Bleed Air Systems - Pneumatics - Airframes & Aircraft Systems #38
Summary
TLDRThis lesson delves into the bleed air systems of modern jet airliners, which are crucial for air conditioning, pressurization, and powering various aircraft components. The system draws air from engine compressors, with backup from the Auxiliary Power Unit (APU) and ground carts. It's designed to handle pressure variations across different engine speeds, using both low-pressure (LP) and high-pressure (HP) air. The air is cooled and regulated to maintain optimal temperature and pressure for various uses. Safety features include duplication of critical components, isolation valves for engine independence, and monitors to prevent over-temperature and over-pressure. The lesson highlights the system's redundancy and safety measures to ensure flight safety.
Takeaways
- 🚀 Modern jet airliners utilize high-volume, low-pressure air systems for various purposes including air conditioning, pressurization, ice protection, and engine starting.
- ✈️ Bleed air, sourced from engine compressors, is the primary supply for these systems, with auxiliary power unit (APU) and ground air supply carts as backups.
- 🔥 The engine bleed air system comprises the engine compressor as the power source, and control devices to regulate temperature and pressure.
- 🔧 The system must maintain a reasonable air supply at low RPM and restrict excessive pressure at high RPM, often by drawing air from two compressor stages.
- 🔄 High-pressure (HP) air is controlled by a pressure-sensitive, pneumatically operated high-pressure shutoff valve (HP SOV) to ensure adequate flow.
- 🌡️ Bleed air from the compressor is too hot for direct use, so it passes through a pre-cooler where engine fan air cools it down to around 175 degrees Celsius.
- 💧 Engine bleed air control valves manage the flow into the pneumatic system, modulating to maintain a maximum duct pressure of approximately 55 psi.
- 🔒 Regulatory requirements mandate that any single component failure in cabin air conditioning or pressurization systems must not compromise safety, leading to system duplications.
- 🛠️ Multi-engine aircraft keep engine supplies separate, with isolation valves that can be opened if one engine supply fails to ensure continued operation.
- ⚠️ The system is equipped with safety measures such as temperature and pressure monitors, with automatic closure of bleed air valves in case of excessive conditions.
- 🔄 In the event of faults, pilots can restore system functionality by opening isolation valves to allow air from one engine to operate the entire system.
Q & A
What is the primary source of air for the high volume low pressure air systems in modern jet airliners?
-The primary source of air for these systems is bleed air from the engine compressors.
What is the role of the Auxiliary Power Unit (APU) in the bleed air system?
-The APU serves as a backup for the bleed air system, providing air when needed.
How does the bleed air system contribute to the aircraft's air conditioning and pressurization?
-The bleed air system is used for air conditioning and pressurization by supplying conditioned air to the cabin.
What are the different uses of bleed air mentioned in the script?
-Bleed air is used for ice protection, engine starting, driving hydraulic pumps, operating air-driven flaps and slats, pressurizing hydraulic reservoirs, potable water tanks, and cargo compartment heating.
How does the bleed air system maintain a reasonable supply of air during varying engine speeds?
-The system takes air from two compressor stages to maintain a reasonable pressure band at all engine speeds.
What is the function of the high-pressure shutoff valve (HP SOV) in the bleed air system?
-The HP SOV is pressure-sensitive and pneumatically operated, opening when there is insufficient air pressure from the LP system to maintain the required flow.
How is the temperature of the bleed air controlled in the system?
-The air from the compressor is passed through a pre-cooler, and a valve modulates the amount of fan air passing through the cooler to control the temperature of the bleed air.
What is the purpose of the engine bleed air control valves?
-These valves control the flow of bleed air into the pneumatic system manifold and are controlled electrically by switches on the flight deck.
Why is it a regulatory requirement to duplicate certain components in aircraft cabin air conditioning or pressurization systems?
-Duplicating components ensures that the failure of any single element does not jeopardize the safety of the aircraft or its occupants.
What happens if there is a failure in the bleed air system that could cause excessive temperature or pressure?
-If the temperature or pressure becomes excessive, the bleed air valve will automatically close, and a warning light in the cockpit will come on.
How can a pilot restore the bleed air system in the event of a fault?
