[pczar3]

I've searched the links on the site but have not found an answer to a very basic question. Are you folks using fuel lube on the threads only or on the mating faces of the flare as well.
Electronics, no problem, fine points of fuel systems.... well I have to ask.
Thanks in advance folks.

Paul

 

[JonJay]

Neither

The mating surfaces of the flare and fitting should be dry. The seal is made my metal to metal contact. Some use lubricant on the threads, but that is not needed either.
Fuel lube should be used on your "pipe threaded fittings".

 

[pczar3]

Thanks for the answer!

That was my guess to keep debris out of the lines. Now I can go back to work!
Thanks again.
Paul

 

[mburch]

I use a small amount of fuel lube on the threaded portion of flare fittings, to prevent galling. But never on the mating surfaces of course.

mcb

 

[Bob Brown]

If you ever get any of that EZ Turn on you and see how sticky it is...you have an exact idea of where I'm going with this. My Tech Counselor (a very experienced builder) said "don't use it on the flares, but put a little on the "B" nut or threads of the male fitting. The idea being that if anything was ever gonna vibrate lose it's original proper torque and begin to "vibrate and rotate" and loosen, it sure wasn't going to very far with EZ Turn on those threads...but since it doesn't work like Loctite, you can still tighten, loosen, remove, etc without galling or tearing up anything. So that's what I did on all of mine, just make sure you carry a rag with you and make sure you don't leave any EZ Turn behind..., ie, make your fuel line installation clean. I also used torque seal on them. Just another data point...

 

[jdmunzell]

I suppose it's also a good idea to put the torque seal where you can actually see it from a finished airplane, inspection time view.

Does anyone use Loctite or Proseal on those B nuts to keep them from ever backing off?

 

[RVG8tor]

Pipe thread treatment

The mating surfaces of the flare and fitting should be dry. The seal is made my metal to metal contact. Some use lubricant on the threads, but that is not needed either.
Fuel lube should be used on your "pipe threaded fittings".

JonJay,

So if I understand correctly fuel lube wound be used instead of some other pipe thread treatment. Did you use the fuel lube on the fittings that go into the brake master cylinders? I have been meaning to get what ever I need for the pipe fitting in the brake system lines. Thanks for any help

Cheers

 

[JonJay]

I do, yes.

JonJay,

So if I understand correctly fuel lube wound be used instead of some other pipe thread treatment. Did you use the fuel lube on the fittings that go into the brake master cylinders? I have been meaning to get what ever I need for the pipe fitting in the brake system lines. Thanks for any help

Cheers

That is the product that I use on brake or any pipe type fittings. There are other products but it has always worked for me for all kinds of things, even as a gasket dressing. I do not know how well it holds up against brake fluid chemically, but the idea is to lubricate the threads so they do not gall, not to stop leaks.

To answer the other question about using proseal or locktight on B nut threads, I would not. Many of the fittings need to be removed for various inpsections like filters and screens. Fuel lube on the threads maybe, but properly torqued fittings should not vibrate loose. So, I leave them clean.

By the way, the design of a fuel fitting flare and B nuts are quite amazing. If they are slightly loose, they leak, but they have to be really loose to leak a lot. So they kind of have an early warning system built in. Pretty amazing design that has withstood the test of time.

 

[MNAv8or]

The mating surfaces of the flare and fitting should be dry. The seal is made my metal to metal contact. Some use lubricant on the threads, but that is not needed either.
Fuel lube should be used on your "pipe threaded fittings".

JonJay has it right, you shouldn't use any fuel lube on flared fittings. I have taken apart 1960's fuel lines with AN flared fittings that haven't been apart since it was built and they were nice and tight. As long as you get them nice and tight, do your leak check (a leak is you signal that it is not tight enough) and your should be good to go, put some torque seal on the fitting, and there ya go. You can glance as the fitting and tell if it has come loose or not.

I'm pretty sure that if AN fittings had a tendency to loosen over time, the FAA would have stepped in already and come up with a system to "lock" the fittings together, whether that be using safety wire and drilling a small hole in the fittings to be able to safety them together or some other means. I would leave them dry as fuel lube is some really sticky stuff and is messy. (I end up with just as much all over my hands as I do on the parts). Unfortunately the jets that I work on we use it on o-rings a lot and it never agrees with me.

 

[briand]

JonJay,

So if I understand correctly fuel lube wound be used instead of some other pipe thread treatment. Did you use the fuel lube on the fittings that go into the brake master cylinders? I have been meaning to get what ever I need for the pipe fitting in the brake system lines. Thanks for any help

Cheers

Isn't there a special lube for the brake systems tapered pipe threads?