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 in- side the altitude chamber. The second ON/OFF valve is called the Leakage ON/OFF valve (G). This valve permits a flow of regulated low- pressure 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. SELECTOR VALVES As you look at the Model 1172AS100 test stand, you may think that with all those different valves, gauges, rotameters, and connections that you could never operate it. However, by operating only four selector valves, you can direct the flow of N₂ to perform the basic functions of the stand. These valves are M, O, D, and F, shown in figure 11-1. The FLOW SELECTOR valve (M) has two positions—CONTROLLER and REGULATOR. When this valve is placed in the REGULATOR position, and you open the OUTPUT valve (C), the flow is routed directly from the item under test through the piezometer (26) and OUTPUT port (23) to the vacuum pump. When the selector valve is placed in the CONTROLLER position, the flow is routed through the suit simulator tank. The REFERENCE PRESSURE SELECTOR valve (0) is a two-position valve. It references pressure to either the altitude chamber or the suit simulator tank from LOW RANGE ALTIMETER (13). The PRESSURE SELECTOR valve (D) has two positions—H₂O (water) and Hg (mercury). In the Hg position, only mercury pressure can be read. In the H₂O position, either inches of water pressure (positive pressure) or inches of water suction (negative pressure) can be read. The LEAKAGE SELECTOR valve (F) has two positions—HIGH and LOW. It routes regulated low pressure through the in-system rotameters. When the valve is placed in the LOW position, leakage is indicated on rotameter (7). The LEAKAGE SELECTOR valve (F) is always left in the HIGH position unless you are reading a leak or bleed below 200 cubic centimeters (CCM). This is done to prevent damage to the low-range rotameter in the event you develop a severe leak. VOL-O-FLO ELEMENTS To understand the function of some of the valves discussed in the following paragraphs, it is necessary to first understand the function of the Vol-O-Flo elements installed between certain control valves and their indicating manometers. There are three Vol-O-Flo elements installed on the test stand. The input Vol-O-Flo works in con- junction with INPUT valve (A) and INPUT FLOW manometer (2). The output Vol-O-Flo is used with OUTPUT valve (C) and OUTPUT FLOW manometer (l). The vent flow Vol-O-Flo is used with either the VENT PRESSURE valve (H) or the VENT AMBIENT valve (1) and the VENT FLOW manometer (3). The Vol-O-Flo elements have two taps—one near the inlet end and one near the outlet end. 11-4