TM 55-1510-215-10
(7) Firewall shutoff valves.
might contain. The temperature of the delivered fuel is
thermostatically regulated to remain between + 21C
CAUTION
and + 32C.
Do not use the fuel firewall shutoff
2-36. Fuel Management
valve to shut down an engine, except
in an emergency. The engine-driven
CAUTION
high pressure fuel pump obtains
essential lubrication from fuel flow.
During normal fuel system operation
all usable fuel of each system can be
When an engine is operating, this
used. However, if a transfer pump
pump may be severely damaged
becomes inoperative, approximately
(while cavitating) if the firewall valve
28 gallons of wing fuel from the
is closed before the condition lever is
respective system cannot be used
moved to the FUEL CUTOFF position.
because gravity feed will stop with
approximately 28 gallons of fuel
Two guarded switches, placarded FIREWALL
remaining within the respective wing
SHUT-OFF VALVE on the fuel management panel, (fig.
tanks (fig. 2-14).
capability at each engine firewall. Each switch is a two-
a. Fuel Transfer System. Fuel used from nacelle
position unit controlling the corresponding firewall shutoff
tanks is replenished by gravity feed alone, until the level
valve. OPEN position opens the firewall shutoff valve
within the tank is depleted to 8 gallons (52 pounds) (fig.
admitting fuel to the engine. In the CLOSED position
fuel flow to the affected engine is cut off, thereby
position on the level sensor float is actuated which
isolating the fuel supply from that engine, although the
causes fuel transfer to start. When the fuel quantity
isolated fuel may be supplied to the opposite engine by
rises to 24 gallons (156 pounds), transfer action is cutoff
crossfeed. A hinged red-colored metal guard engages
by the second switch position on the float. Unless the
each firewall valve switch toggle when the switch is in
pilot uses manual transfer control after the first transfer
the OPEN position. This guard prevents inadvertent
cycle, all subsequent fuel transfer will maintain quantity
movement of the switch to the CLOSED position. The
within the nacelle tanks at a level between 8-24 gallons
guard must be manually disengaged from the switch
(52-156 pounds), until all fuel is used from the wing
toggle to move the switch to the CLOSED position. The
tanks.
firewall shutoff valves are protected by two 5-ampere
circuit breakers placarded FIREWALL VALVE, located
NOTE
on the fuel system circuit breaker panel (fig. 2-12).
During normal fuel system operation
f. Fuel Tank Sump Drains. The fuel system tanks
(not the TRANSFER TEST mode), a
and interconnecting lines may be drained of moisture
fuel transfer pump will be activated
condensate and sediment by means of 10 drains (plus
when approximately 8 gallons remain
two for the ferry system when installed), located at the
in the nacelle tank. If that transfer
system low points on the nacelle tanks, wing tanks and
pump should become inoperative, 28
at fuel filter drain at the inertia separator air bypass duct.
gallons (182 pounds) of fuel in the
inboard wing tank will not be usable
g. Fuel Vent System. Three fuel vents are located
since it cannot gravity feed (fig. 2-13).
under each wing. One serves both the nacelle and wing
With this situation, only 8 gallons (52
tanks, and is protected against icing conditions by an
pounds) or less of fuel will be
electric heating element. (Refer to paragraph 2-57 for
available
for
continued
flight
fuel system anti-icing information.)
(approximately 10 minutes flying
time).
Crossfeed fuel (fig. 2-13),
h. Thermal Pressure Relief Value.
Volume
however, may be used for continued
expansion in the fuel system is relieved by a thermal
engine
operation
utilizing
the
pressure relief valve. Normally, thermal expansion
operative fuel transfer pump and the
occurs only during hot weather while the aircraft is static
auxiliary fuel boost pump from the
on the ground.
opposite engine's fuel system. Do
not operate with the crossfeed in the
i. Engine Oil-to-Fuel Heat Exchanger. An engine
OPEN mode with both auxiliary fuel
oil-to-fuel heat exchanger, located on each engine
pumps operating.
Fuel may be
accessory
case,
operates
continuously
and
inadvertently crossfeed from either
automatically to heat the fuel delivered to the engine
fuel system due to normal variances
sufficiently to prevent the freezing of any water which it
in pump pressure.
2-26 Change 10
