Actuator is a arm, coil, or something like this which converts one energy to mechanical energy for releasing or closing gas or liquid. in other words we can say it is a type of special motor. The actuator can be electrical biased, mechanical biased, thermo biased, hydraulic biased or pneumatic biased.
Electrical Biased Actuator: electrical biased actuators are solenoids which are used to control flow, it can be fluid or pneumatic flow. solenoid also control electrical energy.
Mechanical Biased Actuator: Mechanical biased actuators are hydraulic or pneumatic cylinders which control the flow of fluid or compressed air.
Thermo Biased Actuator: Actuators which are actuated by thermally or magnetically are called thermo biased actuators.