A flow meter, also spelled “flowmeter,” is an instrument used to measure the flow of a liquid or gas in a supply pipe. The device is fitted into a pipe to gauge the quantity of gas or liquid passing through it.
Many flow meters measure the volume of the material flow, while other flow meters measure the speed, and still other flow meters measure material mass. For the most part, flowmeters are used to infer mass flow through calculations that flow meters and flow monitor instruments make after taking various flow measurements, such as absolute pressure, differential pressure, viscosity, and temperature.
Flow meters are used for efficiency purposes and to help companies determine profit gain or loss. More specifically, they are produced so that users of all kinds can be sure of the accuracy of their machines and processes. Manufacturers rely on them for this purpose and, as a byproduct, to help them keep up with their production demands and meet consumer or user expectations. Industries that benefit from the use of flow meters include the automotive, petroleum, gas, utility services, HVAC filters, food and beverage processing, chemical, and raw material industries.
Flow Meters – HydraCheck
Flow Meters – HydraCheck
Flow Meters – Sierra Instruments
Flow Meters – Sierra Instruments
The History of Flow Meters
The earliest manufactured flowmeter was the turbine flowmeter, created in 1790 by Woltmann. It was used to calculate energy loss in open canals. It wasn’t widely used, however, until after World War II. Also, around 200 years ago, Faraday tried, but did not manage, to create an electromagnetic flow meter for measuring the Thames. While scientists and engineers like Faraday found the formulas for flowmeters centuries ago, none were produced commercially until the 1900s. For example, while Gustave Coriolis developed inertial force in 1835, the Coriolis flow meter wasn’t released as a commercial unit until 1977. Likewise, electromagnetic flow meters weren’t sold on the mass market until 1952, and ultrasonic flowmeters weren’t produced commercially until 1963.
Once flow meters did begin to receive attention from potential customers in commercial and industrial markets, the flowmeter industry grew exponentially. Today, that growth rate has not slowed down. In more recent years, flow meters have developed with modern technology, sporting digital readouts, high tech sensors, and more. We believe that, as time goes on, they will become easier to use remotely, using wireless internet, perhaps acting as smart meters. The future also likely holds flow meters with no moving parts whatsoever. Whatever the future holds for the flow meter industry, we know it will pull other industries ahead with it.
Most flow meters are made of the primary device, a transducer, and a transmitter. These three flow meters parts are usually combined so that the flow meter is one complete instrument. In addition, some variations, like positive flow meters, feature a precise output signal for real-time and accurate gas or liquid flow volume measurement. This output signal is directly connected to the force that the passing gas or fluid applies on the sensor of the device. Apart from mass or force, it is also correlated to the velocity of the flow. Output signal accuracy is usually connected to flow meter systems like turbine or rotater wheel, plate, channel, nozzle, laminar, and pilot table systems.
Certain flow meters are manufactured using specific materials in order to maximize results. However, in general, they are made from materials such as stainless steel plate, which is corrosion resistant, or brass, aluminum, PVC, PVDF, and nylon.
When designing a flow meter, manufacturers think about a variety of factors. These include: substance viscosity, flow cleanliness, process pressure, process temperature and size of the pipe. Using such considerations, along with individual specifications and restrictions, they can manufacture custom flowmeter systems for virtually any application.
Every flowmeter type works differently. For example, some flow meters are designed to measure for a specific material, while other flow meters can detect a variety of materials. Also, flowmeters will commonly utilize two different measuring styles: mass flow or volumetric flow. Devices that calculate for mass flow determine the characteristic of a material in terms of pounds or kilograms while systems that measure for volumetric flow will produce results in liters or cubic inches.
In general, flowmeter work by taking measurements and reporting the results.
Flow meters are divided in two categories: gas-based and fluid or liquid-based flow meters.
If we focus on fluid-based flow meters, then we can classify them in five subcategories: differential pressure flow meters, velocity flow meters, positive displacement flow meters, mass flow meters, and open channel flow meters.
Differential Pressure Flow Meters
Differential pressure flow meters were devised on the Bernoulli Equation, which was itself was based on the flow of fluids. They actually work quite simply; they take both a primary and a secondary measurement and report the difference. Note: the first measurement causes a change in kinetic energy by directing the air through a hole in the flow meter, which is measured by the second element.
These meters can be put into various sub-types, such as orifice plates, flow nozzles, venturi flow meters, and rotameters.
Orifice Plate Flow Meter System
Using these systems, you can measure the change in the pressure of the flow, going from upstream to downstream. However, for such measurement, it is important to have the flow in a partly blocked pipe.
