250 litre cylinder
- Thread starter Matt887
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I've not seen a hard and fast rule about the volume in general, but the rules around these things mean it's as muggles says, It's an Approved assembly and requires an Approved bod to work on it.
Have a look at the expansion valve which has the lifting pressure stamped on it. If its 4.5bar then 18L is marginal so 25L EV required, if it has 6bar or higher stamped on it then 18L more than adequate.
Here are details from a Albion unvented cylinder, don't know what the expansion valve setting is.
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It's 6bar the pressure relief is dripping though. Not sure if it's an expansion issue. Or the pressure reducing valve. If the pressure is high after the pressure reducing valve is there anyway of telling if it's due to the pressure reducing valve being at fault or backpressure from a mixer shower/ tap? The balanced cold is capped so not being used. So wil be unbalanced supplies.
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Have you recharged the pressure vessel?
To what pressure?
Do you have instructions for that?
If you haven't then do that first - it would be expected to drip if that's what it needs.
What's the mains pressure?
You say you went to one - have you done the G3 course?
The expansion vessel volume isn't critical but as above needs to be whatever was supplied/specified with the system, under the regs.
Water only expands 4% going from 4°C to boiling (100° ie unpressurised) so in normal say 10° to 60° range it'll only go about 2% =~5 litres. By design, if something fails then it's the T&P or Expansion relief valves which cope, the PVessel isn't relied on.
To what pressure?
Do you have instructions for that?
If you haven't then do that first - it would be expected to drip if that's what it needs.
What's the mains pressure?
You say you went to one - have you done the G3 course?
The expansion vessel volume isn't critical but as above needs to be whatever was supplied/specified with the system, under the regs.
Water only expands 4% going from 4°C to boiling (100° ie unpressurised) so in normal say 10° to 60° range it'll only go about 2% =~5 litres. By design, if something fails then it's the T&P or Expansion relief valves which cope, the PVessel isn't relied on.
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Heating 250L water from 15C to 65C results in a expansion vol of 4.58L (1.83%). With a 18L EV, sssuming a PRV pressure of 3.0bar and with the cylinder properly precharged to 3.0bar will result in a final pressure of 4.36bar or 4.46bar if precharged to 2.8bar (recommended by some, to prevent water hammer).
It would require the precharge pressure to fall (leak, or improperly set) to 1.4bar to lift the expansion valve at 6bar or the PRV pressure to rise to 3.84bar to lift it.
Suggest attaching a car tyre type pressure gauge/pump at the air end and noting the pressure, then run off ~ 5L of hot water which will get rid of the expansion vol and again note the air end pressure. Shut off hot tap, do not draw off any HW and do not reheat the cyl and again note the air end pressure after say 30/60 mins.
It would require the precharge pressure to fall (leak, or improperly set) to 1.4bar to lift the expansion valve at 6bar or the PRV pressure to rise to 3.84bar to lift it.
Suggest attaching a car tyre type pressure gauge/pump at the air end and noting the pressure, then run off ~ 5L of hot water which will get rid of the expansion vol and again note the air end pressure. Shut off hot tap, do not draw off any HW and do not reheat the cyl and again note the air end pressure after say 30/60 mins.
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But 5 litre is the water expansion. Need to relate that to the expansion vessel total volume (which I assume is how they're quoted)
They are all related in this simple spreadsheet, can't post my actual one but you can see the calculations here if you want to build your own.
It's a 6 bar pressure relief. I went for another issue and was shown this. The 18 litre expansion vessel is newish a year and a half old. I have g3 yes I got it with my level 3 in plumbing. I tested the pressure in the system after the pressure relief valve to be around 3.5bar. The cylinder was heating. But obviously was hot still from last time it was on
Which I now believe have been taken over by kingspan Albion
If the expansion valve was still dripping at a cylinder pressure of 3.5 bar then the whole inlet valve group set must be renewed.
Where exactly from (if) the inlet group set is the EV connected, if connected (incorrectly) like the one below then effectively no EV and the expansion valve will expel the expansion volume every time the cylinder re heats but will only drip while the cylinder is re heating.
Where exactly from (if) the inlet group set is the EV connected, if connected (incorrectly) like the one below then effectively no EV and the expansion valve will expel the expansion volume every time the cylinder re heats but will only drip while the cylinder is re heating.
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