Gate valve closed

Recommendedbackflowpreventer

installation

Water mainpressure65 psi

Explosion

FireHose used for propane tankpurging cross

connectedto private

fire hydrant

Propane Gas in theWater Mains

ate repair procedures. Tostart the repair, the tank was“purged” of residual propaneby using water from one of twoprivate fire hydrants located onthe property. Water purgingis the preferred method ofpurging over the use of carbondioxide since it is more positiveand will float out any sludge aswell as any gas vapors. The“purging” consisted of hookingup a hose to one of the privatefire hydrants located on theproperty and initiating flushingprocedures.

Since the vapor pressure ofthe propane residual in the tankwas 85 to 90 psi., and the waterpressure was only 65 to 70 psi.,propane gas backpressurebackflowed into the watermain. It was estimated that thegas flowed into the water mainsfor about 20 minutes and thatabout 2,000 cubic feet of gaswas involved. This was approxi-mately enough gas to fill onemile of an 8-inch water main.

Chlordane andHeptachlor at theHousing Authority

of the gate valve. When theworkman cut the 6-inch line,water started to drain out of thecut, thereby setting up abacksiphonage condition. As aresult, the chemicals weresiphoned out of the truck,through the garden hose, andinto the system, contaminatingthe seventy five apartments.

Repeated efforts to cleanand flush the lines were notsatisfactory and it was finallydecided to replace the waterline and all the plumbing thatwas affected. There were noreports of illness, but residentsof the housing authority weretold not to use any tap waterfor any purpose and they weregiven water that was truckedinto the area by volunteer firedepartment personnel. Theywere without their normalwater supply for 27 days.

Hundreds of people wereevacuated from theirhomes and businesses on anAugust afternoon in a town inConnecticut in 1982 as a resultof propane entering the citywater supply system. Fires werereported in two homes and thetown water supply was con-taminated. One five-roomresidence was gutted by a blazeresulting from propane gas“bubbling and hissing” from abathroom toilet and in anotherhome a washing machineexplosion blew a womanagainst a wall. Residentsthroughout the area reportedhissing, bubbling noises,coming from washingmachines, sinks and toilets.Faucets sputtered out smallstreams of water mixed withgas and residents in the areawere asked to evacuate theirhomes.

This near-disaster occurredin one, 30,000 gallon capacityliquid propane tank when thegas company initiated immedi-

The services to seventy fiveapartments housingapproximately three hundredpeople were contaminated withchlordane and heptachlor in acity in Pennsylvania, in Decem-ber, 1980. The insecticidesentered the water supplysystem while an exterminatingcompany was applying them asa preventative measure againsttermites. While the pesticidecontractor was mixing thechemicals in a tank truck withwater from a garden hosecoming from one of theapartments, a workman wascutting into a 6-inch main lineto install a gate valve. The endof the garden hose was sub-merged in the tank containingthe pesticides, and at the sametime, the water to the area wasshut off and the lines beingdrained prior to the installation

CHAPTER TWO • 5

Boiler WaterEnters High SchoolDrinking Water

No students or facultywere known to have consumedany of the water; however, areaphysicians and hospitals advisedthat if anyone had consumedthose high levels of chromium,the symptoms would be nausea,diarrhea, and burning of themouth and throat. Fortunately,the home economics teacher,who first saw the discoloredwater before school started,immediately covered all waterfountains with towels so thatno one would drink the water.

Investigation disclosedthat chromium used in theheating system boilers to inhibitcorrosion of metal parts enteredthe potable water supplysystem as a result of backflowthrough leaking check valveson the boiler feed lines.

Pesticide inDrinking Water

Car Wash Waterin the Water MainStreet

A high school in NewMexico, was closed forseveral days in June 1984 whena home economics teachernoticed the water in the potablesystem was yellow. Citychemists determined thatsamples taken contained levelsof chromium as high as 700parts per million, “astronomi-cally higher than the acceptedlevels of .05 parts per million.”The head chemist said that itwas miraculous that no one wasseriously injured or killed by thehigh levels of chromium. Thechemical was identified assodium dichromate, a toxicform of chromium used inheating system boilers to inhibitcorrosion of the metal parts.

A pesticide contaminated aNorth Carolina watersystem in April, 1986, prompt-ing the town to warn residentsof 23 households not to drinkthe water. The residents in theaffected area were supplieddrinking water from a tanktruck parked in the parking lotof a downtown office buildinguntil the condition could becleared up. Residents com-plained of foul smelling waterbut there were no reports ofillness from ingesting the waterthat had been contaminatedwith a pesticide containingchlordane and heptachlor.

Authorities stated that theproblem occurred when a watermain broke at the same timethat a pest control service wasfilling a pesticide truck withwater. The reduction in pressurecaused the pesticide from insidethe tank to be sucked into thebuilding’s water main. Thepesticide contaminated thepotable water supply of theoffice building and neighbor-hood area.

This car wash cross-connection and back-pressure incident, whichoccurred in February, 1979,in the state of Washington,resulted in backflow chemicalcontamination of approximately100 square blocks of watermains. Prompt response by thewater department prevented apotentially hazardous waterquality degradation problemwithout a recorded case ofillness.

Numerous complaints ofgrey-green and “slippery” waterwere received by the waterdepartment coming from thesame general area of town. Asample brought to the waterdepartment by a customerconfirmed the reported problemand preliminary analysisindicated contamination withwhat appeared to be a deter-gent solution. While emergencycrews initiated flushing opera-tions, further investigationwithin the contaminated areasignaled the problem wasprobably caused by a car wash,

Pump

Street

High SchoolWater cooler

Bubbler

Bubbler

Leaky check valves

High school boilers

Recommended installationof backflow preventer

Toxic rust inhibitor anddefoamant containingsodium dichromate

Recommended installationof hose bibb vacuum breakerbackflow preventer


Shipboardraw waterpumpingsystem

To washrooms

To washrooms

Potable

water

supply

Cafeteria drinking fountainsand sanitation water

Reduced pressure principle backflow preventers should have been installed at dockside outlets and other locations

Potable supply hose

Wax injectors

To reclaim tanksScrubbers

Potable water supply

RinseRinse

Soap injectors

Hose connectionmade here

Recommendedinstallation ofbackflow preventer Reclaim tanks

Recirculatingpump

To restrooms

or laundry, based upon thesoapy nature of the contami-nant. The source was quicklynarrowed down to a car washand the proprietor was ex-tremely cooperative in admit-ting to the problem andexplaining how it had occurred.The circumstances leading upto the incident were as follows:

• On Saturday, February10, 1979, a high pressure pumpbroke down at the car wash.This pump recycled reclaimedwash and rinse water andpumped it to the initialscrubbers of the car wash. Nopotable plumbing connectionis normally made to the carwash’s scrubber system.

