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 Fixed insertion meters are used on systems where the pressure can be relieved
during installation and removal of the meter. Hot tap insertion meters are
designed for use where system monitoring is necessary without interrupting
line pressure. The meter is inserted through a full-port ball or gate valve.
Hot tap meters require probe length clearance above the mounting flange and
valve to allow full retraction and removal of the meter.
4. RECOMMENDED APPLICATIONS. Vortex shedding meters are designed for use on
clean gas and liquid systems, but they are commonly used on dirty gases and
dirty or corrosive liquids which decrease meter life expectancy.
5. LIMITATIONS. The recommended applications for vortex shedding meters
require the consideration of the following limitations:
q Inaccurate
at low fluid velocities compared to turbine meters.
q Space
availability above the flange for insertion meters.
q Alignment
and location are critical.
q Working
pressure limit of 1,500 psi.
q Common
temperature limit of 560F.
q Pipe
size of 1- to 8-inch diameter.
6. INSTALLATION. The location of a vortex shedding meter in a system is
important. Whenever possible, it is preferable to locate the primary element
in a horizontal line. To ensure accurate flow measurement, fluid must enter
the primary element with a fully-developed velocity profile, free from swirls
or vortices. Such a condition is best achieved by use of adequate lengths of
straight pipe, both preceding and following the primary element.
Straightening vanes can preclude the need for long lengths of straight pipe.
The minimum recommended lengths of piping are shown in Figure 6-7. The
configuration in Figure 6-7 that corresponds closest to the actual piping
arrangement for the meter location should be used to determine required
lengths of straight pipe on the inlet and outlet. These lengths are those
necessary to limit errors due to piping configurations to less than 0.5%. If
these minimum distances are not observed, the flow equations and resultant
flow calculations may result In inaccurate data. For specific applications,
refer to manufacturer's installation criteria,
7. ACCURACY AND RELIABILITY. Vortex shedding meters have an accuracy of
1.0% when calibrated, with a turndown capability up to 10:1 dependent upon
pipe size and fluid properties. The lack of moving parts results in reduced
maintenance and makes this type of measuring device a very reliable means of
flow measurement.
6-12
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