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During engine start, a lockout valve in the engine-driven fuel pump
prevents motive flow through the motive flow valve and the applicable
standby pump is energized to supply starting fuel to the engine .
After the engine is running and engine-driven fuel pump output pressure
is sufficient, the lockout valve will open allowing high-pressure
fuel flow through the motive flow valves. Setting a JET PUMP switch
Off doses the corresponding motive flow valve and prevents fuel system
pressurization until the standby pumps are turned on. The motive
flow valves operate on 28 VDC supplied through the 5-amp L
and R JET PUMP-XFR VAL circuit breakers on the pilot's and copilot's
circuit breaker panels respectively. Loss of power to the motive
flow valve causes the valve to remain in its last position . Motive flow
valves are operative during EMER BUSmode.
STANDBY PUMP SWITCHES
The STANDBY PUMP switches, on the fuel control panel, control the
operation of the standby electric pumps. The switches normally remain
OFF except in the event of a jet pump failure or during fuel
crossflow. Regardless of switch position, the standby pumps are automatically
deenergized during fuselage fuel transfer operations. The
standby pumps are automatically energized when the FUS TANK
XFER-FILL switch is set to FILL or the START-GEN switch is set to
START. The standby pumps operate on 28 VDC supplied through the
15-amp Land R STBY-SLAV PUMP circuit breakers on the pilot's and
copilot's circuit breaker panels respectively.
PM-121
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Change l
Pilot's Manual
Learjet 31A
CROSSFLOW SWITCH
The CROSSFLOW switch, on the fuel control panel, controls the crossflow
valve. The switch has two positions: OPEN and CLOSE. When the
switch is set to OPEN, the power is applied to open the motorized
crossflow valve allowing fuel to flow between the wing tanks. The
crossflow valve is opened automatically when filling the fuselage tank
from the wings and during fuselage fuel transfer operations . To balance
wing fuel, the CROSSFLOW switch should be set to OPEN and the
heavy side STANDBY PUMP switch set to ON. The standby pump on
the light side should be Off. The WING FULL light, when illuminated
by the wing-full float switch, is extinguished when the crossflow valve
closes. The standbypump will continue to operate until the STANDBY
PUMP switch is set to Off. The crossflow valve allows all usable fuel
aboard the aircraft to be available to either engine . The switch should
be set to Off except when correcting an out-of-balance condition. The
crossflow valve operates on 28 VDC supplied through the 5-amp
XFLOW VALVE circuit breaker on the copilot's circuit breaker panel.
Loss of power to the crossflow valve causes the valve to remain in its
last position. The crossflow valve is operative during EMER BUSmode.
FUS TANK XFR-FILL SWITCH
The FUSTANK XFR-FILL switch, on the fuel control panel, is used to
operate the fuel transfer system and to fill the fuselage tank from the
wing tanks. The switch has three positions: XFR, OFF and FILL. The
switch incorporates a magnetic latch in the FILL position and must be
held to that position aminimum of three seconds before the latch will
engage. If the switch is in the FILL position and the LOW FUEL light
illuminates or the squat switch goes to the air mode, the latch will disengage
and the switch will go to the OFFposition . The left fuel transfer
valve operates on 28 VDC supplied through the 5-amp L JET PUMP
XFR VAL circuit breaker on the pilot's circuit breaker panel. Loss of
power to the left transfer valve causes the valve to remain in its last position
. The transfer pump operates on 28 VDC supplied through the 10-
ampFUSXFRPUMP circuit breaker on the pilot's circuit breaker panel.
When the switch is set to FILL, both wing tank standby pumps are energized,
both left and right transfer valves are opened via the fuselage
tank float switch, and the crossflow valve will open. Fuel will then be
pumped into the fuselage tank from the wing tanks until the switch is
turned OFF or the fuselage tank float switch actuates to close the transfer
valves, shut down the standby pumps, and illuminate the green
FUS TANK FULL light. Placing the switch in the OFF position will extinguish
the FUS TANK FULL light and close the crossflow valve.
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ChPaMn-g1e213
Learjet 31A
Pilot's Manual
When the switch is set to XFR, the transfer pump is energized, the left
transfer valve will open, both standby pumps will be rendered inoperative,
and the crossflow valve will open. Fuel will then be pumped
from the fuselage tank to the wing tanks until the wing float switches
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