Fitting a PRV - do I need a check valve?

[jase the space]

I have mains pressure hot water provided by a DPS GXV Heatbank. I am suffering a bit from water hammer which I'll admit is probably mostly down to unsecured pipework.

However I have noticed that when no water is being demanded from within my house I still suffer from occasional hammer - presumably due to changes in pressure on the main (as other households turn there taps on/off).

I want to fit a pressure reducing valve (PRV) to stabilise the pressure and thus reduce the affects of mains pressure instabililty and also to ensure I always have a safe pressure in the house. I am hoping this will also reduce water hammer to some extent. At the moment I have no idea of what pressures I am actually getting.

Some questions:

1) Will the PRV give the stabilising effect I am after?

2) Do I need to fit a check valve (non-return valve) if fitting a PRV?
Does this go before or after the PRV?
(Do all PRVs have an integral check valve anyway?)

3) If fitting a check valve do I need an expansion vessel to handle the expansion of trapped water as it gradually heats up in the house pipework?
If so what sort of size are we talking and where is it best to fit it - on cold side or hot side of heatbank or directly after check valve/PRV?
Would one of those shock arrestors (from what I can gather these are just mini expansion vessels) be sufficient to handle this expansion or do I need something more substantial?


Any comments much appreciated.

 

[jase the space]

Somebody, anybody?

I think I am going to fit a water softener as well (with hiflow hoses/valves) so presumably I need a check valve anyway to meet water byelaws?
Can you get full bore check valves?

 

[ChrisR]

First, get a £12 guage and measure your water pressure, or call your water supplier and ask them what your area would expect. Until you do that you haven't a clue what you're doing. If the pressure is less than say 4-5 bar there's no reason why you should reduce it. It isn't normal to reduce it even if it's higher, though there can be add problems.

If you have a water supply up to current regs you will have a double check valve by the stopcock where the mains comes into the house.

All you probably need is a shock arrestor - they go under various names - ask in a local decent size plumbers merchant.
This would be typical, though I've seen tinier ones. You'd connect it through a small isolating valve which you could adjust to get the best effect - a bit like damping a spring.
http://www.bes.ltd.uk products 11355

 

[jase the space]

Thanks ChrisR.

I know I don't have a check valve installed currently so I guess I'll put one in. House is c.1936 so probably not up to date on regs!

Are you saying the shock arrestor is good enough to handle the expansion of trapped water in the pipes or only there to reduce the hammer and dampen the effects of mains fluctuations?

Is it best to put this after the check valve or does it not matter?

Cheers

 

[Agile]

The NRV should go after the stopcock and the shock arrester should go after the NRV.

Ideally the shock arrester should be pressured to approximate the same pressure as supply pressure.

Tony