Expansion Vessel Why does it leak water out of PRV below 3 b

[chrishutt]

After the vessel was pressurised without limit,

Pressurised without limit? What does that mean?

 

[DP]

Filling loop valve opened to pressurise system to see when PRV would lift and at what pressure as indicated on the pressure guage.

 

[chrishutt]

Chrishutt can you explain why a PRV was passing at 2.4 bar when there was no air in the EV. After the vessel was pressurised without limit, PRV lifted at 3 bar?

Assuming the pressure gauge and PRV were accurate, the only explanation I can offer is that at 2.4 bar the PRV was leaking water due to debris on the sealing surfaces which was subsequently cleared. That's common enough.

If you think about it, the PRV can only respond to the pressure applied to the underside of the washer/jumper. It has no way of sensing whether the system applying that pressure include pockets of air, expansion vessels or whatever. The pressure is the pressure, no more and no less.

The only difference a properly charged expansion vessel makes is to absorb or moderate pressure changes due to temperature changes, hydraulic shocks or leakage. Clearly a flat EV would result in a substantial pressure rise when the system heated up and when 3 bar was reached the PRV would begin to release water. If debris on the washer or sealing surfaces then prevented it closing properly it might well continue releasing water when the pressure dropped back down as the system cooled.