The 4 types of water flow meters you need to know

A water flow meter measures the amount of water flowing through a pipe. You have several kinds to choose from, depending on your application, maintenance needs, and budget. Each kind has a unique working principle, specific benefits, and overall cost-of-ownership. So which one should you choose for your application?

Courtesy of Sierra flow meter

You have four primary types of flow meter: mechanical, vortex, ultrasonic, and magnetic. Let’s go over each now.

Mechanical flow meters

The most popular and cheapest, this meter measures the speed of water running through a pipe with a rotating turbine or piston in it, usually in a propeller, shunt, or paddle wheel design.  The volumetric flow rate of the water is proportional to the speed of the rotating blades. Sadly, these meters can clog in dirty or chunky water, which increases maintenance costs. They also don’t work well with low flow.

 Turbine flow meter
Courtesy of Globalspec Turbine flow meter

Vortex flow meters

Vortices are the “swirls” that form as a fluid moves past an object, like river water around a rock or air currents across a wing. In a vortex meter, a sensor tab flexes from side to side as each vortex flows past, producing a frequency directly proportional to the volumetric flow rate. Multivariable vortex meters measure up to five process variables with one connection: volumetric flow rate, mass flow, density, pressure, and temperature.  Insertion vortex meters work well on very large pipes since you can insert them by hot tapping with a retractor.

Vortex flow meter
Courtesy of Sierra Vortex flow meter

Ultrasonic flow meters

These meters use ultrasound to measure flow. A transit-time ultrasonic meter sends one signal downstream and another upstream. Then the meter compares the travel time for both signals to find the flow velocity. Finally, it uses this calculation to find the volumetric flow rate.

You can also measure energy and temperature using the differences between the hot and cold legs. Clamp-on ultrasonic meters measure water from outside the pipe by sending signals through the pipe walls. This feature makes them ideal for measuring flow in large pipes and a wide range of other processes.

Ultrasonic flow meter
Courtesy of Sierra Ultrasonic flow meter

Magnetic flow meters

Last but not least, magnetic meters use a magnetic field and Faraday’s law of induction to measure flow. Liquid flowing through a magnetic field creates a charge. So when the fluid flows faster, it creates more voltage, proportional to the movement of the water. The meter then processes the voltage into the flow rate. Magnetic flow meters don’t have great accuracy, so you can’t use them for custody transfer. They also don’t work on pure water because it has no ions to measure.

magnetic flow meter
Courtesy of Saba Magnetic flow meter


The best types of flow meter to use depends on your process, because some meters work better than others on a certain product. To learn more, watch videos, read white papers, and use selection tools to find the right product for your applications.

Original publication here

Author: Scott Rouse, Product Line Director @Sierra Instruments

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