Expansion Vessel Again

[watford 99]

Sorry to need to ask yet another basic question but I hope that the more I understand what is going on in my solar thermal setup the better able I will be to keep it running trouble free in future.

My question is this: If I pressurize the expansion vessel to, say, 1 bar and then pressurize the system to, say, 1.3 bar, should I expect to find that the E.V pressure has risen to equal the system pressure?

[Philip R]

Yes,

The 1.0 bar(g) precharged volume in the EV is compressed to 1.3 bar(g) (The gas and water pressure at equilibrium) The precharge gas volume reduced to 1/1.3 (approx 0.77 per unit) volume of the EV, the difference (0.23 per unit volume) being water inside the wet side of the EV.

PhilipR

[watford 99]

Philip R
Thank you for answering my question. I now understand more clearly the replies from KLD (klaus) and Desperate to my earlier question on E.V settings. Sometime previously I had read a filling instruction which led me to think I had to put 3litres of fluid into the E.V. How I was supposed to do this I could not fathom, especiaIly as my E.V is installed gas side up. My understanding now is that 3 litres enter the E.V as a consequence of pre pressurizing an 18 Litre vessel to 1 bar (gauge pressure) and then filling the system to a pressure of 1.2 bar (g). All because P*V =C. It just goes to show how one can get the wrong end of the stick as they say.

Thanks once again.