Rotary Actuators: Rack-and-Pinion and Vane
A rotary actuator turns pressure into a limited rotary motion and replaces a motor plus gearbox on flaps, grippers and diverters. Rack-and-pinion units deliver high, constant torque and exact angles; vane units are compact and light. This guide shows how to pin down type, torque and swing angle for your application with confidence.
View rotary actuatorsRack-and-pinion or vane - which type fits?
Two principles dominate. In a rack-and-pinion actuator one or two pistons drive a rack that turns a pinion and thus the output shaft. This gives constant torque across the whole angle and allows high forces and precise end positions. A vane actuator rotates a vane directly inside a chamber, which makes it very compact and light, but it delivers somewhat lower torque and is harder to seal perfectly.
How do I size the required torque?
The torque must safely overcome load, friction and dynamic forces. First find the static load moment from mass, lever arm and centre of gravity. Add a safety factor of about 1.5 to 2 to cover friction, acceleration and pressure fluctuations. Catalogue torque drops as working pressure falls, so always read it at the pressure you can actually supply.
- Find the load moment from mass times lever arm times gravity.
- Add a 1.5 to 2 safety factor for friction and dynamics.
- Read torque at the actual working pressure, not the maximum rating.
- For fast motion, account for inertia and end-position cushioning.
Which swing angle and end positions do you need?
The swing angle drives the type and version. Standard angles are 90 and 180 degrees, and many actuators offer adjustable stops for intermediate angles. Only rack-and-pinion units with a long rack reach multi-turn motion. Watch for adjustable end positions, cushioning and repeatability when the actuator has to position accurately.
Frequently asked questions
Rack-and-pinion or vane actuator - which is better?
Rack-and-pinion actuators deliver high torque that stays constant across the angle plus exact end positions, but need more space. Vane actuators are more compact and lighter yet give less torque. Choose rack for force and precision, vane for tight installs.
How much safety factor do I need on torque?
A factor of 1.5 to 2 on the static load moment is common. The margin covers friction, acceleration and pressure fluctuations. For fast or off-centre loads lean toward the upper value and check inertia separately.
Why does my rotary actuator not reach the catalogue torque?
Catalogue torque applies at rated pressure. If working pressure drops, torque falls in proportion. Check the actual supply pressure, line losses and valve size before judging the actuator too weak.
Find the right rotary actuator
Our hydraulics specialists help with type, torque and swing angle for your application.
Correct torque
Sizing from load, lever arm and safety factor.
Right type
Rack or vane to match force and available space.
Exact end positions
Adjustable stops and cushioning clearly explained.
Expert advice
Hydraulics specialists support your sizing.