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AN fittings & sealant

rcarsey

Well Known Member
Section 5.27 tells us about using Permatex #2, Tite-seal, or Loctite 565 on pipe thread fittings...

"Because we cannot always fully tighten tapered thread fittings, and because even after fully tightening the fitting a small spiral leak path remains along the full length of threads, a thread sealant must be used during assembly"

I've been applying Permatex #2 to AN threads.. does it also get applied to the nipple/flange side of the fitting as well? (the side where a flanged tube mates to the fitting with an AN nut).

I don't think so? I don't see how it would prevent a leak on this side of the fitting.
 
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No. Only on tapered, NPT threads. The AN side with the 37 degree angle seals dry on the 37 degree face. If the faces are slightly mared and cannot be easly replaced, there are ̶t̶e̶f̶l̶o̶n̶ Aluminum tapered washers you can install in between.

EDIT: The washer are Aluminum
 
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fwiw i recently cleaned year old permatex #2 gasket sealer [non hardening] off of the tube using gasoline as the solvent.
 
fwiw i recently cleaned year old permatex #2 gasket sealer [non hardening] off of the tube using gasoline as the solvent.

I used permatex #2 as recommended by a certain Australian engine company to seal the NPT threads on oil cooler fittings. All four fittings leaked after a few months. A few years later I got tired of wiping off the mess and redid the whole job with Loctite 545. No leaks.
 
I suspect that those leaks were related to contaminants being present on the threads, I thoroughly degreased mine and have had zero problems.
 
FWIW; I have been using Permatex #2 on NPT fittings for too many years to count.
I've used it on cars, trucks, boats, and aircraft and have NEVER had a leak caused by this sealant.
 
No. Only on tapered, NPT threads. The AN side with the 37 degree angle seals dry on the 37 degree face. If the faces are slightly mared and cannot be easly replaced, there are teflon tapered washers you can install inbetween.

No, not tapered teflon washers. :)

They are formed soft aluminum seals and should be able to repair marred surfaces on the 37 degree angle faces.

https://www.aircraftspruce.com/catalog/hapages/del37fittings.php

04-05002.jpg
 
Putting a sealant on the AN threads 'can' allow the nut to tighten before the 2 seats make sufficient contact. Leakage will occur in most cases.

Tom
 
FWIW; I have been using Permatex #2 on NPT fittings for too many years to count.
I've used it on cars, trucks, boats, and aircraft and have NEVER had a leak caused by this sealant.

Contamination or under-torquing was unlikely, as all four threads of two different sizes and fitting geometries failed in the same way. I figured it might have been a bad tube of Permatex, but see little point debugging the failure in an aircraft application when methacrylate sealants are far superior. bobnoffs comment jogged that memory so I thought I'd add my anecdote in case others encountered similar failures.
 
The Permatex Form-a-Gasket, that I used on black pipe natural gas fittings in my house, is soluble in rubbing alcohol. After tightening the joints, I thinned some Permatex with alcohol, then painted exposed pipe threads to keep them from rusting. The point is that Permatex might not be resistant to alcohol in fuel.
 
I suppose this question is pertinent to this thread. I am mounting my engine soon to work on the cowl. Looks like the oil pressure sensor fitting needs to be installed first. Is Loctite 567 OK for that fitting to the back of the engine? For those who have done this how tight does it need to be?
 
Like others, I've used Permatex #2 for many years on many, many threaded connections with no leaks. I have also used Permatex Thread Sealant with PTFE and it works great; for NPT fittings this product makes for a very good seal, yet allows for easier removal if ever needed and it does not harden.

One note about AN tapered fittings - use a couple drops of assembly oil (air tool oil works well too) wiped on the face and threads will allow you to fully assemble by hand while reducing galling potential. And then, once tight by hand, tighten one more 1/4 turn with a wrench and you're done - regardless of the fitting size and no torque wrench required.
 
I used the generic Loc-Tite stuff from the hydraulic hose store on all my pipe fittings - mostly hydraulic fittings for my landing gear. It was called "Pneumatic and Hydraulic Sealant". I figured if it was good enough for Caterpillar tractors, it was good enough for my airplane.
 
... soft aluminum seals and should be able to repair marred surfaces on the 37 degree angle faces.
I carry some of those "Del fittings" in my "parts bag" on a long cross-country. I'm not sure why, but it seemed like a good idea. :confused:
 
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