Basic plumbing - compression joints.

Use a compression stop end.

Richard

In message , Graeme writes

IANAP If the olive and fitting slide over the burrs left by your hacksaw, just fit it and you'll be fine. I suppose you should consider if the pipe is old enough to be an imperial size.

Is this just a temporary capping-off, while the bathroom is being re-furbed? If so the having a handful of pushfit stop ends is handy ...

A compression joint shouldn't have any compound or tape on it. It's designed to seal without anything added to the sealing faces. (In the case of carrying gas, it *must* be assembled according to the relevant BS, i.e. without any sealing added.)

However, if it's been buggered up by fitting badly, then the seals may not work as designed, and can often be bodged by using tape (again, not acceptable for gas). This will not seal for as long as a properly made compression joint. Once the seals have been contaminated with something, it will probably always need bodging to make it seal again because the sealing faces are damaged.

The most common way I see compression fittings damaged is by doing them up using a poorly fitting spanner on the compression ring. This can distort the compression ring into an oval or egg shape, and then it won't seal, and may even leak more as it's tightened. The spanner needs to be a good tight fit so there is no tendancy to roll over the nut corners. The jaws need to be parallel, and if using an adjustable spanner, they must stay parallel under force (cheap adjustables don't). I do sometimes use a single turn of PTFE on the non-sealing half of the olive as a lubricant while tightening and compressing the olive on large pipe sizes, but if you do this, make really sure it doesn't get into the sealing surface of the joint, and after initial assembly which compresses the olive, you can disassemble and remove the tape.

If the capping off is temporary, I will often do it using a pushfit end cap (although they don't like being pushed onto hacksawed pipe ends with any burr as it can damage the O-ring). When doing plumbing, it's good to have some pushfit endcaps to hand anyway in case you have to cap something off you hadn't thought of (e.g. water trickling back out the other end of the cut pipe).

In message , Tim Lamb writes

Yes! Although the house is Victorian, most of the plumbing was installed +/- 40 years ago, so a fair chance it will be metric?

In message , Andy Burns writes

They look handy things to have in the shed. Thanks.

No, this is a permanent capping off, as the room (a ground floor carbuncle on the side of the house) will no longer be a bathroom.

I think, in this case, getting a nice clean 90 degree cut is going to be the most difficult, but I'm not going to try until tomorrow, as, should it all go pear shaped, more chance of finding a proper plumber on a weekday :-)

Ordered! Thank you.

Cut the pipe 'downstream' of where you want the final cut. This should hopefully give you enough spring in the pipe to get a pipeslice in to cut it properly. I really really wouldn't try a hacksaw unless you have room to make a second, third or fourth cut when the first one goes wrong. Not buying a pipeslice, but having to get an emergency plumber in, would be a false economy.

I always use plenty of Boss Green, but others will say you shouldn't. I find the stuff works. Just have some kitchen roll handy, as it's messy.

In message , GB writes

Where I want the cut is about three inches from the wall, so not enough space to rotate my 'traditional' cutter, but plenty for a slice, which I have just ordered.

The cold is already disconnected, so this morning, I removed the cold pipe, tap etc., then cut through and removed the waste pipe and trap, leaving just the hot supply, which is where the pipe needs cutting. It did occur, afterwards, that removing the waste pipe first was probably not a good idea ...

Luckily, there is a drain c*ck close to where I want to cut, so fingers crossed.

A dry compression fitting should seal, but doesn't always. A bit of gloop in there can solve that.

If you're new to this, do the nuts up good & tight. It's surprising how much tightness is needed.

NT

More than likely...

My experience is :

Generally if the pipe is clean and in good condition (not scratched, dented etc), then a compression fitting will seal just fine on its own.

Using some lubrication on the threads to make tightening easier (especially if working in a confined space) can make the job easier. A pipe jointing compound like jet lube will do the trick, but so will a few turns of PTFE tape on the threads[1].

If for some reason you can't get a good seal on a joint (maybe 1 in 100 joints IME), then a few turns of PTFE over the olive will normally fix it. As will application of a jointing compound. (use a proper WRAS approved one though - not something that will harbour microbial growth like putty or old school boss white).

lastly a decent set of spanners help enormously. Using something that is poor fitting can in extreme cases deform the backnut, and that will have difficulty ever making a proper seal.

Then why not use an end feed cap? Provided you clean the pipe and use decent flux and solder properly, never leak.

Do be aware that a dead leg like this sometimes causes noise.

I have a small collection of speedfit stop ends for just this purpose... I find them handy as they are easy to remove by hand without needing tools.

Plus file to deburr it. You may find it's imperial not metric as well.

Whatever you have to hand

In message , "Dave Plowman (News)" writes

Because I have several compression end caps to hand.

Indeed, although the particular basin to be removed has never been used as such in 16 years, so not much is going to change. I am fairly sure the feed pipe to be terminated is a T off another pipe that feeds a downstairs cloakroom.

In message , John Rumm writes

Excellent. I have completely cleaned and almost polished the pipe where I want to cut, and no signs of any dents or deformity.

Will report back :-)

Good advice I picked up on this group was to pull the pipe back a couple of mm before tightening the nut. This allows the pipe to "pull in" as the nut is tightened.

End feed caps cost pennies. Keep your compression fittings for where they are best way.