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Welcome to Aero Guide!
In this video, we take an in-depth look into Aircraft Pneumatic Systems — how they work, where they’re used, and how they compare with hydraulic systems.
From high-pressure systems used in older aircraft like the Fokker F27, to modern medium- and low-pressure pneumatic systems, this lesson breaks down every component and operating principle in a clear, animated format.
You’ll learn about:
🧩 How pneumatic systems use air instead of hydraulic fluid to transmit power
⚙️ The functions of air bottles, valves, compressors, restrictors, and filters
🔧 Key components such as control valves, check valves, and moisture separators
🧠 How pneudraulic systems combine pneumatic and hydraulic pressure
✈️ Real-world uses in brake systems, door actuation, engine starting, deicing, and emergency backup systems
Pneumatic systems remain a vital part of aviation because they’re lightweight, reliable, and simple, even in an age dominated by hydraulics.
Whether you’re a student, trainee technician, or aviation enthusiast, this video provides the foundation you need to understand aircraft air systems.
#aircraftsystems #aviationeducation #aerospaceengineering #pilottraining #flightschool #airframe
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✈️ Aircraft Maintenance Study Resources
Download professionally prepared, fillable & printable PDF question papers designed for:
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0:03
Welcome to Arrow Guide. In this video,
0:06
we'll take a deep look into aircraft
0:08
pneumatic systems. How they work, where
0:10
they're used, and how they compare with
0:12
hydraulic systems. From high-pressure
0:14
systems used in older aircraft like the
0:16
Fauler F-27 to modern medium, and low
0:20
pressure pneumatic systems, we'll
0:22
explore every detail step by step.
0:26
In the past, some aircraft manufacturers
0:28
equipped their aircraft with
0:30
high-pressure pneumatic systems
0:32
operating at around 3,000 psi. One of
0:35
the last aircraft to use such a system
0:37
was the Fauler F27.
0:40
These pneumatic systems operate a lot
0:42
like hydraulic systems, except they use
0:44
air instead of hydraulic fluid to
0:46
transmit power. Pneumatic systems are
0:48
commonly used for aircraft brakes,
0:51
opening and closing doors, driving
0:53
hydraulic pumps, alternators, starters,
0:56
and water injection pumps, and even
0:58
operating emergency devices.
1:01
Both pneumatic and hydraulic systems use
1:04
confined fluids to transmit power.
1:06
Confined simply means the fluid is
1:08
trapped or completely enclosed inside
1:11
the system. The term fluid refers to any
1:14
substance that flows. This includes
1:16
liquids like water and oil and gases
1:19
like air.
1:21
However, there's a key difference
1:22
between them. Liquids are almost
1:24
incompressible. No matter how much
1:26
pressure you apply, a cord of water
1:28
still takes up roughly a quart of space.
1:31
Gases, on the other hand, are highly
1:33
compressible. A cord of air can be
1:35
squeezed into a space as small as a
1:38
thimble. Despite this difference, both
1:40
gases and liquids can be confined and
1:42
made to transmit power efficiently.
1:46
In high-pressure systems, air is stored
1:48
in metal bottles at pressures ranging
1:50
from 1,000 to 3,000 psi depending on the
1:54
system design. These bottles usually
1:56
have two valves. A charging valve where
1:58
a ground operated compressor can be
2:00
connected to add air to the bottle. A
2:03
control valve which acts as a shutff
2:05
valve trapping the air inside until it's
2:07
needed. Although the bottles are
2:09
lightweight, high-pressure systems have
2:11
one main disadvantage. They cannot be
2:14
recharged during flight. That means the
2:16
operation is limited to the amount of
2:18
air in the bottle. So these systems are
2:20
typically reserved for emergency
2:22
functions like extending landing gear or
2:24
applying brakes if the main system
2:26
fails. However, some aircraft include
2:29
air compressors to recharge the bottles
2:31
in flight, extending their usefulness.
2:35
Pneumatic systems share some
2:36
similarities with hydraulics, but not
2:38
all components are the same. They
2:40
usually do not have reservoirs,
2:42
accumulators, or engine-driven pumps
2:44
like hydraulic systems do. Still, they
2:47
have their own unique components to
2:49
regulate and control air flow. Let's
2:51
look at the major ones.
