AIRCRAFT AIR CONDITIONING AND

PRESSURISATION SYSTEMCahit Kutay Uysal

WHAT IS PRESSURISATION?

• Basically, pressurize means to increase the pressure of any specific area.• Most of the commercial aircrafts need to pressurization systems. Because,

the higher the altitude means the lower the air pressure. • The lower air pressure makes it more difficult for human to breathe normally. • This can cause several difficulties to the human body such as HYPOXIA,

TRAPPED GAS and DECOMPRESSION SICKNESS.

AIRCRAFT STRUCTURES

• If an aircraft is to be pressurised, the pressurised section must be strong enough to operational stresses

• In general, the maximum altitude at which an aircraft can fly is limited by the maximum allowable cabin differential pressure • Light aircraft – approx. 3-5 psi • Large reciprocating-engine aircraft – approx. 5.5 psi • Turbine-powered transport aircraft – approx. 9psi

AIR CONDITIONING SYSTEM

AIR CYCLE MACHINE

CONTROLLING THE CABIN PRESSURE AND SOURCES OF PRESSURISATION

- Pressurisation air from the compressor of the engine turbocharger- Hot air cooled by the intercooler- Discharge: Controlled and uncontrolled- Controlled; flows through outflow valve or safety valve- Uncontrolled; air that escapes around door and window seals, cables or other openings- Outflow valve; primary cabin pressure control, regulates the amount of pressurized air that is

allowed to exit the cabin- Safety valve (Positive pressure relief valve); will open in case of a malfunction in the

outflow valve- Dump valve; Releases all cabin pressure when aircraft lands - Negative pressure relief valve; Prevents cabin pressure from going below that of the ambient

air

MODES OF PRESSURISATION

- Unpressurised mode; cabin pressure is same with the atmosperic pressure

- Isobaric mode; the pressure in the cabin remains constant as the flight altitude changes

- The outflow valve is closed to maintain selected cabin altitude- The outflow valve modulates on flight altitude change

- Constant differential mode; the cabin pressure limited by a setted differential pressure value

THANK YOU FOR LISTENING

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