Plumbing keeps popping

[Tabby]

40mm compression fitting, an elbow, keeps popping off, but I cant find anything wrong with it. It gets done up firmly each time, but still comes off. The only thing I suspect about it is that the pipe that comes out is restrained about 8 feet away, so perhaps it pushes sideways (not in & out) in the compression fitting when it warms up. That's really the only idea I have. The fitting is most likely from screwfix, toolsatan or wickes.

Any ideas?

NT

[Mr Pounder]

The fitting is the wrong size for the pipe. Or are you shoving superheated steam down the pipe?

>

[Skipweasel]

40mm - I suspect it's plastic waste pipe. If you can do that up tight enough to make the seal bite into the pipe you're doing well!

[Tim Watts]

Skipweasel ( [e-mail]) wibbled on Monday 14 February

2011 17:03:

Ha - didn't see that... Usual discalimers apply... ;->

OK - hmm. Never had that problem. Given compression is universal, it's hard to blame the pipe assuming it is actually one of 40mm (nom) pushfit or solventweld.

Might be worth degreasing both the pipe and the rubber seal with meths. Is the rubber hard or fairly soft - should be the latter.

[Tabby]

..

Yes its 40mm plastic, oldish solv weld pipe, in good clean condition. The rubber seal looks as new, though not as clean any more.

NT

[Tabby]

Fitting and pipe are 40mm, fitting is universal so it at least should be ok. Nothing hotter than 40C goes down the pipe.

NT

[John Rumm]

This is a plastic waste fitting I take it?

Some extra pipe clips to support around the elbow might help.

[Skipweasel]

Or maybe even keying the surface with a bit of wire-wool.

However, my suspicion would be that repeated thermal contraction and expansion is slowly shuffling the joint apart.

[The Medway Handyman]

Does the pipe enter the fitting dead square on?

Plan B - replace the fitting.

[The Medway Handyman]

Buying it from Toolsatan probably wasn't a good idea :-)

[Tabby]

The whole joint does lack support clips, since there's really nowhere to put them. Today I added some extra support and cable tied the whole thing, maybe not the most elegant option but the best could be done in the circumstances. I didnt think of the lack of clips before, but it is in a location where its not getting disturbed at all. I guess that is the solution, trying to work out how to restrain the pipe.

cheers, NT

[Mr Pounder]

Fitting and pipe are 40mm, fitting is universal so it at least should be ok. Nothing hotter than 40C goes down the pipe.

NT

Not trying to go from metric to the old Imperial are you?

[Lobster]

But are they definitely the same matching diameter though? I've certainly experienced mismatching before, when using pipes and connectors which are outwardly the same; I'm pretty sure this has been the case when trying to use solvent-weld stuff with compression fittings?

David

[Tabby]

AIUI the idea of universal compression is that they fit all versions of 40mm, some of which is definitely not 40mm. I'll measure it when I can & report back.

I think at the end of the day its just not gripping it hard enough, and the only solution is to add restraint to the pipes so they cant come out, whatever the fitting might do.

NT

[John Rumm]

Yup that is the case - one size of compression fist both solvent and push fit sizes of pipe.

Could you not stick a solvent weld elbow on instead - that won't come apart!

[Dave Liquorice]

Not as easily thats for sure but may well break something elsewhere. The forces excerted by expansion/contraction are considerable.

Not sure that the coeffcient of expansion of ABS/PVC is but on an 8' length I wouldn't be surprised to see 1/2" or so over a 30C temperature range.

How about cutting the pipe in the middle removing 1/2" or so and joining with compression coupler? Then think about where the pipe needs to be "fixed" to get the expansion taken up in the compression joints and hopefully not "walk out".

[Onetap]

Expansion.

There is plastic drain pipe made for push-fit &/or compression fittings and there is plastic pipe made for solvent welding. The diameters are close enough to mix the two up but they may or may not be compatible. First off, check the markings on the pipe and fittings, look up manufacturers' installation details and see whether the twain are intended to meet.

Whilst doing that, look at the recommendations to accomodate thermal expansion. I'd think you'd need something like a push-fit union, which incorporates an expansion gap in the pipe lengths to allow them to move into and out of the fitting.

[Tabby]

The pipe layout has issues, I converted it from solv weld to compression so it could be taken apart if needed in future. Having done that the ends are too short now for solv weld. Replacing the last section of the pipe run would be needed to go back to solv weld - its possible in theory, but would be a devil of a job in practice.

There is 30' of pipe run with little opportunity for expansion, and its fixed firmly at both ends, courtesy of concrete, so I suspect thermal cycling may be a big part of the problem. I think what's been done now should work, if it doesn't I guess it'll be concrete breaking time.

Cheers, NT

[Tabby]

Well, the pipework was already pretty evil.

NT