曝光台 注意防骗
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One-way check valves are installed on the engine in the 10th-stage bleed ducts. The
valves prevent the reverse flow of manifold air into the engines. Similar valves are
also used for the APU and the external ground air connector.
Pressure readings for the manifold are derived from two pressure transducers, one for
the left manifold and one for the right manifold. The pressure readings for the left and
right 10th-stage manifold are displayed on the EICAS Status page.
Isolation Valve
The isolation valve is located in the aft equipment bay and is used to isolate the left
and the right manifold. Opening the isolation valve allows air from any of the sources
to be supplied to the left or right manifold as required. The 10th-stage isolation valve
is an electrically controlled, pneumatically operated valve, which either fully opens or
fully closes. The isolation valve is spring-loaded closed when no 10th-stage bleed air
is available or when electrical control power is lost.
The isolation valve is manually commanded open or closed by the 10TH STAGE
ISOL switch/light located on the BLEED AIR Panel. The valve may also be
automatically commanded open or closed by the following conditions:
• open; during engine starts (starter engagement)
• closed; when a pack overpressure occurs
Valve status is indicated by the switch/light OPEN annunciation.
Engine 10th-Stage Bleed Air Valves
The 10th-stage bleed air valves are located in the aft equipment bay and control the
supply of 10th-stage bleed air to the engines for starting, and from the engines for
bleed air supply. 10th-stage bleed air valve operation is similar to the isolation valve.
The valves are manually commanded open or closed by the L (R) 10TH STAGE
switch/lights located on the BLEED AIR Panel. The valves may also be automatically
commanded open or closed by the following conditions:
• open: during engine starts (starter engagement)
• closed: when the associated ENG FIRE PUSH switch/light is pressed
• closed: when a pack overpressure occurs
PNEUMATIC SYSTEM
19-4 For Training Purposes Only
May 03
P I LOT T R A I N I N G GU I D E
Valve status is indicated by the respective switch/light CLOSED annunciation (see
Figure 19-2). Bleed air temperatures and pressures from the engine compressor 10thstage
are unregulated and therefore dependent on engine power settings. Temperatures
and pressures can reach 700°F (370°C) and 170 psi (1172 kPa) at full thrust.
APU Load Control Valve (LCV)
The APU load control valve (LCV) controls APU bleed air supply to the 10th-stage
manifold. The LCV is an electrically controlled, pneumatically operated valve which
either fully opens or closes.
The valve is manually controlled by the APU LCV switch/light located on the BLEED
AIR Panel. When the APU LCV switch/light is pressed the valve opens, which allows
APU bleed air to enter the left bleed air manifold. The APU LCV is automatically
commanded closed by the following conditions:
• excessive APU EGT
• APU LCV interlock protection
Valve status is indicated by the switch/light OPEN annunciation (see Figure 19-2).
APU bleed air temperature and pressure can reach 500°F (260°C) and 50 psi
(345 kPa).
APU Load Control Valve Interlock Protection
A check valve installed in the APU bleed air duct prevents manifold pressure from
entering the APU compressor. The APU LCV interlock provides a second level of
protection, preventing manifold pressure from entering the APU by interlocking the
APU LCV with the 10th-stage bleed air switches.
The APU Electronic Control Unit (ECU) monitors the switch positions of the LCV,
10th-stage isolation valve, and left and right 10th-stage bleed switches. The APU LCV
will automatically close or be prevented from opening whenever the following switch
conditions exist:
• L 10th-stage bleed switch/light is pressed open; or
• both R 10th-stage bleed switch/light and the ISOL switch/light are pressed open
External Ground Air Connector
An external ground air connector is located on the aft fuselage below the left engine.
Ground air may be supplied to the left manifold of the 10th-stage bleed air-system
when a ground air source is attached to the external ground air connector.
PNEUMATIC SYSTEM
For Training Purposes Only
Jan 04
19-5
P I LOT T R A I N I N G GU I D E
14th-Stage Bleed Air
Description
The bleed air for the 14th-stage manifold is taken from a single port on each engine
compressor’s 14th stage. The air is distributed through the 14th-stage bleed air
manifold.
The 14th-stage bleed air is used for:
• wing anti-ice
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