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Thread: Fuel Lines - Single or Double Flare

  1. #1
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    Default Fuel Lines - Single or Double Flare

    My flaring tool for tubing does both double and single flares for AN fittings. I have always thought that the double flare had a little bit of compression from the nut/ferrel when you tightened it down giving an even seal. I took a piece of the 3/8" fuel line and did a double flare to see if the ferrel and nut would fit. They seem just fine. Anyone have any good reason why to not use the double over the single flare?

    Thanks

    Gary

    Dbl Flare 1(002).jpgDbl Flare 2(002).jpg
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  2. #2
    Senior Member jiott's Avatar
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    Default Re: Fuel Lines - Single or Double Flare

    I would be concerned about possible cracking with a double flare on aluminum tubing.
    A single flare is perfectly adequate.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #3
    Senior Member jrevens's Avatar
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    Default Re: Fuel Lines - Single or Double Flare

    I agree with Jim. You can see the surface stress fracturing at the folded bend. It is not nearly as severe with soft copper or stainless steel, for instance. Also, with an AN flare nut you have the additional insert which eliminates rotational rubbing against the back face of the flare when tightening. You might be able to see that the formed flare is sometimes tilted slightly and out of alignment axially after double flaring. All that aside (I guess most of it isn't really relevant anyway), there really isn't any reason to do a double flare in this situation, in my opinion.
    John Evens
    Arvada, CO
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  4. #4
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    Default Re: Fuel Lines - Single or Double Flare

    Quote Originally Posted by jiott View Post
    I would be concerned about possible cracking with a double flare on aluminum tubing.
    A single flare is perfectly adequate.
    Quote Originally Posted by jrevens View Post
    I agree with Jim. You can see the surface stress fracturing at the folded bend. It is not nearly as severe with soft copper or stainless steel, for instance. Also, with an AN flare nut you have the additional insert which eliminates rotational rubbing against the back face of the flare when tightening. You might be able to see that the formed flare is sometimes tilted slightly and out of alignment axially after double flaring. All that aside (I guess most of it isn't really relevant anyway), there really isn't any reason to do a double flare in this situation, in my opinion.
    Thanks guys. Both good inputs and I agree that for cars I know, the double flare was really only a consideration when we were running fuel injection and the pressures were a lot higher (55psi or so). I did a friend's car once using stainless lines and they were a BEAR to get the flare right so single it is.

    Again - thanks.

    Gary
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

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