- Rack & pinion
- Rotary vane
All three styles are available in either direct acting or spring return versions. Direct acting actuators use the air supply to move the actuator in both directions (open and close). Spring return actuators, as the name implies, uses springs to move the actuator back to its "resting" state. Converting from direct acting to spring return is done through simple modifications, typically just adding an external spring module, or removing the end caps from rack and pinion actuators and installing several coil springs.
|Scotch yoke (Limitorque)|
|Rack and pinion (Delval)|
Vane actuators generally provide the most space savings when comparing size-to-torque with rack and pinion and scotch yoke. They have a reputation for long life because then contain fewer moving parts than rack and pinion and scotch yoke actuators. Vane actuators use externally mounted, helically wound "clock springs" for their spring return mechanism.