021 06-00-00 pneumatic - pressurisation and air cond amend0
TRANSCRIPT
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TEXTBOOK
PNEUMATIC PRESSURISATION AND AIR CONDITIONING SYSTEMS
020 00 00 00 AIRCRAFT GENERAL KNOWLEDGE
021 06 00 00 PNEUMATIC PRESSURISATION AND AIR CONDITIONING
SYSTEMS
HP
LP
NO. 2ENGINE
TO DEICINGSYSTEM
TO NO. 2AIR-
CONDITIONINGPACK
TO NO. 1AIR-
CONDITIONINGPACK
FROM NO. 1 ENGINEBLEED-AIR SYSTEM
(SIMILAR TO NO. 2 SYSTEM)
AIR CONDITIONING
TEMP
CONTROL
OFF
RECIRC
CABIN
OFF
RECIRC
F/C FAN1 BLEED 2
COOL WARM COOL WARM
NORM
AUTO
MAN
MIN MAX
BLEED
0
2040
60
80
100
C
DUCT TEMP
OFF
PACKS
F/A
CABIN FLT COMP
CABIN
GAUGE
CABDUCT
F/CDUCT
F/C FAN
OFF
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Table of Contents:
Ai r driven systems _____________________________________________________ 3
Pneumatic systems ____________________________________________________ 4
Ai r condi tioning system _______________________________________________ 14
Pressurisation _______________________________________________________ 25
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Ai r driven systems
"Pneumatic, Vacuum systems" Pneumatic, or air driven systems, can be used to
power gyroscopic flight instruments, provide pressurization and air conditioning,
operate de-icing systems and power landing gear and brake systems in lieu of
hydraulics.
Alternate
Landing Gear
Control System
Alternate
Wheelbrake
System
Wheelbrake
SystemLanding Gear
Control System
Nose Wheel
Steering
F - 27 Pneumatic Landing Gear / Brake System
L.H. Nacelle R.H. Nacelle
Alternate
Storage Bottle
Main
Storage Bottle
Sensing Line
IsolatingValves
Isolating Valves
ROD
Air Filter
Pneumatic Panel
Heading
indicator
Attitude
indicator
Suction relief
valve
Turn and slip
indicator
Needle valve
Vane-type
vacuum pump
Central
air filter
Suction
gage
Oil
Air
Engine Oil
Oil
seperator
luprication
and cooling
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Pneumatic systems
"Gyro pneumatic systems"
Venturi suction systems are simple systems, where a venturi tube mounted on
the outside of the fuselage is directed into the slipstream of the propeller.
Air flowing through the venturi produces a low pressure inside the instruments.
N 330030
L R2 M i n . T u rn
L R
2MIN TURN
Venturi
Suction
regulator
Pressure - reducing
needle valve
Heading
indicator
Attitude
indicator
Turn und Slip
indicator
Propeller Wash
Heading
Indicator
Attitude
Indicator
Turn and slip
Indicator
Needle valve
Venturi suction
Air filterAir flows into the instrument
cases through built-in filters to
spin the gyros.
The likelihood of ice buildup
and venturi blockage during
IFR conditions limits the use of
venturi systems to light VFR
aircraft.
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Modern aircraft equipped with pneumatic gyros use engine driven vane type
pumps.
Two types are in use - wet and dry pumps.
Wet vacuum pumps are lubricated by engine oil. The oil lubricates and cools the
pump, but has to be routed through an air-oil separator and drained back into the
tank before the air can be directed overboard.
Vane Type Air Pump
Inlet Outlet
Case
Rotor
Vane
Shaft
Heading
indicator
Attitude
indicator
Suction relief
valve
Turn and slip
indicator
Needle valve
Vane-type
vacuum pump
Central
air filter
Suctiongage
Oil
Air
Engine Oil
Oil
seperator
lupricationadn cooling
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Dry air pumps are lighter in weight and require no lubrication. They can drive
gyroscopic instruments with the suction they produce, as seen in this schematic.
Dry air pumps can also be used to produce positive air pressure.
Pressure systems are necessary on aircraft which fly at high altitudes where
there is not enough ambient air pressure to drive the gyros.
Twin Engine Vacuum System
Filter
Heading
indicator
Vacuum
regulator
Air
Pump
Suction
gage
Attitude
indicator
Vacuum
regulator
Air
Pump
Manifold check valve
Dry Vane-type
vacuum pumpRotor and vanes are
made from carbon compounds.
