Problems with control valves
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Our plant has an electric control valve made by Shibel; it is connected to 3 power cables (380V) and 2 signal cables (4–20mA). It has been working properly until one day, when it suddenly stopped responding to remote control. When operated locally using the switch on the valve, it functions normally, but remote control no longer works. The power supply is fine, and the signals are also normal. I’m not sure what could be the cause There is also a pneumatic control valve; when its opening degree exceeds 80%, the valve gets stuck and will not operate. Using an electrical positioner to set a limit does not work either. Later, we welded a piece of rebar to the screw on the cylinder that functions like a push pin, thereby forcing the valve shaft to stay at an opening degree below 80%. We opened the cylinder once, and there were no problems – the air supply and signals were all normal. We’re not sure what the cause is; is there a better solution? Thank you all.
I think the control board for the electric valve is broken. There are many reasons why a control valve can get stuck. What type of control valve do you have? V-ball? Disk valve? globe?
It would be best if the original poster could specify the type of structure of the valve as well as the name of the medium used, so that everyone can know how to resolve the issue! QQ: 928976489
Check the electrical components around the signal input
If the electric control valve cannot be controlled remotely, the issue with the remote control signal should be checked first. The ability to control it locally does not mean there is no issue with the signal; based on the owner’s description, it seems more likely that there is a problem with the remote signal. There are many reasons why pneumatic valves get stuck; these can include problems with the valve itself, such as foreign objects in the valve core, as well as issues with the actuator. The actuator involves not only the cylinder but also components such as amplifiers and positioners. We recently dealt with a problem where a pneumatic control valve would not close properly; it was found that the issue was caused by aging of the amplifier diaphragm, which resulted in poor sensitivity to low signals. Normal operation was restored after replacing the amplifier. It is recommended that the poster post some actual photos of the pneumatic control valve, as well as information on the medium used for control.
If remote control is not possible, first check whether the signal cable is properly grounded. Then see if there is any change in the operation mode on the panel when it is switched to local control. If no change occurs, check whether there is a problem with the operation status switch; only then should you consider an issue with the control board
Can a control valve be operated locally as well, rather than adjusting its opening degree based on signals such as pressure or temperature? Seeking advice