Hydraulic solenoid valve, also known as water solenoid valve, works on the following principle: the solenoid valve has a sealed chamber with through holes at different positions, each hole leading to a different oil pipe. The middle of the chamber is the valve, and there are two electromagnets on both sides. The magnetic coil on which side is energized will attract the valve body to which side. By controlling the movement of the valve body, different oil discharge holes will be blocked or leaked out. The oil inlet hole is normally open, and hydraulic oil will enter different oil discharge pipes. Then, the oil pressure will push the piston, which in turn drives the piston rod, and the piston rod drives the mechanical device to move. In this way, the mechanical motion is controlled by controlling the current of the electromagnet.