Topic: fuel line


JohnA    -- 08-23-2020 @ 6:16 PM
  Has anyone used or using flex line that has check valve in one end that runs to fuel pump . I have seen advertised in V8 times. My car sits a lot and am afraid valve mine stick after time. Johna


TomO    -- 08-24-2020 @ 8:04 AM
  John, the valve in the line is a one way valve that opens from the fuel pump suction and the fuel flowing from the tank. To determine if the valve is stuck closed, remove the line and blow through it from the tank end. If you cannot blow though it the line is clogged or the valve is stuck. I suspect that your sediment bowl gasket is leaking or your fuel pump is weak.

I bought one of those and when I read the warning about debris causing the valve to fail, I decided not to use it. Then I went over my fuel system and made sure that all of my connections were secure and that the sediment bowl gasket was nice and fresh.

Then I did some serious thinking and decided that the line with the valve in it was a solution waiting for a problem.

The premise of the valve was that the fuel was being siphoned back to the tank. In order for this to happen, there needs to be an air source at the fuel pump and a vacuum at the tank. The fuel level in the tank must also be below the fuel level in the sediment bowl. The fuel level in the sediment bowl must be higher than the input line or the siphon action would be broken by the air source.

In all fuel pumps the input line is above the fuel level, so gravity should keep the fuel in the sediment bowl. There should never be a vacuum in the fuel tank as it is vented. If all of the connections are made correctly, there should not be a source of air to replace the fuel going back to the tank by the siphon action.

Tom


JohnA    -- 08-24-2020 @ 9:03 AM
  Thanks Tomo--i totally agree and will double check everything. Thanks again


supereal    -- 09-05-2020 @ 10:25 AM
  The check valves in the fuel pump should prevent any siphoning Most, if not all, loss of fuel in the carb bowl is due to "heat soak" under the hood from the engine and exhaust. As noted above, the tank caps should prevent formation of vacuum. I have seen incorrect caps, such as radiator caps, on fuel tanks. They can produce the infamous "vapor lock".


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