Noise from unvented hot water system

[Johntheo5]

Gledhill did suggest that some batches of their UV cylinder insulation didn't get sufficient curing time resulting in these noises!.

 

[Johntheo5]

For interest or for anyone who would like to configure their own to see the effect of different volumes here is my s/sheet with simple formulae for building one. Cannot post file.

 

[Agile]

I think that someone stated that an isolating valve could be fitted into the pipe to the EV.

I have always been under the impression that the generic rules for unvented cylinders would not allow these.

With that in mind when I wanted to increase the pipe resistance on a noisy installation I fitted a partly closed iso valve and wrapped it in silver tape.

 

[Madrab]

There should be nothing that has the ability to restrict or remove the access from the cylinder to the EV or any of the other safety devices on an unvented system. That would include isolation valves.

 

[Agile]

Exactly!

So any earlier comment to the contrary was incorrect.

And if the PRV has been correctly fitted on the cylinder side of a pressure reducing valve then that would protect the cylinder from over pressure as would the T & P release valve near the top as well.

 

[Johntheo5]

There should be nothing that has the ability to restrict or remove the access from the cylinder to the EV or any of the other safety devices on an unvented system. That would include isolation valves.

Exactly!

So any earlier comment to the contrary was incorrect.

And if the PRV has been correctly fitted on the cylinder side of a pressure reducing valve then that would protect the cylinder from over pressure as would the T & P release valve near the top as well.

A EV can never be considered as a safety device since it can and does fail regularly due to diaphragm failure or air leakage, a case can certainly be made for not allowing the installation of a isolating valve but only to protect the EV from exploding in the event of a fire if the isol valve was closed.
The main reason for having a EV installed in a UV cylinder is to only allow a modest rise in cylinder pressure after a full volume reheat, normal rise will be less than 1bar on any cylinder with a EV volume of 1/10th of the cylinder volume and assuming a cold cylinder pressure of 3.0bar. I have seen several UV cylinder installations on the continent with no EVs but all had expansion relief valves, debatable IMO if even these should be considered as a safety device. The only real safety device on any pressure vessel is its own PRV which would be better termed the cylinder safety valve. All pressure vessels can be run safely right up to the safety valve setting since its setting is at the safe working pressure of the cylinder, cylinder test pressure is 1.5 times the working pressure.

 

[Madrab]

The key components that are considered the primary safety design features of an unvented cylinder as part of the legislation is concerned are - A non resetting energy cutout and the temp and pressure relief devices.

As part of the new and revised G3/UVW quals - Hot Water Systems and Safety (HWSS) - which now covers all HW and Advanced HW systems - vented and unvented - there are key elements of an unvented HW setup that are all now considered part of the safety framework that is wrapped around it - The PReducingV, PReliefV, TPRV, EV (expansion space), HLS, Stat and 2Port (interlock) etc - these are all classed as key components of an Unvented Cylinders safety features and all must be checked and tested as part of it's yearly inspection. To say the expansion can't be considered a safety feature since it can fail is, IMO, a little erroneous. That statement could be attributed to any of the mechanical devices attached to the cylinder that could fail just as easily. The expansion vessel (space) absorbs expansion and stops the PRV/TPRV from activating, therefore supporting them. I would consider something protecting a safety device would be, by default, part of that safety system.

 

[Johntheo5]

While mechanical devices like pressure relief valves can and do fail, they generally fail by either leaking or the spring losing some of its tension over time but resulting in it operating at a lower cylinder pressure, they don't fail unsafely like the EV which allways fails in this manner. Is the cylinder T&PRV removed and tested yearly, both the pressure and temperature sides? and if not, why not, leakage afterwards?, then one might say, just make this a renewable yearly item.
EV isolation valves can be purchased with a combined isolation and drain function plus (in some cases) a lockable lever & indicator, obviously if the regulations say NO then it can't be installed whatever ones view's are.

I am a bit more than mildly surprised that pressure gauges aren't installed as standard which would be a great help even to the home owner in helping to identify failing EVs or pressure reducing valves,

 

[Madrab]

I have found that the T&PRV or the PRV passing after testing is a lot less likely on an UnVented system (UV) than say a PRV on a CH system. The UV systems tend to cooler, cleaner and the valves tested more regularly. I think I have had only 2 do it in all the time I have been servicing these units and they were ones that hadn't been serviced in a few years.

PRV's on CH systems on the other hand seems to let by by just looking at them the wrong way. Some say this is due to the more challenging environment they live in (higher temps/chemicals that harden the seals, typical older age, lack of use - a CH PRV should actually be activated as part of the service but rarely are) - and dirt from the system getting trapped on the seat.

I have had PReliefV's jam up where the valve wouldn't open when tested, so they do fail closed, though it is rare. One whose spring failed and jammed, the other where the seal welded itself to the seat.

Do agree about pressure gauges, I am quite a fan of installing a gauge when installing PRedV's or combi valves.

 

[Johntheo5]

One would think allright that CH/ boiler PRVs should be more prone to passing after testing, I have +18 year old oil fired boiler installed on a 50 year old open vented system but have a 3 bar PRV installed right on top of the boiler where the water temperature regularly rises to 90C on boile cut out, (no pump overrun), I regularly "test this" by turning the knob anticlockwise to lift the valve and also on the very rare occasions when the whole system is drained down to vent the boiler, the same PRV is original, I do have a very clean system but no way as clean as a UVsystem.