Mechanical Fuel Pump vent tube.

Discussion in 'Gas Engines' started by missinginaction, Aug 2, 2014.

  1. missinginaction
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    missinginaction Senior Member

    Some time ago as part of my restoration of an older Silverton sedan, I installed new fuel system parts. These included a new fuel pump and I just installed a new Holley carburetor.

    There was never any mention of the vent tube in the carb installation instructions but it's come to my attention that I should install one. The Holley has a capped port that just enters the primary bores at the spark arrestor flange, this got me thinking. It looks like there is a port on the fuel pump to the left of the fuel line fittings. I'd just need to pick up a hose barb fitting (brass) to fit the pump. You can see the pump via the link below.

    http://bpi.ebasicpower.com/p/MAL9-35411

    I'm asking if this is the correct approach. Also, I'm wondering, since the fuel level in the tanks is above the level of the pump when the tanks are over half full whats to prevent the vent tube from filling the engine up with gasoline should the pump diaphram break when the boat is unattended?

    I do have fuel shut offs installed on the tank side of the primary fuel filter. Perhaps the fuel should be shut off when I'm not around.

    Thanks in advance for any thoughts,

    MIA
     
  2. gonzo
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    gonzo Senior Member

    Marine pumps have a double diaphragm. When the first one breaks, it will leak fuel into the cavity where the small hose port is and send it to the carburetor instead of the bilge. Also, the anti-siphon valve in the tank pickup will prevent fuel from free-flowing. Both the small hose and the anti-siphon valve are required by law.
     
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  3. missinginaction
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    missinginaction Senior Member

    Thanks Gonzo, you pointed me in the right direction. I found this little tidbit in the USCG regs. Looks like you can use an automotive hose for the connection between the fuel pump diaphragm and carb. Here's what they say. The red highlighting is mine.

    FEDERAL LAW

    183.558 - Hoses and connections

    (a) Each hose used between the fuel pump and the carburetor must be "USCG Type A1" hose.


    If a hose is used in the fuel line running between the fuel pump and the carburetor, the hose must be "USCG Type A1" and so labeled as required by 183.540. This requirement is applicable whether the fuel pump is engine mounted or mounted remotely from the engine, as permitted by 183.566.

    This requirement does not apply to a tube used to detect fuel pump diaphragm failure.

    TO COMPLY WITH THE LAW

    A hose used between the fuel pump and the carburetor is "USCG Type A1."

    Thanks again Gonzo.

    MIA
     
  4. gonzo
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    gonzo Senior Member

    Usually a clear vinyl hose is used. That way if you see fuel in it, you know that the pump is leaking. When you install the hose, the actuator rod needs to be held up. You can use grease to hold it in place. I made a tool out of a piece of metal strapping; the kind that holds things in place on pallets. It is enough to hold the rod up a bit and then slide the pump in place.
     
  5. CDK
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    CDK retired engineer

    Mercruiser uses a metal tube between the pump and carb for fuel and a cheap plastic hose for fumes and leakage. The hose is clear on a new engine but deteriorates quickly, after a few years it is brown and brittle.

    Is that USCG Type A1 compliant?
     
  6. powerabout
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    powerabout Senior Member

    Never seen a clear hose it is usually tygon tubing
     
  7. tom kane
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    tom kane Senior Member

    Just another of many reasons to have a Remote Fuel System in boats..no fuel pump in hull space to cause trouble...or any other fuel system bit and pieces.
     
  8. gonzo
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    gonzo Senior Member

    You mean, a pressurized fuel line from the tank to the engine?
     
  9. tom kane
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    tom kane Senior Member

    If you are asking me Gonzo what I mean is that you do not need to have any parts of the fuel system on the motor installed in an inboard. Take everything relating to the fuel system of the motor and have it in a Remote area sealed from the inside of the hull.
    Google Remote Safe Fuel System for Boats.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Tom has thought of modern fuel delivery systems as problematic, in spite of the statistics, at least in this country. Appropriately vented, unpressurized systems have been in place for several decades, with the expected drop in fires and over the side spills on pleasure craft, as a result. I'm old enough to remember the days previous to these mandated changes and fires where once common, but not so much any more, mostly as a result of these regulations.

    An argument can be made for fuel delivery isolation and in some special cases, this is done, but again, for the most part in carbureted or EFI pleasure craft, the hazards don't warrant additional steps or legislation.
     
  11. tom kane
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    tom kane Senior Member

  12. powerabout
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    powerabout Senior Member

    How can they be made safer?
     
  13. PAR
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    PAR Yacht Designer/Builder

    Tom, the problem isn't fuel handling or delivery systems design, but neglect and maintenance. You can develop idiot proof systems, but even these will cause issues given lack of care and maintenance.

    I've investigated many "incidents" and darn near all of them can be traced back to (as an example) an owner leaving 20 year old clamps attached to 20 year old hoses, without checking them or renewing them, before the incident. The most often caused fires I find are caused by improperly installed equipment, often owner equipped and typically are directly fuel delivery related, but electrical device installation/maintenance related. They follow the directions on the back of the box, but fail to take standard safe guards or use established procedures or marine grade products (like automotive part substitutions), during the process, leaving themselves vulnerable to a potential problem, particularly once they forget about the installation several years down the road.

    So, you can design a system that is fool proof, but as long as the owner is still "in the loop", you haven't removed the primary problem. This is what the USCG statistics show, once you have more than a casual look at the numbers.
     
  14. powerabout
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    powerabout Senior Member

    I agree Par

    I have never seen a boat catch a engine fuel based fire that didnt deserve to
     

  15. PAR
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    PAR Yacht Designer/Builder

    Yeah, that's what I've found too. I walk aboard and wonder why it didn't happen sooner usually.
     
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