The Test That Passed on the Second Try
A certified tester is checking a 2-inch RP assembly in a commercial building. On the first check, the differential pressure across the first check is 4.0 psi and holds. The relief valve opens at 2.5 psi differential. The second check holds at 1.0 psi. The tester's gauge set has a 0-100 psi range with 2 psi graduations, and the low-side gauge reads slightly below zero when isolated. The tester records a passing result and leaves. A week later the building has a water-quality complaint, and a re-test by another tester finds the relief valve opening at a different value and the first check leaking slightly. The original tester's report shows all values within tolerance.
1. Evaluate the original test for procedural and equipment problems, and identify which recorded values are suspect.
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Several issues undermine the original result. Gauge resolution matters: a 0-100 psi gauge with 2 psi graduations cannot reliably resolve a 1.0 psi second-check holding value or small changes in relief opening, so those readings are not trustworthy at the stated precision. A low-side gauge reading below zero when isolated suggests the gauge was not properly zeroed or that trapped pressure or a misconnected hose affected the reading, which biases every differential measurement. The relief valve opening at 2.5 psi differential is at or near the typical minimum acceptance threshold, so it deserves careful confirmation rather than a casual pass. A slight leak at the first check found later is consistent with a check that was marginal or with a test that did not hold long enough to reveal a slow fall. The recorded values should be treated as unreliable; the test should be repeated with properly calibrated gauges of adequate resolution, zeroed before use, with adequate hold times, and with all readings taken under stable conditions.
2. What would you require before accepting any re-test result, and how should the discrepancy be documented?
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Require that the gauges carry current calibration traceable to a standard and have resolution fine enough for the values being judged, that they be zeroed and checked for hose leaks before the test, and that each check be held long enough to confirm the reading is stable rather than transient. The relief valve opening point should be approached and confirmed deliberately, and the first and second checks should be observed for fall over a defined interval. Document the original test as invalid with the specific reasons: inadequate gauge resolution, a below-zero low-side reading, and hold times insufficient to detect a slow leak. Record the re-test values, the equipment used with calibration dates, the conditions, and the tester's identity. The discrepancy should be reported to the building owner and, where required, to the AHJ, and the assembly should be repaired or replaced and retested before being returned to service.