Fuel Lines - Single or Double Flare

[Geek]

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

3090030901

[jiott]

I would be concerned about possible cracking with a double flare on aluminum tubing.
A single flare is perfectly adequate.

[jrevens]

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.

[Geek]

I would be concerned about possible cracking with a double flare on aluminum tubing.
A single flare is perfectly adequate.


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