Solenoid operators and valves are devices which control the flow of liquids, gases, steam and other media. When electrically energized they either open, shut off or direct the flow of media.

Figure 1:—

The solenoid consists of a coil of wire wound in the form of a cylinder around the bobbin. When an electrical current is introduced it resembles a bar magnet. When energized by an electrical signal, a magnetic field builds up which attracts the movable plunger to the polepiece, against the tension of the main plunger spring. When de-energized, the magnetic field dissipates and the plunger returns to its original position, under the action of the main plunger spring. (See Fig. 1). In order to be usable on AC current as well as DC, the polepiece contains a shading ring to average the alternating sine wave and minimize AC hum. (Note - It is not necessary to use a shading ring for DC applications as DC current does not produce an alternating wave function.) The flowing media is normally permitted to enter the area between the plunger and plunger guide tube, and caution should be used to assure that these components are compatible with the media when selecting a valve.