CHAPTER 11

OXYGEN COMPONENTS TEST STANDS

Learning Objective: Upon completion of this chapter, you will be able to identify, maintain, and perform periodic inspections on oxygen components

test stands.

Aircrew Survival Equipmentmen are responsible for shop testing aircraft oxygen system components, including regulators, emergency oxygen systems, and other items. The AME is responsible for checking system components in the aircraft; however, in case of a suspected malfunction and for periodic maintenance testing, the component is removed from the aircraft and brought to the oxygen shop where it is tested by the PR. This testing is accomplished with the use of various types of test equipment, some of which are discussed in this chapter.

OXYGEN

No one can live without sufficient quantities of food, water, and oxygen. Of the three, oxygen is by far the most urgently needed. If necessary, a well-nourished individual can go without food for many days or weeks, living on what is stored in the body. The need for water is more immediate, but still the need does not become critical for several days. The amount of oxygen in the body is limited at best to a few minutes supply. When that supply is exhausted, death is prompt and inevitable.

Oxygen starvation affects a pilot or aircrewman in much the same way that it affects an aircraft engine-neither can function without it. The engine requires oxygen for burning the fuel that keeps it going. An engine designed for lowaltitude operation loses power and performs poorly at high altitudes. High-altitude operation demands a means of supplying air at higher pressure to give the engine enough oxygen for the combustion of its fuel. The supercharger or compressor performs this function.

The combustion of fuel in the human body is the source of energy for everything the aviator is required to do with his muscles, with his eyes, and with his brain. As the aircraft climbs, the amount of oxygen per unit of volume of air decreases; therefore, the aviator's oxygen intake is reduced. Unless he/she breathes additional oxygen, the eyes, the brain, and the muscles begin to fail. The body is designed for lowaltitude operation and will not give satisfactory performance unless it is supplied the full amount of oxygen that it requires. Like the engine, the body requires a means of having this oxygen supplied to it in greater amounts or under greater pressure. This need is satisfied by the use of supplemental oxygen supplied directly to the respiratory system through an oxygen mask, by pressurizing the aircraft to an atmospheric pressure equivalent to that of safebreathing altitudes, or both.

For purposes of illustration, an aviator's lungs may be compared to a bottle of air. If an open bottle is placed in an aircraft at sea level, air escapes from it continuously as the aircraft ascends. The air pressure at 18,000 feet is only half the amount as that at sea level; therefore, at 18,000 feet the bottle is subjected to only half the atmospheric pressure it was subjected to at sea level. For this reason, it will contain only half the oxygen molecules it had when on the ground.

In like fashion, an aviator's lungs contain less and less air as he/she ascends, and correspondingly less oxygen. Thus, the use of supplemental oxygen is an absolute necessity on high-altitude flights. Above 35,000 feet, normal activity is possible up to about 43,000 feet by use of positive pressure equipment. This equipment consists of a "supercharger" arrangement by which the oxygen is supplied to the mask under a pressure slightly higher than that of the surrounding atmosphere. Upon inhalation, the

oxygen is forced into the lungs by the system pressure. Upon exhalation, the oxygen flow is shut off automatically so that carbon dioxide can be expelled from the mask. Normal activity is possible to 50,000 feet with the use of a pressure breathing oxygen regulator. Above 50,000 feet, the only adequate provision for the safety of the aviator is pressurization of the entire body.

Up to about 35,000 feet, an aviator can keep a sufficient concentration of oxygen in his/her lungs to permit normal activity by use of demand oxygen equipment, which supplies oxygen upon demand (inhalation). The oxygen received by the body on each inhalation is diluted with decreasing amounts of air up to about 30,000 feet. Above this altitude up to about 35,000 feet, this equipment provides 100-percent oxygen. At about 35,000 feet, inhalation alone will not provide enough oxygen with this equipment.