• After the pump brokedown, the car wash ownerwas able to continue operationby connecting a 2-inch hosesection temporarily between thepotable supply within the carwash, and the scrubber cyclepiping.

• On Monday, February12, 1979, the owner repairedthe high pressure pump andresumed normal car washoperations. The 2-inch hoseconnection (cross-connection)was not removed!

• Because of the cross-connection, the newly repairedhigh pressure pump promptlypumped a large quantity ofthe reclaimed wash/rinse waterout of the car wash and into a12-inch water main in thestreet. This in turn was deliv-ered to the many residencesand commercial establishmentsconnected to the water main.

Within 24 hours of theincident, the owner of the carwash had installed a 2-inchreduced pressure principlebackflow preventer on hiswater service and all car washestablishments in Seattle thatused a wash water reclaimsystem were notified of thestate requirement for backflowprevention.

ShipyardBackflowContamination

The cause of the problemwas a direct cross-connectionbetween the on-board saltwater fire protection watersystem and the fresh waterconnected to one of the ships atthe dock. While the shipyardhad been aware of the needfor backflow protection at thedockside tie up area, the devicehad not been delivered andinstalled prior to the time of theincident. As a result, the saltwater on-board fire protectionsystem, being at a greaterpressure than the potablesupply, forced the salt water,through backpressure, into theshipyard potable supply.

Fortunately, a smalldemand for potable water atthe time of the incidentprevented widespread pollutionin the shipyard and the sur-rounding areas.

Water fountains at an EastCoast Shipyard wereposted “No Drinking” asworkers flushed the water linesto eliminate raw river waterthat had entered the shipyardfollowing contamination fromincorrectly connected waterlines between ships at the pierand the shipyard. Some thirdshift employees drank thewater before the pollutionwas discovered and latercomplained of stomach crampsand diarrhea.

CHAPTER TWO • 7

Hexavalentchromiumadded tochilled water

Main plant cooling line

Temperingvalve

Circulatingpumps

Hot waterheater

Lasermachine

Temporarychillerfeed pump

To washrooms

Potab

le wa

ter su

pply

To plant bubblers

To ice making machines

To plant vending machines

Backpressure backflow path

Recommended installation ofbackflow preventer

Chlordane in theWater Main

In October, 1979, approxi-mately three gallons ofchlordane, a highly toxicinsecticide, was sucked back(back-siphoned) into the watersystem of a residential area ofa good sized eastern city.Residents complained that thewater “looked milky, felt greasy,foamed and smelled,” and asone woman put it, “It wassimilar to a combination ofkerosene and Black Flagpesticide.”

The problem developedwhile water departmentpersonnel were repairing awater main. A professionalexterminator, meanwhile, wastreating a nearby home withchlordane for termite elimina-tion. The workman for theexterminator company left one

HexavalentChromium inDrinking Water

In July, 1982, a well meaningmaintenance mechanic, inattempting to correct a fogginglens in an overcooled lasermachine, installed a temperingvalve in the laser cooling line,and inadvertently set the stagefor a backpressure backflowincident that resulted inhexavalent chromium contami-nating the potable water of alarge electronic manufacturingcompany in Massachusettsemploying 9,000 people.Quantities of 50 parts permillion hexavalent chromiumwere found in the drinkingwater which is sufficient tocause severe vomiting, diarrhea,

end of a garden hose that wasconnected to an outside hosebibb tap in a barrel of dilutedpesticide. During the waterservice interruption, thechlordane solution was back-siphoned from the barrelthrough the house and into thewater mains.

Following numerouscomplaints, the water depart-ment undertook an extensiveprogram of flushing of thewater mains and hand deliveredletters telling residents to flushtheir lines for four hours beforeusing the water. Until the waterlines were clear of the contami-nant, water was hand-hauledinto homes, and people wentout of their homes for showers,meals and every other activityinvolving potable water.Fortunately, due to the obviousbad taste, odor and color of thecontaminated water, no oneconsumed a sufficient quantityto endanger health.

and intestinal sickness.Maintenance crews workingduring the plant shutdownwere able to eliminate the cross-connection and thoroughlyflush the potable water system,thereby preventing a serioushealth hazard from occurring.

The incident occurred asfollows:

• Laser machine lenseswere kept cool by circulatingchilled water that came from alarge refrigeration chiller. Thewater used in the chiller wastreated with hexavalentchromium, a chemical additiveused as an anticorrosive agentand an algicide. As a result, thechilled water presented a toxic,non-potable substance unfit forhuman consumption but very

CHLORDANE

Recommended installation of hose bibbvacuum breaker backflow preventer


Heat exchangerUtilitysink

Sink

Sink

Coffeemachine

Boosterpump

Recommended installationof backflow preventers

Backpressurebackflow

MeterWatermain

Waterfountatin

Roof mounted solar panels

Sink

Chemicalfeeder

acceptable for industrial processwater. No health hazard waspresent as long as the pipingwas identified, kept separatefrom potable drinking waterlines, and not cross-connectedto the potable water supply.

• A maintenancemechanic correctly reasonedthat by adding a temperingvalve to the chilled water line,he could heat up the water a bitand eliminate fogging of thelaser lenses resulting from thechilled water being too cold.The problem with the installa-tion of the tempering valve wasthat a direct cross-connectionhad been inadvertently madebetween the toxic chilled waterand the potable drinking waterline!

• Periodic maintenanceto the chiller system wasperformed in the summer,requiring that an alternatechiller feed pump be tempo-rarily installed. This replace-ment pump had an outletpressure of 150 psi, andpromptly established animbalance of pressure at thetempering valve, thereby over-pressurizing the 60 psi, potablesupply. Backpressure backflowresulted and pushed the toxicchilled water from the waterheater and then into the plant’spotable drinking water supply.Yellowish green water startedpouring out of the drinkingfountains, the washroom, andall potable outlets.

Employee HealthProblems due toCross-Connection

supply line! As the storage tankpressure increased above thesupply pressure, as a result ofthermal expansion, the poten-tial for backpressure backflowwas present. Normally, thiswould not occur because aboost pump in the supply linewould keep the supply pressureto the storage tank alwaysgreater than the highest tankpressure. The addition of rustinhibiting chemicals to thistank greatly increased thedegree of hazard of the liquid.Unfortunately, at the same timethat the fire took place, thepressure in the water mains wasreduced to a dangerously lowpressure and the low pressurecutoff switches simultaneouslyshut off the storage tankbooster pumps. This combina-tion allowed the boiler water,together with its chemicalcontaminants, the opportunityto enter the potable watersupply within the building.When normal pressure wasreestablished in the watermains, the booster pumpskicked in, and the contami-nated water was deliveredthroughout the building.

