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Controls And Indicators.- The controls and indicators of the TMU-70/ M are illustrated and identified in figure 5-7. The storage tank pressure gauge (1) indicates the pressure in the inner tank. The storage tank liquid level gauge (2) indicates the level of liquid in the inner tank when the tank is on level ground. The dial is magnetically and mechanically coupled to a float sensor inside the storage tank and is calibrated in gallons. The transfer tank pressure gauge (8) indicates the pressure in the transfer tank. This pressure must be more than that in the storage tank for the liquid to transfer, since the converter is vented into the storage tank during converter filling. The transfer tank liquid level gauge (7), which reads in percent full, is the same type as the storage tank liquid level gauge that reads in gallons. The converter full indicator gauge (9) (marked LIQUID- GAS on the gauge), is a vapor pressure thermometer that monitors the converter vent line temperature. During transfer of liquid to a
Figure 5-7.- TMU-70/ M liquid oxygen servicing trailer controls and indicators. converter, it indicates "GAS" temperature in the converter vent line. When the converter is full, the vent line is filled with LOX. The converter vent line temperature drops and the gauge indicator moves to the "LIQUID" position that indicates a full converter. With the exception of the converter full indicator gauge and the transfer tank liquid level gauge, all gauges have a green band to indicate safe operating pressures and a red band to indicate unsafe pressures. In addition to the indicators covered, there are several valves in the system. The converter vent line shutoff valve (3) controls the flow of oxygen gas vapors from the converter to the storage tank and prevents loss of storage tank gas when the converter is not being filled. The transfer tank vent line shutoff valve (4) controls the flow of oxygen gas vapors from the transfer tank to the vapor space of the storage tank. The valve used to control the gravity flow of LOX to the transfer tank from the storage tank is the transfer tank fill line shutoff valve (5). The transfer tank pressure buildup valve (6) controls the flow of LOX from the bottom of the transfer tank to the pressure buildup coil (PBU). The PBU coil is a heat exchanger that exposes the LOX to ambient temperatures, converting the LOX to gas. As this conversion takes place, the gas expands and the output gas from the PBU is fed back to the transfer tank vapor space, providing the pressure to discharge the LOX to the converter. The fill drain line shutoff valve (10) is used during the storage tank filling operation. It permits the flow of LOX from a central supply tank to the storage tank. This valve is to be opened completely during the filling function and closed after the transfer has been completed. CAUTION The fill-drain line shutoff valve is not used to control flow. Restricting transfer flow may create a dangerous back pressure on the supply line used for filling. Control of transfer flow should be maintained with the service valve of the central supply tank. The storage tank vent line shutoff valve (11) is used to control the release of gaseous vapors from the storage tank to the vent piping manifold. This valve is open during filling to vent all pressure from the storage tank. During idle storage, it is left open to vent all vapors generated by normal LOX boil-off. In flight line service, it is left closed to prevent oxygen vapor contact with flammable liquids or vapors, and to prevent unnecessary loss of LOX.
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