Curing water hammer

[garfield59]

The noise from the cold water pipes seems to be getting worse and I think the offending pipes are between the ground floor ceiling and the bedroom floor. Rather than rip up floorboards just to check and replace pipe clips (if necessary) would it be sufficient to fit a water hammer arrestor valve or PRV. if so, where would I fit it?
I can access the supply pipes in the kitchen to the washing machine and they seem secure but when the washing machine valves close I get a banging of pipework in the void space between floors. I get a "quieter" noise when the cistern stops filling or cold taps are turned off quickly. I can stop the noise when the cistern stops filling by making sure the basin tap is running in which case the flow just increases when the cistern is full.
Any suggestions welcome before the problem of irritating noise becomes a search for a leak!
Many thanks in anticipation of the usual useful responses.
Garfield

[plumbbob]

Stopping water hammer can be a tricky task and is not always successful.

The most common cause of the noise is a "dead" end of pipe somewhere filled with air. When a tap is opened, the trapped air expands and pushes the water back along the pipe. When the tap is quickly shut, the water compresses the air and fills the pipe reaching the end causing the flow to stop suddenly causing the bang.

If nothing else, for health reasons these dead pipes should be removed.

[garfield59]

Thanks for the quick response as usual plumbob.

Trouble is the hammer only started recently after I added some pipework to supply the new upstairs WC. I'm not aware of any dead ends - the only pipe we have ever blanked off was above our bath when we removed the electric shower but that was over ten years ago and I just capped the pipe where it came through the tiles.

I'm puzzled!

Garfield

[plumbbob]

Trouble is the hammer only started recently after I added some pipework to supply the new upstairs WC.

A typical reason why the water hammer has just started. You drained the system and now a piece of pipe is full of air and is the most likely culprit of your water hammer. If it was me, I would head straight for that piece of pipe and remove it. If you have access to the cap, loosen it to bleed off the air. It will at least prove a point.

Dead legs of pipe shouldn't be left anyway. Just think, if you haven't drained the system for 10 years, there is 10 year old water in your drinking supply!!!

[garfield59]

Plumbob, you are a star!

As soon as I read your reply I could see how draining the system for recent work had affected a leg of the system that had been virtually forgotten about.

I cannot easily get to the junction with the rest of the system (it's either behind a built in cupboard or under the bedroom floor) but I can remove the end cap and let the air out and water into the leg. Is there a fitting similar to a radiator bleed valve I could fit in place of the existing 15mm end blanking cap? I could then open it regularly to let fresh water run through the leg until I get the chance to remove it.

Thanks again for the help plumbob - it is appreciated.

[plumbbob]

What about an air vent cap?

ae235.jpg (8.3 KiB) Viewed 438 times

It's odd how coincidences occur, I was doing some major work in a house yesterday. As part of the work I did, I removed no less than four dead lengths of pipe. Not only did the water hammer disappear, but there is no longer brown/green water, which I found in one of the longer dead lengths, trapped in his drinking supply. Yuk!

[garfield59]

Plumbob, once again you've delivered the goods - thank you!

Just found the cap you suggested in the Screwfix catalogue so will get a pack.

Incidentally I turned the mains water pressure down a bit yesterday and the washing machine has stopped triggering any hammer since. However, if only for hygiene reasons, I will still drain the dead leg frequently and remove it when we are next lifting boards upstairs.

Thanks again for the help

garfield