Why does the fuel nozzle automatically shut off during refueling?

[GraceLynn]

Fuel nozzle automatic shutoff occurs because there is a trigger mechanism hidden inside the nozzle. When the fuel level reaches the nozzle tip, the automatic shutoff device activates to stop the fuel supply. It's important to note that stopping at this point doesn't mean the tank is completely full, as the upper portion of the fuel tank always reserves some space for fuel vapor to prevent excessive internal pressure. The nozzle shutoff is somewhat related to refueling speed and ambient temperature. During hot weather, pressure inside the fuel tank increases, and rapid refueling further elevates this pressure, making the fuel more likely to splash and trigger the shutoff mechanism. During refueling, air inside the tank needs to escape upward. When refueling too quickly, the air cannot escape smoothly, preventing fuel from entering properly. This may cause the intake sensor to mistakenly detect the fuel level. The "automatic shutoff" action doesn't affect the actual fuel quantity. However, drivers should pay attention to two things when refueling: first, check if the fuel pump display has been reset to zero before refueling; second, qualified fuel pumps should bear a "Mandatory Inspection Passed" label, while unqualified ones will display an "Out of Service" label.