Valves Flashcards
What is the purpose of bleed air?
Cooling and lowering high temperatures of the internal parts of the engine which suffer from excessive heat.
Provides bleed air for anti-ice
Provides air for fuel heating
Air for airframe services
Cross-ship startups
Bleeds of air during start-up and spool up
Pressurises seals
What will happen if the engine bleeds air from the compressor?
Reduce engine power and increase exhaust temperature.
What happens to the bleed air valves in the event of an electrical failure?
The bleed valve will automatically close and ensure all air flows to the combustion chamber and provide the maximum airflow for cooling, combustion, and therefore power.
Where is bleed air normally taken from?
The rear of the high-pressure compressor
What are the characteristics of Bleed valves, Bands and Blow off valves?
Dumps air from rear HP stage Open at lower power and during start-up Does not meter airflow Either full opened or fully closed Prevents Stall
How is the bleed valve positioned in starting and during aggressive accelerations?
Open
Why is there a need for bleed valves?
Compressors can produce too much air at low speed and load up the turbine during acceleration hence the need to unload the compressor.
Operation of Bleed Valve
When the HP air is not sufficient the LP bypass forces a control diaphragm and valve close. Thus the LP air is enough to open the bleed valve. When HP increases to a set level the diaphragm lifts and ports HP air to the top of the bleed valve forcing it close, This will allow for all air to flow through the compressor to the combustion chamber.
What are bleed bands?
A steel strap wrapped around holes in the compressor casing. When at low speeds or during acceleration the band is loosened by releasing pressure from the pneumatic actuator.
