Field Testing Procedures and Test Equipment
Core Concepts
Testing requires calibrated gauges, proper test kits, and a defined sequence. Know the differential pressure test for check valves and the relief valve opening point for reduced-pressure principle assemblies. Gauges must be calibrated and within accepted accuracy; test results are recorded on standardized forms.
Understand the sequence for a reduced-pressure principle assembly: verify the first check holds, verify the second check holds, then confirm the relief valve opens at the correct differential. For a pressure vacuum breaker, test the air inlet opening and check valve hold. For a double check assembly, test both checks for tightness in each direction.
Recognize conditions that invalidate a test: air in the lines, leaking test cocks, unstable supply pressure, dirty seats, and gauges out of calibration. Know that test cocks must be exercised and that the assembly must be isolated from downstream flow during testing.
Traps in Questions
A common trap is a question describing a test performed without isolating downstream flow or with an uncalibrated gauge; the correct answer is that the test is invalid. Another trap is reversing the order of checks or confusing which valve is being tested.
Worked Example
If the first check holds at 5 psi differential but the relief valve opens below the required differential, the assembly fails. The tester should not "adjust" the result; the assembly requires repair and retest.