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Variable Area Flowmeters (Rotameters)

Process-proven flowmeters. For maximum repeatability and reliability.

As one of the pioneering manufacturers in variable area (VA) flowmeter (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 flowmeters, 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 armored 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 flowmeter 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 flowmeters.

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

Brooks MT3809G variable area flow meter cutaway
MT3809 with Explosion Proof Housing, Variable Area Flow Meter -

Why Use a Rotameter (Variable Area Flow Meter) to Measure Gas or Liquid Flow

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.
variable area flow meters
Oil, gas, fuel mixtures, natural gas, specialty gas

Variable Area Flow Meter Approved for Hazardous Areas Used in Offshore Oil Drilling

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.
Component datasource missing. Select a datasource for this component.
  • 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

1-2% FS

Max Pressure
Refer to Maximum Pressure Ratings Table in Data Sheet
121oC (250oF)
Output Type
Visual Indication
  • 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
Flow Switches
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