Flow Meters | Instrumart (2023)

Flow Meter Resources
Flow Meter Application Advisor

Accurate flow measurement is a critical component of many commercial and industrial processes. Flow meters are instruments designed to quantify the rate or volume of a moving fluid—either liquid or gas—in an open or closed conduit. Whether determining the proper concentrations of ingredients in manufacturing, measuring fuel usage, ensuring proper flow for cooling equipment, or monitoring municipal water and sewer services; flow meters serve in a wide variety of applications. Because of this, a number of flow measurement technologies have been developed. Each of these technologies comes with particular advantages and disadvantages. Understanding the needs of an application is always the first step towards selecting the proper flow meter.

Flow Measurement

Flow measurement can be described in either of two ways:

Volumetric flow in which Q = AV, meaning that the volume of fluid passing through a flow meter (Q) is equal to the cross-sectional area of the pipe (A) times the average velocity of the fluid (V). The only flow meter technology that measures volume directly is the positive displacement flow meter, however, other types of flow meters measure the velocity of the flowing stream to determine the volumetric flow. Examples of flow meter technologies that measure velocity include electromagnetic, turbine, ultrasonic, and vortex flow meters.

Mass flow in which W = RQ, meaning that the mass flow of fluid passing through a flow meter (W) is equal to the fluid density (R) times the volume of the fluid (Q). Examples of flow meter technologies that measure mass flow include Coriolis mass and thermal flow meters.

Other types of flow meters, notably differential pressure and variable area flow meters, do not measure volume, velocity or mass, but rather measure flow by inferring its value from other measured parameters.

Flow Meter Technology

Coriolis Mass Flow Meters

Coriolis meters make direct mass flow measurements based upon the Coriolis effect: the deflection of moving objects when they are viewed in a rotating reference frame. Coriolis flow meters artificially introduce a Coriolis acceleration into the flowing stream. As the fluid is "deflected", the forces generated cause an extremely slight distortion or 'twisting action' of the measuring tube that is directly proportional to the mass flow rate. This distortion is picked up by special sensors and converted to an output signal.

Coriolis mass flow meters can provide flow (mass or volume), density, and temperature measurements of liquids and gases all within a single meter. Since the measurement principle is independent of the physical fluid properties, these meters typically have a very high accuracy. The lack of straight pipe requirements and moving parts makes them a very attractive alternative to other flow meters.

(Video) How Flow Meters Work

Differential Pressure Flow Meters

Differential Pressure flow meters measure the velocity of fluids by reading the pressure loss across a pipe constriction. These meters can contain laminar plates, an orifice, nozzle, or Venturi tube to create an artificial constriction. Highly sensitive pressure sensors measure the pressure before and after the constriction. According to Bernoulli's principle, the pressure drop across the constriction is proportional to the square of the flow rate. The higher the pressure drop, the higher the flow rate.

Differential pressure flow meters utilize a robust, time proven measuring technique for a wide range of clean liquids and gases. The meters are available in a wide range of line sizes with wide temperature and pressure ranges. Installation is relatively easy and the meters often offer temperature and pressure measurements as well, measurements of mass flow compensation . Care should be taken with highly viscous liquids, though, as accuracy can be adversely affected or not achieved.

Magmeters / Electromagnetic Flow Meters

Electromagnetic flow meters are volumetric flow meters that measure the voltage created when conductive liquids move through a magnetic field. According to Faraday's Law, the voltage induced across any conductor as it moves at right angles through a magnetic field is proportional to the velocity of that conductor. With magmeters, the liquid serves as the conductor and the magnetic field is created by energized coils outside the flow tube. Electrodes detect the voltage which is directly proportional to the flow rate.

Electromagnetic flow meters can measure corrosive liquids and slurries, and have the ability to measure flow in both directions with equal accuracy. A conducting fluid and a non-conducting pipe liner are required. Magmeters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions. They are also ideal for applications where low pressure drop and low maintenance are required.

Positive Displacement Flow Meters

Positive displacement flow meters measure the volumetric flow rate of a moving fluid or gas by way of precision-fitted gears or rotors containing cavities through which precisely known volumes of fluid pass. A basic analogy would be holding a bucket below a tap, filling it to a set level, then quickly replacing it with another bucket and timing the rate at which the buckets are filled (or the total number of buckets for the "totalized" flow).

