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Fuel filter placement

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  • Fuel filter placement

    I had issue with my AC Delco fuel pump. All concensus says they will work but not long and not efficient. If the fuel filter is mounted between the fuel tank and the fuel pump how effective will the pump be compared to mounting the fuel filter between the fuel pump and the carb orator?

  • #2
    I need to know what type of A/C Delco the pump is high pressure low pressure?
    you have a model for me?
    it's a automotive type pump what model of car or truck is the application?
    I'm a gyro Dude now! Bensen FTW

    FRANK

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    • #3
      This is a Mac 72. The pump is mcculloch. AC Delco. No model No. Original equip.

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      • #4
        The pump is not Mac, it's just original equip. I want to know if placement of the pump is going to effect the pumps ability to draw from the tank. Most older auto engines have final or only fuel filter just before the carb.

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        • #5
          Correction. Want to know If placement of Gas Filter effects the pumps ability to function.

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          • #6
            Originally posted by Rotorplay View Post
            Correction. Want to know If placement of Gas Filter affects the pumps ability to function.
            Yes, it can!
            A pump can theoretically produce any pressure possible at its output but is limited to how much it can draw at its input.
            The external air pressure is actually pushing the fuel toward the pump.
            If the pump can not lower the pressure enough for the fuel to flow, it won't.

            Consider a fuel pump that can produce self-prime up to 5 ft of head (-2psi) and produce 5psi at its output.
            Now consider a partially blocked fuel filter that produces 3psi of restriction.

            If the filter was located in the Output flow, the pressure would be reduced by 3 psi leaving 2 psi at the carbs.
            If the flow was still adequate for the needs of the engine, you will fly happily along.

            If the filter was located in the Input flow, the pressure would be reduced by 3 psi leaving Zero psi at the Pump.
            The fuel flow would be inadequate for the needs of the engine, you will be on the ground soon.
            This is a common cause of "Vapor Lock" in the fuel lines. The pressure gets so low that the fuel "Boils" due to the reduced pressure.
            At altitudes near sea level, One psi of pressure drop is equivalent to ~2000ft of altitude or heating the fuel by 10F.
            It gets worse at higher altitudes.

            It is typical to install a coarse fuel filter (~100u or more) that has very low resistance before the filter just to prevent large-scale debris from failing the pump.
            And Installing a Fine Filter (~10u or less) after the pump where more restriction is tolerable and to prevent clogging the fuel system of the engine.

            The fuel pickup in your fuel tank should have a very coarse wire screen filter (~1000u) to prevent any mega debris from entering fuel lines.
            This is often sufficient to protect the pumps and a pre-Pump filter is commonly omitted.

            If you are only going to use a single Fuel filter, place it After the Pumps.
            If you add a pre-pump filter, be sure it has minimal resistance.

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