Increasing flow from 100 to 200 liters per minute (lpm) will cause an orifice plate primary flow element to generate:
A. 25 percent of the differential pressure at 100 lpm
B. 50 percent of the differential pressure at 100 lpm
C. The same differential pressure as at 100 lpm
D. 200 percent of the differential pressure at 100 lpm
E. 400 percent of the differential pressure at 100 lpm
The differential pressure across an orifice plate primary flow element will increase as flow increases, so Answers A, B and C are not correct.
Orifice plate primary flow elements produce a differential pressure that is proportional to the square of the flow rate. Therefore, doubling the flow will create (200/100)2 or four times the differential pressure (Answer E).
Additional complicating factors
The squared output relationship applies to concentric orifice plates operating in the turbulent flow regime. Conical, eccentric, integral, quadrant and segmental orifice plate designs generally follow this relationship over a limited range of Reynolds numbers.
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 may 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.