Positive displacement flow meters are very accurate and have high turndown. They work best with clean, non-corrosive, and non-erosive liquids and gases, although some models will tolerate some impurities. They require no straight runs of pipe for fluid flow stream conditioning though pressure drop can be an issue. They are widely used in custody transfer and are applied on residential home natural gas and water metering.

There are two common types of positive displacement flow meters. Nutating disk meters feature a circular disk mounted on a ball inside a precision fitted measuring chamber. As the liquid flows through the chamber, the disk rotates and wobbles upon the ball. Each rotation causes a predictable wobble which creates a cavity of a known size through which the liquid passes. By using an indicator or totalizer, the number of rotations can be counted and the flow rate determined.

(Video) What is a flow meter and how does it work? Explained

Oval gear meters use oval shaped gear-toothed rotors that rotate within a chamber. As these rotors turn, they sweep out and trap a very precise volume of fluid between the outer oval shape of the gears and the inner chamber walls. The flow rate is then calculated based on the number of times these compartments are filled and emptied.

Rotameters / Variable Area Flow Meters

Variable area flow meters / rotameters are among the oldest and most mature principles in flow measurement. Based upon Bernoulli's theorem, these meters consist of a uniformly tapered flow tube, a float, and a measurement scale. As a gas or liquid is introduced into the tube the float rises, its weight supported by the fluid flowing underneath, until the entire volume of fluid can flow past the float. The position of the float corresponds to a point on the tube's measurement scale and provides an indication of the fluid's flow rate.

The operating principle of variable area meters is as simple as it is reliable. They are generally inexpensive, easy to install and feature low, nearly constant, pressure drop. However, concern for orientation of rotameters (floats) must be observed, as they must be mounted vertically and have moderate accuracy. Variable area flow meters are generally not suitable for low-flow applications.

Thermal Flow Meters

Thermal flow meters measure mass flow rate by means of measuring the heat conducted from a heated surface to the flowing fluid. Relying on the principle that a fluid flowing past a heated temperature sensor removes a known quantity of heat as it passes, thermal flow meters measure either how much electrical power is required to maintain the temperature of the heated sensor or the temperature difference between the heated sensor and the flow stream. Either of those values is directly proportional to the mass flow rate.

Thermal flow meters are used almost entirely for gas flow applications. Their design and construction make them popular for a number of reasons. They feature no moving parts, have nearly unobstructed flow path, require no temperature or pressure corrections, and retain accuracy over a wide range of flow rates. Straight pipe runs can be reduced by using dual-plate flow conditioning elements and installation is very simple with minimal pipe intrusions.

Turbine / Paddlewheel Flow Meters

Turbine or paddlewheel flow meters are mechanical meters that have a freely rotating turbine set in the path of a fluid stream. The flowing liquid or gas causes the turbine to spin upon its axis. The rate of spin will be proportional to the velocity of the flow. The simple and reliable design of turbine meters makes them popular choices for large commercial and industrial users such as gas companies and municipal water districts.

Turbine meters are less accurate than some other types of flow meters but since the measuring element does not severely restrict the path of flow, they are able to measure high flow rates with low pressure loss. Though versatile, turbine meters do best in applications with constant conditions in liquids such as water or lower viscosity fluids. Strainers are generally required to be installed in front of the meter to protect the measuring element from gravel or other debris that could enter the flow system.

(Video) The Electromagnetic Flow Measuring Principle

Ultrasonic Flow Meters

Ultrasonic flow meters utilize sound waves to measure the velocity of a fluid from which the volumetric flow rate can be calculated. Unlike most flow meters, ultrasonic meters do not include any moving parts and thus are more reliable, accurate and provide maintenance free operation. Since ultrasonic signals can also penetrate solid materials, the transducers can be mounted onto the outside of the pipe offering completely non-invasive measurement eliminating chemical compatibility issues, pressure restrictions, and pressure loss.

Ultrasonic flow meters are affected by the acoustic properties of the fluid and can be impacted by temperature, density, viscosity and suspended particulates depending on the exact flow meter. Homogenous fluids, as well as, advanced digital signaling can eliminate many of the problems associated with noise and variations in liquid chemistry.

