I have a few questions regarding control valves

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The last edit to this post was made by xuerdangdang on 2009-12-2 at 13:28. Once a control valve is selected, is its valve weight value fixed? For example, it has one value in one system; but will this valve weight value change when it is used in another system or if the pressure difference in the original system changes? If a system has a fixed pressure difference across it (with no changes in the pressures at either end of the system), and the valve’s sensitivity value is also fixed, then what is required now is the relative flow rate at a certain valve opening degree – for example, 50%. This relative flow rate refers to the ratio of the flow rate achieved at a 50% valve opening to the flow rate when the valve is fully open. The key question is: does the flow rate corresponding to a fully open valve refer to the flow rate obtained by simply maintaining a constant pressure difference across the system (without considering the pressures at either end of the valve), or does it require both the system’s pressure differences to be constant as well as the pressures at both ends of the valve at a 50% opening degree in order to determine that flow rate? I might not be able to express myself well in words: Thank you, I hope everyone here can help me