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"Balloon testing" tanks is insufficient

Jamie

Jamie

Well Known Member
I had a fairly bad tank leak recently. Yesterday I got around to pulling the tank. I put a balloon on the tank and pressurized it and spent the next four hours trying to figure out where this tank was leaking from. Nothing. Nada. Zip. Very annoying to say the least.

Mike Stewart was out at the airport tooling around and he suggested more pressure. I rigged up a manometer and pressurized the tank to ~1 PSI. Voila. Found two big leaks on the inboard-most bay.

So word to the wise...if you are building your tanks and pressure testing them don't depend on a balloon to find your leaks.
 
Jamie said:
I had a fairly bad tank leak recently. Yesterday I got around to pulling the tank. I put a balloon on the tank and pressurized it and spent the next four hours trying to figure out where this tank was leaking from. Nothing. Nada. Zip. Very annoying to say the least.

Mike Stewart was out at the airport tooling around and he suggested more pressure. I rigged up a manometer and pressurized the tank to ~1 PSI. Voila. Found two big leaks on the inboard-most bay.

So word to the wise...if you are building your tanks and pressure testing them don't depend on a balloon to find your leaks.
Click to expand...

I have to agree! We did the balloon test and didn't have any leaks until we put it on the plane and filled it. The balloon will help with any big leaks but not tiny ones.
 
I used baloons and then filled each tank and let fuel rest for one week before assembling wings with fuselage.

Edit: of course I tried each rivet with soapy water while the baloon was inflated.
 
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spray with bubble wash...

The ballon does a good job of holding mild pressure as a safety so that the tank will not get blown out while pressurizing but can be a bit deceptive if relied on exclusively for leak testing, especially if it is only used for a short period...

If you mix some kids bubble fluid with some water in a spray bottle and go over all of the rivets any escaping air will be revealed quite clearly.

Filling the tank is not as effective since you only test the wetted rivets without pressure (other than the small amount of hydrostatic from the fluid) and only test leaking from avgas... which i think is made from a much larger carbon based molecular chain than the nitrogen and oxygen in air.

I wonder if we should use helium to test the tanks...
 
manometer

I did the 1psi manometer method and then sprayed every rivet with soapy water. Only leak I found was on my manometer tubing attached with zipties.

IMG_0672.JPG
 
How do you guys feel about filling the tanks with water and letting them sit?, It would be fairly easy to drain through the fuel drain and then leave the cap off for a few days afterwards to let them dry out. Any suggestions??

-david
 
Water is a reasonable test for large leaks, but gasoline is less dense and will leak where water would not.
 
Balloons vary from .3 to 1.0 psi on my electronic manometer

so that is why I used 1.0 psi for my leak test. I could lay my hand on the tank and the pressure would increase about .01 psi. Electronic manometers are used for checking gas furnace manifold pressures/pressure switch settings.
 
pressurize and spray bubbles...

A water manometer is a great method; just realize that the water column will become a barometer and will react to changing atmospheric conditions with a surprising sensitivity so you will have to observe it over a longer period to ensure that the tank is not leaking.

Filling the tank might find your leaks but it will not be much of a sure thing; using a bit of bubble spray applied to the rivets, seams, and joins, on a pressurized tank will find any leaks... cheap, simple, and reliable.
 
Tank Check

On building the RV6 when I was gtting ready to test the tanks for leaks, some of the old timers at the Airdrome asked what I was doing with the balloons , I told them ...See if the tanks leak. They asked if I was going to fly the plane with air (ha ha) so they said why don't you put Gas in there :) Well I put a few gallons in them and Rotated them around on the work bench over a few weeks , no leaks .....4 years later no leaks
Just what I did

Peter
RV 6
 
Filled the tanks with mogas, but.....

I filled the tanks with 20 ltr of mogas and turned them over in all different positions for about a week, untill I was sure I had "wetted" all inside surfaces and had pressure built up inside the tank from the gasoline fumes (going tsssshhhhhhh.... when you open the cap).

Guess what 1? After that successfull test, I still found a "fuel guardian" sensor leaking, that I apparently damaged by overtighthening!

Guess what 2? Still found a "wheeping" screw on one of the fuel level sensors, when I filled the tanks for the first time, even after doing a second successfull test!

I considder my self lucky because I could cure those small leaks pretty easy and did not find any rivets leaking (so far)!

Regards, Tonny.
 
I'd suggest the actual fuel test as well. I did the balloon test with my quick build tanks and all was fine. After a few hours flying an actual leak showed up on one of the z-brackets on the back of the tank which required full tank removal to repair. I'm sure glad I removed all of the screws that hold the tank to the wing before painting the airplane. It would have been pretty ugly to remove painted screws from a brand new paint job. It's also not much fun removing about (21) 1/4" bolts from the back of the tank through an access port and then reinstalling them. A good fuel test now would be well worth it.
 
'Sounds to me that a static test is not sufficient, and that you should fill the tank and then shake the wing violently up and down to stress all joints and openings. 'Only half in jest!
 
I went with a homade (cheap) manometer

I tested my 6's tanks with a little over 2 psi, (about a 4 foot head) and had no leaks after I aluminum taped my gas caps.

The manometer was made out of polyflow line, 1/4" plywood and some cable staples.

Worked great.

Be advised that if you are not doing this in a temperature stable environment you will get inconsistent results.:eek:
 
no blue trail?

Jamie said:
I had a fairly bad tank leak recently. Yesterday I got around to pulling the tank. I put a balloon on the tank and pressurized it and spent the next four hours trying to figure out where this tank was leaking from. Nothing. Nada. Zip. Very annoying to say the least.
Click to expand...

OOC, was there not a tell-tale blue trail?

My tanks passed the balloon and soapy water test - keeping the balloon inflated for days. Since getting it flying, I have fixed a leak in each tank. The leaks were minuscule, just enough to leave evidence near the paint around the tank baffles. I feel fortunate I was able to repair both tanks without major effort. Sounds like you're equally lucky. Gotta love the fun of pulling those tanks off.
 
dhall_polo said:
OOC, was there not a tell-tale blue trail?
Click to expand...

Well, sort of. There was blue everywhere. It was leaking in the wing root so apparently enough air was getting past the wing root fairing to blow fuel everywhere.

It looks like the leak was related to not putting a good fay seal down on the rear baffle->inboard-most rib joint. The other leak was actually my access cover leaking.
 
As an aside...something interesting I found when I pulled the access panel cover were little (almost) perfectly circular pro-seal boogers rolling around in the tank. I really scratched my head over them for about 20 minutes, then I realized that they were a result of dipping the screws in proseal before installing them. The boogers fell out out the nutplates when I removed the screws.
 
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