Welcome to the Blue-White guide to flow meters and their functions. Flow meters are devices used to measure the flow of fluids, such as fuel, water, and other liquids. They are essential for many industries and applications, including industrial process control, medical diagnostics, and energy management. This guide will provide an overview of the different types of flow meters available from Blue-White and information on how to use and maintain them properly.
A flow meter is a device used to measure the flow rate or quantity of a gas or liquid moving through a pipe. Flow meters measure the volumetric or mass flow rate of a liquid or gas. They are used to measure how much of a substance passes through a pipe over a period of time. Flow meters can measure flow in many applications, including water, oil, fuel, air, and steam.
They have applications in many industries, including water treatment, heating and air conditioning, industrial manufacturing, process control, and waste management.
Flow is a term used to describe the movement of materials or energy from one place to another in a continuous and organized manner. This can refer to the flow of fluids such as water, gas, and oil. Flow is an important concept in engineering and manufacturing in understanding how systems and processes work.
In this case, we will refer to flow as it applies to fluids in pipes. And in this application, flow is typically divided into two types: Open channel flow and closed conduit flow.
Open channels are streams with an exposed surface and unrestricted access to the atmosphere. For example, canals and pipelines that are not completely full, such as drains and sewers.
In open channel flow, gravity is responsible for the motion of the liquid. The water level will gradually decrease down the stream as the flow progresses.
Closed conduit flow is the flow of a liquid or gas through a pipe, channel, or another closed vessel. Closed conduit flow typically occurs at a constant velocity and depends on factors such as the pressure difference between the ends of the conduit and its length.
F-420 Acrylic Flow MeterWater supply and district heating pipes are common places to observe closed conduit flow. Even drinking straws are a simple but efficient example of this. The flow rate here is largely determined by the pressure difference between the two ends, the distance between them, and the area of the conduit. Additionally, the hydraulics of the pipeline &#; such as its shape, roughness, and bends &#; also have an impact. All these factors come together to create the rate of flow.
Flow pressure measures how much force is needed to move a liquid or gas through a system. It is measured in pounds per square inch (PSI) or kilopascals (KPa). The flow pressure range can vary greatly depending on the type of system, the size of the pipes, and the type of liquid or gas being pumped. For example, a residential water system typically operates at a much lower flow pressure than an industrial system. Flow pressure can also be increased or decreased by changing the size of the pipes, the number of fittings, and the type of pump.
Any flow will also have a temperature, with the typical range in most industries where they are used being from -40°F to +400°F (-40°C to +204°C). And to measure this, flow meters are designed to measure the flow rate in fluids with a wide range of viscosities, temperatures, and pressures. Flow meters can also detect changes in flow rates and can be used to detect leaks or other irregularities in the system.
Another term is thermal flow measurement, which reads how much heat is transferred while a gas passes a surface. The two main measurements taken with regard to temperature are simple readings via a temperature sensor and a heated flow sensor that measures the heat transfer from the flow of any given material inside the system.
F-460 Polysulfone Flow MeterAs mentioned above, a flow meter is an instrument used to measure the flow rate of liquid or gas. It measures the flow rate by detecting and monitoring changes in pressure, level, or another variable caused by fluid passage through pipes.
Flow meters measure fluids, but fluids can be any liquid, viscous, or gas known to us. Hence, a wide range of flow meters is available on the market. All of these types vary in function and application.
Differential pressure flow meters employ the Bernoulli Equation, which states that a fluid&#;s pressure decreases while its speed increases. These types of flow meters report the difference between the two measurements. The first measurement causes a shift in kinetic energy when the air is forced through a hole in the flow meter, which is then measured by the second element.
The sub-types of differential pressure flow meters are rotameters / variable area flow meters, orifice plates, venturi flow meters, and pitot tube flow meters. These meters measure the pressure difference between two points, allowing for a precise calculation of the fluid flow rate.
