It’s a common issue with pneumatic diaphragm control valves; I’m seeking help
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For a commonly used air-operated control valve, it suddenly stopped functioning properly and could only open to 50% of its capacity. Increasing the air supply pressure allowed it to function again, but after a while it could only open to 20% again. In the aforementioned situation, before taking any action, I tried to move the valve inside the positioner by hand, but there was no response at all. Under normal conditions, it should be possible to reach either 0% or 100%; we also use this method to determine whether the positioner is functioning properly. May I ask, where could the problem lie in the above fault conditions? ? ? ? ?
The system should be inspected, with a focus on cleaning; this includes valve positioners, filters for the air supply, and the actuators of the valve bodies, each of which needs to be checked separately. It also includes whether there is any sticking in the operation of the valve body.
If the air supply is normal, it’s likely that the steel ball inside the amplifier is stuck or stuck together; try cleaning the amplifier.
Disconnect the air supply pipe from the connection point to the actuator diaphragm head, then manually move the feedback rod behind the valve positioner to observe any changes in air supply pressure. If the air supply pressure and flow rate change in response to moving the feedback rod, it is very likely that the diaphragm is leaking.
It’s hard to tell without the drawings, but the first thing that comes to mind is also the amplifier
It’s simple: to determine whether it’s a problem with the actuator, connect an air source directly to the pressure reducing valve in order to supply air to the diaphragm head. The pressure of the air source should not exceed 0.4 Mpa. Check whether the valve can be opened fully; if it can, then it indicates that there is a problem with the actuator. Disassemble it and check whether dust has gotten inside the nozzle.
Check the diaphragm inside the membrane chamber; it’s possible that it is leaking, which results in insufficient thrust.
I think we should focus first on the amplifier to see where there are issues, and then check the valves. As for the diaphragm, it should be fine as long as the air supply is clean; if everything else is okay, then we can check that as well
First, connect the valve directly to the air supply without using a positioner, and check whether the valve operates properly. This way, it becomes possible to determine whether the problem lies with the positioner or with the valve itself, allowing for more accurate analysis and troubleshooting