Vent Valve

Vent valve is located on the fuel tank. During filling the fuel tank, evaporation gas is introduced to the canister through vent valve.
When the evaporation pressure overcomes atmospheric pressure and spring force which are applied to the back side of the diaphragm, the port is opened. Also, the float in the vent valve is to stop the fuel which is supplied when the tank is filled up. Increasing fuel level raises the float to close the port.