Water, water everywhere

[Tricky Dicky]

Today I had a flood in the bathroom. A compression joint connecting the copper pipe work to a short length of plastic pipe to the digital shower mixer failed and being at mains pressure produced a spectacular fountain.

This joint was made mid December and has been fine ever since. The reason for the short plastic pipe was due to the pipe clips I was using meant if I went copper up to the push fit connectors Mira have specified it would have resulted in an awkward little off-set so the plastic pipe solved that. I have been scratching my head as to the cause why after 21/2 months?

At first I thought I may have omitted the insert but it was there, I did note the olive did not seem to have bitten into the plastic as expected so there maybe the nut had not been fully tightened, but that usually results in a weeping join.

I am a bit old school in that I prefer copper and soldered joins and compression fittings as necessary and have never felt 100% confident in plastic and push fit joins other than for low pressure waste pipe applications. Today’s experience has not improved my feelings about plastic pipe in mains pressure applications. It has left me wondering if it was more an external issue namely a temporary spike in water pressure and it just found the weakest point?

Anyway, I cannot say I feel confident in the repair and domestic management was not best pleased with the soaked towels and bedding, especially with the stuff she had ironed only a couple of hours before.

Any opinions on the cause and suggested remedies would be appreciated.

[RJH]

Not sure of the cause - overtightened compression fitting maybe? I'd try a pushfit plastic connector - I've done a fair few plastic-copper connections using them.

[John Rumm]

Not tight enough would be my guess... The rubber seals on the insert will keep it watertight with relatively little compression force, but inadequate tightening allows scope for the pipe to slowly be pushed out of the joint by water hammer and other pressure fluctuations.

To be fair I have never had a problem with plastic, although for plastic to copper joints I would normally use a pushfit fitting. (probably because I keep a sizeable stock of end feed, a handful of pushfit, and fairly few compression fittings.

Torque up the compression a bit more... or use copper and put a small offset "set" in the pipe with a pipe bender.

[Sid.]

Perhaps the main water is higher, mine varies quite a bit.

[Tim+]

You mention a “digital” shower mixer. Does it use a solenoid to shut the water off? Just wondering if the abrupt nature of the shut off could be a factor?

Tim

[SH]

did you put a pipe stiffener at *each* end of the plastic pipe?

And another cause can be incorrect pipe insertion depth into the fitting, some plastic pipe have a repeating black line on the outside of the pipe, the idea being you cut at one of the black lines, and then put pipe stiffener on, then insert into fitting until you reach the 2nd black line on the pipe......

And as others have said, not screwing up the plastic pipe fitting up tight enough. if the pipe is loose, then water hammer will flex the pipe and those knife blades will cut grooves and work its wat to the end of the pipe with each successive water hammer session.

Also clipping down the water pipe will reduce the effect of pipe movement due to water hammer.

S.

[nothanks]

A long time ago (18 years?) I had a near disaster when a 22mm plastic pipe came out of a compression elbow, fortunately the SWMBO at the time happened to come home very soon after it happened and turned the water off before there was much damage. I decided it was probably caused by thermal expansion on a long pipe run trying to move the elbow and the short run on the other side of the elbow preventing it from moving ... resulting in the pipe walking out of the fitting. I replaced the compression elbow with pushfit, restrained the pipe, and allowed the short run to move. I realise that your problem was on a cold pipe, but perhaps repeated hydraulic shock, from the solenoid shutting-off or from general water hammer, pushed the pipe out. I always use pushfit for plastic-copper transition.

[John Rumm]

I get the impression you might be assuming the fitting was push fit? The OP said it was a compression fitting that failed on the plastic pipe.

The insertion depth marks may not be correct for a compression fitting - or even consistent between brands.

[Tricky Dicky]

As a few have said it must have been an under tightened nut as the olive just slid off whereas previous compression joints to plastic have resulted in secure olives that could not be removed. It just puzzled me that there had been no weeping which is a common indication of an under tightened nut or that it did not come apart on first pressurisation as we have quite considerable pressure on the mains.

Anyway SWAMBO has calmed down and the heat pump tumble dryer has been working overtime and stuff is going back in the airing cupboard. We are now worrying if it will happen again, I might put a pencil mark on the pipe and regularly observe it to see if any movement occurs.

Thanks for all the replies.

[John Rumm]

What inserts were you using? The speedfit ones I normally use[1] have several O rings on them to seal in the bore of the pipe and also in the bore of the fitting. The olive is not really required to make the joint water tight in this case - it just needs to grip the pipe well enough to stop it being pulled out.

[1] (and two more rings on the stem of the insert that seal on the inside of the pipe bore)

Probably not a bad idea for peace of mind...

Failing that make up a compression to plastic fitting on the bench, then take it apart and work out how much tightening you need to properly deform the olive enough to bit into the pipe.

[nothanks]

Re my earlier - can you replace the compression fitting with push fit?

[Tricky Dicky]

John Unfortunetly I used the plain inserts which have always worked in the past.

As for push fit fittings I already had the compression fittings spare so simply used them as such joins always worked in the past. If it looks like the problem is likely to repeat using push fit will be an option.

[RJH]

I'd just add - make sure the pipe is clean, round and unscored. I had an issue with an unprotected plastic pipe pushed through a wall, and picked up some light scratched. The pushfit connector didn't seal to the pipe properly.

[John Rumm]

Not actually my post :-)

However, they will work with plain inserts, but will depend more on adequate tightening for the seal as well as just the mechanical restraint.

Either should work...