Manual actuators are the most common type of valve actuators. Manual actuators include handwheels attached to the valve stem directly and handwheels attached through gears to provide a mechanical advantage.
Electric motor actuators consist of reversible electric motors connected to the valve stem through a gear train that reduces rotational speed and increases torque.
Pneumatic actuators use air pressure on either one or both sides of a diaphragm to provide the force to position the valve.
Hydraulic actuators use a pressurized liquid on one or both sides of a piston to provide the force required to position the valve.
Solenoid actuators have a magnetic slug attached to the valve stem. The force to position the valve comes from the magnetic attraction between the slug on the valve stem and the coil of the electromagnet in the valve actuator.