FUSELAGE VALVE/FUS VALVE
SWITCH (GRAVITY-FLOW LINE)
A DC motor-driven fuselage valve is installed
in a second fuel line, connecting the fuselage
tank with the crossflow manifold on the right
side of the crossflow valve (see Figure 5-1).
The valve is controlled by the FUS VALVE
switch on the fuel control panel. When the FUS
VALVE switch is positioned to OPEN, both the
fuselage valve and the crossflow valve are si-
multaneously sequenced open, allowing fuel to
gravity-flow from the fuselage tank to both
wings. The fuselage valve is also controlled by
the XFER–FILL switch. When placed to FILL,
the transfer valve, fuselage valve, and crossflow
valve are sequenced to open and the wing
standby pumps are energized to pump wing
tank fuel through both fuel lines into the fuse-
lage tank. The fuselage valve remains closed
when the XFER–FILL switch is positioned to
XFER. The amber light adjacent to the FUS
VALVE switch will illuminate when the fuse-
lage valve is in transit or is not in the position
selected. The fuselage valve is powered through
the left essential bus FUS VAL circuit breaker.
NOTE
If either wing standby pump switch is
on, the FUS VALVE switch is ren-
dered inoperative, and neither the
fuselage valve nor the crossflow valve
will open if the FUS VALVE switch
is moved to OPEN. Conversely, if the
FUS VALVE switch is already in the
OPEN position (fuselage valve and
crossflow valve open), turning either
wing standby pump switch on will
automatically cause the fuselage valve
and crossflow valves to sequence
closed.
NOTE
Positioning the XFER–FILL switch
to XFER while also positioning the
FUS VALVE switch to OPEN should
be avoided because it will cause both
fuselage transfer lines and the cross-
flow line to be open and the fuselage
pump to be energized. The result of
this action is that some fuel will be
returned to the fuselage tank through
the open gravity-flow line. The white
tank EMPTY light may also illumi-
nate due to a drop in line pressure.
FLOAT AND
PRESSURE SWITCHES
Fuselage Fuel Tank Float
Switch
When filling the fuselage tank, a float switch
mounted inside the tank actuates when the
tank is full. The switch:
• Turns on the green FULL light on the
fuel control panel
• Deenergizes the wing standby pumps
• Closes the transfer and crossflow valves
• Closes the fuselage valve (all airplanes
equipped with the gravity-flow trans-
fer line)
The green FULL light on the fuel control panel
remains illuminated until the XFER–FILL
switch is turned off.
Fuselage Tank Low-
Pressure Switch
The fuselage tank low-pressure switch is in-
stalled in the fuselage transfer line to alert the
pilot when fuselage fuel is depleted. With the
XFER–FILL switch in the XFER position,
the switch senses low pressure in the line and
illuminates the white EMPTY light on the
fuel control panel when either of two condi-
tions exist:
• The tank is empty.
• The fuselage transfer pump fails.
5-12
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international