A linear solenoid is an electromagnetic actuation device that generates motive force in a straight line. It consists of a wire coil with a hollow center and a spring-loaded ferrous metal plunger positioned with one end adjacent to the coil opening. When an electric current is applied to the coil, a powerful magnetic field is generated around it. This magnetic field attracts the plunger that moves rapidly towards it, supplying the movement necessary for actuation. Depending on the solenoid design and purpose, the output motion may be orientated towards or away from the coil body, giving a push or pull output.
A solenoid is essentially a remote-switching device and belongs to an extended family of electromechanical, pneumatic, and hydraulic actuators. They are possibly one of the most reliable, cost-effective, and efficient of all of these devices, with minimal moving parts and long service lives. In addition, they are capable of generating both rotary and linear activation movement with the linear solenoid presented in either push or pull configurations. All work on a common electromagnetic principle, however, with an electrically-energized wire coil used to produce a strong magnetic field around a hollow core. This magnetic force attracts a iron-alloy plunger against spring pressure that supplies the necessary actuation movement.
The linear solenoid is probably the more common of the two types, and generates an actuation movement in a straight line, hence the linear identifier. This type of solenoid is divided into two sub-categories, namely push and pull variants. A linear pull solenoid is constructed in such a way that the active movement is directed towards the coil as the plunger is pulled into the core. The push solenoid operates in the same fashion, except that the plunger is constructed and arranged in such a way that, when pulled into the solenoid core, an extension projects away from the coil providing a pushing motion.
Both push and pull linear solenoid types may be used for a range of common application types, including switch and valve actuation. The choice of which type is used is more often than not dictated by space constraints and specific design requirements of the actuated mechanism. The push type of linear solenoid is, however, exclusively used where percussive action is needed. This type of striking actuation movement is frequently utilized in the fields of robotics and aviation. Electromagnetic counters also often feature push solenoids as their counter mechanism actuators.