(g)
The TVBCA/TVCA valve solenoids, when energy is supplied, stops the flow of muscle air, which causes the valves to open.
(h)
The opened TVBCA or TVCA valve lets the cooling air flow through the turbine vane cooling air ducts and turbine blade cooling air ducts.
(i)
The cooling air flows through the turbine vane cooling air ducts and internally cools the HPT 2nd-stage turbine vanes. The air also cools the outer air seal of the 2nd-stage turbine and the HPT to LPT outer transition duct.
(j)
The cooling air flows through the turbine blade cooling air ducts and to the diffuser case struts where the air joins the cooled 15th-stage HPC air flowing around the No. 3 bearing compartment. The combined air, then, flows to and cools the HPT disks and the 2nd-stage turbine blades.
B. Control
(1) All operations of the turbine case cooling system and the turbine vane and blade cooling system are automatic and require no operator actions.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
TURBINE COOLING SYSTEM - MAINTENANCE/PRACTICES
______________________________________________
1. General_______
A. This procedure gives instructions for the removal of one of the four cooling air ducts for the turbine vane and blade if it shows cracks.
B. This procedure also tells you how to install blank-off covers to the cooling air system. You can operate the engine for a maximum of 50 hours or 5 cycles, whichever is less, with one of the four air ducts removed and blank-off covers installed.
C. For the engines with a borescope plug in the rear elbow of the lower left cooling air ducts, do not remove this cooling air duct and install the blank-off covers.
TASK 75-24-00-042-003-N00
2. Deactivation Procedure for the Turbine Cooling System_____________________________________________________
A. Equipment
(1)
Covers - Blank-off, Round (No. 1) - PWA 85986,
Pratt & Whitney, East Hartford, CT
(2)
Covers - Blank-off, Flat-Sided (No. 2) -PWA 85986, Pratt & Whitney, East Hartford, CT
B.
References
(1)
AMM 75-24-02/401, Turbine Vane and Blade Cooling Air Ducts
C.
Access
(1)
Location Zones
412 Engine 1
422 Engine 2
432 Engine 3
442 Engine 4
(2)
Access Panels 415 and 416 Thrust Reverser Halves, Engine 1 425 and 426 Thrust Reverser Halves, Engine 2 435 and 436 Thrust Reverser Halves, Engine 3 445 and 446 Thrust Reverser Halves, Engine 4
D.
Isolate the Turbine Cooling System (Fig. 201 and 202)
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A
747-400
MAINTENANCE MANUAL
NO. 1 SEE A
BLANK-OFF COVER
COVER BLANK-OFF NO. 2
UPPER LEFT TVC AIR DUCT
FWD LOWER LEFT TVC AIR DUCT COVER BLANK-OFF NO. 2
A
Left Side TVC Air Ducts
Figure 201
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G50561
A
747-400
MAINTENANCE MANUAL
SEE A
NO. 1
UPPER RIGHT
BLANK-OFF
TVC AIR DUCT
COVER
NO. 2 BLANK-OFF COVER FWD
LOWER RIGHT A TVC AIR DUCT
Right Side TVC Air Ducts Figure 202
G50562
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