Water hammer from unvented cylinder

[Johntheo5]

Trying to see this correctly - re the video of the gauge - there's one knock when the tap is opened and the water runs then another when the tap is shut and the water stops?
Not really - there probably isn't anything wrong with the valve in the control group, if it is being impacted by a pressure spike travelling along the balanced feed when a tap is being opened and the same being closed then that may be what's creating the knock at the valve.

May not be a problem with the valve, it's just creating that knock under these certain set of circumstances, wouldn't be the first time I've come across that. Again, bypass the valve to the balanced feed and see what happens

When you say bypass the valve to the balanced feed are you suggesting blanking off the cold (balanced) feed port on the ICV and supplying the cold feed from the mains after the PRV that @Taconite5 has installed?.

 

[Madrab]

When you say bypass the valve to the balanced feed are you suggesting blanking off the cold (balanced) feed port on the ICV and supplying the cold feed from the mains after the PRV that @Taconite5 has installed?.

Exactly - It will tell use one thing - if it is a valve in the Control Group that's creating the knock and yes the cold feed will still be balanced by the PRV @ the mains.

Lots of time spent on this and it's probably time to find the culprit IMO. Easy enough to run through a process of elimination, especially given it shouldn't won't be that difficult to bypass the group, by a tee'ing off just before the ICV and elbow into the cold feed, as long as @Taconite5 is ok with doing a little pipework.

 

[Johntheo5]

Exactly - It will tell use one thing - if it is a valve in the Control Group that's creating the knock and yes the cold feed will still be balanced by the PRV @ the mains.

Lots of time spent on this and it's probably time to find the culprit IMO. Easy enough to run through a process of elimination, especially given it shouldn't won't be that difficult to bypass the group, by a tee'ing off just before the ICV and elbow into the cold feed, as long as @Taconite5 is ok with doing a little pipework.

The "ideal" way I'd like to see that test done is to remove that PRV which is in line with and supplying the ICV PRV and reinstall it in a T off the mains and then take the cold feed from this.

 

[Madrab]

The "ideal" way I'd like to see that test done is to remove that PRV which is in line with and supplying the ICV PRV and reinstall it in a T off the mains and then take the cold feed from this.

Certainly, shouldn't be any need for a PRV on the mains if there is another PRV in the CG if all hot and cold is taken from the UV and the balanced feed, sometimes though that isn't the case, not sure with this system. There could be other outlets fed from the mains, not from the balanced side of things, that may still need their own protection.

TBF though, this is just to run some quick tests and rule things out. If everything is run off the balanced supply then for sure, a primary PRV shouldn't really be needed and is just another component in the mix.

 

[Taconite5]

Certainly, shouldn't be any need for a PRV on the mains if there is another PRV in the CG if all hot and cold is taken from the UV and the balanced feed, sometimes though that isn't the case, not sure with this system. There could be other outlets fed from the mains, not from the balanced side of things, that may still need their own protection.

TBF though, this is just to run some quick tests and rule things out. If everything is run off the balanced supply then for sure, a primary PRV shouldn't really be needed and is just another component in the mix.

Yeah just dishwater, hosepipe and kitchen cold off the mains. The rest of the house goes through the balanced cold.

 

[Johntheo5]

Yeah just dishwater, hosepipe and kitchen cold off the mains. The rest of the house goes through the balanced cold.

Just to recap.

Original install: Only one (ICG) PRV, cold taken off the balanced ICG port, but EV take off from a T downstream of the ICG and not from the port on the ICG.
Don't know if the system worked OK for 6 months or so? before water hammer, but a PRV was/is installed upstream of the ICG.

Piping mods, in no particulr order.

Remove the upstream PRV and install a T piece with the take off blanked and reposition the EV take off to the ICG port, but this probably requires a G3 to do so?, so maybe last option, the present EV take off should be fine as its downstream of the ICG check vave, Caleffi have also confirmed this, but who knows, this change should probably be the last throw of the dice.

As above but reposition the PRV on the T, remove the cold from its balanced port, blank the balanced port and installl the cold take off from this PRV.

If no cure, as above, but then reposition the Balanced Cold & the EV pipes to their ICG ports, the system is then exactly as designed.

Present ICG piping, the EV is piped off a T downstream of the ICG.

 

[Madrab]

Any work to do with the UV safety devices should be performed by a qualified engineer that would include the main EV. The EV take off positioning is fine on the cold feed to the cylinder, as it's there to absorb expansion from the HW cylinder, it doesn't have to be from the take off point on the group. It can even be on the hot draw off side if space is a real issue, though that's not ideal.

I am not suggesting any major changes - one thing at a time IMO so it's known what the single cause is.

All I am suggesting is cut a tee into the mains above the Group. Disconnect the balanced feed from the group outlet and cap that outlet. Then take that tee's supply from the main and connect it to the balanced cold supply pipe. Leave everything else as it is. Then run the same knock tests as before.

 

[Johntheo5]

Have you tried any mods over the weekend to address the problem??

 

[Taconite5]

Have you tried any mods over the weekend to address the problem??

Got held up with other stuff. I will report back on here when I've made some progress. Keen we all learn from this!