Journeyman Plumber ExamWater Supply SystemsHard
A plumber is performing a mandatory annual test on a reduced pressure principle (RPZ) backflow prevention assembly. During the test, the differential pressure relief valve opens to atmosphere when the pressure downstream of the No. 1 check valve is reduced. What is the acceptable pressure difference (differential pressure) at which the relief valve should open, relative to the supply pressure, for the assembly to pass this test?
- AAt least 3.0 PSI
- BAt least 2.0 PSI
- CAt least 4.0 PSI
- DAt least 1.0 PSI
Show answer & explanationAnswer & explanation
Correct answer: B. At least 2.0 PSI
For an RPZ assembly to pass the test, the differential pressure relief valve must open to atmosphere when the differential pressure across the No. 1 check valve (pressure zone) is at least 2.0 PSI. This ensures that the relief valve will operate correctly to protect against backpressure and back-siphonage by maintaining a safe pressure differential.
Why the other options are wrong
- A. 3.0 PSI would indicate proper function, but 2.0 PSI is the minimum for passing the test.
- C. 4.0 PSI is well above the minimum and would indicate proper function, but is not the minimum passing threshold.
- D. 1.0 PSI is insufficient; the required differential is higher to ensure proper function.
RPZ Relief Valve Differential
The differential pressure relief valve in an RPZ assembly must open when the pressure in the zone between the two check valves drops to a specific minimum differential below the supply pressure, ensuring protection.
- RPZs protect against both back-siphonage and backpressure.
- Relief valve opens to atmosphere to maintain a safe pressure differential.
- Minimum differential for relief valve opening is 2.0 PSI.
Memory trick: RPZ Relief needs Two PSI to Protect.