Solenoid valve is an automatic basic component used to control fluid, which belongs to actuator; it is not limited to hydraulic and pneumatic. Solenoid valves are used to control the direction of hydraulic flow. Mechanical devices in factories are generally controlled by hydraulic steel, so solenoid valves are 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 a different oil pipe. There is a valve in the middle of the cavity, and two electromagnets on both sides. The energized valve body will be attracted to which side, and the movement of the valve body is controlled to block or leak different oil discharge holes, and the oil inlet hole is normally open, and the hydraulic oil will enter different oil discharge pipes, and then pass through The pressure of the oil pushes the piston of the oil, the piston drives the piston rod, and the piston rod drives the mechanical device to move. In this way, the mechanical movement is controlled by controlling the electric current of the electromagnet.
Tracing back to the development history of solenoid valves, so far, solenoid valves at home and abroad are divided into three categories in principle (ie: direct-acting type, step-by-step pilot type), and from the difference in valve disc structure and material The difference in principle is divided into six sub-categories (direct-acting diaphragm structure, step-by-step heavy film structure, pilot diaphragm structure, direct-acting piston structure, step-by-step direct-acting piston structure, and pilot piston structure).
Direct acting solenoid valve:
Principle: When energized, the electromagnetic coil generates electromagnetic force to lift the closing member from the valve seat, and the valve opens; when the power is turned off, the electromagnetic force disappears, and the spring presses the closing member on the valve seat, and the valve closes.
Features: It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.
Distributed direct acting solenoid valve:
Principle: It is a combination of direct-acting and pilot-operated. When there is no pressure difference between the inlet and outlet, after power is applied, the electromagnetic force directly lifts up the pilot small valve and the closing part of the main valve in sequence, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is turned on, the electromagnetic force pilots the small valve, the pressure in the lower cavity of the main valve rises, and the pressure in the upper cavity drops, so that the main valve is pushed upward by using the pressure difference; when the power is off, the pilot valve uses a spring Force or medium pressure pushes the closing member, which moves down and closes the valve.
Features: It can also operate under zero pressure difference or vacuum or high pressure, but the power is relatively large, so it must be installed horizontally.
Pilot solenoid valve:
Principle: When energized, the electromagnetic force opens the pilot hole, and the pressure in the upper chamber drops rapidly, forming a pressure difference around the closing member, and the fluid pressure pushes the closing member to move upward, and the valve opens; when the power is turned off, the spring force opens the pilot hole. The hole is closed, and the inlet pressure quickly passes through the bypass hole to form a pressure difference around the valve closing member, and the fluid pressure pushes the closing member to move down and close the valve.
Features: The upper limit of the fluid pressure range is relatively high, and it can be installed arbitrarily (customization is required) but must meet the fluid pressure differential condition.