There are two types of ultrasonic flow meters:

Transit time flow meters measure the travel time of two sound waves. One wave travels the same direction as the flow while the other travels against the flow. At zero flow, sensors receive both waves at the same time, i.e., without transit time delay. As the fluid moves, it takes an increasingly longer time for the downstream wave to reach the upstream sensor. This measured "transit time difference" is directly proportional to the flow velocity and therefore to flow volume. Transit time flow meters require the fluid to be free from suspended solids or gas bubbles and in a closed and full piping system.

Doppler-shift flow meters operate on the principle that the wavelength of an approaching sound source is shorter than the wavelength of that same source as it is moving away. A transducer emits a sound wave which reflects off entrained particles or bubbles back to the transducer. The measured difference in the wavelengths of the transmitted signal versus the reflected signal is proportional to the process' velocity. Doppler flow meters are used for slurries, liquids with bubbles, or gases with sound-reflecting particles. They can also be adapted for use in open channels by integrating with level transmitters.

Vortex Flow Meters

Vortex flow meters use an obstruction, known as a bluff body, in the flow stream to create downstream vortices which are alternately formed on either side of the bluff body. As these vortices are shed from the bluff body, they create alternating low and high pressure zones that oscillate at particular frequencies directly proportional to the velocity of the fluid. The flow rate can be calculated from the fluid velocity.

Vortex flow meters are universally suitable for measuring liquids, gases and steam while remaining largely unaffected by changes in pressure, temperature and viscosity. Without moving parts, vortex meters are easy to install and require little maintenance. The measuring signal is not subject to drift. Consequently, vortex meters can operate an entire life long without recalibration. Due to the nature of a minimum required velocity for each bluff body, vortex meters will tend to need higher velocities and may have some difficulty reading low flow rates.

(Video) How To Read Flow Meters

Additional Flow Accessories

Flow Indicators

Flow Meter Indicators are simple devices that provide visual indication, often through the use of a float or paddle, that there is movement of fluid in the process line.

Flow Meter Monitors

Flow meter monitors are accessories that, generally speaking, convert the signal sent by a flow meter into a viewable flow rate. Though sometimes flow monitors are simple indicators, they often include sophisticated programming that allow control functions as well as other high-level operations.

Flow Switches

Flow switches are devices designed to trigger an action – such as on/off—based upon a preset flow setpoint. Flow switches may or may not read the flow rate.

Flow Transmitters

Flow transmitters are versatile instruments that may serve a number of functions. Basic transmitters may serve simply to relay the signal from the flow meter to a display. More sophisticated models may include control functions and/or advanced communications as part of an integrated flow system.

Flow Regulators

Flow regulators are simple valves that keep flow constant by decreasing the cross section of an orifice proportionally as the pressure increases. They are particularly suitable for networks supplying several users, as they can maintain the flow rate over a wide range of pressures.

Selecting a Flow Meter

The basis of good flow meter selection is a clear understanding of the requirements of the particular application. Therefore, time should be invested in fully evaluating the nature of the process fluid and of the overall installation.

  1. What is the fluid being measured by the flow meter(s) (air, water, etc…)?
  2. Do you require rate measurement and/or totalization from the flow meter?
  3. If the liquid is not water, what viscosity is the liquid?
  4. Is the fluid clean?
  5. Do you require a local display on the flow meter or do you need an electronic signal output?
  6. What is the minimum and maximum flow rate for the flow meter?
  7. What is the minimum and maximum process pressure?
  8. What is the minimum and maximum process temperature?
  9. Is the fluid chemically compatible with the flow meter wetted parts?
  10. If this is a process application, what is the size of the pipe?

If you have any questions or need any help selecting a flow meter, please contact us at sales@instrumart.com or 1-800-884-4967 to speak with an applications engineer.

(Video) An Overview of Flow Meter Technologies


What are the three 3 types of flow meters? ›

Types of Flow Meters
  • Coriolis.
  • DP Meters.
  • Magnetic Meters.
  • Multiphase Meters.
  • Ultrasonic Meters.
  • Vortex Meters.

What is a flow meter used for? ›

A flow meter is a device that measures how much liquid or gas moves through a pipeline in a given period of time. By measuring flow rates, flow meters provide crucial visibility into what's flowing where, within pipes, drainage systems, and other types of infrastructure.

