APU POWER PLANT -APU AIR INLET -FUNCTIONAL DESCRIPTION
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APU POWER PLANT -APU DRAINS -INTRODUCTION
General
APU flammable fluids drain overboard through drains connected to a drain mast. These drains remove fuel or oil that leaks through seals. These drains also remove fuel that does not burn from the combustion chamber and tailpipe.
APU non-flammable fluids drain overboard through drain holes in the APU compartment doors. These drains remove fluids that go into the APU air inlet plenum from the APU air inlet. These fluids go from the APU air inlet plenum into the APU compartment through the APU plenum drain.
Flammable Fluid Drains
Flammable fluid drains through three separate tubes. The drains attach together at the bottom of the APU. They connect with a drain mast on the right APU access door when the door is closed.
Fuel that does not burn during APU start or operation goes through the APU combustor drain valve. The APU combustor drain valve is at the bottom of the combustion chamber. The drain line from the combustion chamber connects to the combustor drain valve. APU combustion chamber pressure closes the combustor drain valve when the APU operates. The valve is open when the APU is off.
Non-Flammable Fluid Drains
The APU plenum drain is at the bottom of the air inlet plenum.
Compartment drains are along the bottom skin of the APU compartment access doors. The APU access doors and compartment structure have drain holes to permit the fluid to flow to the compartment drains.
Training Information Point
Tell-tale drains help find fuel seal failures. Three tell-tale drains are on the APU.
If fuel goes through a drain tube with a tell-tale drain, then the tell-tale drain fills with fuel. You remove the cap of the tell-tale drain to do a check for fluid. If fluid is in the tell-tale drain, the APU component that connects to the drain tube is leaking fuel.
The APU combustor drain valve is an LRU.
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APU POWER PLANT -APU DRAINS -INTRODUCTION
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APU POWER PLANT -APU DRAINS -FUNCTIONAL DESCRIPTION
General
These APU drains send fuel and oil to the drain mast on the right APU access door:
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Combustion chamber fuel drain
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Eductor/Tailpipe fuel drain
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Surge control valve (SCV) actuator seal drain
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Inlet guide vane (IGV) actuator seal drain
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Forward mid-bearing seal drain
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Aft mid-bearing seal drain
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Load compressor bearing seal drain
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Fuel cluster seal drain.
Drains
The APU drains connect directly to the drain mast.
The combustion chamber fuel drain and the eductor/tail pipe fuel drain connect together at the bottom of the APU.
The surge control valve seal drain, the IGV actuator seal drain, and the fuel cluster seal drain connect at the bottom of the APU.
The two mid-bearing seal drains and the load compressor bearing seal drain connect at the bottom of the APU.
The drain lines from the SCV actuator seal drain, the IGV actuator seal drain, and the fuel cluster seal drain have tell-tale drains. These tell-tale drains let you find the source of fluid in these drain lines and do a check of the leakage rate.
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APU POWER PLANT -APU DRAINS -FUNCTIONAL DESCRIPTION
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777 AIRCRAFT MAINTENANCE MANUAL
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APU ENGINE -INTRODUCTION
Purpose
The APU engine supplies power to operate the load compressor and the APU generator.
General Description
The APU gas turbine engine has these main components:
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Two-stage centrifugal compressor
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Reverse flow annular combustion chamber
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Three stage axial flow turbine.
All rotating components in the engine are on a common shaft.
The shaft turns the accessory gearbox and the load compressor. The accessory gearbox turns the APU generator and other APU components.
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