How do control valves ensure both flow rate and pressure simultaneously?
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I’d like to ask everyone: if the available flow rate before the control valve is high, how can we maintain both the flow rate and pressure after pressure reduction by the control valve? Or is it such that each pressure corresponds to a specific flow rate, and once the pressure for throttling is determined, the flow rate is also determined? Thank you!
Personal opinion: This issue should relate to the fields of process engineering and instrumentation; since I’m not an instrumentation specialist, my views may not be accurate. The instrument includes the concept of flow coefficient, which is an important parameter for them when selecting control valves. Once this parameter is determined, changes in flow rate and pressure become interrelated; therefore, it is felt that once one parameter is set, the other should also be set as well.
The flow rate is controlled by the control valve, while the pressure is that of the system; it is not the control valve that generates the pressure, and the subsequent system pressure has nothing to do with this.
From an overall process perspective, that’s the case; if we consider the pressures before and after the control valve, then it becomes relevant. In my opinion, the system pressure is the target, while the control valve serves as a regulating tool, and the result of its operation is the creation of a pressure difference before and after the control valve.
This post was last edited by ylb913 on 2015-1-1 at 10:50. The pressure and flow capacity in front of the control valve are sufficient; the pressure behind the control valve depends mainly on the backpressure and flow rate of the system downstream of it (i.e., the pressure drop issue). ——It is to control the flow rate, without needing to control the pressure behind the valve.
What can generally be controlled is the pressure before the control valve, while the flow rate is regulated through the control valve. It is possible to use frequency conversion technology in front of the valve to achieve a certain pressure, with the flow rate then being adjusted by a control valve. The pressure downstream of the valve depends on the conditions of the subsequent pipelines and equipment.
For example, in the control of fuel oil for our heating furnaces: one fuel oil pump supplies multiple heating furnaces simultaneously; each furnace’s fuel oil line is equipped with a control valve to regulate the flow rate, and a return line control valve is installed on the main pipeline to control the fuel oil pressure. If there is only one control valve and one circuit, and it is necessary to take both pressure and flow into account, then use cascade control.
This control should determine your choices, with adjustments based on feedback from flow signals as well as pressure signals. I’m not sure which one you need to choose for that process. The operation of a valve is related to both pressure and flow rate, depending on your requirements and the conditions under which it is to be used. For reference
I think it has something to do with the flow rate and the pressure difference before and after the control valve