Water Flow Measurement for Pipes and Open Channels

Water flow measurement is common in both industry and life. You may often hear about the use of electromagnetic flowmeters to measure wastewater. The clamp-on ultrasonic flowmeter measures large water pipes. The establishment of a new irrigation system requires monitoring of water flow. Even rivers and open channels need water flow detection. Use various water flow meters to detect flow and output 4-20mA or RS485 digital signals. Helps us effectively monitor and manage water flow.

Next, we will boldly analyze and sort out the method of Water flow measurement.

Ways to Water Flow Measurement

Water Flow Measurement

Water Flow Measurement can be simply divided into the following two situations: closed pipes and open channels.

Among them, pipeline water flow measurement is divided into full pipe and non-full pipe measurement. Open channel water flow measurement can be divided into regular channels and irregular rivers.

Extended Reading: LORA water meter

Water flow measurement in water pipes generally refers to measuring the water velocity or water flow in the pipe.

In closed pipes, water flow measurement can be divided into two situations: full pipe and non-full pipe.

Full Pipe measurement:

Full pipe measurement, as the name suggests, refers to the situation when the pipe is completely filled with water. At this time we usually use electromagnetic flowmeter or ultrasonic flowmeter for measurement.

The electromagnetic flowmeter uses the Faraday electromagnetic induction principle to accurately measure the water flow velocity and then calculate the flow rate.

The ultrasonic flow meter determines the flow rate by detecting the time difference in the propagation of ultrasonic waves in the fluid.

Partially full pipe measurement:

For non-full pipes, the situation is slightly more complicated. A partial pipe means that the water does not fill the entire pipe. In this case, we usually use a special electromagnetic flowmeter to measure it.

Further reading: Inline water flow meters

Open channel flow meters can be used in harsh environments. Such as urban water supply diversion channels, sewage treatment inflow and discharge channels, and corporate wastewater discharge.
Next, we will introduce to you the specific method of open channel flowmeter such as flow measurement.

And when our sight shifts from underground pipes to open channels on the ground, there are different methods for measuring water flow.

Regular drains:

In a regular channel, the shape and size of the flow are known. In this case we usually use a weir or Farrer flume to measure the flow. From the change in height of the water as it passes over these structures, we can calculate the amount of water flowing through.

Irregular river channels:

For irregular river channels, due to the complex and changeable shapes of the river bed and river banks, we generally use a current meter to directly measure the speed of the water flow and calculate the flow of the entire river channel based on the cross-sectional information of the river channel.

Extended reading: Make Ultrasonic Open Channel Flow Meter Work for You

Extended reading: non contact flow meter

Water Flow Measurement Methods

With the development of science and technology and production, many places need to measure the flow of different liquids under different conditions. For this reason, after research, a variety of flow meters have been developed. These methods can be summarized as:

  1. Container method. Including weight method, volume method.
  2. Throttling method. Including orifice plate, nozzle, venturi tube, venturi nozzle, etc.
  3. Weir flow method. Including right-angled triangle weir, rectangular weir, full-width weir and other methods.
  4. Differential pressure method. Including volute differential pressure, elbow differential pressure, runner differential pressure, draft tube differential pressure, etc.
  5. Flow meter method.
  6. Tracer method. Including concentration method, integral method, transit time method, etc.
  7. Water hammer method.
  8. Ultrasonic method.
  9. Metering method. Including electromagnetic flowmeter, turbine flowmeter, vortex flowmeter, etc.
  10. Other methods. Including laser flow measurement technology, Pitot tube method, etc.

Extended reading: Ultrasonic Flow Meters Types & Technical Guide

Types of Water Flow Meter

A water flow meter measures the amount of water flowing through a pipe. We have several kinds to choose from, depending on the application, maintenance needs, and budget.

Extended reading: 2 inch Water Flow Meter

There are four common water flow meter types:

Turbine (also called mechanical), Vortex, Ultrasonic, and Magnetic. We will tell you everything you need to know about them and help you choose one for your application.

The electromagnetic flowmeter can measure the speed of the water by using a simple magnetic field.

When water passes through a magnetic field, a voltage is generated. In this way, higher flow rates always generate more voltage when sent through the electromagnetic flowmeter. The electronic system connected to this meter will receive the voltage signal and convert it into volume flow.

Remember that the water needs ions to generate voltage, which means that the electromagnetic flowmeter cannot be used with pure water without pollutants.

