Pressure testing fuel system

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Pressure testing fuel system

Postby FredHoffman » Fri Nov 17, 2017 9:46 am

I have been pressure testing my fuel system with air and after checking it over 4 times with soapy water now finding no bubbles it still drops from 15psi to about 13psi overnight. I am in a temp controlled shop. Have others tested in this way or am I chasing some thing that cannot be achieved, zero air pressure drop. I suspect fuel might not leak out at all given the molecules are much bigger than air.

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Re: Pressure testing fuel system

Postby danerazz » Fri Nov 17, 2017 10:35 am

I gotta say, 15psi sounds like a lot. I think vans tests theirs by attaching a balloon and just pressurizing enough to inflate it. Then they just see if the balloon stays inflated for a period of time (somebody more familiar can probably explain in greater detail). A balloon would only be a couple of psi. I don’t know if you are including your fuel tanks in this test, if you are I’m surprised you don’t blow them!
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Re: Pressure testing fuel system

Postby kenryan » Fri Nov 17, 2017 12:02 pm

Fred,

I agree with the balloon for the tanks. I think I got the procedure for testing my hoses off of the Earl's instruction sheet:

Cap off both ends of the hose, one with a schrader valve.

Bring up to pressure -- approximately 40-50 psi.

Dunk each end in water for a few seconds and see if any bubbles form.

If no bubbles, consider it good.

I don't know of a procedure for pressure testing the whole system with everything hooked up. I figure the test for that will be to put fuel in. If there are any leaks, hopefully tightening the connection will fix it, but I haven't put fuel in yet, so this is theoretical at this point.
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Re: Pressure testing fuel system

Postby FredHoffman » Fri Nov 17, 2017 10:43 pm

No, the wing fuel tanks are isolated from my test. I am testing from the lines that goes into fuel tank all the way to the firewall. Once this is done I'll be ready to start and do some taxi testing awaiting the DAR inspection. All my lines behind the firewall are aluminum but they were installed after covering so there are a few extra connections. For those starting a build put aluminum fuel lines in before covering !

A friend built a CH750 and said he was able to hold 20 psi for days when his was finished. It was a big effort to do this all with aluminum lines and -AN hardware. Don't know what to do next, I see no bubbles anywhere with soapy water, even soaked the pressure gauge in soapy water. Second time will be with flexible Aeroquip Startlight hose and Aeroquip hose ends.
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Re: Pressure testing fuel system

Postby FredHoffman » Wed Nov 22, 2017 11:06 am

Found the leak. My testing gauge bleeds down, fuel system was airtight from the start. When I got rid of the summit gauge and used a shreadrer valve in its place it held the same PSI for 4 days.
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Re: Pressure testing fuel system

Postby BucF16 » Wed Nov 22, 2017 9:05 pm

Thank you for clarifying! Good luck for the rest of your test.
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