A valve actuator is attached to the valve spindle and enables control from a remote location. Actuators are classified according to their range of movement, or travel:

• Multi-turn actuators – Used for control applications where accurate mid-range performance is required. 
• Part-turn actuators – Used for rapid shut off, such as with butterfly or ball valves.

Actuators are usually driven by electric motors, although some systems are still based on pneumatic actuation.