converter supply flow control valve V-9 controls the flow of oxygen from the liquid oxygen converter through the heat exchanger HE-1 to the buildup and flow valve V-10, and then to the adapter fixture. Linear Flow Elements There are four linear flow elements. Each measures a different flow rate in liters per minute (LPM). By using a hose assembly connected from NIP-5 (converter supply outlet connection) to the correct one of the linear flow elements (NIP-1 for 0-00.25 LPM, NIP-2 for 0-1.0 LPM, NIP-3 for 0-50 LPM, or NIP-4 for 0-150 LPM), and turning the flowmeter selector valve, you can measure leakage from an item under test. Liquid Oxygen Quantity Gauge Capacitor-Type Tester The liquid oxygen quantity gauge capacitor- type tester is located on the upper front panel of the test stand and operates on 115 Vat, 400-cycle current. It is used to measure capacitance and electrical insulation of the capacitance probe. Flow of Oxygen As you turn on the supply of gas, it flows into the test stand through a special bulkhead fitting BF-1 (fig. 11-4), and it is indicated on the 0-3,000 psig pressure gauge PG-3. It then flows to the adjustable pressure regulator R-1. The regulator is preset to deliver 160 psig to the remainder of the test stand through oxygen supply valve V-6. Oxygen supply valve V-6, a needle-type valve, admits oxygen to the adapter fixture and controls oxygen pressure to an item under test. From the adapter fixture, the test gas is routed to the follow- ing valves, gauges, and disconnects: Test gas enters the bell jar bottom coupling C-1. Your test item is also attached to this coupling. From C-1 it flows to the needle metering valve V-2, which allows the flow to continue to a test pressure gauge PG-1. NOTE: When opening valve V-2, you must close valve V-10. This prevents oxygen from entering the converter side of the test stand. The test pressure gauge PG-1 indicates the pressure applied to the item under test. The oxygen flow also goes from the adapter fixture to the differential pressure gauge shutoff valve V-8. This valve prevents pressure from being admitted to the high side of the differential pressure gauge DF-1 when the gauge is not being used. Another flow from the adapter fixture is to the system bleed valve V-5. This valve is a needle-type valve, and it is used to bleed the pressure from the test stand. On every test stand you will find a safety valve. In this case, we have a relief valve V-4 that prevents excessive pressure buildup in the test stand. The valve is leaktight at 160 psig, and is set to relieve at 180 psig. MAINTENANCE Maintaining and preparing the test stand for use is divided into five separate tasks: installation, visual inspection, correction card preparation, calibration, and leak testing. These tasks, fully described in the following paragraphs, are out- lined briefly below: 1. Installation includes selecting a suitable space, mounting, connecting to a suitable power supply, and an oxygen source. 2. The visual inspection is performed to ensure the test stand has not been damaged during shipment and installation. 3. Correction/calibration cards (fig. 11-6) provide an easy reference upon which indicated flows and pressures are recorded. Actual mandatory flows and pressures are taken from NAVAIR 17-15BC-20 and are prerecorded on the correction/calibration cards. The actual LPM flow must be converted to the indicated inches of H₂O flow and to millimeter (mm) flow by using the applicable flowmeter calibration graphs. This conversion is performed by the metrology calibra- tion team. NOTE: Additional actual pressures and flows have been added to the correction cards in figure 11-6. Addition of these pressures and flows reflect required actual pressures and flows needed to bench test RSSK kits and all models of LOX converters now in service. 4. Periodic leakage tests are conducted on the accessories section, bell jar assembly, and the entire test stand. 5. Calibration of the test stand is required to be performed prior to use. Calibration procedures are performed at 6-month intervals by the onsite metrology calibration team. Additional calibra- tions are not required. 11-16