APU Load Compressor Figure 001
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IGV - Actuator and Assembly
Figure 002
CES -a linear variable differential transformer. The two stage hydraulic servo control valve is powered by the metered fuel supplied on demand from the ECB control system. The fuel enters the IGVA through metered jets and move the spool valve in response to control inputs. from the torque motor. The power piston has a 25.4 mm (1 inch) stroke and develops up to 107 daN (240.5455 lbf) force to move the IGVs rapidly to control the APU. This is essential in case of sudden mechanical overload and the APU must unlaod quickly. The LVDT is a 5 wire device excited by signals from the ECB. it has primary and secondary windings and a movable ferous core. Shaft movement changes induction between the windings and therefore allows metered fuel to move the spool valve. This movement will cause the IGVA power piston to move and change the angle of the IGVs through the gear ring. The ECB monitors the IGV actuator operation.
5. Operation/Control and Indication
________________________________ The adjustable IGVs control the load compressor airflow (output) for the necessary input to the aircraft system (Ref. 49-51-00). The aircraft system transmits a demand signal to the Electronic Control Box (ECB) 59KD to give the necessary IGV control. During the start sequence, fuel pressure is used to keep the hydraulic (fuel) servo actuator at the fully extended position and the IGVs closed (15 degrees). This makes sure that:
-there is minimum airflow through the compressor,
-during acceleration, the shaft load on the APU engine is kept to a
minimum.
Above 95% rpm the position of the IGVs is 22 degrees.
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LOAD COMPRESSOR - DESCRIPTION AND OPERATION
___________________________________________
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/PRESS SNSR 316 316AR 49-23-17 LOAD COMPRESSOR DISCH TEMP. SNSR 316 316AR 49-23-16 ACTUATOR - INLET GUIDE VANE 316 316AR 49-23-51
3. System Description
__________________ (Ref. Fig. 002, 003) 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. An Inlet Guide Vane (IGV) assembly which has 24 vanes controls the amount of air bled 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 common ring gear engages with the gear segments to synchronize the vane position. Pressurized fuel from the Fuel Control Unit (FCU) supplies the power to the IGV hydraulic (fuel) servo actuator. This hydraulic (fuel) servo actuator sets the position of the IGVs.
A ball bearing supports the forward end of the rotating group and is separated from the load compressor airside by a carbon seal. Because the load compressor delivers air to the cabin and various pneumatic components, this carbon seal is aided by a pressurized labyrinth seal. A drain is located between the labyrinth and carbon seal. Oil in this drain indicates a failed carbon seal. The housing of the centrifugal compressor will contain the debris if a compressor hub failure occurs.
4. Component Description
_____________________
(Ref. Fig. 003)
A. Variable Inlet Guide-Vane (IGV) The IGV assembly has 24 IGVs. They are installed radially at the load compressor inlet.
Load Compressor - Component Location
Figure 001
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APU Load Compressor Figure 002
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IGV Control - Block Diagram
Figure 003
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B. The IGV Actuator The IGV actuator is the hydromechanical servomechanism which controls the opening angle of the IGVs. To adjust the correct IGV angle, the IGV actuator moves the IGV assembly geartrain. It uses the high pressure fuel supplied from the Fuel Control Unit (FCU) (Ref. 49-32-00) as the hydraulic power source. The internal return spring ensure that the the IGV's will be held in their closed position during the APU start sequence. The ECB monitors the IGV actuator operation. The IGV actuator has the subsequent primary components:
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