SMC direct acting solenoid valve principle: when energized, the electromagnetic force generated by the electromagnetic coil to close the parts lifted from the seat, the valve opened; Power off, the electromagnetic force disappears, the spring force to close the parts on the seat, the valve is closed. (two), step by step direct acting solenoid valve principle: it is a combination of direct acting and guiding principle, when the inlet and outlet pressure difference ≤0.05Mpa, energized, the electromagnetic force directly guide the small valve and the main valve close parts in turn up, the valve open. (three), pilot solenoid valve principle: when energized, the electromagnetic force to open the pilot hole, the upper chamber pressure drops rapidly, forming a low and high pressure difference around the closing parts, pushing the closing parts to move up, the valve to open; Power off, spring force to close the pilot hole, 3 way solenoid valve/direct action VS