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C r o s s - C o n n e c t i o n C o n t r o l H a n d b o o k

B AC K F L O W PREVENTION

F-F-CCCH.qxd 7/9/07 1:58 PM

Man has long recognized theneed for pure drinking water,but only in the last 50 or 60years has there been any realeffort to prevent contaminationcaused by cross-connections.

Although double check valvescame into use around the turnof the century to isolate firemains and industrial water linesfrom the potable water supply,little interest was shown in theindividual treatment of plumb-ing fixtures.

In 1929 the major breakthroughcame when a device consistingof two check valves with arelief valve between them wassuccessfully tested in Danville,Illinois. However, this valve wasnot produced commercially andit was not until the late 1930’sthat the real development ofeffective vacuum breakers andbackflow preventers took place.

It was in this period that ordi-nances for cross-connectioncontrol began to be enforced.The Safe DrinkingWater Act, signed into law byPresident Ford, placed moreemphasis on the responsibilityfor drinking water protection.The need for cross-connection

control exists in all types ofpremises, whether industrial orresidential. Backflow preventiondevices help protect the publicsafety by preventing potablewater contamination in suchcritical areas as municipalwater systems, food processingplants, medical and dentalwater supplies, and manyindustrial applications.

Contents

Page

Backflow — What is it? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Case Histories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 3

Typical Cross-Connections . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 5

Backflow Prevention Devices . . . . . . . . . . . . . . . . . . . . . . . . . . 6

How Backflow Prevention Devices Work . . . . . . . . . . . . . . . . . 7

Device Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 9

Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

A Brief History ofCross-ConnectionControl

Bibliography“Cross-Connection ControlManual” (EPA-570/9-89-007)U.S. Environmental ProtectionAgency, Water Supply Division,Washington D.C. (1973)

Recommended Practice forBackflow Prevention andCross-Connection Control,AWWA M14, American WaterWorks Association, Denver,CO, 1990.

“Manual of Cross-ConnectionControl,” Foundation forCross-Connection Control andHydraulic Research, Universityof Southern California;Los Angeles, Calif. 90007

American Society of SanitaryEngineering (ASSE), ProfessionalQualification Standards,Backflow Prevention Assemblies- Series 5000, Bay Village,Ohio.

Canadian Standards Association,Manual for Selection,Installation, and Field Testing,CAN/CSA-B64.10-94

An informative booklet, for thepurpose of a better disseminationof the facts about potential hazards to public health throughbackflow contamination.

Copyright 1997


Backflow…What is it?

Backflow? You may have heardof it, and you may understandsome of what it involves. Thisbooklet will help you to under-stand it better; exactly what itis, and how to prevent it.

Backflow is the undesirablereversal of the flow of water ormixtures of water and otherundesirable substances fromany source (such as usedwater, industrial fluids, gasses,or any substance other than theintended potable water) intothe distribution pipes of thepotable water system. Thereare two types of backflow con-ditions: backpressure andbacksiphonage.

Backpressure: Occurs whenthe user system is at a higherpressure than the supply watersystems allowing undesirablesubstances to be “pushed”back into the potable watersystem. Some causes are:booster pumps, potable watersystem connections for boilers,interconnection with other pip-ing systems operating at higherpressures, or higher elevationsin user systems such as high-rise buildings.

One specific example of thiswould be a steam heating sys-tem with the make-up waterline piped directly into the boil-er. The higher pressure in theboiler could force the chemical-ly treated boiler water backthrough the make-up water lineand into the potable water sys-tem.

Backsiphonage: Occurs whennegative or reduced pressureexists in the supply pipingallowing undesirable sub-stances to be “drawn” into thepotable water supply. Somecauses are:undersized supply piping, sup-

ply line breaks, reduced supplysystem pressure on the suctionside of an on-line boosterpump, or sudden upstreamhigh demand. An example ofthis is a child drinking milk witha straw. The child “sucks” onthe straw and the milk flows upthe straw and into the child’smouth. What the child is actu-ally doing is creating a subat-mospheric pressure in hismouth and the atmosphericpressure (14.7psia at sea level)is pushing down on the surfaceof the milk and forcing the milkup the straw and into thechild’s mouth.

There is one other very impor-tant term that must be under-stood before we can proceed.The term is “Cross-Connection,”and it is defined as any actualor potential connectionbetween a potable water sys-tem and any other source orsystem through which it is pos-sible to introduce into thepotable system any used water,industrial fluid, gas, or othersubstance other than theintended potable water withwhich the system is supplied.By-pass arrangements, jumperconnections, removable sec-tions, swivel or change-overdevices and other permanentor temporary devices throughwhich, or because of which,backflow can or may occurare considered to be cross-connections.