Guess you like: Magnetic Flow Meters types and technical guide

Extended Reading: 3 inch (3″) Water Meter

Turbine flow meters easily become the most common flow meters around, mainly because these flow meters are more affordable than other types.

The mechanical flow meter measures the water flow through the rotation of the turbine, which uses a basic propeller, blade, or split flow design. The flow rate of water is equal to the speed of the blades.

If mechanical flow meters are to be used, they may become clogged if the water is dirty or more contaminated than expected.

Therefore, you probably should not use this kind of flowmeter to measure the flow of slurry. Since these flow meters can become clogged, they are more frequently maintained than other flow meters.

Know more about: Turbine type Flow Meter for Liquid & Gas technology

The vortex flowmeter is a unique flowmeter that measures the flow of water by using vortex flow.

When the fluid pushes over the obstacle, it will produce a vortex and form a vortex. The flowmeter is equipped with a sensor tab. As long as the vortex flows through the sensor tab, the tab will bend, which will produce a frequency output indicating the flow rate of the water.

If you decide to choose a multivariable vortex flowmeter, it can measure up to five different variables that are useful for your specific application.

These variables include mass flow, temperature, density, flow rate and pressure. These meters are especially suitable for large pipelines.

Extended reading: High Pressure Rotameter for Liquids/gas-Upto 25 Mpa

Ultrasonic flow meters are designed to use ultrasonic technology to measure the speed of water as it passes through the pipeline.

You should understand two basic types of ultrasonic flow meters, including runtime flow meters and clamp-on ultrasonic flow meters.

If you choose a run-time flow meter, send a standard ultrasonic signal downstream before sending another signal upstream. These two signals are then compared to determine the water flow rate. This is mostly a pipeline water flow meter. It is often used for household water.

For clamp-on ultrasonic flowmeters, can be placed outside the pipe and are designed to emit acoustic pulses through the pipe wall in order to receive the measured value. Since they can be installed outside the pipeline, they can be used for almost any application and can be used with larger pipelines.

Extended reading: Industrial VS Residential inline water flow meters

Rotameter is also called float flowmeter. Rotameter is composed of three units: float flow sensor part, displacement-angle conversion mechanism part, and information conversion processing part. It is a traditional variable area flow measurement device. When the flow rate changes, the float moves up and down in the vertical tapered tube. The circular flow area formed between the cone and the float changes. It is a volumetric flow meter that realizes flow measurement based on this principle.

Extended reading: Metal Tube Flow Meter-Variable Area Flow Meters Principle

Rotameter can measure water and gas. But you must explain the medium and flow range with the manufacturer when selecting the model. The method of calibration by the manufacturer is different. The completed flowmeter cannot be used mutually.

Extended reading: Liquid Bitumen/Asphalt Flow Meter

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There are several methods/flow meters that can be used to measure open channels:

Use a flow meter to directly measure the flow of the river. There are many types of flow meters, mainly including differential pressure, electromagnetic, launder, and weir flow meters. It can be selected and used according to the actual flow rate range and test accuracy requirements.

Extended Reading: Chilled Water Flow Meter

Put the river water into a container of known capacity. Measure the time it takes to fill the container. Repeat the measurement several times. Find the average value t(s). A method to calculate the amount of water.

This method is simple and easy to implement, and the measurement accuracy is high. It is suitable for rivers with small river flows. However, there should be a proper drop between the overflow outlet and the receiving water body or an error can be formed by the aqueduct.

Select a straight river section. Measure the area of ​​the cross-section of the water flow within a 2m interval of the river section. Find the area of ​​the average cross-section.
Put a buoy in the upper reaches of the river and measure the time it takes for the buoy to flow through a certain section (L). Repeat the measurement several times. Get the average of the required time (t), and then calculate the flow velocity (L/t). The flow can be calculated as follows:

In the formula, Q is the water flow, the unit is m^3/min. v is the average flow velocity of the water flow, and its value is generally 0.7L/t, and m/s.S is the average cross-sectional area of ​​the water flow, the unit is m^2.

Calculate the river flow by measuring the cross-sectional area of ​​the water flow, measuring the river water velocity with a flow meter.
During the measurement, the number of vertical and horizontal measurement points at the point must be determined according to the depth and width of the channel. The method is simple, but it is easily affected by water quality and difficult to achieve continuous measurement.

Understanding the relationship between Flow Rate and Pressure may help you calculate mass or volume flow.

Acoustic Doppler flow measurement is developed using the principle of Acoustic Doppler. It can simultaneously measure the cross-sectional shape, water depth, velocity, and flow of the river bed at one time, and is suitable for flow monitoring of large rivers.

