Cabin Atmosphere Control Systems

Question 1

Is there any special requirement as to the type of oxygen used in an aircraft system, and if so, what is it?

Answer 1

Only aviator’s breathing oxygen should be used.

Question 2

Describe the operating principle of a continuous-flow oxygen system.

Answer 2

High-pressure oxygen flows from the storage cylinder to a pressure regulator where its pressure is reduced and then to the mask outlets whenever the system is turned on.

Question 3

Describe the operating principle of a pressure-demand oxygen system.

Answer 3

Demand systems allow oxygen to flow from the cylinder to the regulator and then to the mask only when the user inhales. Pressure-demand systems provide oxygen to the mask at higher than atmospheric pressure when used at extremely high altitudes, forcing oxygen into the user’s lungs.

Question 4

What should be used to purge an oxygen system of moisture?

Answer 4

Oxygen, dry air, or dry nitrogen.

Question 5

What action must be taken when an oxygen system has been open to the atmosphere?

Answer 5

The system must be purged of any moisture.

Question 6

Describe the safety precautions that should be observed when servicing oxygen systems.

Answer 6

Avoid all contact with petroleum-based oil or grease, don’t smoke, keep everything very clean, service systems outdoors if at all possible, and keep the caps on the bottles to protect the valves.

Question 7

What is a Roots blower?

Answer 7

A type of engine-driven compressor.

Question 8

Name two different types of independent cabin air compressors?

Answer 8

Positive-displacement and centrifugal.

Question 9

What is the source of pressurization air in most jet aircraft?

Answer 9

Engine bleed air.

Question 10

What device provides the principle means of controlling cabin pressure?

Answer 10

The outflow valve.

Question 11

What unit regulates the position of an outflow valve?

Answer 11

The cabin pressure controller.

Question 12

Name several methods used on reciprocating-engine aircraft for providing heated cabin air.

Answer 12

Exhaust shroud heat exchangers, combustion heaters, and electric heaters.

Question 13

What is the function of the ventilating air in a combustion heater?

Answer 13

Ventilating air transports the heat from the heater into the cabin and prevents combustion gases from entering the cabin if the combustion chamber develops a crack.

Question 14

What are the sources of ventilating air in a combustion heater?

Answer 14

Ram air in flight, a blower on the ground, or possibly a compressor if the airplane is pressurized.

Question 15

Name the basic components of an air-cycle cooling system.

Answer 15

The compressor and expansion turbine, heat exchangers, and various valves.

Question 16

Describe the basic operating principles that allow an air-cycle system to produce cool air.

Answer 16

Hot engine bleed air is cooled in the primary heat exchanger, compressed, then cooled again in the secondary heat exchanger. This air is expanded across the turbine where energy is extracted and the pressure is reduced. This produces a large temperature drop.

Question 17

Describe the basic operating principles of a water separator.

Answer 17

Cool, moist air is swirled so that water droplets are separated by centrifugal force, captured by a sock, and drained.

Question 18

Name the principle components of a vapor-cycle system.

Answer 18

A compressor, condenser, expansion valve, and an evaporator.

Question 19

In what significant way is a vapor-cycle cooling system different from an air-cycle system?

Answer 19

Vapor-cycle systems use a refrigerant liquid, usually Freon®.

Question 20

Why is oil added to the refrigerant in a vapor-cycle air conditioning system?

Answer 20

To lubricate the compressor.