Expansion Vessel - unvented cylinder

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kipperphill

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Hi

I have a continuing problem with our system. I posted about this at Christmas, and I have been working with our heating engineer on and off since to try and solve the problem.

It is a new system comprising Glowworm Ultracom SXI2 and a Stelflow 210 cylinder.

It all works absolutely fine (very well in fact) but whenever the bath taps are turned on full (or two showers are operated at the same time etc), the expansion vessel vibrates and makes a very loud horrible noise - like a loud howling - for about 10 seconds.

These are the things the Heating Engineer has tried:

- changing the pressure of the vessel. This seemed to work at first - but only when the pressure of the vessel was very low (say 1 bar). Presently it is (I am told) pumped to 2 bar. The Engineer has not as far as I know measured the pressure of the water and matched it - he has just been trying different pressures.

- upgraded the pipes from the mains (1/2 inch from road (not changed), then new 22mm pipe to cylinder)

Does anyone have any ideas of things I can try before I go to the cost of getting a different Engineer out?

If I am adjusting the pressure of the vessel to experiment (e.g. with a car pump), do I drain the water out of it first, or do it when pressured?

Many thanks for any help.

Cheers
KP
 
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I had to sort out one of these after several people had failed.

But to get an idea of whats going on you do need to check the operating pressure of the cylinder AND the supply pressure on a dynamic basis when say 10 li/min is being taken. Then again at 20 li/min

If the cylinder pressure is too close to the supply pressure then it may be possible to solve it by just reducing the cylinder pressure to about 60% of the supply pressure at 10 li/min.

If that does not solve the problem then its necessary to add some resistance and inductance to the pipe to the EXV. If its in 22mm then merely changing it to 15 mm may solve it.

However, in many cases its necessary to add some resistance and one or usually two isolating valves spaced apart will usually solve it.

Because one should not really fit isolating valves in this position ( although ideal for servicing ) I then wrap them with silver tape to reduce any chance of anyone closing them.

The air pressure should be set to equal the pressure output of the reducing valve but that MUST be done with the cylinder depressurised.

Tony Glazier
 
is your expansion vessel feed from the bottom? I had this problem a few years ago, someone on the forum suggested turning the exv on its side, sorted out the problem, I think it had something to do with air getting trapped against the diagragm.
 
It should make little difference.

But I always prefer bottom fed because that drains by gravity.
 
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No DaftyDIY'er should touch an Unvented cylinder, you need a Unvented ticket(G3) to work on UVCs.

And what Telly Tony has done/suggested is completely illegal, do you have an Unvented ticket T??

The OP is clearly messing around with his own cylinder!!!!!
 
Thanks all.

I am thinking about having a play, yes. However, this is only after having a Heating Engineer have a go at it about 6 times since it was installed.

Please let me know the sort of danger we are talking about if all I do is turn the EV on its side and play with its pressure a bit?

I don't plan to drain the system before doing it or fit any valves as that is out of my league...

The instructions that came with the Cylinder say to install it vertically - which the Engineer has done.

Cheers
Phillip
 
Ariston have been saying this for long time and it is in their literature,The reason they say it is stop this type of problem please do not attempt to do what Agile has said for your own safety :rolleyes:

As much as i hate to agree with Dick puller for once he is totally right in his advice to you :)
 
kipperphill said:
Thanks all.

I am thinking about having a play, yes. However, this is only after having a Heating Engineer have a go at it about 6 times since it was installed.

Please let me know the sort of danger we are talking about if all I do is turn the EV on its side and play with its pressure a bit?

I don't plan to drain the system before doing it or fit any valves as that is out of my league...

The instructions that came with the Cylinder say to install it vertically - which the Engineer has done.

Cheers
Phillip
Click to expand...

The EV is not a safety device. It's there to prevent water weeping through the pressure relief valve as the hot water expands on heating. The safety devices are:

the pressure relief valve on the cold water supply after the reducing valve
the combined pressure and temperature relief on the cylinder
and the two port valve on the heating coil wired in series with the thermal trip (assuming it's indirectly heated).

These are what protect the system from over pressurisation.
 
Happyplumber said:
Ariston have been saying this for long time and it is in their literature,The reason they say it is stop this type of problem please do not attempt to do what Agile has said for your own safety :rolleyes:

As much as i hate to agree with Dick puller for once he is totally right in his advice to you :)
Click to expand...

Charmer..... :LOL: :LOL:
 
Aristons schematics show two arrangements which can potentially trap air.
ACV's MI's are opposite to this.
 
All expansion vessels should be sited with there tapping at the top. However many combi have them the wrong way up. But hey the only way most manufacturers make any money is with spares. Another reason you should never fit combis.
 
Just matching the EV pressure to the dynamic pressure cures this problem 9/10 times.
 
D

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