Fuel Filler Cap: Description and Operation

Fuel Tank Cap:

PURPOSE
Prevent fuel evaporation and contamination.

OPERATION
If the pressure of fuel vapor in the fuel tank should exceed that for which fuel system is designed, the pressure relief valve opens to relieve the pressure.

The vacuum relief valve opens to relieve the vacuum created in the fuel tank.

CONSTRUCTION
A ratchet tightening device on the threaded fuel filler cap reduces the chances of incorrect installation, which would prevent sealing fuel vapors. After the gasket on fuel filler cap and the filler neck flange contact, the ratchet produces a loud clicking noise, indicating the seal has been set. This cap has a pressure relief valve and a vacuum relief valve inside.