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Answer Posted / aftab ahmed mazari
Following procedure should be done for control valve
calibration.
Suppose it is spring loaded and direct action.(Direct
action means at top of diapgargm signal and with the
increase of signal, stem will move downwards or the stem
will extend).Also valve is signal to close. Check its Bench
Set. Suppose it is 6 to 21 PSI.
1. Set pressure regulator of positioner at about 30 PSI.
2. Apply 3 PSI (4 mA if positioner is smart or electronics)
signal to Positioner.Gradullay increase signal. Note the
movement of stem.
3. 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%.
4. If error, remove it from zero and span of positioner.
5. If facing any error problem, give signal 50% and then
remove error. Rest will be ok automatically.
6. 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.
7. 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.
aftabmazari@yahoo.com
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