Fuel tank leak checking
I ordered some EZ-Lube from Aircraft Spruce this past weekend and it showed up on Friday. Seems that getting the fuel caps to seal during leak testing is very difficult. The EZ-Lube goes on the o-ring to help it seal.

Fuel tank checking can be done a couple of ways. Some builders put balloons on the fuel inlet/vent tube and pressurize the tank until they are inflated. Let them set for 24 hours and if they are still inflated.. your good.

The other method I think is a bit more accurate and almost as easy. I made up a manometer with a piece of 1/2" ID clear tubing from Home Depot. I attached it to the fuel fitting and then capped off the vent line. I attached the tubing in a U shape to a piece of plywood and filled it with some colored water. Once the tank was all sealed up, I turned the air compressor very low and blew some air into the tank from the fuel drain valve. I put enough pressure to seperate the two columns of water about 16" or so. (Don't over-pressurize your tank!!)

The first try yielded a very fast drop of pressure... UGGH! Out with Mr. Bubbles to look for leaks. First leak was the capped fuel vent, so I used some fuel lube on it. The next TWO leaks were on the access cover. I didn't have two of the screw tightned all of the way so it was blowing big bubbles. The 4th leak was at the fuel cap, which was expected. I put some more ez-lube on it. Took a couple of trys to get it positioned so it wouldn't leak.

At this point I am declaring a leak free tank. It's only been a couple of hours... but I think things are good and tight.

I've heard about keeping the shop temperature constant while checking as it can make a difference in the water column levels... well, my shop temp is dead on 69 degree's but my columns are fluctuating up and down by 1/2" or so. I marked it then was out of the shop for 5 min and come back to a 3/8" drop. Crap.... I marked where it had dropped to, just to see if it kept dropping. 30min later it was above the original mark.. and 30 min after that it was up 1/2" from the top mark. It is very windy out today and I think there must be some fronts moving through.

Manometer setup
Changing levels/pressure

(Time: 1.5 hours)
- posted by Matthew @ 11/27/2003 10:47:23 PM