The following procedure should be done for control valve calibration.
Suppose it is spring-loaded and direct action. (Direct action means at top of diaphragm signal and with the increase of signal, the stem will move downwards or the stem will extend). Also, the valve is a signal to close. Check its Bench Set. Suppose it is 6 to 21 PSI.
Control Valve Calibration
Set pressure regulator of positioner at about 30 PSI.
Apply 3 PSI (4 mA if positioner is smart or electronics)
signal to Positioner.Gradullay increase signal. Note the
movement of stem.
Apply 6 (8 mA),9 PSI (12 mA), 12 PSI (16 mA) and 15 PSI
(20 mA) signal. Valve stem should move accordingly and
indicator must show 25%,50%,75% and 100%.
If error, remove it from zero and span of positioner.
If facing any error problem, give signal 50% and then
remove error. Rest will be ok automatically.
Suppose valve is normally closed and at any vent service
and signal to close as I mentioned earlier, then make shut
close of valve at 14.5, or 14.7 PSI. Valve may start
closing at 2.75PSI.
If valve is at control operation, like level, pressure
etc, then calibrate it accurately.No need to calibrate it
at 2.75 and 14.5 PSI.