Rotary actuators are designed specifically to provide a limited angle of rotation. These are distinct from hydraulic motors and as a consequence are of simple design as no timing valve is necessary. Three common types rotary actuator: rack and pinion, vane and helical screw are shown in Figures 1and 2.

Applications
Rotary actuators are used for the following applications:

Steering systems     Gate valves                 Boom slew of backhoe
Manipulator drive     Tunnelling machine      Container handling

Most of the actuators will carry side loads and can usually be supplied with position indication, cushioning valves, mechanical stops and a variety of shaft attachment features.