Variable Area Flowmeters

Variable Area Flowmeters

A variable area flowmeter, also known as a variable area flow indicator, is a flow measurement device used to measure flow rates of various fluids, steam, and gases. Hence, this is a widely used device in industrial processes pertaining to water treatment, chemicals, scientific research, and other flow related applications. The volumetric flow of a fluid can easily be measured using these flow meters. It consists of a vertical tapered tube with a float inside that moves vertically in response to the fluid flow.

At Cannon Water Technology, we offer various types of variable area flowmeters sourced from reputed manufacturers such as Seametrics, Blue-White, and so on. We also offer related accessories such as tri-clamps, flow cell indicator, gasket, cleaning module, and so on. The flow meters listed here are specially designed to serve challenging industrial environments and measure the flow rates of fluids with different consistencies and textures, including semi-solids, liquids, particulate fluids, and slurries.

How Does a Variable Area Flow Meter Work?

These flow meters feature a conical tube with a float inside it. The fluid flows through the tapered tube and forces the float to position itself such that sufficient area is left for the fluid to pass. This float will rise high when the flow increases. When used to measure the flow rate of liquids, the float rises due to the liquid’s buoyancy and its velocity head.

When used for measuring gas flow, this buoyancy can be neglected, and float raises in response to the velocity head. The float of the flow meter moves proportionately to the flow rate of the fluid and the annular area between the tube wall and the float. There comes the point when the upward force of the flowing fluid and gravitational force exerted by the float’s weight downwards equalize. The float will remain constant in this position and won’t move up or down. The flow meter assumes a distinct position with every continuous flow rate.

The position of the float will change according to gravity. The flow meters feature in-line floats, but they may also feature pistons or vane. The flow meters must be oriented and mounted vertically to the device for appropriate results. The changed position of the float indicates the flow rate of the fluid under consideration.

What are the Components of Variable Area Flowmeters?

Variable area flow meters consist of several key components that work together to measure and indicate the flow rate of fluids. The main components of a variable area flowmeter are:

  • Tapered Tube: The flowmeter features a transparent or translucent tapered tube through which the fluid flows. The tube has a larger diameter at the bottom and a smaller diameter at the top, creating a pressure differential.
  • Float: Inside the tapered tube, there is a float or piston that moves vertically in response to the fluid flow. The float is typically cone-shaped or spherical and is buoyant in the fluid.
  • Guided Rod: A guided rod or guide wire is attached to the float and helps maintain its vertical alignment within the tube, preventing it from tilting or getting stuck.
  • Scale: Alongside the tapered tube, there is a graduated scale that provides a visual indication of the flow rate. The scale is marked in units such as liters per minute (L/min) or cubic feet per hour (CFH), corresponding to the flow rate.
  • Float Position Indicator: Some variable area flowmeters have a float position indicator, such as a magnetic or mechanical pointer, that moves in tandem with the float inside the tube. This provides an additional visual indication of the float position and the corresponding flow rate.
  • Inlet and Outlet Connections: The flowmeter has inlet and outlet connections where the fluid enters and exits the device. These connections are usually designed to match the plumbing or piping system being used.
  • Mounting Options: Variable area flowmeters may come with various mounting options, such as panel mount, wall mount, or pipe mount, to suit different installation requirements.

Types of Variable Area Flow Meters We Offer

Our rotameters flow meters are quite easy to install, use, and maintain. Here are some types of variable area flow indicators we offer.

  • Magnetic Flowmeters: Also called magnetic inductive flowmeters or magmeters, these devices are mainly used to measure the flow rate of conductive liquids. They use electromagnetic induction to measure the flow rate. Once the magnetic field is applied to the fluid, it produces voltage which is measured based on the fluid movement. We offer fixed depth insertion magmeters with a flow computer.
  • Rotameters: These variable orifice flow meters have a tapered tube with a float inside it. The float height increases or reduces based on the flow rate, and gradually stabilizes at a position. This position of the float within the tube indicates the flow rate. Most models of these flow meters can measure the flow rates of highly corrosive fluids.

Beneficial Features of Variable Orifice Flow Meters

Here are some beneficial features of our variable area flow meters.

  • Our variable area meters offer a highly accurate flow rate output with accuracy around ±2% of full-scale reading, even if repeated measurements are taken. If calibrated regularly, this accuracy level is maintained over the years.
  • Mostly made of premium quality materials such as Hastelloy, stainless steel, PVC, machined acrylic, and so on, they are designed to handle corrosive and abrasive fluids with varied consistencies and flow.
  • Most rotameter models have a non-linear scale by about 5%, while for others, it is linear.
  • These flow meters are suited for low to medium flow rate applications.
  • They are easy to install, regardless of the fittings or pipe length. Most of them are suitable for pipes between 4 and 10 inches.

How to Select the Right Variable Area Flow Meter?

While we offer you the best services and assist in the selection process, here are some points that may help select the right variable area meter depending on your application.

