Figure 6-8.—Level indicating panel (rear view).the two liquids (gasoline and seawater) varies andconverts this differential to gallons of gasoline. Thereare four components to this gage:• In-tank reservoir, an upper and lowerreservoir for each of the inner and outer tanks (atotal of four reservoirs)• A panel in the pump room, which contains thefollowing:Differential pressure gageMultifunction selectorFlow-limiting valveSeawater pressure gagePurge valveFlow indicatorOperating instructions• Water-filled connecting lines connect the in-tank reservoirs to the gage panel.• Seawater supply for purging consists of the fol-lowing:Firemain cutout valveStrainerPressure-reducing valvePressure gageBypass purge lineBypass purge valveMost of the components are installed to aid inpurging the system. Only three items are necessaryfor the actual gaging of the tanks. These are thedifferential pressure gage, water-filled connectinglines, and the upper and lower in-tank reservoirs.When the storage tanks are full (100%) ofseawater, a constant differential pressure existsbetween the upper and lower in-tank reservoirs, andthe differential pressure gage reads ZERO. As thestorage tanks are filled with gasoline, a varyingdifferential pressure is developed between the upperand lower in-tank reservoirs. This varyingdifferential pressure, created by the difference inspecific gravities of the two liquids (gasoline andseawater), is transmitted to the gage panel throughthe water-filled connecting lines. The differentialpressure gage senses this varying differentialpressure and converts it to gallons of gasoline presentin the storage tank.The differential pressure gage (fig. 6-9) measuresthe varying pressure differential from the tank andFigure 6-9.—Differential pressure gage.6-9
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