Taylor-Wharton High Capacity GST Storage Tanks - Manual (Page 10)

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VAPOR PHASE ISOLATION VALVE, and a bypass valve connecting the instrument lines should
be installed between the isolation valves and the device. During operation this bypass valve will
remain closed; its function being to equalize the pressure on each side of the differential pressure
gauge. The pressure gauge will be connected to VAPOR PHASE ISOLATION VALVE so that
pressure at the top of the vessel is measured.
For some customer specific Final Piping Options a LIQUID LEVEL GAUGE with electrical
switches is available for installations requiring low and high level warnings. The gauge switches
can be wired to sound an alarm or light indicator lamps on either low or high tank liquid level.
VACUUM SYSTEM
Several tank components are provided for vacuum system maintenance. The VACUUM
PUMPOUT VALVE is the port used to pump air from the tank insulation space. It is normally
blanked-off and never opened unless the tank requires a field re-evacuation after a repair. The
VACUUM PROBE is a thermocouple that is installed to allow connection of a vacuum gauge to
measure the quality of the vacuum in the insulation space. The VACUUM PROBE ISOLATION
VALVE is opened during vacuum measurement to expose the vacuum probe sensors to the tank
insulation space. This valve is normally closed to protect the integrity of the vacuum and insulation.