PRV hunting(?)

Tommi68

I am working on a pneumatically actuated Spirax PRV, circa 2014, on the steam supply to a plate and frame HX for domestic hot water. It is 'hunting' or surging around it's setpoint of 45psi. The pressure swing is usually 40-50psi, but it frequently swings between 40-65psi.

There are two HX on separate steam supplies, so there is one unit in reserve for maintenance or emergencies. Lately, when this steam line is opened during a maintenance change-over, the PRV hunts between 30-100+psi, activating the safety release valve. This extreme hunting usually settles down after 20 minutes, and operated in the 40-65 range before setting into the 40-50psi range.

This PRV is on a 215psi supply, a PP5 positioner on a Spirax 1-1/2" valve, with a remote Spirax PN600 controller.

Is this hunting, or surging normal? What can I do to reduce/eliminate this?

Thanks

Jamie Hall

That is hunting — and, depending on exactly how the reducing valve is piped there could be two (maybe more) general possibilities. the most likely is that it is slightly gummer up and the sensing an valve mechanism can't move freely. There may be a maintenance manual for it… the other is that if it has a separate sensing line, that may have become at least partly blocked — and could even be as simple as some condensate trapped in it.

EBEBRATT-Ed

PRV could be worn out or may be operating out of its range.

PRVs are sized to control within a certain pressure range and with a certain flow.

They will usually hunt when trying to control at a smaller load than they are designed for.

In the past some would install two PRVs in parallel. One would be sized at 1/3 of the load and the other one would be sized at 2/3 of the load

Tommi68

https://forum.heatinghelp.com/discussion/comment/1851463#Comment_1851463

I will look for a manual on this valve. There may be oil/water contamination in the air supply. The sensing line to the controller does have a pitch back to the tapping.