Expansion Vessels

[coodem]

Start of by thanking everyone here for giving such a useful site, This is the first time I have needed the post, usually I find what Im after by searching the forum

i'm going to be draining my system, so while I'm at it I thought I would check the pressure on both vessels

1 x Zilmet (18l size and it is red) There is no static pressure written on it, just the max pressure, This one is used for the central heating. I estimate the system is around 110 litres. What should this be pressurised to?

The other is a Varem, guessing around 9l in size, it is grey, and attached to a sealed system hot water tank Ariston 250l. It says to charge to 3.5bar static. It is at 2.5b at the moment. Is it better to leave at 2.5 or should I put it to 3.5, Seem to be mixed opinions 1.8, 2.2

Just in case I thought I would mention the rest of the system

12 radiators
Potterton Profile 60E
Ariston 250Sti indirect unvented
Static water pressure 3.5b

Many thanks

coodem

 

[oilman]

The air pressure should be checked with no water pressure. For the grey one, close the supply valve and open a hot tap until the water stops flowing. Then check and adjust the pressure. It should be 3.5 bar.

For the red one, you need to open the pressure relief valve on the boiler, let the pressure drop to zero, then check the pressure. Should be equal to the height of the system (34 feet = 1 bar), but your boiler may have a 1 bar pressure switch so you will need to set the vessel pressure to 1 bar. Then turn the water pressure up to slightly more than the air pressure.

 

[coodem]

oilman, thank you for the fast response

Just want to check 1 thing abut the "red vessel"

It is in the loft on its own, And the boiler is a conventional boiler. I dont think it has a 1b pressure sensor, as it will work with zero pressure in the system.(just my logic, correct me if Im wrong) So basicly, all I need to do is relieve all the pressure, which will be done by draining the system, I will leave the drain on the system open while I check the pressure, then when I have pressurised the system and after bleeding all the air, keep the pressure just above 1b.(this will be done when system is cold)

 

[coodem]

Just to add, to make sure all is clear

It is a 2 storey house, the PV is not built into the boiler, it is stand alone in the loft and is about 25ft above ground level in the loft and 20ft above the boiler.

Is the height above ground or above the boiler?

So am I right by saying if the vessel is only 17ft high, put 0.5 bar into it, and if it were 25ft, put 0,75b

 

[nickso]

just put one bar into both water and vessel.....its going to make no noticable difference and its easier to keep a track of.

 

[oilman]

Just to add, to make sure all is clear

It is a 2 storey house, the PV is not built into the boiler, it is stand alone in the loft and is about 25ft above ground level in the loft and 20ft above the boiler.

Is the height above ground or above the boiler?

So am I right by saying if the vessel is only 17ft high, put 0.5 bar into it, and if it were 25ft, put 0,75b

There should be a pressure relief valve on the system, just use that to relieve the pressure. No need to drain the system. 0.5 bar will be fine.

 

[ChrisR]

The grey (HW) vessel pressure isn't critical (either) 2.5 bar would be fine I'd say. It'll absorb sudden changes in pressure better.
Remember a "Megaflo" design hads a precharge pressure of zero.