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Thread: To return or not to return

  1. #11
    tucsonchris's Avatar
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    Oct 2008
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    Default Re: To return or not to return

    I'm debating this same issue. Here's what I'm confused about.

    If my header tank is full--which it would be all the time unless I was minutes from fuel exhaustion--then I have continuous gravity pressure trying to make the fuel flow from the tanks, to the header, and then to the engine. the fuel doesn't care if it travels through the bottom fitting or the top fitting of the header. Having said that, there would be constant back pressure to the fuel return line. But the fuel return line is supposed to dump vapor (and I presume small amounts of fuel, into the header--which it cannot do because it is being met with the fuel coming FROM the header. Now I'm guessing the fuel pump provides extra pressure, but I've seen the little jet inside the banjo bolt through which the fuel and vapor are supposed to travel, and I can't imagine there is much pressure left after that.

    Any ideas?

  2. #12
    Senior Member Dorsal's Avatar
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    Default Re: To return or not to return

    The pressure from the pump will be ~4-5 psi, the head pressure is ~1 psi, with the engine running you will get a small amount of flow through the restrictor back to the header tank. My understanding is that this provides a more continuous flow of fuel through the lines when idled down on a long decent on a hot day. This flow is to help prevent the fuel in the lines from vaporising over the hot engine by introducing a steady supply of cooler fuel. Not sure how much this all matters but I believe this is the theory behind the return line.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  3. #13
    Senior Member Dorsal's Avatar
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    Default Re: To return or not to return

    One thing I do on my 912-S that helps a lot is have Firesleeve on all the fuel lines. Firesleeve is an excellent insulator and will probably do as much or more in keeping the fuel from getting hot and vaporizing than the return line will.
    I agree, I do the same just for that reason, then heat shrink over the ends to keep oil and stuff out of the fire sleeve. I personally don't think the return is necessary but I put it in anyway, couldn't see the harm in it.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

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