X-90 Fuel Filler Cap - Description and Operation for Improved Efficiency
Fuel Filler Cap: Description and Operation
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 vacuum relief valve inside.
When the pressure in the fuel tank becomes negative (vacuum), the vacuum is usually relieved by the TPC valve which is included in the fuel
vapor line. Only when the vacuum becomes high especially the vacuum relief valve opens.