747-400 AMM 飞机维护手册 大气 AIR 1(9)

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 C.  The No. 3 bearing cooling system includes a heat shield and buffer cooling system for the No. 3 bearing compartment. The heat shield and buffer cooling system is used to prevent damage to the No. 3 bearing compartment from the hot environment, approximately 1000°F (538°C), which is around it. The buffer cooling system supplies cooled, pressurized air from the buffer air cooler for the No. 3 bearing to the outer side of the forward and aft carbon seals in the No. 3 bearing compartment.

Engine Bearing Location
Figure 1

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2.  No. 3 Bearing Buffer Air Cooler (Fig. 2)
_______________________________
 A.  The buffer air cooler for the No. 3 bearing is an air-to-air type heat exchanger.
 B.  The buffer air cooler, which is held by a midspan assembly, is installed in the intermediate case at the 2 o'clock position.
 C.  The buffer air cooler uses fan discharge air to cool 12th-stage HPC bleed air and then sends the cooled air to the No. 3 bearing compartment.
 3.  Operation
_________
 A.  Functional Description (Fig. 3)
 (1)  
The buffer air cooler for the No. 3 bearing gets 12th-stage HPC bleed air, which goes through the buffer air cooler and is cooled by fan discharge air. The cooled 12th-stage air is fed through an external tube to the inner buffer cavity where it is also cooled as it scrubs the sump wall.

 (2)  
The cooled air is then discharged through a series of bleed holes to the bearing compartment where it is mixed with 15th-stage HPC air. The mixed air cools/insulates the No. 3 bearing compartment from its environment of HPC discharge air.

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No. 3 Bearing Buffer Air Cooler Location
Figure 2

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OIL JETS

Figure 3

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NO. 3 BEARING BUFFER AIR COOLER - REMOVAL/INSTALLATION
______________________________________________________
 1.  General
_______
 A.  This procedure gives the instructions for the removal and installation of the buffer air cooler of the No. 3 bearing.
 B.  The buffer air cooler is found on the intermediate case at the 2 o'clock position.
 C.  You must open the right thrust reverser to get access to the buffer air cooler.
 D.  The removal and installation instructions for the midspan support assembly of the buffer air cooler are also included.
 TASK 75-22-01-004-001-N00
 2.  No. 3 Bearing Buffer Air Cooler Removal (Fig. 401)
_______________________________________
 A.  References
 (1)
AMM 71-11-04/201, Fan Cowl Panels

 (2)
AMM 71-11-06/201, Core Cowl Panels

 (3)
AMM 78-31-00/201, Thrust Reverser System

 B.  
Access

 (1)  
Location Zone
 412 Engine 1 - Intermediate Case 2 o'clock
　
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