Problems related to positioner

i have an control valve with SRD991(FF type) make positioner… normally on close loop, valve open at 50% positioner Air fail valve goes to Fail safe position. But while at Air return back valve move above 50% then slowly it comes to 50%… how to rectify this problem…? any suggestion or what action to be take on Positioner

Try to bypass the positioner, Check the valve travel? If OK, then install back the positioner. Check the feedback arm, then calibrate it again.

Check the valve action on fail-safe. Visual check the stopper on top of diaphragm casing. If stopper provided how much percent check whether its split range. If FF check, the interlock, and sequence for the split.|

Dear Sir, Firstly you should determine what kind of actuator you use, pneumatic, motorized or hydraulic. Secondly to determine the reason of problem, do the following steps. 1- check the movement of valve and make sure it moving without any other unwanted forces. 2- secondly check the feedback (about 2 month ago I faced similar problem, it was the corrosion in teeth of feedback arm that change the variable resistance for deciding the position). 3- check the other controlling device. 4- check if there are a mechanical problems such as leakage in air. 5- also make sure the position controller has calibrated in the correct way ( the calibration method depends on your system and the manufacturing manual )

For any helps, I will be so happy to help you

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