Quiz Corner: Horizontal tanks and level measurement

Approximately how full is a horizontal tank in which the differential pressure level transmitter measures 90 percent level?


Q: Approximately how full is a horizontal tank in which the differential pressure level transmitter measures 90 percent level?

A. 100 percent
B. 97 percent
C. 90 percent
D. 83 percent
E. 80 percent

Perhaps stating the obvious, a horizontal tank is a cylindrical tank resting on its side. Therefore the percentage of liquid fill will not be linear with the percentage of level. For example, a relatively small amount of material added to an empty tank will increase the level measurement more quickly than the amount of liquid fill would indicate. Similarly, less than 10 percent of additional capacity is available when the tank level is at 90 percent.

Therefore, Answers A, C, D and E are not correct. Answer B is most reasonable.

Additional complicating factors

This analysis assumes that the 90 percent level measurement corresponds to a 90 percent level in the tank. This would not necessarily be the case if level transmitter taps or diaphragms are not located tangent with the top and bottom of the tank, as is often the case because of physical constraints and the location of existing nozzles.


David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes LLC, which offers engineering, seminars, strategic, marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. He has more than 40 years of experience and has written more than 10 books and 350 articles about flow measurement, instrumentation and process control. Spitzer can be reached at 845-623-1830 or via spitzerandboyes.com. Click on the "Products" tab to find his Consumer Guides to various flow and level measurement technologies.  

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