There are various options of auxiliary fuel tank installations,
which are located in the fuselage, they will not be discussed here.
Fuel is stored within vented areas of
the wing and wing center section. These fuel storage areas are divided
into three main tanks, one for each engine. The tanks are located in the
interspar area of each wing. They are identified as Tank1, Tank2 and Tank3.
Normally each tank supplies its respective engine which is referred to
as "tank to engine". Tank No1 is contained entirely in the left
wing , Tank No3 entirely in the right wing. Tank No2 consists of an integral
portion in each wing and removable cells in the wing center section.
Low points on all the integral tanks are fitted with fuel sump drain valves
to permit draining of accumulated water from the tanks and for draining
fuel when the tank is defueled.
Tanks can be fueled from the pressure refueling station at the right wing,
via this system any or all of the tanks can be filled rapidly. Tanks may
also be defueled through this pressure system. Overwing filler points
are provided for tanks 1 and 3. Fuel may be transferred from tanks 1 and
3 into tank 2. Transfer of fuel from one tank to another is possible on
the ground only, through a manually operated defuel valve located at the
lower right hand wing root. When overwing refueling is taking place it's
normal for some operators to shut down the APU.
An electronic capacitance type indicating system provides fuel quantity
indications on the flight engineers panel and at the refuel station. vent
surge tanks are provided to accommodate fuel surges, any fuel in the vent
surge tanks drains directly into the adjacent No1 or No3 tanks. Tanks
are vented through the surge tanks to a single opening at each wing tip.
The vent system also provides ram air pressure within the tanks. The center
tank cavity is vented and drained overboard through a separate system
of vent and drain lines.
Fuel Boost Pumps Eight AC motor driven fuel boost pumps are located in the fuel tanks,
two per tank in one and three and four boost pumps in tank 2. AC power
to the boost pumps is distributed so that failure of any single AC bus
will not cause complete loss of all boost pumps in any one tank. A fuel
boost pump bypass valve allows engine driven fuel pumps to draw fuel from
the main tanks if all boost boost pumps in a tank are inoperative.
Valves with a red band are fuelling valves,
yellow band are dump valves, black band cross feed valves, white
band nozzle valves, beige cross manual defuel valve, white circles refuel
station, Black lumps engines.
Fuel Heaters A fuel heating system is provided to prevent the formation of ice
crystals in the fuel being delivered to each engine. Fuel flowing to the
engine is passed through an air to fuel heat exchanger just prior to entering
the fuel filter. Heating is accomplished by ducting 13th stage engine
compressor air through the heat exchanger. After passing through the heat
exchange, the air is dumped into the CSD oil cooler exhaust air duct.
Control for the system is via switches on the flight engineers panel.
Valve operation is confirmed by Blue in transit lights. When operating
you will see a rise in oil temperature to the engine receiving fuel heat.
Icing lights are provided and are also located on the same panel as the
control switches. The icing light will come on if a differential pressure
exists across the main fuel filter. The difference in pressure is assumed
to be caused by ice crystals partially blocking the filter. If the icing
light does not go out with the application of fuel heat, the filter may
be clogged. Dripsticks A calibrated dripstick is installed in each tank. These can be used
to determine the fuel level in each tank in the normal taxi attitude.
When the locking sealing cap and the hollow dripstick assembly is withdrawn
from the wing lower surface, fuel enters the open top of the stick and
flows out through a drip hole near the base (indicated by an arrow on
the surface). The dripstick should be pushed up slowly until fuel stops
and then inched down again until you obtain a steady drip/flow of fuel.
Reading the calibrations on the stick from the top down, The calibrated
reading plane is the inner surface of the recess. Calibrations maybe in
inches, pounds or Kgs.
They are located on the tank center lines. No1 and No3 are near the inboard
end of the respective tank. No2 is near the inboard end of the integral
tank on the right side. Additional dripstick may be installed. The normal
minimum stickable fuel value is 938 lbs.