15mm Compression Joints pull the pipe out a bit before tightening?

[405 TD Estate]

When tightening compression joints it always seems a bit kind-of hit and miss and they seem to need to be VERY tight to not leak - so tight I worry about damaging the joint or pipe.

I normally put grease on the threads which makes them easier to tighten but of course doesn't reduce the pressure on the parts..

After fitting a radiator the screw cap had started to crack after it was leaking a tiny bit and I tightened it some more. So I'm wondering if I'm doing something wrong, perhaps the pipe should be pulled out a little bit from the joint before tightening? or anything else?

Also are the silver joints stronger than gold ones?

[stuart noble]

In my limited experience compression joints leak if

a) the pipe isn't 100% aligned with the fitting, i.e. approaching at a slight angle. b) the pipe isn't fully pushed into the fitting. Sometimes difficult to keep it pushed in when both hands are holding spanners. c) the cut isn't made with a proper pipe cutter

[The Medway Handyman]

I'd totally agee with Stuart. Given you heed his advise above, they don't need to be as tight as you describe to seal.

[Ed Sirett]

Agreed, a tiny smear of a suitable jointing compound also help a lot.

[405 TD Estate]

Jointing compound - on the olive or threads?

[Ron Lowe]

Agreed, too.

To add some more:

The pipe ought to be clean, free from scratches / gouges, and properly round. The olive ought to be able to slide up and down freely, but not loosely.

With the pipe in the fitting, it ought to be possible to do up the nut right up to the olive by hand. It should then only take a gentle nip up with a spanner.

Problems can be: Over-tightening in the first instance ( a possibility from your description ); Poor condition pipe ( deeply scratched, painted, ovaled out from mis-use or impropper cutting ). Pipe entering at an angle as already mentioned. Allow the pipe to be as free to move side-ways as possible, so it can find a natural alignment.

If you want to use any sealing compound, it ought to go on the sealing element ( the olive ) rather than the thread. The thread is not the sealing element in a compression fitting.

[Andy Dee]

But some lubrication on the thread always helps too, especially on some fittings where the thread seems to be a bit "rough". I usually put a smear of compound under and on the olive, then on the thread.

A

[Derek Geldard]

And a "Wee drop of embalming fluid" behind the ears ?

Derek.

[John]

Cleanliness and a bit of lubrication. No PTFE tape.

[John Rumm]

You can use the PTFE for a bit of lubrication...

[Dave Starling]

Where does the PFTE go? I love seeing ptfe just sneaking out of the nut of a compression joint! Thats enough to put smile on the face of any miserable plumber! Even a friendly builder I know does that, bless his cotton socks :)

I read this thread with interest and the idea of putting lubrication on the threads is hogwash! I've done thousands of compressions and never needed to! So what if they squeak a bit? I agree with a smear of compound of your choice on the water facing part of the olive *only*. Many people say no compound, but it saves dismantling later on a weeping joint so is a worthwhile precaution in my mind.

But please - no ptfte tape on threads, ever!

[Dave Plowman (News)]

You must be using enormous torque to damage a 15mm compression fitting.

If you have leaks after normal tightening, something is wrong.

Is the pipe clean, round, straight and free from bad scratches? Is it going fully into the fitting? Are you using good quality fittings?

A lick of Fernox LS-X silicone sealer round the olive before tightening won't harm - but really shouldn't be needed.

[The Medway Handyman]

I've found that 'rough' thread on some makes of compression fittings, oddly enough mainly on the ones from my local plumbing supplies place. TBH I find that Wickes compresion fittings are the best.

I use 2 turns of PTFE tape as a lubricant.

[The Medway Handyman]

I usually buy compression fittngs from Wickes or Screwfix, which ever is nearest, no problems with either. The last lot I bought to re stock the van were from a local plumbing supplies place and they are a PITA as well as being more expensive.

No idea of specific manufacturers, but they obviously do vary.

PTFE tape is a great thread lubricant! The compresion fittings from my local plumbing supplies place simply wouldn't do up tight enough without PTFE tape lubrication.

[Grimly Curmudgeon]

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

Depends what you mean by that. Your 'gentle nip up' might actually mean a good quarter turn or more. Most people's 'nip up' would leave it prone to loosening off.

[Dave Plowman (News)]

It shouldn't be needed but will do no harm.

[405 TD Estate]

I haven't been cleaning the pipe as i would for a soldered joint - maybe that's it?

Also some of the pipe's are slightly mis-aligned - maybe that's it?

Kinda wishing I'd taken the chrome off a bit of the pipes and soldered the things. I guess you guys find soldered joints a lot more reliable as well...? There again I don't know how round the pipe would be after I file the chrome off..

[John Rumm]

Chrome pipe is a slightly different ball game - it tends to need a more serious doing up to get a good seal IME.

[Ed Sirett]

Since the joints are supposed to be manufactured to BS 864 (or it's EN equivalent) they /ought/ to be reasonably similar.

However there are several options:

1)The manufactuers are not holding to the standard. 2) The standard allows for a tolerance band. 3) Some of the fittings are not to BS 864 just supposedly good enough.

I tend not to used anything on the threads or if I'm using silicone greases for the olive I might put a little on the threads. However the latter make the tightening more 'squeaky' IME. PTFE removes the squeakiness in the tightening but will make the joints slightly harder to do up.

[Ed Sirett]

That's over the top,but clean so that pipe is smooth is needed.

A small amount of misalignment is possible, some olives are better than others in this area.

I'd definitely leave the chrome on and use a little resin (LS-X, Loctite thread seal, etc) on the oilve/chamfer part.