Wear generates a microscopic
carbon deposit which acts as
lubricant
Twin Engine Pressure System
Pressure
regulator
Pressure
regulatorInline
filter
Inline
filterManifold check valve
Inlet
filter
Inlet
filter
Air PumpAir Pump
Gyro
pressure
gage
Pilots
gyros
Copilots
gyros
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Bleed air"
Turbine engine powered aircraft usually use bleed air from the engine
compressor.
This air is free from contamination and can be safely used for cabin
pressurization and air conditioning.
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Some aircraft use independent cabin compressors driven by bleed air to increase
the volume of air taken into the cabin.
Another design uses a jet pump flow multiplier to increase the volume of air.
The jet pump is essentially a venturi inside a line from the outside of the aircraft.A nozzle blows a stream of high-velocity compressor bleed air into the throat of
the venturi which produces a low pressure that draws air in from the outside.
This outside air is mixed with the compressor bleed air and carried into the
aircraft cabin.
Compressor Bleed Air
Ambient Air
To Cabin
Jet pump
Flush air inlet Outside skin
Pressure
vessel
Outflow
valve
Turboprop
engine
Bleed air
Flush air inlet Outside skin
Pressure
vessel
Outflow
valve
Turboprop
engine
Bleed air
Compressor turbine
Compressor
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"APU bleed air"
The Auxillary Power Unit installed on most larger airplanes is usually capable of
providing bleed air to operate air cycle-machine-based air conditioning systems
on the ground.
Some APUs are designed to
operate in flight and can, if
required, provide bleed air for
pressurization and air-
conditioning as a backup inemergencies.
Pre-cooler
Pressure
regulatorand
relief valve
Water
seperator
AIRFOIL
DEICING
ECS
PACK
LH
APU
ECS
PACK
RH
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"Ground Service Cart"
To pre-condition the airplane on the ground predominantly diesel powered
ground servicing carts can provide pre-heated or pre-cooled air at high volumes.
Ground service connections on the outside of the fuselage allow the supplied air
to be ducted into the aircraft air condition ducts.
Ground service connectors usually house a check valve to avoid loss of ship-
supplied air once the cart is disconnected.
To prevent the aircraft from becoming pressurized on ground at least one door
should be left open if an air cart is connected and operating.
Air conditioning
ground coupling
CABIN AIR
FLT COMPT AIR
FLT COMPT CABINBAGGAGE
COMPARTMENT
Ground air
service connector
CONDENCER
MIXING
BOX
EXPANSION
TURBINE
AIR CYCLE
MACHINE (ACM)
COMPRESSOR
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"Indications and warnings"
As an example of bleed air related indication and warnings in a modern glass
cockpit, look at the system of the Embraer 145.
There are 5 types of indication for the air conditioning system.
- the indication on the engine indicating and crew alerting system display,
- the indication on the environmental page on the multi function display,
- the engine indicating and crew alerting system caution messages,
- the engine indicating and crew alerting system advisory massages and
- the central maintenance computer massages on the maintenance page of the
captains multi function display.
0
AA
KG KG
CRZ
88.288.2
OFF
4000
7.4
81818181
1540 1540
94.3 94.3
800800
790 790
UP UPUP
100 1
KGH KGH
88.288.2
RTN T/0 FUEL HYD ELECM/PRNG
ECSA/I
FMSBSNB3.5NM1 MIN
-38-12446
SATTATTAS
CABIN TEMP
ECS BLEED
TEMP
C
C+28
+28
CKPT TEMP
OXY
PRESS
1800 PSI
N
TGTTX
10
BSNB25 25
155
LUMEL
PACK 1 OVLDPACK 2 OVLDPACK 1 OVHT
PACK 2 OVHTRAM AIR VLV FAILPACK 1 VLV FAIL
PACK 2 VLV FAILPACK 1 VLV CLSDPACK 2 VLV CLSD
MAINTENANCE MESSAGES 1/03
AIR COND 1 LEAKAGE10/03 20:50 OCCUR:01
AIR COND 2 LEAKAGE10/03 20:50 OCCUR:01
DIG TEMP CONTROL 1 FAIL10/03 20:50 OCCUR:01
DIG TEMP CONTROL 2 FAIL10/03 20:50 OCCUR:01
DUCT TEMP SENSOR 1 FAIL10/03 20:50 OCCUR:01
DUCT TEMP SENSOR 2 FAIL
10/03 20:50 OCCUR:01
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"Interface with other systems"
Hot engine bleed air, mainly used for pressurization and air conditioning, can also
be used for anti-ice and de-ice purposes such as engine intake and wing leading
edge heating and de-ice boot inflation.
