Firewall Shutoff Valves.
Do not use the fuel firewall shutoff
valve to shut down an engine, except
in an emergency. The engine-driven
high- pressure fuel pump obtains
essential lubrication from fuel flow.
When an engine is operating, this
pump may be severely damaged
(while cavitating) if the firewall valve
is closed before the condition lever
is moved to the FUEL CUTOFF
The fuel system incorporates a fuel line shutoff
valve mounted on each engine firewall. The firewall
shutoff valves close when the fire extinguisher T-
handles on the instrument panel are pulled out. The
firewall shutoff valves receive electrical power from the
main buses, and also from the hot battery bus which is
connected directly to the battery. The valves are
protected by 5-ampere circuit breakers placarded
FIREWALL VALVE #1 or #2 on the over- head circuit
breaker panel (fig. 2-5), and FIREWALL SHUTOFF #1
or #2 on the hot battery bus circuit breaker board.
g. Fuel Tank Sump Drains. A sump drain wrench
is provided in the aircraft loose tools to simplify draining
a small amount of fuel from the sump drain.
There are five sump drains and one filter
drain in each wing (Table 2-3).
An additional drain for the extended range
fuel system line extends through the bottom of the wing
center section adjacent to the fuselage. Any time the
extended range system is in use, a part of the preflight
inspection would consist-of draining a small amount of
fuel from this drain to check for fuel contamination.
Whenever the extended range system is removed from
the aircraft and the fuel line is capped off in the
fuselage, the remaining fuel in the line shall be drained.
h. Fuel Purge System. Each engine is provided
with a fuel purge system. The system is designed to
ensure that any residual fuel in the fuel manifolds is
consumed during engine shutdown. During engine
operation, compressor discharge air is routed through a
filter and check valve, pressurizing a small air tank
mounted on the engine truss. On engine shutdown the
pressure differential between the air tank and fuel
manifolds causes air to be discharged from the air tank,
through a check valve, and into manifolds, out through
the nozzles and into the combustion chamber. The fuel
forced into the combustion chamber is consumed,
causing a momentary rise in engine TGT.
i. Fuel Vent System. Each fuel system is vented
through two ram vents located in the underside of the
wing adjacent to the: nacelle, and a flush vent, located
on the underside of the wing adjacent to the wing tip.
To prevent icing of the vent system, one vent is
recessed into the wing and the other ram vent protrudes
out from the wing and contains a heating element. The
vent line at the nacelle contains an inline flame arrestor.
j. Engine Oil-to-Fuel Heat Exchanger. An engine
oil-to-fuel heat exchanger located on each engine
accessory case, operates continuously during engine
operation to heat fuel delivered to the engine sufficiently
to prevent the freezing of water which it may contain.
The temperature of the delivered fuel is thermostatically
regulated to remain between 21° C and 32° C.
2-33. FUEL SYSTEM MANAGEMENT.
a. Fuel Transfer System. When the auxiliary
tanks are filled, they will be used first. During transfer of
auxiliary fuel, which is automatically controlled, the
nacelle tanks are maintained full. A check valve in the
gravity feed line from the outboard wing prevents
reverse fuel flow. Normal gravity transfer of the main
wing fuel into the nacelle tanks will begin when auxiliary
fuel is exhausted. The system will gravity feed fuel only
to its respective nacelle tank, i.e. left or right (fig. 2-18).
Fuel will not gravity feed through the crossfeed system.
b. Operation With Failed Engine-Driven Boost
Pump or Standby Pump. Two pumps in each fuel
system provide inlet head pressure to the engine- driven
primary high-pressure fuel pump. If crossfeed is used, a
third pump, the standby fuel pump from the opposite
system, will supply the required pressure. Operation
under this condition will result in an unbalanced fuel
load, as fuel from one system will be supplied to both
engines. while all fuel from the system with the failed
engine driven and standby boost pumps will remain
2-34. FERRY FUEL SYSTEM.
Provisions are installed for connection to long
range fuel cells.