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Reference Manual
00809-0100-4102, Rev AA
Section 3: Installation
May 2013
Installation
3.4.2 Impulse piping
Best practices
The piping between the process and the transmitter must accurately transfer the pressure to
obtain accurate measurements. There are five possible sources of error: leaks, friction loss
(particularly if purging is used), trapped gas in a liquid line, liquid in a gas line, and density
variations between the legs.
The best location for the transmitter in relation to the process pipe depends on the process
itself. Use the following guidelines to determine transmitter location and placement of impulse
piping:
Keep impulse piping as short as possible.
For liquid service, slope the impulse piping at least 1 inch per foot (8 cm per m) upward
from the transmitter toward the process connection.
For gas service, slope the impulse piping at least 1 inch per foot (8 cm per m) downward
from the transmitter toward the process connection.
Avoid high points in liquid lines and low points in gas lines.
Make sure both impulse legs are the same temperature.
Use impulse piping large enough to avoid friction effects and blockage.
Vent all gas from liquid piping legs.
When using a sealing fluid, fill both piping legs to the same level.
When purging, make the purge connection close to the process taps and purge
through equal lengths of the same size pipe. Avoid purging through the transmitter.
Keep corrosive or hot (above 250 °F [121 °C]) process material out of direct contact
with the sensor module and flanges.
Prevent sediment deposits in the impulse piping.
Keep the liquid head balanced on both legs of the impulse piping.
Avoid conditions that might allow process fluid to freeze within the process flange.