Taylor-Wharton Bulk Tank Safety Data - Manual (Page 11)

11
Functional Descriptions
Vacuum System
Taylor-Wharton tanks are vacuum-sealed. The space between the casing
and the liquid container is filled with high quality insulation, pumped to a
high vacuum, and sealed at the factory. An absorbent is factory installed in
the vacuum space to help maintain the vacuum by absorbing any outgas-
sing from the materials in the vacuum space. The evacuation valve is
sealed at the factory, but may be used for field re-evacuation by qualified
personnel if necessary.
A thermocouple type vacuum gauge tube, located on the head of the
casing, should be used to check tank vacuum in the field. The casing is
protected against internal overpressure by a bursting disc or safety relief
life plate device located on the upper head of the tank.
Filling Circuits
The tank is filled with product through the fill connection with two hand
valves. The liquid fill valve line extends to the bottom of the liquid container.
The gas valve line extends to the top of the liquid container. Filling from the
top of the container tends too decrease tank pressures; while filling from
the bottom tends to increase tank pressure. The blowdown valve is opened
for venting and throttled to maintain desired tank pressure during liquid
phase filling. The full trycock valve is used to determine when the tank is
full.
Gauge Circuits
Pressure in the liquid container is displayed by the tank pressure gauge.
The liquid contents gauge provides an indication of the amount of liquid
product in the tank. The contents gauge is calibrated in inches of water
column and a gauge chart is used to convert the gauge reading s to
pounds and gas equivalent values. The contents gauges indicates the
difference in pressure between the top and the bottom of the tank and
provides an approximation of the amount of liquid in the tank. It should not
be considered accurate enough for precise measurement of the amount of
liquid added to or withdrawn from the tank.