City Water

Boiler

Make-UpWater Line

1


“All of this is very interesting,but does it REALLY happen?”you may ask. The answer tothat is an emphatic YES! Beloware listed some typical cases ofbackflow that actuallyoccurred.

Case No. 1The year was 1933. Peoplefrom all over the world werecrowding into one of America’slargest cities to see the“World’s Fair.” An epidemic ofAmoebic Dysentery broke outand official records show that98 people died and 1,409 oth-ers became seriously ill.Hundreds, possibly thousandsof other affected people werenever counted by investigatingagencies since when theybecame ill, they went home. Aspecial investigating committeeof public health authoritiesfound the main reason of thiscatastrophe to be “…old andgenerally defective plumbingand cross-connections poten-tially permitting backsiphonagefrom fixtures, such as bathtubsand toilets…”

Case No. 2In December, 1964, a hospitalin the State of Michigan had itspotable water system contami-nated. The cause was anunprotected autopsy table inthe hospital’s morgue.

Case No. 3It was in July of 1955 in SanPedro, California, a U.S. NavyDestroyer pumped salt waterthrough five obsolete checkvalves into the street mains in a90 square block of the town.

Case No. 4This unusual death was causedby backsiphonage in a suburbof one of California’s largestcities. A man was spraying hislawn with a commercial weedkiller that contained an arseniccompound. His applicator wasan aspirator device on his gar-den hose, to which wasattached a bottle of the arsenicpoison. When he had finishedspraying, the man turned offthe hose, disconnected theapplicator, and since it was awarm day, turned the hose onagain to get a drink of water. Ashort time later, he was deadfrom arsenic poisoning. Atsome time while he was spray-ing, a backsiphonage conditionhad occurred and the arsenicwas carried back into the hose.

Case No. 5In 1969 in Utah, raw irrigationwater was pumped through afarm standby irrigation connec-tion into over half of the entiretown’s potable water system.The standby connection wasnot protected with a backflowprevention device.

Case Histories

City Main

PumpIrrigation

Water

2


Case No. 6In August, 1969, 83 footballteam members and coachingstaff were stricken with infec-tious hepatitis due to subsur-face hose bibs and a nearbyfire. The fire trucks in fightingthe fire reduced the main pres-sure enough to cause back-siphonage from the hose bibs.

Case No. 7In the summer of 1970 in NewJersey, a soft drink vendingmachine in the Caddy house ofa golf club was connected tothe building heating system inwhich hexavalent chromiumhad been added. Eleven casesof nausea were reported by thecaddies.

Case Histories

City Main

Heating SystemLine Treated with a

Hexavalent Chromium

3


Spray Hose in Sink This type of cross-connectionis commonly found in the foodindustry and in janitor’s sinks. Ahose has been connected tothe faucet on the sink. Whenthe faucet is left running, a lossin pressure of the supply maincan siphon this used waterback into the potablewater system.

Submerged InletsIn many industrial installationsthat use chemically treatedbaths, the make-up water lineruns directly into the tank. Ifthere is backsiphonage, thetoxic chemicals can be suckedback into the potablewater system.

Hose BibsAt first glance, a hose bibseems innocuous, but it is thethings people do with the hosethat creates problems. In thisexample, a man is trying toblow a stoppage out in a sewerline, but with a sudden drop inline pressure, this contaminatedwater can be backsiphonedinto the potable water system.

TypicalCross-Connections

PotableWater Line

Make-UpWater Line

HNO3 Solution

4


Lawn SprinklersOn a large number of lawnsprinkler installations, thesprinkler head is below theground level. Water which mayhave been in contact with fertil-izers and weed killers can thenbe backsiphoned through aleaky valve into the potablewater system.

IrrigationPumping SystemsOn many farms water ispumped from irrigation waterchannels into the sprinkler sys-tem. A large number of theseinstallations are also connectedto the domestic water systemfor times when there is little orno irrigation water available. Itis possible that the pumpdevelops more pressure thanthere is in the domestic supplymain and the irrigation watercan then be pumped througha leaky or partially opencrossover valve.

Fire Sprinkler SystemsOn a large number of fire sprin-kler systems, there is a hookup connection for the fire truckpumper to increase pressureand flow in the sprinklersystem. At times a “wettingagent” is added to the waterto increase the effectivenessof the water in combating thefire. If the system is not pro-tected, it is possible for thepumper to pump this “wet”water back into the city’sdomestic water supply.

