Fuel Tank Switching Valve: Description and Operation

FUEL RESERVOIR
An in-line reservoir has been included in the fuel system. Under normal operating conditions, valving in the in-line reservoir allows the high-pressure pump and engine to be supplied with fuel directly from the tank while return flow is routed directly back to the tank. When the pick-up tube is exposed to air, the high pressure pump draws fuel from the reservoir. When the pick-up is again submerged, normal operation resumes.
There are two types of reservoirs single function and dual function. A single function reservoir is used with single tank vehicles. The dual function reservoir is used with dual tank vehicles. A dual function reservoir combines the function of the reservoir with the function of a mechanically actuated selector valve.

FUEL SELECTOR VALVE/DUAL FUNCTION RESERVOIR
Vehicles with dual tanks have three electric fuel pumps. Two low pressure in-tank fuel pumps, located in both the front and rear tanks, pump fuel into a reservoir. A high pressure in-line fuel pump then takes the fuel from the reservoir to the fuel injectors.
This system can draw fuel from either the front or rear fuel tank unit. With the ignition switch in START or RUN, current flows through a fuse link to the fuel pump relay.
The dual function reservoir replaces the six port selector valve, used on earlier models. The dual function reservoir switches the tank from which the engine draws fuel mechanically, instead of electrically.
The dual function reservoir operates as follows:
Fuel pressure created by the selected in-tank fuel pump exerts force on a 3 inch fluoro-silicon diaphragm which is in turn connected to a T-bar and two shafts. This force moves the valve shaft, simultaneously opening and closing supply and return ports. When the alternate fuel tank is selected, pressure is exerted on the opposite side of the diaphragm, moving the valve shafts to open the alternate fuel tank ports.