The control valve does not regulate stably
Thread Content
Dear experts: I have a question. There is a pneumatic on-off control valve in my workshop. When it is set manually to 0, the valve stem indicates the 0 position; when set to 50%, the valve stem is at the 50% position. However, when set to 100%, the valve stem fluctuates up and down and cannot remain fixed at the 100% position. What could be the cause of this?
There might be a leak somewhere, or the actuator itself could be faulty. The actuator can be disconnected, and air at the rated pressure can be supplied directly to it to see if there is still any fluctuation. If there is no fluctuation, then it’s a problem with the actuator that needs to be adjusted.
Try increasing the pressure of the pressure regulator on the instrument air pipe
I think the key is to check the gas circuit: 1, check whether there is any leakage or cross-flow in the sealing of the actuator’s gas chamber; 2, the nozzle/diaphragm of the positioner is dirty, which affects exhaust from the nozzle.
Check the locator and filter for any air leaks!
Check whether the output signal is stable; if it is stable, then check whether the air supply is stable and whether the output of the locator is steady, and then consider the valve.
It’s probably a problem with the valve positioner.
The operation and maintenance of control valves mainly rely on the valve positioner. Therefore, anyone working with control valves must be familiar with the operation of positioners. I don’t know what brand the valve actuator is Are there any pneumatic amplifier options? Did someone touch it before the fluctuations started, or did they begin suddenly? The piezoelectric valve in Siemens positioners has high requirements for instrument air and is prone to failure; try replacing it with another one. If 0%·50% is normal, installation issues can be ruled out. The 100% position fluctuation, as mentioned above, is mainly due to issues with the pneumatic components, such as pneumatic amplifiers, positioners, and check valves. Pneumatic amplifiers, also known as boosters, can be adjusted just like one-way control throttle valves.
It’s likely due to the valve positioner; for mechanical positioners, adjust the base adjustment knob and the throttle orifice of the pilot valve. If it’s a smart positioner, replace the piezoelectric valve.
Try increasing the air pressure; it’s possible that the membrane tip is leaking. Use a spray bottle to check the seal at the membrane tip for leaks