Water hammer from unvented cylinder

[Taconite5]

I would suggest installing it before the PRV because the PRV closes when the upstream pressure is > 3.0bar so the arrestor wouldn't be of any benefit if installed on the balanced cold, (if the hammer is in the mains leg), the UVC EV should act as a arrestor to relieve the pressure in the balanced main cold if this is where the hammer is occuring as the ICG NRV will then open in the UVC direction.

Wait isn’t the NRV between the balanced cold and the UVC EV/cylinder feed? It’s what stops hot water going back into the balanced cold?

 

[Taconite5]

Can you do a video and post it on YouTube?

Sure can - which bit do you want to see?

 

[Johntheo5]

Wait isn’t the NRV between the balanced cold and the UVC EV/cylinder feed? It’s what stops hot water going back into the balanced cold?

It is, but when you shut a tap taken off the balanced cold and when/if the pressure builds up very rapidly due to the water flow stopping abruptly then the PRV will close very rapidly, the pressure is then trapped in the mains up as far as the PRV but any pressure that may have built up in the balanced portion will be relieved as the NRV will open but this doesn't do anything to relieve or stop the pressure build up in the mains portion.

 

[Taconite5]

It is, but when you shut a tap taken off the balanced cold and when/if the pressure builds up very rapidly due to the water flow stopping abruptly then the PRV will close very rapidly, the pressure is then trapped in the mains up as far as the PRV but any pressure that may have built up in the balanced portion will be relieved as the NRV will open but this doesn't do anything to relieve or stop the pressure build up in the mains portion.

View attachment 416149

Thanks that diagram really helps!

I'm wondering if it's the balanced cold causing the problem then. I'm going to fit a T here and see if I can take some pressure readings.

 

[dilalio]

Thanks that diagram really helps!

I'm wondering if it's the balanced cold causing the problem then. I'm going to fit a T here and see if I can take some pressure readings.

Do you have a toilet valve that shuts off quickly?