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.

Test your knowledge on aircraft maintenance with questions 68 and 69. Identify the correct positions and scenarios related to relief valves and cabin pressure air leaks. No explanations provided for the answers.