What is a Flow Meter and Its Types

Thousand years ago, people know the concept of flow meter and their measurement when farming, irrigation, and water conservancy became essential to humans. In Egypt country, ancient people used weir rudiments to evaluate the flow of water in the Nile River. So it indicates whether the harvest would be favorable (or) unfavorable. These meters are mainly used for two purposes the process control and verify & product quality improvement so that the material cost will be reduced and efficiency will be increased. The applications of flow meters mainly include in industries like pharmaceuticals, metallurgy, petrochemicals, home energy, pulp & building. Day by day, the development of meters and their application has changed but their necessity remains the same as accuracy. This article discusses an overview of the flow meter.

What is a Flow Meter?

Definition: A device that is used to gauge the mass of liquid or gas or volume is known as a flow meter. Alternate names of this device are flow rate sensor, liquid meter, flow gauge, indicator based on the industry but the working principle is the same. These meters are used to measure open channels such as streams or rivers. Some types of meters mainly focus on liquids and gases in a pipe. The main benefits of these meters are improving the accuracy, resolution, and precision of the liquid.


The working principle of flow meter is to measure the amount of gas, liquid otherwise streams around the device. These devices work with the same end goal but in different ways. They offer repeatable & accurate flow measurements for different applications like semiconductor processing, process control, etc.

This meter calculates either mass or volume. The liquid flow in the pipe can be equal to the cross-sectional area within a meter & the velocity of the liquid flow (Q = A * v). The flow of mass can be calculated by using this formula like ṁ = Q ∗ρ (Q = the flow rate of liquid & ρ is the density of the fluid). In many cases, the flow of mass is the main consideration, particularly in gases selling/buying, chemical reactions, combustion, etc.

Types of Flow Meters

These are classified into different types based on its application like a mechanical, optical and open channel.

Mechanical Flow Meters

These types of meters measure the flow of liquid with the help of moving parts arrangement, known liquid volumes through a sequence of chambers or gears. These meters are classified into four types which include the following.


Positive Displacement Flow Meter

The PD (positive displacement) flow meters work by counting or isolating identified volumes of a gas or liquid. Flow measurement can be obtained by counting the no. of accepted isolated volumes. Each meter includes its distinct mechanism to count liquid volumes in a specific no. of cycles. These meters give high accuracy & good repeatability and they do not need a power supply for their function and straight-up & downstream pipe for their installation.

Mass Flow Meter

This type of meter is used to provide an estimated flow rate to the consumer by measuring the volume of the substance flowing through them. These are weight-oriented meters used where weight oriented measurement is required like in chemical industries.

Differential Pressure Flow Meter

This meter works on incompletely blocking the flow of liquid within a pipe to create a disparity in the static pressure among the up & downstream part of the device. The difference in the differential pressure can be measured to decide the liquid flow rate. At present 40% of these meters are used in industries to measure different fluids like gases, highly thick liquids. These are very popular due to their simple design & less cost.

Velocity Flow Meter

This meter is used to measure the velocity of the stream to analyze the volumetric rate of liquid flow. These meters are less sensitive when the internal liquid movement is higher. These meters mainly include paddlewheel, turbine, electromagnetic, vortex shedding & sonic or ultrasonic flow meters.

Optical Flow Meter

In industrial liquid flow measurement, an optical type meter is a recent development to measure the liquid’s velocity through a pipe. This technology is named as L2F or Laser-Two-Focus and it uses two laser rays for detecting the light diffusion particles carried by the flowing liquid.


Open Channel Flow Meter

This kind of meter is used to measure the flow of liquid that is open to the environment at some end in the liquid flow measurement lane. This liquid can be completely open to the atmosphere or enclosed in a closed tube with partially filled liquid and simply unlock to the atmosphere at the fitting end of the meter itself.


The flow of open-channel mainly occurs while fluid flows within a channel or conduit with an open surface. The best example of this flow is rivers, canals, irrigation ditches, streams, etc.


1). How is flow measured?

In general, flow can be measured in two different ways like based on volumetric & weight

2). How do I calculate the flow rate?

For instance, if you fill up a 10 Liter bucket in 2 minutes, then the flow rate can be calculated as 10/2 = 5 Liters per 1 minute.

3). Where are flow meters used?

These are used to measure the mass or volume of a liquid or gas based on the industry.

4). Which flow meter is the most accurate?

Coriolis mass type is the most accurate but it is expensive

5). How do you calibrate a flow meter?

Flowmeter calibration can be done in different ways by adjusting & contrasting of the meter to conform to a standard under test.

6). What is the unit for measuring flow?

The flow of liquid is frequently measured in units of cubic feet/second, cubic meters/second, and gallons/minute.

Thus, this is all about an overview of a flow meter. It is one kind of device used to measure the gas flow rate, steam otherwise liquid throughout a pipe. Different types of applications need mass flow measurement like compressed air, natural gas, burner control, boiler efficiency, mixing and blending of gas, water & steam flow. Here is a question for you, what are the advantages and disadvantages of flow meters?