Liquid PTFE any good? ... better than tape?

[Eric The Viking]

In the interests of accuracy, I think it was actually 3/4" BSP (female) to 15mm compression. I do tend to get 3/4" and 1" muddled up because of the ID and OD measurements (no longer do plumbing very often these days). Sorry.

It wasn't how it was specified (precious little info available on the supplier's web page), but the function it was supposed to serve. In context it was illogical to make an adapter with a parallel thread, as it couldn't be effectively sealed. I didn't say it was "defective" as such, just not correct/usable. The threaded socket was also far too deep, but couldn't be hacksawed down because the spannerable bit was narrow and on the extreme outer end.

In the past I have been driven to alter stock fittings (using a router table as I don't have a lathe), to make adapters where none were available (this one was beyond me however).

 

[Robin Whitfield]

I've faffed trying to find/modify similar sounding parts in the past, generally finding it easier to replace the part that it was meant to be connecting to rather than creating some monster adapter that never wants to seal.

You see it regularly with coffee machine connections trying to connect them to standard appliance taps when there's a pump and filter involved. Speaking of which, I've got such a mess (not installed by myself I might add) to sort at some point. It's been weeping for over 2 years now with no huge issues though so it tends to be a job floating around the bottom of the list. I think I even purchased the parts to fix it sometime last winter...

 

[Steve_Scott]

What straight threads have you come across that need PTFE? Straight threads aren't used for sealing fittings, that's what tapered threads are for.

Quite right... a parallel threaded connection should not have the water seal made on the threads, but rather a sealing face should be provided to facilitate the use of a washer/o-ring.

 

[Steve_Scott]

It wasn't how it was specified (precious little info available on the supplier's web page), but the function it was supposed to serve. In context it was illogical to make an adapter with a parallel thread, as it couldn't be effectively sealed. I didn't say it was "defective" as such, just not correct/usable. The threaded socket was also far too deep, but couldn't be hacksawed down because the spannerable bit was narrow and on the extreme outer end.

There are British/EU standards for thread dimensions on plumbing fittings. If I recall correctly, there is a minimum thread/throat depth but no maximum defined in BS EN 1254-4. Even so, you tend to find manufacturers don't offer you much more brass than they can get away with! A mating male thread should either be parallel and shorter such that an external washer can be used before the fittings bottom out, or you could use a taper male thread and sealant (I am a convert to loctite 55 but I'm not a fan of introducing circumferential stress into brass parts as its inviting SCC failures when plumber's over-tighten the fittings).

 

[cammy9r]

I use PTFE on parallel threads as its a lubricant too. Allows a nice bind free nip up on the olive or whatever. Taper threads get Loctite 55. I have standard thin tape, thicker gas tape and liquid and the 55 and use whatever I see the job needs. Also have boss white and green to hand too.

 

[Dave Moore]

Any comments on the best PTFE - is it tape or liquid?
I've run out of liquid and wondering if I should use tape (I have plenty) or buy more liquid. Having asked the question, I've never had a leak from using liquid PTFE - but same for tape (if done properly). I just wonder if liquid is more forgiving as if there is a "leak" the liquid is pushed into a better seal.

Rog

We use Loctite 55 ptfe string at work, it’s better than liquid and tape. It is impregnated with a sealant which goes off once fitted. We buy ours from BSS for about £10 but it goes a long way.