Pneumatic / Vacuum
Bleed-air sources and distribution, its uses, leak detection, and vacuum systems.
Pneumatic / vacuum, summary notes
- The pneumatic (bleed-air) system taps hot, high-pressure air from the engine COMPRESSOR (at more than one stage, selected by valves for the pressure needed), supplemented by the APU load compressor and a ground air cart.
- Bleed air is pressure- and temperature-regulated and fed to a distribution manifold with ISOLATION valves so systems can be separated and one source can feed the whole aircraft if needed.
- USES include air conditioning and pressurisation, wing/engine ANTI-ICE, engine STARTING (the air-turbine starter), hydraulic reservoir and potable-water pressurisation, and (on some) hydraulic pump drive.
- A bleed-air LEAK is dangerous (hot, high-pressure air near structure/wiring) and is detected by OVERHEAT sensing loops that warn the crew to shut off the affected duct.
- Older/light aircraft use engine-driven VACUUM pumps to run air-driven gyros; suction is regulated and filtered.
- ⚠ Exam trap: pneumatic air is tapped from the engine COMPRESSOR (bleed), and feeds air conditioning, anti-ice, engine start and pressurisation; a bleed-air LEAK is detected by OVERHEAT detection loops, not smoke detectors.
Name four aircraft services supplied by engine bleed (pneumatic) air.
Engine bleed air commonly supplies: (1) air conditioning and cabin pressurisation (via the packs); (2) thermal anti-icing of the wing leading edges and engine cowls; (3) engine starting through the air-turbine starter; and (4) pressurisation of the hydraulic reservoirs and the potable-water system. It may also feed cargo heating and, on some types, drive hydraulic pumps.
Pneumatic / vacuum concept map
Pneumatic / Vacuum
Pneumatic / vacuum quiz
Pneumatic / Vacuum, quiz
1. In the system shown, air taken from the engine compressor passes through the unit before reaching the packs. That unit is the:
PrecoolerCompressorTurbine2. Pneumatic (bleed) air is tapped from the:
Engine compressorExhaustFuel tank3. Which is a use of bleed air?
Air conditioning, anti-ice and engine startCharging the batteryMeasuring airspeed4. A bleed-air leak is detected by:
Overheat sensing loopsSmoke detectorsFuel gauges5. Isolation valves in the pneumatic manifold allow:
Systems to be separated or one source to feed allFuel crossfeedGear retraction6. Bleed air is taken from more than one compressor stage to:
Provide the pressure needed at different power settingsCool the fuel by passing bleed air across the fuel oil heat exchanger before combustionAdd thrust, since air taken from the compressor is returned to the exhaust at higher velocity7. On the ground, pneumatic air can come from:
The APU or a ground air cartThe batteryThe RAT8. Bleed air also pressurises the:
Hydraulic reservoirs and potable waterFuel dump systemLanding gear tyres