which thread sealant?

D

dougg

Well-Known Member
Joined
3 May 2010
Messages
259
Visit site
I'm going to be swapping my 50mm seacocks along with the 50mm m+f elbows that go with them.

What are most people using on the threads, PTFE?

Thanks
 
Last edited:
nigelmercier said:
Until it comes undone.
Click to expand...

Has anyone ever experienced a 50 mm seacock unscrewing itself from a skin fitting? I use a bar about a metre long with a piece of angle welded on the end to engage the little nib inside the skin fitting. The valve is held with either Stilsons or an adjustable spanner, either of which is about half a metre in length. With a decent amount of force applied to the combination I cannot see them coming apart no matter what sealant was used. Bearing in mind the number of posts from people who cannot separate them I think self-unscrewing is a non-existent problem.

I use PTFE tape or, if I can get it, liquid PTFE, which is superb stuff. In the absence of these I use Sikaflex 291. None of these is a thread locking product, they are there to prevent leakage of water between the threads.
 
vyv_cox said:
I use a bar about a metre long with a piece of angle welded on the end to engage the little nib inside the skin fitting. The valve is held with either Stilsons or an adjustable spanner, either of which is about half a metre in length...

I use PTFE tape or, if I can get it, liquid PTFE, which is superb stuff...
Click to expand...

I use this liquid PTFE at home, agree it it excellent: http://amzn.to/1gno30y

OK, I concede that if you can get that much grunt onto a fitting, then it won't come undone. I'm currently contemplating if I can get a 200mm long spanner onto my through-hull fittings, or whether I will need to cut the end off.
 
Just done 6 fittings with Loctite 572. Seems excellent. Nice and clean to use, slow setting, allows position adjustment without damaging the seal.
 
KellysEye said:
PTFE tape is designed for water pipe compression joints not through hulls.
Click to expand...

Incorrect, as usual. PTFE tape is a sealant used in a wide range of industries, for products including oil, natural gas, oxygen, water, medical gases, seawater, refrigerant gases and many others. The offshore oil industry uses tons of it and we had a standard specifying its method of application.

From Wiki - In some countries the tape is colour coded, e.g. yellow for natural gas, green for oxygen and some specific medical gases Slightly different codes are used in the UK, where tape may be used from coloured reels, e.g. yellow reels for gas, green for potable water.

PTFE should never be used on compression fittings. It is perfectly acceptable for threaded joints between valves and skin fittings. Sikaflex is perfectly OK as a thread sealant but don't be fooled into thinking it is like glue when set - it isn't.
 
KellysEye said:
PTFE tape is designed for water pipe compression joints not through hulls.
Click to expand...
No, it's intended for sealing threaded connectors, which is why it is a perfectly reasonable thing to use when joining an elbow to a skin fitting. Compression joints don't need a sealant, and if yours do then you've cocked up putting them together. Here's a typical description, in this case RS PTFE Tape PTFEONEWRAP12X5 for Sealing http://uk.rs-online.com/web/p/ptfe-tapes/0231964/
PTFE One Wrap Tape

Extra thick PTFE tape designed for sealing threaded joints in just one wrap.

Only requires 50% overlap on threads for BS21 thread up to 2 inch
Reduced material usage
For sealing against all common gases and liquids
Length 5m
Suitable for potable water
Satisfies BGC IM/16, BS 6974 : 1989 and BS5292 Type C tests
Conforms to BS7786 1995 Grade H
Click to expand...
 
vyv_cox said:
PTFE should never be used on compression fittings. It is perfectly acceptable for threaded joints between valves and skin fittings. Sikaflex is perfectly OK as a thread sealant but don't be fooled into thinking it is like glue when set - it isn't.
Click to expand...
Agree about compression fittings.

However, PTFE tape is slippery and reduces the torque required to tighten and loosen the joint. I'd rather have something that at least gives some grab.
 
nigelmercier said:
However, PTFE tape is slippery and reduces the torque required to tighten and loosen the joint. I'd rather have something that at least gives some grab.
Click to expand...

Not if it is used correctly. The tape breaks down at the contact points on the flanks of the threads and accumulates in the troughs, where it provides the sealing. If the friction is reduced to the extent that you propose you are using too much.
 
>PTFE tape is designed for water pipe compression joints not through hulls.
>>No, it's intended for sealing threaded connectors

Indeed you are right, sorry about that, it's the gin with the cornflakes that does it ;-)
 
vyv_cox said:
If the friction is reduced to the extent that you propose you are using too much.
Click to expand...
I use thin PTFE tape, with about a dozen turns on a ½" thread. This equates to 3 or 4 turns of thicker tape. My usual guideline is that the threads start to look rounded at the top, pretty much like in the clip on this page: http://norcal.swagelok.com/blog/bid/88017/Skill-Applying-PTFE-tape-to-tapered-pipe-threads

They also make it clear that it is only for tapered threads, so even though I use it on parallel threads, it isn't really right.

But yes, I probably use too much rather than too little :)
 
Last edited:
You must log in or register to reply here.

Other threads that may be of interest

S
Real world anchor winch cable size
2
Replies
26
Views
731
vyv_cox
vyv_cox
K
Lewmar 185 TT Thruster. 3kW Thruster in trouble again!
Replies
1
Views
77
Kinsale373
K
howardclark
Which rope?
Replies
17
Views
476
phlip
P
M
New mooring / riser on existing grid
2
Replies
22
Views
419
NormanS
N
M
Which jacket? - (classic) SLAM replacement
Replies
10
Views
315
RunAgroundHard
RunAgroundHard

Share this page

Top