5. Close-up
________
 Subtask 49-21-00-410-054
 A. Install the APU (Ref. TASK 49-11-11-400-004).

R  EFF : 001-049, 101-105, 107-107, 151-199, 49-21-00Page 402 201-210, Aug 01/05
 CES  LOAD COMPRESSOR - DESCRIPTION AND OPERATION

___________________________________________

R **ON A/C 001-003, 051-099, 401-499,
 1. General
_______
 The single-stage load compressor is driven directly from the power section.
 It supplies compressed air (bleed air) to the aircraft pneumatic system.
 2. Component Location
__________________
 (Ref. Fig. 001)

 -------------------------------------------------------------------------------FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA | | | | DOOR | REF.
 -------------------------------------------------------------------------------LOAD COMPRESSOR INLET TEMP. SNSR 316 316AR 49-23-15 LOAD COMPRESSOR DISCH TEMP. SNSR 316 316AR 49-23-16 ACTUATOR - INLET GUIDE VANE 316 316AR 49-23-51
 3. System Description
__________________
 (Ref. Fig. 001)

 **ON A/C 001-003, 051-058,
 The machined titanium single-stage centrifugal impeller is attached to the single main shaft of the engine. A curvic coupling transmits the drive torque from the engine to the centrifugal impeller. The compressor includes an Inlet Guide Vane (IGV) assembly which has 14 axially adjustable guide vanes. These guide vanes control the amount of low pressure bleed from the APU load compressor. The IGV assembly is installed immediately upstream of the load compressor impeller. The IGVs are held at the outboard end and have gear segments that turn the vanes to the required position. A cylindrical rack engages with the gear segments to synchronize the vane position. Pressurized fuel from the Fuel Control Unit (FCU) supplies the power to a hydraulic (fuel) servo actuator. This hydraulic (fuel) servo actuator sets the position of the IGVs. The IGV actuator attaches directly to the load compressor scroll and eleminates the requirement for a bellcrank housing and mechanism. This reduces weight, increases reliability, and ensures more accurate positioning of the IGVs due to fewer moving parts in the linkage.

 APU Load Compressor Figure 001 
R  EFF :  001-003, 051-099, 401-499,  Page 249-23-00 Config-1 Aug 01/05
 CES 

 A roller bearing supports the forward end of the rotating group and is seperated from the load compressor by a carbon face seal. Because the load compressor delivers air to the cabin and various pneumatic components, this carbon face seal is additionally aided by a labyrinth seal. The seal housing assembly contains eight 0.054 in. bleed ports. These ports are used continually to purge and pressurize the labyrinth seal with clean compressed air, so that the pressure differential across the carbon face seal will not reverse. This ensures that no oil can escape into the load compressor area, in case of carbon face seal failure. The housing of the centrifugal compressor will contain the debris if a compressor hub failure occurs.

R **ON A/C 059-099, 401-499,
 The machined titanium single-stage centrifugal impeller is attached to the single main shaft of the engine. A curvic coupling transmits the drive torque from the engine to the centrifugal impeller. The compressor includes an Inlet Guide Vane (IGV) assembly which has 14 axially adjustable guide vanes. These guide vanes control the amount of low pressure bleed from the APU load compressor. The IGV assembly is installed immediately upstream of the load compressor impeller. The IGVs are held at the outboard end and have gear segments that turn the vanes to the required position. A cylindrical rack engages with the gear segments to synchronize the vane position. Pressurized fuel from the Fuel Control Unit (FCU) supplies the power to a hydraulic (fuel) servo actuator. This hydraulic (fuel) servo actuator sets the position of the IGVs. The IGV actuator attaches directly to the load compressor scroll and eleminates the requirement for a bellcrank housing and mechanism. This reduces weight, increases reliability, and ensures more accurate positioning of the IGVs due to fewer moving parts in the linkage. A roller bearing supports the forward end of the rotating group and is seperated from the load compressor by a carbon face seal. Because the load compressor delivers air to the cabin and various pneumatic components, this carbon face seal is additionally aided by a labyrinth seal. The seal housing assembly contains eight 0.054 in. bleed ports. These ports are used continually to purge and pressurize the labyrinth seal with clean compressed air, so that the pressure differential across the carbon face seal will not reverse. This ensures that no oil can escape into the load compressor area, in case of carbon face seal failure. To avoid a low buffer-air pressure situation during start or high altitude operation a simple by-pass valve is incorporated into the buffer air system. It acts as a metering device to ensure a sufficient supply of compressed buffer air to the labyrinth seal during all operation modes of the APU. The housing of the centrifugal compressor will contain the debris if a compressor hub failure occurs.
　
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