what (not) to use on fuel line fittings

[Greg Hermann]

>On Sat, 27 May 2000 19:19:42 -0400, Chris Conlon <synchris at ricochet.net>
>wrote:
>
>>At 10:37 AM 5/26/00 -0700, Garfield Willis wrote:
>>
>>>BTW, one last thing, teflon tape is NEVER used on aircraft fuel
>>>plumbing. Just NEVER, for the very reason you cite above.
>>

(snipped lots of good stuff about why not to use pipe sealants or teflon
tape on critical systems)!!

All of which is very true.

There is a place for tapered pipe threads. It is in joints that are not
expected to be disassembled, EVER!! Sealants are OK for non-critical stuff.
If using tapered pipe threads in a critical system, put them together DRY,
and use a SEAL-WELD to seal them!! (Like I said, they are really only to be
used where disassembly is not expected to happen anyway.

Which is precisely why socket weld fittings were developed--if you are
going to weld it anyway, why bother with the threads ??!!

Use a flange set, a union, or an AN fitting where things are intended to be
disassembled periodically.

Another, all but forgotten, alternative for such locations, or for use
where one is changing from pipe stuff to AN stuff, and where sealants and
welding are both unacceptable/impractical, is  STRAIGHT pipe threads! These
have the same diameter (without the taper) and pitch and range of sizes as
tapered pipe threads, but rely on a lock nut and an O-ring  for their seal.
Straight pipe threads are perfectly acceptable for periodic disassembly,
they are very vibration resistant, and no sealant is required! O-rings can
be selected for proper compatability with the process fluid.

Greg


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