Tuning Fisher 1290 Vapor Recovery Valve

[rbsmetana]

Enquiring if anyone out there has experience with tuning a Fisher type 1290 vapor recovery valve. After extensive testing I have found the valve to be quite unstable with regards to maintaining a blanket pressure within an enclosure. The valve tends to go right by the set point and continues to cycle in pressure well above and below the pressure set point. Even during times at which the valve maintains a constant pressure any parameter change including flowrate going into the enclosure or small variations in the vacuum system pressure tends to send the system into an unstable pressure control regime. Any help would be appreciated.

 

[pmover]

are you certain that the problem lies with the control valve? afterall, a control system is only as good as the sensor, controller, and control element are. i've seen many installations where the sensor and controller are performing adequately, but the mechanical (hardware) equipment was flawed. is it possible to gather sensor, controller input/output, and position data on control valve? if so, one should be able to determine/locate the problegood luck!
-pmover