A cross-connection incidentoccurring in a modernseven-story office buildinglocated in a large city in NewHampshire, in March, 1980,resulted in numerous cases ofnausea, diarrhea, loss of timeand employee complaints as tothe poor quality of the water.

On Saturday, March 1,1980, a large fire occurred twoblocks away from a seven-storyoffice building in this largeNew Hampshire city. OnSunday, March 2, 1980, themaintenance crew of the officebuilding arrived to perform theweekly cleaning, and afterdrinking the water from thedrinking fountains, andsampling the coffee from thecoffee machines, noticed thatthe water smelled rubbery andhad a strong bitter taste. Uponnotifying the Manchester WaterCompany, water samples weretaken and preliminary analysisdisclosed that the contaminantsfound were not the typicalcontaminants associated withfire line disturbances. Investi-gating teams suspected thateither the nearby fire couldhave siphoned contaminantsfrom adjacent buildings into thewater mains, or the contamina-tion could have been caused bya plumbing deficiency occurringwithin the seven story buildingitself.

Water ph levels of thebuilding water indicated thatan injection of chemicals hadprobably taken place within theseven-story building. Tracing ofthe water lines within thebuilding pinpointed a 10,000gallon hot-water storage tankthat was used for heat storagein the solar heating system. Itdid not have any backflowprotection on the make-up

CHAPTER TWO • 9

Operating room

Air conditioning units

Glycol/waterpressurizedholding tank

Submerged inletcross-connection

Dialysis roomRecommneded installation

of backflow preventer SlightlyopenmanualvalveDialysis

filtrationunit

Intensive careRestroom

Autopsy

Washroom

Laundry facility

Backpressure backflow

Main watersupply

Recommended installationof backflow preventer

Boilerroom

Dialysis MachineContamination

potable supply line and fedthrough a manually operatedcontrol valve. With this valveopen, or partially open, potablemake-up water flowed slowlyinto the glycol/water mixture inthe holding tank until it filledto the point where the pressurein the closed tank equaled thepressure in the potable watersupply feed line. As long as thepotable feed line pressure was atleast equal to, or greater than,the holding tank pressure, nobackflow could occur. The stagewas set for disaster, however.

It was theorized thatsomeone in the medical centerflushed a toilet or turned on a

faucet, which in turn droppedthe pressure in the potablesupply line to the air condition-ing holding tank. Since themanually operated fill valve waspartially open, this allowed theglycol/water mixture to enterthe medical center potablepipelines and flow into thedialysis equipment. The dialysisfiltration system takes out tracechemicals such as those used inthe city water treatment plant,but the system could nothandle the heavy load ofchemicals that it was suddenlysubjected to.

The effect upon the dialysispatients was dramatic: patientsbecame drowsy, confused andfell unconscious, and werepromptly removed to intensivecare where blood samples weretaken. The blood samplesrevealed a build-up of acid andthe medical director stated that,“Something has happened indialysis.” Dialysis was repeatedon the patients a second andthird time.

Tests of the water supply tothe filtration system quicklydetermined the presence of “anundesirable chemical in thewater purification system.” Thepartially open fill valve wasthen found that it had permit-ted the glycol water mix todrain from the air conditioningholding tank into the medicalcenter’s potable supply linesand then into the dialysisfiltration system equipment.

Creosote in theWater Mains


Ethylene glycol, an anti-freeze additive to airconditioning cooling towerwater, inadvertently entered thepotable water supply system ina medical center in Illinois inSeptember, 1982, and two ofsix dialysis patients succumbedas a direct or indirect result ofthe contamination.

The glycol was added tothe air conditioning water, andthe glycol/water mix was storedin a holding tank that was anintegral part of the medicalcenter’s air conditioning coolingsystem. Pressurized make-upwater to the holding tank wassupplied by a medical center

Creosote entered the waterdistribution system of asoutheastern county waterauthority in Georgia, inNovember, 1984, as a result ofcross-connection between a¾-inch hose that was beingused as a priming line betweena fire service connection and thesuction side of a creosote pump.The hose continually suppliedwater to the pump to ensurethe pump was primed at alltimes. However, while repairswere being made to a privatefire hydrant, the creosote back-siphoned into the water mainsand contaminated a section ofthe water distribution system.

Detailed investigation ofthe cause of the incidentdisclosed that the woodpreservative company, as part oftheir operation, pumpedcreosote from collective pits toother parts of their operation.The creosote pump wouldautomatically shut off when thecreosote in the pit was loweredto a predetermined level. Afterthe creosote returned to ahigher level, the pump wouldrestart. This pump would loseits prime quite often prior tothe pit refilling, and to preventthe loss of prime, the woodpreservative company wouldconnect a hose from a ¾-inchhose bibb, located on the fireservice line, to the suction sideof the pump. The hose bibbremained open at all times in aneffort to continuously keep thepump primed.

Repairs were necessary toone of the private fire hydrantson the wood preservativecompany property, necessitatingthe shutting down of one of twoservice lines and removal of thedamaged fire hydrant for repair.Since the hydrant was at asignificantly lower level thanthe creosote pit, the creosoteback-siphoned through a ¾-inch pump priming hoseconnecting the creosote pit tothe fire service line.

After the repairs weremade to the hydrant, and thewater service restored, thecreosote, now in the fire lines,was forced into the main waterdistribution system.

Kool-Aid LacedWith Chlordane

CHAPTER TWO • 11

Street main

Street main

Creosote pump

Creosotecontaminated flow


Private shut-off

Processwater


In August, 1978, a profes-sional exterminator wastreating a church located in asmall town in South Carolina,for termite and pest control.The highly toxic insecticidechlordane was being mixedwith water in small buckets,and garden hoses were leftsubmerged in the buckets whilethe mixing was being accom-plished. At the same time,water department personnelcame by to disconnect theparsonage’s water line from thechurch to install a separatewater meter for the parsonage.In the process, the water wasshut off in the area of thechurch building. Since thechurch was located on a steephill, and as the remaining waterin the lines was used byresidents in the area, the churchwas among the first places toexperience a negative pressure.

The chlordane was quicklysiphoned into the water lineswithin the church and becamemixed with the Kool-Aid beingprepared by women for thevacation bible school. Approxi-mately a dozen children andthree adults experienceddizziness and nausea. Fortu-nately, none required hospital-ization or medical attention.

