Taylor-Wharton High Capacity GST Storage Tanks - Manual (Page 9)

9
VALVES are open. When tank pressure decreases to the PRESSURE BUILDING REGULATOR
setpoint, it opens and liquid flows from the bottom of the tank through PRESSURE BUILDING
COIL. This liquid product is vaporized in the coil and expanded gaseous product returns to the top
of the tank maintaining tank pressure. When tank pressure increases above the regulator’s set point
it closes and the pressure building process stops.
The THERMAL EXPANSION RELIEF VALVE will relieve pressure buildup from trapped liquid
between the pressure building regulator and the inlet valve.
SAFETY DEVICES
The tank vacuum jacket is protected from overpressure by the VACUUM JACKET LIFT PLATE.
Overpressure protection for the pressure vessel is provided by dual TANK PRESSURE RELIEF
VALVES and RUPTURE DISCS. The pressure relief valves provide primary protection for the
inner vessel; the rupture disks are secondary safety devices. A RELIEF SYSTEM DIVERTER
VALVE permits the operation of one set of protection devices while the other set is isolated. This
arrangement prevents both sets of safety devices from being isolated from the tank at the same time
and permits maintenance of the devices without the need to vent tank pressure. Either one of two
types of diverter valves may be installed on the tank.
Tanks equipped with diverter ball valves:
To activate one set of devices while isolating the other
move the selector valve handle all the way to the end of its travel toward the devices to be activated.
Tanks equipped with diverter globe valve:
Turn the RELIEF SYSTEM DIVERTER VALVE
handle counterclockwise (in direction of arrow on hand wheel) to the end of its travel to open port
#1 and to close port #2 for servicing the relief devices. Likewise, turn the handle clockwise to the
end of its travel to open #2 and close port #1 for servicing.
Line THERMAL EXPANSION RELIEF VALVES are installed in the tank external piping at
points where liquid or cold gas could become trapped.
INSTRUMENTATION
Tank pressure is indicated by a tank PRESSURE GAUGE. Liquid level is indicated on the
LIQUID LEVEL GAUGE. Piping with LIQUID LEVEL GAUGE ISOLATION VALVES and an
EQUALIZATION VALVE connect the gauges to the tank. The LIQUID LEVEL GAUGE is
calibrated in inches of water and a conversion chart located next to the liquid level gauge is used to
convert the gauge reading to volume of liquid.
For some customer specific Final Piping Options the liquid level and pressure indicating devices
are not supplied. VAPOR PHASE ISOLATION VALVE is connected to a pressure tap that is
attached to the top of the pressure vessel. LIQUID PHASE ISOLATION VALVE is connected to a
pressure tap attached to the bottom to the pressure vessel. These connections provide the customer
a means of connecting a differential pressure gauge to determine liquid level and a pressure gauge
to determine tank pressure. When installed the differential pressure gauge’s high-pressure port will
be connected to LIQUID PHASE ISOLATION VALVE, the low-pressure port will be connected to