4.5 psi and an Expired Calibration
A certified tester arrives at a 2-inch RPZ serving a commercial laundry. The tag shows the last test was 13 months ago. The test kit's calibration certificate is dated 14 months ago; the program requires an annual calibration certificate on file. With the No. 2 shutoff closed and flow established through the test cocks, the high-side gauge reads 68 psi and the differential gauge across check No. 1 reads 4.5 psi. Check No. 2 reads 1.5 psi. The relief valve opens at 2.8 psi differential and re-seats drip-tight at 1.2 psi. No discharge is observed from the relief port during the leakage test. The building manager says the assembly 'passed last time, so just write it up the same way.'
1. Evaluate each test result against its acceptance criterion and state the overall outcome.
Read the worked answer
Score each one, then sum up.
| Test | Reading | Criterion | Result |
|---|---|---|---|
| Leakage (relief discharge with No. 2 closed) | none | no discharge | Pass |
| Check No. 1 differential | 4.5 psid | min 5.0 psid | Fail |
| Check No. 2 differential | 1.5 psid | min 1.0 psid | Pass |
| Relief opening point | 2.8 psid | min 2.0 psid | Pass |
| Relief re-seat / tightness | 1.2 psid | tight at 1.0 psid or above | Pass |
Overall: the assembly fails on check No. 1 only. Four of five criteria pass, which is exactly the situation that tempts a tester to fudge.
Two judgment notes:
- 4.5 is close enough to the 5.0 threshold that gauge error could flip the result. That is a reason to verify, not a reason to round up.
- Check No. 2 passing a forward-differential test does not prove it seals against reverse (back) pressure. If downstream backpressure is suspected, that is a separate investigation.
2. What do you do about the calibration certificate, and how does it affect the report?
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Stop. Do not produce a compliance report from this kit.
- The certificate is 14 months old against an annual requirement. The results are not traceable to a calibrated instrument, so they cannot support a pass or a fail determination for the file. Reporting a number from an out-of-calibration kit - in either direction - is a falsification of a compliance document, not a rounding decision.
- Obtain a calibrated kit, retest the full sequence, and report only those results. Note in the file why the first attempt was voided.
- Retain the calibration certificate with the test report; many programs audit for exactly that pairing.
The manager's request ('write it up the same way') is not a test. Prior results do not carry forward, and the device is 13 months out from its last test, which is itself a compliance violation that must be reported, not concealed.
Also note: an out-of-calibration incident is a program-level problem, not just this job. Check the interval tracking for the whole kit fleet; a single expired certificate usually means the reminder system failed for all of them.
3. The retest with a calibrated kit confirms check No. 1 at 4.2 psid. Write the corrective action plan.
Read the worked answer
1. Confirm the reading. Repeat check No. 1 with the calibrated kit and, if available, a second gauge. 4.2 versus a 5.0 minimum is a real failure but a modest one, and most causes are correctable.
2. Isolate and disassemble. Close the upstream shutoff, depressurize, and remove check No. 1.
3. Inspect for the usual causes, in this order:
- Debris, scale, or pipe dope on the seat or disc - the most common cause of a low-but-holding differential.
- Nicks or wear on the disc; hardened or swollen rubber.
- Weak, broken, or out-of-spec spring (compare free length to the manufacturer's value).
- Seat retained loosely or installed backwards after prior service.
4. Repair. Clean the seat, replace the disc and spring with OEM parts. Do not shim, stretch, or otherwise alter the spring to raise the differential - that changes the assembly from its listing and is not a repair.
5. Retest the full sequence after the repair. A repair without a retest is an unfinished job, and the retest covers all five criteria, not just the one that failed.
6. Document. Record the as-found values, the parts replaced, the as-left values, and the calibration certificate reference. A report that shows only the passing as-left numbers is incomplete.
7. If it still will not hold 5.0 psid after cleaning and a proper rebuild, replace the check assembly or the device - and tell the owner why, because a repaired-then-failing device usually means the body or seat is damaged.