-The pilot can restore the system by opening the isolation valve, allowing air from one engine to operate the entire system.
Outlines
🛫 High-Volume Low-Pressure Air Systems in Jet Airliners
This paragraph discusses the bleed air systems in modern jet airliners, which are primarily supplied by air from engine compressors and can be supplemented by the Auxiliary Power Unit (APU) or external air supply carts. The bleed air is utilized for various purposes including air conditioning, pressurization, ice protection, and powering air turbine motors for engine starting and hydraulic pumps. The system is designed to maintain a consistent pressure and temperature, with air taken from different compressor stages to manage pressure variations. The paragraph also explains the operation of high-pressure shutoff valves and non-return valves, as well as the use of pre-coolers to regulate the temperature of the bleed air. The bleed air control valves are electrically controlled and are designed to maintain a maximum duct pressure. The system is also equipped with safety features to handle over-temperature and over-pressure situations, ensuring the safety of the aircraft and its occupants.
🔧 Bleed Air System Safety and Backup Mechanisms
The second paragraph delves into the safety and backup mechanisms of the bleed air system. It explains the regulatory requirement for duplicating critical components in aircraft systems to ensure safety. The system is designed such that each engine supplies its own services, with isolation valves that can be opened in case one engine supply fails. The paragraph also discusses the use of a two-pointer duct pressure gauge to monitor pressure in both left and right ducts, and the presence of engine bleed air valve position indicators. It highlights the system's ability to automatically close the bleed air valve in response to excessive temperature or pressure, activating warning lights in the cockpit. In case of faults, pilots can restore the system by opening the isolation valve. The paragraph concludes by mentioning the role of the Auxiliary Power Unit and external air connections in supplying air to the bleed air manifold, and the temperature monitors that prevent damage from excessive temperatures due to leaks.
Mindmap
Keywords
💡Bleed Air
💡Auxiliary Power Unit (APU)
💡Pressurization
💡Ice Protection
💡Air Turbine Motors
💡Hydraulic Reservoirs
💡High-Pressure Shutoff Valve (HP SOV)
💡Pre-cooler
💡Non-Return Valve (NRV)
💡Isolation Valve
💡Duct Pressure Gauge
Highlights
Modern jet airliners use high-volume low-pressure air systems supplied by engine compressors or auxiliary power units.
Bleed air is utilized for air conditioning, pressurization, ice protection, and powering various aircraft systems.
The engine bleed air system includes the engine compressor, control devices, and temperature and pressure regulation mechanisms.
Air from different compressor stages is used to maintain a reasonable pressure band at all engine speeds.
The high-pressure shutoff valve (HP SOV) controls the high-pressure source and is pressure-sensitive and pneumatically operated.
The non-return valve (NRV) shuts off the low-pressure (LP) supply when the HP SOV is open.
As engine speed increases, the LP air pressure rises, eventually closing the HP shutoff valve.
Bleed air from the compressor is too hot for direct use and must pass through a pre-cooler.
A cooling matrix with engine fan air as the cooling medium is used to reduce the temperature of the bleed air.
Engine bleed air control valves are controlled electrically and act as pressure regulators for the pneumatic system.
A regulatory requirement ensures that any single component failure in cabin systems does not compromise safety.
Multi-engine aircraft keep supplying engines or sides separate, with each engine supplying its own user services.
Isolation valves can be opened to feed other side services if an engine supply is lost.
The system is equipped with a two-pointer duct pressure gauge to monitor pressure in both left and right ducts.
Excessive temperature or pressure in the system triggers automatic closure of the bleed air valve and a warning light.
Pilots can restore the system by opening the isolation valve in case of faults.
Temperature monitors are mounted along the bleed air manifold to detect leaks and prevent damage.
The auxiliary power unit air is fed into the left duct, and the isolation valve must be open to supply all services.
External air connections feed air into the right duct, requiring the isolation valve to be open for full service supply.
