Fig. VII.15: A schematic of Solenoid

Fig. VII.15 shows a schematic of a solenoid valve. The blue bar indicates an electromagnet that gets energized on flowing current through the helix. The red colored piston is a metallic object whose movement is controlled by the duration of energization of electromagnet. In normal situation the spring forces the piston to move far and block the fluid flow in the pipeline. As the electromagnet gets energized, the piston is pulled back yielding the fluid to flow unrestricted.