fuel to the engine after start. The engine-driven
pump then increases the fuel supply pressure
to the engine fuel controller. Fuel from the en-
gine-driven motive flow pump is routed back
to the four scavenge jet pumps, the transfer line
jet pump, and the main jet pump in each wing
for motive flow. The scavenge jet pumps move
fuel to that area of the wing where the main
jet pump is located (collector tank), and the
main jet pump continues the cycle by supply-
ing fuel to the engine. Refer to Figure 5-8.
MOTIVE-FLOW FUEL AND JET
PUMPS
High-pressure fuel from the engine driven
motive flow fuel pump is the source of mo-
tive flow fuel to operate the jet pumps. The
motive flow fuel pump is mounted on the
front, left side of the accessory gear box, and
the hydraulic pump is mounted to the front of
the motive flow pump. A common shaft from
the accessory gearbox drives both pumps.
The single purpose of the motive flow fuel
pump is to build the pressure up for jet pump
operation in the wing tank. Jet pumps require
no electrical power and have no moving parts.
The fuel is routed from the engine through a
line to the jet pumps in the wing tanks, where
it passes through a small orifice into a ven-
turi. The low pressure created in the venturi
draws fuel from the tank, resulting in a low
pressure, high-volume output (motive flow)
(Figure 5-9).
Motive flow pressure is unregulated and will
vary from approximately 150 psi to 420 psi,
depending on the engine speed. Consequently,
jet pump discharge pressure also varies with
engine rpm. At idle, discharge pressure is ap-
proximately 10 psi, while at high power set-
tings, discharge pressure is approximately 20
psi.
There is a main jet pump next to the electric
standby pumps and four scavenge pumps lo-
cated at various points in each wing tank
(Figure 5-1).
Another jet pump is located in each fuselage-
to-wing tank transfer line for the purpose of
pulling fuel from the fuselage tank. High pres-
sure fuel from the corresponding motive flow
pump is routed to the jet pumps in each trans-
fer line. The venturi principle draws fuselage
fuel forward to the wings when the engines are
running.
FILTERS
The fuel supply for each engine passes through
an airframe filter and an engine mounted fuel
filter before entering the fuel control unit
(FCU). The airframe filters are located under
the center of the fuselage and are accessible
through the same hinged panels that provide
access to the fuel drain valves (Figure 5-13).
The airframe filter has a bypass capability if
the filter becomes blocked.
The engine mounted fuel filter is located be-
tween the low-pressure stage and the high-
pressure stage of the engine-driven fuel pump.
The engine mounted filters also have a bypass
capability.
An amber “L or R FUEL FILTER” CAS mes-
sage will appear if the respective engine or
airframe fuel filter has an impending bypass
while on the ground. In flight, the CAS mes-
sage will be white.
MAIN FUEL SHUTOFF VALVES
A main fuel shutoff valve for each engine fuel
supply line is located in the center wing sec-
tion. These valves, also referred to as firewall
shutoff valves (FWSOV), normally remain
open, but provide a means of shutting off fuel
from the wing tank to the engine for certain
malfunctions or for maintenance.
The shutoff valves are electrical motor driven
valves and are controlled through the left and
right FIRE PUSH switches located on the en-
gine/fuel control panel on the center console
(Figure 5-7). The switches have hinged clear
plastic covers, with a red outline, that must be
L E A R J E T 4 5
P I L O T T R A I N I N G M A N U A L
5-14
FOR TRAINING PURPOSES ONLY
FlightSafety
international