To PTFE or Not? FAQ

Only use it on tapered fittings. On everything else (parallel and compression) use Boss White (or similar).

Did you wind the PTFE so it bites "into" the thread? If not, then when you tighten it gets pulled-out out rather than driven in.

I just do a few wraps, no forming into a string, you'd have to really overdo the number of wraps to not allow it to find somewhere to squish to ...

Forgot to add: you can also use hemp on awkward joints. IMHO hemp works better, and allows adjustment better, than PTFE.

LSX is also good for solving minor weeping leaks ...

You have to also wind it in the correct direction.

It's got to be wound in the correct direction

The correct way and what you are trying to screw in will start to tighten quickly

The wrong way and the ptfe tape will travel outwards and off from the thread.

Note in this video which way the tape is wound

For water I use the thicker PTFE tape initially designed for gas taper fittings. Less faffing about and is more reliable than many turns of 'thin' PTFE tape.

Assuming that it has not got a fibre or rubber washer that can seat on the top edge of the BSP female fitting you have, then you will need to use PTFE

I can't tell from the pictures if either of the threads are taper fittings. Ideally for a good seal on threads they should both be taper fittings. If both are parallel, then you can still get a good seal with PTFE - you just need to use more, and in the right place.

My approach :

Hold the male fitting in your left hand with the thread pointing to the right. Start winding PTFE tape on the thread at the open end, and in a clockwise direction (i.e. up in front of the fitting, over the top away from you, down the back, and back under) You want a couple of turns to get started, then you wind "up" the thread towards your left hand. As you get higher you want to be building a thickness of tape. It may need to be 10 turns at the thick end. Basically you are winding a tapered spiral of tape that gets thicker the further up the thread you go. The idea being when screwed into the female socket, the first couple of turns go in easy, but then it progressively tightens as it goes deeper. It should go fairly tight, and not bottom out.

If you want to build thickness more quickly or steeply, that is when you can add a twist to the tape to get double layers further up the thread. (Personally I don't twist, but will rotate the roll of tape such that I am winding it on "edgeways" - the tape then scrunches up into a narrower width of tape).

(the direction matters - you want the tape winding direction to be such that you are winding it on tighter as you screw it into the socket, rather than unwinding it).

For a shock arrester it is not too critical how much tape is used and where since you don't care when it finally "goes tight". If it were a bib style tap on a wall plate, then that can take more trial and error!

Forever Chemicals rule OK ...

"Safe"

Apparently one of many things that kill us after we are dead...

It is the imprecision of which way up an outside top will end up once it has made a watertight seal which makes me always use PFTE.

We have an outside tap which screws into a BSP plate on wall. Like the idiots that we are, we (well, I) forgot to get the plumber to install an inline stop valve within the house, so I have to remove the tap every winter to stop it cracking when it freezes - for the winter months I replace it with a blanking cap.

So every spring, I have the "delightful" job of trying to refit the tap so it is the right way up while making a watertight seal. I can either have the top upside down or I can have a slow dribble from the joint.

So I have experimented with PTFE tape. The technique that I have found works best is to twist the tape into a "rope", lay that in the thread of the tap, wrap a layer of tape over the whole lot and then screw it in. If I have to do this process as few as three times before I get the tap upright and a watertight seal, then I feel satisfied. Some years it takes me as many as ten times, which quickly uses up a roll of PFTE.

The annoying thing is that once the builders had installed the outside tap, they fitted kitchen cabinets which mean that there is no access to the pipes within the house to retro-fit an inline stop valve.

snipped-for-privacy@please.invalid (AnthonyL) wrote in news: snipped-for-privacy@news.eternal-september.org:

Just don't bother, smear a decent thread sealant around the male threads before assembly and you will never need a roll of ptfe tape again. Never had a leak from such as these:

That said I would use a sealing washer instead on a bottoming out parallel threaded fitting.

I might live to regret saying this, but my house has an outside tap that was in place when I moved in over 25 years ago and was probaly installed when the house was built in 1988. There is no isolating valve and I have had no issues with the tap in cold weather, despite it being on the colder side of the house.

Similar here ~35 years, the pipe to the tap goes direct through a cavity wall into the back of the tap ... fingers crossed eh?

Ditto, I have quite a few outside taps (at least 5 scattered around 9 acres) and they're all just off-the-shelf brass outdoor taps and they have all survived for many years without issues.

If I remember right it's only a couple of plastic things have failed due (probably) to frost. For example in the recent cold spell an MDPE wall plate split, not so badly as to waste a lot of water but needed replacing.

The thing that does occasionally happen is fittings being pushed off the end of a pipe, I had two do this in the recent cold snap.

Didn't I read somewhere recently that PTFE tape is not a sealant but lubricates the thread to allow a smoother tighter joint ?

It depend how you use it.

On a compression joint winding ptfe tape around the thread doesn't seal anything as the seal is the copper or brass olive on the pipe. Some ptfe paste can be used on the olive to lubricate it to make it easier for the positioning of the olive on the pipe prior to it being compressed on the pipe.

The olive also mates to two tapered surfaces, one inside the tightening nut and one inside the rest of the fitting. If there is a slight leak on a compression joint that cannot be fixed by nipping up the nut a bit it may be fixed by winding a few turns of ptfe tape around the olive. This makes the olive slightly bigger and able to mate better with the two tapered surfaces in the nut and fitting. It can be a very effective bodge or perhaps a necessary fix for "chinese sourced" cheap plumbing fixings. In my experience not all olives are of the same quality and I have better quality spares that I would substitute if I think the supplied olive is suspect.

Putting ptfe tape or paste on the threads of a compression fitting can lubricate it and make it easier to do the nut up. This may have the disadvantage on giving you the impression that the compression fitting is being fitted correctly. You will not get a good connection if the pipe is slightly skewed to the fitting. If it is the tightening nut will soon get very difficult to turn but maybe not realised if the thread is lubricated. The tightening nut is easily started and turned if the pipe is straight with respect to the fitting.

In this case it is not a compression fitting. It is a male screw thread into a female screw thread (either straight or tapered). In these cases ptfe tape, a hemp string or jointing compound are all valid methods of sealing the joint.

Other plumbing fixings may use a rubber or fibre washer for sealing.

I'll see your 25 and raise to 39. There is an isolating tap but it's difficult to get at so we don't use it.

I always cut a cardboard box to drop over the tap, so although it might be cold outside at least it isn't exposed to the sky (which if clear can be colder). Hasn't failed yet, but then it hasnt been at negative temps here for very long at a time either.

#Paul

Sadly the original tap, a 1/4-turn cylindrical-hole-through-centre-of-a-sphere type, that the builders fitted when they moved the outside tap to this location, cracked the winter before last. It's on a patio in an L between two parts of the house, on a south-eastern face of the house so it gets all the sun it can in the winter.

Ironically that tap makes a perfectly watertight seal with the threaded plate on the wall, with the tap upright (apart from leaking from the crack in the body of the tap, obviously) whereas the like-for-like replacement that I bought only seals without PTFE when it is facing upside-down, and so needs the PTFE tape to seal when I back it off by