22 Backflow Prevention Practice Questions & Answers

1. 1. Backflow is the reversal of flow that carries non-potable water into the potable supply. Which pair of conditions accounts for every occurrence of backflow?

   • A.Backsiphonage and thermal expansion
   • B.Water hammer and a failed regulator
   • C.Backpressure and water hammer
   • D.Backsiphonage and backpressure✓ Answer

   There are exactly two mechanisms. In backsiphonage, pressure on the supply side falls below atmospheric and the vacuum pulls water backward through the cross-connection. In backpressure, pressure downstream of the connection rises above supply pressure and pushes water backward. Water hammer and thermal expansion can help create a pressure condition, but they are not separate backflow mechanisms.

   Source: USC FCCCHR Manual of Cross-Connection Control — causes of backflow; Irrigation Association Certified Irrigation Technician content outline, Backflow FunctionalityReport a problem with this question

2. 2. A water main breaks two blocks upstream while a landscape irrigation system is running, and pressure in the street main falls below atmospheric. Water in the laterals begins moving back toward the meter. Which mechanism is at work, and what produced it?

   • A.Backpressure, produced by air entering the broken main
   • B.Backsiphonage, produced by the zone valve closing too quickly
   • C.Backsiphonage, produced by negative pressure on the supply side✓ Answer
   • D.Backpressure, produced by the loss of supply pressure at the meter

   A break, a hydrant flowing for fire service or any high-rate withdrawal can drop supply pressure below atmospheric, and the resulting vacuum siphons water out of the downstream system. Backsiphonage is defined by that negative supply-side pressure; nothing downstream has to be pressurized for it to occur.

   Source: AWWA M14, Backflow Prevention and Cross-Connection Control — backsiphonageReport a problem with this question

3. 3. A zone sits 30 ft above the point of connection and the mainline stays full when the supply is shut off for a repair. Using 0.433 psi per foot of elevation, that column pushes about 13 psi back toward the point of connection. What condition is this, and what does it rule out?

   • A.Backpressure, and it makes an atmospheric vacuum breaker suitable
   • B.Backsiphonage, and it rules out a double check assembly
   • C.Backsiphonage, and it rules out a reduced pressure assembly
   • D.Backpressure, and it rules out vacuum-breaker-type devices✓ Answer

   Elevation head downstream of the point of connection is a source of backpressure: the standing column pushes water back toward the supply whenever supply pressure falls below it. Vacuum-breaker-type protection, whether atmospheric, pressure type or spill resistant, works only against backsiphonage, so wherever backpressure is possible the choice narrows to a double check assembly for a low hazard or a reduced pressure assembly for a high hazard.

   Source: AWWA M14, Backflow Prevention and Cross-Connection Control — backpressure from elevation head; Irrigation Association Basic Irrigation HydraulicsReport a problem with this question

4. 4. A landscape system is fed from the potable main, has a booster pump downstream of the point of connection, and the water purveyor classifies landscape irrigation as a health hazard. Which assembly satisfies both of those conditions?

   • A.A pressure vacuum breaker assembly, set above the highest outlet
   • B.A double check valve assembly, installed after the isolation valve
   • C.A reduced pressure principle assembly, installed above final grade✓ Answer
   • D.An atmospheric vacuum breaker on each zone, after the zone valve

   Run the two axes. The booster pump can raise downstream pressure above supply pressure, so backpressure is possible and every vacuum-breaker type is eliminated. The purveyor's health-hazard classification then eliminates the double check assembly, which handles backpressure but is limited to low hazard. Only the reduced pressure principle assembly covers both mechanisms at a high hazard.

   Source: ASSE 1013, Reduced Pressure Principle Backflow Prevention Assembly; USC FCCCHR Manual of Cross-Connection Control — assembly selectionReport a problem with this question

5. 5. Cross-connection control classifies hazards by degree. Which of these is a high-hazard (contaminant) condition rather than a low-hazard (pollutant) one?

   • A.Water discolored by rust picked up from a fitting
   • B.Water warmed by sitting in exposed above-ground pipe
   • C.Water in a lateral that has taken on a musty odor
   • D.Water carrying injected fertilizer through the mainline✓ Answer

   A contaminant is anything that could cause illness or death if it reached the potable supply, and any injected chemical, reclaimed water or auxiliary supply falls in that class unconditionally. A pollutant only impairs the water aesthetically, changing its taste, odor, color or temperature without threatening health.

   Source: USC FCCCHR Manual of Cross-Connection Control — degree of hazard, pollutant versus contaminantReport a problem with this question

6. 6. Why do water purveyors commonly treat an ordinary lawn irrigation system with no chemical injection as a threat to the potable supply?

