Pneumatic Aircraft Systems - As stated earlier, a medium pressure pneumatic system is used on modern wide-body commercial aircraft. Such aircraft are designed with a very sophisticated pneumatic system that ensures a pneumatic supply as a source of thermal energy and pressure energy to be used in/as:
1.6.2 Sources of supply: A medium pressure pneumatic system uses a pneumatic manifold system as shown in Figure 1.6 which is used in typical aircraft. Such systems can be pressurized from the following pneumatic sources:
Pneumatic Aircraft Systems
Engine Bleed Air: The pneumatic system of aircraft can take the engine bleed air as a primary source. This is the great advantage of having pressurized air from the engine without using an air compressor as a separate unit. The air is blown from convenient stages or stages and directed through appropriate ducts to the pneumatic system of the aircraft. See the examples in Figures 1.6 and 1.7.
Boeing 777 Interactive Aircraft Systems Diagram
Blowing air: Modern aircraft are usually equipped with an auxiliary power unit, which is nothing more than a small gas turbine engine. The APU is used as an alternate and emergency source of air supply for the pneumatic system if the aircraft engine fails or malfunctions.
Ground cart: Ground cart can only be used as a source of compressed air on the ground; when the aircraft engine or APU is not running. Air can be supplied from the ground source directly to the pneumatic ducts of the aircraft from where different systems, subsystems or components can be operated on the ground.
1.6.3 Pneumatic systems for air conditioning and deicing: Some large jet aircraft use compressor exhaust air from the engines to provide a relatively large volume of compressed air at low pressure to heat the leading edge of the wing and prevent the formation of ice, to provide air to start the engine, and to pressurize and control the temperature of the air in the aircraft cabin. Such systems are under pressure only when the engines are running. See the illustration in Figure 1.8.
Figure 1.8: Pneumatic system of a jet transport aircraft, which uses compressor exhaust air to operate the air conditioning and deicing control systems. Pneumatic systems are sometimes used for: • Brakes • Opening and closing doors • Operating hydraulic pumps, alternators, starters, water injection pumps, etc. • Operation of emergency equipment
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Liquids are practically incompressible; a quart of water still occupies about a quarter of the space no matter how hard it is compressed. Gases are highly compressible pneumatic system components that do not use reservoirs, hand pumps, accumulators, regulators or engine-driven or electrically powered power pumps to build normal pressure. But similarities exist in some components.
5 Air compressors On some aircraft, permanently installed air compressors have been added to recharge the air bottles when pressure is used to operate a unit. Relief valves Relief valves are used in pneumatic systems to prevent damage. They act as pressure limiting units and prevent excessive pressure from bursting lines and blowing out seals. Control Valves Control valves are also an essential part of a typical pneumatic system. Check Valves Check valves are used in both hydraulic and pneumatic systems.
6 Limiters Limiters are a type of control valve used in pneumatic systems. The small exhaust port reduces the air flow rate and the operating speed of a drive unit. Filters Pneumatic systems are protected from dirt by various types of filters. 1. Micron filter 2. Screen type filter
The moisture separator in a pneumatic system is always located downstream of the compressor. Its purpose is to remove any moisture caused by the compressor. A complete moisture separator consists of a reservoir, a pressure switch, a dump valve and a control valve. Chemical drying Chemical drying are incorporated into a pneumatic system at several points. Their purpose is to absorb any moisture that may collect in the lines and other parts of the system. Each dryer contains a cartridge that should be blue in color.
