Rosemount 1151GP - Page 20

Reference Manual
00809-0100-4360, Rev BA
August 2008
Rosemount 1151
2-10
Drain/Vent Valves
Drain/vent valve orientation is also dependent on the process being
measured:
• For liquid service, mount the side drain/vent valve upward to allow the
gases to vent.
• For gas service, mount the drain/vent valve down to allow any
accumulated liquid to drain.
To change the drain/vent valve orientation from top to bottom, rotate the
process flange 180 degrees.
Impulse Piping
The piping between the process and the transmitter must accurately transfer
the pressure in order to obtain accurate measurements. In this pressure
transfer, 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
• Temperature-induced or other density variation between the legs
The best location for the transmitter in relation to the process pipe depends on
the process itself. Consider the following general guidelines in determining
transmitter location and placement of impulse piping:
• Keep impulse piping as short as possible.
• Slope the impulse piping at least 1 inch per foot (8 centimeters per
meter) upward from the transmitter toward the process connection for
liquid.
• Slope the impulse piping at least 1 inch per foot (8 centimeters per
meter) downward from the transmitter toward the process connection
for gas.
• 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 prevent
blockage.
• Vent all gas from liquid piping legs.
• For steam service, fill impulse piping with water to prevent contact of
live steam with the transmitter.
Steam or other elevated temperature processes can cause damage to the sensor. Do
not allow the temperature inside the process flanges to exceed the transmitter limit of
220 °F (104 °C).