   • A.Sprinkler nozzles atomize water and strip its disinfectant
   • B.Polyethylene lateral pipe leaches solvent into the water
   • C.Zone valves hold water at a temperature that breeds algae
   • D.Heads sit in soil and ponded water that carries bacteria✓ Answer

   Buried heads and drained laterals stand in soil, and heads in a low spot can be submerged in ponded water carrying soil bacteria and animal waste. If the supply loses pressure, that water is the first thing drawn back through the connection, which is why irrigation seldom qualifies for low-hazard treatment even without chemicals.

   Source: AWWA M14, Backflow Prevention and Cross-Connection Control — hazard assessment of lawn irrigation systemsReport a problem with this question

7. 7. What makes a properly installed air gap the most reliable form of backflow protection, and what does it cost the system?

   • A.It stops backpressure only, and must be tested by a certified tester
   • B.It stops both mechanisms with no moving parts, but leaves no pressure✓ Answer
   • C.It stops both mechanisms, but must be rebuilt after each hard freeze
   • D.It stops backsiphonage only, and adds heavy friction loss downstream

   An air gap is a physical vertical separation between the supply outlet and the flood-level rim of the receiving vessel, so there is no continuous water path back to the main and no check, spring or poppet that can foul. Its cost is that it destroys line pressure, so a system fed through an air gap needs a reservoir and a booster pump.

   Source: USC FCCCHR Manual of Cross-Connection Control — air gap as the benchmark methodReport a problem with this question

8. 8. A code requires an air gap of at least twice the diameter of the effective opening and never less than 1 inch. The supply pipe discharging into a reservoir has a 3/8 in. effective opening. What vertical gap is required?

   • A.1-1/2 in., four times the opening size
   • B.1 in., the absolute minimum the rule sets✓ Answer
   • C.3/4 in., twice the opening diameter
   • D.3/8 in., equal to the opening size

   Twice a 3/8 in. opening is only 3/4 in., which is below the floor the rule states, so the floor governs and the gap must be 1 in. Both parts of the rule apply at once and the larger of the two results is the requirement.

   Source: USC FCCCHR Manual of Cross-Connection Control — air gap sizing rule as supplied in the stemReport a problem with this question

9. 9. A technician installs a shutoff valve downstream of an atmospheric vacuum breaker so that a zone can be isolated. What is the consequence for the device?

   • A.The device begins protecting against backpressure as well
   • B.The device stays pressurized and its poppet cannot vent✓ Answer
   • C.The device becomes field-testable once shutoffs are present
   • D.The device vents constantly and floods the valve box with water

   An atmospheric vacuum breaker vents only when line pressure is released, so it must not be held under continuous pressure. A closed valve anywhere downstream traps pressure against the poppet, which sticks in the sealed position and cannot open to admit air, and the device silently stops protecting. This is why no valve of any kind may be installed downstream of one.

   Source: ASSE 1001, Atmospheric Type Vacuum Breakers — no downstream valves, not for continuous pressureReport a problem with this question

10. 10. In an irrigation system that relies on atmospheric vacuum breakers for backflow protection, where does each one belong?

    • A.Downstream of the zone valve, one on each zone it serves✓ Answer
    • B.Downstream of the mainline, one for every two zones
    • C.Upstream of the meter, ahead of the main isolation valve
    • D.Upstream of all zone valves, one for the whole system

    Because no valve may sit downstream of an atmospheric vacuum breaker, it cannot be placed at the point of connection ahead of the zone valves. Each one goes downstream of the control valve for the zone it protects, which means one per zone, and an anti-siphon valve simply combines that device and the zone valve in one body.

    Source: ASSE 1001, Atmospheric Type Vacuum Breakers; Irrigation Association, Landscape Irrigation Systems Installation and Maintenance — anti-siphon valve installationReport a problem with this question

11. 11. A pressure vacuum breaker assembly is proposed for a landscape irrigation service. Which statement describes its correct application?

    • A.Approved for low or high hazard, but only where backpressure is absent✓ Answer
    • B.Approved for low or high hazard, including where backpressure occurs
    • C.Approved for low hazard only, and also where backpressure occurs
    • D.Approved for low hazard only, and only where backpressure is impossible

    Hazard level and backflow mechanism are separate axes, and candidates routinely reverse this pairing. A pressure vacuum breaker has a spring-loaded air inlet and one check, so it may stand under continuous pressure with valves downstream and is accepted at low or high hazard, but it can only relieve a vacuum and offers no protection at all against backpressure.

    Source: ASSE 1020, Pressure Vacuum Breaker AssemblyReport a problem with this question

12. 12. A double check valve assembly has two independently acting spring-loaded check valves and two resilient-seated shutoffs. What is its correct application?

