Actuators are operated in the same way as solenoids. They are used to move mechanisms remotely. Some examples of actuators on a vehicle are, door locks, pre-engaged starter motors and fuel cut off valves. Consider the diagram below.
Like a solenoid or relay an actuator has a winding. When current flows around the winding, the winding is energized.
Two types of actuator are used, a short rated version and a continuously rated version.
The short rated actuator is used for simple on/off operation. This type of actuator has one winding which cannot be operated for longer than 15 seconds. An example where this type of actuator could be used would be a door lock.
The continuously rated actuator has two windings. The first winding is used to pull the actuator arm into the winding, the second is used to hold the actuator arm in the winding. The pull in winding may require a current of as much as 35 amps. The hold in winding may only require a current of 4 amps. The continuously rated actuator is designed so that it can be operated for longer than 15 seconds. This-type of actuator is often used in pre-engaged starter systems to move the starter pinion into mesh.