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Textbook Pneumatic – Pressurisation and Air 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 NO. 2 ENGINE LP TO DEICING SYSTEM AIR CONDITIONING OFF OFF RECIRC RECIRC CABIN 1 BLEED 2 F/C FAN NORM 40 20 °C 60 0 DUCT TEMP 80 100 MIN MAX BLEED CABIN CAB F/C DUCT DUCT OFF GAUGE F/C FAN OFF AUTO MAN COOL WARMPACKS COOL WARM TEMP F/A CABINCONTROL FLT COMP TO NO. 1 AIR- CONDITIONING PACK TO NO. 2 AIR- FROM NO. 1 ENGINE CONDITIONING BLEED-AIR SYSTEM PACK (SIMILAR TO NO. 2 SYSTEM) Pneumatic / Pressurisation / Air Conditioning Table of Contents: Air driven systems _____________________________________________________ 3 Pneumatic systems ____________________________________________________ 4 Air conditioning system _______________________________________________ 14 Pressurisation _______________________________________________________ 25 © Infowerk Page 2 Pneumatic / Pressurisation / Air Conditioning Air 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. Air Central Oil air filter seperator Heading indicator Oil Attitude Engine Oil indicator luprication Suction and cooling gage Turn and slip Vane-type Suction relief indicator vacuum pump valve Needle valve F - 27 Pneumatic Landing Gear / Brake System Sensing Line L.H. Nacelle R.H. Nacelle Main Alternate Storage Bottle Storage Bottle Isolating Valves Isolating Valves ROD Air Filter Pneumatic Panel Alternate Alternate Wheelbrake Landing Gear Nose Wheel Landing Gear Wheelbrake System Control System Steering Control System System © Infowerk Page 3 Pneumatic / Pressurisation / Air Conditioning 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. Propeller Wash Venturi Suction Pressure - reducing regulator needle valve L R 030 N 330 L 2Min.Turn R 2 MIN TURN Heading Attitude Turn und Slip indicator indicator indicator Air flows into the instrument Air filter cases through built-in filters to Heading Indicator spin the gyros. The likelihood of ice buildup and venturi blockage during Attitude IFR conditions limits the use of Indicator venturi systems to light VFR Venturi suction aircraft. Turn and slip Indicator Needle valve © Infowerk Page 4 Pneumatic / Pressurisation / Air Conditioning Modern aircraft equipped with pneumatic gyros use engine driven vane type pumps. Vane Type Air Pump Inlet Outlet Shaft Vane Case Rotor 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. Air Central Oil air filter seperator Heading indicator Oil Attitude Engine Oil indicator luprication Suction adn cooling gage Turn and slip Vane-type Suction relief indicator vacuum pump valve Needle valve © Infowerk Page 5 Pneumatic / Pressurisation / Air Conditioning 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 Vacuum Manifold check valve Vacuum regulator regulator Air Suction Air Pump gage Pump Attitude indicator Heading indicator Dry Vane-type vacuum pump Rotor and vanes are made from carbon compounds. Filter Wear generates a microscopic carbon deposit which acts as lubricant Twin Engine Pressure System Inline Inline Pressure Pressure Manifold check valve regulator filter filter regulator Inlet Inlet filter filter Air Pump Air Pump Gyro pressure gage Pilot´s gyros Copilot´s gyros © Infowerk Page 6 Pneumatic / Pressurisation / Air Conditioning “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. © Infowerk Page 7 Pneumatic / Pressurisation / Air Conditioning Some aircraft use independent cabin compressors driven by bleed air to increase the volume of air taken into the cabin. Flush air inlet Outside skin Compressor turbine Pressure vessel Outflow valve Bleed air Turboprop engine Compressor 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. Flush air inlet Outside skin Pressure vessel Jet pump Outflow valve Bleed air Turboprop engine Ambient Air Compressor Bleed Air To Cabin © Infowerk Page 8 Pneumatic / Pressurisation / Air Conditioning "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 APU’s are designed to operate in flight and can, if required, provide bleed air for pressurization and air- conditioning as a backup in emergencies. ECS ECS PACK PACK LH RH APU Pre-cooler Pressure regulator and relief valve Water seperator AIRFOIL DEICING © Infowerk Page 9 Pneumatic / Pressurisation / Air Conditioning "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. BAGGAGE FLT COMPT CABIN COMPARTMENT CABIN AIR FLT COMPT AIR CONDENCER MIXING BOX COMPRESSOR AIR CYCLE EXPANSION MACHINE (ACM) TURBINE Ground air service connector 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 © Infowerk Page 10 Pneumatic / Pressurisation / Air Conditioning "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. 155 FMS -38 SAT 88.2 CRZ 88.2 PACK 1 OVLD BSNB -12 TAT PACK 2 OVLD 3.5NM 88.2 88.2 PACK 1 OVHT 446 TAS PACK 2 OVHT 1 MIN RAM AIR VLV FAIL A A PACK 1 VLV FAIL PACK 2 VLV FAIL PACK 1 VLV CLSD 800 800 PACK 2 VLV CLSD N LUMEL BSNB 25 25 94.3 94.3 10 790KGH 790 KGH 1540KG 1540 KG TGT UP UP UP TX ECSOXY BLEED 0 PRESS TEMP 81 81 81 81 CABIN TEMP +28 °C 4000 CKPT TEMP +28 °C 1800 PSI 7.4 100 1 ECS M/P OFF RTN T/0 A/I FUEL HYD ELEC RNG MAINTENANCE MESSAGES 1/03 AIR COND 1 LEAKAGE 10/03 20:50 OCCUR:01 AIR COND 2 LEAKAGE 10/03 20:50 OCCUR:01 DIG TEMP CONTROL 1 FAIL 10/03 20:50 OCCUR:01 DIG TEMP CONTROL 2 FAIL 10/03 20:50 OCCUR:01 DUCT TEMP SENSOR 1 FAIL 10/03 20:50 OCCUR:01 DUCT TEMP SENSOR 2 FAIL 10/03 20:50 OCCUR:01 © Infowerk Page 11 Pneumatic / Pressurisation / Air Conditioning "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 NO. 2 ENGINE LP TO DEICING SYSTEM AIR CONDITIONING OFF OFF RECIRC RECIRC CABIN 1 BLEED 2 F/C FAN NORM 40 20 °C 60 0 DUCT TEMP 80 100 MIN MAX BLEED CABIN CAB F/C DUCT DUCT OFF GAUGE F/C FAN OFF AUTO MAN COOL WARMPACKS COOL WARM TEMP F/A CABINCONTROL FLT COMP TO NO. 1 AIR- CONDITIONING PACK TO NO. 2 AIR- FROM NO. 1 ENGINE CONDITIONING BLEED-AIR SYSTEM PACK (SIMILAR TO NO. 2 SYSTEM) © Infowerk Page 12 Pneumatic / Pressurisation / Air Conditioning 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 Quilted Fabric 1.00" Min Clearance Door Seal Side view of Quilted Fabric and Retainers Bleed air pressure reduced to 18 psi is used to inflate the door seal © Infowerk Page 13 Pneumatic / Pressurisation / Air Conditioning Air conditioning 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.
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