In specific types of machines, it is important to be able to measure the flow of fluid that is passing through certain parts of that machine. When fluid needs to be measured, there is usually some sort of sensor or flow meter that is built into the machine. There are many different types of flow meters that are used in various types of machinery. Common types of flow meters that you are bound to run into include rotameters, flow nozzles, venturi tubes, orifice plates, turbine flow meters, pitot tubes, and positive displacement flow meters. There are a lot of different things that you need to take into account before choosing the exact type of flow meter you need for your particular application.




Rotameters are also referred to as variable area flow meters. These are usually some sort of plastic or glass tube that is placed upright. The tube is graded, so one end is larger than the other. The larger end of the tube should be at the top. Inside the tube is a meter that floats in the fluid as it passes through. The float rises in the tube due to the fluid flow. You can read the flow rate by measuring how high the float is in the tube.


Flow Nozzles


Flow nozzles are often placed horizontally and measure the flow of air or gas that passes through. These nozzles are one of the more inexpensive ways to measure flow and are used in a variety of industrial applications.


Venturi Tubes


Venturi tubes measure flow rate by creating pressure differences in a given area. In the tube, the fluid is pressurized and measured. As the fluid flows out of the tube, it recovers the pressure it had before passing through the tube up to 80 percent.


Orifice Plates


Orifice plates are placed between the upstream and downstream sides of a pipe, which is obstructed partially by the plate. The plate then measures the flow of the fluid passing through it. They are also fairly inexpensive and can be used in a variety of ways. However, orifice plates have fairly low turndown rates and become more inaccurate as they get worn down.


Turbine Flow Meters


Turbine flow meters use turbine blades in order to measure fluid flow. As the fluid passes through a pipe or tube, it comes in contact with the blades of the turbine. This contact usually results in the blades beginning to move or rotate. The blades will usually rotate at a certain speed, which is used to determine the flow of the fluid.


Pitot Tubes


Pitot tubes are often used in applications for ventilation to measure fluid flow. It functions by changing kinetic energy or movement into potential energy.


Positive Displacement Flow Meter


Positive displacement flow meters use fixed volumes of fluid to measure flow. This is usually done with rotors. The faster the rotation of the rotors is, the more fluid is displaced. This type of flow meter usually handles fluids like Freon, heating oils, printer ink, and so on.


Determining Your Flow Meter


You need to ask yourself a lot of questions before you decide which flow meter is right for you. First, you will want to know what type of fluid you will be measuring, requirements for accuracy, maximum pressure, location of the meter, and compatibility of the meter with the materials you will be using. There are a lot of different considerations to take in before selecting your flow meter. Remember that different types of meters will provide varying levels of accuracy, and some have higher pressure drops than others.


Flow meters can be used in all kinds of applications, including:


  • Dirty and clean water
  • Dirty and clean gas
  • Steam
  • Compressed air
  • Viscous fluids
  • Lubricating oil
  • Corrosive fluids
  • Cryogenic fluids


The type of flow meter that you end up using for your projects depends a lot on the type of fluid that you will be measuring and how accurate you need the measurement to be. Inexpensive types of meters may be suitable if you can accept lower turndown rates. You may also need to take into account the direction of flow and the amount of pressure that the fluid is subjected to. Some flow meters allow fluids to stay exactly as they are while others may convert the energy the fluid makes in order to produce a measurement. Make sure you understand what you need your flow meter to do for you before you purchase one.