Which of the following orifice plates is most accurate?
A. Concentric
B. Conical
C. Eccentric
D. Quadrant
E. Segmental
Commentary
The concentric orifice plate (Answer A) is the most commonly specified orifice plate. Orifice plate standards, such as AGA-3, API 2530, ASME-MFC-3M, and ISO 5167, describe these flowmeters for use in industrial and custody-transfer applications to include water and natural gas. A case could be made that a concentric orifice plate that is properly designed, installed and maintained is the most accurate of these orifice plates.
However, not all fluids are clean and non-viscous like water and natural gas. Conical orifice plates (Answer B) are not frequently applied due to a lack of generally accepted coefficient data. Eccentric orifice plates (Answer C) can be used when entrained gases are present in liquids or when liquid is present in gas. Quadrant orifice plates (Answer D) can operate at low Reynolds numbers associated with more viscous liquids. Segmental orifice plates (Answer E) can be used in applications where entrained gas or particles would build up in front of an eccentric orifice plate installation.
Additional Complicating Factors
Concentric orifice plates are typically specified when orifice plate technology is selected. Other primary element technologies and/or other flowmeter technologies should be considered when the application is not suitable for concentric orifice plates.
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 in the navigation menu to find his “Consumer Guides” to various flow and level measurement technologies.
