DOC AIRBUS | AMM A320FEXHAUST SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The APU exhaust system ducts the APU exhaust gases overboard. Its secondary function is to decrease the exhaust noise level. To keep aerodynamic losses during APU operation to a minimum, the duct has a sufficiently large diameter. The exhaust system discharge is positioned at the very aft end of the aircraft, where a low pressure area is generated during flight. This design makes sure that exhaust gases does not re-enter the APU air intake system.
All components in contact with exhaust gases are made of corrosion resistant materials. All components exposed to high temperatures are made of fireproof or fire resistant materials. A flexible connection allows for relative movement between the APU and the muffler assembly and allows for any vibrations and inertia loads during operation. Drainage provisions are incorporated into the muffler assembly. One ventilation louver each at the top and the bottom of the muffler compartment limits the structure temperature to 110 deg. C max. The muffler assembly surface temperature does not exceed 232 deg. C.
** ON A/C NOT FOR ALL The APU exhaust system ducts the APU exhaust gases overboard. Its secondary function is to decrease the exhaust noise level. To keep aerodynamic losses during APU operation to a minimum, the duct has a sufficiently large diameter. The exhaust system discharge is positioned at the very aft end of the aircraft, where a low pressure area is generated during flight. This design makes sure that exhaust gases does not re-enter the APU air intake system.
All components in contact with exhaust gases are made of corrosion resistant materials. All components exposed to high temperatures are made of fireproof or fire resistant materials. A flexible connection allows for relative movement between the APU and the muffler assembly and allows for any vibrations and inertia loads during operation. Drainage provisions are incorporated into the muffler assembly. One ventilation louver each at the top and the bottom of the muffler compartment limits the structure temperature to 110 deg. C max. The muffler assembly surface temperature does not exceed 232 deg. C.
2. Component Location
** ON A/C NOT FOR ALL 
APU Exhaust Muffler - Component Location| ------------------------------------------------------------------------------- |
| FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA |
| | | | | DOOR | REF. |
| ------------------------------------------------------------------------------- |
| EXHAUST MUFFLER BODY 315/ 315AL/ 49-81-41 |
| 316/ 316AR/ |
| 317 317AL |
| HOT NOZZLE ASSEMBLY 315/ 315AL/ 49-81-42 |
| 316 316AR |
| BELLOWS 315/ 315AL/ 49-81-42 |
| 316 316AR |
| V-CLAMP INSULATION SEGMENTS 315/ 315AL/ 49-81-41 |
| 316 316AR |
3. System/Component Description
A. Major Components
(1) Exhaust Muffler Body
(a) Muffler Substructure
This is a riveted corrosion resistant steel (CRES) structure, made of frames, an outer tube and provisions for external seals and insulation segments. It has the function of:
This is a riveted corrosion resistant steel (CRES) structure, made of frames, an outer tube and provisions for external seals and insulation segments. It has the function of:
- the load carrying structure of the complete muffler assembly,
- the muffler resonator,
- attaching the muffler assembly to the rails in the tailcone muffler compartment.
(b) Tail Pipe Assembly
The central part is made of feltmetal (sound attenuation CRES sheet metal). The end pieces are made of solid CRES sheet metal. The aft tube section is welded to the muffler substructure. The central tube section is put in from the front and positioned against the aft tube section. The forward tube section, which has a provision for the piston ring, is then put in and riveted to the muffler substructure. The feltmetal tube section is captured between the end sections with sufficient space to allow for thermal expansion.
The central part is made of feltmetal (sound attenuation CRES sheet metal). The end pieces are made of solid CRES sheet metal. The aft tube section is welded to the muffler substructure. The central tube section is put in from the front and positioned against the aft tube section. The forward tube section, which has a provision for the piston ring, is then put in and riveted to the muffler substructure. The feltmetal tube section is captured between the end sections with sufficient space to allow for thermal expansion.
(c) Insulation Covers
The complete exterior surface of the muffler is covered with 2 large insulation blankets and several small insulation segments. These are held in position with lockwire fastened to the buttons on the insulation components.
The function of these is to reduce the muffler assembly surface temperature to a maximum of 232 deg. C for all ambient temperatures or APU operating conditions.
