The fundamental classification of the actuators is based on the type of the energy which is converted into the mechanical motion and on the type of the performed motion (linear or circular).
The hydraulic and pneumatic actuator converts stored potential energy of the pressurized fluid or gas medium. The pressurized medium has to be generated by pumps or compressors, which again has to be driven by some kind of electric motor or other type engine. The pressurized fluid or gas also has to be “brought” to the actuator by a system of pipes and hoses.The electric actuator converts electric energy directly to mechanical. This conversion is generally accomplished by utilizing electromagnetic effects. In some special design other physical effects can be utilized to convert the electrical energy into mechanical. However, the vast majority of electric actuators use some type of electric motor. The mechanical energy output from the motor (the rotational speed and the torque) frequently has to be “conditioned” i.e. the speed has to be reduced; the torque has to be boosted. This is accomplished by some kind of mechanical transmission (gear, belt stageetc.) Electric Linear Actuators also need to convert the rotary motion into linear.