Control valves moves up slowly/travel deviation - No action from any control Element - Valves been driven by DVC6200 PD !!!
The sliding stem control valve (globe) with pneumatic piston cylinder Actuator's controller has been recently upgraded from DVC 6020PD by DVC 6200PD.
On the first instance after taking in service (Anti surge control, compressor) it has observed the valves move up at 3 different occasions without any change in the output from CCC controller.
The set points & deviations were 40% & +40%, 66% & +30%, 55% & +45%. The valve have been controlled through 2 volume boosters.
What could be the possible causes. Eagerly waiting for the members feedback.
Rgds./Rkb.