Regulating valve failure
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The locator is working properly, the membrane is fine, the air pressure is normal, and the packing area is in order. The signals in the control room are normal. But the stroke is very small when it’s closed. What could be the reason?
The valve stem is installed a bit high; it just needs to be lowered
Debris inside the valve results in insufficient travel of the valve spool
There are debris inside the valve, causing the valve core to get stuck or the feedback to be weak, which results in irregular movement
1. Disconnect the valve body and test the actuator individually to check if it is functioning properly. 2. The feedback rod is connected in the wrong position; it should be reconnected to the correct position according to the valve’s stroke.
What type of positioner are you using? If the travel distance is normal when it’s turned on, but very small when it’s turned off, it’s likely due to issues with calibration. The linearization or working area of the locator to be used has not been set properly. Check it out!
1. Check the safety barrier and the signal wires leading to the site； 2. Measure the 4-20mA value at the installation site ； 3. Are there any foreign objects in the valve seat? ； 4. Is the air supply pressure of the pressure reducing valve indicating an incorrect value? ； 5. Redo the calibration of the locator.
It is possible that the pressure difference specified during selection was incorrect; as a result, when the valve is closed and the valve stem moves downward, it encounters resistance from the material pressure, which reduces the stroke length. The number of springs in the diaphragm chamber can be increased to address this issue.
There is an object blocking the valve seat or valve cage, which prevents the valve from opening and closing properly; the valve should be disassembled to check it
There is an object blocking the bottom of the valve, or the valve stem does not move smoothly
Connect compressed air directly to the valve’s inlet, without using a positioner, to see if the valve moves smoothly – that’s exactly what I did