I would like to consult about the limit issues of pneumatic control valves and electric control valves
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Dear sea friends, I would like to ask whether, in terms of engineering practices, there are often requirements that control valves should not be closed completely (for example, only to 30% at most) or opened completely (for example, only to 70% at most)? If so, how can it be achieved? Is it implemented directly on the control valve or on the PID regulator? I appreciate your guidance.
This requires a complete set of regulating actuators. It is implemented by the valve actuator (valve positioner, feedback travel switch, …), PLCs, DCSs, and other control and display devices.
In terms of process requirements, it is generally not necessary to prevent control valves from being fully open or fully closed, unless there are specific demands imposed by the process control. Limits on the opening degree of control valves: 1. This can be achieved using the DCS system – by setting upper and lower limits on the control panel for that circuit; certain permissions are required to make changes, and this method is simple to implement. 2. It can also be accomplished through mechanical limits on the on-site control valves, which should be specified during design and procurement； Or unilateral limiting of the upper or lower limit can be achieved via a handwheel.
It is generally more convenient to do this on the DCS side (with the opening limit indicated on the display); doing it on the control valve side makes it difficult for maintenance personnel to adjust the valve, as it may lead them to assume that there is a fault with the valve
I checked the manual for the PID regulator; it contains options related to limiting the control output. For example, it is possible to set an upper limit of 90% or a lower limit of 10%; this application seems to be used for setting the limits of valves, right? It means setting it in the regulator or in the DCS, but there’s no need to do it at the control valve itself, right?
It works best on DCS; configuration takes care of everything
Of course, some locators have this function