Need help detecting tank leak

[rwarre]

Today I tried to do the tank leak test with Van's kit and the balloon. When I tried to inflate the balloon, it would barely expand. I attached all of the fittings etc. with the kit. I tried spraying soapy water to maybe find where air might have been escaping but that did not work. I thought that maybe my pop rivet heads needed prosealed and did that. I was very generous when prosealing the tank and can't believe that there would be a leak from the stiffeners or ribs. Any suggestions, insights would be much appreciated.

 

[Mel]

First thing to check is the fill caps. They're not very good at holding "air." Remove the caps, lubricate the O-rings, place plastic wrap over the hole, and replace the caps.

 

[Chappyd]

When I tested my tanks, I ended up taping over the filler caps. I also checked for leaks using soapy water, but brushing it on. 1 was leak free, the other had a leak but was easy to find and fix. Balloons stayed inflated for 3 days. I didn't use Vans kit. I put a ballon on the fuel outlet and blew it up with air shot into the vent through a piece of tubing, then closed the tubing with hemostats. If you have air coming out that quickly, the soapy water trick should still work. Listen and feel around the tank with your hand too.

 

[Beer30?]

Check the baffle

On one of my tanks, I had some leaks at the corners of the baffles where I did not put enough proseal. I was able to make some corner pieces to rivet over them, so I didn't have to open the tanks. I was able to find these with soapy water though. I believe that the majority of the leaks are usually around the baffles.

 

[painless]

If you are using capacitance senders, check your BNC connectors. I had a small leak there when testing my tanks.

 

[flion]

After I built my tanks, I didn't have any leaks. But several years later, when I was ready to begin plumbing the tanks to the fuselage, I pulled the sender cover plates so I could check the pickup tubes (mine were prosealed in before Van ever issued his AD). I used the cork gasket with fuel lube and the first time I had an issue with forgetting to lube the screws. This time, one of my tanks refused to hold air at all until I realized I had forgotten to tighten the screws back down. Silly me, I had tightened at four cardinal points and gotten distracted before tightening the other eight. Once they were tightened, the balloon stayed up.

On the other tank, I uncovered a pinhole leak in one of the end flanges where a rib flute wasn't filled completely. I resorted to putting the tank in our bathtub to locate this one. A tiny drill bit, toothpick and cleaner, followed by a dab of proseal packed in the opening fixed this leak in no time.

By the way, has anyone else used the balloon method to test their pitot/static connections (less instruments, of course)? It seemed to work just fine for me.

 

[rwarre]

Leak found

I found the source of leak in my fuel tank. Air is escaping through the rear flange on the inboard rib where it attached to the baffle. There is proseal between the rib flange and baffle. This is baffling. I thought the proseal was supposed to form a barrier and make a seal. Can I proseal over the rib/baffle edge or should I drill out the rivets and try to force more proseal between the mating surfaces.

 

[flion]

If you didn't use too little proseal or the gap is not too large, then proseal should fill up the gap. That's also assuming that the proseal is fully cured and if it is, you will not be able to split the flange and rear baffle without risking damage to your tank. Others may have different (i.e. better) fixes, but what I would do would be to dribble a shot-glass full of acetone over the affected area from the inside and add some pressure to force it through the leak. Once you are sure it's coming through, reopen the tank and thoroughly dry out the tank with compressed air. Then use a small bit of sloshing compound inside the tank over the leak area and, again, pressurize the tank to force it through the leak. Once you see it coming through, remove the pressure. Repeat the last step until no more slosh makes it through and then clean and coat the inside of the tank in the leak area with a thin layer of proseal. Test for leaks again, of course, but that should fix it.

I'm not a big fan of slosh, but controlled usage like that should not cause a problem and it will flow through the leak better than proseal.