What Is a Hydraulic Rotary Actuator?

Paul Scott
Paul Scott
Woman holding a book
Woman holding a book

A hydraulic rotary actuator is a mechanical device that uses pressurized oil to operate an internal mechanism that supplies a rotary output motion. The internal mechanisms used to supply the motion vary according to the specific intended end use of the actuator, and include rack and pinion, helical, and vane types. Oil-driven rotary actuators generally offer rotational movement ranging from only a couple of degrees to 360-degree full rotation. As they do not supply continuous rotational movement, their use is generally restricted to the actuation of valves and other mechanisms that require a full turn or less to operate. The rotary hydraulic actuator is, however, exceptionally powerful and well-suited to applications where extremely high torque loads are encountered.

The hydraulic rotary actuator is one of a family of mechanical agents used to supply remote operation of secondary devices. Unlike electrical, electromechanical, and pneumatic actuators, these devices use highly-compressed hydraulic-grade oil to operate an internal mechanism which, in turn, supplies the rotational output motion. The specific internal workings of these actuators vary and may be based on rack and pinion, helical gear, or scotch vane-type mechanisms, with each offering particular benefits suitable for specific operational conditions. All types will consist of a common group of components, including an oil reservoir, external oil pump, and the actuator unit itself.

The basic operating principle used to run a hydraulic rotary actuator is fairly simple. The pump moves oil out of the reservoir under high pressure to an inlet point on one side of the actuator unit casing. Once it enters the sealed interior of the unit, it presses against a piston or the face of a vane, moving it in the process. This motion is translated into a rotary output by the internal mechanism of the particular actuator. Once the actuator has reached the end of the duty cycle, a control valve set located on the external oil line directs the flow of oil to the opposite side of the casing to reverse the action when required.

Due to the restrictions involved with hydraulic systems, the hydraulic rotary actuator can generally only supply one full turn in any cycle. This restriction sees the actuators used primarily to actuate devices, such as butterfly and ball valves which don't require more than a full turn to operate. The inherent high power values of hydraulic systems do mean, however, that the hydraulic rotary actuator is, in any given configuration, the most powerful of all actuator types, making them ideal solutions for high-torque applications.

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