(3)
The low pressure turbine case is designed to permit installation of stator vane clusters, at each stage, directly to the case at the outer diameter buttresses. The inner diameter of the vane clusters in each stage incorporate a honeycomb seal segment which forms a seal land ring. The seal land ring is the static member of the inner vane seal.
(4)
Cooling air is provided to the low pressure turbine to reduce and regulate temperatures in the transition duct outer diameter area, the inner diameter of the rotors, inner cavity areas, and the stator seal areas. High pressure compressor air is used to cool the 3rd-thru 5th-stage inner and outer areas, and 4th-stage low pressure compressor air is used to cool the 6th-stage inner cavity.
(5)
The LPT case is cooled by the LPT case cooling manifolds to increase the low pressure turbine efficiency at cruise conditions. The manifolds circulate fan discharge air to cool the surface of the low pressure turbine case, which results in shrinkage of the case and decreased turbine blade tip clearances.
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72-00-00
ALL ú ú N01 Page 24 ú Jun 10/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
LOW PRESSURE TURBINE
SEE A
TURBINE SHAFT
A
A
4TH-STAGE
LPT (ROTATING) 5TH-STAGE REAR
AIRSEAL TURBINE HUB
4TH-STAGE
3RD-STAGE LPT (INNER) LPT DISK 3RD-STAGE LPT DISK
SEALING RING 5TH-STAGE
LPT (ROTATING)
AIRSEAL
TRANSITION
DUCT AREA
TURBINE (LPT) CASE LOW PRESSURE TURBINE (LPT) VANE CLUSTERS
LOW PRESSURE TURBINE (LPT) VANE CLUSTERS
A-A
Low Pressure Turbine (LPT) Figure 14 A
L-A0669
6TH-STAGE LPT DISK
LOW PRESSURE
TURBINE (LPT)
BLADES
L-A0670
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72-00-00
ALL ú
ú N01 Page 25
ú Oct 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(6)
The low pressure turbine case is a single piece, machined weldment of six nickel alloy forgings. Internal slotted supports provide hooked engagement with stator vane feet and with outer airseal shroud segments positioned behind each of the four vane stages. The outer airseal shroud segments incorporate abradable honeycomb rubstrips which align with knife-edge seals on the turbine blade outer shrouds.
E.
Turbine Exhaust Case (Fig. 15)
(1)
The turbine exhaust case which is a main structural support member for the engine is attached to the external rear flange of the LPT case and provides a housing for the No. 4 bearing. The structural case also provides the aft power plant to strut attachment point and rear ground handling attachment points.
(2)
The turbine exhaust case is the transition duct for the exhaust gas flow from divergent (through the turbines) to convergent (through the exhaust nozzle).
(3)
Provision are made in the rear mount rails for the attachment of the aft lower engine mount links to carry engine vertical, side, and torsional loads to the airframe structure. The engine rear ground handling provisions consist of two holes through the rear mount on the horizontal centerline.
(4)
There are four sensing probes installed between the exhaust case struts. The first two probes measure the gaspath total temperature (TT4.95) and the other two measure gaspath total temperature (TT4.95) and gaspath total pressure (PT4.95).
(5)
For additional information on the turbine section, refer to AMM 72-50-00/001.
9. Accessory Drives (Fig. 16)
________________
A. The accessory drives consist of a main gearbox and an angle gearbox. The main gearbox transmits power from the engine to the accessories mounted on the gearbox and provides specific speeds, torque, and mounting provisions required for the accessories to perform their various functions. The angle gearbox transmits power from the engine high pressure rotor (N2) to the main gearbox and from the starter on the main gearbox to the engine high pressure rotor (N2).
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