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. All water flow meter types have unique working principles, specific benefits, and costs. This article will help you find the right one for your process.
There are 4 common water flow meter types: turbine (also called mechanic), vortex, ultrasonic, and magnetic. Let’s go over each now.
Water flow meter types
Turbine water flow meter
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, such as process water, which increases maintenance costs, so we recommend electromagnetic process flow meters. They also don’t work well with low flow.
Vortex water flow meter
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.
Ultrasonic water flow meter
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.
If you would like to know, check out our article on ultrasonic water flow meters.
Electromagnetic water flow meter
Last but not least, electromagnetic water flow 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 flow meter then processes the voltage into the flow rate. Electromagnetic water 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, so they can only be called water flow meters with a qualification.
Depending on the brand, you can also have a confusing range of liners to choose from. You need to know the chemical compatibility, flow velocity, and potential abrasion in your application. So this information will factor into your choice of the best liner for your application.
Water makes for a simple flow application because you don’t need a special liner material. For pure water, you can go with a simple liner like hard rubber or polyurethane, but if you anticipate corrosive chemicals or process water, you will need something else.. If you are unsure what to choose, give us a call and our experts will be happy to help.
Electromagnetic process flow meter
Electromagnetic flow meters are especially suited to measure process water flow since chunky liquids can clog turbine or vortex flow meters.
Keep in mind that your process water dictates the equipment you use. Some chemicals may attack your flow meter and shorten its lifespan. If your process water contains chemicals, you’ll need a Teflon liner to prevent corrosion. Otherwise, just go with polyurethane or hard rubber liners.
The ideal water flow meter type is determined by the details of your process because some flow meters work better than others in certain situations. You can save a lot of time and energy by making an informed choice, so if you are still confused, don’t hesitate to give us a call.
This article is based on a publication by Scott Rouse Product Line Director @Sierra Instruments.