Selection of control valves
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How are the pressure before and after the control valve determined? Is it the pump that is located before the valve? Is the output pressure of the pump equal to the pressure before the valve? It’s the tank behind the valve; so how is the pressure behind that valve determined? Please ask the experts for advice!
That’s more or less it, but the calculations also take into account the static pressure difference caused by the liquid level difference and the resistance losses!
1. How are the pressure before and after the control valve determined? Just like the tap water supply in your home, a pressure measurement point can be installed before the valve to measure the pressure; the pressure behind the valve can also be adjusted according to your needs. But for tap water, what you need is flow control, not pressure. 2. Is the pump located before the valve? Is the output pressure of the pump equal to the pressure before the valve? It could be said so, but it’s not precise; there are other conditions involved, such as the resistance up to the valve under your control and other contributing factors. The output pressure of a pump is an inherent characteristic of the pump; in actual use, it may not reach the designed pressure, as the pump’s capacity has certain limits. 3. The valve is located after the tank; how is the pressure behind that valve determined? Please refer to the first answer. Additionally, for those working in the chemical industry, I recommend the reference book \"Principles of Chemical Engineering\"; it is difficult to meet the requirements of the job without reading this book.
HG/T20570.5 covers the calculation of the system characteristics of pumps, and it includes calculations related to control valves. It is necessary to assume a pressure drop value, select a CV value, then determine whether the proportion of the pressure drop is reasonable, and finally make a decision
I think it’s more reliable to calculate the pressures separately for the front and back ends; after all, the automation engineering field requires the pressures before and after the valve in order to determine the flow characteristics. A reliable formula should be: before the valve – pump outlet pressure minus the pressure drop to the control valve (pipe friction, head loss, elbow losses, etc.); after the valve – the working pressure of the tank minus the pressure drop to the control valve (pipe friction, head loss, elbow losses, etc.). After all, the selection of control valves still requires considering the pressure drop requirements specified in the process to determine the appropriate type of control valve.