collapsed compression joints

[Redeye]

after a rather more eventful weekend than i was hoping for, i'm hoping somebody can explain this....

i finished plumbing in everything in my new bathroom a couple of weeks ago. no real problems and all went quite well. so, i was a bit surprised to be woken at 1am on saturday to the sound of water running and a hysterical girlfriend. it appears that one of the compression joints has spontaneously exploded, allowing mains pressure water to go everywhere. fortunately no real damage done, just a lot of mopping up to do downstairs.

the bit i don't understand is why this joint went so suddenly. here's the facts :

1. the pipe had just slipped straight out leaving the olive in the service valve that the pipe had escaped from.
2. the joint hasn't leaked at all in the last 2 weeks.
3. the pipe was running from a service valve horizontally about 4" across then going to a flexi-hose which connects vertically to the adapters which go up to the mixer tap.
4. the pipe wasn't supported by pipe clips, although it's a short run and hardly moves at all anyway.
5. i'd put a couple of wraps of PTFE tape over the olive as i'd been advised that this can help stop small leaks (was this my downfall?)
6. all the other compression joints i've made are absolutely fine and have been for 2 weeks.

i'd quite like to understand why this joint has failed so spectacularly before i go trying to fix it.

thanks dan

[john2]

Best to remove all tape, provided the fittings are clean, unscratched and undamaged. Tighten until the olive just grips the pipe. Add an extra 1/6 turn to compress the olive. No doubt proper plumbers will disagree.

john2

[Ian Stirling]

Because you diddn't tighten it up enough. The olive should form a tight metal-metal seal, with no need for PTFE. The only case where PTFE is actually needed is if you've got damaged pipework, or fittings, and can't really replace easily.

You should _NOT_ be able to 'pull' the pipe out as happened in this case, without actually damaging the fitting, and exerting much, much more force than it saw.

[The Natural Philosopher]

Th olive should be tightened enough to permanently deform the pipe. In practice you can keep on going till you can't go no more, but somewhere in between 'just leakproof' and 'fully home' is a happy medium.

I am not sure how I do it, but in practice when screwing up they get tighter and tighter and then they don't get any harder to turn at all.that mean you are now deforming the copper, not taking up the slack, and its time to stop..or add that 1/6th turn for good luck.

[Guy King]

The message from "Redeye" contains these words:

Comiserations. Happened to my parents in law over Christmas. They'd not even moved into the house fully - just had new carpets and wallpaper etc, and had never even seen most of it fitted. Pipe went while they were away for a week - mains feed to loft tank came apart. Previous owner was a plumber!

Just the electricity to dry the house out came to nearly a grand. Thank heavens for insurance.

Anyway - never ever put PTFE tape on compression joints. They rely solely on metal to metal contact. If the olive has slipped off the pipe then it wasn't done up properly.

[Redeye]

okay, thanks for the feedback.

i've come to the conclusion that i've followed bad advice which is probably the cause of the problem. i'd also been warned not to overtighten compression joints, but advice here seems to suggest that isn't possible.

anyway, i think i'll replace some of my compression joints with push fittings in the hope of avoiding a repeat disaster (although i've got a push fit joint leaking slightly at the moment as well !!).

[Roger Mills]

As others have said, it wasn't done up properly - and don't use PTFE tape!

If you're not sure when it's tight enough - and you get used to the 'feel' when you've done a few - do it up and then take it apart again and check that the olive is firmly crimped onto the pipe. If you want a belt and braces job, smear a bit of Boss White (not PTFE tape) round the olive before you re-assemble it - but that shouldn't be necessary on a new fitting with new pipe.

[Guy King]

The message from "Redeye" contains these words:

Well, it is if you're a gorilla...

[Mungo]

My caution with mains pressured water extends to the belief that properly-installed soldered fittings are the way to go unless the consequences of a failure won't be too damaging. Of course, this then thwarts any changes because they aren't as readily undo-able as compression fittings.

I haven't used the new Monsoon 3 bar shower pump yet but its my first exposure to push fittings and I must admit to being quite impressed (with no experience of them this isn't saying much!). That plus the perceived speed in installation as well as easier installation in restricted locations makes push fittings sound interesting...

Mungo

[mike]

"Redeye" wrote in news: [e-mail]:

I think it's this that did you, making you think you had a seal when you hadn't.

You should NEVER put jollop on a compression joint (unless, unless...) but in case of a bodge like that - old pipe, short pipe, unremoveable olive etc you will need to muller it well down and make damn sure it won't budge

mike

[Ian Stirling]

Or it's 8mm pipe. With 22mm compression fittings, you'll have a job breaking the fitting so that it won't seal by overtightening. It's probably possible, but you'll need a long spanner, and the pipe to be restrained quite securely.

[daddyfreddy]

I'd guess the pipe was not fully home when you tightened it. The PTFE tape wouldn't have caused it.

[Guy King]

The message from Ian Stirling contains these words:

Doesn't everyone use two spanners? Perhaps that's where all the people who've been having compression joint fittings are going wrong, they're just using one spanner!

[Ian Stirling]

Two spanners helps - but you've still got an unbalanced torque left.

[Dave Plowman (News)]

Use proper open ended spanners and tighten them till they groan. You won't overtighten them unless using something silly like large Stilsons.

[EricP]

Compression joints are not PTFE territory.

[Chris Bacon]

Don't you *have* to use two spanners (or a spanner and a "grip", or two pairs of Stillsons)?

[Ian Stirling]

Depends. If it's a valve, or something else assymetric you can hold it with one hand, and sort-of do it up with the other.

[Guy King]

The message from Ian Stirling contains these words:

Mitigated with offset spanners. Anyway, it was the self limiting by the user of the applied torque to do up the fitting I was wondering about. With only one spanner even quite inept people will limit the tightness because the other half of the fitting is starting to turn.

[Guy King]

The message from Chris Bacon contains these words:

I'd have trouble doing otherwise, but I was wondering whether failing to do so might be the root of the trouble people are having with compression fittings.