Putting gas in tanks

[s10sakota]

Has anyone leaked checked their fuel tanks by actually putting fuel in them?

I'm thinking that the most likely place for the tanks to leak would be the rear of the tank.

So why not put the tank on a table with the leading edge facing up, and put about a gallon of fuel in the tank? That should be enough for 1/2 to an inch of fuel on the bottom.

Has anyone done this? Is there any reason NOT to do this? I just don't trust the balloon test. There's too many places for air to leak out like the fuel caps and the balloon itself.

I would hate to 'think' the test is good, bolt the tanks on, paint the wings, and the find out there is a small leak somewhere!

Thoughts??

[bhester]

The leak could be at any rivet. Put the fuel cap on and seal the cap with duct tape to eliminate the cap from the test. Use the drain to put a very small amount of air pressure in the tank. If your using a air tank let the pressure in the tank out until it is below 20 psi you are only going to put a enough air in to inflate the balloon. By using a balloon you can make sure you don't put to much in, if you put too much in the balloon will burst. If there is a leak it is going to deflate pretty quick. The change in the temp will cause the balloon to slowly deflate and inflate over time. Use soapy water and a spray bottle to check around all areas that might leak.

[APACHE 56]

Originally Posted by s10sakota

So why not put the tank on a table with the leading edge facing up, and put about a gallon of fuel in the tank? That should be enough for 1/2 to an inch of fuel on the bottom.

I did the balloon test and it passed. However, about that time there were a series of posts on the forum regarding tank leaks and the onerous process of fixing them. So I did the six sigma test. I put the wings on a big very well padded bench and filled to capacity with avgas. No leaks.

Another major motivation was the hassle of removing the tanks (should that be necessary) after you have them painted.

[s10sakota]

I did the balloon test and sprayed the tank with soapy water. The only leaks I could find were at the balloon itself...



...and the tank drain (which has the bicycle pump fitting in it). Obviously the fitting is going to come out, but I'm wondering if there is any type of sealant I should put on the threads of the actual drain fitting to prevent leaks there?

[bird]

Yep, permatex # 2 is a good sealant for that.

Bird

[s10sakota]

Sorry for a dumb add-on question, but when the airplane gets painted, does the fuel drain come out or is it just taped over for paint? If it has to come out again, I won't seal it up now!

[Pat Hatch]

Originally Posted by s10sakota

Has anyone leaked checked their fuel tanks by actually putting fuel in them?

I'm thinking that the most likely place for the tanks to leak would be the rear of the tank.

So why not put the tank on a table with the leading edge facing up, and put about a gallon of fuel in the tank? That should be enough for 1/2 to an inch of fuel on the bottom.

Has anyone done this? Is there any reason NOT to do this? I just don't trust the balloon test. There's too many places for air to leak out like the fuel caps and the balloon itself.

I would hate to 'think' the test is good, bolt the tanks on, paint the wings, and the find out there is a small leak somewhere!

Thoughts??

Mark, that's exactly what I did. With three airplanes. I put 6 gallons of 100LL in each tank then sat them on the rear baffle for a day or so. Then I sat them on one end for a day, and so on. I also sat them in the cradle with the leading edge down for a day. This is the only reliable method to truly guarantee leak-free tanks, in my opinion. I think air molecules are larger than fuel molecules so in theory you might pass the pressure test and still have a leak with fuel.

[s10sakota]

Glad I'm not alone Pat! I'm going to do the exact same thing tomorrow. I just need to get the Permatex-2 to install the fuel drain!

[Pat Hatch]

Originally Posted by s10sakota

Sorry for a dumb add-on question, but when the airplane gets painted, does the fuel drain come out or is it just taped over for paint? If it has to come out again, I won't seal it up now!

Mark, you should not seal the fuel drain now. It will be removed a few times prior to paint; for example, if you test your tanks with fuel and then have to drain it. In any case, just a little Permatex #2 is all you need. You'll want to be able to remove it for maintenance, like if you need to change the O-ring some day.

[bhester]

I've used Fuel Lube on my drains with no leaks. I also keep a spare drain valve in my tool bag. You will need to replace the small o-ring in the future and having a spare drain vavle in really nice.