The working principle of the pilot piston solenoid valve:
Normally open: When the solenoid valve coil is energized, the solenoid core is closed, the pressure relief hole is closed, and the solenoid valve main piston is pushed by the medium pressure to close the main valve port and the medium is cut off. When the solenoid valve coil is de-energized, the main valve port of the solenoid valve opens and the medium flows.
Normally closed: When the solenoid valve coil is energized, the solenoid core is attracted, the pressure relief hole opens, and the solenoid valve main piston is pushed by the medium pressure to open the main valve port and the medium flows. When the solenoid valve coil is de-energized, the main valve port of the solenoid valve is closed and the medium is cut off.