The complete exterior surface of the muffler is covered with 2 large insulation blankets and several small insulation segments. These are held in position with lockwire fastened to the buttons on the insulation components.
The function of these is to reduce the muffler assembly surface temperature to a maximum of 232 deg. C for all ambient temperatures or APU operating conditions.
(d) Piston ring
This component is riveted in a recess on the inner liner forward-tube-section. It is in continuous contact with the hot nozzle assembly. Thus it seals the clearance between these assemblies and allows for relative movement between them.
This component is riveted in a recess on the inner liner forward-tube-section. It is in continuous contact with the hot nozzle assembly. Thus it seals the clearance between these assemblies and allows for relative movement between them.
(e) FR84 Fire Wall Seal
A circumferential fireproof seal is installed on a bracket on the muffler substructure. It seals the gap between the fire wall cutout in FR84 and the exhaust muffler assembly.
A circumferential fireproof seal is installed on a bracket on the muffler substructure. It seals the gap between the fire wall cutout in FR84 and the exhaust muffler assembly.
(2) Hot Nozzle Assembly
This component is directly attached to the APU turbine flange with a V-clamp. It is in contact with the tail pipe assembly through the piston ring and the muffler body through the externally installed bellows. APU movement is not transmitted to the muffler assembly. A drain port is installed at the lowest point (Ref. AMM D/O 49-17-00-00).
This component is directly attached to the APU turbine flange with a V-clamp. It is in contact with the tail pipe assembly through the piston ring and the muffler body through the externally installed bellows. APU movement is not transmitted to the muffler assembly. A drain port is installed at the lowest point (Ref. AMM D/O 49-17-00-00).
(3) Bellows
It is the flexible connection between the hot nozzle and the muffler body. It is also a back-up seal to prevent exhaust gas leakage into the APU compartment. It is attached to both items with band clamps. It allows movement between the APU and the muffler body.
It is the flexible connection between the hot nozzle and the muffler body. It is also a back-up seal to prevent exhaust gas leakage into the APU compartment. It is attached to both items with band clamps. It allows movement between the APU and the muffler body.
(4) V-Clamp Insulation Segments
To make sure that the surface temperature does not exceed 232 Deg. C, the connection between the APU turbine flange and the hot nozzle assembly is insulated. Two half-circle insulation segments cover the interface, held in position with lockwire fastened to the buttons on these items.
To make sure that the surface temperature does not exceed 232 Deg. C, the connection between the APU turbine flange and the hot nozzle assembly is insulated. Two half-circle insulation segments cover the interface, held in position with lockwire fastened to the buttons on these items.
B. Muffler Assembly Installation
Support rails align the assembly with the APU. Longitudinal positioning is provided at the rear attachment brackets only. Lateral positioning is made by fixing the assembly to the left rail. The distance between the rails is 6mm larger than the distance between the muffler assembly attachment brackets. Thus the muffler assembly is positioned 3mm to the left of the APU longitudinal axis. The attachment at the right rail allows for thermal expansion differences.
The 3mm displacement is taken up at the muffler assembly/APU turbine flange interface by the bellows and the sealing ring.
Support rails align the assembly with the APU. Longitudinal positioning is provided at the rear attachment brackets only. Lateral positioning is made by fixing the assembly to the left rail. The distance between the rails is 6mm larger than the distance between the muffler assembly attachment brackets. Thus the muffler assembly is positioned 3mm to the left of the APU longitudinal axis. The attachment at the right rail allows for thermal expansion differences.
The 3mm displacement is taken up at the muffler assembly/APU turbine flange interface by the bellows and the sealing ring.
4. Operation
APU operations cause thermal expansion of the muffler assembly:
APU operations cause thermal expansion of the muffler assembly:
- Radial expansion:
This causes the muffler to expand approx 6mm in diameter This expansion is taken up through the 6mm gap allowed at the mounting rail and the compression of the seals - Forward axial expansion:
This leads to a reduction of the distance between the muffler assembly and the APU. This is taken up internally by the sealing ring moving within the flange. The bellows compress to take up the expansion. - Rearward axial expansion:
The muffler gets longer and the compression is taken up by the rear fairing seal.