Sealant for fittings

[OhioLSA]

What is the best sealant to use on the threads of pipe fittings on the fuel tanks? On the RV forum, folks recommended Tite-Seal, so I got some to try. It doesn't seem to ever set up -- it remains semi-liquid, so it (slowly) flows out of the threads. I did the balloon test on my tanks, and the tanks seem to be OK, but there was a tiny amount of leakage around one fitting on each tank. Also, being a newbie at fuel system plumbing, do you use sealant on flared tubing joints, or is that taboo? Thanks in advance!

[Salter]

no sealant on flared tubing. If you are having leaks on fuel lines that have the Tite-seal you need to re-do that fitting with tite-seal. When you flare your tubing for the compression fittings always use a little oil to lubricate the tool before the flare.

[OhioLSA]

OK, thanks!

[Bdflies]

A long time friend of mine is an engineer whose designed and built pipe handling equipment, all his life. All hydraulic powered. He absolutely despises teflon tape on anything. Long ago, he gave me a partial tube of Loctite PST sealant. Great stuff! Now, it's sold as Loctite 567. That's my go-to sealant for pipe threads. I wouldn't say that it ever 'hardens', but it doesn't leak.
Salter is 100% right about lubricating the flaring tool! If a flare fitting does seep just a bit, clean the mating surfaces and dab on a little permatex gasket sealant, on the sealing surfaces only. The awful, smelly, brown snotty stuff that makes an awful mess that's near impossible to clean up... It's saved my bacon, more than once!

Neither of these methods is found in 43.13-2b. Your mileage may vary.

Bill

[BTAZ]

In my opinion(which I know everyone has), there is no way in HE** I would put anything on a fitting, whether tapered pipe thread or flare, that would have ANY chance of getting into the line.

For low pressure tapered pipe thread, a very small dab of "Fuel Lube"(I think now called "Ez Turn") applied only to the male fitting at least three threads back from where the thread starts.

For high pressure fittings(oil lines for example), I use Loctite High Temperature Thread Sealent(http://www.loctite.com.au/3320_AUE_H...=8802651668481). again applied with care so it cannot get inside the tubing.

Neither of the above takes much(less then the head of a match size) as it is only filling the void between the threads.

If you have to remove a pipe fitting, clean both the male and females halves carefully so as to not introduce any contamination into the line.

If a flare fitting doesn't seal, inspect it carefully for cracks or nicks on the mating surfaces. If needed, there are "Flare Savers" (http://www.gen-aircraft-hardware.com...agename=flrsav) that might help you out.

In my experience, you have to have a wrench holding the flare to tapered pipe half of the set when tightening the flare nut on the mating line as there is more torque needed on the flare nut then is needed for the tapered pipe thread.

There was a recent lawsuit brought against Vans(only dismissed recently) by the surviving relatives of a builder that used RTV in his fuel system(against the advice of many people). The RTV plugged up his fuel flow transducer and he killed himself and a young child in the ensuing forced landing.

Perhaps used carefully it might be OK, but there are approved lower risk methods so why chance it.

[N3UW]

I completely agree with you. Very little thread sealent is needed. Too much can be disastrous. I would also never put any type of sealant on a flared fitting. I have used the flare savers before and they are great. If they do not seal the leak then the connection should probably be redone. MAkre sure that if you use the flare savers that you replace them if you open up the fitting. A fuel system in an aircraft is a place to be extremely careful and conscious of any possible contamination that could interfere with fuel flow to the engine,

[jaredyates]

Pipe threads require sealant, flare fittings must not have sealant. I have used Loctite 565 with good results. I can't remember where I read the advice to use it, but I'd suggest Googling if you'd like to have more confidence. As I understand it, they call these products anaerobic thread sealers because they only set up in the small spaces between the threads. So even though excess goop on the outside of the fitting will not set up, it will set up in the unobservable tiny place where we need it. Ditto on using any product sparingly and keeping it out of the system.

[OhioLSA]

Thanks Jared, for the additional explanation. I've heard of similar cases, such as some epoxy products which supposedly cure from the inside out, but whose outer layer perhaps never hardens.