NOTE
Models 24D, E, and F have one fuse-
lage drain valve; models 25B and D
have two; and model 25C has three.
There is one drain valve located at the fuel vent
sump. The valve must be completely drained
during the exterior preflight inspection to pre-
vent possible blockage of the fuselage ram-air
vent line.
FUEL TRANSFER
SYSTEM
CROSSFLOW VALVE
A DC motor-driven valve is installed in the
crossflow manifold connecting the two wing
tanks. It is opened during fuselage fuel trans-
fer and filling operations and for wing-to-
wing fuel balancing. The valve is controlled
by the CROSS FLOW switch or the
XFER–FILL switch on the fuel control panel
and is powered through the right main bus
FILL and XFER circuit breaker. Additionally,
on those airplanes equipped with the gravity-
flow transfer line, the valve is controlled with
the FUS VALVE switch, which is powered
from the FUS VALVE circuit breaker on the
left essential bus.
The amber light adjacent to the CROSS FLOW
switch illuminates when the valve is in tran-
sit or is not in the position selected. An optional
green or amber FUEL XFLO annunciator light
(see “Annunciator Panel” section) on the glare-
shield illuminates continuously whenever the
crossflow valve is fully open.
If wing fuel imbalance occurs, crossflow is ac-
complished by opening the crossflow valve and
turning on the standby pump in the heavy
wing, while ensuring that the standby pump in
the light wing is off. The transfer rate is ap-
proximately 50 pounds of fuel per minute.
Opening the crossflow valve to balance fuel
should not be attempted when a red FUEL
PRESS light is illuminated unless it can be ac-
complished below 25,000 feet. To do so would
divert pressure being delivered to the affected
engine-driven pump by the operating standby
pump on that side. Asymmetric power set-
tings may be used to balance fuel, if necessary.
The above considerations do not apply to sin-
gle-engine operations, and normal crossflow
operations may be performed as usual.
TRANSFER VALVE/XFER–
FILL SWITCH (NORMAL
TRANSFER LINE)
The fuel transfer line connects the fuselage
tank with the crossflow manifold. A DC motor-
driven transfer valve installed in the line con-
trols fuel movement between the fuselage and
wing tanks. The valve is controlled by the
XFER–FILL switch located on the fuel con-
trol panel. When the switch is positioned from
OFF to XFER, the transfer and crossflow
valves are sequenced open and the fuselage
transfer pump is energized automatically,
while both wing standby pumps, if operating,
are deactivated. When the switch is positioned
from OFF to FILL, the transfer and crossflow
valves are sequenced open, and both wing
standby pumps are energized automatically.
When the switch is positioned from either
XFER or FILL to the OFF position, the trans-
fer pump or wing standby pumps (whichever
the case may be) are deenergized and the trans-
fer valve and crossflow valves are sequenced
closed. The amber light adjacent to the
XFER–FILL switch illuminates when the
valve is in transit or is not in the position se-
lected. The valve is powered through the right
main bus FILL and XFER circuit breaker.
NOTE
The transfer line is connected to the
right side of the crossflow valve. On
all 25C models, and 25D models with
the optional gravity-flow line, the
transfer line is connected to the left
side of the crossflow valve. (See
Fuselage Valve/FUS VALVE
Switch.) In either case, should the
fuselage transfer pump fail, fuel can
be expected to gravity-flow through
the transfer line.
5-11
FOR TRAINING PURPOSES ONLY
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