D 250 Pickup L6-359 5.9L DSL (1992)
ROLL-OVER VALVE
All fuel tanks of the closed type use a roll-over valve mounted on the top of the fuel tank. In addition to the roll-over valve there is a one way
check valve mounted on the fuel return line, in the tank, which prevents fuel from backing up into the return line from the tank. Under loss of fuel
pressure conditions, or conditions such as roll-over where tank pressure may exceed fuel return pressure, the check valve closes, preventing fuel
loss from tank.