'Bang' from Unvented HW tank Expansion Vessel

[Disk]

New Install 12 months ago.
Greenstar 24i Boiler
150 litre unvented HW tank
Separate 25 litre wall mounted Exp Vessel, pressure ok at 3bar. (originally 12ltrs then 18ltrs.)
Pressure Reducing, Non return, Temp & Pressure relief valves etc fitted.
HW tank Thermostat, set at 45 but producing 60 at tap.
Mnfctrs Engineer has checked system ok and complies with regs.
He has variously changed the EV and PRV just in case.
The system works and we get HW & Heating.

The problem is that since installation the EV keeps going 'Bang' when a HW tap is turned on.
Its pretty certain that its the Bladder in the EV 'explosively' expanding or contracting.
However its not every time a tap is turned on. It is very irregular. Some days it happens maybe once, others it can be a number of times on the trot and all through the day.
Additionally there have been odd times when the pipe between HW tank and EV vibrated badly when a tap was turned on.
It doesn't seem to matter whether boiler is or has been on.
It even happens occasionally when no tap or any thing else is on.
The trouble is that apart from any damage its doing to the bladder, there are times when it frightens the life out of us, particulary at night when its quiet.
The Engineer has checked and changed components but cannot figure out whats causing it.

Does any one have any ideas please?

 

[KPlumbing]

Did you call the engineer out for this same problem? If you did then what parts did he replace?

 

[Disk]

He's replaced:
1. the EV, firstly for an 18ltr then for a 25ltr.
2. the PRV and Non return valve which come as a composite unit adjacent to the HW tank.
3. He's installed another PRV on the incoming CW feed just after the CW stop valve as the feed enters the house.

 

[Disk]

Yes, it was for this problem.
It has been the same since the system was installed 12 months ago despite the various changed components.

 

[Pioneer]

Your expansion vessel may be upside down! If the pipework enters from the bottom there is the potential to trap an air bubble against the diaphragm which would cause the symptoms you describe. The ariston cylinders we fit clearly state in the instructions to fit the vessel horizontally or with the pipework entering from the top so any air bubbles can escape.

 

[picasso]

do you know what the pressure is on your incoming mains water and who checked the precharge on the expansion vessel ?

 

[Gasguru]

What make/model is the cylinder?

How is the vessel mounted ie is the scrader (air valve) at the top, bottom or side?...some manufacturers require the valve to be sideways or at the bottom to prevent trapped air in the water side of the diaphragm.

 

[Disk]

Picasso, I don't know what the incoming cold pressure is at but there is a PRV to 3bar just after the stop valve into the house, along with another in the combined PRV/non return valve just before entry to the HW tank.
I assumed that the precharge on the EV was checked by the Engineer before fitting since it was a new vessel.

 

[Disk]

Pioneer, Gasguru,
The EV is currently fitted with the Schroeder valve at the top, although when the Engineer fitted the first replacement vessel he did put it up the other way but it made no difference.
In fact I queried it with the Engineer when he did fit it the other way and he said it wasn't a problem.
The paperwork for the HW tank and EV that I have shows the EV with the connection at the bottom, although it is only a schematic

 

[picasso]

potable water expansion vessels can come with a precharge of 5 bar, its worth checking its been lowered to suit your system.

 

[Kingsway]

Turn vessel around the other way

 

[rojaca]

Is it a Santon UVHW Cylinder?

 

[Disk]

Thankyou to all who have replied.
The HW tank is a Range Tribune and the EV is a Varem, as supplied by Range.
One or two have suggested turning the EV around so that the pipework comes out from the top but thinking about that, wouldn't the water, at least some of it, in the EV become locked in what is effectively a 'dead end'? It would then presumably have the potential to become 'unpotable' and therefore present a health risk?

 

[mickyg]

Has the EV pressure actually been checked against your incoming supply pressure? If the EV pressure is much higher you can get noise issues, although usually more of a vibrating than a banging.

 

[Disk]

We get the vibrating/juddering of the pipe to the EV as well, although like the bang its very irregular with no recognisable pattern and is less frequent than the bang.
I checked the EV pressure myself the other day (Water supply off, Taps turned on) and according to my tyre pressure gauge it's in excess of 3.5bar, (the gauge only reads up to 3.5bar at its stop).
I've told Range and they say that they are still trying to get details from their Engineer but they've been telling me that for the last month.
I am tempted to reduce the pressure myself but wonder how accurate my gauge is and whether I should be touching a pressurised system anyway.