Variable Area Flow Meter

ProFlowUSA flow meters, often referred to as “rotameters,” measure flow rate of a liquid or gas by relating linear displacement of an internal “float” or sharp-edged orifice tube to a corresponding flow rate.  As the flow rate increases, the orifice area that the flow moves through also increases – thus, the term “Variable Area”.  Variable Area meters either allow flow through a peripheral orifice formed between a tapered wall and a float as in the traditional rotameter, or an annular orifice and an internal tapered metering pin in the Device Head.  The attributes of the Variable Area flow meter are a linear relationship between flow rate, pressure differential and piston displacement.  Flow rate is read on the Variable Area meters in both Analog or Digital Display by aligning the position of the piston/float to an adjacent calibrated scale.

  • Relative low cost and ease of installation
  • Robust and easy to maintain
  • No need for auxiliary power
  • Works with both liquids and gases




A variable area flow meter, also known as a rotameter, is a type of flow meter used to measure the flow rate of a fluid in a pipe or duct.  It consists of a tapered tube with a float inside that moves up and down based on the flow rate of the fluid.

The tapered tube has a larger diameter at the bottom and a smaller diameter at the top.  The fluid flows through the tube from the bottom to the top, and the float is pushed upwards by the force of the fluid flowing past it.

The position of the float inside the tube is proportional to the flow rate of the fluid, with a higher flow rate pushing the float higher up the tube.  The float is typically calibrated with markings on the outside of the tube that indicate the flow rate of the fluid.

Variable area flow meters are commonly used for measuring the flow rate of liquids and gases in a variety of applications, including in chemical processing, water treatment, and HVAC systems.  They are easy to install, low cost, and provide a visual indication of the flow rate.  However, they may not be as accurate as other types of flow meters, particularly at low flow rates.


Variable Area Flowmeter for liquids and gases

  • Modular design: from mechanical indicator to 4…20 mA / HART®, and Totalizer
  • Any installation position:  Vertical, horizontal or in fall pipes
  • Flange: DN15…150 / 12…6″; also NPT, G, hygienic connections, etc.
  • -196…+400°C / -320…+752°F; max. 1500 psig

The ProFlow Rotogear is the standard variable area (VA) flowmeter for the process and OEM industry.  The VA meter combines mechanical flow measurement of liquids or gases with state-of-the-art communication capabilities.  The device is modularly extendable.  Additional electronic modules can be added or replaced at any time without process interruption.  In this way, its functionality adapts to new requirements – from analogue flow measurement without auxiliary power to digital integration into a fieldbus system.

Show more

The variable areas flow meter is available in various materials and in many different versions.  The sturdy all-metal flowmeter can be also used in applications with high pressures (up to  1500 psig), temperatures (-196…+400°C / -320…+752°F) or aggressive media.  It even allows installation in horizontal or fall pipes up to DN150 / 6″.  A special version for use in hygienic applications is also available.  The Variable Area Flow Meter is intrinsically safe and explosion-proof. 

Product highlights
  • Simple, low-cost installation:  Able to measure and display without auxiliary power supply
  • Unique modularity and serviceability:  Limit switches, 2-wire 4…20mA, totalizer with LCD and pulse output, 
  • Universal ex-concept:  Explosion proof and intrinsically safe
  • Various stainless steel and alloy sensor materials
  • Optional stainless steel housing for corrosive atmospheres
  • Ingress protection IP66 and IP68 / NEMA4X and NEMA6
  • Full scale value for liquids:  10…120,000  l/h / 5…32,000 GPH
  • Full scale value for gases:  0.7…2800 m3/h / 25…100,000 SCFH
  • Turndown ratio 10:1 (optional 100:1)
  • Accuracy:  ±1.5% 
  • Optional hygienic design for use in the food and pharmaceutical industry
Typical applications

Chemical and other process industries:

  • Additives (e.g. catalysts, foam inhibitors, emulsifiers)
  • Acids, bases, phosgene and other chlorides substances, sulphuric substances
  • Condensate and cooling water
  • Nitrogen inertia of vessels and tanks
  • Sample flow monitoring for process analysis
  • Gas sparging in liquids

Oil and gas industry

  • Injection skids for corrosion-, scale- and hydrate-inhibitors
  • Nitrogen, flue gases, etc.
  • Emulsifiers

Machinery and apparatus 

  • Gas seal monitoring for compressors
  • Coolants and cooling water, lubricants, air supply
  • Dry-run prevention of pumps
  • Gas and oil measurement for industrial furnaces

Pharmaceutical industry

  • Demineralized water, alcohol, solvents, insulin etc.
  • Cleaning agents
  • Air measurement in clean rooms

Food and beverage industry

  • Vegetable oil, drinking water, milk, carbon dioxide
  • Cleaning agents

Water and wastewater industry

  • Oxygen sparging into aeration basins
  • Air injection to reduce iron content

Conventional and nuclear power industry

  • Heavy water, borated water, tritium etc.
  • Hydrazine
  • Sulphuric acid
  • Phosphate, nitrogen, hydrogen, Sulphur
  • Purified water, saline water etc.
  • Steam, air, gases, boiler washing water etc.
  • Diesel, return fuel oil flows etc.

Additional information


1/2", 3/4", 1", 1-1/2", 2", 3", 4", 6"

Pressure Class

150LB, 300LB, 600LB, 1500 LB


Flanged, Triclamp


24VDC, Battery


No, Yes

Communication Protocol



4-20 MA, 0-10 VDC


General Duty, Explosion Proof, Intrinsically Safe


Meter Model Series metal tube horizontal flowmeter
Flow range Water 2.5 l/h to 200 m3/h
Air 0.07 to 4500m3/h (201.013bar)
Flow span 10:1
Accuracy Standard accuracy: 1.5% High accuracy: 1.0%
Standard accuracy (PTFE-Liner): 2.5% High accuracy (PTFE-Liner): 1.5%
Connections Flange connection
Standard: DIN2501DN15-DN200 )
Special: DIN2512DN15-DN200
The GB JIS users’ needs
Threaded fittings DIN11851SC40-SC80[1-1/2-3]
According to demands of users
Steam Jacket Connections Internal threads 1/2
Flange connection DN15 PN40 DIN2501
According to demands of users
Max.  Allow. pressure 250bar
Temperature range Fluid temperature
-40 to+200Standard type
-20 to+125PTFE-Liner type
-40 to+400High temperature type
Ambient temperature
-40 to+70
Materials SS304,SS304L,SS316,SS316L
Hastelloy C
According to demands of users
Protection class IP67
Supply power 12-28V DC, two-wire system, battery power




There are no reviews yet.

Only logged in customers who have purchased this product may leave a review.

You may also like

Translate »