There are closed chambers in the solenoid valve. There are through holes in different positions. Each hole is connected with different oil pipes. The middle part of the cavity is a piston. On both sides are two electromagnets. Which side of the magnet coil is energized? Side, by controlling the movement of the valve body to open or close different oil drain holes, and the oil inlet hole is normally open, the hydraulic oil will enter different oil drain pipes, and then the pressure of the oil pushes the piston of the oil cylinder, and the piston Drive the piston rod, and the piston rod drives the mechanical device. This controls the mechanical motion by controlling the current through and off of the electromagnet.