Flowmeter selection is not easy — so expect no silver bullets in this article. I cannot teach you a cookbook method for finding the “right” flowmeter. But I will attempt to explain a little bit about what makes specifying flowmeters such a difficult process.
First off, finding the right flowmeter is complicated because there are so many technical issues to confront . Also, the process is further complicated because there are so many vendors and technology types to choose from.
Right now there are more than a dozen flowmeter technologies, each of which has been interpreted in a variety of different ways. Add to that, each technology and variation can generally be purchased from multiple suppliers, making the number of choices even more staggering.
The following chart tabulates the number of manufacturers and suppliers of some flowmeter technologies (see table below). The list is not meant to be exhaustive, but rather to give you a quick feel for how quickly the numbers add up.
Technology
Coriolis Mass
DP Flow Transmitter
Magnetic
Ultrasonic
Vortex & Fluidic
Subtotal
22
12
63
75
53
225
12
46
63
40
177
(Spitzer & Boyes LLC, www.spitzerandboyes.com)
Other flowmeter technologies include open channel, positive displacement, target, thermal, turbine, variable-area, bypass, and insertion flowmeters. Consider also that many manufacturers offer a few flowmeter models that use the same technology, and the number of options continues to grow.
There are likely more than 250 suppliers and more than 200 manufacturers of the five technologies listed above. As a result, it should be no surprise that flowmeter selection is not easy or straightforward.
Consider also that the above table only accounts for the number of suppliers and manufacturers and does not factor in different models offered by the same manufacturer or supplier. For example, ultrasonic suppliers typically offer 3 to 6 models. In fact, I’m aware of one supplier that offers approximately 15 models and numerous special flowmeter systems.
In addition, not all flowmeters within a given technology will necessarily work properly in a given application. For example, some years I was confronted with an application where a series of vortex shedders located in a boiler feed line were presenting problems for the operators. Symptomatically, these flowmeters would measure 50-60 percent of full scale flow when the boilers were off and there was no fire in them. When I was analyzing this application, I found out that my predecessor had already contacted the supplier and replaced the flowmeters with new models that were supposed to fix the problem. As the new instrument engineer in the plant, I was charged with taking care of the problem. My suggestion to replace the existing vortex shedders with new ones was met with little enthusiasm. Still, I replaced the vortex shedders of one manufacturer with vortex shedders of another manufacturer. The new vortex shedders are still working properly after approximately 20 years of operation.
So you see, the number of available choices is, in part, what makes flowmeter selection so difficult. If there were only one flowmeter in the world — or at least only one of each technology type —flowmeter selection would be a lot easier. But the expense of increased operational problems and poorer performance means a cookbook approach to flow measurement is still a long way off.
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.
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