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Thursday, July 8, 2010

Q: What is the difference between a rotary and a linear valve actuator? What are some common applications/examples of each actuation method?

A: Linear actuators are used to actuate linear valves such as globe, three-way (diverting or mixing) and angle valves. Pneumatic linear actuators have the simplest construction and provide very precise control of flow.

Rotary actuators, with shafts performing up to 90-degree rotary motion, are mounted on rotary valves such as ball, butterfly, rotary plug and segmented ball valves. These actuators are derived from linear actuators, and use a gearbox or lever system to convert the linear into a rotary motion. The actuator construction, where compressed air acts on a rotary vane instead of a piston, has not established itself on the market.

In contrast to the pneumatic version of rotary actuators, the rotary motion of electric actuators is inherent. A complex linear unit is needed to transform the rotary motion into a linear stroke.