Linear solenoids convert electrical energy into mechanical power via a plunger with an axial stroke in either a push or pull action. These transducers consist of a coil of wire, sometimes wrapped around an iron core, which generates a magnetic field when a voltage is applied. Because the magnetic field can be confined in a volume, its strength can be adjusted.
Linear solenoids can be either unidirectional (push or pull) or bidirectional (push/pull). They are generally larger and significantly less expensive than rotary solenoids, but have fewer life cycles. When selecting products, buyers should consider maximum stroke, torque, and response time. Maximum stroke is the full linear travel of the solenoid’s plunger, from the fully-extended to the fully-seated position. The response time is the time needed to move the plunger full stroke under no load.
Types of Linear Solenoids
Linear solenoids are often classified as pull and/or push devices.
- Pull solenoids bring the plunger into the solenoid’s body along the electromagnetic path. Applications include switchgear, valve actuation, brakes and clutches, and throttle control.
- Push solenoids move the plunger out of the solenoid’s body. Often, they have a spring return to bring the plunger back to the home position.
Bidirectional push/pull solenoids are also available. There are two subtypes: conical and flat. Conical devices are suitable for a medium-stroke or long-stroke long stroke applications. Flat devices provide short strokes and strong force.
In addition to push, pull and push/pull products, linear solenoids may be classified as continuous or intermittent.
- Continuous duty solenoids are designed for operating conditions with continuous, heavy-duty use. They are more durable than intermittent solenoids and physically larger in size.
- Intermittent duty solenoids are rated for on-off applications at less than 100% duty cycle.
The GlobalSpec SpecSearch database provides information about these linear solenoids, which are defined according to their construction.
- Open-frame solenoids are box-like, C-frame, or D-frame devices with air gaps in their metal frames to provide heat dissipation. Small, open-frame devices are sometimes used in vending machines to dispense products.
- Tubular solenoids are tube-shaped devices with a full metal case. They are designed to minimize flux leakage and operational noise.
- Clapper solenoids feature a hinged design and are designed for low-force, long-life applications. They are sometimes called flappers. Applications include refrigerators ice chutes and the control of the airbox flap on motorcycles.
- Laminated solenoids have a laminated frame and insulated laminations that allow the magnetic field to develop while minimizing eddy currents. Unlike other solenoids, which are designed for use with direct current (DC) power, laminated solenoids can use alternating current (AC) with a silicon bridge rectifier.