The host and transducer of the flowmeter are installed in a waterproof container. All are immersed in water when working and are connected with a portable computer through a waterproof cable. The operation and control of the flowmeter are carried out on the portable computer.
From the initial blind zone above 1m, it is reduced to the so-called “zero blind zones”. The profile unit is reduced to the current 0.05~0.25m. It is possible to apply it on wide and shallow rivers.

Extended reading: Insertion Ultrasonic Water Flow Meter – Designed for Agricultural Irrigation, Garden Management

Read more about: 5 Types of Flowmeters | 2023 New Guide to Flowmeter Types 

Featured Water Flow Measurement Devices

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Flow is the volume of fluid that passes in a unit of time. In water resources, flow is often measured in units of cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or other various units.

Read more about: Flow Unit Conversion Table

Users can also choose unit of flow rate. For volume flow, L/s, L/min, L/h, m3/s, m3/min and m3/h are available; while for mass flow, kg/s、kg/m、kg/h、t/s、t/m、t/h can be selected from. It is up to the habits and application requirements to pick up a proper unit.

Extended reading: Liquid Bitumen/Asphalt Flow Meter

There are many ways to calculate flow.
For example, Using the Flow Rate Formula: Q​ = ​A​ × ​v​.
where ​Q​ is the flow rate, ​A​ is the cross-sectional area at a point in the path of the flow and ​v​ is the velocity of the liquid at that point.

Or, Flow Rate Calculation Using Pressure:

Extended reading: Orifice Plate Flow Meter

A water flow meter is an instrument that can measure the amount of water passing through a pipe. There are a variety of water flow meter technologies to choose from. It depends on the water measurement application, budget terms, and maintenance requirements. Each of these flowmeter types has novel process principles, overall use value and unique advantages in use.

The water flow meter can measure hot water, cold water, clean water, dirty water and mud.

Extended reading: Hot Water Flow Meters Improve Heating-Boiler System

To measure the flow of water in a river, you can use the following methods:

  • Choose a suitable measuring point: Find a relatively regular place in the river with smooth water flow for measurement.
  • Using a current meter: Deploy a current meter (such as an electromagnetic current meter or buoy) into the river to measure flow velocity at different depths and locations.
  • Calculate the cross-sectional area: measure the width and depth of the river, draw the flow cross-section, and calculate the cross-sectional area.
  • Integrating the data: Multiply the flow velocity by the cross-sectional area to get a value for flow, usually expressed in cubic meters per second (m³/s).
  • Multi-point measurements: To get a more accurate estimate of flow across an entire river channel, measurements may need to be taken at a number of different locations and then averaged.

For example, radar flow measurement is currently a commonly used method. It consists of a vertical pole, a horizontal arm, a chassis, a solar power supply system, a collection equipment, a radar flow meter, and a radar water level meter.

Choose a suitable position for the pole and cross arm on the shore. The length can be used to fix the sensor radar current meter and radar water level meter above the river surface, facing the water flow, and can monitor the river surface flow rate and real-time water level at the same time. The collection and transmission equipment RTU in the chassis is then used to receive and process the real-time data and then wirelessly transmit it to the remote platform. Time can be set for real-time viewing, threshold alarm, etc.

For mechanical flow meters, there is usually a rotating needle or a series of rollers to display the flow rate. Record the readings on all rollers, from left to right, which represent the total amount of water that has flowed through since installation.

For electronic flow meters, just read the value on the digital display directly. The electronic flow meters we supply from Sino-Inst can display instantaneous flow and cumulative flow.

Read more about: Flow Meter Selection Guide

More Liquid and Gas Flow measurement techniques

Sino-Inst offers over 30 water flow meter products for Water Flow Measurement. About 50% of these are differential pressure flow meters. 40% are water meters (like the Insertion Turbine Flow Meter), and 40% are water treatment (like the Annubar flow meter ).

A wide variety of water flow meter for Water Flow Measurement options are available to you, such as free samples, paid samples.

Sino-Inst is a globally recognized supplier and manufacturer of water flow meters, located in China.

The top supplying country is China (Mainland), which supply 100% of the water flow meter respectively.

Sino-Inst sells through a mature distribution network that reaches all 50 states and 30 countries worldwide. Water flow meter products for Water Flow Measurement are most popular in Domestic Market, Southeast Asia, and Mid East.

You can ensure product safety by selecting from certified suppliers, with ISO9001, ISO14001 certification.

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About KimGuo11

Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects. Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.