Calling all fuel tank leak experts

[HighFlying]

So I completed my RV-10 fuel tanks, specifically for the left tank, I gave it about two weeks to cure before doing the balloon test. Filled the tank with air and inflated balloon, did the soap water check for leaks. All good at this point, no bubbles. Let it sit for 3 days and the balloon didn't change or otherwise lose air. Did not do the manometer test that many suggest. However, I did add about 5 gallons of car gas to let slosh around in different orientations. Big however, I did not open a vent. I began noticing some leaks around the rear baffle on the bottom corner of the outboard rib (directly below the fuel cap). Being somewhat perplexed and turning the tank over and seeing other potential leaks, I then popped the fuel cap lid and heard a 3 sec pssss. Ah, tank was pressurizing itself from fuel vapors. At that point all leaks stopped. Let it sit for a day in different orientations ensuring it was vented at atmospheric pressure, no leaks. Since it is easy access through the fuel filler, I plan to add more proseal at the corner joint where the pressurized leak was observed, but is there anything else I need be concerned about given the above scenario? Should have thought about venting the tank prior to adding gas, hope I did not compromise the overall integrity. Thoughts???

 

[lr172]

That is a tough one. I recently resealed a couple RV-4 tanks. Generally, the proseal will hold fuel after about 24 hours but won't hold real pressure for weeks. After a couple days of cure on the last tank, I leak tested it (used 1 PSI) and then installed it and put 5 gallons of gas in it as a final leak test. Was bumping up to a deadline with pickup. Get a call from the airport that there was a large puddle of gas under my plane. Go there and fuel is STREAMING from a hole in the tank I just installed. Turns out that the vent line in the fuselage was completely blocked and the sun was doing a great job of heating and expanding the gas I put in it. Apparently the previous leak points were large enough to act as vent sources and prevented a collapsed tank.

If you got a good solid release of pressure upon removing the cap, there is a good chance that the proseal was cured enough to not have failed. If it did fail, it would have released the pressure through that failure point and there would be no release when you opened the cap. If it did compromise the proseal somewhere but not enough to leak pressure, I don't think you would be able to find it. May be wise to pressurize it again to 1 PSI and attack with soapy water, just to be sure, as it is possible the leak point was very small and could release some, but not all of the pressure.

I have de-sloshed/re-sealed 6 tanks. So, knowledgeable but not really an expert. Pretty sure there is a guy on here who does this for a living with the airforce. Hopefully he will see this.

Larry