Water Hammer

3 Sep 2005
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United Kingdom
Hi Guys,

We've had major water hammer for some time and, as I don't really want to rip the house apart to get at all the pipework I'm considering fitting a shock arrester just after the main inlet stopcock ... something pneumatic such as ...


(Altecnic Shock arrestor SS Exp. Vess. Pneu. ZI-300016S/S £32.65)

Before I do, are they any good or should I start lifting floorboards :confused:

All advice would be greatly appreciated.

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You can get them much cheaper, but wouldn't it be better to get to the root of the problem? The water hammer will be generated by a float valve or stop valve and amplified by loose pipework. It shouldn't be too difficult to pin down the source and rewasher.
it happens with every valve in the house, all taps and all cisterns, both showers ... The dishwasher & washing machine make pictures jump off the walls :LOL: ... Knocking isn't restricted to one area either, knocking is heard all over the place.

I can minimise the effect by reducing the water flow by semi-closing the main stopcock but its not ideal as we have 2 thermostatic showers fed from the combi (Worcester Highflow 3.5) which are nice and powerful with the normal incoming pressure.

Edited: Sorry, I forgot to ask, where's best to get them from (assuming they actually work)
I remember one occasion where nothing I did had any effect on the water hammer I got after I'd converted a flat to a combi. The pipes were really well fixed, and it wasn't anything to do with the only float valve. But every time I turned the tap off it started, and went on for 15 seconds, almost spooky. Even cut a pipe to get any air out - no different.
Put one of these

on, and ..... it was just as loud but slowed down!
So I put an iso valve in series with it (just on a tee) and could adjust the noise nearly right out. The tap still turned off with a quiet thunk but the customer didn't notice. I saw a smaller thing in a merchant recently too, probably just as good.
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ChrisR, I'm not trying to teach granny to suck eggs. I meant the poster.
Yes, the main stop valve was replaced 4 weeks ago (it took me all day to locate the main isolator in the street) :LOL:
Maybe it's the main isolator in the street? Have you asked the water company to check this?

Try part no. 11355 here
the one you've pointed out is a MUCH cheaper version than the thing I originally looked at :eek:

At that price I'll fit it immediately after the main stop valve and see what happens.

Thanks for all the help.
Pressure reducing valve and shock arrestor from a PTS branch, cheap as chips and I`m on commission :LOL:
Chris H's is the one whose pic I showed - sorry I should have showed the text too!

I believe, though I'm not sure where from, that they should go near the source of the trauma - ie the water outlet tap. Do let us know if you experiment!

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