Recommended installationof hose bibb vacuum breaker backflow preventer

Chapter Three

A cross-connection1 is thelink or channel connectinga source of pollution with apotable water supply. Thepolluting substance, in mostcases a liquid, tends to enter thepotable supply if the net forceacting upon the liquid acts inthe direction of the potablesupply. Two factors are thereforeessential for backflow. First,there must be a link betweenthe two systems. Second, theresultant force must be towardthe potable supply.

An understanding of theprinciples of backflow andbacksiphonage requires anunderstanding of the termsfrequently used in theirdiscussion. Force, unless com-pletely resisted, will producemotion. Weight is a type offorce resulting from the earth’sgravitational attraction.Pressure (P) is a force-per-unitarea, such as pounds per squareinch (psi). Atmospheric pressure isthe pressure exerted by theweight of the atmosphere abovethe earth.

Pressure may be referred tousing an absolute scale, poundsper square inch absolute (psia),or gage scale, pounds persquare inch gage (psig).Absolute pressure and gagepressure are related. Absolutepressure is equal to the gagepressure plus the atmosphericpressure. At sea level theatmospheric pressure is 14.7psia. Thus,

Pabsolute = Pgage + 14.7psior

Pgage = Pabsolute – 14.7 psiIn essence then, absolute

pressure is the total pressure.Gage pressure is simply thepressure read on a gage. If thereis no pressure on the gage otherthan atmospheric, the gagewould read zero. Then theabsolute pressure would beequal to 14.7 psi which is theatmospheric pressure.

The term vacuum indicatesthat the absolute pressure is lessthan the atmospheric pressureand that the gage pressure isnegative. A complete or totalvacuum would mean a pressureof 0 psia or -14.7 psig. Since itis impossible to produce a totalvacuum, the term vacuum, asused in the text, will mean alldegrees of partial vacuum. In apartial vacuum, the pressurewould range from slightly lessthan 14.7 psia (0 psig) toslightly greater than 0 psia(-14.7 psig).

Backsiphonage1 results influid flow in an undesirable orreverse direction. It is caused byatmospheric pressure exerted ona pollutant liquid forcing ittoward a potable water supplysystem that is under a vacuum.Backflow, although literallymeaning any type of reversedflow, refers to the flow producedby the differential pressureexisting between two systemsboth of which are at pressuresgreater than atmospheric.

Water Pressure

For an understanding of thenature of pressure and itsrelationship to water depth,consider the pressure exerted onthe base of a cubic foot of waterat sea level. (See Fig. 1) Theaverage weight of a cubic footof water is 62.4 pounds persquare foot gage. The base maybe subdivided into 144-squareinches with each subdivisionbeing subjected to a pressure of0.433 psig.

Suppose another cubic footof water were placed directlyon top of the first (See Fig. 2).The pressure on the top surfaceof the first cube which wasoriginally atmospheric, or0 psig, would now be 0.433psig as a result of the super-imposed cubic foot of water.The pressure of the base ofthe first cube would also beincreased by the same amountof 0.866 psig, or two times theoriginal pressure.

Theory of Backflowand Backsiphonage

62.4#/ft3

0.433 psig

Sea l

evel

12"

12"12"

FIGURE 1.Pressure exerted by 1 foot ofwater at sea level.

1See formal definition in the glossary ofthe appendix


If this process wererepeated with a third cubic footof water, the pressures at thebase of each cube would be1,299 psig, 0.866 psig, and0.433 psig, respectively. It isevident that pressure varieswith depth below a free watersurface; in general each foot ofelevation change, within aliquid, changes the pressure byan amount equal to the weight-per-unit area of 1 foot of theliquid. The rate of increase forwater is 0.433 psi per foot ofdepth.

Frequently water pressureis referred to using the terms“pressure head” or just “head,”and is expressed in units of feetof water. One foot of headwould be equivalent to thepressure produced at the baseof a column of water 1 foot indepth. One foot of head or1 foot of water is equal to 0.433psig. One hundred feet of headis equal to 43.3 psig.

Siphon Theory

Figure 3 depicts the atmo-spheric pressure on a watersurface at sea level. An opentube is inserted vertically intothe water; atmospheric pres-sure, which is 14.7 psia, actsequally on the surface of thewater within the tube and onthe outside of the tube.

level exactly balances theweight of a column of water33.9 feet in height. Theabsolute pressure within thecolumn of water in Figure 4 ata height of 11.5 feet is equal to9.7 psia. This is a partialvacuum with an equivalentgage pressure of -5.0 psig.

As a practical example,assume the water pressure at aclosed faucet on the top of a100-foot high building to be 20psig; the pressure on theground floor would then be63.3 psig. If the pressure at theground were to drop suddenlydue to a heavy fire demand inthe area to 33.3 psig, thepressure at the top would bereduced to -10 psig. If thebuilding water system wereairtight, the water wouldremain at the level of the faucet

because of the partial vacuumcreated by the drop in pressure.If the faucet were opened,however, the vacuum would bebroken and the water levelwould drop to a height of 77feet above the ground. Thus,the atmosphere was supportinga column of water 23 feet high.

Figure 5 is a diagram of aninverted U-tube that has beenfilled with water and placed intwo open containers at sea level.

If the open containers areplaced so that the liquid levelsin each container are at thesame height, a static state willexist; and the pressure at anyspecified level in either leg ofthe U-tube will be the same.

The equilibrium conditionis altered by raising one of thecontainers so that the liquidlevel in one container is 5 feet

If, as shown in Figure 4,the tube is slightly capped anda vacuum pump is used toevacuate all the air from thesealed tube, a vacuum with apressure of 0 psia is createdwithin the tube. Because thepressure at any point in a staticfluid is dependent upon theheight of that point above areference line, such as sea level,it follows that the pressurewithin the tube at sea levelmust still be 14.7 psia. This isequivalent to the pressure at thebase of a column of water 33.9feet high and with the columnopen at the base, water wouldrise to fill the column to a depthof 33.9 feet. In other words, theweight of the atmosphere at sea

0.433 psig24"

0.866 psig Sea

Leve

l

14.7psia14.7 psia

sea level

FIGURE 2.Pressure exerted by 2 feet ofwater at sea level.

FIGURE 3.Pressure on the free surface of aliquid at sea level.

FIGURE 4.Effect of evacuating air from acolumn.

FIGURE 5.Pressure relationships in acontinuous fluid system at thesame elevation.


