Sizing rotary and swivel actuators by torque
A pneumatic rotary actuator must deliver the required torque reliably and decelerate the load cleanly at the end of travel. Design, swivel angle and moment of inertia decide service life and process safety. This guide shows how to size rack-and-pinion and vane actuators by torque and inertia step by step.
View rotary actuatorsHow do I work out the required torque?
Torque is the key sizing figure. Add the static load moment from weight and lever arm, the friction moment of the bearing and, for fast cycles, the dynamic acceleration moment. Apply a safety factor of 1.5 to 2 to this sum so pressure fluctuations and start-up friction are covered. The rated torque of an actuator usually applies at 6 bar and drops almost linearly at lower pressure.
Rack-and-pinion or vane - which design fits?
Rack-and-pinion actuators deliver constant torque across the whole angle, allow more than 180° and set precisely with stops. Vane actuators are compact and light but limited to about 270° and give a slightly angle-dependent torque. For high torque and repeatability, rack-and-pinion is the first choice.
- A double pinion or twin pistons double the torque at the same body width.
- For exact end positions choose adjustable stops with fine setting.
- For vacuum or gripping tasks check torque output in both directions of rotation.
How do I control inertia and cushioning?
The moving mass stores kinetic energy at the end of the swing that the actuator must absorb. If it exceeds the permissible energy, the end positions hit hard and wear the gear teeth or vane seal. Check the moment of inertia against the maker's limit and pick the right cushioning: elastic buffers for small, adjustable shock absorbers for large energies.
Frequently asked questions
What safety factor should I apply to the torque?
A factor of 1.5 to 2 on the sum of load, friction and acceleration moment is common. This covers pressure fluctuations, start-up friction and wear without oversizing the actuator unnecessarily.
Why does my rotary actuator deliver less torque than the catalogue?
Rated torque usually applies at 6 bar. At lower working pressure it drops almost linearly, and friction plus back pressure reduce it further. Always calculate with the real pressure at the actuator.
Rack-and-pinion or vane actuator - which is better?
Rack-and-pinion delivers constant torque, more than 180° of angle and high stiffness but builds larger. The vane actuator is compact and light but limited to around 270° and lower torque.
Size the right rotary actuator
Our pneumatics specialists help with torque, design, swivel angle and cushioning for your application.
Correctly sized
Torque calculated cleanly with a safety factor.
Right design
Rack-and-pinion or vane by angle and torque.
Safe end positions
Moment of inertia and cushioning clearly explained.
Expert advice
Pneumatics specialists support the sizing.