Master Plumber Exam Backflow Prevention and Safety 2 — Questions and Answers
Question 1: Which backflow preventer is required when the downstream system contains a non-health hazard pollutant but not a contaminant?
- Reduced pressure zone (RPZ) assembly
- Double check valve assembly (DCVA) (Correct answer)
- Atmospheric vacuum breaker (AVB)
- Pressure vacuum breaker (PVB)
Correct answer: Double check valve assembly (DCVA)
A double check valve assembly is the minimum required protection for low-hazard (pollutant) cross-connections where health risk is not present.
Question 2: What is the minimum air gap distance required between a potable water supply outlet and the flood level rim of a fixture under most US plumbing codes?
- 1 inch
- 2 times the diameter of the supply pipe or 1 inch, whichever is greater (Correct answer)
- 1/2 inch
- 3 inches
Correct answer: 2 times the diameter of the supply pipe or 1 inch, whichever is greater
The air gap must be at least twice the diameter of the supply pipe or 1 inch, whichever is greater, to prevent backflow by siphonage.
Question 3: A pressure vacuum breaker (PVB) differs from an atmospheric vacuum breaker (AVB) primarily because the PVB:
- Cannot be installed under continuous pressure
- Contains a spring-loaded check valve and can remain under continuous pressure (Correct answer)
- Is only used for high-hazard applications
- Does not require annual testing
Correct answer: Contains a spring-loaded check valve and can remain under continuous pressure
The PVB has an internally loaded check valve that allows it to remain under continuous supply pressure, unlike the AVB which must not be under continuous pressure.
Question 4: When testing a reduced pressure zone (RPZ) assembly, which condition indicates the device has passed?
- The differential pressure across the first check is less than 2 psi
- The relief valve opens during the test
- The differential pressure across the RPZ is at least 5 psi above the inlet pressure
- The second check holds at least 1 psi with no differential reading (Correct answer)
Correct answer: The second check holds at least 1 psi with no differential reading
A passing RPZ test requires the second check to hold tight (no differential relief) and proper differential pressure readings across both checks and the relief valve.
Question 5: Which type of cross-connection is created when a garden hose is left submerged in a swimming pool connected to the potable water system?
- Direct cross-connection (Correct answer)
- Indirect cross-connection
- Auxiliary cross-connection
- Pressure cross-connection
Correct answer: Direct cross-connection
A direct cross-connection is a physical link between a potable supply line and a non-potable source, such as a hose submerged in a pool.
Question 6: Under the Uniform Plumbing Code (UPC), backflow preventers installed on irrigation systems serving areas that use pesticides or fertilizers must be at minimum:
- Atmospheric vacuum breaker (AVB)
- Double check valve assembly (DCVA)
- Reduced pressure zone (RPZ) assembly (Correct answer)
- Air gap
Correct answer: Reduced pressure zone (RPZ) assembly
Chemicals such as pesticides and fertilizers represent a high-hazard (health risk) condition, requiring an RPZ assembly as the minimum protection.
Question 7: What is backpressure backflow?
- Backflow caused by a loss of supply pressure creating a vacuum
- Backflow caused by downstream pressure exceeding supply pressure (Correct answer)
- Backflow caused by thermal expansion in a closed system
- Backflow caused by a broken water main upstream
Correct answer: Backflow caused by downstream pressure exceeding supply pressure
Backpressure backflow occurs when the downstream pressure rises above the supply pressure, forcing contaminants upstream into the potable system.
Master Plumber Exam Backflow Prevention and Safety 2
Which backflow preventer is required when the downstream system contains a non-health hazard pollutant but not a contaminant?