Transcripts
in this lesson we will discuss the high
volume low pressure air systems used by
modern jet airliners
the system is normally supplied with
bleed air from the engine compressors
this can be backed up with air from the
auxiliary power unit APU
ground by external air supply carts
this air is used for air conditioning
and pressurization
ice protection
and is a power source for the air
turbine motors used for engine starting
driving hydraulic pumps and air driven
flaps and slats
it is also used for pressurizing
hydraulic reservoirs and potable water
tanks
and for cargo compartment heating
the engine bleed air system consists of
the power source the engine compressor
and control devices the temperature and
pressure regulation during operation
because of the great variation of air
output pressure from a gas turbine
engine between idle and maximum rpm
there is a need to maintain a reasonable
supply of air during low rpm as well as
restricting excessive pressure when the
engine is at high rpm
this is usually done by taking air from
two compressor stages to maintain a
reasonable pressure band at all engine
speeds
here we show a typical bleed air system
low pressure LP air is taken from an
early compressor stage
and high-pressure HP air is taken from a
later stage
you
the high-pressure source is controlled
by the high-pressure shutoff valve HP
sov this valve is pressure sensitive and
pneumatically operated it is open when
there is insufficient air pressure from
the LP system to maintain the required
flow
when this valve is open HP pressure will
close the non-return valve NRV shutting
off the LP supply
as the engine speeds up the LP air
pressure will increase until it closes
the high-pressure shutoff valve so that
in most stages of flight bleed air will
come from the LP stage
the air from the compressor is too hot
for its required purpose so it is passed
through a pre-cooler in order to reduce
its temperature
this usually takes the form of a cooling
matrix with engine fan air being used as
the cooling medium
valve modulates to vary the amount of
fan air passing through the cooler and
thus control the temperature of the
bleed air at a predetermined level
usually about 175 degrees Celsius
the engine bleed air control valves
control the flow of bleed air into the
pneumatic system manifold
they are controlled electrically by
switches on the flight deck
when selected open the bleed air valve
acts as a pressure regulator the valve
position is automatically modulated to
maintain a maximum duct pressure of
approximately 55 pounds per square inch
if the output pressure is below this the
valve will be fully open
some aircraft have separate bleed air
and pressure regulating valves
however they function in the same manner
as the combined valve
it is a regulatory requirement that any
single component in an aircraft's cabin
air conditioning or pressurization
systems the failure of which could
jeopardize the safety of the aircraft or
the people in it must be duplicated
to this end most multi-engine aircraft
keep the supplying engines or sides
separate with each engine supplying its
own user services
these are kept independent by isolation
valves which are normally closed but
which may be opened if an engine supply
is lost to feed the other side services
the system is fitted with a two-pointer
duct pressure gage one pointer displays
the pressure in the left duct and the
other the right
some systems have engine bleed air valve
position indicators however in the
system shown here the valve position is
shown by the switch position unless a
warning light is indicating a problem
if the temperature of the air downstream
of the bleed air valve becomes excessive
the valve will automatically close
a warning light in the cockpit which is
monitoring the system for both excessive
temperature and pressure will come on
excessive pressure in the system can be
caused by failure of the high pressure
shutoff valve to close when required a
pressure sensor monitors duct pressure
upstream of the bleed air valve in the
event of excessive pressure the bleed
air valve will once again automatically
close and the warning light will come on
in the event of either of these faults
the pilot can restore the system by
opening the isolation valve allowing the
air from one engine to operate the
entire system
the air in the bleed air manifold is hot
in excess of 180 degrees Celsius so any
air leaking from the manifold could
cause a great deal of damage
there are temperature monitors mounted
adjacent to the manifold all along its
length
if any of these monitors senses an
excessive temperature caused by a bleed
air leak the wing duct overheat light
for the affected side will illuminate
the pilot can isolate the leaking area
by closing the appropriate bleed valve
and ensuring that the isolation valve is
closed
in the system shown here the auxiliary
power unit air is fed into the left duct
so in order for it to supply all
services the isolation valve has to be
opened
similarly the external air connection
feeds air from an external source into
the right duct so again the isolation
valve needs to be open for it to supply
air to all of the services
that is the end of the lesson in this
lesson you have learned that most modern
gas turbine engine aircraft have a bleed
air system supplied with air tapped from
the engines compressors
the air is used by a number of systems
as shown here
the air supply is backed up by the
auxiliary power unit and on the ground
by external air supply carts
the system is duplicated
tected from over temperature and
overpressure
you
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