Noisy pipes

[Lobster]

I'm prompted to ask this today after one of our kids had a friend for a sleepover last night... none of ours ever need to use the bathroom during the night but this kid evidently has a smaller bladder than ours and we were woken at 5 am by the almighty crashing sound of the plumbing after he'd flushed the toilet. Bless.

Bit odd this. The noise developed a few months ago for no apparent reason. What happens now is that whenever a tap is turned *off*, or the valve on a toilet cistern *closes* after it's refilled, there's a massive *thunk* which makes the whole house reverberate.

There's no 'oscillation' noises while the water's running, and if you're careful and turn the tap off slowly, you can avoid the thunk (10-year-old guests, take note).

My thought is that it must be being caused by a length of unsupported pipework somewhere in a stud wall or under a floor (maybe popped out of a clip?) If so, unfortunately all my efforts to find it have failed; I've checked everywhere accessible but just can't localise the noise at all; I've tried lightly touching the pipework everywhere I can to see where the vibration is at maximum, and even injected expanding foam into a boxed-in area I suspected, all to no avail.

Any ideas? Could it be caused by anything else than unsupported pipework?

Thanks David

[Steven Campbell]

I had something similar. I found by closing or opening the mains tap by a quarter of a turn, it solved the problem.

[BigWallop]

The system sounds like it is mains supply all round, is this correct? The mains supply where it enters the house could be your culprit. Check it for sturdiness around the main stopcock. If it moves even the tinniest bit, it might be causing the hammering you hear.

Also, if you have any check valves on the system. These too can cause hammering as they loosen off after being under tension of flowing water. You may be able to adjust the valve using the little screw head thing on the side of it, and it prevents the valve from closing to quickly and causing the hammer across the pipes.

[Colin Wilson]

Not sure whether they're common, but I recently spotted an expansion=20 vessel for pipework that is supposed to stop water hammer.

(they might also be known as "shock arresters", a quick google brings=20 up prices from =A316 for a box of 25, right up to =A325 each)

[Lobster]

Sorted!

You got me on the right track... our house has a somewhat quirky water mains supply in that we have *two* mains stopcocks in different areas of the house; one originally fed an outside tap years ago and got 'assimilated' into the house supply by the plumber who worked on our extension some years ago - as both supplies were old 1.5" copper he reckoned it might help maximise our flow rate /pressure.

Anyway, upon investigation yesterday I found that one of the two stopcocks was turned off; evidently it must have been like that since I last did some plumbing... a few months ago! Until today I'd never put two and two together...

Many thanks! David

[John Kenyon]

Not sure whether they're common, but I recently spotted an expansion vessel for pipework that is supposed to stop water hammer.

(they might also be known as "shock arresters", a quick google brings up prices from £16 for a box of 25, right up to £25 each)

The use of a vertical blind stub in the pipework where the pipe transitions from a vertical to a horizontal run will probably do the trick. (i.e. incoming pipe comes up to a T piece, which has a short length of capped pipe continuing upwards, the pipe continues via the "arm" of the T piece.)

The airing cupboard of my flat is festooned with these stubs.

Another, even cheaper option where the hammer is occurring at a ballcock valve, is to tie a piece of string from the ballcock into the water and tie an old CD on the end. This acts as a damper on the ballcock valve, and stops it bouncing up and down on the surface ripples in the tank.

/john