Sealant for fuel system pipe fittings

The place to raise issues, ask questions, swap ideas and discuss anything related to aircraft engineering, maintenance and building.
NB Any opinions expressed in this forum are not necessarily those of LAA Engineering

Moderators: John Dean, Moderator

Post Reply
smiffy68
Posts: 7
Joined: Thu Jul 10, 2014 10:30 am

Sealant for fuel system pipe fittings

Post by smiffy68 » Tue Oct 16, 2018 11:55 am

Hello

I'm in the process of replacing the fuel system in a Kitfox. There are a number of 1/4" NPT brass fittings to reassemble. I know PTFE is a no, no, but I don't know which variant of Loctite is the accepted. Is Loctite 542 the one to use?
Kevin Smith
040930

mike newall
Posts: 330
Joined: Mon Jan 28, 2008 2:56 pm
Location: N Yorkshire

Re: Sealant for fuel system pipe fittings

Post by mike newall » Tue Oct 16, 2018 12:26 pm

Fuel Lube is easiest - non setting.

Get in touch on PM with an address and I will send you a smear in a tiny poly bag :mrgreen:

You don't need much and it is very, very sticky.......
025807

tnowak
Posts: 505
Joined: Wed Jan 02, 2008 11:00 am

Re: Sealant for fuel system pipe fittings

Post by tnowak » Wed Oct 17, 2018 8:31 am

Kevin,

I have the Loctite stuff (592) as I have recently done similar with my new fuel fittings.
I can send some if you like.
Tony
Tony Nowak
008249

mike newall
Posts: 330
Joined: Mon Jan 28, 2008 2:56 pm
Location: N Yorkshire

Re: Sealant for fuel system pipe fittings

Post by mike newall » Wed Oct 17, 2018 11:41 am

Fuel Lube despatched
025807

smiffy68
Posts: 7
Joined: Thu Jul 10, 2014 10:30 am

Re: Sealant for fuel system pipe fittings

Post by smiffy68 » Sat Oct 20, 2018 4:48 am

Fuel Lube received thanks!

Will give it a go when my new tank finally arrives!

Loctite 592 in reserve if any problems!

Thanks chaps. :D
Kevin Smith
040930

Bill McCarthy
Posts: 488
Joined: Mon Jan 07, 2008 4:06 pm
Location: Caithness

Re: Sealant for fuel system pipe fittings

Post by Bill McCarthy » Sat Oct 20, 2018 10:45 am

Why are you using a sealant ? If you are using perfectly good fittings, they don’t need sealant, especially the 592 stuff - getting the fittings apart again, if required, will be a problem. Introducing any form of contaminant to fuel lines - you know what happens !
032125

coxargus
Posts: 53
Joined: Fri Sep 11, 2015 2:57 pm

Re: Sealant for fuel system pipe fittings

Post by coxargus » Sat Oct 20, 2018 3:55 pm

I use 592 but ensure that the first three or four threads of the male fitting are left 'clean'. It's anti-galling properties allow you to get the fitting really snug.

592 does not set dead hard and there is absolutely no problem unscrewing the fittings - have done it many times.

Cleaning old sealant off the threads I have found to be a different matter! - especially the female ones.

Frank
Frank Cox
041606

Bill McCarthy
Posts: 488
Joined: Mon Jan 07, 2008 4:06 pm
Location: Caithness

Re: Sealant for fuel system pipe fittings

Post by Bill McCarthy » Sat Oct 20, 2018 5:04 pm

Loctite 592 is a thread “locking” agent, not a sealant, and right there you have highlighted the problem with residue left on threads after they are undone - how can you be absolutely sure that you are making up the joint again without getting some of the stuff into the system. Galling ought not to be a problem (unless the fittings are in stainless steel). If there is concern about leakage, then either the joint is not assembled correctly or it the wrong choice of fitting in the first place.
032125

Leesr
Posts: 46
Joined: Thu Sep 25, 2008 12:04 pm

Re: Sealant for fuel system pipe fittings

Post by Leesr » Sat Oct 20, 2018 10:01 pm

Bill McCarthy wrote:Why are you using a sealant ? If you are using perfectly good fittings, they don’t need sealant
NPT fittings do need sealant, Bill. The threads are truncated, so there is leakage through the spiral form. That's why everyone else here is recommending a thread sealant.

Rob
Rob Lees
015666

tnowak
Posts: 505
Joined: Wed Jan 02, 2008 11:00 am

Re: Sealant for fuel system pipe fittings

Post by tnowak » Mon Oct 22, 2018 7:44 am

Bill,

You are probably thinking of a different Loctite product:
Quote (from manufacturer's website):

"Thick acrylic dimethacrylate ester lubricating thread sealant paste which prevents galling on pipe threads and fittings.

LOCTITE® 592 is an opaque, off-white, thick acrylic dimethacrylate ester lubricating thread sealant paste which prevents galling on pipe threads and fittings. It provides immediate low pressure sealing and allows the readjustment of fittings shortly after assembly. The joint seals against pipe burst pressure after 72 hours. Suits applications up to +399 °F (+204 °C). Unsuitable for plastic piping.
Prevents galling on pipe threads and fittings
Provides immediate low pressure sealing and allows the readjustment of fittings shortly after assembly
High viscosity
Anaerobic cure"

I believe it is also recommended by Continental or Lycoming.
Tony
Tony Nowak
008249

Post Reply