Solenoid valve is an automatic fundamental element used to control fluid. It belongs to an actuator and is not limited to hydraulic and pneumatic. It is used to adjust the direction, flow rate, speed, and other parameters of the medium in the industrial control system. Solenoid valves are divided into three principal categories: 1. Direct acting solenoid valves; 2. Step by step direct acting solenoid valve; 3. Pilot-operated solenoid valve;