1. Solenoid valves are classified into three main categories based on their operating principle:

Direct-acting solenoid valve

Principle: When energized, the solenoid coil generates electromagnetic force to lift the closing element from the valve seat, opening the valve. When de-energized, the electromagnetic force disappears, and the spring presses the closing element back onto the valve seat, closing the valve.

Features: Can operate normally under vacuum, negative pressure, and zero pressure, but the nominal diameter is generally no more than 25mm.

Step-by-step direct-acting solenoid valve

Principle: It combines direct-acting and pilot-operated principles. When there is no pressure difference between the inlet and outlet, energizing directly lifts the pilot valve and the main valve closing element sequentially, opening the valve. When the inlet and outlet reach the starting pressure difference, energizing pilot valves causes the electromagnetic force to increase the pressure in the lower chamber of the main valve and decrease the pressure in the upper chamber, thus using the pressure difference to push the main valve open. When de-energized, the pilot valve uses spring force or medium pressure to push the closing element downward, closing the valve.

Features: Can reliably operate under zero pressure difference, vacuum, or high pressure, but requires higher power and must be installed horizontally. Pilot-operated solenoid valve

Principle: When energized, electromagnetic force opens the pilot orifice, causing a rapid drop in pressure in the upper chamber. This creates a pressure differential around the closing element, with lower pressure at the top and higher pressure at the bottom. The fluid pressure pushes the closing element upward, opening the valve. When de-energized, spring force closes the pilot orifice. The inlet pressure quickly passes through the bypass orifice, creating a pressure differential around the closing element, with lower pressure at the bottom and higher pressure at the top. The fluid pressure pushes the closing element downward, closing the valve.

Features: High upper limit of fluid pressure range; can be installed arbitrarily (customization required), but must meet fluid pressure differential conditions.

2. Solenoid valves are classified into six subcategories based on differences in valve structure, materials, and operating principles: direct-acting diaphragm structure, step-by-step direct-acting diaphragm structure, pilot-operated diaphragm structure, direct-acting piston structure, step-by-step direct-acting piston structure, and pilot-operated piston structure.

3. Solenoid valves are classified according to their function: water solenoid valves, steam solenoid valves, refrigeration solenoid valves, cryogenic solenoid valves, gas solenoid valves, fire-fighting solenoid valves, ammonia solenoid valves, gas solenoid valves, liquid solenoid valves, miniature solenoid valves, pulse solenoid valves, hydraulic solenoid valves, normally open solenoid valves, oil solenoid valves, DC solenoid valves, high-pressure solenoid valves, explosion-proof solenoid valves, etc.