Flow nozzles can be used for measuring both air and gas flow rates. They are simple in design and cost is minor.
Venturi Tube Gauge
These flow gauges help in measuring the liquid flow rate. The device checks the change in pressure, which occurs due to a cross sectional flow area in the flow path.
Rotameters, also known as variable area flow meters, utilize a rotating float that moves vertically through a tapered tube. This type of flow indicator measures the pressure applied on the fluid by the Earth's gravity. The rotameter is most commonly used for measuring gases and liquids. Advantages include linear output, simplicity, low cost, low-pressure drop, and wide range ability.
Velocity Flow Meter
Velocity flow meters calculate the flow of fluid by sensing the speed at more than one point in the piping system. To produce a reading, they use a depth measurement and the average air velocity of the flow. Using them, process engineers are able to maintain the required flow throughout the stream. Note: Velocity flow meters have a greater range than differential pressure devices.
Some types of velocity flow meters include: pitot tube flow meters, calorimetric flow meters, turbine flow meters, and electromagnetic flow meters.
Pitot Tube Flow Meter
Pitot tube flow meters check the velocity of flow by translating its kinetic energy into potential energy. The most popular, most used, and cheapest fluid flow meters, these devices are installed in most ventilation and HVAC systems today.
Calorimetric Flow Meter
Calorimetric flow meters have two temperature sensors that are fixed closely, and serve as a touching base for the liquid. Due to their intelligent design, these flow meters can provide highly accurate air flow readings.
Hydraulic Flow Meter
Hydraulic flow meters measure the flow rate or volume of liquid inside a hydraulic system. Their general applications are testing, troubleshooting and maintaining hydraulic systems. Using hydraulic flow meters, operators of hydraulic systems can measure how efficiently and effectively their systems are running and properly address any problems into which they run.
Turbine Flow Meter
Turbine flow meters work using flow, which moves or rotates it (the turbine). When this happens, the meter measures the speed of the turbine. Primarily used with clean and viscous liquids, turbine flow meters are very accurate; they have an accuracy of 0.5% of the reading. The meter has a multi-bladed rotor that is mounted at right angles to the flow. The outputs are a sine wave or square wave frequency, and if you need signal conditioners, it can also be mounted, but only on explosion proof classifications.
Electromagnetic Flow Meter
The electromagnetic flowmeter, or magnetic flow meter, is a type of volumetric flow meter that functions based on Faraday's law of electromagnetic induction.
Vortex Flow Meter
Vortex flow meters measure flow rate by placing an obstruction directly in a flow path and forcing liquids or gases to move around it. When the flow moves around this obstruction, or bluff body, two symmetrical vortices are created on the opposite side, changing the pressure of the flow. A flow sensor, placed between these vortices, measures these pressure changes and transmits the data to an electronic signal conditioner outside the meter.
Ultrasonic Flow Meter
Ultrasonic flow meters measure fluid velocity using ultrasound technology, which lets them calculate flow volume. There are two main types of ultrasonic flow meter: in-line flow meter varieties and clamp-on flow meter varieties.
Positive Displacement Flow Meter
Positive displacement flow meters, or PD flow meters, measure viscous liquid flow using their rotors as sensor or flow measuring elements. The volumes of the airflow are displaced in these devices by mechanisms such as vanes, gears, pistons, or diaphragms. The rotation of the rotors is directly related to the volume of the flow being blown toward it.
They are used in measurement when straight pipe is not available, or as a replacement for turbine meters and paddlewheel sensor, when too much turbulence is in the flow.
Mass Flow Meter
Mass flow meters, or true mass flow meters, are used for the direct measurement of mass flow.
Thermal Mass Flow Meter
Thermal mass flow meters take measurements with two sensors that work together. A temperature sensor reference and an active heat sensors take measurements by calculating how much heat loss occurs in the flowing liquid, and thus these flow meters can determine the flow rate based on this amount.
Mass Gas Flow Meter
Also known as Coriolis flow meters, these flow meters work on the basis of the Coriolis Effect. In other words, they base measurements on pressure, density, and fluid viscosity. They measure these using a temperature sensor and a differential pressure transducer, or a heated sensing element. They also have built-in digital displays and analog outputs. They are popular for leak testing and low flow measurements.
Open Channel Flow Meter
Open channel flow meters allow the engineers to determine the flow by checking the height of the liquid. They are only used with flows that are exposed to the air on the top.
Other flow meter types include the: air flow meter, spring and piston flow meter, water flow meter, fuel flow meter, flow switch, peak flow meter, and digital flow meter.
