Thursday, May 13, 2010

Q. How do manual, electric, pneumatic, and hydraulic valve actuation methods differ? what type of actuation is suitable to different environments?

A: Let’s start with the most often used actuators - the pneumatics. The automated and control valves in process plants are usually operated by pneumatic actuators. They are, by far, the most commonly used actuators due to their being light weight and rugged. Their low cost and high reliability make them very popular. Pneumatic actuators are commonly used in a potentially explosive atmosphere. The failsafe action of single-acting actuators is system-inherent.

Manual shutoff valves are used to isolate or bypass control valves. They are only occasionally operated and used for on/off applications, when the response time is not critical.

Electric actuators are mainly used in applications where compressed air is not available; for example, in small systems for building automation, or in some areas of power plants. However, the implementation of failsafe action (fail open or fail close) upon power supply failure or emedown in large electric actuators requires a technically complex construction.

Hydraulic actuators are used in applications where the required force and/or stroke cannot be accommodated by pneumatic or electric actuators.