Design specifications for control valve feedback
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I would like to ask whether the current design standards in the chemical industry specify that control valves of a certain type must be equipped with feedback
It seems there are no strict regulations. But there’s no feedback on the valve position – isn’t that too dangerous?
I’m not sure if there are any regulations regarding this, but regulating valves are used in all cases
It seems not; earlier mechanical positioners had no feedback, while modern intelligent positioners do have it, but it doesn’t seem very useful. It’s possible to tell whether the valve has moved or not by checking the parameters being monitored (level, temperature, flow rate, etc.).
I worked at a chemical company in China for 10 years, and I didn’t see many control valves that came with feedback mechanisms. They said it’s dangerous upstairs; I could only laugh. By checking the adjustment target, one can tell whether the valve is working properly.
Generally, it depends on the owner’s requirements; if there are no special requests, then nothing is added, and it’s sufficient to simply observe the controlled quantity, without needing to worry about how wide the valve is open. Moreover, this is generally determined through discussions between the process engineers and the client; if necessary, it will be indicated in the PID process diagram. The instrumentation team then decides, based on the functional blocks in the PID diagram, whether a locator with valve position feedback is needed, or limit switches, or both, or none at all.
Most modern intelligent positioners can use the Hart protocol to transmit 4-20mA valve position signals to the DCS system.
This is a requirement specific to the Process (Safety) field; it was not proposed by the instrumentation department, nor is it mandated by any standards. Since most of the current positioners are intelligent, they come equipped with built-in valve position detection modules; the valve position can be obtained via HART communication, or a separate 4-20 mA feedback signal can be generated. I have used a separate valve position feedback transmitter once, for the heating steam valve of the reboiler in an propylene distillation tower; if this valve was opened fully, it would result in an extremely high flow rate of vapor to the flare stack (exceeding the design capacity of the flare). At that time, there was no systematic SIL assessment; in accordance with the design guidelines of that era, which recommended \"monitoring the opening degree of steam valves\" as a preventive measure, separate valve position feedback transmitters were installed.