The concentric reducing tube problem
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I would like to ask: in these two PID designs, are concentric reducer pipes installed before and after the pneumatic actuator? Is this done to account for the difference between the nominal diameter of the actuation valve and that of the pipes?
Yes, the connection dimensions of the valve are different from the pipe diameter
Adding reducers before and after the control valve is a common practice in design; by reducing the diameter, it becomes easier to control the control valve, and moreover, control valves with smaller diameters are less expensive
Secondly, small-diameter control valves are inexpensive =================== So why not make the pipelines before and after them smaller as well? Wouldn’t that save even more money?
The pipeline is small – does the overall pressure drop need to be considered?
Oh, so we need to take into account the issue of pipe resistance as well =================== Can it be understood in this way: actually, a 4-inch diameter pipeline is sufficient for the flow rate requirements, since the size of the control valve is also 4 inches. But due to pipe resistance, does the actual diameter of the pipeline need to be 6 inches? ? @The wise are enlightened
It’s not understood in that way; the size of the pipe should be determined accordingly. When selecting a control valve, it is necessary to take into account the pressure drops before and after the valve to facilitate regulation. Additionally, control valves with large pipe diameters are very costly