Gas tank

[ABarker]

This is my first post, I would like to know thoughts on check valves in model engine gas tanks, some plans call for them and some do not.

 

[coulsea]

It depends on quite a few factors. A check valve keeps the fuel up to the mixer/carb by preventing it from falling back down the fuel line. The check valve takes effort to operate which may be too much for a very small engine so the solution is to raise the fuel tank to just below the mixer.
A fast running engine will be better able to keep the fuel up but a hit and miss engine has more time between sucks for the fuel to run back down.
The size of the fuel line will affect the movement of fuel in both directions.

 

[Brian Rupnow]

Yes, when a hit and miss engine goes into "miss" mode, the fuel all runs back into the tank. Then when they try to "hit" there is no fuel immediately available, so they quit. A regular i.c. engine can get by without a check valve, but they may be difficult to start because they have to suck the fuel from the tank up to the carburetor each time they are started. I have done a lot of "experimenting" with check valves, and on a small bore engine a 5/32" diameter ball is about as big as you can use in the valve. Any larger and the engine won't have enough suction to get the ball up off it's seat.

 

[l.dullum]

Use a small diameter (0.060" O.D.) fuel line, put a full loop in it between the tank and the carb, and position the tank so that the top fuel level is just below the jet outlet in the carb venturi. My hit & miss engines will suck the tank dry with this arrangement without the use of a check valve.

 

[mayhugh1]

Use a small diameter (0.060" O.D.) fuel line, put a full loop in it between the tank and the carb, and position the tank so that the top fuel level is just below the jet outlet in the carb venturi. My hit & miss engines will suck the tank dry with this arrangement without the use of a check valve.

clever idea! ... simple, effective, and free.