14.7psia

9.7psia

14.7 psia or0.0 psig

or -5.0 psig

0.0psia

or-14.7psig

Vacuum pump

“Zero” AbsolutePressure

Sea level

39.9

'11

.5'

14.7psia

14.7psia

4.7 psia

10.3 psia 23'

10'

CHAPTER THREE • 13

above the level of the other. (SeeFig. 6.) Since both containersare open to the atmosphere, thepressure on the liquid surfacesin each container will remain at14.7 psia.

If it is assumed that a staticstate exists, momentarily,within the system shown inFigure 6, the pressure in the lefttube at any height above thefree surface in the left containercan be calculated. The pressureat the corresponding level in theright tube above the free surfacein the right container may alsobe calculated.

As shown in Figure 6, thepressure at all levels in the lefttube would be less than atcorresponding levels in the righttube. In this case, a staticcondition cannot exist becausefluid will flow from the higherpressure to the lower pressure;the flow would be from theright tank to the left tank. Thisarrangement will be recognizedas a siphon. The crest of asiphon cannot be higher than33.9 feet above the upper liquid

level, since atmosphere cannotsupport a column of watergreater in height than 33.9 feet.

Figure 7 illustrates howthis siphon principle can behazardous in a plumbingsystem. If the supply valve isclosed, the pressure in the linesupplying the faucet is less thanthe pressure in the supply lineto the bathtub. Flow will occur,therefore, through siphonage,from the bathtub to the openfaucet.

shown that as a fluid acceler-ates, as shown in Figure 8, thepressure is reduced. As waterflows through a constrictionsuch as a converging section ofpipe, the velocity of the waterincreases; as a result, thepressure is reduced. Under suchconditions, negative pressuresmay be developed in a pipe.The simple aspirator is basedupon this principle. If thispoint of reduced pressure islinked to a source of pollution,backsiphonage of the pollutantcan occur.

flow from the source of pollu-tion would occur when pressureon the suction side of the pumpis less than pressure of thepollution source; but this isbackflow, which will be discussedbelow.

The preceding discussionhas described some of themeans by which negativepressures may be created andwhich frequently occur toproduce backsiphonage. Inaddition to the negativepressure or reversed forcenecessary to causebacksiphonage and backflow,there must also be the cross-connection or connecting linkbetween the potable watersupply and the source ofpollution. Two basic types ofconnections may be created inpiping systems. These are thesolid pipe with valved connec-tion and the submerged inlet.


14.7psia

14.7psia

10.3 psia

10'

8.2 psia

15'

5'

FIGURE 6.Pressure relationships in acontinuous fluid system atdifferent elevations.

Valve open

Closed supply

Valve open

Submerged inlet

FIGURE 7.Backsiphonage in a plumbingsystem.

The siphon actions citedhave been produced by reducedpressures resulting from adifference in the water levels attwo separated points within acontinuous fluid system.

Reduced pressure may alsobe created within a fluid systemas a result of fluid motion. Oneof the basic principles of fluidmechanics is the principle ofconservation of energy. Basedupon this principle, it may be

+30 psig +30 psig-10 psig

FIGURE 8.Negative pressure created byconstricted flow.

FIGURE 9.Dynamically reduced pipepressures.

Booster pump

To fixtureFrom pollutionsource

+50 psig

-10psig

One of the commonoccurrences of dynamicallyreduced pipe pressures is foundon the suction side of a pump.In many cases similar to the oneillustrated in Figure 9, the linesupplying the booster pump isundersized or does not havesufficient pressure to deliverwater at the rate at which thepump normally operates. Therate of flow in the pipe may beincreased by a further reductionin pressure at the pump intake.This often results in the creationof negative pressure at thepump intake. This often resultsin the creation of negativepressure. This negative pressuremay become low enough insome cases to cause vaporizationof the water in the line. Actu-ally, in the illustration shown,

Figures 10 and 11 illustratesolid connections. This type ofconnection is often installedwhere it is necessary to supplyan auxiliary piping system fromthe potable source. It is a directconnection of one pipe toanother pipe or receptacle.

Solid pipe connections areoften made to continuous orintermittent waste lines whereit is assumed that the flow willbe in one direction only. Anexample of this would be usedcooling water from a waterjacket or condenser as shown inFigure 11. This type of connec-tion is usually detectable butcreating a concern on the part

of the installer about thepossibility of reversed flow isoften more difficult. Uponquestioning, however, manyinstallers will agree that thesolid connection was madebecause the sewer is occasion-ally subjected to backpressure.

Submerged inlets are foundon many common plumbingfixtures and are sometimesnecessary features of the fixturesif they are to function properly.Examples of this type of designare siphon-jet urinals or waterclosets, flushing rim slop sinks,and dental cuspidors. Oldstylebathtubs and lavatories hadsupply inlets below the floodlevel rims, but modern sanitarydesign has minimized oreliminated this hazard in newfixtures. Chemical and indus-trial process vats sometimeshave submerged inlets wherethe water pressure is used as anaid in diffusion, dispersion andagitation of the vat contents.Even though the supply pipemay come from the floor abovethe vat, backsiphonage canoccur as it has been shown thatthe siphon action can raise aliquid such as water almost 34feet. Some submerged inlets

difficult to control are thosewhich are not apparent until asignificant change in water leveloccurs or where a supply maybe conveniently extended belowthe liquid surface by means of ahose or auxiliary piping. Asubmerged inlet may be createdin numerous ways, and itsdetection in some of thesesubtle forms may be difficult.

The illustrations includedin part B of the appendix areintended to describe typicalexamples of backsiphonage,showing in each case the natureof the link or cross-connection,and the cause of the negativepressure.

Backflow

Backflow1, as described in thismanual, refers to reversed flowdue to backpressure other thansiphonic action. Any intercon-nected fluid systems in whichthe pressure of one exceeds thepressure of the other may haveflow from one to the other as aresult of the pressure differen-tial. The flow will occur fromthe zone of higher pressure tothe zone of lower pressure. Thistype of backflow is of concern inbuildings where two or morepiping systems are maintained.The potable water supply isusually under pressure directlyfrom the city water main.Occasionally, a booster pump isused. The auxiliary system isoften pressurized by a centrificalpump, although backpressuremay be caused by gas or steampressure from a boiler. A

reversal in differential pressuremay occur when pressure in thepotable system drops, for somereason, to a pressure lower thanthat in the system to which thepotable water is connected.

The most positive methodof avoiding this type ofbackflow is the total or com-plete separation of the twosystems. Other methods usedinvolve the installation ofmechanical devices. All meth-ods require routine inspectionand maintenance.

Dual piping systems areoften installed for extra protec-tion in the event of an emer-gency or possible mechanicalfailure of one of the systems.Fire protection systems are anexample. Another example isthe use of dual water connec-tions to boilers. These installa-tions are sometimes inter-connected, thus creating ahealth hazard.