    • A.Backsiphonage and backpressure alike, but at low hazard only✓ Answer
    • B.Backsiphonage only, at low or high hazard, under continuous pressure
    • C.Backpressure only, at high hazard, and with no valves downstream
    • D.Backsiphonage and backpressure, at low or high hazard alike

    Two checks in series will hold against a vacuum upstream and against pressure pushing from downstream, so the assembly covers both mechanisms and may stay under continuous pressure. What it cannot do is relieve to atmosphere, so a leaking first check leaves only one barrier and no warning, which is why its approval stops at low hazard. It is the mirror image of the pressure vacuum breaker.

    Source: ASSE 1015, Double Check Valve Backflow Prevention AssemblyReport a problem with this question

13. 13. A landscape system will inject liquid fertilizer into the mainline. What backflow protection is required, and where does it go?

    • A.A reduced pressure principle assembly, upstream of the injection point✓ Answer
    • B.A double check valve assembly, placed downstream of the injection point
    • C.A pressure vacuum breaker, placed downstream of the injection point
    • D.An atmospheric vacuum breaker per zone, upstream of the injection point

    Introducing any chemical makes the system a health hazard without qualification, and an injection pump can also generate backpressure, so only the reduced pressure principle assembly qualifies. It must sit between the potable supply and the injection point, because protection placed downstream of where the chemical enters leaves the mainline and the service unprotected.

    Source: ASSE 1013, Reduced Pressure Principle Backflow Prevention Assembly; International Plumbing Code Section 608, protection where chemicals are introduced into an irrigation systemReport a problem with this question

14. 14. A specification calls for a pressure vacuum breaker to stand at least 12 in. above a reference elevation. On a sloping site where several heads sit on a berm, that reference elevation is taken from what?

    • A.The top of the water meter at the connection
    • B.Final grade directly beneath the assembly body
    • C.The highest downstream outlet and piping it protects✓ Answer
    • D.The flood-level rim of the nearest valve box

    The rise exists so that atmospheric pressure entering the air inlet can break any siphon in the piping below it, which only works if the inlet is above everything it protects. Measuring from grade or from the assembly's own inlet is the common field error, and a head on a berm or a drip line up a slope resets the reference to that higher point.

    Source: ASSE 1020, Pressure Vacuum Breaker Assembly — elevation above the highest downstream outletReport a problem with this question

15. 15. How does a spill-resistant vacuum breaker assembly differ from a pressure vacuum breaker assembly?

    • A.It removes the need for shutoffs and test cocks entirely
    • B.It may be installed below the outlets that it protects
    • C.It holds water back from the air inlet, allowing indoor use✓ Answer
    • D.It adds backpressure protection to the vacuum breaker design

    The spill-resistant design keeps the air inlet from discharging water on start-up, so the assembly can be used indoors or over finished surfaces where a pressure vacuum breaker's spillage would be unacceptable. Everything else is unchanged: it is still a backsiphonage-only assembly, still accepted at low or high hazard, and still has to stand above the highest downstream outlet.

    Source: ASSE 1056, Spill-Resistant Vacuum Breaker AssemblyReport a problem with this question

16. 16. In construction, what distinguishes a reduced pressure principle assembly from a double check valve assembly?

    • A.An air inlet that opens to atmosphere on the inlet side
    • B.A third spring-loaded check valve downstream of the second
    • C.A differential relief valve between the two check valves✓ Answer
    • D.A pressure regulator that limits the zone between the checks

    Both assemblies use two independent checks, but the reduced pressure type adds a hydraulically operated relief valve that holds the zone between them below inlet pressure. If either check leaks, the relief valve dumps the intermediate zone to atmosphere rather than letting water pass toward the supply, which is what earns the assembly its high-hazard rating.

    Source: ASSE 1013, Reduced Pressure Principle Backflow Prevention Assembly — differential pressure relief valveReport a problem with this question

17. 17. The relief port of a reduced pressure principle assembly on an irrigation service is discharging steadily rather than dripping intermittently. What should the technician conclude?

    • A.The downstream zone valves are closing faster than the checks
    • B.The first check valve is fouled or leaking and needs service✓ Answer
    • C.The relief valve spring was set too high at the factory
    • D.Normal operation whenever supply pressure fluctuates during the day

    The relief valve opens when the differential across the first check falls too low, so a brief drip during a pressure swing is normal and expected. Continuous discharge means the first check is no longer holding its differential, usually because debris is sitting on the seat, and the assembly needs to be serviced rather than watched.

