Thorp Air Command - T18.net

here is my setup. I have wing tanks that gravity flow to a fuel pump under the pilots feet. From that pump, the fuel is pumped up into the main tank. Each wing tank has its own vent out of each wing. The main tank of course has a vent too. I get overboard venting out of the wing vents just after takeoff when full and it streaks fuel down the underside of the wing, which I then have to clean up.

Please check my thinking regarding fuel expansion: If I put a one way check valve on the wing tank vents so that air can only come into the tank, wouldn't the wing tank fuel expand up through the fuel lines, through the electric pump in the cockpit, and into/out of the main tank vent?

I agree with your thinking on expansion. I don’t think you are likely to vent extra from the main tank unless you already vent from the wings as the fuel heats up. I use to fly an Air Tractor that vented fuel in flight. Never saw it vent fuel on the ground. The boss’s Skyhawk does the same thing when the left tank is full.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I wouldn’t put a check valve in there. You might actually pressurize something you don’t want to. Wing tanks can vent pretty easily. Just make sure the line goes up and forward before it exits the wing. Also, have the vent opening facing into the wind. I met some guys that make the vent line do a few loops before exiting, but I’m really not a fan of that.
Cubes

yes, it does vent really easily. I cant stand it. I appreciate the tips. I've tried up and forward and loops. I do have the vent facing forward with a 45 degree angled face. Loops seem to work best, but still get too much venting during flight. No venting on the ground. First world problems I guess....

The Skyhawk vents forward to a forward facing tube. Riding the rudder in the Skyhawk or the 502 will stop it on them.

Cubes is correct (of course). Accidentally pressurizing a fuel tank would be bad. A wet wing starts getting as wet outside as it is inside kind of bad. If you install check valves make sure pressure can’t build up in the tanks.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

The Cessna's wing tanks vent into a negative pressure area and there are instructions in the mx manual as to how far below the wing they must be and that puts them behind the lift strut.
The Citabria has a similar vent but that points forward just the same as the Cessna's but is behind a small plastic fairing.
Maybe pointing the vent directly into the airstream adds too much pressure to the tank and all it can do is vent??
Speedbird 1.

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N872DD
200hp Lycoming