Fuel tank leak test

[jsalley]

Completed my RV-12iS fuel tank a week ago, and leak tested today. I initially put a balloon over the filler neck (securely taped), pumped up with air until the balloon inflated. Used a commercial gas leak bubble fluid on every seam and rivet, and had no bubbles. However, the balloon deflated over the next hour. Replaced the balloon with a nitrile glove per KAI, and it again deflated after an hour with no bubbles around the taped-on glove. How long should the balloon/glove stay inflated? Should I use something other than soapy solution to check for leaks after pressurizing?

 

[Kyle Boatright]

Completed my RV-12iS fuel tank a week ago, and leak tested today. I initially put a balloon over the filler neck (securely taped), pumped up with air until the balloon inflated. Used a commercial gas leak bubble fluid on every seam and rivet, and had no bubbles. However, the balloon deflated over the next hour. Replaced the balloon with a nitrile glove per KAI, and it again deflated after an hour with no bubbles around the taped-on glove. How long should the balloon/glove stay inflated? Should I use something other than soapy solution to check for leaks after pressurizing?

The balloon or glove staying inflated isn't what you're looking for. That can be caused by a number of things like temperature or atmospheric pressure changes. You're looking for soap bubbles. Me? I'd run the test a couple of times and if no soap bubbles are found, I'd consider myself good to go.

 

[CTCole]

The temp issue Kyle Boatright mentions can make a big difference. When I was leak-testing, at one point I had the nitrile glove deflating slowly (e.g. overnight). I found that if I placed my hand on the tank, it added enough heat in just a few minutes to re-inflate the glove.

 

[PaulvS]

Completed my RV-12iS fuel tank a week ago, and leak tested today. I initially put a balloon over the filler neck (securely taped), pumped up with air until the balloon inflated. Used a commercial gas leak bubble fluid on every seam and rivet, and had no bubbles. However, the balloon deflated over the next hour. Replaced the balloon with a nitrile glove per KAI, and it again deflated after an hour with no bubbles around the taped-on glove. How long should the balloon/glove stay inflated? Should I use something other than soapy solution to check for leaks after pressurizing?

If the balloon deflates after one hour then there is definitely a leak somewhere else other than through the walls of the balloon. Maybe it is coming out around the tank vent, or the fuel outlet or return line? Normally a balloon will stay inflated, or gradually deflate, over a week or so. As Kyle says though the leak testing process is to use the soap solution to identify bubbles and so there must be a spot that has been missed during testing. I used "helium grade" balloons during testing and these did not deflate prematurely.

 

[Bob Y]

And don’t forget to spray your soap solution around the base of the balloon. Had tough times getting a good seal.

 

[jsalley]

The balloon or glove staying inflated isn't what you're looking for. That can be caused by a number of things like temperature or atmospheric pressure changes. You're looking for soap bubbles. Me? I'd run the test a couple of times and if no soap bubbles are found, I'd consider myself good to go.

Found the problem - actually not a problem at all. Kyle nailed it. Glove was deflated this morning in the cool-ish garage. After leaving the garage door open for an hour (91 degrees outside), it was fully inflated again. Added a little more air and bubble checked again - no leaks, but spraying the cool solution on the tank caused the glove to start deflating. Used my hands on the tank to warm it - glove inflated again. I guess aluminum really is good at heat transfer! Anyway, plan to bubble test once more, and check it off as done if it stays good. Thanks all.