Fuel Filler Cap: Description and Operation

PURPOSE
The fuel tank filler cap assembly provides pressure and vacuum relief functions prevent the fuel tank from collapsing from too much vacuum or over expansion of fuel vapors causing too much pressure in the system.

OPERATION

Fuel system vacuum relief is provided after negative 1.7 kPa (0.5 in-Hg). provides pressure relief above 14 kPa (2 psi). Under normal operating conditions, the fuel tank filler cap operates as a check valve, allowing air to enter the fuel tank as fuel is used, while preventing fuel vapors from escaping the fuel tank.

CONSTRUCTION
The fuel tank filler cap is a sealed cap with a built-in pressure-vacuum relief valve

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-quarter turn before unthreading.

The fuel tank filler cap is attached to the vehicle with a tether using the fuel tank filler pipe-to-housing bolt at the two o'clock position.