The illustrations in part Cof the appendix depict installa-tions where backflow underpressure can occur, describingthe cross-connection and thecause of the reversed flow.

CHAPTER THREE • 15

FIGURE 11Valved connection betweenpotable water and sanitary sewer.

City supply

Sanitary sewer

Condenser

FIGURE 10.Valved connections betweenpotable water and nonpotablefluid.

Non potable Potable


Chapter Four

A wide choice of devicesexists that can be used toprevent backsiphonage andbackpressure from addingcontaminated fluids or gasesinto a potable water supplysystem. Generally, the selectionof the proper device to use isbased upon the degree of hazardposed by the cross-connection.Additional considerations arebased upon piping size, location,and the potential need toperiodically test the devices toinsure proper operation.

There are six basic types ofdevices that can be used tocorrect cross-connections: airgaps, barometric loops, vacuumbreakers—both atmosphericand pressure type, double checkwith intermediate atmosphericvent, double check valveassemblies, and reduced pressureprinciple devices. In general, allmanufacturers of these devices,with the exception of thebarometric loop, produce themto one or more of three basicstandards, thus insuring thepublic that dependable devicesare being utilized and marketed.The major standards in theindustry are: American Societyof Sanitary Engineers ASSE),American Water Works Associa-tion (AWWA), and the Univer-sity of California Foundation forCross-Connection Control andHydraulic Research.

Air Gap

Air gaps are non-mechanicalbackflow preventers that arevery effective devices to be usedwhere either backsiphonage orbackpressure conditions mayexist. Their use is as old aspiping and plumbing itself, butonly relatively recently havestandards been issued thatstandardize their design. Ingeneral, the air gap must betwice the supply pipe diameterbut never less than one inch.See Figure 12.

(2) The air gap may be easilydefeated in the event that the“2D” requirement was purposelyor inadvertently compromised.Excessive splash may be encoun-tered in the event that higherthan anticipated pressures orflows occur. The splash may be acosmetic or true potentialhazard—the simple solutionbeing to reduce the “2D”dimension by thrusting thesupply pipe into the receivingfunnel. By so doing, the air gapis defeated.(3) At an air gap, we expose thewater to the surrounding airwith its inherent bacteria, dustparticles, and other airbornepollutants or contaminants. Inaddition, the aspiration effect ofthe flowing water can drag downsurrounding pollutants into thereservoir or holding tank.(4) Free chlorine can come out oftreated water as a result of the airgap and the resulting splash andchurning effect as the waterenters the holding tanks. Thisreduces the ability of the waterto withstand bacteria contamina-tion during long term storage.(5) For the above reasons, airgaps must be inspected asfrequently as mechanicalbackflow preventers. They arenot exempt from an in-depthcross-connection control pro-gram requiring periodic inspec-tion of all backflow devices.

Air gaps may be fabricatedfrom commercially availableplumbing components orpurchased as separate units andintegrated into plumbing andpiping systems. An example ofthe use of an air gap is shown inFigure 13.


Methods and Devicesfor the Prevention ofBackflow andBack-Siphonage

An air gap, although anextremely effective backflowpreventer when used to preventbacksiphonage and backpres-sure conditions, does interruptthe piping flow with corre-sponding loss of pressure forsubsequent use. Consequently,air gaps are primarily used atend of the line service wherereservoirs or storage tanks aredesired. When contemplatingthe use of an air gap, someother considerations are:(1) In a continuous pipingsystem, each air gap requiresthe added expense of reservoirsand secondary pumpingsystems.

FIGURE 12.Air gap.

Diameter“D”

“2D”

Barometric Loop

The barometric loop consists ofa continuous section of supplypiping that abruptly rises to aheight of approximately 35 feetand then returns back down tothe originating level. It is a loopin the piping system thateffectively protects againstbacksiphonage. It may not beused to protect against back-pressure.

Its operation, in theprotection against back-siphonage, is based upon theprinciple that a water column,at sea level pressure, will notrise above 33.9 feet (Ref.Chapter 3, Fig. 4 Page 13).

In general, barometricloops are locally fabricated, andare 35 feet high.

Atmospheric VacuumBreaker

These devices are among thesimplest and least expensivemechanical types of backflowpreventers and, when installedproperly, can provide excellentprotection against back-siphonage. They must not beutilized to protect againstbackpressure conditions.Construction consists usually ofa polyethylene float which isfree to travel on a shaft and sealin the uppermost positionagainst atmosphere with anelastomeric disc. Water flowlifts the float, which then causesthe disc to seal. Water pressurekeeps the float in the upwardsealed position. Termination ofthe water supply will cause thedisc to drop down venting theunit to atmosphere and therebyopening downstream piping toatmospheric pressure, thuspreventing backsiphonage.Figure 15 shows a typicalatmospheric breaker.

In general, these devicesare available in ½-inch through3-inch size and must beinstalled vertically, must nothave shutoffs downstream,and must be installed at least6-inches higher than the finaloutlet. They cannot be testedonce they are installed in theplumbing system, but are, forthe most part, dependable,trouble-free devices forbacksiphonage protection.

Figure 16 shows thegenerally accepted installationrequirements—note that noshutoff valve is downstreamof the device that wouldotherwise keep the atmosphericvacuum breaker under constantpressure.

Figure 17 shows a typicalinstallation of an atmosphericvacuum breaker in a plumbingsupply system.

CHAPTER FOUR • 17

FIGURE 13.Air gap in a piping system.

Supply piping

Tank or reservoir

FIGURE 14.Barometric loop.

FIGURE 15.Atmospheric vacuum breaker.

35'

FIGURE 16.Atmospheric vacuum breakertypical installation.

FIGURE 17.Atmospheric vacuum breaker inplumbing supply system.

Flow condition

Seal

Non flow condition

Not less than 6"

Hose BibbVacuum Breakers

These small devices are aspecialized application of theatmospheric vacuum breaker.They are generally attached tosill cocks and in turn areconnected to hose suppliedoutlets such as garden hoses,slop sink hoses, spray outlets,etc. They consist of a springloaded check valve that sealsagainst an atmospheric outletwhen water supply pressure isturned on. Typical constructionis shown in Figure 18.

When the water supply isturned off, the device vents toatmosphere, thus protectingagainst backsiphonage condi-tions. They should not be usedas backpressure devices. Manualdrain options are available,together with tamper-proofversions. A typical installation isshown in Figure 19.

