All of my race cars have AN fittings and I use hard lines whenever possible to
minimize pedal travel from flexible line stretch or expansion (yes, I know
there is very little with braided Teflon). However, when working with the
metal lines, I have always double flared the ends in spite of the fact that I
am using the sleeve and the female-threaded tube nut AN system (steel, of
course--sometimes stainless steel if I feel flush). I have had no failures
and no leaks. Is this simply "overkill" or does it offer some/any advantage?
Or worse case, is it a potential problem? Any expert opinions would be
welcome
Dick Buckingham, Jr.
Brian Evans wrote:
> Blatantly copied from the Dimeband Garage web site:
>
> "The SAE 45 degree double flare usually has a male-threaded tube nut that
> bears directly on the OD of the flared tube- so you need a double flare to
> help control galling that can result in stress cracking right at the flare.
> In short, you need "give" there. Problem is, the deformation that results
> is kind of irreversible, so the next cycle or two will result in your
> having to use astronomical torques to keep the flare from weeping. Worse is
> trying to use a single flare in an SAE flare nut and seat, and worse still
> if the seat is brass- the flared tube is sqaushed from both sides, even as
> it is deformed by the nut galling on it. The brass seat deforms and work
> hardens. It may seal once, with a ton of torque and some luck. It's not
> recommended practice - it's not even a good idea.
>
> Racers (and aircraft, which is where the system originated as the
> "Army-Navy" or AN standard in WWII) use the single 37 degree flare. The AN
> single flare is still a concave flare, but its 37deg angle seals by
> stretching, not squashing. The tube is supported by a separate sleeve that
> the female-threaded tube nut bears upon. This isolates the flare from the
> torques imparted by the nut. So rather than trying to get a seal despite
> the presence of rotating torques and the resulting galling, you press the
> flare between precisely-machined (steel!) seat and precisely-machined
> support sleeve. The sealing area under compression is at least double that
> of the SAE flare. An additional bonus is that the OD of the nut is a lot
> larger than the 3/8" of an SAE nut, which means you won't kill as many
> trying to get the proper sealing torque. (Even so, you should always use a
> proper flare nut wrench on any tube nut.) "
>
> So you're right - the double flare helps reduce the damage caused by
> galling. In the case of Girling "bubble" flares I think that the squashing
> and deformation of the bubble is critical, and you can only squash it once.
>
> brian
>
> At 11:29 AM 7/27/01 -0400, you wrote:
> >Note: normal people can delete this before reading -- abnormally intense
> >brake pipers can read on.
> >
> >>From: Brian Evans <brian@uunet.ca>
> >>What I do now is simply cut off the old girling or SAE flare from
> >>the >bundy tube, and re-flare the existing tube in place
> >
> >Brian,
> >
> >Yes, this seems to be the concensus ... no one (yet) has mentioned a
> >source for Girling-to-AN adapters (or Girling to anything else, for that
> >matter), so the easiest thing to do is cut & re-flare the hard pipe.
> >
> >>One big bennie is that the AN flare is a single flare and almost
> >>foolproof to make.
> >
> >This brings up an interesting question, for which I THINK I know the
> >answer ... have been reading lots of stuff on types of flares for brake
> >pipe, and nearly every "expert" says, somewhere, that one should NEVER use
> >a single-thickness flare (i.e. they all recommend a double-thickness
> >flare, like the SAE 45-deg inverted flare). However, obviously the AN
> >system uses a single-thickness flare! And we all know that works.
> >
> >I suspect that the single thickness is OK on the AN system because the AN
> >flare nut has a second piece -- the sleeve -- under the nut, so it doesn't
> >transfer the tightening torque to the flare & therefre doesn't gall the
> >flare. Other systems (notably SAE) do not have the sleeve under the nut,
> >so tightening the nut tends to gall the flare, and I guess that's why they
> >use a double-thickness flare. Comments?
> >
> >Regards,
> >Mark
> >
> >_________________________________________________________________
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>
> Brian Evans
> Director, Canada
> MCI Wholesale Internet Services
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