Fuel Tank Leak Testing

[4kilo]

I now have my first tank leak tested! After 12 hours the balloon attached to the vent line has not decreased noticably in size, so I think I can consider the tank to be without leaks.

There were, however, two unsuccessful tests first. Needless to say, it is somewhat deflating to see the balloon shrivel up within a couple of hours. What I found out is that the leak was actually around the valve stem inserted into the drain fitting. By greasing the fitting with vasoline, I was able to eliminate that leak and get a successful test.

Moral of the story: Make sure that your test equipment has no leaks before you jump to the conclusion that your newly constructed tank leaks.

Pat

[Spike]

[captain_john]

That is cool Pat!

I will letcha know how mine turn out soon!

CJ

[4kilo]

After getting all of my fittings greased up and installed in my auxilliary tank, I fitted the balloon and pressurized the tank. As I secured the pump, I thought I heard an ominous hissing noise. It was so quiet that I had to turn everything in the apartment off to listen, but there it was. As I stood there fuming, the balloon began to shrink. Not a happy feeling.

Actually, the leak was fairly easy to find, but it was in a horrible location - the flange of the outboard end rib. Since I slathered lots of sealant on the spot, and made a good fillet, I cannot even guess how there could be any leak at that spot, but there it was.

I did remember reading a while back about using green threadlocker to seal pinhole leaks, so I gave it a try. The stuff is supposed to penetrate just about any small opening, and if the opening is small enough, seal it.

After using the green threadlocker and giving it a chance to cure, I re-pressurized the tank. That was over two days ago, and the balloon has not shrunk at all. As long as avgas will not disolve the threadlocker, I now have another tank with no leaks.

Pat

[bmurrish]

Pat, have you thought about putting a dab of proseal over the spot you put the threadlocker on?

[greylingr]

Stupid question for the day: What do you guys use to grease the fittings and tank hole plug?

[captain_john]

Rudi, Van sells a test kit.

I mooched one from Wicked Stick. The only part you really need is the schrader valve that screws into the drain plug. You pump it up with a bicycle pump.

http://www.vansaircraft.com/cgi-bin/cat ... =tank-test



In the directions, Van doesn't mention any lube on the threads. I didn't lube them at all. I simply tightened it to the point where it didn't leak.

CJ

[greylingr]

Hi John,

Thanks I got a kit like that from Vans... I need to be a bit clearer:

A couple of guys have reported they get leaks around the tank filler cap (Dan also) and some of the connections. After applying 'fuel lube' it went away. I asked around here if anyone keeps "Fuel Lube" but they look at me if I am crazy.

So what do you use to grease it all up?

Petroluem Jelly or similiar I don't want anything to react with the Fuel, or disolve and leave a leak later?

Thanks

[Patty 'O Wrench]

the airline industry uses Parker "O" lube for the o rings and seals that may touch oil or fuel(kerosene) I've used it for years around the GA stuff.
there is a product out there called "Thread Lube" but you'll have to do some research on it. the actual AN fittings should be self sealing, if they aren't, the mating surfaces may be damaged. Good luck!
the wrench

[4kilo]

I don't remember where I read it, but somewhere in the Van's literature they recommend using petroluem jelly for lubing the O rings in the fuel caps. I used petroluem jelly to lube the O rings in the delux caps I obtained from Van's, and they did not leak at all. I did get a small leak around the schrader valve installed in the drain fitting, so I used some petroluem jelly on the valve threads.

When I install the actual drain valves, I will be using some other more permanent thread goop, because the petroluem jelly is supposed to be soluble in fuel.

Pat