Cooling Fan issues, Inverter pump, Shuddering

Well, that was weird, though. He had that regulator really dialed back.

I don't remember that he mentioned a brand for that particular tester, or where he got it. I wonder if its instructions are online. His initial step of 'calibrating' it was some weird business.

A leakdown tester is two pressure gauges one right after the other, with a known restricting orifice in between. Often, they are just two quite ordinary pressure gauges, both marked in psi.



The gauge on the air-supply side will read what you've set with the regulator, and the gauge on the downstream side will read some number of psi less. The instrument should come with a key where you look up the left and right psi readings and find the % leakage. The key will be specific to the brand and model of tester, because there isn't a standard for the restricting orifice across tools. (Exception: FAA does impose a standard, for testers used on aircraft.)

The tester Eric was using swaps the normal psi scale on the downstream gauge for some customized percent-reading dial. But I would have to see the instructions that came with it to see whether Eric got something mixed up. That 'calibration' didn't really make much sense. And he had it throttled back to 15 psi? No wonder he struggled to hear where it was going.

If you read the instructions for the OTC tester pictured above, you'll see they recommend setting the regulator for "10 psi less than the maximum pressure produced by the air source, but not to exceed 100 psi". The "10 psi less" is intended to get you near the maximum pressure the source can sustain during your test, since that will always be lower than its pressure at no airflow.

In other words, they're looking for plenty of air. You'll see the psi-to-percent key for that tester doesn't even give values for left-gauge settings below 75 psi.

If you follow those instructions and supply 75, 90, or 100 psi to the tester, you will not have Eric's difficulty hearing where the leakage is going.