|David W. Spitzer|
My initial gut reaction is that whoever designed the piping had little or no instrumentation background. Further, all of the instrumentation work performed in conjunction with the installation is suspect.
Why? People familiar with flow measurement know that flowmeters often require a good velocity profile upstream of the flowmeter to measure accurately. Throttling a control valve causes its velocity profile downstream to become distorted. Flowmeter performance can be significantly degraded by locating the control valve (and its distorted velocity profile) upstream of a flowmeter. Locating the control valve downstream of the flowmeter keeps its velocity profile distortion downstream—far from the flowmeter—so it does not affect the flow measurement.
Additional Complicating Factors
I have yet to encounter an application where a control valve is legitimately required to be located upstream of the flowmeter. I suspect that there might be a handful of such applications out there somewhere—if only because there always seem to be a few exceptions to the rule. If you find such a process, please let me know so I can incorporate it into my seminars.
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.