2 replies to this topic

[Bader989]

We have two Flow control valve setup in parallel, getting same signal from FIC (flow rate SM3/D) as attached drwaing.

What is the best control logic implementation to maintain them one in duty and other one standby?

Please notice that, both control valve are air fail to open and according to operation philosophy the valve is mostly full open.

 

Best Regards

Bader

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[Bobby Strain]

If you want the second valve to be active without operator selection, set the valve positioners such that the active valve opens over half the controller output range. And the second valve operates over the other half. Otherwise known as split-range control. Of course, this will provide the opportunity for both valves to fully open. But if this is of no consequence, it's an easy solution.

 

Bobby

[Zauberberg]

It all depends on what needs to be achieved with this control loop. If the normal operating scenario is to have one valve in modulating control and the other one fully closed, then implementing a simple software switch is sufficient. If the second valve is supposed to be partially open as well (e.g. taking excess flow which cannot be handled by the first valve only), then the split range control is what you need. If you can explain in details what is required to be controlled by this loop, we can give you a better and more precise answer.