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What is / where is anti siphon valve?

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  • What is / where is anti siphon valve?

    I'm just about done pumping all of the gas / water out of my tank. I took the pick up tube and valve off the tank. The tube that sucks the gas up and the valve that you can shut off the fuel supply. I looked in there and it looks good. No debris or gunk.

    I also see two hoses coming out of the tank. One is small and one is big (1" maybe).

    I imagine one of the hoses is the vent hose but what could the other be?

    And where or what is the anti siphons valve? You guys say to check it but where is it and how do I check it?

    '89 25' Donzi R25 5.7 OMC / Cobra

  • #2
    Re: What is / where is anti siphon valve?

    Here is a pic I found with the Google machine. Its off of a 90 degree elbow. Just a ball and a spring inside...


    1969 StarCraft Chieftain, 4.3 Mercruiser Alpha One Gen II

    Link To Restoration Page


    Its What I Don't Say You Should Be Worried About...


    • #3
      Re: What is / where is anti siphon valve?

      That looks like what I got but after the 90 degree fitting connected straight to the tank I have a 1/4 turn ball valve then a nipple for the hose. I looked inside all of it and only the ball valve has a ball and I done see any spring.

      '89 25' Donzi R25 5.7 OMC / Cobra


      • #4
        Re: What is / where is anti siphon valve?

        someone might have removed it but it should be there right out of the 90 elbow i will try to get a pic of one but it looks like a barbed fuel line fitting with a spring and ball inside it and i think its like a coast guard safety thing .. not sure though ... any help here


        • #5
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          Re: What is / where is anti siphon valve?

          yes,you are correct,the anti-siphon ball and spring should be there?its dangerous if not installed because if your fuel line breaks(cracks) it will allow fuel to leak into bilge area causing a fire or explosion(and thats why coast gaurd requiers boats to have them...and will be located on fuel tank above pick-up tube...good luck (easy fix)