The sealing device is integrated with the nozzle body, and when the oil flows quickly, it will create negative pressure inside the pressure sensing system. Normally, the negative pressure is maintained by gas supplemented by the ventilation pipe to maintain balance. When the fuel tank level rises and overflows, and the vent pipe is closed, the negative pressure in the pressure sensing system quickly rises. The diaphragm drives the switch card to move, causing the gun mechanism to shift out. Within 0.3 seconds, the self sealing closing action can be completed to prevent the medium from overflowing