What are the two 2 fundamental types of flow meters? ›

There are two categories of flow meters: gas and fluid or liquid. Fluid flow meters have five subcategories: differential pressure, velocity, positive displacement, mass flow, and open channel.

What is the most accurate flow meter? ›

Coriolis flow meter accuracy is among the highest for flow meter technologies.

Which are the three most common used flow meters? ›

This element converts turbulent flow into a more streamlined (laminar) flow.
  • Thermal flow meters. Thermal flow meters utilize the thermal properties of fluid for fluid flow measurements through the use of heaters and a thermal sensor. ...
  • Coriolis flow meters. ...
  • Ultrasonic flow meters.
Mar 22, 2020

What is the average cost of a flow meter? ›

Prices typically are in the range of $100 to $600. Accuracy is typically 1 to 3% of full scale. An accuracy measured against the full range of the device will double at 50% of full scale and triple at 33% of full scale.

What is the difference between a flow meter and a water meter? ›

The quick and dirty difference is that a water meter measures the volume of water as it passes through the meter and a flow meter measures the speed at which the water passes through the meter.

How do you measure fluid flow? ›

A pitot tube is used to measure fluid flow velocity. The tube is pointed into the flow and the difference between the stagnation pressure at the tip of the probe and the static pressure at its side is measured, yielding the dynamic pressure from which the fluid velocity is calculated using Bernoulli's equation.

How do you measure water flow in a pipe? ›

Acoustic meters, magnetic meters, and venturi meters with flow recorders are suitable devices for measuring flow rates. Acoustic meters are versatile and can be used inside pressured pipes, in partially filled pipes, or in open channels. Acoustic meters can also be mounted externally on plastic pipes.

What is a flow meter also known as? ›

A flow meter (or a flow sensor) is type of flow instrument that is used to indicate the amount of liquid, gas, or vapor moving through a pipe or conduit by measuring linear, non-linear, mass, or volumetric flow rates.

Where is the best place to install a flow meter? ›

The preferred location around the circumference of a horizontal pipe is on top. If trapped air or debris will interfere, then the sensor should be located further around the pipe from the top but not more than 45 degrees from top dead center.

What is the most common flow measuring device? ›

Differential pressure flow meters are, by far, the most common units in use today. These meters, which boast high accuracy, calculate fluid flow by reading pressure loss across a pipe restriction. Estimates are that over 50 percent of all liquid flow measurement applications use this type of unit.

What is a healthy flow rate? ›

The average flow rate for females is 15 mL/sec. Ages 14 to 45 -- The average flow rate for males is 21 mL/sec. The average flow rate for females is 18 mL/sec. Ages 46 to 65 -- The average flow rate for males is 12 mL/sec.

Which is better mechanical flow meter or digital flow meter? ›

In conclusion, mechanical flow meters are great for low-precision applications on a budget and will provide accurate readings with certain fluids at specific temperatures. Digital flow meters will provide more reliable flowrate measurements at a higher cost.

How do I know if my flow meter is accurate? ›

In flow meters, that means how close the output of the meter is to its calibration curve. This is expressed as a percentage, e.g. ±1%. It means that any given reading can be in error 1% above or below the calibration curve. In general it can be said; the lower the percentage, the more accurate your flow meter.

What flow rate do I need? ›

If your flow rate is less than 10 litres per minute, you may have what is considered low water pressure. Anywhere between 10 and 15 litres per minute is acceptable but can be improved. A flow above 15 litres per minute is considered good.

What is the most used and cheapest way to measure fluid flow? ›

Pitot Tubes

The pitot tube are one the most used (and cheapest) ways to measure fluid flow, especially in air applications like ventilation and HVAC systems, even used in airplanes for speed measurent.

What is the maximum pressure for a flowmeter? ›

The Flowline Series is a range of rugged inline mechanical flowmeters that provide visual indication of fluid flow in hydraulic systems. Capable of measuring flows ranging from 1 - 360 L/PM. Maximum allowable working pressure: 350 bar (5076 psi).

What is the difference between orifice and vortex flow meter? ›

Minimal maintenance is required with a Vortex Flow Control because they are self-activating with no moving parts or power supply requirements. In contrast to a Vortex Flow Control Valve, an Orifice Flow Control Chamber is delivered as a one-piece unit ready to install, which means reduced installation time and costs.

