Flow Instruments .
Differential pressure sensing lines should be run together to the extent
practical to keep both lines at the same temperature and with no hydraulic
head difference between the lines. If they are insulated, they should be
Differential pressure transmitters vented to the atmosphere should have
the vent connection hard-tubed without a valve and turned down. For
outdoor applications, an insect screen should be considered.
Liquid Level Instruments .
Liquid level instrument connections should be made directly to the vessel
and not on flow lines.
The lower instrument connection should be on the side of the vessel.
Bottom connections are not recommended because of the possibility of
trapping solids in the sensing lines.
A stilling well is preferred where displacement or float-type elements are
located inside a vessel subject to turbulence.
Differential pressure-level instruments should be located below the
process connection on the vessel unless a gas purge or compensated
isolation chamber is used.
Liquid level devices should be placed away from areas of turbulence to
prevent inaccurate level measurement.
Leak Detection . Conductivity probes should be protected from freezing
conditions. A film of ice over the probe could render the leak detection system
Freeze Protection . Consider the need for freeze protection during design to
prevent instrumentation systems from freezing, to ensure reliable performance