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VA Flowmeters 


Variable Area Flow Meters are used to measure the volume flow of liquids, gases & steam. They are a reliable, versatile principle of operation and are designed to operate at a relatively constant pressure drop. They measure fluid flow by observing the position of a float withing a tapered tube. They are also known as Rotameters.


We can offer flow meters with glass, acrylic or fully stainless steel construction materials, in a broad variety of flow ranges (suitable for gases and liquids) and a selection of special options including switch contacts, continuous 4 - 20 mA output signals, totalisers, HART or Profibus communication protocols and more.


They are simple and a cost effective measuring solution to use in many system designs across various industries. Whether you're looking for a C&I or process solution, our VA flowmeters can be sized and selected to meet your individual requirements.

What are Variable Area Flow Meters and How Do They Work? 


Variable Area Flow Meters typically consist of a tapered tube through which fluid flows. Inside the tube is a float, buoyant in the fluid, and as the flow rate changes the float moves up or down. The position of the float within the tapered tube provides visual indication of the flow rate.


Here at Boiswood we are an approved supplier of Kobold flowmeters. These flowmeters are based on the principle of the well-known float-type flowmeters. These instruments are provided instead with a cylindrical flow tube with conical slots around the periphery. This eliminates the usual problems of guiding the cylindrical float within a tapering measuring glass.


The novel design including the provision of an appropriately dimensioned annular gap of constant width between the float and the flow tube has enabled the sensitivity to dirt to be considerably reduced. The float comprises permanent magnets actuating a bistable reed contact external to the flow circuit, that is, the flowing medium is hermetically separated from the electrical contact.


In addition it is embedded in a height-adjustable switch housing, thus ensuring that the contact cannot be damaged even by an aggressive atmosphere. As the medium enters the instrument the float rises. Once its magnetic field reaches the contact tips of the reed switch the contact closes. As the flow increases the float rises further until it reaches its stop. This prevents the float from going beyond the contact range of the magnetic operating tube, that is, the contact remains closed, thus ensuring bistable switching.


With the models SMV-2... and SMV-3... the magnetic field also activates an external, that is, hermetically separated indicator, as a result of which flows are measured accurately even at high operating pressures. The magnetic field and the indicator are designed so as to ensure that the pointer follows even abrupt changes in flow rate.


Types of Variable Area Flow Meters



Typically consist of a tapered tube with float inside. As fluid flows through the tube, the float rises and its position is indicates the flow rate. These are commonly used for measuring gases or liquid in various applications in diverse industries including:

  • Chemical Processing
  • Water Treatment
  • Laboratory Settings
  • Pharmaceuticals
  • HVAC Systems
  • Oil & Gas Productions
  • Food & Beverage Industry


Rotameters are widely used as they are versatile, reliable and known for their simplicity.


Piston type meters

Often known as a positive displacement meter. It's a flow meter which measures fluid flow by counting the number of discrete volumes that pass through the meter (usually cubic units). It consists of a piston or rotating impeller that moves with the flow, dividing the fluid into known volumes. These meters are known for their accuracy and suitability to measure low to medium flow rate of liquid where precise volume measurement is essential. There are commonly used in the following industries:

  • Oil & Gas Productions
  • Water Utilities
  • Chemical Processing
  • Pharmaceuticals
  • Food & Beverage Industry
  • Aviation
  • Automotive


Piston type meters are valued for their accuracy and reliability where exact volume measurements of fluid is critical.


Selection Criteria for VA Flowmeters


  • Type of fluid - ensure the flow meter is suitable for the fluid you need to measure.


  • Accuracy of measurement - understand the flow range/turndown you need to measure.


  • Surrounding environment - ensure the flow meter can withstand environmental surroundings which can include the temperature exposure, pressure, density, flammable, corrosiveness, toxicity & viscosity.


  • Materials of Construction - choose a flow meter based on the construction materials which can withhold temperatures and pressure of the atmospheric conditions.


  • Hygiene Requirements - identify any hygiene requirements for the flow meter to ensure the flow meter adheres to strict processing standards.


Our knowledgeable technical support team at Boiswood can support you in selecting the correct flow meter to fulfil the needs of your application, ensuring efficiency & accuracy to support the high performance of your business.


Why choose Boiswood
for your Variable Area Flow Meters

Quality Products & Service Levels
World-class quality products backed by unrivalled service levels. We only partner with the best manufacturers in industry. You can trust in our 35+ years of experience.
Competitive Pricing Structures
Competitively priced products that we strive to keep consistent. We always ensure special pricing structures are considered.
Excellent Delivery Schedules
Attractive lead times that are monitored and managed, ensuring customers receive on-time deliveries. We can also ship our products internationally.
Ultra-Fast Response Times
Tired of chasing for answers? We pride ourselves on our unmatched response times. You can rely on us to provide extremely quick answers to technical and commercial queries.
Free Technical Support
On-going support for our customers to meet any evolving technical requirements. We can help size and specify solutions for even the most bespoke applications.
OEM & Custom Configurations
We sit alongside design teams to specify the right solution for your application, no matter how demanding. Whether it’s out-of-the-box or a custom design, we are up for the challenge.
Tailored Stocking Profiles
Need your products tomorrow? We’ve got you covered with our ever-growing stock profile and product portfolio. We can hold stock for you based on your consumption rates.
Servicing & Assembly Capabilities
Official and manufacturer certified in-house servicing, testing and assembly for our core products, including custom panels and subassemblies.
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