How long do flow meters last? ›

What is the expected life of your flow meter? In some applications such as subsea oil/gas production, your flow meter must have a life expectancy of 25 years or more with no possibility for maintenance. In other applications, a simple disposable device with a one to two year lifespan is perfectly acceptable.

Is a magnetic flow meter better than a mechanical flow meter? ›

What are the differences between the two flow meters? The primary difference between a mechanical meter and a magnetic meter is that a mechanical meter has moving parts and a mag meter doesn't.

How accurate are portable flow meters? ›

Most of the literature on ultrasonic flowmeters have reported the accuracy of the equipment to be in the range between 2 to 5 percent.

Is a flow meter better than a regulator? ›

As we already said, a regulator operates on pressure instead of volume. This means a flowmeter will always be more accurate than a regulator for flow volume. A flowmeter is an outer tube with another glass tube inside, marked for flow in CPH and liters per minute or LPM. A small ball bearing inside indicating the flow.

Are peak flow meters covered by insurance? ›

Most insurance companies will completely cover the cost of traditional peak flow meters, which are those with a spring system that measures the rate of air output. Some insurance companies, such as Aetna[3] , do not cover the cost of an electronic peak flow meter, because they consider them to be experimental.

Is a flow meter the same as a flow switch? ›

Flow meters simply monitor flow rates and the user has to check the flow rate themselves, as and when rather than at a predetermined set point, to detect if there are any issues. Whereas flow switches detect the presence of the flow, at a predetermined set point, alert the user, and perform a designated action.

Is a flow meter the same as a flow transmitter? ›

Differences between the Flow Meter and Flow Transmitter

The flow meters' are designed to measure the flow rate. On the other hand, the flow transmitters not only measure the flow rate but also help in controlling and monitoring it.

Do magnetic flow meters work on water? ›

Magnetic flow meters are well suited for a variety of applications across a range of industries including pulp and paper, metals and mining, water and wastewater, food and beverage, chemical and petrochemical and oil and gas.

What are the four common measures of flow? ›

Natural Gas Flow Meter Types

There are four natural gas meter types often used for flow measurement. They are mass flow meters, velocity flow meters, differential pressure, and PD meters.

What are the different types of water flow meters? ›

There are four primary types of water flow meters: mechanical water flow meters, vortex volumetric flow meters, ultrasonic flow meters or magnetic flow meters.

How much water can flow through a 4 inch pipe per minute? ›

4-inch pipe: 3,400 gallons per minute.

What is the simplest and more reliable method to measure flow in a pipe? ›

Primary devices are generally considered the most accurate way to measure flow in open channels. An area-velocity meter is an open channel flow meter that measures flow by making two separate measurements of depth and velocity. The depth is converted to cross sectional area using the geometry of the pipe or channel.

What is the flow of water in a 2 inch pipe? ›

Water Flow (GPM/GPH) based on Pipe Size and Inside/Outside Diameters
Assume Average Pressure (20-100PSI). About 12 f/s flow velocity
2"1.95 - 2.05"127
2-1/2"2.35 - 2.45"190
3"2.9 - 3.05"273
4"3.85 - 3.95"480
9 more rows

How many flow meters are there? ›

Each type goes about measuring the flow rate of a fluid in a different way. We're going to look at five main types of flowmeters you can find on the market today, including differential pressure flowmeters, velocity flowmeters, positive displacement flowmeters, mass flowmeters and open-channel flowmeters.

What is the rule of thumb for flow meters? ›

The general rule of thumb for straight piping is a five-diameter length of piping upstream and three diameters downstream from the meter (measured from the center of the tube).

Do flow meters need to be vertical? ›

- Flowmeters can be mounted either horizontally or vertically. Although most applications are horizontally oriented, mounting the meter vertically actually offers some slight advantages.

What are the two types of flow meters? ›

There are two categories of flow meters: gas and fluid or liquid. Fluid flow meters have five subcategories: differential pressure, velocity, positive displacement, mass flow, and open channel.

What are the three methods of measuring flow? ›

A Venturi meter, an orifice plate meter and a rotameter that demonstrates typical methods of measuring the flow of an incompressible fluid and shows applications of Bernoulli's equation.

