Water hammer questions

[Meggalar]

Hi,
We're currently suffering with a water hammer problem where we get a loud bang/clunk noise when we turn the cold/hot water on or off. This can happen from any tap in the house.
We never used to have this problem and I can't seem to get rid of it. I've tried draining down the cold water and re-filling but this hasn't worked.
The only I thing I can think I've done is to take the thermostatic shower mixer off the wall and put it back on.
Could this have introduced air into the system?
Or can you get this purely from a pipe coming loose, although not sure what would have caused that.

Any suggestions very welcome.
Thanks
Richard

 

[Madrab]

The main causes of water hammer is a ball/float/solenoid valve or 1/4 turn taps that close too quickly or loose pipework.
Air in the system would actually reduce/eliminate water hammer as that's how a water hammer arrestor works, not create it.
You say it's created by closing taps so doesn't sound like a valve is creating it, so i'd be looking for a loose pipe.

 

[polesapart]

Cures for water hammer include pressure reducers, shock arrestors, repiping with larger/better configured/better fixed/ different material pipes

and

sometimes turning down the mains stopcock suffices.

 

[gigz]

sometimes turning down the mains stopcock suffices.

I agree with this one, when you fitted the shower you will have opened the stoptap too much/too little. Have a fiddle with the stoptap whilst trying the taps.

 

[Madrab]

Did you have to turn your stop cock off or was the shower was fitted correctly and had iso valves that you turned off?

 

[Meggalar]

Thanks for all your replies.
The banging noise seems to occur just on the cold water. I've prised up a floorboard to look at the pipes and couldn't see any movement when we also got the banging noise.
I've found it tricky to locate the exact source of where the noise is coming from, although it now appears to be under the floorboards towards the rear of the airing cupboard/hot water cylinder.
I've tried turning the water pressure down and up but this hasn't made any difference.

When I took the shower mixer off it was a case of turning the stopcock off and draining the cold water down before then removing the shower mixer. I did fit isolator valves but their too awkward to get to unfortunately!

I didn't want to but it seems the next stage is to take up more floorboards.

Thanks
Richard

 

[gigz]

Have you tried altering the stop tap ? Also water hammer is worse with quarter turn taps (they slam the valve shut as opposed to a soft close)

 

[Armo74]

Check all taps arnt dripping first a perished tap washer can sometimes cause this.
You also need to check the float valve in your CWSC that feeds your cylinder.
Pipes that are not clipped properly are a problem and if left can potentially leak at weak joints caused by the vibration.

 

[Meggalar]

Thanks.
By the stop tap I assume you are referring to the stopcock tap under the kitchen sink in our case?

We don't have a Cold Water Storage Cistern and the taps appear to be all fine.
I've managed to get a hand to the cold water pipes in the bathroom but can't feel any vibration, I guess it could be unclipped at some point and then clipped afterwards which might stop the vibration but not the sound.

I'll start on the floorboards and see what I find.
Thanks for all your advice so far.

 

[texasholden]

We get water hammer problems whenever the garden hose is connected to the external tap, and the tap is left open (the hose is closed via a spray gun at the far end).

If we close the external tap, the banging stops. I don't know why this is but I very much doubt it's anything to do with trapped air in the hose of elsewhere.

Seems to me to be more down to resonance in the pipework?

Just wanted to put the thought out there...

 

[Madrab]

That's exactly what water hammer is, when an outlet valve is closed too quickly, it causes a pressure wave which travels within the water in the pipework. It is that shock wave that causes pipework to resonate, more so when it reaches a part that isn't secured properly.

Is your cold water pressure very high? If so sometimes turning down the mains stop cock a little can help.

 

[Meggalar]

Hi,
Just thought i'd update the thread.
I couldn't find any loose pipes.
However (touch wood) the banging has stopped, the only thing I have done is replace the thermostatic shower mixer bar. To do this I turned the stopcock off and drained some of the water down before replacing it, since then the banging has stopped.
I'm not quite sure what the logic of this is to be honest.

Thanks