Prior to speaking about flowmeters at a recent ISA meeting in Salvador, Brazil, I was asked my opinion as to which flowmeter is the “best.” The person asking the question probably needed the answer for his supervisor. In reality though, what he really needed was a more in-depth appreciation for flow measurement.
There is no such thing as a “best” flowmeter, and even if the person in question here had clarified his request by asking which technology is best, or which manufacturer is best, or which model is best, I would not have been able to provide an answer. Different flowmeters are a good fit for different scenarios, and finding the right solution depends very much on the industry in which the flowmeter will be used and the specific application within the industry, among other factors.
This was not the only time that this question has surfaced. It happens over and over to most of us — people looking for the “quick fix” that will answer all of their questions and solve all of their problems. Suppliers make every effort to posture their flowmeters as the best, and this is as it should be. When was the last time a supplier visited and told you that he/she was selling poor quality product? As such, it is ultimately up to the user to select the proper product for the application.
While I cannot tell you which flowmeter is the best flowmeter, I can offer a tip that will help the flowmeter you choose perform to the best of its ability.
For liquid service, keep the flowmeter full of liquid so that it can function properly. Best results are typically obtained when the geometry of the flowmeter and piping is such that the flowmeter can be oriented to fill itself (self-filling) and not accumulate noncondensable gas during operation. Such an orientation eliminates the need to remove gas during startups (after the pipe is empty) and during the zero calibration of some flowmeters. For safety reasons, it is desirable for the flowmeter installation to also be self-draining so the technician will not “take a bath” when removing the flowmeter primary from the piping.
Keeping the flowmeter full is not always as simple as it seems. For example, some Coriolis mass flowmeter geometries can be oriented to be self-filling and self-draining. Other geometries can be oriented to be self-filling or self-draining, but not both. And a few Coriolis mass flowmeter geometries can be oriented to be neither self-filling nor self-draining.
To reduce the amount of operational intervention and maintenance problems, flowmeters should be selected and the piping installations should be designed to keep the flowmeter full of liquid. At times, best results may require an orientation of the flowmeter that may look awkward in some installations. General rules of thumb, such as locating flowmeters in vertical risers, may not apply with certain geometries. Careful hydraulic design of all wetted components in the flowmeter system is often necessary for proper measurement.
Conversely, for gas applications, the flowmeter should be kept full of gas and not be allowed to accumulate liquid. Similarly, careful hydraulic design is important to avoid measurement problems.
Now you tell me … which is the best flowmeter?
About the Author
David W. Spitzer, P.E., is a regular contributor to Flow Control. He has more than 25 years of experience in specifying, building, installing, start-up, and troubleshooting process control instrumentation. He has developed and taught seminars for almost 20 years and is a member of ISA and belongs to ASME, MFC, and ISO TC30 committees. Mr. Spitzer has published a number of books concerning the application and use of fluid handling technology, including the popular The Consumer Guide to… series, which compares flowmeters by supplier. Mr. Spitzer is currently a principal in Spitzer and Boyes LLC, offering engineering, product development, marketing, and distribution consulting for manufacturing and automation companies. He can be reached at 845 623-1830.
For More Information: www.spitzerandboyes.com
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