Tracing back on the development history of electromagnetic valves, so far, electromagnetic valves at home and abroad are divided into three categories in principle (namely: direct action type, step by step pilot type), and six sub categories in terms of valve disc structure and material differences and principle differences (direct action diaphragm structure, step by step heavy plate structure, pilot diaphragm structure, direct action piston structure, step by step direct action piston structure, and pilot piston structure).

Direct acting solenoid valve

Principle: When powered 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, and the spring presses the closing part against the valve seat, causing the valve to close.
Features: It can work normally under 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 action and pilot type principle. When there is no pressure difference between the inlet and outlet, after being energized, the electromagnetic force directly lifts the pilot small valve and the main valve closure part upwards, and the valve opens. When the inlet and outlet reach the starting pressure difference, after being energized, the electromagnetic force leads the small valve, and the pressure in the lower chamber of the main valve increases while the pressure in the upper chamber decreases, thereby using the pressure difference to push the main valve upwards; When the power is cut off, the pilot valve uses spring force or medium pressure to push the closing part downwards, causing the valve to close.
Features: It can also operate under zero pressure difference, vacuum, and high pressure, but with high power, requiring horizontal installation.

Pilot operated solenoid valve

Principle: When powered on, the electromagnetic force opens the pilot hole, causing a rapid decrease in pressure in the upper chamber, creating a pressure difference of up, down, and up around the closing element. The fluid pressure pushes the closing element upwards, causing the valve to open; When the power is cut off, the spring force closes the pilot hole, and the inlet pressure quickly forms a pressure difference of lower and higher around the closing valve through the bypass hole. The fluid pressure drives the closing valve to move downwards and close the valve.
Features: The upper limit of the fluid pressure range is relatively high, and it can be installed arbitrarily (customized), but it must meet the conditions of fluid pressure difference.