David W. Spitzer

Flowmeter selection can be quirky. Sometimes you have already seen the application before and have the benefit of having previously evaluated it. In this case, you might select a flowmeter with reasonable confidence that you have made a good selection. The advantage of previous experience is that a flowmeter selection for the current application is made quickly and efficiently.The disadvantage of previous experience is that it can “color” your thinking. I suggest that the confidence with which one makes a flowmeter selection based upon previous evaluation is proportional to the amount of time spent on the original evaluation (i.e., thoroughness) and inversely proportional to the amount of time since the original evaluation was performed.

For example, about 20 years ago I was charged with measuring the flow of a liquid flowing at 120-200 C in steam-jacketed pipe that was blown clear with steam after use. I seem to recall that the liquid had a specific gravity of approximately 1.10 and a viscosity of approximately 10 cP at flowing temperature. In addition, the fluid changed to a hard concrete-like substance when it froze.

Finding a flowmeter for this application was not easy 20 years ago. The process and steam flow conditions were somewhat harsh and tended to eliminate most flowmeter technologies. In the final analysis, specifying a flowmeter for this application amounted to identifying a solution that would not plug and could be easily removed from the process line and opened to chisel away the concrete-like material without damaging the flowmeter.

Many new and better flowmeters have been developed in the 20 years since the original analysis was performed. However, given the same application today, I might quickly look at some of the newer flowmeters in the context of the removal/chiseling requirements, but if the original analysis was thorough (and the amount of time spent on it significant), I would probably end up selecting the same flowmeter again.

David W. Spitzer is a regular contributor to Flow Control with more than 35

years of experience in specifying, building, installing, startup,

troubleshooting and teaching process control instrumentation. Mr. Spitzer

has written over 10 books and 150 technical articles about instrumentation

and process control, including the popular “Consumer Guide” series that

compares flowmeters by supplier. Mr. Spitzer is a principal in Spitzer and Boyes LLC, offering engineering, expert witness, development, marketing, and distribution consulting for manufacturing and automation companies. He can be reached at 845 623-1830.