Hammer Arrestors

[Cello]

I note that one of the internet videos showing how to install a pressure reducing valve also shows water hammer arrestors being installed to, e.g. washing machine supply outlets. Is this necessary or just a precautionary measure?

 

[lame plumber]

depends if you have water hammer or not

 

[kay-jay]

its to take expansion when the prv is the first valve after a fixed jumper stopcock

 

[Cello]

Thanks for these comments. Firstly, there is no water hammer at present and the main reason that I am installing a pressure reducing valve is that the supply is at 85 psi and visitors get a free shower if I don't warn them to be careful with the taps when they wash their hands after going to the loo! Presumably, when I set a lower pressure, there will be even less risk of water hammer anyway. Secondly, the comment about closed systems is an excellent observation. I had thought of this as the pipework after the prv will be a closed system when the system is pressurised. Consequently, I was going to install a hammer arrestor immediately after the prv where there is a convenient gap in the kitchen cupboard to install it.

 

[kay-jay]

should be between the stopcock and the prv. all outlets after the prv should be fine

 

[Cello]

Thanks for the advice, I can easily install the prv where you suggest. The stopcock is in the kitchen and there is only approx. 2 feet of pipe to the point at which I want to install the prv. I realise that when the stopcock is closed, the pipe between the stopcock and prv would be closed and I assume that this would be the problem if, for instance, this section of pipe warmed up and the water expanded inside. After the prv, there is the whole householdworth of pipework and my initial reasoning was that when all taps etc are closed, this would also be a closed system. If so, why does this section not need protecting from overpressure?

 

[Cello]

Correction to first line... "Thanks for the advice, I can easily install the hammer arrestor where you suggest."