Actuators for valves can be classified up several characteristics:

By the type of movement

• Multi-turn.
• Quarter-turn.
• Linear.
• Lever.

By the energy source

• Manual
• Electric: they can be drived 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.
• Oleo-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.