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 E.  Blade tips of the 1st- and 2nd-stage turbine rotors are made of a hard material to lightly rub into the abradable ceramic, outer airseal duct segments for efficient rotor (tip) sealing. The cooling air supply of the 1st-stage blades is sealed by two knife-edge seals attached to the forward side of the rotor hub. The 2nd-stage HPT (rotating) airseal is attached to the rear of the turbine front hub and acts as the inner gaspath seal of the 2nd-stage vanes and a spacer between the two-stage rotor. The 1st-stage rotor has an inner spline and mates directly to the rear compressor hub.
 F.  The turbine case and vane assembly consists of the turbine case, twenty-one duct segments of the 1st-stage HPT, twenty-one clusters of the 2nd-stage vanes with two vanes per cluster, and twenty-one duct segments of the 2nd-stage HPT. Extensive sealing reduces leakage from the gaspath and cooling air passages. The duct segments of the 1st- and 2nd-stage HPT incorporate an abradable ceramic coating for efficient sealing. The outer buttress of the 2nd-stage vane clusters is secured to the turbine case by a tongue and groove fit. The vane cluster buttress at the rear outer diameter is secured to the rear inner flange of the turbine case. The cooling air of the 2nd-stage vanes comes from the 12th-stage compressor through four externally routed tubes which mount to bosses on the turbine case. The airflow is modulated to reduce flow at cruise conditions for improved engine performance. The segmented honeycomb airseal inner land and rotor rimseal lands of the 2nd-stage HPT are mounted on the inner diameter of each of the 2nd-stage vane clusters, to seal the inner area of the vanes. Cooling air for the seals flows through 2nd-stage vanes and nozzles mounted on the inner diameter of the vanes.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
G.  The case cooling manifolds of the high pressure turbine (HPT) surround the external turbine case and circulate fan discharge air to cool the surface of the case during cruise power operation. This cooling causes shrinkage of the case and decreased tip clearances between the blade tips and duct segments, resulting in improved turbine efficiency.
 4.  Low Pressure Turbine (LPT) (Fig. 3)
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 A.  The low pressure turbine (LPT) is attached to the external rear flange of the HPT case and provides the rotational driving force for the low pressure compressor (LPC) by extracting energy from the hot combustion gases and transforming the energy into motional energy or work. This energy drives the LPC through a turbine shaft, which runs through the center of the engine.
 B.  The LPT consists of four rotor stages and four stator vane stages. Cooling air is supplied to the case wall at the forward inner diameter, disk rim and blade root areas, and the inner rotor cavity areas. The LPT case is also cooled by the case cooling manifolds to improve cruise operating efficiency. A removable plug, located at the 4:30 o'clock position, provides access for borescope inspection of the 2nd-stage HPT and the 3rd-stage LPT.
 C.  The rotors of the low pressure turbine are a cantilevered rotor design, with the hub of the 5th-stage rear turbine as the primary rotating structural member. The 5th-stage hub provides a bolted attachment provision for the LPC driveshaft at the inner diameter and for the 4th-and 6th-stage LPT disks near the outer diameter. The 4th-stage disk mounts forward of the 5th-stage hub with a bolted attachment to the 3rd-stage disk. The 6th-stage turbine rotor is cantilevered to the rear of the 5th-stage hub.
 D.  Rotating knife-edge airseals are located between the 3rd- and 4th-stage, and 4th- and 5th-stage turbine rotors. These airseals are secured by the adjacent turbine disks. The airseal knife-edges along with integral knife-edges on the 6th-stage disk, align with an abradable honeycomb vane inner seal land to form the vane inner seal, which prevents gaspath leakage around the inner diameter of the vanes.
 E.  The 3rd-stage rotor blades are coated with an aluminized material, while the remaining stages are uncoated. Outer shrouds of the turbine blades incorporate interlocking hardfaced notches and double knife-edges seals, except for 6th-stage blades which have a single knife-edge seal. These knife-edges align with the abradable honeycomb (outer) airsealing ring segment installed in the turbine case.
 5.  Turbine Exhaust Case (Fig. 4)
　
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