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 2.  Diffuser Case (Fig. 1)
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 A.  The diffuser case is a main structural element for the engine which supports the No. 3 bearing and the rear of the high pressure rotor system. The case serves as a housing for the compressor exit (15th-stage) stator, fuel injectors (nozzles), and combustion chamber. The outer wall of the diffuser case forms the outer contour of the diffused (expanded) gaspath and contains mounting provisions for the externally removable fuel injectors and two ignitor plugs. In addition, eight removable plugs provide access for borescope inspection of the stator vanes of the compressor exit, fuel injectors, blade/vane clusters of the 1st-stage HPT, and annular liners of the combustion chamber. Four mounting bosses provide service to the bleed for the airplane pneumatic system.
 B.  The inner structure of the case is supported by twenty-four integrally cast hollow struts at the forward end and forms the inner contour of the diffused gaspath and the attachment flange for the No. 3 bearing housing. The structure provides radial load carrying support for the bearing compartment through the struts. The hollow struts provide radial passages across the gaspath for oil supply, breather, and scavenge tubes and for tubes supplying cooling air to the No. 3 bearing compartment and the high pressure turbine.
 3.  Compressor Exit Stator (Fig. 1)
______________________
 A.  The compressor exit stator is bolted to a flange in the diffuser case, forward of the struts and divergent diffuser airflow nozzle. The stator is an integrally cast vane, shroud, and transition duct assembly.
 B.  The vanes straighten the circular whirl-pattern airflow from the 15th-stage HPC rotor and direct the airflow axially rearward. The inner and outer shrouds form a transition duct for HPC discharge gaspath into the diffuser airflow nozzle.
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 72-40-00
 ALL  ú ú N01 Page 1 ú Feb 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
A
SEE A
FWD
L-A0274 DIFFUSER/COMBUSTOR CASE A
A
NO. 3 BEARING NO. 3 BEARING
COMPARTMENT
DIVERGENT DIFFUSER AIRFLOW NOZZLE
COMPRESSOR EXIT STATOR
INNER WALL OF THECOMBUSTION CHAMBER
FUEL INJECTOR (NOZZLE)
OUTER COMBUSTION CHAMBER
DIFFUSER 
CASE  DIFFUSER CASE 
STRUT 
DOWELED END 
(COMBUSTION CHAMBER 
RETAINING) BOLT 
OUTER WALL OF THE 
A-A  COMBUSTION CHAMBER 
L-A0275 
Combustion Section 
Figure 1 

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 ALL  ú ú N01 Page 2 ú Feb 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
4.  Combustion Chamber (Fig. 1)
__________________
 A.  The combustion chamber is fabricated in two sections. The inner combustion chamber is a part of the turbine section (AMM 72-50-00/001). The outer ombustion chamber is a part of the diffuser and combustor section. The two combustor chambers form a short double pass flow type burner utilizing a welded rolled ring construction for the liner section and a cast bulkhead. The inner surfaces, which are exposed to combustion gases, are coated with a magnesium zirconate material as a thermal barrier protection.
 B.  The outer chamber is retained to the outer wall of the diffuser case at the forward end by twelve doweled end bolts. The rear of the chamber is positioned and retained to the turbine nozzle by a guide and circumferential clamp assembly. The guide and clamp assembly are adjusted during assembly to provide a slip-fit sealing feature with the outer diameter of the combustion chamber.
 C.  The combustion chamber provides mixing of the fuel from the fuel injectors with the proper amount of air for optimum combustion. Combustion of the fuel is contained within the forward and middle section of the chamber, aft of the fuel injectors. The rear portion of the chamber allows for complete mixing of the remaining airflow with the hot combustion gases and for the transition to the turbine nozzle.
 5.  No. 3 Bearing and Compartment (Fig. 1)
　
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