Backflow Prevention Assembly Testing
What Testing Actually Proves
Field testing verifies that an assembly's check elements and relief valve hold tight under specified pressure differentials. Each assembly type has a defined test sequence, and candidates must know the order and the pass criteria, not just the device names.
Core Test Concepts
For a reduced pressure principle assembly, the test confirms: the first check holds against backpressure, the second check holds against backpressure, and the differential relief valve opens at the correct point and reseats. For a double check assembly, both checks must hold. For a pressure vacuum breaker, the air inlet must open and the check must hold. Test gauges must be calibrated, and readings recorded on approved forms.
Traps That Appear in Questions
- Testing in the wrong sequence, which can mask a failing check.
- Ignoring gauge calibration dates - an out-of-calibration gauge invalidates results.
- Misreading the relief valve opening point relative to the first check differential.
- Failing to account for supply pressure fluctuations during the test.
- Confusing "holds" criteria values with device ratings.
Rule of Thumb
Test in the manufacturer's specified order, stabilize pressure before each reading, and record actual gauge values - never estimate. If any element fails its hold criterion, the assembly fails and requires repair and retest.
Worked Example
During an RP assembly test, the relief valve discharges continuously. The tester should suspect a fouled first check or debris on the relief valve seat. The correct response is to note the failure, repair, and retest - not to adjust the relief spring to stop the discharge.