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Flow Switches
Rotameters for Liquid and Gas
How to Visualize a Rotameter Measuring Flow Rates

A rotameter often has a ball or other shaped piece (also called a “bobbin”) which is supported by the flow of fluid through a tube. A low or high flow of fluid will create sufficient pressure under the float to raise it in the tube. The height that the moving piece gives an indication of the flow. Since the tube is transparent, graduations can be added to a scale representing a minimum and maximum flow.

The word “Rotameter” began as a trade name by the German company Rota, but they are also known as Variable Area Flow Meters.

Variations: While from the outside, rotameters may not look the same, but the basic principle is used with innovative variations to display the flow. Brooks is a well-known company and trusted manufacturer / supplier of the highest quality Rotameters.

Variable Area Flow Meters (Rotameter)

Process-proven flow meters. For maximum repeatability and reliability.

As one of the pioneering manufacturers in variable area (VA) flow meter (rotameter) technology, Brooks Instrument has created a diverse and proven portfolio of gas flow meters, installed and in use across virtually every industry. From inline flow meters to low volume flow meters, Brooks offers high-performance gas and water variable area flow meter technology for the broadest range of industrial flow meter applications.

This broad portfolio of industrial flow meters includes armoured metal and glass tube mechanical flow meters, each engineered to provide years of repeatable, reliable measurement of gas and liquid flow rates. They feature:

  • Reliable, easy-to-read displays on all mechanical flow meter types — gas, fluid and flow meters for water
  • Fail-safe inline flow indication under any circumstance
  • Integral flow controller to compensate for varying pressures.
  • Materials and designs to suit multiple pressure ranges and chemical compounds for industrial flow meters.
  • Field-replaceable components and custom scales
  • Integration of optional flow switches, automated valves or alarms

Trust the expertise of the Brooks Instrument team for valuable insight on the right fluid flow meter for your needs.  Talk to us for more on our range of industrial flow meter types for gas and water and see why Brooks Instruments leads the world in variable area flow meters.

Key Applications

  • Basic liquid (including water) or gas flow measurement
  • Rotating equipment flow measurement
  • Process analyzers
  • High-pressure flow on offshore oil platforms
  • Chemical injection
  • Purge liquid or gas metering

MT3809 with Explosion Proof Housing, Variable Area Flow Meter


What is a Rotameter?

A rotameter or variable area flow meter is an industrial flow meter that measures the volumetric flow of liquids and gases. There is no difference between a rotameter and a flow meter, and these terms are interchangeable. Inside a flow meter, a gas or liquid moves a float until it reaches equilibrium — the technique to measure the flow rate. Variable area flow meters are used across a wide range of industrial applications because they are an economical and reliable way of measuring very low to high flow rates. Brooks Instrument industrial flow meter experts have identified six key reasons industrial users choose variable area flow meters.


Offshore oil platforms require accurate flow measurement to pump drilling mud at controlled, high pressures through the drill pipe to cool and lubricate the drill bit. A Brooks Instrument metal tube variable area flow meter enables consistent, repeatable pumping of drill mud under these severe process conditions.

Glass Variable Area Flow Meters

  • Improved accuracy over plastic flow meters
  • Suitable for wider flow ranges and and more gas types
Fluid Type
  • Clean Gases & Liquids
Flow Range (Full Scale Capacity)
  • Air: 170 scfm – 280 m3n/hr
  • Water: 98 gpm – 22,000 l/h

Accuracy: 1-2% FS
Max Pressure: Refer to Maximum Pressure Ratings Table in Data Sheet
Temperature: 121oC (250oF)
Output Type: Visual Indication

Metal Variable Area Flow Meters

  • For use in high/low pressure and temperature applications
  • Ideal for measuring fluids in hazardous, remote areas
  • Simple design is easy to install and maintain
Fluid Type
  • Clean Gases, Liquids & Steam
Flow Range (Full Scale Capacity)
  • Air: 750 scfm – 1200 m3n/hr
  • Water: 440 gpm – 100,000 l/h


  • 1-10% FS
  • Class 1.6 – 4 VDI/VDE

Max Pressure:

  • 1379 bar / 20,000 psig


  • 420oC (788oF)

Output Type:

  • Visual Indication
  • 4 – 20mA Analog w/HART® 7
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