Atr 72/42 600 Interactive Aircraft Systems Diagrams
9 High Pressure System For high pressure systems, air is usually stored in metal bottles Pressure ranging from 1000 to 3000psi It has two valves Load valve and ground driven compressor
Pressure ranging from 100 to 150 psi Does not include air bottles. Draws air from the compressor section of the jet engine Low pressure system Pressure ranging from less than 100 psi Used in reciprocating aircraft types Driven by electric motors or engine aircraft
For this website to work, we record user data and share it with processors. To use this website, you must agree to our Privacy Policy, including the Cookie Policy. Some aircraft manufacturers have in the past equipped their aircraft with a high pressure (3,000 psi) pneumatic system. The last aircraft to use this type of system was the Fokker F27. Such systems work much like hydraulic systems, except that they use air instead of liquid to transmit power. Pneumatic systems are sometimes used for:
Both pneumatic and hydraulic systems are similar units and use limited fluids. The word confined means enclosed or completely enclosed. The word liquid implies liquids such as water, oil or anything that flows. Since both liquids and gases flow, they are considered liquids; however, there is a big difference in the characteristics of the two. Liquids are practically incompressible; a quart of water still occupies about a quarter of the space no matter how hard it is compressed. But gases are highly compressible; A liter of air can be compressed into a thimbleful of space. Despite this difference, gases and liquids are both fluids and can be confined and made to transmit energy. The type of unit used to supply compressed air to pneumatic systems is determined by the air pressure requirements of the system.
How It Works
High Pressure Systems For high pressure systems, air is usually stored in metal bottles at pressures ranging from 1,000 to 3,000 psi, depending on the specific system. [Figure 1] This type of air bottle has two valves, one of which is a loading valve. A ground-driven compressor can be connected to this valve to add air to the bottle. The other valve is a check valve. It acts as a shut-off valve that traps air in the bottle until the system is activated.
Although the high pressure storage cylinder is light in weight, it has a definite disadvantage. Since the system cannot be recharged in flight, operation is limited by the small supply of bottled air. Such an arrangement cannot be used for continuous operation of a system. Instead, the supply of bottled air is reserved for emergency operation of systems such as landing or brakes. However, the usefulness of this type of system increases if other air pressure units are added to the aircraft. [Figure 2]
Pneumatic system components Pneumatic systems are often compared to hydraulic systems, but such comparisons can only apply in general terms. Pneumatic systems do not use reservoirs, hand pumps, accumulators, regulators, or engine-driven or electrically powered pumps to build normal pressure. But similarities exist in some components.
Air compressors On some aircraft, permanently installed air compressors have been added to recharge the air bottles when pressure is used to operate a unit. For this purpose several types of compressors are used. Some have two stages of compression, while others have three, depending on the maximum working pressure desired.
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Relief valves Relief valves are used in pneumatic systems to prevent damage. They act as pressure limiting units and prevent excessive pressure from bursting lines and blowing out seals.
Control Valves Control valves are also an essential part of a typical pneumatic system. Figure 3 shows how a valve is used to control the emergency air brakes. The control valve consists of a three-port housing, two control valves, and a two-lobe control lever.
In Figure 3A, the control valve is shown in the off position. A spring holds the left valve closed so that compressed air entering the pressure port cannot flow to the brakes. In Figure 3B, the control valve is placed in the on position. One lobe of the lever holds the left poppet open, and a spring closes the right poppet. The compressed air now flows around the open left head, through a perforated passage, and into a chamber below the right bore. Since the right foot is closed, high pressure air exits the brake port and into the brake line to apply the brakes.
To release the brakes, the control valve returns to the off position. [Figure 3A] The left lip now closes, stopping the flow of high-pressure air to the brakes. At the same time, the right valve opens, allowing the compressed air in the brake line to exit the vent port and into the atmosphere.
Sources Of Power For Aircraft Gyroscopic Instruments
Check Valves Check valves are used in both hydraulic and pneumatic systems. Figure 4 shows a flap type pneumatic control valve. Air enters the left port of the check valve, compresses a light spring, forces the check valve to open, and releases the air from the right port. But as air enters from the right, the air pressure closes the valve, preventing air flow from the left port. So, a pneumatic control valve is a one-way flow control valve.
RestrictorsRestrictors are a type of control valve used in pneumatic systems. Figure 5 shows an aperture type restrictor with a
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