HP
LP
NO. 2ENGINE
TO DEICINGSYSTEM
TO NO. 2
AIR-CONDITIONING
PACK
TO NO. 1AIR-
CONDITIONINGPACK
FROM NO. 1 ENGINEBLEED-AIR SYSTEM
(SIMILAR TO NO. 2 SYSTEM)
AIR CONDITIONING
TEMP
CONTROL
OFF
RECIRC
CABIN
OFF
RECIRC
F/C FAN1 BLEED 2
COOL WARM COOL WARM
NORM
AUTO
MAN
MIN MAX
BLEED
0
2040
60
80
100
C
DUCT TEMP
OFF
PACKS
F/A
CABIN FLT COMP
CABIN
GAUGE
CAB
DUCT
F/C
DUCT
F/C FAN
OFF
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Bleed air is used to inflate door seals, power pneumatic autopilot servos and with
the use of a venturi to generate suction, to control cabin outflow valves or drive
pneumatic instrument gyros.
Inflatable ( pneumatic) door seal
Bleed air pressure reduced to 18 psi
is used to inflate the door seal
Quilted Fabric
1.00" Min Clearance
Door Seal
Side view of
Quilted Fabric and Retainers
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Ai r condi tioning system
"Conditioning the air in an airplane" used to just mean turning on the heat to
warm the cockpit and cabin as airplanes generally fly in low temperature at high
altitudes.
Now with people accustomed to more creature comforts, cooling systems are
used to make the cabins more comfortable when the aircraft is on the ground.
Airplane pressurization and air conditioning requires outside or "ambient" air to
be forced into the aircraft cabin.
The easiest way to achieve this is by using an air-scoop that extends into the
slipstream. This ram air flow might be sufficient for low flying single or small multi-
engine aircraft.
Airplanes that cruise at altitudes of 10,000 ft or more require air supplied at a
higher pressure to maintain an air pressure in the cabin which is comfortable and
safe for crew and passengers.
The source for this air depends largely on the type of propulsion used on a
particular airplane.
2000 ft
4000 ft6000 ft
8000 ft
10.000 ft
12.000 ft
14.000 ft
16.000 ft
18.000 ft
20.000 ft
22.000 ft
Non pressurized
Pressurization or
supplemental Oxygen required
Sea Level
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"Cooling systems". Vapor cycle cooling systems use a compressor to pump a
refrigerant through a closed system achieving a cooling effect once the gas
expands into a heat exchanger - the so-called evaporator.
Vapor Cycle System
Re-ciculated cabin air
Blower
Cold air
Inlet Outlet
Compressor
Condenser
Hot exhaust air
Ambient air
Receiver
dryer
Thermostatic
expansion valve
Heat exchanger - evaprator
Ovbd
PrimaryHeat
Exchanger
Secondary
Heat
Exchanger
Ram air inelt
Emerg
ram
Groundconnection
Reheater
Condenser
Environment control systempackAIRCOND / PNEUMATIC
CKPT CABIN
PAXRECIRC
C H C H
ATTND
PACK 1 PACK 2
XBLEED
BLEED 1 APU BLEED BLEED 2
WING 1
START 1
WING 2
START 2GND
CONN
START 2
LEAK LEAK
From engine To cabinT
T
T
T
T
T2C T1
CollectorWater
Fan
Air cycle cooling systems are
the true air conditioning
systems since they are
capable of controlling the air
temperature over a wide range
from maximum hot to
maximum cold depending on
the environment.
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"Heating systems"
Most small aircraft use one of two types of heating systems:
The exhaust system heaters where air flows around the exhaust components and
picks up heat before it is carried into the cabin.
Or combustion heaters that use fuel from the aircraft fuel tanks to operate an
independent heater.
Exhaust System Heater
From engine cylindersOverboard
To cabin
Cabin heat
box
Exhaust
overboard
Heater muff
Ram air
Combustion air scoop
Fuel FilterPump
Heated
air
ExhaustDrain
Fuel
filter
Ignition unit
Spray nozzle
Combustion chamber
Fuel tank
Exhaust shroud
DrainDrainVentilating
air scoop
Sealed fuel control assembly
COMBUSTION HEATER
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"Sources of air supply"
Airplane pressurization and air conditioning requires outside or "ambient" air to
be forced into the aircraft cabin.
