Solenoid valve

Electromagnetic valve is an industrial equipment controlled by electromagnetism. It is an automatic basic component used to control fluid. It belongs to actuator, not limited to hydraulic and pneumatic. It is used to adjust the direction, flow, speed and other parameters of the medium in the industrial control system. The solenoid valve can cooperate with different circuits to achieve the desired control, and the control accuracy and flexibility can be guaranteed. There are many kinds of solenoid valves, different solenoid valves play a role in different positions of the control system, the most commonly used are one-way valve, safety valve, direction control valve, speed regulating valve, etc.

Chinese name

Solenoid valve

Foreign name

electromagnetic valve

Affiliated industries

Industrial control

main features 

Safe, convenient, many models, wide use

Common types

Check valve, safety valve, directional control valve, etc

Selection principle

Applicability, reliability, safety and economy

1 working principle

There is a closed cavity in the solenoid valve, and through holes are opened at different positions. Each hole is connected with different flowing medium pipes (such as compressed air or oil). There is a piston in the middle of the cavity and two electromagnets on both sides. The valve body will be attracted to which side when the magnet coil is energized. Different exhaust holes or oil drain holes can be opened or closed by controlling the movement of the valve body, When the air inlet or oil inlet is normally open, the compressed air or hydraulic oil will enter into different exhaust pipes or oil discharge pipes, and then push the piston of (air, oil) cylinder through the pressure of medium (compressed air or oil). The piston drives the piston rod, and the piston rod drives the mechanical device. In this way, the mechanical movement is controlled by controlling the current on and off of the electromagnet.

2 main categories

1. Solenoid valves are divided into three categories in principle

1) Direct acting solenoid valve:

Principle: when electrified, the electromagnetic coil generates electromagnetic force to lift the closing part from the valve seat and open the valve; When the power is cut off, the electromagnetic force disappears, the spring presses the closing part on the valve seat, and the valve closes.

Features: in vacuum, negative pressure, zero pressure can work normally, but the diameter is generally not more than 25 mm.

2) Step by step 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 lift the small pilot valve and the main valve closing parts up one by one and open the valve. When the pressure difference between the inlet and outlet reaches the starting pressure, the electromagnetic force will pilot the small valve, the pressure in the lower chamber of the main valve will rise, and the pressure in the upper chamber will drop, so as to use the pressure difference to push the main valve upward; When the power is cut off, the pilot valve uses spring force or medium pressure to push the closing part and move downward to close the valve.

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

3) Pilot operated solenoid valve:

Principle: when the power is on, the electromagnetic force opens the pilot hole, and the pressure of the upper chamber drops rapidly, forming a high and low pressure difference around the closing part. The fluid pressure pushes the closing part upward, and the valve opens; When the power is cut off, the spring force closes the pilot hole, the inlet pressure rapidly forms a pressure difference between the lower and the higher around the valve closing part through the bypass hole, and the fluid pressure pushes the valve closing part downward to close the valve.

Features: the upper limit of fluid pressure range is high, which can be installed at will (need to be customized), but must meet the conditions of fluid pressure difference.

2. According to the difference of valve structure, material and principle, solenoid valve can be divided into six sub categories: direct acting diaphragm structure, step-by-step direct acting diaphragm structure, pilot diaphragm structure, direct acting piston structure, step-by-step direct acting piston structure and pilot piston structure.

3. Solenoid valves are classified according to their functions: water solenoid valve, steam solenoid valve, refrigeration solenoid valve, low temperature solenoid valve, gas solenoid valve, fire solenoid valve, ammonia solenoid valve, gas solenoid valve, liquid solenoid valve, micro solenoid valve, pulse solenoid valve, hydraulic solenoid valve, normally open solenoid valve, oil solenoid valve, DC solenoid valve, high pressure solenoid valve, explosion-proof solenoid valve, etc.