Fuel Filler Cap: Operation

The Fuel Filler Cap incorporates a two-way relief valve that is closed to atmosphere during normal operating conditions. The relief valve is calibrated to open when a pressure of 172 mbar (2.5 psi) or vacuum of 20 mbar (8 in H2O) occurs in the fuel tank. When the pressure or vacuum is relieved, the valve returns to the normally closed position.