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Mechanical Turbine Water Meters
Hedland Variable Area Flow Meters

Flow Meter Selection GuideIn Part 1 of this series (Flow School - Fundamentals), we talked about all the application specific information you need to begin the Flow Meter Selection process. By now you should have a general idea of which technology(s) may work well in your application. And, to be sure you're heading in the right direction, we want you to know more about the individual charactoristics of each type of flow meter. With that in mind, we’ll continue our flow meter fundamentals with a basic description of some of the more popular flow measurement technologies, beginning with the turbine meter...

The Turbine Meter is a volumetric measurement device which operates by sensing the linear velocity of the fluid passing through it. Using a known cross-sectional area of the meter housing enables it to determine the volumetric flow rate. As fluid passes through the meter, it conveys an angular velocity (RPM) to the rotor, which is proportional to the linear velocity of the flowing fluid.
Since the linear velocity of the flowing fluid though a given area is directly proportional to the volumetric flow rate, it follows that the speed of rotation of the rotor is directly proportional to the volumetric rate.
GPI Turbine Meter Cutaway
What did he just say?

Huh...The design of liquid turbine meter is relatively simple. It consists of a cylindrical housing similar to a pipeline spool piece, a precision balanced free-running rotor and a pick-up assembly positioned as close to the rotor as practical without penetrating the housing wall.

Fluid passing through the meter causes the turbine to rotate.  Small pieces of ferrous metal embedded in some or all of the turbine fins pass through the magnetic field generated by the pick-up coil.  This disturbance in the magnetic field is interpreted by the flow computer as a pulse.

Quantifying the total number of pulses in a given time period allows the meter to accurately interpret/measure the total volume of fluid passing through the meter.

Typical Applications:
In general, Liquid Turbine Meters are well suited for measurement of any low viscosity liquid (50 cP is the suggested max) which is chemically compatible with the materials of construction of the turbine meter. Available materials include 316SS, Brass, Aluminum, PVDF, PVC, and Epoxy Coated Carbon Steel. Consider using a liquid turbine meter in applications where you're currently using a Variable Area (Rotameter) Flow Meter, but may need more information than just rate of flow. Most Turbine Meters can be equipped with flow computers/displays offering flow rate and flow totals. Applications to avoid would be any fluid whose properties (Viscosity and/or Specific Gravity) can change based on environmental conditions, etc. The most common example would be motor oil which can be very thin when heated and very thick when cooled. Turbine meters are calibrated to specific fluid properties and any changes to that can greatly affect the accuracy of the meter.

Meet the Author
Flow Specialist - Bill Michie Written By: Bill Michie  
Flow Applications Specialist
Cross Company
Instrumentation Group

Phone: (866) 905-9790 (M-F, 8am-5pm Eastern)
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