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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
F. The pneumatic system is used to start the engines on the airplane. Bleed air from a pneumatic source flows in the reverse direction through the pneumatic system to the engine start system.
G. The bleed air is diverted to the engine start system by the pressure regulating and shutoff valve (PRSOV). Each engine uses a bleed air regulator to pneumatically control the PRSOV. The bleed air regulator eliminates the control pressure to the PRSOV actuator which ensures the PRSOV will remain closed during starting.
2. Pneumatic Manifold (Fig. 2)__________________
A. The pneumatic distribution system connects air supply sources from the APU, engines, and ground air source to user systems through the pneumatic manifold system and their appropriate control valves. The pneumatic manifold system extends from the engine at one wing to the crossover duct in the air conditioning bay below the center wing section to the other engine at the opposite wing. An electrically actuated isolation valve in the crossover duct separates the left and right side system. The APU bleed air duct is connected to the crossover duct on the left side of the isolation valve and the pneumatic ground service connection is connected to the crossover duct on the right side of the isolation valve.
B. From the engine, bleed air source is ducted primarily from the 5th-stage port where it passes through the 5th-stage check valve before it is ducted together with the 9th-stage (high pressure) duct. Air for nose cowl thermal anti-ice (TAI) is tapped off downstream of the 5th-stage check valve. Bleed air from the 9th-stage ports are ducted through the 9th-stage manifold and high stage valve before it is joined together with the 5th-stage duct. The air is then ducted through the PRSOV to regulate the pressure and the precooler heat exchanger to regulate the temperature before it is discharged into the strut duct. The strut duct is connected to the engine starter duct and to the wing leading edge duct. Air for wing thermal anti-ice (TAI) is tapped off from the wing leading edge duct through the wing thermal anti-ice valve. The left and right wing leading edge ducts are routed inboard inside the wing leading edge fairings where the ducts are joined to the crossover duct in the air conditioning bay.
C. Bleed air source can also be supplied with use of the APU. The APU bleed air duct runs under the passenger floor from the APU along the left side of the aft cargo compartment, then inside the keel beam through the wheel well to the air conditioning bay where it joins the crossover duct on left side of the isolation valve. The APU bleed air (shutoff) valve, a pneumatically actuated solenoid controlled valve installed in the duct downstream of the APU, controls the airflow from the APU. A reverse flow APU check valve installed in the duct section downstream of the APU bleed air (shutoff) valve prevents damage to the APU compressor from bleed air backflows from the engine(s) or ground air source. A pressure relief valve is installed in the duct section between the APU bleed air valve and APU check valve to relief excess pressure in the pneumatic manifold.
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A 737-300/400/500MAINTENANCE MANUAL
DUCT PRESSURE DUCT PRESSURE TRANSMITTER TRANSMITTER
FROM APU
Pneumatic Manifold System Schematic Figure 2
E02665
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A 737-300/400/500MAINTENANCE MANUAL
D. A three-inch diameter tap with an integral check valve for pneumatic ground service connection is installed on the right side of the crossover duct to allow system pressurization from an external ground air source.
E. There are two duct pressure transmitters installed in the crossover duct to monitor duct pressure on either side of the isolation valve.
F. The pnematic manifold serves as the central reservoir for the supply of pressurized air for air conditioning, hydraulic system pressurization, water tank pressurization and turbofans through their applicable control valves from pressure taps in the pneumatic duct.
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