Hệ Thống Khí Nén (None: Pneumatic System)

What Is an Aircraft Pneumatic System?

The pneumatic system is a compressed air distribution network that provides motive power for multiple aircraft systems simultaneously. Unlike hydraulic systems that use liquid, pneumatic systems transmit energy through compressed gas — almost universally bleed air extracted from engine compressor stages on conventional aircraft — distributing it to the cabin, wings, engine nacelles, and system reservoirs.

How It Works

Bleed air taps are located at the intermediate and high-pressure compressor stages of turbofan engines. Depending on altitude and power setting, the system selects the most fuel-efficient stage. A Pressure Regulating and Shut-off Valve (PRSOV) reduces bleed pressure from up to 45 bar (650 psi) at the engine to the pneumatic distribution pressure of approximately 3–4 bar (44–58 psi). Pre-coolers cool this air using fan bypass flow before it enters the distribution manifold.

The APU provides an independent bleed source for ground operations and as an airborne backup. Cross-bleed valves allow one engine's bleed air to supplement or replace another's, enabling single-engine taxi and engine-start-from-bleed procedures.

The pneumatic system feeds directly into the Environmental Control System for cabin conditioning, into the Ice Protection System for wing and nacelle anti-icing, and into hydraulic reservoir pressurization circuits to prevent pump cavitation. Engine starting on most turbofans is accomplished by a starter/generator motor driven by pneumatic air, spinning the core to light-off RPM before fuel introduction.

Key Components

• Bleed Air Valves: Stage-selector and shutoff valves controlling airflow from each compressor tap.
• Pre-Coolers: Fan-air heat exchangers reducing bleed temperature from 200+ °C to manageable levels.
• Distribution Manifold: High-temperature ducting routing conditioned bleed air to consuming systems.
• Overheat Detection: Pneumatic duct leak detection loops (typically Kidde or Fenwal systems) monitoring for hot air leaks.
• Cross-Bleed Duct: Connects left and right pneumatic manifolds for redundancy and engine starting.

Aircraft Examples

• Boeing 737 NG/MAX: Conventional two-engine bleed system; pneumatics power ECS packs, wing anti-ice, and hydraulic reservoirs.
• Airbus A330: Two engine bleeds plus APU; pneumatic manifold runs the length of the fuselage at temperatures up to 230 °C (446 °F).
• Boeing 787-9: No conventional pneumatic system — the first large commercial jet to eliminate engine bleed air, replacing pneumatics with electric systems throughout.
• Airbus A350: Partially reduced bleed extraction compared to A330; retains pneumatic ECS but uses electric anti-icing on some surfaces.