David W. Spitzer
David W. Spitzer

What is the typical design velocity of a liquid flowing in a pipe?

A. 1 meter per second

B. 3 meters per second

C. 5 meters per second

D. Any of the above

Commentary

If you already selected Answers A, B, or C, you likely “jumped the gun” because the question is incomplete if the service and fluid properties have not been defined.

Piping for liquids with low viscosity (such as water) are typically designed to operate at between 2 and 3 meters per second (Answer B). However, lower velocities may result when the piping is oversized to include provisions for future plant expansion and future increased flow.

Industrial Automation Insider 300x250Special consideration is often given in applications where solids can drop out and plug the piping unless a high liquid velocity is maintained (Answer C). On the other hand, while higher velocity may reduce the probability of solids settling out, higher velocity also accelerates pipe wear.

In other applications, liquid viscosity may be so high that even flow at low velocity (Answer A) may result in an extremely high pressure drop in the piping.

I suggest that Answer D is pragmatic.

Additional Complicating Factors

There are many factors that can dominate the fluid velocity design in pipes. Can you think of any others?

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David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC offering engineering, seminars, strategic marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. He has more than 35 years of experience and has written over 10 books and 250 articles about flow measurement, instrumentation and process control.

Mr. Spitzer can be reached at 845 623-1830 or www.spitzerandboyes.com. Click on the “Products” tab to find his “Consumer Guides” to various flow and level measurement technologies.