large volume of air into the altitude chamber. When you open the chamber bleed valve (K), ambient air flows into the chamber through the chamber bleed port (CB). The altitude in the chamber drops until the pressure inside the chamber equalizes with the pressure at sea level.

PRESSURIZING THE CHAMBER BLEED SYSTEM

Open the vacuum control valve (B1) and ascend to 10,000 feet; then close the valve to stabilize your altitude. A drop in altitude on the low-range altimeter (13) indicates a leak. If there is no drop in altitude, open the chamber bleed valve (K) and descend to sea level. When you reach sea level, close the chamber bleed valve (K). The test stand is now ready to test the flow measuring system.

FLOW MEASURING SYSTEM

This system is the largest and most important system on the test stand. The purpose of the flow measuring system is to measure flows of air, nitrogen, or air/nitrogen mixture from an item under test. As you can see in figure 2-11, the system consists of vol-o-flow elements, flow indicating manometers, control valves, and selector valves. The flow measuring system is made up of the output, input, and vent flow subsystems. The different subsystems function with the vacuum running.

Output

The output flow system originates at the piezometer (26) and flows through the output port (23) to the flow selector valve (M). It is then directed to either the output vol-o-flow element or the suit simulator tank. W h en the flow selector valve (M) is placed in the REGULATOR position, the flow is directed to the output vol-o-flow element. The volume of flow is controlled by the output valve (C) and is indicated on the output flow manometer (l). The only time this system is used with the flow selector valve (M) in the SUIT SIMULATOR position is when the full pressure suit breathing regulator is tested.

Figure 2-11. - Model 1172AS100 flow measuring system.