In a turbine engine, what is the primary purpose of the bleed valve?

• A. To vent compressor air to the atmosphere to maintain blade angle of attack and provide stall-free engine acceleration and deceleration
• B. To regulate engine oil pressure
• C. To control fuel flow to the engine
• D. To shut off airflow to the combustor during start

Answer: (A)

Bleed valves are used to vent a portion of compressor air to prevent compressor surge and stall, especially during rapid throttle changes. By bleeding air away from the compressor, the pressure ratio across the compressor isn’t driven too high relative to the air flow, which keeps the rotor blades operating with a stable, attached flow. This allows the engine to accelerate and decelerate smoothly without surge. The air bled off is usually dumped overboard or used for other systems, but its primary purpose here is to maintain compressor stability. It isn’t about oil pressure, fuel flow, or shutting off air to the combustor during start.