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49-72-11
ALL ú ú 01 Page 403 ú Jul 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
APU EXHAUST SYSTEM - DESCRIPTION AND OPERATION
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1. General
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A. The APU exhaust system sends the exhaust gases overboard from the APU
engine. The APU exhaust system also decreases the noise level of the
exhaust gases. The APU exhaust system has an exhaust duct and an aft
fairing assembly. The aft fairing assembly includes the aft fairing,
exhaust duct heat shield (referred to as the heat shield), and exhaust
duct muffler. The exhaust duct and the aft fairing assembly are
installed in the tail compartment of the airplane.
2. Exhaust Duct
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A. The exhaust duct has a heat shield and the exhaust duct muffler. The exhaust duct muffler is installed in the heat shield. There is a cylindrical air space between the exhaust duct muffler and the heat shield. A felt metal lining is installed on the inner surface of the exhaust duct muffler to decrease the noise level of the exhaust gases. Two fire detection elements attach to the exhaust duct. One fire detection element goes along the forward end of the exhaust duct muffler. The second fire detection element goes laterally along the heat shield. This second fire detection element is attached to the top and the bottom of the heat shield (AMM 26-15-00/001). The forward end of the heat shield is held by the APU shroud. A drip pan attaches to the heat shield to keep the heat shield from all hydraulic leaks. A bonding jumper is attached to the heat shield. The bonding jumper supplies a positive electrical ground to the airplane structure. The exhaust duct muffler does not touch the exhaust port of the APU turbine section. There is a clearance between the exhaust port and the exhaust duct muffler. The aft end of the exhaust duct is held by the aft fairing.
(1) AIRPLANES WITH THE DUCT ALIGNMENT ASSEMBLY; A duct alignment assembly is installed on the heat shield to align the exhaust duct with the exhaust port of the APU turbine section.
3. Aft Fairing
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A. The aft fairing holds the aft end of the exhaust duct. It has a machined casting that moves with the airplane tail cone. The aft fairing has two short cylindrical ducts. The outer duct connects to the heat shield of the exhaust duct. The inner duct connects to the exhaust duct muffler. The aft fairing has holes to decrease the temperature of the air intake for the exhaust duct. The aft fairing attaches to the airplane tail cone and to the heat shield of the exhaust duct with bolts.
4. Operation (Fig. 2)
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A. The high velocity exhaust gases from the APU engine flow overboard through the exhaust duct during the APU operation. The exhaust duct temperature is decreased by aspiration. The exhaust gas flow in the exhaust duct muffler causes a negative pressure. This negative pressure occurs at the clearance between the exhaust port of the APU turbine section and the forward end of the exhaust duct muffler. The negative pressure pulls the ambient air through the holes in the aft fairing. This ambient air goes to the aft end of the turbine exhaust port where it mixes with the exhaust gases. This mixture of the ambient air and the exhaust gases goes overboard.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
49-81-00
ALL ú ú 05 Page 1 ú Nov 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
COOLING AIR INTAKE FOR THE EXHAUST DUCT
FELT METAL LINER
AFT FIRE DETECTION
FAIRING ELEMENT FOR SEE A
THE HEAT SHIELD
EXHAUST DRIP PAN DUCT MUFFLER
FWD
APU SHROUD
HEAT SHIELD
FIRE DETECTION ELEMENT FOR THE EXHAUST DUCT MUFFLER
COOLING AIR INTAKE FOR THE EXHAUST DUCT EXHAUST PORT
BONDING
FELT METAL JUMPER
LINER
AFT
FAIRING A 1 FIRE DETECTION EXHAUST
ELEMENT FOR DUCT
THE HEAT SHIELD MUFFLER DRIP PAN
CAP FOR THE DRIP PAN
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