Spring and Piston Flow Meter
To measure the flow, this type of flow gauge uses annular orifice that is formed by a tapered cone and piston. Scales on piston flow meters are based on specific gravities of fluid; for oil meters, it is 0.84 and for water meters, it is 1.0. Their unique selling point is the simplicity of design. They have become economical alternative to rotameters, since they can be installed easily to transmit electrical signals.
Flow switches feature a flowmeter regulator component that serves as a switching unit for controlling flow. They may also trigger a visual or audible alarm.
Digital Flow Meter
A digital flowmeter is defined as any flow measurement device with a digital display.
Advantages of Flow Meters
Flow meters are a great investment because they can improve the efficiency of a facility by assisting in monitoring fluid consumption or other applications. While every flow meter variety offers different pros and cons, flow meters in general do have many advantages. As a whole, flowmeters are: low maintenance, easy to use, versatile, and durable. Also they have have no or few moving parts, which makes them less likely to break and less complicated to fix.
Accessories for your flow measurement device that you might consider getting, depending on your application, include: a signal output module, a remote assembly kit, a sensor kit, or a mass flow controller.
To properly install a flow meter, you first need to know the area where the flow indicators will be located. Note that you cannot install meters in the area where vibrations or a magnetic field is present, as either one of these can interfere with the meter. Also consider the direction of flow. In liquid applications, we advise you to avoid downward flow. In addition, some meters need to be installed in a straight pipe to work properly, though the required length of pipe can be compensated using straightening vanes.
For more tips and for detailed instructions on installing your flow meter, talk to your supplier.
Proper Care for Flow Meters
Each type of flow meter has specific guidelines that must be followed for proper use. For example, when using gas flow meters, the flow meters must remain full of gas. Liquid in gas flow meters can affect the flow meter's accuracy. Similarly, in order for liquid flow meters to work properly, they must remain full of liquid. Gas in liquid flow meters can affect the accuracy of flow meters' readings, as well as contaminants of any kind.
Always make sure that your flow meters are ISO-certified. If workers will be around them, also make sure that they’re approved by OSHA. It’s also of great importance that you check to see what standard adherences your industry or region require.
Things to Consider
If you are looking for a flow meter, use the following considerations to help you choose an appropriate flow gauge for your process.
One of the most important points to have in your consideration is the medium, in which you will mount the device. A point to be noted here is that gas and liquid friendly flow meters have different features (i.e. liquid-friendly flow meters are usually water resistant).
You need to know about is the range of flow of the medium, either gas or fluid, in your system. The range of flow will help you to eliminate some options that do not work properly in the range. Some meters work better with low flow rate, while some with higher rate. You can check the capability of a meter in terms of range of flow in the specifications that comes with a product.
- How accurate does your output signal to be?
It is important to determine the required flow measurement accuracy, since the performance of a flow gauge may not be acceptable over the full range of flow. You can get it determined in terms of percentage of calibrated span, actual reading, or full-scale units. Absolute accuracy is critical in certain applications, where a product is sold based on meter reading. In some other applications, repeatability can be a more important factor than absolute accuracy. Determining you need will help you to have a meter that will work optimally.
- What’s your projected flowmeter environment?
You need to keep in mind the the maximum and minimum temperatures that your system will likely reach. This will help inform your decision regarding material choices.
- What are the properties of your fluid?
You need to know the characteristic of the fluid, such as its specific gravity, whether it’s Newtonian or non-Newtonian, its conductivity, and the vapor pressure at operating temperature. You also need information about the fluid's composition, toxicity, presence of particles in fluid, size of particles, and light transmission qualities-- whether it is opaque or translucent.
- What are you system measurement and reading requirements?
A meter should be able to measure both the instantaneous quantity (Qi), the rate at which water is pumped, and the total quantity of water flowed over time (Qa). The Qa is usually recorded in gallons. However, some meters can measure Qa in acre-feet. These types of meters are used in agriculture applications.
Do you have the right info?
To ensure that only a right flow meter is installed for a particular system, get the checklists, questionnaires, and specification sheets from the manufacturer. These sheets are specifically designed to give the critical information necessary to match the flow meter with the requirement.
Even if you’re equipped with all of the answers to the questions above, you will still struggle to purchase the right flow meter and flow control related products without a quality manufacturer to guide you. How do you tell if a manufacturer is right for you? You’ll know because they’ll treat you like you matter, and they’ll want to find a creative solution for you; they’ll show that they care about your success, not their bottom line. Find this manufacturer by browsing the list reputable and hardworking flow meter suppliers we have listed above.
