Solenoid valves are electromechanical devices used to control the flow of liquids or gases in automation and fluid control systems. They consist of a coil, plunger, and valve body, which work together to open or close the valve when an electrical current is applied. Commonly used in industrial automation, HVAC, and hydraulic/pneumatic systems, solenoid valves offer fast response times, precise control, and reliability. Key types include direct-acting, pilot-operated, and latching solenoid valves, available in various materials (brass, stainless steel) and configurations (2-way, 3-way). Popular applications include water/gas shut-off, process automation, and refrigeration systems.