FUEL TRANSFER
SYSTEM
CROSSFLOW VALVE
A 28-VDC motorized valve is provided to in-
terconnect the left and right wing tanks (see
Figures 5A-1 through 5A-3). It is opened dur-
ing fuel transfer and filling operations and for
wing-to-wing fuel balancing. The valve is
controlled by the CROSS FLOW switch and
the FUS FILL switch (23 models) or XFER
FILL switch (24, 24B, and 25 models).
An amber light adjacent to the CROSS FLOW
switch illuminates when the valve is in tran-
sit or is not in the position selected on all
Learjets except the 23 models.
If wing fuel imbalance occurs on airplanes
SNs 23-003 through 23-069, crossflow is ac-
complished by opening the crossflow valve and
allowing the fuel to balance by gravity. On all
other Learjets, open the crossflow valve and
turn on the standby pump in the heavy wing
while ensuring that the standby pump in the
light wing is off. The transfer rate is approx-
imately 50 pounds of fuel per minute.
NOTE
Opening the crossflow valve to bal-
ance the fuel should not be attempted
when a red FUEL PRES light is il-
luminated unless it can be accom-
plished below 25,000 feet. To do so
diverts pressure being delivered to
the affected engine pump by the op-
erating standby pump on that side.
Asymmetric power settings may be
used to balance fuel, if necessary.
The above considerations do not
apply to single-engine operations,
and normal crossflow operations may
be performed.
FUSELAGE FUEL TRANSFER
Fuel in the fuselage tank must be transferred for-
ward to the wing tanks to supply the engines.
To prevent overpressurization of the wing tanks
and the tip tanks, the fuel quantity in the tip
tanks must be decreased before fuel transfer.
On model 23 airplanes not incorporating jet
pumps, when the fuselage transfer (FUS) switch
(see Figure 5A-1) is moved to the ON position,
the fuselage tank transfer valve and the cross-
flow valve are opened, and the fuselage tank
pump is energized to pump fuel equally into
two wing tanks. The fuselage tank EMPTY light
(see “Annunciator Panel” section) is illuminated
when fuel pressure in the transfer line drops
below the setting of a pressure switch in the
transfer line. When the EMPTY light is on, the
fuselage transfer switch should be turned off to
close the valves and shut down the transfer pump.
On airplanes SNs 23-070 through 23-099, the
standby pumps switches (see Figure 5A-5)
must be in the OFF position when transferring
fuselage tank fuel.
On 24, 24B, 25, and 23 models with jet pumps,
when the fuel transfer switch (see Figure 5A-3)
is moved to XFER, the crossflow valve and
fuselage transfer valves are opened and the
fuselage tank pump is turned on. If operating,
the standby pumps are automatically shut
down to allow fuel to be pumped to the wing
tanks. When pressure drops in the transfer
line, the fuselage tank EMPTY light (see
“Annunciator Panel” section) will illuminate.
When the tank is empty, the transfer switch
should be moved to the OFF position to close
the valves and shut off the fuselage tank pump.
FLOAT, PRESSURE, AND
TEMPERATURE SWITCHES
Fuselage Tank Float Switch
A float switch in the fuselage tank prevents over-
filling of the tank by terminating the fill operation.
On airplanes SNs 23-003 through 23-069,
when the float switch senses a full fuselage
tank, the refuel valve is closed, the left standby
pump is shut down, and the FULL light (see
“Annunciator Panel” section) on the fuel panel
is illuminated. The crossflow valve is not af-
fected by the float switch.
5A-12
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
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