B
We have a 2" Fisher ET body valve with a 657 actuator (6 - 30 psi) with 2 and 5/16 inch trim on a compressor recycle (Fail Open). I have been told that the valve has been set up to ensure that under process conditions (8,000 kpa upstream - 1,200 kpa downstream) the valve should start to open as the controller output drops below 100%. (The bench set on the valve is 22psi.)
In practice, when the unit goes into low suction override control, the valve does not start to open until the controller output is at 65%.
We installed a Fieldvue positioner and the valve now opens at 95%.
It's great to solve a problem. It would be greater still to understand why a positioner is required. My guess is that 99% of compressor recycle valves in natural gas field production don't have them. I would like to keep it that way if possible.
In practice, when the unit goes into low suction override control, the valve does not start to open until the controller output is at 65%.
We installed a Fieldvue positioner and the valve now opens at 95%.
It's great to solve a problem. It would be greater still to understand why a positioner is required. My guess is that 99% of compressor recycle valves in natural gas field production don't have them. I would like to keep it that way if possible.