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Re: [T3] Brake bleeding and other hydraulics


On 13 May 2005 at 14:00, Constantino Tobio wrote:

> Hmm. Do the fuel lines always maintain pressure? What keeps enough fuel
> in the lines to pressurize the lines and get enough fuel in on startup?

There is a check valve of sorts built into the fuel pump, but after you shut 
down a hot engine, there is enough heat there to slowly boil the gas, which 
will force the fuel back into the tank, replacing it with vapor.

Later, as the engine cools down slowly, the vapor condenses. If the fuel system 
were perfectly sealed this would draw fuel back into the lines from the tank, 
but the seals aren't perfect, so air gets drawn in instead.

Thus if you try to restart an engine that was shut down hot, you'll find that 
all the lines and injectors are filled with air rather than gas, so nothing 
happens until the pump works long enough to push fuel thru the whole system, 
forcing the air out. The air comes out via the return line, which bubbles it up 
inside the gas tank.

-- 
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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