collapsed compression joints

[Mike Clarke]

The indentation of the pipe makes me to wonder if replacing old olives when re-using compression joints might not always be a good thing. I'm wondering what happens if the new olive doesn't line up exactly with the groove created by the old one, this could lead to a much shorter area of tight contact with the pipe and perhaps a less reliable seal. I've not had much experience with plumbing so I'm not trying to put forward a case for or against replacing olives, just looking for advice. The compression joints I've made invariably leaked slightly to start with but sealed OK after a bit more tightening. I'll be replacing quite a few radiator valves with TRVs soon so I'd welcome any opinions on this from the experts.

[George Tingsley]

Ok never say never But as Calor say in their web page a compression fitting with pipe olive coupling and nut in perfect condition should not have any gunk applied to interfere with the mating surface or contaminate the water or gas supply I once went to a gas fire that was not working when I dismantled it I removed a 6 inch length of ptfe tape that was blocking the jet how that got inside the pipe only God knows

Never in this case means best working practices people new to plumbing should be aware that compression fittings were never designed to need additional sealing around the olive and should avoid making joins like the top picture as routine

sooner or later you will encounter the stopcock buried under kitchen cabinets or the elec shower with only nut-olive protruding out of a tiled wall which will leak and be impractical to replace Then you can try ptfe or boss white to affect a cure I keep a tube of Hermetite instant gasket in the toolbox for such bodgery

[George Tingsley]

The is no torque guide listed from compression fitting manufactures there are also different shapes of olives both copper and brass which in theory need a different amount of force to affect a satisfactory seal Buy an isolating valve and length of copper pipe from Homebase as many diyers may do the supplied olives are the worst I have ever seen and the pipe is the softest I have ever come across even light pressure will push the olive deep into the pipe and make a watertight seal impossible

3/4 of a turn is a good starting point and works for most fittings try it

[G.W. Walker]

Who knows, TBH? My thinking was that a paste has almost no mechanical strength, and will get evenly smeared, but that tape could resist spreading due to its own strength, but I'll happily admit that this is utter conjecture on my part.

Sounds like a nice 4th year project for an engineering student ;-)

G.

[Mungo]

that the cut-away picture on this web site ought to go in the FAQ (if it isn't there already - haven't checked)?

Mungo

[Chris Bacon]

If copying these things is OK, yes, it could help people.

[Doctor Drivel]

Wrapping PTFE on the threads of a compression joint serves no purpose whatsoever. In fact a lot of it may prevent the nut being screwed fully home.

[Doctor Drivel]

George, you have got to take into account some of them here are not that bright. Richard here has been told on numerous occasions on how to use compression joints, but still comes out with the same crap.

[Mungo]

Put the link into the faq, not necessarily the whole picture.

Mungo

[George Tingsley]

Wrong im sorry to say Having now read all the massages in this subject It appears to me that most of the regular experts

[Dave Plowman (News)]

Calor show the entire pipe and olive coated with red Hermetite or something and suggest this prevents the pipe being seated correctly on the fitting shoulder. Wrapping PTFE round the olive doesn't.

Probably a 'plumber' making work for a 'mate' later. There's no way it could get inside the pipe from being wrapped round an olive - unless the pipe was cut by dribble's hacksaw at his usual 45 degrees.

[Dave Plowman (News)]

Fernox LX is the daddy for this.

[Ed Sirett]

Agreed. Given that, invariably, any joint that is undone you find the olive crimped onto the pipe.

[Doctor Drivel]

You are talking though your rear end boy. I think you should stick to drains. Look at the the the cutaways you posted. Read what I wrote.

[Dave Plowman (News)]

I should point out that not all show obvious signs of indents - just some.

But if you're simply re-making a compression fitting, there's no need to change the olive.

[Dave Plowman (News)]

[George Tingsley]

That was a reply to Mr Drivel who says you should not use ptfe tape on fitting threads and is now drivelling on about leaks from threads I don't think its worth the effort replying to him he must be your DIYing brother You on the other hand don't seem to be able to accept that over tightening is bad news on compression fittings Here a few more web pages that contradict your earlier advice that you should

USE OPEN ENDED SPANNERS AND TIGHTEN THEM TILL THEY GROAN

over to you again feel free to point me to any source that agrees with your advice or would you now like to admit that you don't know what you are talking about

[Chris Bacon]

[snip]

It's sort of possible that DP was referring to doing up fittings until they make a sort of squeak, which clean brass on brass does when under load. This "technique" isn't to be relied on, though.

It's always possible, having tightened the joint, to undo it and examine the olive/pipe, doing the fitting up again with a small extra tweak after (assuming everything looks OK).

[Doctor Drivel]

I am full pro. You come across as a bodger. You certainly don't fully understand how a compression joint makes its seal.

I repeat, wrapping PTFE on a parallel thread on a compression fitting body that a compression nut runs along, serves no purpose whatsoever except waste PTFE tape.

[Doctor Drivel]

"Wherever possible, use a layer of PTFE tape around the thread of the compression fitting. This tape will be pushed into the thread by the tightening of the nut and seal any overlarge gaps within the union of the threads. "

Again....wrapping PTFE on a parallel thread on a compression fitting body that a compression nut runs along, serves no purpose whatsoever except waste PTFE tape. The parallel thread is for the compression nut to run along. It is not a thread that makes a seal at all, it is there for the nut to run along and tighten onto the olive.

PTFE does nothing to make a seal on the compression nut parallel threads. The nut has a thread one end and a hole the other for the pipe to run through. None of the ends of the nut, threaded or not, make a seal. It is possible to make a seal on the parallel thread by using Loctite, but if there is a leak it will just leak out between the pipe and nut at the other end, which has no threaded joint at all.