Flow Meters manufactured in Britain
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Paddlewheel Flow Meters

Paddlewheel flow meters are another type of flow meter that uses a rotating element to measure fluid velocity. Here are some key features:

  • They contain a paddle wheel with radial vanes or blades that protrude into the flow stream. As fluid flows past, it causes the paddle wheel to spin.
  • Suitable for clean, non-viscous liquids like water, oils, etc. Not recommended for dirty or slurry flows which can foul the paddles.
  • Paddle wheel meters have a simple, rugged design with few moving parts. This makes them low cost and reliable.
  • They can handle a wide range of flow rates and pipe sizes. Useful for flows from 1 inch to several feet diameter.
  • Accuracy is around ±2% to ±5% full scale. Repeatability is good.
  • Installation requires proper orientation – the paddle wheel must be precisely parallel to the flow direction.
  • Overall, paddlewheel flowmeters are simple, inexpensive meters for clean liquid flows in larger pipe diameters. They are less accurate than turbine meters but provide adequate performance for basic flow monitoring.

Paddlewheel Principles of Operation

Paddlewheel flow meters monitor the flow of liquids. They consist of three primary components: the paddlewheel sensor, the pipe fitting and the display/controller. The sensor itself consists of a freely rotating wheel/impeller with embedded magnets, this is inline with the flow and will rotate when inserted in the flowing medium. As the magnets in the blades spin past the sensor, the paddlewheel meter generates a frequency and voltage signal which is proportional to the flow rate. The faster the flow, the higher the frequency and the voltage output.

The Metri paddlewheel is designed to be inserted into a pipe fitting, either ‘in-line’ or insertion style. These are available with wide range of fittings styles, connection methods and materials such as PVDF, polypropylene, and stainless steel. Similar to turbine meters, the paddle wheel meter requires a minimum run of straight pipe before and after the sensor.

Flow displays and controllers are used to receive the signal from the paddlewheel meter and convert it into actual flow rate or total flow values. The processed signal can be used to control the process, generate an alarm, send signals to external etc.

Paddlewheel flow meters (also known as Pelton wheel sensors) offer a relatively low cost, high accuracy option for many flow system applications, typically with water or water like fluids.

Paddlewheel Flow Meter principles

Paddlewheel Flow Meter Advantages

  • Low cost solution with high flow system accuracy
  • Easy to install and operate, resulting in a low cost of ownership
  • No pressure drop making it ideal for gravity flows
  • Insertion flow meter design lowers installation and maintenance costs

Paddlewheel Flow Meter Limitations

  • Paddlewheel meters work best with clean fluids as particulates can prevent the paddle from spinning properly
  • Not suitable for gases
  • Requires a turbulent flow profile (consistent fluid velocity across the pipe diameter) for accuracy
  • Requires a straight run of pipe before and after the flow meter to allow swirl patterns in the flow stream to dissipate
  • Paddlewheel meters may not function properly with high viscosity fluids where the flow profile is laminar
  • The pipe must be full; any air in the line may lead to inaccuracies

Typical applications for paddlewheel meters include the accurate measurement of preset fluid volumes in dispensing systems, control of chemical metering pump output, flow verification, irrigation systems and alerting users to flow rate increases or decreases outside a programmed range.