The easiest way to achieve this is by using an air-scoop that extends into the
slipstream.
This ram air flow might be sufficient for low flying single or small multi-engine
aircraft.
Air-scoop
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Airplanes that cruise at altitudes of 10,000 ft or more require air supplied at a
higher pressure to maintain an air pressure in the cabin which is comfortable and
safe for crew and passengers.
The source for this air depends largely on the type of propulsion used on a
particular airplane.
"Air cycle machines"
Gas turbine powered transport aircraft use compressor bleed air for pressurizing
the cabins with temperature controlled air.
AIR SUPPLY:
Turbo - Chargers
Blowers or Compressors
Gas -Turbine Bleed Air
For airconditioning and pressurization
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Our schematic shows the air conditioning system for a twin-engine jet transport
aircraft with the engines mounted on the aft fuselage.
This airplane has two independent air conditioning systems that supply the cabin
with heated and cooled air that is mixed to produce pressurized air at the right
temperature.
Hot compressed bleed air is taken from the engines and from the auxiliary power
unit. It passes through pressure regulating and shutoff valves, flow limiters and
flow control valves to the air cycle machine where it is cooled.
Some of the hot air is tapped off before it goes through the cooler and is mixed
with the cold air by a temperature control valve to achieve the correct
temperature.
Gas turbine powered transport aircraft use compressor bleed air for pressurizing
the cabins with temperature controlled air.
Compressor
Expansion turbine
Air cycle machine
Ground air
conditioner
connection
Mix chamber
Temperature
control valve
Anti-icethermostat
Aft
pressure
bulkhead
Water seperator
Water seperator temperature control valve
Manual
crossfeed
valve Flow conrol valve
Pressure regulating
& shutoff valve
8th stage
bleed check
valve
Anti-icing
pressure
regulating
shutoff valve
13th stage
augmentation valve
Ground pneumatic
connection
Primary heat
exchanger
Secondary heat
exchanger
APU load control
valve
Cooling air
selector valve
Ground
cooling fan
From L.H. engine
From R.H. engine
Sonic venturi
Ram air valve
Ram
air
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"ACM cooling"
The cold air for cooling the airplane is produced by removing heat energy from
the hot compressor bleed air.
The hot bleed air from the engines and APU flows into a primary heat exchanger
where it gives up some of its heat to ram air that flows through ducts.
After leaving the heat exchanger it flows through the air cycle machine where it is
further compressed by the centifugal compressor.
The temperature rise caused by this compression allows more heat energy to be
removed as the air flows through the secondary heat exchanger.
After leaving this heat exchanger the air gives up much of its energy as it spins
the expansion turbine which drives the air-cycle machine compressor.
Still more energy is extracted in the last stage of cooling as the air expands upon
leaving the turbine. When it leaves the expansion turbine the air is cold.
Compressor
Expansion turbine
Air cycle machine
Primary heatexchanger
Cooling air
selector valve RamSecondary heat
exchanger
Cold air to temperaturecontrol valve
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"Flow control valves"
Most flow control valves use butterfly valves to reduce or increase the flow of air
in a duct.
The position of the valve can be changed electrically through an electric motor or
pneumatically, through a bleed air actuated piston and cylinder assembly.
Flow rates can be a fixed setting for optimum performance of the air conditioningsystem or a variable setting allowing the crew to control the air flow within pre-set
limits.
Actuator housingSolenoid
Electricalconnector
Actuator cover
Access tofilter
Flow controlvalve
Butterfly Valve
High pressure shut off valve
TO NO. 1AIR-
CONDITIONINGPACK
TO NO. 2AIR-
CONDITIONINGPACK
FROM NO. 1 ENGINEBLEED-AIR SYSTEM
(SIMILAR TO NO. 2 SYSTEM)
TO DEICINGSYSTEM
FROM CABINSUPPLY DUCT
NO. 2ENGINE
HP
LP
AIR CONDITIONING
TEMP
CONTROL
OFF
RECIRC
CABIN
OFF
RECIRC
F/C FAN1 BLEED 2
COOL WARM COOL WARM
NORM
AUTO
MAN
MIN MAX
BLEED
0
2040
60
80
100
C
DUCT TEMP
OFF
PACKS
F/A
CABIN FLT COMP
CABIN
GAUGE
CAB
DUCT
F/C
DUCT
F/C FAN
OFF
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"Temperature control"
Temperature is controlled within the air conditioning system by mixing hot engine
bleed air with cold ACM discharge air.
