LOCATION AND DESCRIPTION OF MAJOR COMPONENTS (cont)
b. Fuel Crossfeed/Boost System. The fuel crossfeed/boost system (fig. 102) consists of the pilot and CPG
FUEL panels, the boost pump pressure switch, fuel crossfeed/shutoff valves, the fuel boost pump shutoff (air)
valve, the fuel boost pump, and the 4-way supply check valve.
(1) Pilot FUEL Panel.
The pilot FUEL panel is located in the left side of the pilot console. The ENG 1
and ENG 2 switches control the activation of the fuel crossfeed/shutoff valves. In order for the fuel to flow to the
engines (or crossfeed to the opposite engine if selected), the respective fuel ENG switch must be ON. When the
ENG switch is in the ON position, the CROSSFEED switch is enabled. This controls the positioning of the fuel
crossfeed/shutoff valve. The CROSSFEED switch simultaneously controls the position of both fuel
crossfeed/shutoff valves. The BOOST switch electrically opens the boost pump shutoff (air) valve. The pilot
CROSSFEED switch must be in the AFT TK position for the BOOST switch to latch on. If the BOOST switch is
activated with the CPG ORIDE switch in the CPG position, the fuel crossfeed/ shutoff valves reposition to the aft
tank. This condition may result in a dual engine flameout if the crossfeed does not properly position.
(2) CPG FUEL Panel.
The CPG FUEL panel is located in the left side of the CPG console. With the
ORIDE switch in the PLT position, only the pilot FUEL panel switches have control of fuel system operation. When
the ORIDE switch is in the CPG position, the CPG FUEL panel switches are enabled. The TK SEL switch
operates the same as the pilot FUEL panel CROSSFEED switch. The BOOST switch operates the same as the
pilot FUEL panel BOOST switch.
(3) Boost Pump Pressure Switch.
The boost pump pressure switch is mounted on the right-upper aft
side of the ammunition bay. The boost pump pressure switch gives an indication of boost pump operation to the
pilot. It is normally open and closes when boost pump output pressure reaches 8.5 to 10 psi.
(4) Fuel Crossfeed/Shutoff Valves.
The right fuel crossfeed/shutoff valve is mounted on the left forward
section of the engine 2 firewall. The left crossfeed/shutoff valve is mounted on the upper forward section of the
engine 1 firewall. The fuel crossfeed/shutoff valves provide a means of selecting a fuel source for the engines and
a positive fuel shutoff during maintenance or emergencies. They are 3-way, 4-position ball valves, electrically
controlled from either crew station.
(5) Fuel Boost Pump Shutoff (Air) Valve.
The fuel boost pump shutoff (air) valve is located on the
right-aft side of the main transmission deck. The pump controls airflow to the air-driven motor of the boost pump.
The fuel boost pump (air) shutoff valve is a solenoid operated poppet valve that is electrically energized open and
spring-loaded closed. The valve has one electrical connector and two ports for airflow (inlet and outlet).
(6) Fuel Boost Pump.
The fuel boost pump , mounted on the right aft area of the aft fuel cell, provides
fuel under pressure to the engines during starting and high altitude operation. The fuel boost pump consists of an
air motor, a fuel boost pump and a fuel boost pump canister. The fuel boost pump canister contains a 100 mesh
inlet screen, a spring-loaded outlet flapper valve, a spring-loaded inlet flapper valve, a pressure relief valve, and a
thermal relief valve. The fuel boost pump is automatically started and shutdown during the engine start sequence.
Shutdown occurs at approximately 52% NG.
(7) 4-Way Supply Check Valve.
The 4-way supply check valve, mounted to the bottom of the aft fuel
cell, permits fuel to bypass the fuel boost pump during normal operation. It allows fuel to flow to the fuel boost
pump canister during operation. The 4-way supply check valve, in conjunction with the fuel boost pump canister
flapper valves, prevents draining of the fuel lines after engine/APU shutdown.