Which of the following orientations can be used to install a Coriolis mass flowmeter to measure the mass flow of a liquid in a vertical pipe flowing down?
A. U-tube down
B. Inverted U-tube
C. Horizontal (parallel to grade)
D. Flag position
Coriolis mass flowmeters in liquid service must be completely full of liquid to measure accurately. The inverted U-tube orientation (Answer B) could accumulate gas and should not be used for liquid applications.
The U-tube down orientation (Answer A) and horizontal orientation (Answer C) could be acceptable but would entail modification of the upstream and downstream piping. Therefore, the flag position (Answer D) would appear to be the most practical answer; however, the flowmeter must be kept full of liquid for accurate measurement.
Additional complicating factors
Liquids are generally pumped upward or horizontally from one location to another. Pumped downward flow can sometimes occur, for instance, in order to get around an obstruction. However, most flow downward occurs using gravity, so keeping the flowmeter full of liquid can be a challenge in many installations.
For example, a U-tube Coriolis mass flowmeter oriented in a flag position (Answer D) located in piping that is hydraulically submerged would be an acceptable installation. However, if the flowmeter is not hydraulically submerged in the downward pipe (as is often the case), a hydraulically submerged condition for the flowmeter should be created, such as by modifying the piping to flow down, then up through the flowmeter and then down again.
In addition, not all Coriolis mass flowmeters have U-tube geometry, so the piping orientation should be designed to ensure that gas is not allowed to accumulate in the flowmeter.
David W. Spitzer is a principal at Spitzer and Boyes, LLC, which offers engineering, focused market research, writing/editing white papers, strategic marketing consulting, distribution consulting, seminars and expert witness services for manufacturing and automation companies. Spitzer has written more than 400 technical articles and 10 books about flow measurement, instrumentation and process control. He can be reached at 845-623-1830 or via spitzerandboyes.com.