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 bearing longevity; abrasiveness of solid particles present has a negative
effect. Hard, abrasive particles in the process stream are the major cause of
turbine flowmeter bearing wear. To minimize stream contamination by solids, a
strainer should be installed upstream of the turbine flowmeter. Recommended
strainer mesh sizes are given in specific product literature.
3.1 Turbine Meter Designs. Turbine meters are applied in two distinct
designs, full-bore and insertion types. Full-bore turbine meters have a
rotating element equal to pipe diameter; they measure the total flow. Turbine
meters are available for pipe sizes greater than one-half inch in diameter.
They are designed for liquid or gas measurement. Full-bore turbine meter
costs increase exponentially as line size increases, making them uneconomical
for large line sizes. Insertion meter costs are the same regardless of line
size, making them an attractive alternative. Insertion meters measure a
sample of fluid flow at a local velocity. Insertion meters can be used to
measure liquid, gas, and steam when pipe sizes are 3 inches or larger
(Figure 6-3).
3.2 Recommended Applications. Full-bore meters are primarily applied either
to clean, low particulate fuel oil or water. Corrosive materials can be
q easured if a stainless steel rotor is used. Turbine meter applications for
steam measurement must be so specified to obtain the correct bearing and
turbine materials. Insertion meters are excellent for steam applications.
The small, low inertia rotor has a rapid response time. In addition, cost of
the meter is independent of the pipe size. Whether the full-bore or insertion
type meter is used, the turbine meter is often chosen because of its turndown
ratio. Turbine meters have a minimum flow turndown ratio of 10:1. Turndown
ratio can be up to 50:1 depending on pipe size and fluid velocity. An
insertion turbine meter can also be used as an analytical tool. Because of
its ability to move across a pipe section and to orient the rotor head at
various angles to the flow stream, the meter can determine the nature of
unsymmetrical flow patterns and detect any swirl within the pipe. Turbine
meters have an advantage over other types of meters because they are capable
of measuring forward and reverse flow.
3.3 Limitations. Several of the limitations that may preclude application of
a turbine meter are as follows:
q Turbine
meters are restricted to clean fluids.
q Insertion
turbine meters require a clear space of at least 4 feet
perpendicular to the pipe for installation.
q Temperature
operating range for standard units is -73C (-100F) to
+427C (+800F). Special ranges are available.
Pressure limit is 3,000 psig.
q
6-3
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