Selection of valves before and after the flow meter and control valve assembly, as well as bypass valves
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Valve assemblies composed of flow meters and control valves are commonly used in the chemical industry. For reasons such as maintenance, flow meters and control valves generally require upstream and downstream isolation valves as well as bypass valves; the question is what type of valve to choose. Generally speaking, globe valves have a certain degree of regulating capability, but their sealing performance is not very good. Ball valves, on the other hand, offer better sealing performance but inferior regulating capabilities; therefore, ball valves are suitable for use as shut-off valves and are often employed as upstream and downstream valves. The idea behind using globe valves as bypass valves is that in case a regulating valve fails and needs to be repaired, it can be manually controlled temporarily. However, most chemical plants currently opt for shutting down the plant temporarily when a regulating valve malfunctions, rather than using manual control. Additionally, there is a particular concern regarding the poor sealing performance of globe valves – during normal operation, any errors in the control of regulating valves, especially flow meters, could occur. How should these contradictions be properly handled? Discussion is welcome.
Valve assemblies composed of flow meters and control valves are commonly used in the chemical industry. For reasons such as maintenance, flow meters and control valves generally require upstream and downstream isolation valves as well as bypass valves; the question is what type of valve to choose. Generally speaking, globe valves have a certain degree of regulating capability, but their sealing performance is not very good. Ball valves, on the other hand, offer better sealing performance but poorer regulating capabilities; therefore, they are suitable for use as shut-off valves and are often used as the first and last valves in a system. Oh, and I still don’t know that one :D
Our hospital’s regulations regarding this apply mainly to the requirements for bypass systems. When it is necessary to service or replace flow meters or control valves, it is possible to close the valves located before and after them; in other words, these valves serve only as on/off devices. However, when it is actually necessary to adjust the flow rate during maintenance or replacement, globe valves are usually used, as they enable flow regulation. If only a switch is needed, choose a gate valve. . . . . . I’m not sure if I’ve made it clear.» ?