copper fuel line gasoline from tanks to valves to filters

Discussion in 'Inboards' started by sdowney717, Jul 10, 2011.

  1. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    can you use 3/8 copper lines?
    I dont mean from anywhere the engine gasoline fuel pump is mounted backwards to a bulkhead valve or filter, or forward from pump to carb.
    But how about from tank to selector valve to a bulkhead mounted filter?
  2. Stumble
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    Stumble Senior Member

    from the Diesel Handling and Use Guide distributed by the US DOE

    "Brass, bronze, copper, lead, tin, and zinc may accelerate the oxidation of diesel and biodiesel fuels and potentially create fuel insolubles (sediments) or gels and salts when reacted with some fuel components. Lead solders and zinc linings should be avoided, as should copper pipes, brass regulators, and copper fittings. The fuel or the fittings will tend to change color and insolubles may plug fuel filters. Affected equipment should be replaced with stainless steel, carbon steel, or aluminum."

    So not really. In addition solid tubing on boats introduces a lot of problems with vibration and flexing (leading to failed joints) that are better avoided if possible. Flexible hose is usually preferred as it minimizes these problems, and is pretty cost effective.
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  3. PAR
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    PAR Yacht Designer/Builder

    Copper was widely used on gas lines for several decades, but should be avoided now. It doesn't like vibration and can develop cracks or pin holes. Unless you're building a concourse show winning antique with copper lines, use rubber or braided stainless.
  4. Tahoerover
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    Tahoerover Junior Member

    Never seen braided stainless with a USCG approvals. Do you have a source?
  5. Mark Cat
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    Mark Cat Senior Member

    Gasoline fuel system design for boats is covered by USCG 33CFR and ABYC for pleasure craft in the US. ISO generally follows ABYC for H-24 ABYC also provides ISO compliance.

    Per ABYC for Gasoline powered inboards; Fuel distribution and return lines shall be seamless copper, nickle copper, or copper nickle with a minimum wall thickness of 0.029 inches or USCG Type A1-15 hose if the line is within an engine compartment.

    Usually for hose, I just use USCG Type A1-15 thought the system.

    Proper Gasoline inboard fuel system design requires a comprehensive knowledge of the requirements in many different areas, from hose type to corrosion to ventilation to tankage to electrical grounding to spud design to clamp width to hardlines around batteries to....

    For gasoline hardlines we have the flexing problem on joints (especially welded) between connections that can mover relative to one another. However, it is possible to isolate these elements by using flexible hose. So we could have a flexible hose between the hardline (Mounted to a frame) and the tank, and between the hardline and the engine.

    Hope this helps,

  6. CDK
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    CDK retired engineer

    I know next to nothing about your ABYC or USCG and like to keep it that way.

    From an engineering viewpoint copper lines are fine for any fuel, albeit with 2 restrictions:

    On seagoing boats the copper lines should not touch walls at any point, so straps or saddles must be plastic or plastic lined to avoid rapid corrosion.

    And the fuel line should be immobilized near the engine where a braided rubber hose of 1 -2 ft. connects it to the engine.
  7. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I was thinking of using copper tube. The USCG also has requirements for tube ends as they have to have a nipple so a rubber hose wont easily come off. You can take a needle nose plier and force the end a little wider.

    What is the max length from fuel pump to carb they allow?
    I have A1 fuel line everywhere right now.
    But I think copper is more durable. My first boat had copper.
    My engine fuel pump line I rerouted away from the engine centerline running it from pump along the top of the engine stringer bed to the front of the motor, then vertically up and over to the carb. I did this to keep it away from the hot exhaust manifold area and I think generally it lets the fuel remain cooler keeping the line off the top of the motor. I also want to minimize hot start issue, percolation, etc... It is likely longer than regs allow as they have regs for everything, even seemingly harmless little items.
  8. Mark Cat
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    Mark Cat Senior Member has guidelines on the type of tubing for different applications.

    Here is video on how to make a tube bead. Talked about is how to anneal hard tubing to make it soft enough to bead.

    To hold the tubing one approach is to use a SS316 or SS304 fully cushioned (Neoprene) P-Clamp secured to the boat.

    For copper tubing you can terminate with flare or beads how this is done specifically is through selecting the correct tool for the type of tubing and end treatment.

  9. AndrewK
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    AndrewK Senior Member

    I worked for an oil company, when customer complaint samples came and the sample was oxidised the first question asked was there any copper tubing in the fuel system.
    When stainless or copper clad steel tubes are readily available why not use them.
  10. Mark Cat
    Joined: Jun 2011
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    Mark Cat Senior Member


    The question about copper came from the original poster per gasoline installations, which falls under USCG CFR 33 for pleasure boats.

    Why must we follow USCG CFR 33? For USA, Its the law.

    For the designs I am involved with, the largest gasoline powered craft is about 30 feet. For this size generally you will see the use of Polyethylene tanks and A1-15 fuel hose. You can use hard lines but there is really no need, and for fuel injected engines we have to accommodate a return if needed and many of the system diagrams are set up better for hose.

    From a saltwater material standpoint if seamless tubing is used with no soldered or brazed joints, I do not see an issue with SS316L tubing, nor AL 5086 tubing, other than the common galvanic considerations.

    However, I do not have a track record in using these materials for gasoline marine applications due to CFR.

    Cost is also a consideration for SS316L as compared to AL 5086 or Hose.

    The Hose manufacturers do a very good job per gasoline requirements and it is very easy to route and proven itself when using the correct SS316L clamps.


  11. Carteret
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    Carteret Senior Member

    I don't care for the vibration problems either. If using flared fittings, one cracked flare will drive you crazy until you find it. The thick walled USGG below bilge aproved rubber fuel lines are the way to go.
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