By Mike Dyer, McCrometer, Inc.
Proper operation of water treatment processes depends on accurate flow measurements. Also, flow data is often required by regulatory agencies.
Selecting the right flow meter requires detailed knowledge of the application as well as an understanding of different types of meters. This comparison of V-Cone® and Coriolis meters will help to show the pros and cons of these two types of meters.
Operating Principles
Coriolis and V-Cone meters measure liquids and gases using two different technologies.
Coriolis meters operate on the principles of motion mechanics, specifically the Coriolis force. Named after the French scientist Gaspard-Gustave de Coriolis, this involves measuring the force resulting from the acceleration caused by mass moving toward or away from a center of rotation. Most Coriolis meters have two U-shaped tubes. Flow travels through the vibrating tubes and creates a twisting action. The degree of twist is directly proportional to the mass flow. Mass can easily be converted to volume if desired.
V-Cone meters are differential pressure-type meters. The V-Cone meter features a centrally located cone inside a tube. The cone reshapes the velocity profile and creates a low-pressure area immediately downstream of itself. The difference between the static line pressure and the low-pressure area is measured by two pressure sensors and used to determine the flow rate. Note that fluid density must be known in order to calculate the flow rate.
Matrices and Applications
Both V-Cone and Coriolis meters can measure a wide variety of liquids, gases, and slurries.
Coriolis meters are especially adept at measuring gas where the molecular weight changes, because they measure mass directly.
Both meters can be used for water/wastewater, oil and gas, chemical/pharmaceutical, and many other industrial applications.
Limitations
All meters have limitations, so it’s important to have detailed information about the application when choosing which meter to install.
Coriolis meters may be very sensitive to process noise and vibration. Filters can be used to offset this problem but add expense and complexity to the meter. Buildup on the pipe wall or tubes, such as scaling or biofilm, may create inaccuracies. In addition, fluids or gases must be homogeneous for accurate flow readings.
V-Cone meters offer more flexibility regarding size limitations. These meters can be installed on pipe sizes of ½ inch to 120 inches in diameter. Coriolis meters are typically used on pipes 6 inches or less in diameter. Specialty installations are available in sizes up to 16 inches, but these large meters become very heavy, bulky, and extremely expensive.
Installation Factors
Coriolis meters are immune to velocity profile distortion and swirl. V-Cone meters provide their own flow conditioning effect. Therefore, no straight pipe runs are needed for either the Coriolis or V-Cone meters. Generally, both meters can work well in tight locations or for retrofit projects, although Coriolis meters are bulkier. Both technologies can be installed vertically or horizontally. However, it is always important to provide installation details to the manufacturer.
Maintenance
Because neither of these meters have moving parts, maintenance is near zero for both. The Coriolis and V-Cone meters are both designed to operate in harsh environmental conditions and have a long life expectancy.
Accuracy
V-Cone meters are highly accurate, with only a ±0.5 percent rate of inaccuracy. Coriolis meters are one of the most accurate meters available, with inaccuracy rates of ±0.1 to 0.2 percent.
Cost
Coriolis meters are much more expensive than V-Cone meters. Coriolis meters cost more than three times as much as V-Cone meters.
Choosing The Best Meter For Your Application
Both V-Cone and Coriolis meters are excellent devices that provide highly accurate flow measurement.
However, the V-Cone meter provides more flexibility for various pipe sizes and configurations. V-Cone meters are less bulky and heavy. They are also less sensitive to vibration and non-homogeneous fluids or gases.
Perhaps the most important factor is that of cost. For measuring flows of highly expensive products, such as crude oil—or where extreme accuracy is critical, the high cost of a Coriolis meter is justified. For most water and wastewater applications, the V-Cone provides a high level of accuracy with cost efficiency. Since the V-Cone needs no straight pipe runs, it’s a great option for treatment plant retrofits or other applications with tight configurations.
The Importance of Technical Assistance
The ability to accurately measure flow is important. Choosing the wrong meter can be costly, both financially and in terms of process operation.
When deciding which flow meter will work best for your project, engage the assistance of a technical expert. Manufacturers’ representatives have deep knowledge and experience that can help in making the right decision.
