Installation of valve positioners
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When installing a valve positioner, the cam has a Face A and a Face B – how should one decide which face to use in the field? This is a situation that arises frequently; sometimes it takes a long time to adjust the control valve properly, and eventually switching between Face A and Face B solves the problem. I would like to ask: how can one determine whether to use Face A or Face B?
I’d like to know that too; could you send a photo?
First and foremost, it must be clear that Face A and Face B represent the direct and reverse actions of the valve positioner; whether to choose A or B depends on the on-site control valve and the central control regulator. When the regulator outputs 4 mA, if the control valve is a air-operated shut-off valve and the valve positioner is currently using the direct-acting mode on side A, then the distance between the nozzle and the baffle of the valve positioner is at its maximum, resulting in the lowest output from the valve positioner; as a result, the control valve does not move. Since it is an air-operated shut-off valve, the valve is now open to its maximum extent. If you close the valve completely at this moment, then you can switch from side A to side B; at that point, the distance between the nozzle of the valve actuator and the baffle is minimal, the back pressure is at its maximum, the output is at its highest level, and the control valve operates. Since it is a gas-operated valve, it will close completely at this time
An increase in signal causes the feedback rod to rotate counterclockwise; use cam surface B； An increase in signal causes the feedback rod to rotate clockwise, using surface A of the cam.