  • Knowing your application requirements in terms of existing pipe dimensions, the types of fluids used, and more is key. This helps select the right type of material in terms of its physical and chemical properties, temperature, pressure, corrosion resistance, and so on. With the right pipe dimensions, you can fit the flow meter well.
  • Determine the mounting position and the available options you have with the flow meter model vis-à-vis the area available. Check for the configuration if it is to be fitted with an integrated system in an industrial process.
  • While most of these meters offer digital and analog outputs in mA, check if it fits the required signal output range to control the system.
  • Check if the meter can withstand harsh operating environments, high pressures and temperatures or as required in your application.
  • Identify the type of fluid to be measured. As the properties like densities, viscosities, and chemical composition of fluids differ. Check if the material of the flow meter is compatible with the fluid used.
  • Determine the maximum and minimum flow rates that the meter has to endure. Variable area flow meters can be availed in different flow rates, so, choosing the one that meets your needs is important.
  • Check the temperature and pressure ranges of the flow meter and ensure it must be capable of handling specific conditions.
  • Does your application demands accuracy? Remember, that higher precision comes at higher costs. Ensure to balance your needs with your budget.
  • For many applications across industries like petrochemicals, food and beverage, and pharmaceuticals, the devices must meet specific certifications.

Applications of Variable Area Flowmeters

Variable area flow meters are used:

  • For liquid and gas measurement
  • As process analyzers
  • For chemical injection
  • For measuring high-pressure flow on offshore oil platforms
  • For purging liquid or gas metering

We regularly supply these variable area flowmeters to our clients across the following industries

At Cannon Water, we make sure that we offer you the best and most high-quality products for all your water treatment needs. Quality is our topmost priority, and hence we source our products from trusted manufacturers. These products are carefully chosen and included in our list after much consideration.

Our experts watch industry trends and are aware of the changing customer needs, which makes us offer only the best and most in-demand devices through our website. These flow meters are often combined with other flow meters and water treatment devices for the best results in many process industries. If you have any questions regarding our variable area flowmeters, please feel free to contact us. Our customer support team will be happy to assist you.


  • What is variable area flow meter?

The Variable area flowmeter is an instrument for measuring the flow of liquids and gases in pipelines.

  • What is the advantage of variable area meter?

Variable area flowmeters offer several advantages like simple and visual flow indication, wide flow range, compatibility with different fluids, minimal pressure drop, reliability and low maintenance that make them suitable for certain applications.

  • How to Select a Variable Area Flow Meter?

Selecting a variable area flowmeter involves considering several factors such as fluid and its properties, flow range, desired accuracy, assess environmental conditions, installation requirements to ensure the appropriate choice for your application.

  • What is the accuracy of a variable flow meter?

The typical accuracy of a variable area flow meter is within the range of ±2% to ±5% of the full scale. This means that the measured flow rate can deviate by up to ±2% to ±5% from the actual flow rate.

  • What is the range of variable area flow meter?

Variable area flow meters are available in various sizes, ranging from small meters suitable for low flow rates to larger meters capable of handling higher flow rates. The range of flow rates covered by variable area flow meters can span from a few milliliters per minute (mL/min) to several hundred liters per minute (L/min).

  • Can I use your variable flow meters in direct sunlight applications?

Yes, you can use many models of variable flow meters in direct sunlight applications.

  • Can these variable flow meters be used for measuring both liquids and gases?

Some models available with us are compatible with both liquids and gases. You can contact our team today to discuss these requirements.

  • What are the limitations for using variable flow meters?

The variable area flow meters offered by us are designed for use across broad flow ranges. However, their uses may be limited by factors, such as changes in fluid density and viscosity, low accuracy, limited measurement ranges, and so on. Some of our models are not ideal for measuring turbulent flows.

  •  Do all your variable area flow indicator support corrosive applications?

Most models from Blue-White offered by us can support corrosive applications. They are equipped with Hastelloy floats and guide rods.

  • How can I read the flow rate on variable area meter?

You can read the flow rate by observing the float position in the meter’s tapered tube. Most flow meters feature a scale on the tube where you can read the flow rate based on the float position.

  • Is calibration necessary for variable area flow meters?

Yes, periodic calibration would help maintain their performance in the long run. The frequency of this calibration would depend on the critical nature of the application, flow rate, and other factors.

  • Can variable area flow meters be installed in any orientation?

Yes, you can install them in any orientation. However, we recommend you to check the installation guidelines provided by the manufacturer to understand the best orientation for your application. 

  • What is the accuracy of a variable flow meter?

The typical accuracy of a variable area flow meter is within the range of ±2% to ±5% of the full scale. This means that the measured flow rate can deviate by up to ±2% to ±5% from the actual flow rate.

  • What is the range of a variable area flow meter offered by you?

Variable area flow meters are available in various sizes, ranging from small meters suitable for low flow rates to larger meters capable of handling higher flow rates. The range of flow rates covered by variable area flow meters can span from a few milliliters per minute (mL/min) to several hundred liters per minute (L/min).