Electrically-operated butterfly valves control the amount of hot air added to the
cold ACM discharge air.
Hot bleed air
Expansion turbine
Compressor
Air cycle machine
Cooling air
Primary heat
exchanger
Cold ACM air
Butterfly valve
ACM butterfly valvePack bypass
butterfly valve
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Dual valve systems can vary the ratio of airflow between the ACM and uncooled
air. The result is a temperature-controlled air conditioning pack.
Each pack consists of ACM, heat exchangers, ducting and control valves.
Each pack feeds into a common mixing chamber from where ducts route the
conditioned air into the cabin and cockpit air supplies.
The temperature of individual ducts may be controlled by adding or restricting
additional hot air using trim valves.
Each pack consists of ACM, heat exchangers, ducting and control valves.
Temperature control panels are typically located in the cockpit with sub panels at
flight attendant stations.
COMPRESSOR
EXPANSION TURBINE
AIR CYCLE MACHINE
GROUND AIR
CONDITIONER
CONNECTION
MIX CHAMBER
TEMPERATURE
CONTROL VALVE
ANTI-ICE
THERMOSTAT
AFT PRESSURE
BULKHEAD
WATER SEPERATOR
WATER SEPERATOR TEMPERATURE
CONTROL VALVE
MANUAL
CROSSFEED
VALVE FLOW CONTROL VALVE
PRESSURE REGULATION
& SHUTOFF VALVE
8TH STAGE BLEED
CHECK VALVE
ANTI-ICING
PRESSURE
REGULATION
VALVE
13TH STAGE
AUGMENTATION VALVE
GROUND PNEUMATIC
CONNECTION
PRIMARY HEAT
EXCHANGER
SECONDARY HEAT
EXCHANGER
APU LOAD
CONTROL VALVE
COOLING AIR
SELECTOR VALVE
GROUND
COOLING FAN
FROM R.H. ENGINE
SONIC VENTURI
RAM AIR VALVE
RAM
AIR
FROM L.H. ENGINE
Ducting and
control valves
Ducting and
control valves
Heat exchanger
Air cycle machine
Heat exchanger
Air cycle machinePack 1
Pack 2
AIR CONDITIONING
TEMP
CONTROL
OFF
RECIRC
CABIN
OFF
RECIRC
F/C FAN1 BLEED 2
COOL WARM COOL WARM
NORM
AUTO
MAN
MIN MAX
BLEED
0
2040
60
80
100
C
DUCT TEMP
OFF
PACKS
F/ACABIN FLT COMP
CABIN
GAUGE
CAB
DUCT
F/C
DUCT
F/CFAN
OFF
CABIN TEMP LIGHTING NVS SYSTEM
CABIN
OVERHD
PSU
TEST
O N/ OF F P AU SE
CABIN
SIDEWALL
PSU
ON/OFF
LAVATORY
WARDROBE AIRSTAIR
DOOR
BUFFET
OVERHD
OFF PAUSE
FAULT DEGRADED
Cockpit
Flight attendant
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"Humidity control"
If a given amount of air is cooled the relative humidity increases in relation to the
temperature decrease.
In an air conditioning system this would lead to condensation in the packs and
ducts.
To reduce the humidity in the system condensers can be incorporated in the pack
downstream of the heat exchangers.
DUCT TEMP
SENSORDUCT O TEMP
SWITCH
TO FLIGHT COMPARTMENTCOMPRESSORDISCHARGEOVERTEMPERATURESWITCH
DUCT TEMPSENSING BULB
BLEED AIR
SILENCERS
TEMPERATURETRIM VALVES
PACK TEMPERATURECONTROL VALVES
RAM AIROVERBOARD
HEATEXCHANGERFILTER
WATER
NOZZLE
RAM AIRSILENCER
TC
WATER
TRAPRECIRCULATIONAIR FAN
GROUND AIR
SERVICE
CONNECTOR
(S.O.O. 8069)
AIR CYCLE
MACHINE (ACM)
MIXING
BOX
CONDENSER
RAM AIR
BAFFLE
REFER TO TEMPERATURE CONTROLDESCRIPTION AND OPERATION
COMP
TURB
PLENUM
FAN
EXHAUST
PACK
BYPASS VALVE
TURBINE
BYPASS VALVE
BLEED AIR
FROM No.1
AND No.2
NACELLES
RAMSCOOP
LEFT WING REFRIGERATION PACK
CHECK
VALVE
WATER SEPARATOR
Alternately water
separators may be
installed as stand-alone
units downstream of the
ACM.