    Source: USC FCCCHR Manual of Cross-Connection Control; AWWA M14 — field troubleshooting of reduced pressure assembliesReport a problem with this question

18. 18. Why must a reduced pressure principle assembly be installed above grade and never in a pit or a spot that can flood?

    • A.Below grade the certified tester cannot physically reach it
    • B.Submerging the body voids the annual test the purveyor requires
    • C.Below grade the constant damp weakens the two check springs
    • D.Submerging the relief port makes the assembly a cross-connection✓ Answer

    The assembly depends on the relief port discharging freely to atmosphere. If flood water covers that port, the port becomes a submerged inlet, and dirty water can be drawn into the reduced pressure zone and past a leaking check, so the safety feature turns into the very hazard it exists to prevent.

    Source: USC FCCCHR Manual of Cross-Connection Control — reduced pressure assembly installation above grade, relief port never submergedReport a problem with this question

19. 19. What physically distinguishes a backflow prevention assembly from a backflow prevention device?

    • A.An assembly carries an air inlet, so it vents to the atmosphere
    • B.An assembly is set at the point of connection, a device is not
    • C.An assembly has a bronze body, while a device has a plastic body
    • D.An assembly carries two shutoffs and test cocks, so it can be tested✓ Answer

    An assembly is built with two resilient-seated shutoffs and test cocks so a tester can isolate it and read the pressure differential across each internal component in the field. A device such as an atmospheric vacuum breaker, a hose-bibb vacuum breaker or a dual check has no such fittings, so its condition can only be judged by inspection or by replacing it.

    Source: AWWA M14, Backflow Prevention and Cross-Connection Control — assemblies versus devicesReport a problem with this question

20. 20. Under a typical cross-connection control program, when must a testable backflow assembly be tested, and by whom?

    • A.Every fifth year, by an inspector working for the water purveyor
    • B.At installation, after any repair and every year, by a certified tester✓ Answer
    • C.Only after a repair or relocation, by a licensed plumbing contractor
    • D.At installation and after any repair, by the technician who installed it

    An assembly can fail silently, since a fouled check gives no outward sign on a double check and only a drip on a reduced pressure assembly, so its condition has to be proved by gauge test rather than assumed. Programs therefore call for a test at installation, after any repair or relocation, and at least annually by a tester the authority has certified, with the result reported to the purveyor.

    Source: AWWA M14, Backflow Prevention and Cross-Connection Control — testing at installation, after repair or relocation, and annually by a certified testerReport a problem with this question

21. 21. A technician is winterizing a system in a freezing climate. How should the backflow assembly itself be handled?

    • A.Open the test cocks, set both shutoffs part open, and drain it✓ Answer
    • B.Close both shutoffs fully and cap the relief port against ice
    • C.Leave both shutoffs wide open and let the mainline drain past
    • D.Wrap the assembly in insulation and leave it under pressure

    Water trapped in the body, the check chambers and the test cock passages will freeze and split the bonnet, which is the classic spring start-up callback. Partly opening both shutoffs and opening the test cocks lets every internal cavity drain and vent. Insulation may be added, but the relief port of a reduced pressure assembly and the air inlet of a vacuum breaker must never be sealed shut.

    Source: Irrigation Association, Landscape Irrigation Systems Installation and Maintenance — winterization of backflow assembliesReport a problem with this question

22. 22. On a commercial service, the reduced pressure principle assembly is discharging continuously and has clearly failed. The customer asks the irrigation technician to fit a replacement assembly and certify that it passes. What is the appropriate course of action?

    • A.Rebuild the first check on site and record the assembly as passing
    • B.Arrange the work through a licensed plumber and certified tester✓ Answer
    • C.Replace the assembly and log the repair in the customer's file
    • D.Isolate the service, fit the new assembly, and retest it himself

    Work on the containment assembly protecting a potable service, and the test that certifies it, are regulated activities: the plumbing work belongs to whoever the jurisdiction licenses for it and the passing test must be signed by a certified tester and reported to the purveyor. The irrigation technician's job is to recognize the failure, report it and arrange the correct trades rather than sign a result he is not certified to give.

    Source: Irrigation Association Certified Irrigation Technician content outline — identify state and local requirements; AWWA M14, certified tester requirementReport a problem with this question

Practice questions based on the Irrigation Association's published Certified Irrigation Technician content — basic irrigation principles, basic electrical principles and basic hydraulics — together with standard irrigation installation, hydraulics and backflow-prevention references. This site is not affiliated with or endorsed by the Irrigation Association. Irrigation work is governed by local plumbing and irrigation codes, water-purveyor rules and licensing that vary by jurisdiction; backflow assemblies in particular must be selected, installed and tested to the rules in force where you work. Confirm current exam requirements with the Irrigation Association before testing. About IA certification →