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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
D. The 2.5 bleed valve assembly is attached to the fan exit inner case at the LPC exit. The purpose of the bleed valve is to ensure stable operation at low power levels, and to increase stall margin during starting and when required during other operating conditions. The bleed system is actuated through linkages by a hydraulic cylinder (2.5 bleed valve actuator) mounted on the intermediate case. Bleed air is exhausted through the inner fan exit case into the fan discharge airstream to provide maximum diffusion to the bleed air and minimum effect on the fan discharge airstream.
5. Intermediate Case (Fig. 4)
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A. The intermediate case is attached to the forward end of the high pressure compressor (HPC) and is a major structural member that supports the thrust bearings for the LPC and HPC rotors. The intermediate case assembly consists of the intermediate case, the 4th-stage compressor stator, and the angle gearbox and bevel gear, which transmits power from the HPC rotor (N2), via the radial driveshaft, to the main gearbox, via the horizontal driveshaft. Refer to 72-60-00/001 for more information on the accessory drives. The main structural element of the intermediate case assembly is a steel compressor intermediate case and an aluminum fan exit rear case attached through nine steel struts to form the intermediate case.
B. The intermediate case is a large investment casting which supports the No. 1, 1.5, and 2 bearings and transmits the thrust loads generated by the LPC and HPC rotors to the airframe structure through two mount brackets. An additional puck arrangement on the upper rear face of the intermediate case provides for an airframe/engine mount connection to carry engine vertical and side loads. For more information on the forward engine mount, refer to 71-21-00/001. The No. 1 ball bearing is supported by a cone support attached to the inner front flange of the intermediate case. The No. 2 ball bearing is supported by the inner rear flange of the intermediate case. The primary (main gas generator) airstream passes through the intermediate case on its way from the LPC to the HPC. Aerodynamic panels attached to the outer diameter provide the inner containment for the secondary (fan discharge) airstream.
C. The nine struts that span the secondary (fan discharge) airstream are welded to the intermediate case and are attached to the fan exit rear case by pin rivets to provide stiffness requirements.
D. The fan exit rear case is an aluminum weldment which is attached to the fan exit case and vane assembly. Aerodynamic panels (fan exit liner segments) attached to the inner diameter of the fan exit rear case provide the outer containment for the secondary (fan discharge) airstream. The fan exit liner segment, located at the 6 o'clock position, features a drain hole which precludes the entrapment of fluid in the bottom of the intermediate case.
E. The 4th-stage compressor stator consists of eighty aluminum vanes retained in aluminum inner and outer shroud rings. The stator is bolted to the inner forward flange of the intermediate case. The vanes serve to direct the primary (main gas generator) airflow as it exits the LPC.
6. High Pressure Compressor (HPC) (Fig. 5)
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NO. 2 BALL BEARING
SEE B
SEE A NO. 1 BALL BEARING NO. 1.5 ROLLER BEARING
PUCK B
MOUNT BRACKETSFAN EXIT LINER SEGMENT (8 PLACES)
FWD
INTERMEDIATE
CASE
SEE D
4TH-STAGE
COMPRESSOR
STATOR
A SEE C L-A0701
Intermediate Case
Figure 4 (Sheet 1)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
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