Water hammer

[Alan Ambrose]

Hi,

 

We live in a new barn conversion about 5 years old. It seems to be well built and by a good builder. About a year ago, we started occasionally getting a little 'water hammer' sound - a tapping about 1 once per second. This was relieved by turning on a tap for a few seconds. The sound might come back 10 minutes later, otherwise it would stay away for a day.

 

OK I thought - the expansion vessel on the incoming main must have died. I'll replace it and the problem will go away. So, I replaced it with a like-for-like vessel - an 'Aquasystem 18 Litre Potable Expansion Vessel'. From memory, I think I checked the preset pressure etc.

 

But the problem hasn't gone away...

 

Any ideas?

 

TIA, Alan

 

 

 

[saveasteading]

2 hours ago, Alan Ambrose said:

Any ideas?

 

We do know that something is causing it, so a change of pressure somewhere. Perhaps when a cistern has filled. I doubt if a plumber would be able to help.

If they did it would probably be a tut-tut who put this in? 

 

Of course it reverberates everywhere, but do you think it is from the tank area? Hot or cold?

 

There are water hammer arresters  which can be put into the line. I assume they have a compressible chamber to absorb the pressure and the noise. I have no idea if they work, but it sounds feasible and simple, and £30 plus labour.

Next try Youtube.

 

 

[Mattg4321]

I had to put one of those arrestor things into a previous house. It improved it by 75%, so worth doing. 
 

Normally caused by unsecured pipework and water being turned off abruptly. Washing machine solenoids or mixer taps etc. That’s my understanding anyway. Seems odd if it’s just happening ‘by itself’. 

[Marvin]

Hi @Alan Ambrose

 

Do you have a water tank in the loft or a header tank for the heating?

[j_s]

Our newish washing machine causes it or as said turning the water off abruptly we get it mildly. 

[Iceverge]

Is the washing machine unable to cope with a large volume and pressure of water and so has to cycle the solenoid to throttle the flow?

 

Maybe some kind of inline flow reducer would work? 

 

No huge knowledge here. Just spitballing. 

[Alan Ambrose]

>>> Do you have a water tank in the loft or a header tank for the heating?

 

No, this is a modern-ish set-up with UVC and expansion tank on the incoming main - at least, I think so - it's a bit difficult to see where everything goes as some of it is hidden at the back of the airing cupboard.

 

I think I'll take it apart again and maybe install a surge arrestor and some pressure gauges and see how we go from there. The curious thing is why it happened after 3-4 years from new? I guessed 'fault on expansion tank' which seems to be wrong. The only other possibility I can think of is that mains pressure has gone up over that time - which seems possible but unlikely.

[Alan Ambrose]

OK I finally found time to pursue this. I measured the pressures and did a bit more examination:

 

The incoming pressure is 6.1 bar and, after the cold water shut-off ball valve, goes straight into a Reliance CWIC355090 Monobloc ( https://www.reliancevalves.com/sites/rv/files/2022-06/Reliance Valves 22mm Compact One Piece Inlet Control Group Data Sheet.pdf ) 3.5 bar PRV with 6 bar relief. This also has a 'balanced cold water take off'.

 

The expansion tank air pressure was about 2.5 bar (with the hot water pressure released) and I topped that up to 3.5 bar. I see the hot water pressure itself is 3 bar normally. About 0.2L of hot water comes out when I shut off the incoming water pressure and open a hot tap. I sort of convinced myself the hammer was less when I topped up the expansion tank a bit.

 

I see that some of the pipes could be better supported and I ordered this kit ( https://www.amazon.co.uk/dp/B0956LDKSQ ) which should arrive today.

 

Then I had a bit of a brainwave - the hammer is largely coming from the cold tap but the expansion tank is on the hot circuit. Duh. So, its likely the HW set-up is fine. I should say that it's hard to see the exact pipe routing and connections as the pipes are mostly behind the HW tank.

 

So, I may need a low volume expansion tank / arrestor on the cold side? The only problem is that it may be very difficult to fit with the pipes where they are.

Edited March 2, 2023 by Alan Ambrose