PressureVacuum Breakers

This device is an outgrowth ofthe atmospheric vacuumbreaker and evolved in responseto a need to have an atmospher-ic vacuum breaker that could beutilized under constant pressureand that could be tested in line.A spring on top of the disc andfloat assembly, two added gatevalves, test cocks, and anadditional first check, providedthe answer to achieve thisdevice. See Figure 20.

These units are available inthe general configurations asshown in Figure 20 in sizes½-inch through 10-inch andhave broad usage in theagriculture and irrigationmarket. Typical agricultural and

industrial applications areshown in Figure 21.

Again, these devices maybe used under constant pressurebut do not protect againstbackpressure conditions. As aresult, installation must be atleast 6- to 12-inches higherthan the existing outlet.

A spill resistant pressurevacuum breaker (SVB) isavailable that is a modificationto the standard pressurevacuum breaker but specificallydesigned to minimize waterspillage. Installation andhydraulic requirements aresimilar to the standard pressurevacuum breaker and thedevices are recommended forinternal use.


Hose bibb vacuum breaker

¾ inch thru 2 inches

2½ inches thru 10 inches

Spring

Gate Valve

Gate Valve

Test cock

Test cock

First check valve

FIGURE 18.Hose bibb vacuum breaker.

FIGURE 19.Typical installation of hose bibbvacuum breaker.

FIGURE 20.Pressure vacuum breaker

Double Check withIntermediateAtmospheric Vent

The need to provide a compactdevice in ½-inch and ¾-inchpipe sizes that protects againstmoderate hazards, is capable ofbeing used under constantpressure and that protectsagainst backpressure, resultedin this unique backflowpreventer. Construction isbasically a double check valvehaving an atmospheric ventlocated between the two checks(See Figure 22).

Line pressure keeps thevent closed, but zero supplypressure or backsiphonage willopen the inner chamber toatmosphere. With this device,extra protection is obtainedthrough the atmospheric ventcapability. Figure 23 shows atypical use of the device on aresidential boiler supply line.

Double Check Valve

A double check valve isessentially two single checkvalves coupled within one bodyand furnished with test cocksand two tightly closing gatevalves (See Figure 24).

The test capability featuregives this device a big advan-tage over the use of twoindependent check valves inthat it can be readily tested todetermine if either or bothcheck valves are inoperativeor fouled by debris. Each checkis spring loaded closed andrequires approximately a poundof pressure to open.

This spring loadingprovides the ability to “bite”through small debris and stillseal—a protection feature notprevalent in unloaded swingcheck valves. Figure 24 shows across section of double checkvalve complete with test cocks.Double checks are commonlyused to protect against low tomedium hazard installationssuch as food processing steamkettles and apartment projects.They may be used undercontinuous pressure and protectagainst both backsiphonage andbackpressure conditions.

CHAPTER FOUR • 19

Vent

2nd check1st check

Drain

Air gap

Automatic feed valveSupply

Return

Boiler

FIGURE 21.Typical agricultural andindustrial application ofpressure vacuum breaker.

FIGURE 22.Double check valve withatmospheric vent.

FIGURE 23.Typical residential use of doublecheck with atmospheric vent.

FIGURE 24.Double check valve.

At least 6"Process tanks

12" minimum abovethe highest outlet

Hose bibb

Double Check DetectorCheck

This device is an outgrowth ofthe double check valve and isprimarily utilized in fire lineinstallations. Its purpose is toprotect the potable supply linefrom possible contamination orpollution from fire line chemicaladditives, booster pump fireline backpressure, stagnant“black water” that sits in firelines over extended periods oftime, the addition of “raw”water through outside firepumper connections (Siameseoutlets), and the detection ofany water movement in the fireline water due to fire lineleakage or deliberate watertheft. It consists of two, springloaded check valves, a bypassassembly with water meter anddouble check valve, and twotightly closing gate valves. SeeFigure 25. The addition of testcocks makes the device testable

to insure proper operation ofboth the primary checks andthe bypass check valve. In theevent of very low fire line waterusage, (theft of water) the lowpressure drop inherent in thebypass system permits the lowflow of water to be meteredthrough the bypass system. In ahigh flow demand, associatedwith deluge fire capability, themain check valves open,permitting high volume, lowrestricted flow, through the twolarge spring loaded checkvalves.

Residential Dual Check

The need to furnish reliable andinexpensive backsiphonage andbackpressure protection forindividual residences resulted inthe debut of the residential dualcheck. Protection of the mainpotable supply from householdhazards such as home photo-graph chemicals, toxic insectand garden sprays, termitecontrol pesticides used byexterminators, etc., reinforced,a true need for such a device.Figure 26 shows a cutaway ofthe device.

It is sized for ½-, ¾-, and1-inch service lines and isinstalled immediately down-stream of the water meter. Theuse of plastic check modulesand elimination of test cocksand gate valves keeps the costreasonable while providinggood, dependable protection.Typical installations are shownin Figures 27 and 28.


Residentialdual check

Water meter

Water meter

1¼" meter thread female inlet with1" NPT thread female union outlet

FIGURE 25.Double check detector check.

FIGURE 26.Residential dual check.

FIGURE 27.Residential installation.

FIGURE 28.Copper horn.

100 psi 95 psi

Out 47 psi

50 psi

Supply 60 psi

94 psi

Reduced PressurePrinciple BackflowPreventer

Maximum protection isachieved against backsiphonageand backpressure conditionsutilizing reduced pressureprinciple backflow preventers.These devices are essentiallymodified double check valveswith an atmospheric ventcapability placed between thetwo checks and designed suchthat this “zone” between thetwo checks is always kept atleast two pounds less than thesupply pressure. With thisdesign criteria, the reducedpressure principle backflowpreventer can provide protec-tion against backsiphonage andbackpressure when both thefirst and second checks becomefouled. They can be used underconstant pressure and at highhazard installations. They arefurnished with test cocks andgate valves to enable testingand are available in sizes ¾-inchthrough 10 inch.

Figure 29A shows typicaldevices representative of ¾-inchthrough 2-inch size and Figure29B shows typical devicesrepresentative of 2½-inchthrough 10-inch sizes.

CHAPTER FOUR • 21

FIGURE 29A.Reduced pressure zone backflowpreventer (¾-inch thru 2-inches).

FIGURE 29B.Reduced pressure zone backflowpreventer (2½-inches thru 10-inches).

