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Figure 6-7
6-18
PM-121
Change 4
Learjet 31A
Pilot's Manual
PRESSURIZATION SYSTEM
Cabin pressurization is provided by conditioned air entering the cabin
through the air distribution ducts and controlled by modulating the
amount ofair exhausted from thecabin. The pressurization system consists
of a cabin primary outflow valve, a cabin safety valve, differential
pressure relief valves, cabin altitude limiters, a vacuum shutoff solenoid
valve, a pressurization vacuum regulator, a pressurization module,
two bleed-air shutoffvalves, two emergency pressurization valves,
cabin altitude warning and emergency pressurization aneroid switches,
two emergency pressurization override switches, an amber CAB
ALTcaution light, and an auralwarningsystem . Allsystem controls are
located on the pressurization and copilot's switch panel. All system annunciators
are located on the glareshield annunciator panel. Power for
the control circuits is 28 VDC supplied through the 7.5-amp PRESS
CONT circuit breaker on the copilot's circuit breaker panel, and the tamp
CABIN AIR circuit breaker located on the pilot's circuit breaker
panel.
CREW MASK-SCOTT ATO MC 10-15-01
Figure 6-S
PM-121
6-19
Change 4
Pilot's Manual
Learjet 31A
NORMAL PRESSURIZATION
Normal pressurization is controlled by regulating control pressure to
the cabin primary outflow valve. The control pressure may be regulated
automatically by the CABIN CONTROLLER or manually by the
manual UP-DN control lever. Apressurization vacuum regulator in the
tailcone provides regulated vacuum (servo pressure) to operate the
valve. With the squat switch in airmode, and the pressurization AUTOMAN
switch in AUTO, the aircraft pressurization system is completely
independent of the aircraft electrical system . If the aircraft is inadvertently
allowed to ascend and exceed the controlling limits of the pressurization
controls, the normal differential pressure relief valve will
cause the primary outflow valve to open and maintain a 9.4 psi (64.8
kPa) differential . Should the normal differential pressure relief valve
fail, the maximum differential pressure relief valve will modulate the
cabin safety valve to maintain a 9.7 psi (67 kPa) differential. Cabin altitude
limiters are installed in the servo pressure vacuum lines to the primary
outflow valve and cabin safety valve to limit cabin aftitude to
11,500 feet should a differential relief valve fail and allow the primary
outflow valve or cabin safety valve to remain open. Should the cabin altitude
reach 11,500 feet, the altitude limiters will vent cabin pressure to
the primary outflow valve and cabin safety valve control chambers
causing the valves to close. Should a rapid descent cause a negative
pressure in the cabin, both the primary outflow valve and cabin safety
valve will open to vent ambient atmospheric pressure to the cabin.
EMERGENCY PRESSURIZATION
In the event of normal cabin airflow malfunction, emergency pressurization
is provided by routing engine bleed air directly into the cabin
through the emergency pressurization valves . Emergency pressurization
is accomplished automatically by pressurization aneroid switches
when thecabin altitude increases to 9500 (±250) feet or manually by setting
the BLEED AIRswitches to EMER. The emergency pressurization
valves will open, the bleed-air shutoff/pressure regulator valve will go
to the low-pressure setting ducting engine low-pressure bleed air directly
into the cabin air sidewall and floor diffusers. This bypasses the
conditioned air plumbing in the tailcone area to maximize the inflow of
bleed air to the cabin. The emergency pressurization valves are deenergized
to the open position for emergency air flow, and energized closed
for normal bleed-air flow. Each valve is independent of the other and,
whenever both valves are open, temperature control and bleed air for
wing, and windshield anti-ice will be unavailable. Operating power for
emergency valve actuation is 28 VDC supplied through either the 7.5-
amp L and REMER PRESS circuit breakers on the pilot's and copilot's
circuit breaker panels. Power for emergency valve actuation is available
during EMER BUS mode.
6-20
PM-121
Change 3
Learjet 31A
PM-121
Original
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PRESSURIZATION SYSTEM SCHEMATIC
Figure 6-9
Pilot's Manual
6-21
Pilot's Manual
Learjet 31A
PRESSURIZATION CONTROLS AND INDICATORS
BLEED AIR SWITCHES
TheLand RBLEEDAIRswitches, located on the copilot's switch panel,
control the respective left and right bleed-air shutoff/pressure regulator
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