PTFE Tape - how many winds?

[David in Normandy]

When fastening together plumbing with brass screw fittings how many turns of PTFE tape is normal to wrap around the threads?

[YAPH]

How long's a piece of string?

I generally give it a couple of turns at the leading end of the screw, building up more toward the back making a sort of cone shape.

One of those things you learn by experience. And PTFE tape is cheap :-)

[Airsource Ltd]

Enough to stop it falling off (i.e. a bit more than one) and then not too much, except for radiator tails which need loads (4-5 wraps) As you look at the thread end, wrap the tape clockwise, then screwing it in won't unwrap the tape.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember David in Normandy saying something like:

Twelve. Or six. Or fourteen. Who knows? Nobody. Try eight to start with and if it's too loose put more on.

[John Rumm]

If you are just using it for lubrication (rather than sealing on the threads) two or three is ample. For a proper seal on a thread you usually need more.

The difficult ones to judge are things like taps into wall mounting bosses where you need enough turns in the right place to not only seal but also bring the tap to a suitably upright position. John's taper approach works well there. For some things hemp as boss white are still easier (immersion heaters for example).

[YAPH]

Loctite thread sealing cord (like dental floss on steroids) is good for this since you can back it off if you need and it'll still seal, unlike PTFE.

Aaargh, noooo! Apart from the fact that it's illegal (not suitable for potable water) think of the poor sod who's got to remove it next time, when the boss white's set like rock. PTFE is great for this: lubricates the thread and helps it to seal if the fibre washer's a bit reluctant. I apply a couple of turns to the main thread and bunch a load up by the flange.

[Tim S]

YAPH coughed up some electrons that declared:

Do immersion heaters heat potable water (assuming potable=drinking as opposed to bath filling)?

But I agree with this... Boss white + hemp: once it goes off it never comes off :) Especially on something with the diameter of an immersion supported by an expensive but somewhat fliddy copper tank. Think it'd use it on rads, but probably not much else.

I wish they did boss green without the fibre crap in it - I tried some, it's bloody useless. Falls off before you can get the joint together.

Boss white says non-toxic - is it legal to use it with PTFE string rather than hemp, say on a bib tap outside? (Thought it was the hemp being a bug breeding ground that was the main problem) I find PTFE tape on a such taps is a PITA. A tug on the hose the wrong way and the ruddy tap starts undoing. That's one time I do want the whole lot to set solid.

What do you reckon about the liquid thread sealants that have appeared in recent times?

Cheers

Tim

[John]

I just hope the OP didn't mean Compression Fittings!

[YAPH]

yes: technically it's potable: rules apply

[YAPH]

Traditional Boss White contains Linseed oil (I think) which (AIUI) is why it's a no-no for potable. The newer (and harder to find) Boss White Universal is OK for potable as well as gas. My Boss Green is relegated to a corner of the van, awaiting a clear-out.

I find PTFE tape on a such

Tried the Talon stuff but didn't get on with it, and the blue stuff Toolstation do (True Blue?) but find between Loctite string, Boss universal and PTFE I don't use it any more. (It was messy and didn't stick things tight, like outside taps: a judicious amount of Loctite thread is my current recipie for that.)

[Tim S]

YAPH coughed up some electrons that declared:

Oh - OK then.

I'll file that in the grey gooey wikipedia...

That must mean that primatic cylinders are now banned (potential linkage of potable water with black mouldy scunge in rads)?...

[Tim S]

YAPH coughed up some electrons that declared:

Yes, it certainly smells that way. I like the smell.

I see it's not just me then, re Green Useless Stuff.

Thanks for the tip on the Universal - I'll see if I can get one for my toolbox.

Just to be clear on the taps, you mean loctite 572 (pipe sealant) as opposed to regular Loctite threadlock compounds (as in normally used on bolts etc)?

Cheers

Tim

[John Rumm]

Well to be fair - I have the potable version of something similar (not actually made by Boss)...

(not actually sure I would want to drink gravity fed hot water from a tank anyway, regardless of what thread sealer has been used ;-))

Last time I needed to resort to this technique it was an immersion boss that was a very sloppy fit in the tank, and the washer such that it was, was not really up to the job. I had two attempts with PTFE (using first copious, and then obscene amounts), and it still was not having it!

[David in Normandy]

No I meant brass screw joints. For example I had an 1/2" male to male joint I needed to screw into a pressure reduction valve near the cold water inlet to the house. So I assume from your comment that the tape should not be used on compression fittings? I did wonder. Just after the joint mentioned above there was an compression fitting and I guessed not to use tape on that since the olive should be stopping the water leaking not the threads on the joint. The rest of the plumbing from there is all soldered end feed joints.

I just wasn't sure how many winds of PTFE tape to do on the screw joint. In the end I did 4. The joint screwed together firmly without seeming too tight or too sloppy. I've since turned the mains water back on again and it isn't leaking so it must have been ok.

My plumbing book mentions putting the tape on in the correct direction so it doesn't unravel while being assembled, it just failed to mention how many turns. I don't like guessing if there is a "best practice" to follow.

[YAPH]

Not sure the number but thread in a red plastic dispenser, bit like dental floss. Screwfix do it.

[PeterC]

When I first used PTFE tape (many fortnights ago) I learned 2 things very quickly:

direction of tape(!) try the thread bare to see how much slop is available

With BSPT, the amount of tape can be useful to control depth if there's a risk of the joint bottoming out.

[Tim S]

YAPH coughed up some electrons that declared:

Ah - we're talking about different things... 572 is a liquid thread lock/sealer, made for plumbing (gas too apparantly - although I cannot see that or WRAS approval on Loctite's site, only Loctite 55 is mentioned as being CORGI approved and nothing is mentioned as WRAS).

Think I'll go with the dental floss (have some already) and Universal. Seems a bombproof combination I can use anywhere if required.

Cheers

Tim

[The Medway Handyman]

There is always a controversy around here re PTFE tape on compression fittings. You are right, they seal on the olive not the thread, but many, me included put a wind or two around the thread because it makes doing it up tight easier. IOW its used as a lubricant not a seal.

[David in Normandy]

What is BSPT ?

[Harry Stottle]

When I bought some PTFE tape for gas usage, it gave instructions on the tape reel, - One lap as shown, (small drawing of tape on thread), 50% overlap, For BS21 threads up to 2".