156 – The Weirdest Vacuum System Problem I’ve Ever Seen

Airplane Owner Maintenance - By Dean Showalter

Although a shop vac might not pull as much vacuum as an engine driven vacuum pump, it can still be useful for some parts of the troubleshooting process. This was just one thing we did on the path to solving a very strange vacuum problem. Listen to the story in today’s podcast episode.

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Now for today’s episode… we’re featuring two squawks on a twin Cessna.

Squawk #1: The left fuel gauge was completely inoperative, both for the main tank and the aux tank.

In this episode, we talk about the troubleshooting process that led to changing the fuel quantity indicator. The gauge from eBay worked great, and the system was back to normal.

Squawk #2: The vacuum system had a weird problem… the vacuum gauge showed that both vacuum pumps were functioning, but the vacuum was very low (approx. 1 inch of Hg instead of 5 inches.) Apparently it doesn’t take much vacuum to pull the inop indicator in (the little red button for the left and right vacuum pumps in the vacuum gauge.) This squawk was challenging! Actually, the solution turned out to be simple, but the discovery process was not so simple.

We checked an extensive list of components, both in the vacuum system and in the surface deice system, since the two are inter-related, and the squawk had two parts: the vacuum indication was very low, and the wing deice boots were not being pulled firmly against the surface of the wing (which requires good vacuum.)

Here’s the deice valve in the right engine compartment, one of the components we tested in this process.

Thankfully, we did not end up ordering any high-priced components in this scenario, because the solution turned out to be very simple… we removed an elbow between two vacuum hoses, and installed plugs in them instead. Listen to the audio for the details.

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