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Hedland Variable Area Flow Meters
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Flow Fundamentals - Variable Area Flow MetersIf the advanced flow computers found on most of our GPI Turbine Meters offer way more information that you need, consider using a VA Meter…

Also known as Rotameters and Variable Area meters, VA Meters work well for measuring both liquids and gas. Not sure what I'm talking about? Think about the last time you visited someone in the hospital. They may have been wearing a nasal cannula which was hooked up to a small Flowmeter with a tapered tube and a ball that floated up and down within the glass tube. If that sounds familiar, you know what a VA meter is…

A variable area meter is a flow meter that measures volumetric flow of liquids and gases. VA Meters typically consist of a Tapered tube (Glass or Metal) and a float which could also be described as a shaped weight. There are numerous float shapes in use, but spheres and ellipsoids are the most common. The float is pushed up by the drag force of the flow and pulled down by gravity. As the flow increases, the float rises in the tapered tube until reaching a point where the upward force exerted by the flow and downward force of gravity are in balance. As the float settles to a stable position, a reading can be taken typically by using the top of the float as a point of reference against an internally mounted flow scale.

Advantages/Disadvantages
With the exception of those meters equipped with transmitters, alarms, etc., standard VA meters require no power. They are simple to use and because the flow tube span increases proportionally as the float moves up, the scale is considered to be approximately linear. Other than those VA Meters that are equipped with a spring loaded float, gravity dictates that VA meters be used in a vertical position with the flow going up. Like a turbine meter, VA meters are set up for specific conditions. Any change in specific gravity, viscosity, process temperature, etc., can affect the overall accuracy of the meter.
Applications
Typical applications for a VA Meter include Chemical Injection and Dosing, Boiler Control, Purge Applications, Tank Blanketing and just about any simple flow measurement application measuring gasses and/or clean, low viscosity liquids.

Meet the Author
Flow Specialist - Bill Michie Written By: Bill Michie  
Flow Applications Specialist
Cross Company
Instrumentation Group

Phone: (866) 905-9790 (M-F, 8am-5pm Eastern)
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