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and door seal systems. The pneumatics system receives its air supply from the midstage
and high-stage ports of the engines. Cooling air is supplied to the precooler by a
fan port while bleed air is extracted from either the mid-stage or high-stage port,
depending on need. Temperature control is provided by both an electro-pneumatic
control system (bleed air manifold temperature control) and a fully pneumatic subsystem
(anti-ice augmentation temperature control). Pressure regulation is fully pneumatic for
both manifold pressure regulation and dual setting high-stage switching pressure control.
The bleed air manifold can be termed that portion of the system from the right and left
bleed air pressure regulator and shutoff valves and precoolers inboard. It is essentially a
distribution point for all airplane pneumatic services, except those tapped off at each
engine for engine services. The manifold is, as a whole, located in the tail compartment.
Manifold air temperature is held to approximately 400° F; air pressure is held to
approximately 40.5 ±3.5 psi (±5.5 psi under high input air flows).
Bleed air from the APU is used to pressurize the bleed air manifold for use by airplane
services such as ground air conditioning and engine starting. The temperature of this air
is a held to a maximum of 591° F; air pressure is held to a maximum of 53.9 psi.
The airplane incorporates an external air connection which may be used on the ground
for the same services as the APU. When used with a source comparable to the APU, the
external air will pressurize the bleed air manifold. The external air connection point is
located in the underside of the fuselage, just forward of the hydraulic system service
access door.
Door seals requiring pneumatic pressure for inflation receive pressure from the bleed air
manifold through the door seal regulator. The regulator reduces the pressure to 17-19 psi
for this application. The door seal system is described in Section 2A-52-00, Doors.
Two ducts are tapped into the bleed air manifold: one for the cockpit air conditioning
system; the other for the cabin air conditioning system. Each duct has an air conditioning
shutoff valve, which is a combination shutoff and flow regulating valve. One of its
functions is to maintain a constant flow to the system. It also has a shutoff function, which
will close the valve when it is desirable to terminate airflow into this system. The
remainder of the air conditioning system is described in Section 2A-21-00, Air
Conditioning.
Two additional ducts are also tapped into the bleed air manifold: one for the left wing
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-36-00
Page 1
October 11/02
Revision 8
anti-icing; the other for the left wing anti-icing. Each duct has an anti-ice valve controlling
the airflow. Downstream of the valves, the right wing and left wing ducts join, delivering
part of the air into a crossover duct. When on, the wing anti-icing system creates the
highest demand on the bleed air manifold. The wing anti-icing system is described in
Section 2A-30-00, Ice and Rain Protection.
2A-36-20: Pneumatics Distribution and Indication System
1. General Description:
The pneumatics distribution and indication system supplies 7th stage or 12th
stage bleed air to the bleed air manifold where it is available to the systems that
require bleed air, and provides visual indication of the pressure and temperature
of the bleed air within the bleed air manifold. System design is such that 7th stage
(mid stage) bleed air is the preferred air source and 12th stage (high stage) bleed
air serves as an alternate or supplemental source whenever 7th stage pressures
are not adequate for the airplane’s needs. A check valve is incorporated in the 7th
stage duct to prevent backflow of the higher-pressure 12th stage air. This check
valve is commonly referred to as the LP check valve.
In the standard airplane configuration, 7th stage bleed air will supply all bleed flow
during takeoff, climb and cruise conditions. The 12th stage bleed valve will remain
closed due to existing 7th stage pressure being greater than 18 ±2 psi. Should 7th
stage pressure fall below 18 ±2 psi for any reason, the 12th stage bleed valve will
open and regulate pressure to 18 ±2 psi. In all cases, bleed air passes through
manifold pressure regulator valves into the left or right bleed air manifold, where
pressure is maintained at a maximum of 40.5 ±3.5 psi by these valves. Under high
input air flows, manifold pressure tolerance increases to ±5.5 psi.
The pneumatics distribution and indication system consists of identical and
independent left and right sides. For the purposes of this description, however, the
　
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