Cascade Overflow Valve: Operation
WARNING: This page is about a different car, the 2004 Dodge Pickup and 2004 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
When the fuel control actuator (FCA) is opened, the maximum amount of fuel is being delivered to the fuel injection pump. The cascade valve regulates how much excess fuel is used for lubrication of the injection pump, and is also used to route excess fuel through the drain circuit and back into the fuel tank.