Solenoid valve is used to control fluid automation basic components, belongs to the actuator; not limited to hydraulic, pneumatic. Solenoid valve is used to control the direction of hydraulic flow, the mechanical device in the factory is generally controlled by hydraulic steel, so it will be used.
The working principle of the solenoid valve is that there is a closed cavity in the solenoid valve, and there are through holes in different positions. Each hole leads to different oil pipes. In the middle of the cavity, there are two electromagnets on both sides. When the magnet coil is energized, the valve body will be attracted to which side. By controlling the movement of the valve body, different oil drainage holes will be blocked or leaked. The oil inlet hole is normally open, and the hydraulic oil will enter Different oil drainage pipes, and then through the oil pressure to push the oil rigid piston, the piston in turn drives the piston rod, the piston rod drives the mechanical device. In this way, the mechanical movement is controlled by controlling the current of the electromagnet.

Tracing the development history of solenoid valves, up to now, solenoid valves at home and abroad are divided into three categories in principle (i.e. direct acting type and step-by-step pilot type), and six sub categories (direct acting diaphragm structure, step-by-step lamination structure, pilot membrane structure, direct piston structure, step-by-step direct acting piston structure and pilot piston structure) are divided into six sub categories according to the differences in disc structure and material Structure).

Direct acting solenoid valve:
Principle: when electrified, the electromagnetic coil produces electromagnetic force to lift the closing part from the valve seat and open the valve; when the power is off, the electromagnetic force disappears, and the spring presses the closing part on the valve seat, and the valve is closed.

Features: in vacuum, negative pressure, zero pressure can work normally, but the diameter is generally less than 25 mm.

Distributed direct acting solenoid valve:
Principle: it is a combination of direct acting and pilot type. When there is no pressure difference between the inlet and outlet, the electromagnetic force will directly lift the small pilot valve and the closing part of the main valve in turn, and the valve will be opened. When the inlet and outlet reach the start-up pressure difference, after power on, the electromagnetic force pilot small valve, the pressure of the lower chamber of the main valve rises, and the pressure of the upper chamber decreases, so as to push the main valve upward by using the pressure difference; when the power is off, the pilot valve uses the spring force or medium pressure to push the closing part and move downward to close the valve.

Features: it can also operate under zero pressure difference, vacuum and high pressure, but the power is large, so it must be installed horizontally.

Pilot operated solenoid valve:
Principle: when electrified, the electromagnetic force opens the pilot hole, and the pressure in the upper chamber drops rapidly, forming a high differential pressure around the closing part, and the fluid pressure pushes the closing part to move upward and the valve opens; when the power is off, the spring force closes the pilot hole, and the inlet pressure rapidly passes through the bypass hole, and the chamber forms a low pressure difference around the valve closing part, and the fluid pressure pushes the closing part downward Move and close the valve.
Features: the upper limit of fluid pressure range is high, which can be installed arbitrarily (need to be customized), but must meet the condition of fluid pressure difference.