Fuel Filler Cap: Description and Operation
DESCRIPTIONThe fuel tank filler cap contains an integral pressure and vacuum relief valve. The vacuum valve allows air into the fuel tank to replace the fuel as it is used. The vacuum relief valve opens after a vacuum of -3.4 kPa (-0.5 psi). The pressure valve acts as a backup pressure relief valve in the event the normal venting system is overcome by internal pressure or restriction of the normal venting system. The pressure relief is 11 kPa (1.6 psi). Fuel tank filler cap damage or contamination that stops the pressure vacuum valve from working may result in deformation of the fuel tank.
The fuel tank filler cap is a threaded screw-on design with a pre-vent feature that allows the fuel tank to vent for the first three-quarters of a turn before unthreading. It is attached to the vehicle with a tether. The fuel tank filler cap assembly should be replaced, if needed, with the proper pressure/vacuum relief cap to prevent possible system malfunction. Always use care, even when removing a fuel tank filler cap in good working order.