N0. 3 BEARING AREA SEAL PRESSURIZATION
L-A0465
Main Bearing Numbering/ Compartment Locations Figure 17 (Sheet 5)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
N0. 4 BEARING AREA SEAL PRESSURIZATION
L-A0466
Main Bearing Numbering/ Compartment Locations Figure 17 (Sheet 6)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
D. The No. 2 bearing is a thrust bearing for the high pressure compressor (HPC). The No. 2 bearing is a split inner race, angular contact ball bearing mounted forward of the rear compressor rotor. The lubrication and cooling oil is supplied under the inner race and introduced to the bearing through the inner race split, similar to the No. 1 bearing.
E. The No. 3 bearing is a preloaded cylindrical roller bearing mounted forward of the high pressure turbine. The preload to prevent skidding is mechanically applied by grinding the outer surface of the outer race elliptical and the inner surface of the outer race round. Mounting this race in a round housing forces the inner surface to assume an elliptical shape, thus creating a two-point preload of the bearing. The retainer is an one piece inner land riding cage, and is silver plated. Cooling oil is fed under the race and lubrication is provided by splashed oil from the seal plates and scoop.
F. The No. 4 bearing is a standard non-preloaded cylindrical roller bearing mounted aft of the front compressor drive turbine. Cooling oil is fed under the race and lubrication is provided by splashed oil from the seal plates and scoop, similar to the No. 3 bearing.
11. Bearing Supports (Fig. 17)
________________
A. The engine incorporates three main bearing support structures. Both the low pressure and high pressure compressor rotors are supported at the front by the intermediate case structure. The high pressure compressor and high pressure turbine are supported by the diffuser case structure. The low pressure turbine is supported by the turbine exhaust case structure.
B. All bearing support structures are made up of a system of inner and outer cones or rings, connected through the flow path by airfoil shaped struts.
C. Intermediate Case Support
(1)
The loads from the No. 1, 1.5, and 2 bearings are carried by the compressor intermediate case across the engine flow path to the fan exit rear case.
D.
Diffuser and Combustor Case Support
(1)
The inner section of the diffuser case provides structural support for the No. 3 bearing compartment. The inner section of the diffuser case is connected radially to the outer portion by 24 struts. Bearing loads are carried from the inner case through the struts of the outer case.
E.
Turbine Exhaust Case Support
(1)
The inner cone section of the tubine exhaust case provides structural support for the No. 4 bearing compartment. Bearing loads are transfered across the gaspath to the outer case section through 15 radial struts.
12. Bearing Compartment Seal Pressurization (Fig. 17)
_______________________________________
A. The main bearing compartments are enclosed by carbon seals which are pressurized by compressor air to ensure that oil is not permitted to enter the airstream.
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