AN6 fuel Pipe Fittings PTFE Tape or Not?

Neville B

Supporter
Hello
Just installing my fuel lines and using AN6 Fittings, there seems to be conflicting information about whether or not to use PTFE tape

Can anyone advise please?

Thanks
 

Randy Folsom

Supporter
Neville,

AN fittings rely on the angled surfaces for the seal. The threads simply hold those surfaces tightly together. Any sealant is going to negatively impact the seal.

NPT pipe threads are tapered so that as tightened, the threads are squeezed together. Pipe sealant does two things, it lubricates the threads so they can be more easily tightened and the sealant fills voids.

Hope this helps. Cheers, Randy
 

Howard Jones

Supporter
I use this stuff. It works very good on pipe threads and gasoline. I've had a 1 pt can of this for years and I'm still using it. Get the 4 oz size and it will last a long time. Tape was not allowed where I worked. Little pieces get into the small orifices and plug them up like master cylinders, jets, sensors, Proportioning valves, and especially ball and seat valves like Residual Pressure Valves and needles and seats.


Or get if from Aircraft Spruce and ask for a catalog. This catalog is the complete source for everything (materials and hardware) you need to build a car. I use it like a Bible.

 
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If you ever have an AN fitting that just will not seem to seal up. There are aluminum conical washers "seals" that are specifically made for AN fittings to aid it sealing.

We use them often on hydraulic systems in aviation.

 
As others have said, for AN no tape or sealant of any kind.

However, I would recommend using an appropriate lubricant for the threads during tightening...along with the proper holder and tightening tool. The holder is the soft metal/aluminum holder that commonly goes into a bench vise and holds the fitting on four sides (not just two).

Ideally use a 6-point wrench where possible rather than a 12-point or open ended wrench in order to minimize damage to the fitting and anodizing. A very small dab of Permatex anti-seize is what I use for the threads. For AN6 I would go around 15-17 ft/lbs.
 

Neville B

Supporter
Thanks for all the replies

Sorry if I am being thick but can someone give me an example of a pipe fitting

From Mick Muck "AN fittings, no. Pipe fittings, yes."

Thanks again
 
Thanks for all the replies

Sorry if I am being thick but can someone give me an example of a pipe fitting

From Mick Muck "AN fittings, no. Pipe fittings, yes."

Thanks again
Pipe fitting are tapered threads, it is the threads that seal, not the interface of the two ends. Pipe fittings are on the gas lines in your home.
 
AN fittings also must be torqued to the correct amount. Make sure you do not over tighten them.
Yes, and often if an AN fitting leaks, it is because one of the tapered surfaces is galled. Sometimes, if you are lucky, you can get them to seal by "re-indexing" the male and female to give a different sealing surface. This is a "get by" fix, once galled they should have new ends.
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
Yes, and often if an AN fitting leaks, it is because one of the tapered surfaces is galled. Sometimes, if you are lucky, you can get them to seal by "re-indexing" the male and female to give a different sealing surface. This is a "get by" fix, once galled they should have new ends.
Curious how this Indexing actually works Since there is only one starting point to the threads on both male and female.. I must’ve missed something somewhere…
 
Curious how this Indexing actually works Since there is only one starting point to the threads on both male and female.. I must’ve missed something somewhere…
The end on a female fitting floats, you can index the hose. If it didn't float, the hose would twist as you tightened the fitting.
 

Scott

Lifetime Supporter
Permatex Aviation Form-A-Gasket No. 3 is great stuff, but I would ABSOLUTLY NOT use it for automotive fuel lines. You may be thinking that if it's used in aviation for fuel lines (amongst other things), it must be good enough for your project car. Not so fast. Aviation fuel has zero ethanol in it but, depending on where you live and the time of year, your pump gas may have up to 10% ethanol. I think that 7 states mandate ethnol blending and unless the pump states no ethanol, you're not sure what the ethnol content is. The issue is that ethanol will soften Permatex Aviation-Form-A-Gasket. According to the data sheet:

"If the sealant has been dried for a long time or at high temperatures, cover the sealant with alcohol and allow to soften overnight."

Ethanol is an alcohol and is therefore not compatible with the sealant. E85 is obviously a non-starter, but I'm sure that someone will state that they've used it with automotive pump gas for years without an issue. Maybe their gas had low or no ethanol or maybe the threads were really tight or maybe they're lucky or maybe they have a pending leak. However, I've seen leaks occur on cars and a boat that were running pump gas. In MA where I live the ethanol content seems to be 5-12% as measured by an inline flex-fuel sensor. Current legislation is looking to allow up to E15 to be sold year round and my guess is that the number is only going to increase. There's also a small chance that if you don't store the car properly the fuel will phase separate and you wind up with a layer of pure ethnol which is basically what Permatex prescribes to remove sealant that has cured over a long time or at high temp.

From a performance point of view ethnol is great stuff, you just need to account for it. My SLC is flex-fuel capable up to E98. There are other products that are just as good and are resistant to ethanol. I found another sealant (forgot what it was), but later decided to replace all NPT connections with AN or ORB fittings.

Long and short, Permatex Aviation Form-A-Gasket No. is great stuff but I would not use if for automotive fuel lines.
 
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