By the type of movement

• Multi-turn
• Quarter-turn
• Linear

By the energy source

• Manual
• Electric: they can be driven by direct and alternate current.
• Pneumatic: they use pressured air or gas to create motion. They are widely used in the industry due to their low cost. In case of failure they are easy to diagnose or repair in field, rather than electric actuators.
• Hydraulic and Electro-Hydraulic

Functionality

• On/Off valve service
• Positioning to % open
• Modulating to control changes on flow conditions
• Emergency Shut Down (ESD)

Other characteristics

• Explosion-proof
• Safety integrity level (SIL)
• Enclosure: IP and NEMA