Troubleshooting a Control Valve
1.Start with the fail mode of the valve
If the valve fails closed and is leaking
a) Disconnect the positioner or controller input.
b) If the valve has a hand wheel, check to see that it is backed out.
c) Check to see if the bench range is correct.
d) Check to see if there is trash in, or damage to, the valve seat.
2.Next check the positioner.
3.Next check the controller.
Do not rely on the control room to generate signals. Generate your own with equipment that you know is properly calibrated. Do not assume anything.
Remember that control valves only do what you tell them to. Many control valve problems turn out to be a problem somewhere else.
-If you have any query on above or control valves, please write to me in comments.