Flow Meter Types
- are used to measure the flow of air.
are used to measure the force of acceleration resulting from a moving
object towards or away from the center of rotation.
are used to measure the flow of fluids and gases
in a pipe by introducing constriction that causes the pressure to drop.
The pipe must be clean to result in accurate measurements.
- Electromagnetic flow meters measure by creating a magnetic field that is channeled into the liquid
and causes a voltage signal to be sensed that is proportional to the
flow of liquid.
- Flow indicators allow the operator to view the liquid as it is moving. Some models come
equipped with lights to enhance the visibility of the fluids.
measure flow at one position in a pipe, and then, based on the measurement,
they estimate the flow rate for the entire pipe.
- Flow switches are used to monitor fluid or gas flow while it is passing through its valve body, then to send an electrical control sign if the flow rate is too high or too low.
- Flowmeters are used to measure the flow of air, fluids and gases.
- Fuel flow meters are ultrasonic, turbine or positive displacement flow meters
which measure fuel usage rate and remaining fuel quantities in transportation
devices and stationary pumps.
are used to measure gas flow and are one of the more popular flow meters.
This meter is relatively unaffected by changes in temperature or pressure
in the tube or pipe.
are used to measure the flow of liquids when they are open to the atmosphere.
are used by patients with asthma or other lung disorders to measure
the amount of air patients take into their lungs. These flow meters
allow physicians to determine the severity of the illness.
trap liquid to measure its flow by rotating parts
that move between seals and the meter body.
- have a rotating float that moves vertically through a tapered tube.
measure the amount of force that is exerted on a target in a particular
liquid or gas. This should not be used to measure high viscosity liquids
because the target can be damaged.
are meters that use thermal properties of fluids to measure the flow.
The meter is heated and as the liquid flows by, it can tell the flow
rate by the amount of heat lost.
consist of a rotor that measures the fluid when it passes through the
blades. The blade speed is translated into the speed of the fluid
use sound to determine flow rate. Both Doppler Effect meters and time-of-flight
meters are different kinds of this type.
measure by letting the flow stream change the opening
in the meter with a movement of an internal part.
- Vortex flow meters calculate flow rate by measuring the differential pressure of
vortices created downstream from a partial obstruction, or "bluff body"; they
are highly resistant to vibration and are often used in harsh environments.
- are flow meters designed for measuring flow rates of water in various channels, tubes, partially filled pipes, streams, and rivers.
Flow Meter Terms
Absolute Pressure – Atmospheric pressure plus gage pressure in flow
Accumulator – Area where fluid is under pressure and stored as a source
of power within flow meters.
Bluff body - An obstruction, often wedge-shaped, placed in the middle of a
gaseous or liquid flow designed to create a downstream vortex in vortex flow
meters as a means of measuring flow rate.
Control Point – The temperature flowmeter instruments need to maintain to
perform designated functions of flow meters.
Coriolis Force – The force that occurs when a mass has a velocity moving
outward in a rotating plane of flow meters.
Counter Weight – A mass that is added to a particular substance to create
a more balanced and stable apparatus for flow meters.
Current – The flow rate of electricity within flow meters.
Density – A substance’s mass per unit of volume in flow meters.
Flow – The travel of materials in response to a force, such as pressure
within flow meters.
Flow Nozzle – A constriction made of a contoured plate that forms a hole
in flow meters for the flow stream so a flowmeter measurement can be taken.
Flow Rate – The velocity of flow in flow meters.
Head-Loss – The loss of pressure in flow meters or a flowmeter system
that is measured with a length parameter (such as amount).
Hot-Tap – Allows for flow meters to be inserted or removed without
causing a complete system shutdown.
Integrator/Totalizer – A flow meters device that measures the total flow
Manometer – Measures fluid pressure. This is a U-shaped flowmeter tube
containing liquid which adjusts with the pressure in the flowmeter tube.
Mass Flow Rate – The volumetric flow rate of a liquid or gas times its
density, expressed as pounds per hour or kilograms per minute in flow meters.
Potential Energy – The potential of energy when a liquid is in a position
or height above a flowmeter place to which it can potentially flow.
Transducer – The part of flow meters that sense fluid as it passes
through the flowmeter device.
Transmitter – The part of flow meters that produce the usable flowmeter
information from the transducer of flow meters.
Weldolet – A connection for a metal pipe that is used to aid as a fitting
for insertion-type sensors or flow meters.
Flowmeter Informational Video