Why are electric valves generally not used as control valves?
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In coal chemical industries, why are electric valves rarely used as control valves? Are they generally used only as on/off valves? ? ? ?
In the case of electric valves, when the main power supply is lost, there is no safe position available, such as a fully closed state, which does not meet the safety requirements specified by the process. As a on/off valve, the electric valve is generally used in programmable processes, such as the switching valve in dryers.
We are used only as quick shut-off valves in emergency situations; after all, operating some of the larger manual valves can be quite laborious
Under certain special conditions, it can also be used as a control valve; for example, in areas where there is no instrument air. In areas where instrument air is available, electric valves are generally not used as control valves, as they are expensive and difficult to maintain. Electric valves are widely used in power plants, while they are rarely used in petrochemical plants.
Electric valves are used for regulation in many cases; it’s just that you don’t see them often. For example, the control valves for primary fans in power plants, the small dampers for secondary fans, the gate valves in the flue of exhaust fans, the control valves for return air fans, water supply control valves, and so on – there are many such components. In terms of operational stability, they are no inferior to pneumatic valves; in areas where no air source is available, electric valves can fully serve as a substitute
1. Pneumatic control valves are generally spring-return type, which makes them \"inherently safe\"; they can return to a safe position when the air supply is lost. Therefore, pneumatic valves have inherent advantages over electric valves. 2. Pneumatic valves of typical sizes operate at faster speeds than electric valves. 3. Pneumatic valves of general sizes are cheaper than electric valves.
Electric control valves are widely used; in most cases where pneumatic control valves can be used, electric control valves can serve as a replacement； Electric on-off valves are different; their switching speed is much slower compared to pneumatic valves, making them unsuitable for many applications that require rapid switching.
Well, the drawings I saw also show electric cut-off valves and pneumatic control valves