TYPES OF OXYGEN

Aviator's breathing oxygen (MIL-O-27210C) is supplied in two types (I and II). Type I is gaseous oxygen, and type 11 is LOX. Oxygen procured under the above specification is required to be 99.5 percent pure. The water vapor content must not be more than 0.02 milligram per liter when tested at 70F and at sea level pressure. This is practically bone dry.

Technical oxygen, both gaseous and liquid, is procured under specification BB-0-925. The moisture content of technical oxygen is not as rigidly controlled as that of breathing oxygen; therefore, the technical grade should never be used in aircraft oxygen systems.

The extremely low moisture content required of breathing oxygen is not to avoid physical injury to the body, but to ensure proper operation of the oxygen system. Air containing a high percentage of moisture can be breathed indefinitely without any serious ill effects. However, the moisture affects the aircraft oxygen system in the small orifices and passages in the regulator. Freezing temperatures can clog the system with ice and prevent oxygen from reaching the user. Therefore, extreme precautions must be taken to safeguard against the hazards of water vapor in oxygen systems.

OXYGEN COMPONENT TEST STAND 1172AS100

Regulator test stands are designed for testing oxygen regulators for flow capacities, oxygen concentrations, pressure characteristics, and various leakage tests at different simulated altitudes. There are several models of test stands capable of testing the oxygen regulators, converters, etc. We will cover only the ones that most oxygen shops throughout the Navy use. If you happen to work in an oxygen shop that is using outdated equipment, ask the petty officer in charge of the work center to show you the literature that covers that equipment. In this rate _{training manual,} we will discuss only the 1172AS100 test stand used for testing oxygen regulators.

The Oxygen System Components Test Stand, Model 1172AS100, tests and evaluates miniature oxygen breathing regulators as well as panel and console mounted oxygen breathing regulators. (See figure 11-1.)

Oxygen system components test stands are supplied by more than one manufacturer. The operation, maintenance, and parts are, with a few minor exceptions, identical. Where there are differences in applications, or where operational procedures differ, they will redescribed in the individual regulator chapters of NAVAIR Publication 13-1-6.4. Therefore, before you attempt to test any oxygen component, you should refer to that manual.

The oxygen system components test stand consists of a nitrogen pressure source and a ^{vacuum system.} It includes the valving and instrumentation necessary to measure, test, and evaluate the performance and operating characteristics of oxygen system components at altitudes up to 150,000 feet.

Performance of the test stand is dependent upon the skill of the operator. You must be thoroughly familiar with the instruments, controls, and connections that comprise the systems that are incorporated within the test stand (fig. 11-1).

ON/OFF VALVES

There are two ON/OFF valves on the test stand. These valves are colored red and have two positions-ON and OFF. The first valve is called the inlet pressure ON/OFF valve (L). This valve permits a flow of regulated high-or low-pressure nitrogen to the input connection (18) located inside the altitude chamber. The second ON/OFF valve is called the Leakage ON/OFF valve (G). This valve permits a flow of regulated lowpressure nitrogen gas (N2) through the selected in-system rotameter (7) or (8). You select either the low-range or the high-range rotameter by using the leakage selector valve (F). Valve (G), the leakage ON/OFF valve, also permits a supply of N2 to go to the input connection (18) inside the chamber. The only time you will be using ON/OFF valve (G) is when you are adjusting the bleed on a miniature oxygen regulator (this is covered in the NAVAIR 13-1-6.4) and when you are measuring leakage on oxygen components.