Fuel Filler Cap: Description and Operation

Fuel Tank Pressure/Vacuum Filler Cap:

PURPOSE
Acts to control fuel tank pressure and vacuum relief.

OPERATION
The Vacuum Relief Valve
Acts as a secondary point for air to enter the fuel tank to replace the fuel as it is used. It opens only in the event that the primary entry point through the carbon canister and evaporative emission valve become restricted. The vacuum valve opens after vacuum in the tank reaches 3.4 kPa (-0.5 psi).

The Pressure Relief Valve
Acts as a backup pressure relief in the event the normal venting system is overcome by excessive generation of internal pressure or restriction of the normal venting system. The pressure relief range is 11.1-1.14 kPa (1.6-2.1 psi).

CONSTRUCTION
Contains an integral pressure and vacuum relief valve, has a threaded screw-on design with a pre-vent feature that allows the fuel tank to vent for the first three-quarter turn before unthreading.