Figure 6-8.Level indicating panel (rear view).
the two liquids (gasoline and seawater) varies and
converts this differential to gallons of gasoline. There
are four components to this gage:
In-tank reservoir, an upper and lower
reservoir for each of the inner and outer tanks (a
total of four reservoirs)
A panel in the pump room, which contains the
Differential pressure gage
Seawater pressure gage
Water-filled connecting lines connect the in-
tank reservoirs to the gage panel.
Seawater supply for purging consists of the fol-
Firemain cutout valve
Bypass purge line
Bypass purge valve
Most of the components are installed to aid in
purging the system. Only three items are necessary
for the actual gaging of the tanks. These are the
differential pressure gage, water-filled connecting
lines, and the upper and lower in-tank reservoirs.
When the storage tanks are full (100%) of
seawater, a constant differential pressure exists
between the upper and lower in-tank reservoirs, and
the differential pressure gage reads ZERO. As the
storage tanks are filled with gasoline, a varying
differential pressure is developed between the upper
differential pressure, created by the difference in
specific gravities of the two liquids (gasoline and
seawater), is transmitted to the gage panel through
the water-filled connecting lines. The differential
pressure gage senses this varying differential
pressure and converts it to gallons of gasoline present
in the storage tank.
The differential pressure gage (fig. 6-9) measures
the varying pressure differential from the tank and
Figure 6-9.Differential pressure gage.