AIRCON + PRESSURISATION CONTD

Cabin Pressure and Air Conditioning Systems

• Inward relief valve is spring-loaded to the closed position.
• A cabin pressure air leak from the front of the fuselage is most undesirable because of the drag created.
• An exhaust heater is a type of heater that uses a muff or air ducting built around the engine exhaust system and directs air around the muffler.

Pressurization Systems

• Inward relief valves are interconnected in pressurized aircraft to allow controlled pressure during descent.
• Safety valves relieve at a specific pressure to prevent over-pressurization.
• The rate of change of cabin pressure is selected by the pilot and controlled by the pressure controller.
• Cabin differential pressure is the difference between cabin pressure and atmospheric pressure.
• If the ambient pressure is 2.9 PSI, the pressure inside the cabin at cruising altitude would be 11.4 PSI.

Air Conditioning Systems

• Before filling a vapor cycle cooling system, apply suction to remove air and moisture.
• Cabin differential is determined by the height at which the aircraft is flying and the selected cabin height.
• The rate of flow of air from the punkha louvers should not be less than 25 ft/min.
• An aircraft cabin is air-conditioned and pressurized to maintain human efficiency and comfort during flights at high altitudes.

Air Conditioning and Pressurization Controllers

• A cabin pressure controller maintains a particular cabin altitude by controlling the outflow valve position.
• A silencer is installed in a pressurization system to reduce the noise from the blowers and/or compressors.
• To avoid discomfort, the rate of change of pressure should be low, particularly during descent.

Vapor Cycle Cooling Systems

• In a vapor cycle cooling system, heat is removed from the charge air by changing a liquid into a vapor.
• An inward relief valve will operate when cabin pressure is lower than ambient pressure.
• If an aircraft is operating at 40,000 ft, the pressurization ensures that the equivalent height of the aircraft above sea level is maintained.

Additional Facts

• Cabin humidifiers are operated at high altitudes.

• Ditching control is used for closing all valves and inlets.

• The purpose of a mass flow controller is to ensure that a constant mass of air is delivered to the cabin at all times.

• Failure of the normal maximum differential pressure control is catered for by cabin safety relief valves.

• A turbo fan CAU used for air cycle cooling will decrease pressure and temperature of the charge air.

• The cabin differential pressure is the difference between cabin pressure and atmospheric pressure.

• The outflow of air from the cabin is regulated by the outflow valves.

• When air is pressurized, the oxygen content increases.

• Cabin pressure differential is the difference between cabin pressure and ambient pressure.

• In a 'bootstrap' cooling system, the supply of air is first compressed, then passed through a heat exchanger and across an expansion turbine.### Cabin Pressurization

• The cabin pressure is equivalent to an altitude of less than 10,000 ft.

• The pressure controller activates the cabin discharge valve.

Pressure Controller

• The pressure controller prevents pressure controller hunting by setting the flight altitude 500 ft higher than the actual flight altitude.

Cabin Rate of Climb

• The cabin rate of climb is shown on a specific indicator.

Water Separator

• A water separator is installed in a pressurization system to extract surplus water from the charge air.

Turbo-Fan Cold Air System

• After passing through the primary heat exchanger, the supply air flows to the fan.
• The heat exchanger in a turbo-fan system is cooled by ambient ram air.

Cabin Temperature

• The effective temperature of a cabin is determined by temperature and humidity.

Inward Relief Valve

• An inward relief valve is installed in a pressurization system to prevent a high negative differential pressure in the pressure hull of an aircraft.

Pressurization System

• The amount of compressed air delivered to the cabin is reasonably constant, regardless of altitude.

Vapour Cycle System

• When dissipating heat in a vapour cycle system, vapour converts to a liquid.