Quote:
Originally Posted by Roger
I think you need to revisit your "Physics 101" because you couldn't be more wrong. By your explanation, gas should shoot out every time he opens the fill cap since he is in effect adding a vent by doing that.
Fuel weeps out because there is an air pocket that warms, thus expanding. Since his one vent is below the fuel level, the air pressure builds up and forces fuel out. If that air pocket was vented the pressure would equal the outside air pressure and there would be nothing to force the fuel out.
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From the way he described it that is exactly what would happen is he removed the fuel cap when the boat was jacked up as he described. Your description of why the fuel weeps is absolutely correct, but what you didn't say is that when the air pocket is cool the
VACUUM behind the fuel is what is holding the fuel in the tank. If he breaks that vacuum and allows atmospheric pressure into the tank the fuel is going to come shooting out until the fuel level is below the vent.
Try this little experiment. Take a can of liquid (beer soda juice or water) and poke a little hole in the side. The liquid will run out but only slowly. Now do the same thing but open the top, the liquid will shoot out of the hole. Same thing applies to his fuel tank, no atmospheric pressure on the top and it only leaks slowly. Add atmospheric pressure and the fuel is going to run out much much quicker.
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