Seeking help with selection of control valves
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This post was last edited by liu530014416 on 2022-5-22 09:16. The process conditions are 3 Mpa before the valve and 1.9 Mpa after it; the normal flow rate is 25 m3/h. Currently, a one-seat valve designed for emergency use is in operation. The problem is that when the valve is fully closed, there is an internal leakage of 5 m3/h. What type of control valve should be selected to meet the process requirements?
Since the single-seat valve currently in use has an internal leakage of 5 m3/h when fully closed, should the selection be changed?
Internal leakage of control valve: 5 m?? This leakage rate is far too high; there are national standards governing it. Check it and then ask the supplier to provide a suitable control valve.
The pressure difference before and after the valve is too large; a double-seat valve should be chosen
This post was last edited by dellkey on 2022-5-21 at 22:25. The selection of control valves is very important
Valve selection is very important. Please provide the process parameters so that I can do the calculations for you; leakage is closely related to the diameter of the valve
Is the actuator’s closing force sufficient? Is the valve core damaged or worn? In case of flashing or cavitation, change to a sleeve + drilling!
There must be a problem with the valve; the leakage rate has reached 20% of the flow rate. If the pressure difference before and after the valve is less than 2 times, it’s actually not that difficult to handle; just choose another valve manufacturer – there’s no need to get too stuck on the selection process
Required data: 1) Fluid； 2) Corrosivity ； 3) Environmental conditions ； 4) Process parameters ； 5) Installation requirements ； Then determine the flow coefficient, select the material, define the connection dimensions and pressure rating; an actuator is required ；
It has been found that the control valve is not working properly; the first step when replacing it is to determine the reason why the previous one was ineffective. Approximately 20% of cases involve internal leakage, and there are two main reasons for this: one is severe damage to the valve core, which can be determined by whether the internal leakage occurs right when the control valve is put into use or after it has been in use for some time. In the case of damaged valve cores, the issue should be addressed by considering the material of the valve core or the design of the valve ； Second, the thrust of the actuator is insufficient; if it is confirmed that the valve core is not severely damaged, the problem is likely to lie with the actuator. In some older designs (common in certain domestic valves), the thrust of the actuator is calculated based on the operating pressure difference; although this may seem to meet the specified requirements during selection, leakage during shutdown under actual operating conditions can be significant. For some high-end control valves, the operating pressure difference is always determined based on the pressure resistance of the valve body (which makes the valves much more expensive). It is recommended that the poster provide information on the manufacturer, structure of the old valve, as well as the process medium and temperature, so that everyone can offer suggestions. .