Fuel Filler Cap: Description and Operation

Pressure-Vacuum Filler Cap:

PURPOSE
The fuel filler cap is used to relieve excess fuel tank pressure or vacuum.

OPERATION
The fuel filler cap uses a two-way (vacuum and pressure) relief valve that is closed during normal operating conditions. The relief valve is calibrated to open only when pressure in excess of 1.5 psi or vacuum in excess of 1.8 inch Hg develops in the fuel tank. When vacuum or pressure is relieved, the valve returns to its normally closed position.

NOTE: It is normal to encounter an air pressure release when removing the fuel filler cap.