Solenoid valves are divided into three main categories in principle:
1) Direct acting solenoid valve:
Principle: When the power is on, the electromagnetic coil generates electromagnetic force to lift the closing part from the valve seat, and the valve opens; 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: It can work normally under vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.
2) Step-by-step direct-acting solenoid valve:
Principle: It is a combination of direct action and pilot type principle, when there is no pressure difference between the inlet and the outlet, after the power is on, the electromagnetic force directly lifts the pilot small valve and the main valve closing part up in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is applied, the electromagnetic force pilot small valve, the pressure of the lower cavity of the main valve rises, and the pressure of the upper cavity drops, so that the pressure difference is used 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 also be operated at zero pressure difference or vacuum and high pressure, but the power is large, and it must be installed horizontally.
3) Pilot operated solenoid valve:
Principle: When the power is applied, the electromagnetic force opens the pilot hole, the pressure of the upper chamber drops rapidly, and the pressure difference between the upper and lower levels is formed around the closing piece, and the fluid pressure pushes the closing part to move up, and the valve opens; When the power is cut off, the spring force closes the pilot hole, and the inlet pressure quickly forms a low and high pressure difference around the closed valve through the bypass hole, and the fluid pressure pushes the closing part to move down to close the valve.
Features: The upper limit of the fluid pressure range is high, and it can be installed arbitrarily (need to be customized) but must meet the fluid pressure differential conditions.
2. Solenoid valves are divided into six sub-categories from the difference in valve structure and material and principle: 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: solenoid valves for water, steam solenoid valves, refrigeration solenoid valves, low temperature solenoid valves, gas solenoid valves, fire 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.
