After a very long, tedious, and messy job of finishing the fuel tanks, one may wish to know whether or not they will leak. I know I did, but I'm just kind of curious in that way. There's a fuel tank test kit from Van's which I dutifully purchased. The contents were a Schrader valve, a cap for the fuel line and a page of xeroxed instructions for testing the tank. Not too bad for six bucks, I guess. For those not familiar, August Schrader is the guy who invented the valve we all use to keep the air in our tires.
The Schrader valve is placed into the fuel drain fitting and the AN cap over the fuel line, and a balloon over the vent line. The balloon was not included in the kit. The instructions were simple: just tape over the fuel cap (I guess the fuel filler caps are not air tight). Then put the balloon on. Then fill the tank with air.
I attached a short section of aluminum tube to the vent fitting to make a right angle turn providing more room for the balloon. Also, using a surprising amount of electrical tape, I made the end of the tube larger to better fit the balloon. Then using safety wire around the neck of the balloon it is fastened to the vent pipe.
It is at this point that the tanks are ready to fill with air. The purpose of the balloons is to protect the tanks from over pressurizing and to provide a visual indicator of success! If the tanks are overfilled, the balloons will just burst before the tanks are damaged. Which is exactly what happened to my first few balloons. The air filling the balloons is definitely a lagging indicator because of the small diameter vent line. Eventually I learned to stop filling the tank when the balloon was only 2/3 full and it will coast on up to full as the pressure in the tank and the balloon equalize.
Once the balloons are full, each rivet and seam is tested with soapy water. Initially, I had some leakage around the access plate on both tanks. Tightening the screws did the trick. All that is left to do is wait...
Waited long enough?
Well, I waited 3 days with no discernible loss of pressure. That is really all I would expect the balloons to last anyway. If I had been a little smarter, I think I would have inflated a few 'control' balloons as a test of their ability to just hold air. I'm hoping that if air can't find its way out in 72 hours, then aviation fuel won't either. Fingers crossed.
Incidentally, I took the tape off of my fuel filler caps to test their leakage. They are not leaking, so it seems that the tape was unnecessary. That must be the deluxe part of my "Deluxe locking fuel cap."
Time to move on.
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