The solenoid valve uses an electromagnet to move the plunger attached to the valve to open or close it. Switching off the power to the electromagnet allows the spring or other force to return the plunger to its original position. Automatic irrigation systems typically use solenoid valves to control water. delivery.

When an electromagnetic current flows through a coil wire wound or shaped around the armature core, it generates a magnetic field around the coil. The strength of this magnetic field increases as the number of turns of the coil increases. The more coil turns, the stronger the magnetic field. When this happens, the armature core is pulled toward the fixed core to close the air gap between the two cores.

The function of the spring in the electromagnet is that the armature core can be retracted to its original position when the electromagnet is turned off and the magnetic charge is released. The magnetic pull force can be calculated to be approximately proportional to the square of the electromagnetic current and inversely proportional to the square of the distance between the two cores, which is the amount of air gap between the two cores.