E. Air Cycle Machine (Fig. 6)_________________
(1)
Description
(a)
The air cycle machine is divided into three parts; a fan, a compressor, and a turbine. Each part has a different impeller. There is a compressor impeller, a radial-inflow turbine impeller, and an axial-flow fan impeller. All three impellers are attached to the same shaft.
(b)
The shaft is held in its position by three air bearings. A double-acting thrust air bearing controls the axial loads of the shaft. It is between the turbine and the compressor. Two journal air bearings control the radial loads of the shaft. One is between the turbine and the compressor. The other is between the compressor and the fan. Maintenance of the air bearings is not neccesary. Air is supplied by the turbine inlet assembly to pressurize and to decrease the temperature of the bearings.
(c)
Each part of the air cycle machine has its own air inlet and outlet. The turbine also has an extra inlet and three tubes connected to it.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
DIFFUSER
AIR BEARINGS
TURBINE OUTLET
TURBINE
TURBINE INLET
REVERSE PITOT PICKUP
A
757
MAINTENANCE MANUAL
FAN
A
SEE A
ANTI-ICE
MUFF
COMPRESSOR OUTLET A (TO SECONDARY
HEAT EXCHANGER) TURBINE OUTLET
(TO CONDENSOR) COMPRESSOR INLET (FROM PRIMARY HEAT EXCHANGER)
TURBINE INLET
HOT AIR INLET (FROM REHEATER)
(FROM LOW LIMIT
AND TEMPERATURE
CONTROL VALVES)
A
COMPRESSOR INLET
COMPRESSOR FAN INLET
FAN
FAN OUTLET
FAN INLET
AIR
BEARINGS
A-A
Air Cycle Machine
Figure 6
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(2)
Function
(a)
The air-cycle-machine fan is used to draw air through the primary and secondary heat exchangers. When the airplane is in flight, air flows through the heat exchangers because the ram air inlet door is open. When the airplane is not in flight, air will only flow through the heat exchangers when the fan pulls it through.
(b)
The air-cycle-machine compressor increases the temperature and the pressure of air from the primary heat exchanger. The outlet from the compressor flows through a water-removal process. The water is removed more easily because of the high air pressure.
(c)
The air-cycle-machine turbine causes the shaft to turn. The turbine decreases the temperature and the pressure of the air. The low temperature at the turbine outlet may cause ice on the turbine outlet. To prevent ice or to decrease the air temperature in the cooling pack, hot air is supplied to the turbine outlet. The supply of hot air is controlled by the low-limit-control valve and the temperature control valve.
(d)
One of the tubes connected to the turbine also supplies hot air from the compressor outlet. The second tube supplies the turbine outlet pressure to the low limit control valve. The third tube supplies cold air to the water extractor inlet.
F.
Reheater (Fig. 7)
________
(1)
Description
(a)
The reheater is a plate-fin, single-pass, cross-flow, air-to-air heat exchanger. The plate-fins are at right angles to each other. The core, which is a plate-fin heat transfer matrix, is brazed together as a unit. The housing assembly is welded to the core. All the parts of the reheater are made of aluminum alloys.
(2)
Function
(a)
The reheater decreases the air that flows from the secondary heat exchanger to the condensor. It also increases the temperature of the air that flows from the water extractor to the turbine. The temperatures are changed in the reheater as the heat of the air is transmitted through the thin plate-fins.
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