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.

 

[Johntheo5]

Strange all right, cold test, everything downstream of the (ICG) PRV will be at 3.0bar, when you open a "hot" tap everything downstream of the PRV will still be at the same but lower pressure depending on the flowrate, say, maybe 2.8 bar but when you shut the hot tap the pressure will return to 3.0bar, you then open a balanced cold tap, if the flowrate is the same as with the hot tap then the balanced pressure will be lower than the UVC pressure because the NRV will close, you might have say 2.8bar in the balanced side and 3.0 bar in the UVC but that shouldn't cause any problems .

Hot test, if the full 180L contents are reheated from a present 15C to 60C, then, assuming a 18L EV precharged to 3.0bar will result in a UVC final pressure of 3.77bar and 2.92L of water will have flowed from the bottom of the UVC into the EV, you now have 3.77bar in the UVC and 3.0bar in the balanced, when you open the hot tap, 2.92L of HW will flow before the pressure falls back to 3.0bar, if the flowrate is say 10LPM, it will take 17.5 seconds, the system should then operate as above, if the hot tap is only opened for a few seconds then the UVC pressure will still be say 3.6bar and the balanced 3.0bar, when a balanced cold tap is opened you will still have 3.6bar in the UVC and 2.8bar in the balanced side, again, can't see any problem with this?

You asked about the quality of Caleffi products, I would think that they are up there with the rest/best but I suppose you can all ways get a faulty item.

 

[Madrab]

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.

Absolutely - but if there is water hammer in the balanced cold then any pressure wave travelling up the balanced cold could force it's was past the NRV, which could also cause it to knock.

If the hammer is being caused by outlet(s) on the balanced cold supply side then It has to be a pressure wave travelling back up the balanced feed and hitting one of the valves in the control group, especially if that's where the knock is localised.

I'd be tempted to bypass the balanced outlet from the control group by taking a feed from the mains upstream of the ICG's PRV into the balanced supply pipe and then cap off the balanced outlet on the control group. Given the mains is covered by a separate PRV then that can be used to regulate the pressure and balance the cold supply with the unvented and see what effect that has. Should be relatively easy to do.

 

[Taconite5]

Strange all right, cold test, everything downstream of the (ICG) PRV will be at 3.0bar, when you open a "hot" tap everything downstream of the PRV will still be at the same but lower pressure depending on the flowrate, say, maybe 2.8 bar but when you shut the hot tap the pressure will return to 3.0bar, you then open a balanced cold tap, if the flowrate is the same as with the hot tap then the balanced pressure will be lower than the UVC pressure because the NRV will close, you might have say 2.8bar in the balanced side and 3.0 bar in the UVC but that shouldn't cause any problems .

Hot test, if the full 180L contents are reheated from a present 15C to 60C, then, assuming a 18L EV precharged to 3.0bar will result in a UVC final pressure of 3.77bar and 2.92L of water will have flowed from the bottom of the UVC into the EV, you now have 3.77bar in the UVC and 3.0bar in the balanced, when you open the hot tap, 2.92L of HW will flow before the pressure falls back to 3.0bar, if the flowrate is say 10LPM, it will take 17.5 seconds, the system should then operate as above, if the hot tap is only opened for a few seconds then the UVC pressure will still be say 3.6bar and the balanced 3.0bar, when a balanced cold tap is opened you will still have 3.6bar in the UVC and 2.8bar in the balanced side, again, can't see any problem with this?

You asked about the quality of Caleffi products, I would think that they are up there with the rest/best but I suppose you can all ways get a faulty item.

Yeap got all that. I can't see a problem either.

What are the chances of two ICGs being faulty and behaving the same way? Hmmmm.

Well I de-pressurised the system about 1.5 hours ago, used every tap in the house, toilets, HW heating on, even running the washing machine. No noise yet. I want to believe this is it but we shall see in the morning.

 

[Taconite5]

Absolutely - but if there is water hammer in the balanced cold then any pressure wave travelling up the balanced cold could force it's was past the NRV, which could also cause it to knock.

If the hammer is being caused by outlet(s) on the balanced cold supply side then It has to be a pressure wave travelling back up the balanced feed and hitting one of the valves in the control group, especially if that's where the knock is localised.

I'd be tempted to bypass the balanced outlet from the control group by taking a feed from the mains upstream of the ICG's PRV into the balanced supply pipe and then cap off the balanced outlet on the control group. Given the mains is covered by a separate PRV then that can be used to regulate the pressure and balance the cold supply with the unvented and see what effect that has. Should be relatively easy to do.

Could pipe routing have an effect on this?

I only ask because with it being a new build there's other houses but the plumber has done slightly different routes to to get to ICG. Mine has a lot of sharp 90 deg bends in it.

Yeah before that I'm tempted just to fit an arrestor to the balanced cold just to see if that changes anything.