water hammer

[sparkticus]

Hi all, while working on an electrical installation yesterday, I was distracted and asked to "investigate" an issue of water hammer. No idea what that has to do with electrics but that's what happens when you are the only guy on site

1) Combi boiler
2) 15mm copper cold supply to boiler
3) 15mm copper hot supply from boiler to two thermostatic shower showers and two basins (showers about 9 litres/min)
4) Two toilets/cisterns

- The hammer only happens when the hot DHW is used.
- Happens if water is hot or cold (boiler off)
- Bypassed the boiler (disconnected the cold supply to boiler, disconnected the hot draw-off and connected the two together) still got the hammer.
- Measured water pressure, a very high 7.5bar!

The hammer does not appear to be pipes banging together. Appears to be some resonance within the pipes. The showers are themostatic but I don't know what make they are. Both showers and both basins (hot taps) exhibit the problem. Cold taps, showers on cold only and toilet does not exhibit the problem. I can stop the hammer by reducing the flow (via outside stop cock) to virtually nothing then increasing it again. The hammer stays away until taps or shower are turned off/on again then the hammer is back.

Could this be the high water pressure? I could fit an adjustable pressure regulator and take it down to say 3bar. Is this the right approach?

 

[Charnwood]

Hammer arrestor. About 20 quid.
Although it might be as simple as making sure all the pipework is bracketed properly.

 

[sparkticus]

Hammer arrestor. About 20 quid.
Although it might be as simple as making sure all the pipework is bracketed properly.

Thanks Charnwood. Just found an arrester on plumb centre website. Should I also reduce the pressure with a regulator?

 

[picasso]

A pressure reducer would be a good idea, 7.5 bar to too high, reduce it to about 3 bar dynamic.