CHECK VALVE CONNECTIONS

There are four connections located within the altitude chamber that have check valves incorporated, and require insertion of a bayonettype fitting to open the connection and route the flow (fig. 11-1). These connections are as follows:

1. The LOW PRESSURE connection (19) provides for a controlled flow of low-pressure nitrogen through LEAKAGE CONTROL valve (E) to the item under test.

2. The 20 to 200 CCM LEAKAGE connection (20) connects the test item to OVERBOARD LEAKAGE rotameter (6), and is used when testing components for leakage or bleed.

3. The REFERENCE TAP connection (21) is a reference tap to differential pressure indicating manometers (PRESSURE/SUCTION manometer (4) and Hg manometer (5)). It also has a reference line that connects piezometer (26) into REFERENCE TAP connection (21) downstream from the check valve.

4. The HELMET REFERENCE TAP connection (24) is a reference tap connected to both suit simulator tank through SUIT SIMULATOR REFERENCE SHUTOFF valve (R) or LOW RANGE ALTM (13) through REFERENCE PRESSURE SELECTOR valve (O).

NOTE: The CHAMBER REFERENCE port (N/N), also located within the chamber, References chamber pressure to ALT CONTROLLER (B), PRESSURE/ SUCTION manometer (4), Hg manometer (5), LOW RANGE ALTM (13), and HIGH RANGE ALTM (12).

Line traps, float check valves, and relief valves are not shown in figure 11-1.

Line traps are incorporated in PRESSURE/ SUCTION manometer (4) and Hg manometer (5) to trap liquids in case manometers are overloaded.

The float check valves incorporated in the OUTPUT FLOW manometer (l), the INPUT FLOW manometer (2), the VENT FLOW manometer (3) and the PRESSURE/SUCTION manometer (4) help to prevent a loss of liquid in case the manometers are overloaded.

The relief valves are incorporated in the REGULATED LOW PRESSURE gauge (11) and the suit simulator tank. The relief valve on the REGULATED LOW PRESSURE gauge (11) is preset at 200 to 230 psig and protects the gauge and rotameter system in case of gauge guard failure. The PRIMARY relief valve is preset at 15 psig and the SECONDARY relief valve is preset at 25 psig. These relief valves prevent overpressurization of the suit simulator tank.

VACUUM PUMP

The VACUUM PUMP (VP) operates from a 2 horsepower electric motor (fig. 11-3). The pump rotation is clockwise, when viewed from the rear of the test stand. The pump has the capability of evacuating the chamber at a rate of 22.5 cubic feet per minute (cfm) at 81 mm Hg (51,600 feet) simulated altitude. It is used to evacuate the chamber or draw flow of air, nitrogen, or air and nitrogen from an item under test. The VACWM

Figure 11-3.-Vacuum pump.

PUMP vent (54) must be opened one to two turns when you operate the pump (fig. 11-1).

WARNING

ALWAYS ENSURE THAT THE PUMP MOTOR HAS A FOUR-PRONG ELEC-TRICAL CONNECTION PLUG. ON MODEL 1172AS100 ENSURE THAT THE GROUNDING LUG IS IN PLACE AND SECURELY CONNECTED. A SIDE VIEW OF THE VACUUM PUMP IS SHOWN IN FIGURE 11-3.

SAFETY PRECAUTIONS

Before you attempt to operate the test stand, review the following safety precautions. These safety precautions must be observed before, during, and after test stand operation.

1. Ensure that the test stand is properly secured prior to opening the supply cylinder valve. Position the HIGH PRESSURE REGULATOR to LOAD, then to VENT, and ensure that the LOW PRESSURE REGULATOR is backed out and the other valves are turned fully to the right.

2. Keep the chamber door closed whenever possible.

3. Keep the test stand doors closed at all times.

4. Keep the test stand work tray closed when it is not in use.

5. Check the pump lubricant prior to turning the pump on (run for 2 minutes and check lubricant for proper level).

6. Keep your hands and head clear of belts and pulleys while checking the lubricant level.

7. Ensure the test stand is properly grounded by using the grounding lug.

8. Never use regulated high pressure and regulated low pressure together.

9. When the oxygen monitor alarm sounds, leave the room.

10. Do not panic when the test stand malfunctions.

11. When you use nitrogen, ensure that the room is well ventilated.

12. Use proper tools for the job you are performing.

13. Do not inhale lubricant, oxygen cleaning compound, or mercury fumes.

14. Wash pump lubricant or mercury from hands immediately.

15. Secure the test stand completely after use.

16. Never leave the test stand unattended while the pump is running.

17. When transporting the compressed nitrogen cylinder, you should ensure the protective cap is on.

MAINTENANCE

Maintenance on the oxygen components test stand is discussed in the following paragraphs.