TypicalCross-Connections

City Main

City Main

5

Pump

IrrigationWater


There are several differenttypes of mechanical backflowprevention device. An alterna-tive to a mechanical device, isa physical separation, or airgap. The air gap is a physicalbreak in the system. The differ-ent types, of mechanicaldevice, are used in different sit-uations (if there is backpres-sure or backsiphonage) and fordifferent degrees of hazard.

The degree of hazard is basedon the fluid (or other substance)that may backflow into thesupply piping system. The fluidmay be toxic or nontoxic andcould create a “non-health” or“health” hazard.

A non-health (non-toxic) hazardcross-connection is any pointon a water supply systemwhere a polluting substancemay come in contact withpotable water aestheticallyaffecting the taste, odor orappearance of the water, butnot hazardous to health.

A health hazard (toxic) cross-connection is any point on awater supply system where acontaminating substance maycome in contact with potablewater creating an actual healthhazard, causing sickness ordeath.

Double CheckValve Assembly (DC)The double check valve assem-bly (DC) is composed of twosingle, independently actingcheck valves. The unit also hastwo tightly closing, resilientseated, shutoff valves locatedat each end of the device andfour test cocks for the testingof the check valves.

Reduced PressurePrincipal Assembly (RP)Commonly referred to as an RPor RPP, this device consists oftwo independently actingcheck valves, together with anautomatically operating pres-sure differential relief valvelocated between the two checkvalves. The first check valvereduces the supply pressure ata predetermined amount sothat during normal flow, and atcessation of normal flow thepressure between the twocheck valves shall be lowerthan the supply pressure. Ifeither check valve leaks, therelief valve will discharge toatmosphere. This will maintainthe pressure in the zonebetween the two check valveslower than the supply pressure.The unit also has two, resilientseated, shutoff valves (oneupstream and one downstreamof the checks) and properlylocated test cocks for fieldtesting.

Pressure VacuumBreaker (PVB)The pressure vacuum breaker(PVB) is a device that containswithin a single body, a singleloaded check valve and aloaded air opening valve whichopens to admit air wheneverthe pressure within the body ofthe device approaches atmos-pheric. The device has twotight closing, resilient seated,shut-off valves, and it is fittedwith test cocks, appropriatelyplaced, for testing the device.

Dual Check Valve (DuC)The dual check (DuC) is adevice which has two single,independent acting checkvalves in series. It does nothave any testcocks and is gen-erally not field tested.

Dual Check withAtmospheric Port (DCAP)This device has two independ-ent acting check valves witha relief valve located betweenthe checks. The device is nottestable and should only beused for lower degreesof hazard.

Atmospheric VacuumBreaker (AVB)An atmospheric vacuum break-er (AVB) is a device which hasa moving element inside, whichduring flow prevents waterfrom spilling from the deviceand during cessation of flow,drops down to provide a ventopening. This device shouldnot remain under pressure forlong durations, and it cannothave any shutoff valve down-stream of it.

Air GapAn air gap is a physical separa-tion between the free flowingdischarge end of a potablepipe line and an open or non-pressure receiving vessel. Tohave an acceptable air gap, theend of the discharge pipe hasto be at least twice the diame-ter of the pipe above the top-most rim of the receiving ves-sel, but in no case can this dis-tance be less than one inch.

This may seem to be the sim-plest, most effective and leastexpensive type of protection.However, the chance for futurecross-connections, the cost ofadditional pumps to pressurizethe system often makes this anexpensive protection system.

Backflow PreventionDevices

6


This figure shows an RP deviceduring a backsiphonage condi-tion. If you will notice, bothchecks are closed tight and thepressure differential relief valveis discharging to atmosphere.This is due to the fact that therelief valve is designed to main-tain a lower pressure in thezone between the two checkvalves than the supply pres-sure.

In this figure of an RP device,there is a backpressure condi-tion. The second check isfouled with a piece of pipescale which permits the higherpressure to flow back into thezone. Here the relief valve dis-charges the water to atmos-phere maintaining the pressurein the zone lower than the sup-ply pressure.

In this view of a pressure vacu-um breaker, a backsiphonagecondition has caused the checkto close against its seat and theair-inlet has opened so that thepressure in the body of thedevice is atmospheric. If thecheck was fouled by some for-eign material, only air would bepulled back into the domesticsupply system instead of thenon-potable water downstreamof the device.

