1. An actuator is a component of an engine that is responsible for moving or controlling parts of an engine. 2. An actuator requires a control signal and a source of energy. The control signal is relatively low energy and may be electric voltage or current, pneumatic or hydraulic pressure, or even human power. 3. When the control signal is received, the actuator responds by converting the energy into mechanical motion. 4. An actuator is the mechanism by which a control system acts upon an environment. The control system can be simple (a fixed mechanical or electronic system), software-based a human, or any other input. 5. An electric actuator is powered by a motor that converts electrical energy into mechanical torque. 6. A hydraulic actuator consists of cylinder or fluid motor that uses hydraulic power to facilitate mechanical operation. 7. A mechanical actuator functions to execute movement by converting one kind of motion, such as rotary motion, into another kind, such as linear motion