Water hammer from unvented cylinder

[dilalio]

The balanced cold take-off on the ICG is before the NRV, so the hot usage should not make a difference to the pressure on the cold side of the ICG.

 

[Johntheo5]

So everything is yellow is contained under the kitchen cupboard. Probably no more than 1m long.

Everything in green is in the cylinder cupboard.

The pipe leading to the cylinder from the kitchen is probably a good 10m long as it weaves between joists above the ceiling and up about 4-5m from ground level.

Yeap the 4.5 was before the PRV fitted.

It's the bit about when pressure has built up in the HW system (and the HW cylinder inlet is hot up to the EV), I'm wondering now if this pushing on the NRV the ICG so it doesn't "bang". As soon as I draw off some hot water I've relieved the system so then when I switch to cold it's sending a shock into the ICG. Does this make sense? If this is the case I'm really confused how to fix this! Are Caleffi ICG's any good? Perhaps if I got a G3 to fit another brand?

Or it doesn't hammer if I drain the system and refill. Then I use the hot - switch to cold and it's back again.

I'd prefer to just have the one ICG PRV with a mains pressure of 4.5bar, the PRV is then fully in control to maintain that 3.0bar, it probably has nothing to do with your problem but I just don't think its a good idea to have two PRVs in series at such a low dP of, 4.5-3.0, 1.5bar.

You drained the UVC down last night, when you carried out the same tests after refilling, was the UVC still full of cold water or did you wait until it had fully reheated?

 

[Taconite5]

I'd prefer to just have the one ICG PRV with a mains pressure of 4.5bar, the PRV is then fully in control to maintain that 3.0bar, it probably has nothing to do with your problem but I just don't think its a good idea to have two PRVs in series at such a low dP of, 4.5-3.0, 1.5bar.

You drained the UVC down last night, when you carried out the same tests after refilling, was the UVC still full of cold water or did you wait until it had fully reheated?

Yeah I'll remove it at some point. I just had a theory at the time it was going from 4.5 to 3 in the ICG that it was too much hence the hammer.

I waited till it reheated, Thats why the cylinder inlet was warm and the pipe leading up to the EV. Yet it didn't hammer when running a cold - no noise at all. How it should be....

I then switched to hot for no more than a second, heard the hammer. Switched back cold and it's then there on the cold no matter what I do.

I can repeat this step over and over again.

 

[Taconite5]

The balanced cold take-off on the ICG is before the NRV, so the hot usage should not make a difference to the pressure on the cold side of the ICG.

So it doesn't really make a difference then if a hammer arrestor is before or after the ICG...

 

[Johntheo5]

Yeah I'll remove it at some point.

I waited till it reheated, Thats why the cylinder inlet was warm and the pipe leading up to the EV. Yet it didn't hammer when running a cold - no noise at all. How it should be....

I then switched to hot for no more than a second, heard the hammer. Switched back cold and it's then there

I can repeat this step over and over again.

Just to be absolutely clear, did you (not) carry out that test in the same sequence but without waiting for the cylinder to reheat.
Also post the EV capacity.

 

[Taconite5]

Just to be absolutely clear, did you (not) carry out that test in the same sequence but without waiting for the cylinder to reheat.
Also post the EV capacity.

I waited for reheat that time.

I just did the same test now without waiting for heat just to see if that makes any difference. Did the same thing. It stops hammering for a bit. Something then happens over time which makes it all come back.

It seems from de-pressurising it does something that fixes the issue. But I know from experience it'll be back again tomorrow.

I have a video comparison of the two scenarios now to show the difference anyway.