2:53
Some aircraft are equipped with
2:55
permanently installed air compressors to
2:57
recharge air bottles automatically.
3:00
Compressors may have two or three stages
3:02
of compression depending on the pressure
3:04
requirements of the system. Relief
3:07
valves protect the system from excessive
3:09
pressure. They act as safety devices
3:12
preventing high pressures from bursting
3:14
lines or damaging seals.
3:16
Control valves are essential components
3:18
in pneumatic systems used to manage the
3:21
direction and flow of compressed air.
3:23
The example shown here illustrates how a
3:25
control valve operates in emergency air
3:28
brake system. The valve consists of a
3:30
three port housing, two puppet valves,
3:32
and a control lever with two loes. When
3:35
the valve is in the off position, a
3:37
spring keeps the left poet closed,
3:40
preventing compressed air from flowing
3:42
from the pressure port to the brakes.
3:44
When the lever is moved to the on
3:45
position, one lobe of the lever opens
3:48
the left poet while a spring closes the
3:50
right puppet. This allows compressed air
3:53
to pass through the valve body and into
3:55
the brake port, applying the brakes. To
3:58
release the brakes, the control valve is
4:00
moved back to the off position. The left
4:02
poet closes, stopping the flow of
4:05
high-pressure air, while the right poet
4:07
opens, venting the brake line to the
4:09
atmosphere.
4:11
Check valves are used in both hydraulic
4:13
and pneumatic systems to control the
4:15
direction of flow. When air enters from
4:17
the left port, it pushes against a light
4:20
spring, forcing the valve open and
4:22
allowing air to flow through to the
4:24
right port. However, if air tries to
4:26
enter from the right, the internal
4:28
pressure pushes the valve closed,
4:30
blocking reverse flow. In short, a
4:32
pneumatic check valve allows air to flow
4:35
in only one direction, making it a
4:37
one-way control valve that prevents
4:39
backflow in the system. Restrictors are
4:42
a type of control valve used in
4:44
pneumatic systems to regulate air flow.
4:47
A simple orifice type restrictor has a
4:49
large inlet port and a small outlet
4:51
port. The smaller outlet limits the air
4:54
flow which in turn reduces the speed of
4:56
the connected actuating unit. A variable
4:59
roostrictor on the other hand allows
5:01
adjustable control of air flow. It uses
5:04
a needle valve threaded at the top and
5:06
pointed at the lower end. By turning the
5:08
needle, the operator moves the point
5:10
into or out of a small opening, changing
5:13
its size. Since all incoming air must
5:16
pass through this opening, the needle
5:17
position directly controls the airflow
5:20
rate and thus the operating speed of the
5:22
system.
5:24
Filters protect pneumatic systems from
5:26
dirt and contaminants that could damage
5:28
components or restrict air flow. A
5:31
common type is the micronic filter,
5:33
which includes a housing with two ports,
5:35
a replaceable cartridge, and a relief
5:37
valve. Air enters through the inlet,
5:40
circulates around the cellulose
5:41
cartridge, then passes through its
5:43
center to the outlet port. If the
5:45
cartridge becomes clogged, pressure
5:47
builds up, forcing the relief valve to
5:50
open and allowing unfiltered air to
5:52
bypass temporarily. Another type is the
5:55
screen type filter, which uses a
5:57
permanent wire screen instead of a
5:59
replaceable cartridge. It includes a
6:01
cleaning handle that extends through the
6:03
housing top. Rotating the handle scrapes
6:05
dirt off the screen, restoring air flow
6:08
without removing the filter.