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Pressurisation
"Aircraft pressurization systems"
High altitude is a hostile environment in which the human body cannot survive
without a great deal of help.
However, it is the ideal environment for long distance flight.
Turbine engines operate efficiently and the lower density of the air decreases
drag. The humidity at high altitudes is low, so weather conditions are excellent
most of the time.
Trial flights flown in the 1930's with pilots wearing pressurized suits proved the
existence of strong high altitude winds today called jet streams.The first pressurized airplane flew in 1936. A special version of the Lockheed
Model 10 Electra with turbocharged engines had a fully pressurized cabin and
was able to make flights to an altitude of 25,000ft maintaining a cabin altitude of
10,000 ft or less.
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"Principles of pressurization"
Aircraft are pressurized by sealing off a strengthened portion of the fuselage
called the pressure vessel and pumping air into it.
The cabin pressure is controlled by one or more outflow valves, usually located at
the rear of the pressure vessel.
The opening of these valves is controlled by the cabin pressure controller whichregulates the amount of air allowed to leave the cabin in order to achieve and
maintain a desired differential pressure or cabin altitude.
-1
0
1
2
34 5
6
7
8
9
101000 ft
CAB ALT
CABINE ALTITUDE
NORM
AUTO
DUMP
CABSETBARALT
M
A
N
INCR
RATE
Control panel
Outflow
valve
Outflow
valve
Cabin pressure
controller
Air conditioning pack
CABIN AIR
FLT COMPT AIR
FLT COMPT CabinBaggage
compartment
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"Modes of pressurization"
There are three modes of pressurization:
- the unpressurized mode,
- the isobaric mode and
- the constant differential mode.
"Unpressurized mode"
In the unpressurized mode the cabin altitude is always the same as the flight
altitude. The outflow valve remains fully open and the cabin pressure is the same
as the ambient air pressure.
100020003000400050006000
10000
15000
20000
Sea level
02
ALT
4
6
81012
14
FT x1000
20
302
1
0
RATEFPM x1000
2
1UP
DOWN
01
2
34
5
6
DIFF PSI
CABIN
tail section
(unpressurized)Cabin
(Pressure Vessel)
Outflow Valve
fully open
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"Isobaric mode"
In the isobaric mode the cabin altitude always remains constant.
The cabin pressure is maintained at a specific cabin altitude as the flight altitude
changes.
The cabin pressure controller begins to close the outflow valve at a selected
cabin altitude.
The outflow valve closes and opens or modulates to maintain the selected cabin
altitude up to the flight altitude that produces the maximum differential pressure
for which the aircraft structure is rated.
100020003000400050006000
10000
15000
20000
Isobaric Mode
Sea level
02
ALT
4
6
81012
14
FT x1000
20
302
1
0
RATEFPM x1000
2
1UP
DOWN
01
2
34
5
6
DIFF PSI
CABIN
tail section
(unpressurized)Cabin
(Pressure Vessel)
Outflow Valve
closed
Max Differential Pressure
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"Constant-differential mode"
In the constant-differential mode the cabin pressure is maintained a constant
amount above that of the outside air pressure.
Cabin pressurization puts the structure of an aircraft fuselage under a tensile
stress as the pressure inside the pressure vessel tries to expand it.
The cabin differential pressure expressed in "psid" is the difference between the
internal and external air pressure and is a measure of the stress on the fuselage.
When the cabin differential pressure reaches the maximum for which the aircraft
structure is designed the cabin pressure controller automatically shifts to the
constant-differential mode and allows the cabin altitude to increase, but maintains
the maximum allowable pressure differential.
100020003000400050006000
10000
15000
20000
Sea level
02
ALT
4
6
81012
14
FT x1000
20
302
1
0
RATEFPM x1000
2
1UP
DOWN
01
2
34
5
6
DIFF PSI
CABIN
Diff Pressure Constant
Diff Pressure Build Up