Relief valve (rotated 90˚ for clarity)

Reduced pressure zone1st check valve 2nd check valve

94 psi 93 psi100 psi


The principles of operationof a reduced pressure principlebackflow preventer are asfollows:

Flow from the left entersthe central chamber against thepressure exerted by the loadedcheck valve 1. The supplypressure is reduced thereuponby a predetermined amount.The pressure in the centralchamber is maintained lowerthan the incoming supplypressure through the operationof the relief valve 3, whichdischarges to the atmospherewhenever the central chamberpressure approaches within afew pounds of the inlet pres-sure. Check valve 2 is lightlyloaded to open with a pressuredrop of 1 psi in the direction offlow and is independent of thepressure required to open therelief valve. In the event that

the pressure increases down-stream from the device, tendingto reverse the direction of flow,check valve 2 closes, preventingbackflow. Because all valvesmay leak as a result of wear orobstruction, the protectionprovided by the check valves isnot considered sufficient. Ifsome obstruction preventscheck valve 2 from closingtightly, the leakage back intothe central chamber wouldincrease the pressure in thiszone, the relief valve wouldopen, and flow would bedischarged to the atmosphere.

When the supply pressuredrops to the minimum differen-tial required to operate therelief valve, the pressure in thecentral chamber should beatmospheric. If the inletpressure should become lessthan atmospheric pressure,

relief valve 3 should remainfully open to the atmosphere todischarge any water which maybe caused to backflow as aresult of backpressure andleakage of check valve 2.

Malfunctioning of one orboth of the check valves or reliefvalve should always be indi-cated by a discharge of waterfrom the relief port. Under nocircumstances should pluggingof the relief port be permittedbecause the device dependsupon an open port for safeoperation. The pressure lossthrough the device may beexpected to average between10 and 20 psi within thenormal range of operation,depending upon the size andflow rate of the device.

Reduced pressure principlebackflow preventers arecommonly installed on high

hazard installations such asplating plants, where theywould protect against primarilybacksiphonage potential, carwashes where they wouldprotect against backpressureconditions, and funeral parlors,hospital autopsy rooms, etc.The reduced pressure principlebackflow preventer forms thebackbone of cross-connectioncontrol programs. Since it isutilized to protect against highhazard installations, and sincehigh hazard installations are thefirst consideration in protectingpublic health and safety, thesedevices are installed in largequantities over a broad range ofplumbing and water worksinstallations. Figures 31 and 32show typical installations ofthese devices on high hazardinstallations.

Directionof flow

1 2

3

Reversed direction of flow

Reduced pressure principle backflow preventerWate

r main

Meter

Main

Reduced pressure principlebackflow preventer

FIGURE 30.Reduced pressure zone backflowpreventer — principle of operation.

FIGURE 31.Plating plant installation.

FIGURE 32.Car wash installation.

CHAPTER ONE • 23

FIGURE 33.Typical bypass configurationreduced pressure principledevices

FIGURE 34.Typical installation reducedpressure principle devicehorizontal illustration.

Typical fire line installation doublecheck valve vertical installation.

FIGURE 35.Typical installation reducedpressure principle device verticalillustration.

Reduced pressureprinciple device

Water meter

Note: Device to be set 12" minimum from wall.

Air gap

Drain 12" min. 30" max.


Water meter

Air gap

Elbow

Drain

Note: (1) Refer to manufacturers installation data for vertical mount.(2) Unit to be set at a height to permit ready access for testing and service.(3) Vertical installation only to be used if horizontal installation cannot be achieved.

Reduced pressure principle device

Note: Devices to be set a min. of 12" and a max. of 30" from the floor and 12" from any wall.


Air gap

Drain

Air gap

Drain

Double checkvalve

Alarm check

Grade

OS&Y gate valve

Fire pipe

Siamesecheck

Siamesefitting


FIGURE 36.Typical installation double checkvalve horizontal and verticalinstallation.

FIGURE 37.Typical installation residential dualcheck with straight set andcopperhorn.

Note: Vertical installation only to be used if horizontal installation cannot be achieved.

Double check valve

Double check valve

(unit to be set at a heightthat permits ready accessfor testing and service)

Water meter

Copperhorn with water meter

12" min. 30" max.

Residential dualcheck valve

Residentialdual check

¾" ball valve

¾" ball valve

¾" K-copper

Water meter

Copperhorn with water meter

Chapter Five

Prior to initiating a test ofany backflow device, it isrecommended that the follow-ing procedures be followed:

1. Permission be obtained fromthe owner, or his representative,to shut down the water supply.This is necessary to insure thatsince all testing is accomplishedunder no-flow conditions, theowner is aware that his watersupply will be temporarily shutoff while the testing is beingperformed. Some commercialand industrial operationsrequire constant and uninter-rupted water supplies forcooling, boiler feed, seal pumpwater, etc. and water serviceinterruption cannot be tolerat-ed. The water supply tohospitals and continuousprocess industries cannot beshut off without planned andcoordinated shut downs. Therequest to shut down the watersupply is therefore a necessaryprerequisite to protect thecustomer as well as limit theliability of the tester.

Concurrent with therequest for permission to shutoff the water, it is advisable topoint out to the owner, or hisrepresentative, that while thewater is shut off during the testperiod, any inadvertent use ofwater within the building willreduce the water pressure tozero. Backsiphonage couldresult if unprotected cross-

connections existed whichwould contaminate the buildingwater supply system. In orderto address this situation, it isrecommended that the ownercaution the inhabitants of thebuilding not to use the wateruntil the backflow test iscompleted and the waterpressure restored. Additionaloptions available to the buildingowner would be the installationof two backflow devices inparallel that would enable aprotected bypass flow aroundthe device to be tested. Also, ifall water outlets are protectedwithin the building with“fixture outlet protection”backflow devices, cross-connections would not create aproblem in the event ofpotential backsiphonageconditions occurring whiledevices are tested, or for anyother reason.2. Determine the type of deviceto be tested i.e., double checkvalve or reduced pressureprinciple device.3. Determine the flow direc-tion. (Reference directional flowarrows or wording provided bythe manufacturer on thedevice.)4. Number the test cocks, bleedthem of potential debris, andassemble appropriate test cockadapters and bushings that maybe required.

5. Shut off the downstream(number 2) shut-off valve. (Ref.Item (1) above.)6. Wait several moments priorto hooking up the test kit hoseswhen testing a reduced pressureprinciple device. If water exitsthe relief valve, in all likelihood,the first check valve is fouledand it is impractical to proceedwith the testing until the valveis serviced. This waiting periodis not necessary when testingdouble check valves.7. Hook up the test kit hoses inthe manner appropriate to thedevice being tested and thespecific test being performed.

Test personnel are cau-tioned to be aware and followlocal municipal, county, andstate tes

Documents

An Engineer's Guide to Plumbing Cross- Connections · 2012. 5. 29. · PDHonline Course M108 (3 PDH) An Engineer's Guide to Plumbing Cross-Connections 2012 Instructor: Randall W