6:11
After compression, air can carry
6:13
moisture which may freeze or corrode
6:15
components. That's why a moisture
6:17
separator is placed downstream of the
6:19
compressor. It removes water vapor using
6:21
a reservoir, dump valve, check valve,
6:24
and sometimes a relief valve. After air
6:27
leaves the moisture separator, about 98%
6:30
of water has already been removed. To
6:33
eliminate the remaining traces of
6:35
moisture, the air passes through a
6:37
chemical dryer, also known as a desicant
6:39
dryer. This unit has a tubular housing
6:42
with inlet and outlet ports and contains
6:44
a replaceable desicant cartridge. The
6:47
cartridge is filled with a dehydrating
6:49
agent and fitted with bronze filters at
6:51
each end. Any moisture not removed by
6:54
the separator is absorbed by the
6:55
desicant material, ensuring the air is
6:58
completely dry before it reaches the
7:00
rest of the system.
7:02
Many aircraft include a high-pressure
7:04
pneumatic backup system to operate the
7:06
landing gear or brakes if the main
7:08
hydraulic system fails. In these
7:11
systems, nitrogen pressure doesn't
7:13
directly move the actuators. Instead,
7:16
it's used to push hydraulic fluid to
7:18
them. This combination of pneumatic and
7:20
hydraulic operation is known as
7:22
hydraulics. Nitrogen for the emergency
7:24
landing gear extension is stored in two
7:27
bottles, one on each side of the nose
7:29
wheel well. When the outlet valve is
7:31
opened, nitrogen is released into the
7:34
emergency system. Each bottle is
7:36
pressurized to about 3,100 PSI at 70° F,
7:41
enough for one full gear extension.
7:44
After use, maintenance personnel must
7:46
recharge the bottles.
7:49
The outlet valve is connected to a cable
7:51
and handle assembly labeled emergency
7:53
landing gear located on the co-pilot's
7:56
console. Pulling the handle fully upward
7:59
opens the outlet valve, releasing
8:01
nitrogen into the gear extension
8:03
circuit. Pushing it downward closes the
8:05
valve and vents the remaining nitrogen
8:07
overboard. A process that takes about 30
8:10
seconds.
8:12
During emergency gear extension,
8:14
compressed nitrogen flows to the landing
8:16
gear dump valve where hydraulic pressure
8:19
isolates the landing gear system from
8:21
the main hydraulics.
8:23
Medium pressure pneumatic systems,
8:25
typically operating between 50 and 150
8:28
PSI, do not usually include an air
8:31
bottle. Instead, they draw bleed air
8:34
from the compressor section of a turbine
8:36
engine. This bleed air is used for
8:38
engine starting, engine, and wing
8:40
deicing, and sometimes to power
8:42
hydraulic systems through an airdriven
8:44
hydraulic pump. It also serves to
8:46
pressurize hydraulic reservoirs in the
8:48
aircraft. Many aircraft equipped with
8:51
reciprocating engines use vein-type
8:53
pumps to supply low pressure air for
8:55
various pneumatic functions. These pumps
8:58
are typically engine-driven or powered
9:00
by electric motors depending on the
9:02
aircraft design. A vein type pump
9:04
consists of a cylindrical housing with
9:06
two ports, an inlet and a pressure
9:08
outlet and a drive shaft fitted with
9:10
sliding veins. The drive shaft is
9:13
mounted offc center within the housing.
9:15
So as it rotates, the veins create
9:17
chambers of varying sizes. When the
9:19
shaft turns, air enters the inlet port
9:22
into the largest chamber. As rotation
9:25
continues, the chamber becomes smaller,
9:27
compressing the trapped air. Once
9:29
compressed, the air is forced out
9:31
through the pressure port into the
9:33
pneumatic system. Because there are
9:35
multiple chambers operating in sequence,
9:37
the pump delivers a continuous flow of
9:39
air at pressures ranging from 1 to 10
9:41
psi. This steady low pressure air flow
9:44
is most commonly used to inflate and
9:47
operate pneumatic deicing boots on
9:49
aircraft wings and tail surfaces.
9:52
To summarize, pneumatic systems play a
9:55
vital role in aviation from powering
9:57
brakes and landing gear in emergencies
9:59
to operating deicing and starting
10:02
systems. Although hydraulic systems are
10:04
more common today, pneumatics remain
10:06
essential due to their simplicity,
10:08
reliability, and lightweight design.
10:11
Thanks for watching.
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