PNEUMATIC - DESCRIPTION AND OPERATION
1. General
A. The purpose of the pneumatic system is to supply compressed air from the 8th- and 13th-stage engine compressor bleeds or from the APU or from a ground cart to a pneumatic manifold for air conditioning and pressurization, engine starting, and for the thermal anti-icing system. The controlling valves of the systems drawing compressed air from the pneumatic manifold are covered in their respective chapters. For air conditioning and pressurization, refer to Chapter 21, Engine Bleed Air Compression Control System; for engine starting, refer to Chapter 80, Pneumatic Starting System; for thermal anti-icing, refer to Chapter 30, Wing Thermal Anti-Icing System.
B. The main supply of compressed air to the manifold is obtained from 8th- stage compressor bleeds. When the supply of air of 8th-stage bleed is not adequate to meet air conditioning system demands, the 13th-stage bleed air is used. Air from the engine compressor bleeds is directed through precoolers (heat exchangers) to the pneumatic manifold (Fig. 1). A high pressure bleed control system is provided in order to regulate the airflow and supply the air demand for the air conditioning system. Refer to Chapter 21, Air Conditioning for full information on high pressure bleed control system. For pressure and temperature indication of the bleed air, pressure transmitters and temperature switches are provided.
C. The engine bleed air distribution system interconnects the engine bleeds of the engines and APU and contains the necessary valves to shut off bleed air at each engine and isolate various ducts.
D. The bleed air precooler system consists of the two similar subsystems which provide the precooling of bleed air. One subsystem is the left side, which cools the air supplied by engine No. 1 and the other is the right side which cools the air supplied by engine No. 2. Each subsystem functions automatically as long as the engine is running. Each subsystem consists of a thermostatically controlled precooler valve and an air-to-air heat exchanger. The cooling air for the heat exchanger is engine fan air bleed. The precooler valve is attached to the discharge port of the heat exchanger and the valve position is controlled by cooling air exit temperature.
E. Two pressure transmitters are provided for pressure indication of the bleed air. One transmitter is used for each engine. Both pressure transmitters are connected to a dual pressure indicator on the overhead panel. The engine bleed temperature indication consists of overtemperature switches on the ducting system, which are connected to the overhead panel trip lights. The temperature switches illuminate the trip lights and the corresponding engine bleed valve closes when the bleed air temperature exceeds approximately 490°F.
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Pneumatic System Schematic 512
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
F. The bleed air cleaner system (Fig. 1) consists of two similar independent subsystems which purge the bleed air of impurities. Each subsystem functions automatically whenever engine bleed air is used from its respective engine for air conditioning, and the airplane is on the ground or the flaps are extended. Each subsystem consists of an inertial type air cleaner and an electrically controlled pneumatically operated purge valve. The air cleaner is located in the pneumatic manifold outboard of the air conditioning duct for the respective engine. For a more detailed description of the air cleaner system, refer to Air Cleaner System, Chapter 21.
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ENGINE BLEED AIR DISTRIBUTION SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The purpose of the engine bleed air distribution system is to direct high temperature compressed air from the engine bleeds to the air conditioning system, to the engine starting system, and to the thermal anti-icing system. The engine bleed system consists of ducts that interconnect the two engines, an isolation valve, and engine bleed valves to isolate each engine and deliver air as required. Bleed air from the eighth stage is delivered to the main manifold through two separate ducts. The main duct delivers the air through the precooler system heat exchanger, the second duct bypasses the heat exchanger and delivers the increased flow of air through the bleed valve directly to the manifold. Bleed air from the 13th stage, after passing through the modulating and shutoff valve in the air conditioning compression control system merges with the main ducting system prior to entering the precooler. (See figure 1.) A check valve on each eighth stage bleed duct prevents reverse flow of the high spool bleed air into the eighth stage engine ports. Relief valves are installed in the main manifold (figure 2) to prevent excess pressure from rupturing the ducts. A pneumatic ground service connector and check valve is provided for the connection of a ground pneumatic cart.
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