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James Maher wrote:
There is a third option.
Seal the vent when not flying.
The vent in my fuel tank is a -4 size AN bulkhead elbow.
I screw a cap on this fitting when not running the engine.
When the cap is removed there is usually a hissing sound indicating a vacuum or pressure in the tank. This also prevents fuel vapors from escaping which can be a hazard themselves.
Jim Maher
Jim, back when I was driving a truck, the company had a big air tank out back. About a 50 gal tank and it hadn't been used for years. I'm sure the seals were mostly dry rotted, but the thing was designed to hold at least 150psi. We were out back messing around on a slow, hot summer day at about mid morning, and on a whim decided to pull the draincock. The thing spat a little mud and then a clear stream of water. It probably had a pint of water built up.
Sealing your tank will slow the process down (a good thing), and only the smallest of holes is necessary to keep from blowing your tanks. I don't have the plans with me to compute the exact area, but just 1psi of pressure will put over 600lbs of force on the face of your tank (and about the same on the bottom and back). Please, drill a hole in your cap. Use some micro-bits and make it as small as you can, or screw it on very loosely so the air can push out (or in) around the sides. This may also save your bacon on the day that your forget to remove it (Murphy says that you will eventually).
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