failure has occurred. Four or five motorized
shutoff valves are installed throughout the
fuel system for isolating various tanks and
fuel lines. Drain valves for the sumps and fuel
vent system are located at the low points in the
fuel system to drain any accumulation of water,
sediment, and/or fuel. Two high-pressure
relief valves, one in each fuel line between the
e n g i n e m a i n f i r ew a l l s h u t o ff va l v e a n d
engine, are installed to relieve any pressure
bu i l d u p c a u s e d b y t h e r m a l ex p a n s i o n o f
trapped fuel when the engine is shut down.
Figures 5A-1 through 5A-3 illustrate the early
series Learjet fuel system.
5A-3
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
EMPTY
LOW
FUEL
CROSS
FLOW
FUS
FILL
ON
OFF
EMPTY
FUEL FILTER
L FUEL PRESS
FUS
FULL
TIP TANK
EMPTY LIGHT-LH
CROSSFLOW
VALVE
LH
TIP
TANK
LH WING TANK
FUSELAGE
TANK
TRANSFER
SWITCH
TRANSFER
VALVE
FUEL
FILTER
MAIN FUEL
SHUTOFF VALVE
LH ENGINE
FLOWMETER
FUSELAGE FUEL TANK
FUEL COUNTER
F
I
R
E
W
A
L
L
S
H
U
T
O
F
F
0 0 0 0
SUPPLY
LOW PRESSURE
TRANSFER/
FILL
LEGEND
FUEL PROBE
FILLER CAP
ELECTRICAL
CHECK VALVE
BOOST PUMP
FLOAT SWITCH
SHUTOFF VALVE
PRESSURE
SWITCH
Figure 5A-2.
Fuel System–SNs 23-070 through 23-099