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near the combustion chamber.
Fuel Flow Divider and Flow Divider Solenoid Components
These are the main fuel flow divider components:
* Ball check valve
* Inlet filter
* Flow divider solenoid.
Functional Description
When the fuel solenoid valve opens, fuel flows to the fuel flow
divider through the inlet filter in the flow divider.
The fuel flow divider directs fuel to the primary fuel manifold for
initial start and acceleration.
The flow divider solenoid makes sure fuel does not go to the
secondary manifold at the incorrect time. When the flow divider
first sends fuel to the secondary manifold, the fuel pressure in
the primary manifold momentarily decreases while the
secondary manifold fills with fuel. If the primary fuel pressure
decreases at the incorrect time, the APU flames out or goes
under speed.
A spring holds the flow divider solenoid in the open position.
The flow divider solenoid closes when the ECU energizes the
solenoid.
The ECU energizes the flow divider solenoid closed from 7
percent to 30 percent speed. This prevents APU flame out and
shutdown during a start.
At 25-40 percent speed (approximately 120 psi), the check valve
inside the flow divider T fitting opens and supplies fuel to the
secondary manifold unless the fuel flow divider valve is in the
closed position.
The ECU again energizes the flow divider solenoid at higher
altitudes. This prevents an APU under speed and shutdown with
the addition of electrical load above 25,000 feet.
The ECU uses these values to find when the flow divider
solenoid should be energized:
APU FUEL SYSTEM - FUEL FLOW DIVIDER AND FLOW DIVIDER SOLENOID
EFFECTIVITY
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* Inlet pressure (P2)
* Inlet temperature (T2)
* APU speed.
APU FUEL SYSTEM - FUEL FLOW DIVIDER AND FLOW DIVIDER SOLENOID
EFFECTIVITY
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APU FUEL SYSTEM - FUEL FLOW DIVIDER AND FLOW DIVIDER SOLENOID
APU FUEL SYSTEM - FUEL FLOW DIVIDER AND FLOW DIVIDER SOLENOID
EFFECTIVITY
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Fuel Manifolds
A primary fuel manifold and a secondary fuel manifold supply
fuel from the fuel control unit to the fuel nozzles.
The manifolds are around the APU combustion chamber.
Both manifolds supply fuel when the APU is on speed below
25,000 feet. Only the primary manifold supplies fuel up to 30
percent speed during APU start and above 25,000 feet for all
APU operation.
Fuel Nozzles
Ten fuel nozzles atomize and inject fuel into the combustion
chamber. The fuel nozzles are installed around the combustion
section.
The 10 fuel nozzles have these components:
* Primary and secondary screen
* locating pin
* Air shroud
* Nozzle tip.
Training Information Point
NOTE: Do not remove all fuel nozzles at the same time. The
fuel nozzles put the combustor in position. If you
remove all nozzles at the same time the combustor can
move out of position. If the combustor moves out of
position, you can not install the replacement fuel
nozzles.
You can remove and install both the fuel manifolds and fuel
nozzles without removal of the APU.
The fuel nozzles have a locator pin to make sure installation is
correct.
APU FUEL SYSTEM - MANIFOLDS AND NOZZLES
EFFECTIVITY
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APU FUEL SYSTEM - MANIFOLDS AND NOZZLES
APU FUEL SYSTEM - MANIFOLDS AND NOZZLES
EFFECTIVITY
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Purpose
The APU combustor drain provides a drain for fuel that may
accumulate in the combustor after an unsuccessful start. This
prevents a possible hot start on the next start.
Location
The combustor drain is at the lowest point of the combustor
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