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 conjunction 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.

Figure 11-1.-Controls and indicators for Oxygen System Components Test Stand Model 117AS100.

(See figure 11-2.) Baffles inside the element create a flow restriction. As air or nitrogen enters the element, a pressure buildup is created at the inlet end; as it flows past the baffles, a pressure drop occurs at the outlet end. The inlet (pressure buildup) tap is connected to the bottom of the indicating manometer, and the outlet (pressure drop) tap is connected to the top of the manometer. As the control valve is opened, gas flows from the valve through the Vol-O-Flo, and the pressure drop thus created allows the fluid in the manometer to rise. The operator reads the amount of flow passing through the V0l-O-Flo on the indicating manometer.

CONTROL VALVES

A control valve regulates, or restricts, a specified flow. Two types of control valves, measuring and nonmeasuring, are used on the test stand. Measuring control valves have measuring devices (gauges or manometers) to visually measure the flow through the valve as it is opened. Nonmeasuring control valves have no indicating devices. There are six measuring and three nonmeasuring control valves on the test stand.

Measuring Control Valves

The measuring control valves (fig. 1 l-l) are as follows:

1. The INPUT valve (A) allows a measurable flow of air into the altitude chamber. It can only be used during simulated altitude conditions. As the chamber altitude increases, pressure inside the chamber decreases, and the ambient air pressure outside the chamber is greater. When valve (A) is opened, air from outside the chamber flows through valve (A); through the input Vol-O-Flo element, indicating the amount of air flow on the INPUT FLOW manometer (2); and through the INPUT port (22) into the chamber.

2. The VACUUM CONTROL valve (B1) on Model 1172AS100 allows direct evacuation of the altitude chamber to the desired simulated altitude by decreasing pressure in this chamber.

3. The OUTPUT valve (C), when opened, draws a direct flow from the item under test through the piezometer (26), OUTPUT port (23), FLOW SELECTOR valve (M) and the output Vol-O-Flo element to the vacuum pump. As the flow passes through the output Vol-O-Flo, the pressure is displayed on the OUTPUT FLOW manometer (1).

4. The LEAKAGE CONTROL valve (E) controls the flow to the LOW-PRESSURE connection (19), which is located inside the chamber. As the name of the valve implies, it is used to perform various leak tests on oxygen components. When you use the LEAKAGE CONTROL valve (E) to perform leakage tests on components, a line with bayonet fittings must be installed between the LOW-PRESSURE connection (19) and the REFERENCE-TAP connection (21 ). This allows the flow passing

Figure 11-2.-VOI-O-FIO element.

through valve (E) to be indicated on PRES-SURE/SUCTION manometer (4) or Hg manometer (5), whichever you have selected. Any leakage would be registered on rotameters (7) or (8).

5. The VENT PRESSURE valve (H) controls a vent flow of low pressure through the suit simulator tank to the item under test at sea level. When valve (H) is opened, nitrogen (N2) flows through the vent flow Vol-O-Flo element, and is indicated on VENT FLOW manometer (3). The flow then passes to the suit simulator tank, through FLOW SELECTOR valve (M), OUT-PUT connection (23) and piezometer (26) to the item under test. Valve (H) is primarily used for testing relief valves.

6. The VENT AMBIENT valve (I) serves the same purpose as VENT PRESSURE valve (H), except that valve (H) is used at sea level with supply pressure, while valve (I) is used at altitude and uses ambient air as the pressure source to conserve N2. Therefore, valve (I) can be considered an economizer valve, used only "at altitude."