What is the proper tap location for an orifice plate flowmeter?
A. 1 inch upstream and 1 inch downstream of the orifice plate
B. 0 diameters upstream and 0 diameters downstream of the orifice plate
C. 1 diameter upstream and 0.5 diameter downstream of the orifice plate
D. 8 diameters upstream and 2.5 diameters downstream of the orifice plate
Any of these tap locations could be correct — depending upon the application and its design. The mechanical location of flange taps (Answer A) and corner taps (Answer B) is typically maintained by purchasing special flanges that are predrilled to accurately locate these taps relative to the orifice plate. Radius taps (Answer C) and full flow taps (Answer D) are typically located in the pipe itself. Vena contracta taps (not included as an answer) are located 1 diameter upstream and at the vena contracta, determined by orifice geometry, downstream.
Additional complicating factors
Selection between flange/corner taps and pipe taps is typically related to cost and/or the ability to accurately locate pipe taps in small lines. Selection between flange taps and corner taps is largely determined by personal and/or geographic preference.
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.