Airtight test of a fuel tank
Assembly of tankBreath in water
I was afraid of oil leak from a cap, while assembling a fuel tank. So I tried a airtight test, pressurizing the tank in water of a bucket. I blew a tube in my mouth. A bubble came out. To seal, I screwed tight. Blowing again, a bubble came out from the other side of the cap fringe at this time. I screwed again, no bubbles came out at last. The cap can rotate by my fingers, no good. I had better use a cheap tapered rubber packing for chemical tubes to get tight seal.

Partion Shrinkage
PartitionHike of forming
I took out the cylindrical seal. The photos shows the mouth of the tank. As matter of fact, the leaks were out of the points at partition line of plastic forming. A forming shrinkage was observed. I do not think this type of the packing is suitable for aircraft. It is incapable of a long time usage at all.

Vance, a member of RCGroups, suggested to me, 'Modelers have been using those kinds of tanks for years. Sometimes a tank will be able to hold fuel without leaking, but not be airtight. When I first got it, I wasn't too impressed with the opening either, but the tank is configured perfectly for this particular plane. I had to use a little sandpaper on the opening to get rid of the molding flash and smooth it up so it would seal properly.' I tried filling oil, and I got oiltight in running an engine. I thank Vance very much.

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