What is accurate flow measurement? ›

Flow meter accuracy is how close the measurement is to the true value. In flow meters, that means how close the output of the meter is to its calibration curve. This is expressed as a percentage, e.g. ±1%. It means that any given reading can be in error 1% above or below the calibration curve.

What is average daily flow? ›

(4) “Average daily flow (ADF)” means the total volume of wastewater flowing into a wastewater facility during some defined period of time, divided by the number of days in that period of time, and expressed in units of mgd.

What is normal water flow for a house? ›

The average household needs 100 to 120 gallons per person per day, and a flow rate of about 6 to 12 gallons per minute.

Which is the most common type of air flow meter? ›

The use of differential pressure as an inferred measurement of a liquid's rate of flow is well known. Differential pressure flow meters are, by far, the most common units in use today.

What are the 5 type of flow? ›

Laminar Flow
  • Unidirectional laminar flow.
  • Pulsatile laminar flow.
  • Oscillatory laminar flow.

What is the most accurate way to measure airflow? ›

Checking the Air Flow of Your HVAC with an Anemometer

An anemometer is a device that measures wind speed and direction, so it only makes sense that it would be an accurate way to measure your HVAC's airflow.

What is the difference between flow sensor and flow meter? ›

Flow meters, also known as flow sensors, are used to measure the flow rate of a liquid or gas. There are a variety of different types of flow meters, including ultrasonic, electromagnetic, Karman vortex, paddlewheel, floating element, thermal, and differential pressure types.

How accurate is an air flow meter? ›

A field accuracy of 5% is quite typical for most mass flow meters and the output still provides valuable insight into your compressed air system!

What are the 2 types of flow? ›

There are mainly two kinds of flow, such as:
  • Laminar flow - Laminar flow would be the continuous movement of flowing fluid that follows or respects streamlines. ...
  • Turbulent flow - Turbulent flow is characterized by erratic property modifications in the flow.

What are 3 examples of flows? ›

A river flowing down a mountain; air passing over a bird's wing; blood moving through a circulatory system; fuel moving through an engine.

What does Bernoulli's theorem state? ›

First derived (1738) by the Swiss mathematician Daniel Bernoulli, the theorem states, in effect, that the total mechanical energy of the flowing fluid, comprising the energy associated with fluid pressure, the gravitational potential energy of elevation, and the kinetic energy of fluid motion, remains constant.

What are the two primary methods of measuring flow rate? ›

As mentioned above, flow is measured in two ways: in volume or mass per unit of time.
  • Volume Flow. The volumetric flow of a substance is defined as the measurement of the volume quantity that flows/passes through a given area or section per unit of time.
  • Mass Flow.
Apr 4, 2022

What instrument is used to measure flow? ›

Flow Measurement Instrumentation Used in Engineering Design of Processes
  • Flow nozzle.
  • Orifice plates – concentric orifice, eccentric orifice, conditioning orifice.
  • Pitot tube.
  • Averaging pitot tube, annubar.
  • Variable area flowmeter, rotameter.
  • V-cone flow element.
  • Venturi tube.
  • Wedge flow element (slurries, heavy liquids)

What is the difference between water meter and water flow meter? ›

The quick and dirty difference is that a water meter measures the volume of water as it passes through the meter and a flow meter measures the speed at which the water passes through the meter.


1. Flow Meters for Water and Wastewater Applications
2. Coriolis Flow Meter (Principle of Operation)
3. Liquid & Gas Measurement: 4 Types of Flow Meters for Oil and Gas
(Kimray Inc)
4. How Do Magnetic Inductive Flow Meters Work?
5. Tech Review: Compressed Air Flow Meters
6. Magnetic Flow Meter Technology Introduction


Top Articles
Latest Posts
Article information

Author: Otha Schamberger

Last Updated: 30/08/2023

Views: 6228

Rating: 4.4 / 5 (75 voted)

Reviews: 90% of readers found this page helpful

Author information

Name: Otha Schamberger

Birthday: 1999-08-15

Address: Suite 490 606 Hammes Ferry, Carterhaven, IL 62290

Phone: +8557035444877

Job: Forward IT Agent

Hobby: Fishing, Flying, Jewelry making, Digital arts, Sand art, Parkour, tabletop games

Introduction: My name is Otha Schamberger, I am a vast, good, healthy, cheerful, energetic, gorgeous, magnificent person who loves writing and wants to share my knowledge and understanding with you.