Field Test Results That Do Not Match the Gauge
A certified tester is testing a 4-inch reduced-pressure principle assembly in a vault. The differential pressure gauge reads 0 psi with both test cock valves open. When the tester closes the high-side bleed and opens the low-side, the gauge still reads 0. The tester's gauge was calibrated 14 months ago. The assembly was installed 3 years ago and passed last year. The tester suspects the gauge but also notices the relief port is dry and the downstream gauge reads 60 psi. The purveyor requires annual testing and a passing report to avoid a violation notice due within 10 days.
1. List the likely causes of the 0 psi reading and the diagnostic steps in order.
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Possible causes: (1) gauge failure or loss of calibration; (2) test cock clogged or closed; (3) hose kinked or disconnected; (4) air trapped in the gauge or hoses; (5) both test cocks open so the gauge sees equal pressure; (6) gauge not zeroed; (7) actual assembly condition such as a failed check.
Diagnostic order:
- Confirm both test cocks are open and hoses are clear; verify the gauge zeroes with hoses disconnected.
- Bleed air from the gauge and hoses.
- Close the high-side bleed and open the low-side to isolate each side.
- Compare with a second calibrated gauge.
- If the gauge is faulty, stop and retest with a calibrated gauge; a gauge calibrated 14 months ago may exceed the required annual calibration interval depending on the standard and purveyor requirement.
The dry relief port and 60 psi downstream reading are consistent with normal operation, so the 0 psi is most likely instrumentation.
2. What should the tester do about the 10-day reporting deadline?
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The tester should not submit a passing report based on a faulty gauge. The tester should obtain a calibrated gauge, retest, and submit accurate results. If the retest cannot be completed before the deadline, the tester should notify the purveyor of the delay in writing, explain the gauge failure, and provide the retest date. Submitting a false pass is a violation and exposes the tester to decertification. If the retest passes, submit the report with the correct gauge information and calibration date. If it fails, submit a failed report and notify the owner of the need for repair.
3. Explain the calibration and equipment requirements that apply to this test.
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The differential pressure gauge must be calibrated at the required interval (commonly annually) and the calibration must be traceable. The tester should carry the calibration certificate and record the gauge serial number and calibration date on the test report. Hoses must be in good condition, and test cocks must be clear. The tester should verify gauge zero before and after testing. Using an out-of-calibration gauge invalidates the test. The tester should also follow the manufacturer's test procedure for the specific assembly model, since relief valve opening points and check differentials vary.