Pilot operated solenoid valve principle: when energized, the electromagnetic force of the pilot hole to open, the upper chamber pressure drops rapidly, in the formation of the closing member of the pressure difference between the upper and lower around the high fluid pressure to promote the closure of the piece to move upward, the valve opens; power failure, the spring force of the pilot hole to close the inlet pressure through the bypass hole, the rapid chamber pressure in the closing member around the valve, the valve opens. Rapid chamber in the shut-off piece around the formation of the lower low on the high pressure difference, fluid pressure to push the shut-off piece downward movement, close the valve.
Direct-acting solenoid valve corresponding to the speed of fast, short action time is very high frequency when the general selection of direct-acting; pilot-operated solenoid valve using a small valve to open a large valve, large flow, large caliber selection of pilot-operated.