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controls fuel flow automatically to maintain a selected High Pressure (HP) speed
and provide rapid, surge-free acceleration and deceleration control. A solenoidoperated,
high idle setting ensures acceptable acceleration is available during
final approach.
Fuel is supplied from the aircraft fuel system to an engine driven Low Pressure
(LP) fuel pump which delivers it through the engine fuel cooled oil cooler, filter and
flowmeter and to an engine driven variable output HP fuel pump. From the HP
pump, fuel is delivered to a fuel regulator, which meters it into two separate flows
to the spray nozzles. The main flow passes through the N1 shaft governor to the
HP fuel cock, while the primary flow passes directly to the HP fuel cock. Both
flows are then distributed respectively to the primary and main spray nozzles.
The HP fuel shutoff valve fuel cock has three positions: SHUT, START and OPEN.
Only two of these positions, SHUT and OPEN, are utilized while operating the
engine. The START position, although not selected, permits a supplementary fuel
flow to the main spray nozzles to facilitate easier starting under certain conditions.
The N1 shaft governor prevents the LP compressor shaft from exceeding its
limitation by trimming the fuel flow from the HP fuel pump.
2. Subsystems, Units and Components:
(See Figure 1.)
The engine fuel system consists of the following subsystems, units and
components:
• Low pressure fuel pump
• Oil cooler
• Fuel filter
• High pressure fuel pump
• Low pressure shaft governor
• High pressure fuel shutoff valve
• Fuel tubes and manifolds
• Fuel nozzles
3. Description of Subsystems, Units and Components:
(See Figure 1.)
A. Low Pressure Fuel Pump:
The LP fuel pump attaches to the front face of the high-speed (HS)
gearbox. It is sometimes known as the LP backing pump. The pump keeps
the fuel pressure at the inlet to the HP fuel pump at a value high enough to
prevent cavitation. The LP fuel pump has a splined shaft at its front end
that engages a driving shaft in the HS gearbox. The basic design of the LP
fuel pump is a housing with a fuel inlet and outlet port. A drains connector
allows for fuel to go to the engine drains tank.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-73-00
Page 1
May 31/01
Revision 4
B. Oil Cooler:
The LP fuel pump delivers the fuel from the aircraft supply to the oil cooler.
The LP fuel decreases the temperature of the oil in the cooler before the
fuel goes to the fuel filter.
C. Fuel Filter:
The 10 micron LP fuel filter attaches to the left-hand side of the
intermediate case. The basic design of the fuel filter is a housing which has
a paper element in the inner chamber. The element removes unwanted
matter from the fuel that comes from the fuel-cooled oil cooler and prevents
foreign material from passing on to the HP pump.
D. High Pressure Fuel Pump:
The HP fuel pump attaches to the rear face of the high-speed gearbox. A
shaft gear in the gearbox turns the drive shaft in the front of the fuel pump.
The fuel pump receives LP fuel from the fuel filter and flowmeter. The pump
then supplies the fuel, at a high pressure, to the Fuel Flow Regulator
(FFR).
The HP fuel pump has a rotating assembly which has seven inclined hollow
cylinders. The cylinders attach to an adjustable cam plate. The cam plate
angle can therefore change to adjust the stroke of the pistons. A servo
system controls the output of fuel to the FFR.
E. Low Pressure Shaft Governor:
The LP shaft governor limits the fuel flow to the fuel spray nozzle in some
operating conditions. This ensures that the LP compressor shaft does not
exceed its maximum speed limit.
F. High Pressure Fuel Shutoff Valve:
The HP fuel shutoff valve is a plunger-type valve operated by a rack and
pinion. It attaches to the left-hand side of the HS gearbox with four bolts. In
the full-flow position, the pilot flow and main flow of fuel go to the fuel
manifolds. In the closed position the plunger closes off the flow of fuel to
the manifolds, in this position the fuel, together with the servo-fuel for the
HP fuel pump, goes to the LP outlet. The valve connects, through its
operating lever and a control linkage, to a manual control in the crew
compartment (see Figure 2).
G. Fuel Tubes and Manifolds:
Fuel tubes allow fuel to go from the inlet connector at the LP fuel pump
through the subsequent units to the fuel spray nozzles. The tubes are
made of stainless steel with ferrules welded on to their ends. The grooves
in these ferrules are for rubber seal rings which prevent leakage of fuel
　
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