1. The solenoid valve is divided into three categories in principle:

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 off, the electromagnetic force disappears, the spring presses the closing member on the valve seat, and the valve closes.

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

Stepped direct-acting solenoid valve

Principle: It is a combination of direct-acting and pilot-operated principle. When there is no pressure difference between the inlet and the outlet, after the power is applied, the electromagnetic force directly lifts the pilot small valve and the main valve closing part in turn, 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 chamber of the main valve rises and the pressure in the upper chamber decreases, so the main valve is pushed upwards by the pressure difference. Force or media pressure pushes the closing piece and moves down to close the valve.

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

Pilot operated solenoid valve

Principle: When power is applied, the electromagnetic force opens the pilot hole, the pressure in the upper chamber drops rapidly, and a pressure difference between the upper and lower parts is formed around the closing member. The fluid pressure pushes the closing member to move upward and the valve opens. The hole is closed, and the inlet pressure passes through the bypass hole to quickly form a lower and upper pressure difference around the valve closing member. The fluid pressure pushes the closing member to move downward and closes the valve.

Features: The upper limit of the fluid pressure range can be arbitrarily installed (customized) but must meet the fluid pressure differential conditions.

2. The difference between the valve structure and material and the principle of the solenoid valve is divided into six sub-categories: direct-acting diaphragm structure, step-wise direct-acting diaphragm structure, pilot diaphragm structure, direct-acting piston structure, Step by step direct acting piston structure, pilot piston structure.

3. Solenoid valve is classified according to function: 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, miniature 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.