In this view of a double checkvalve, there is backpressurefrom a source downstreamwhich has caused the secondcheck to close tightly againstthis reverse pressure. The firstcheck has closed tightly byitself, thus giving two barriersagainst the backflow condition.

How Backflow PreventionDevices Work

In this picture of an atmosphericvacuum breaker, a back-siphonage condition exists. Thiscondition has caused thecheck-float to drop away fromthe air-inlet and seat on thecheck seat, which prevents thenon-potable water from beingbacksiphoned. If the check-float did not seat properly, againonly air would be sucked backinto the domestic water system.

97psi

100psi 105psi

100psi 105psi

80psi 92psi

7


Device Selection Installation

Having a device on the connec-tion is not enough, the deviceMUST be installed correctly. Thefollowing details and illustrationswill help you in the properinstallation of the devices.

Reduced PressureDevice In these figures, the RP deviceis shown on the service connec-tion. The RP can also be usedfor internal protection. The mini-mum clearance of 12" abovethe floor or grade is to ensurean air gap between the reliefvalve and any water that mightpuddle beneath the device. Themaximum height is so that thedevice will be easy to work onduring testing and maintenance.If the device is in a protectiveenclosure or mounted against awall, the minimum distances areso that the device can be testedand maintained.

RP - Reduced Pressure Assembly

DC - Double Check Assembly

PVB - Pressure Vacuum Breaker

AVB - Atmospheric Vacuum Breaker

DuC - Dual Check

DCAP - Dual Check with Atmospheric Port

The selection of the propertype of device is important.Depending upon the fluid thatcan backflow, whether it istoxic or non-toxic; and whetherthere can be backpressure orbacksiphonage; it will governthe type of device selected. Thefollowing chart will help youto decide what type of deviceto use.

Side View

ProtectiveEnclosure

30" Max12" Min

12" Min

Water Meter

Water MeterTop View

24" Min

RP DC PVB AVB DuC DCAP

ContinuousPressure � � � � �

PossibleBack-pressure

� � � �

PossibleBack-siphonage

� � � � � �

Nontoxic � � � � � �

Toxic � � �

8


Installation Testing

Double Check ValveIn these figures, the doublecheck assembly is shown onthe service connection, it canalso be used for internal pro-tection as well. The minimumand the maximum distancesare the same as they are for the RP device.

Dual CheckThe dual check is usuallyinstalled immediately down-stream of the water meter inresidential installations (notshown).

Pressure VacuumBreakerThe pressure vacuum breakercannot be installed where therecan be backpressure. It shouldonly be used where there maybe backsiphonage. The pres-sure vacuum breaker can haveshutoff valves downstream ofthe device. The PVB must beinstalled at least 12" above thehighest outlet or, if it is feedingan open tank, at least 12"above the highest overflow rimof the tank. The following figureshows a typical installation on asprinkler system.

Atmospheric VacuumBreakerJust as the pressure vacuumbreaker, the atmospheric vacu-um breaker cannot be installedwhere there can be backpres-sure, only where there can bebacksiphonage. The atmos-pheric vacuum breaker cannothave any shutoff valves down-stream of it. It also must beinstalled at least 6" above thehighest outlet or the topmostoverflow rim of a nonpressuretank. The following illustrationshows the AVB on a sprinklersystem.

All mechanical devices shouldbe inspected on a regular basisto ensure they are working cor-rectly. Pressure vacuum break-ers, double check and reducedpressure principle assembliesshould be tested at time of ini-tial installation and annuallythereafter. Acceptable test pro-cedures are published by TheUniversity of SouthernCalifornia (USC), The AmericanWater Works Association(AWWA), The American Societyof Sanitary Engineering (ASSESeries 5000), and The CanadianStandards Association(CAN/CSA B64.10). Please con-sult the regulatory authority inyour area for more specificinformation.

Side View

ProtectiveEnclosure

30" Max12" Min

12" Min

Water Meter

Water Meter

Top View

Flow

Hose Bib

24" Min

12" Minimum AboveHighest Outlet

NOTE: Unit Cannot Have AnyShutoff Downstream of it

Flow

6" Minimum AboveHighest Outlet

9


F-F-CCCH 0629 © FEBCO, 2007

A Division of Watts Water Technologies, Inc. USA: 4381 N. Brawley • Ste. 102 • Fresno, CA • 93722 • Tel. (559) 441-5300 • Fax: (559) 441-5301 • www.FEBCOonline.comCanada: 5435 North Service Rd. • Burlington, ONT. • L7L 5H7 • Tel. (905) 332-4090 • Fax: (905) 332-7068 • www.FEBCOonline.ca


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