Rosemount Model 8732C Integral Mount Magnetic Flowmeter System
B-4
Flowtube Orientation
Upstream Piping Length Magnetic flowmeters are less sensitive to liquid velocity profile
variation than most other flowmeters. However, to ensure specification
accuracy over widely varying process conditions, install the flowtube
with a minimum of five straight pipe diameters upstream and two
straight pipe diameters downstream from the electrode plane. This will
allow disturbances to settle out prior to measurement. This procedure
is usually adequate to allow for disturbances created by elbows, valves,
and reducers.
Vertical Installation Vertical installation allows upward process fluid flow and is generally
preferred. Upward flow keeps the cross-sectional area full, regardless
of flow rate. Orientation of the electrode plane is unimportant in
vertical installations.
NOTE
Avoid downward vertical flows where back pressure is inadequate to
ensure that the flowtube remains full.
Horizontal Installation Horizontal installation should be restricted to low piping sections that
are normally full. Orient the electrode plane to within 45 degrees of
horizontal in horizontal installations. A deviation of more than 45
degrees of horizontal would place an electrode at or near the top of the
flowtube–making it more susceptible to insulation by air or entrapped
gas at the top of the flowtube.
Magnetic Flowmeter Sizing
The flowtube size is a very important consideration because it affects
flow velocity. It is often necessary to select a magmeter that is larger
or smaller than the adjacent piping to ensure the fluid velocity is in
the range of 1 to 30 ft/s (0.3 to 9.1 m/s). Table B-1 shows guidelines for
sizing normal velocities for magmeters in different types of
applications (operation outside these guidelines may also give
acceptable performance).
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