David W. Spitzer
David W. Spitzer

Which of the following flowmeters measure the actual volume of fluid passing through the flowmeter?

A.    Coriolis mass
B.    Magnetic
C.    Orifice plate
D.    Oscillating piston
E.    Oval gear
F.    Thermal
G.    Turbine
H.    Venturi
I.     Vortex shedder

Commentary
Positive-displacement flowmeters constantly entrap fluid and measure the actual volume of the fluid. There are many positive-displacement flowmeter geometries available to meet various application requirements. Applications can vary from ubiquitous to highly specialized. Examples include domestic water flowmeters and components in a two-phase flow measurement system, respectively. Flowmeters that utilize positive-displacement technology are the only flowmeters that measure the actual volume of the flowing fluid.

Industrial Automation Insider 300x250Coriolis mass, magnetic, orifice plate, thermal, turbine, Venturi, and vortex-shedding flowmeters are not positive-displacement flowmeters. Oval gear and oscillating piston flowmeters are positive-displacement flowmeters.
The correct answers are Answers D and E.

Additional Complicating Factors
From an academic perspective, flowmeters that measure the actual fluid volume should use volumetric units of measurement. This is usually the case for positive-displacement flowmeters. For example, my domestic water flowmeter measures in cubic feet.

However, there are some applications where other measurement units are used. For example, some positive-displacement flowmeters display in mass flow units when the fluid density is known and stable.
 

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.  Spitzer and Boyes is also the publisher of the Industrial Automation Insider. David can be reached at 845 623-1830.

Spitzer can be reached at 845 623-1830 or www.spitzerandboyes.com. Click on the “Products” tab to find his “Consumer Guides” to various flow and level measurement technologies.