Electro-Hydraulic Actuators-Compared to Other Types

Compared to other types, electro-hydraulic actuators require only electrical power to the motor and an electrical input signal from the controller. Electro-hydraulic actuators are ideal for isolated locations where pneumatic supply pressure is not available but where precise control of valve plug position is needed. Units are normally reversible by making minor adjustments and might be self-contained, including motor, pump, and double-acting hydraulically operated piston within a weatherproof or explosion-proof casing.

The next one is the manual actuator. It is useful where automatic control is not required, but where ease of operation and good manual control is still necessary. They are often used to actuate the bypass valve in a three-valve bypass loop around control valves for manual control of the process during maintenance or shutdown of the automatic system. Manual actuators are available in various sizes for both globe-style valves and rotary-shaft valves. They are much less expensive than automatic actuators.Rack and pinion designs provide a compact and economical solution for rotary shaft valves. Because of backlash, they are typically used for on-off applications or where process variability is not a concern. Traditional electric actuator designs use an electric motor and some form of gear reduction to move the valve. Through adaptation, these mechanisms have been used for continuous control with varying degrees of success.

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