A variable area flow meter is a differential pressure flow meter. Variable area flow meters are simple, versatile, and cost-effective devices that operate at a relatively constant pressure drop and measure liquids, gases, and steam flow. The variable area flow meter is popular for industrial and commercial flow indication because it has a linear scale, a relatively long measurement range, and a low-pressure drop &#; plus, they are simple to install and maintain.
The orifice plate flow meter is a differential pressure flow meter used in clean liquid, gas, and stream mass flow measurements. It is available for a wide range of pipe sizes and allows for measuring fluid flows in larger pipes (over 6&#; in diameter).
Venturi flow meters allow the fluid to flow through a constricted section of pipe called a throat, where a pressure difference is created. The liquid speeds up and creates a pressure differential as it passes through, which is then used to calculate the volumetric flow rate of the fluid. Venturi meters are often used in applications requiring high precision levels with large volumes of liquid at low-pressure drops. They&#;re also suitable for liquids with a high solids content. Additionally, they are relatively easy to install because they have no moving parts. They can be fitted via flanged, welded, or threaded-end fittings, making them a popular choice for many applications.
Pitot tube flow meters are a common and cost-effective tool for measuring fluid flow rate in a pipe or duct. The pitot tube is inserted into the pipe to measure the difference in pressure between the upstream and downstream of the flowing fluid.
The installation process for a pitot tube is relatively straightforward, as it typically involves drilling a hole into a pipe and inserting the pitot tube into the fluid path with its impact port facing directly into the fluid flow.
Pitot tube flow meters remain attractive for many applications due to their low cost and easy installation process. They&#;re frequently used in HVAC and commercial aquatics systems, for example. Moreover, they offer minimal pressure drop, meaning they do not significantly impede the flow rate of the fluid.
A Positive Displacement Flow Meter is a device that measures the flow rate of a fluid by measuring the amount of fluid that is displaced by a series of chambers or rotors. This type of flow meter is highly accurate, durable, and efficient and is commonly used in industries such as oil and gas, food and beverage, and chemical processing.
PD or Positive Displacement flowmeters utilize a rotating mechanism within a precision-engineered chamber to capture fluid pockets, like filling a beaker with liquid and pouring it down an aisle, counting each fill.
A reciprocating piston meter is a positive displacement flow meter that measures the volumetric flow rate of liquids and gases. It consists of a chamber with a piston, an inlet and an outlet valve, and a pressure transducer. The piston is driven by an external power source, such as an electric motor, magnetic field, or pneumatic cylinder, and moves back and forth in the chamber. As the piston moves, it displaces a fixed volume of liquid or gas, and the flow rate is calculated based on the speed of the piston and the volume displaced. The inlet and outlet valves open and close to control the flow rate, and the pressure transducer measures the pressure inside the chamber.
An oval-gear meter is a positive displacement flow meter that measures fluid or gas flow through two oval-shaped gears with close-fitting teeth. The gears are connected to each other and are placed in a chamber that has a known volume. As the fluid or gas passes through the chamber, the gears rotate, and the volume of the chamber is displaced. The displacement of the volume is measured, and the flow rate of the fluid or gas is calculated.
A nutating-disk flow meter works by passing fluid through a disk that is mounted on a shaft, which is connected to a motor. The disk is free to rotate around the shaft as the fluid passes through, causing the disk to rotate, or nutate, at a rate proportional to the flow rate. The rate of rotation and nutation is then measured and converted into a flow rate.
A rotary-vane flow meter uses a rotary vane, a type of impeller, to create a pressure differential across the meter, which is then used to calculate the flow rate. The inner part of the rotary vane meter consists of several vanes, each connected to a central shaft. As the fluid passes through the meter, the vanes rotate, causing a series of gears to turn. The gears are connected to a mechanical counter that records the total flow rate. The rotary vane meter is highly accurate and reliable, often used in the automotive industry to measure fuel and oil flow rates. The rotary vane meter is also used in medical applications, such as anesthetic delivery systems. The design of the rotary vane meter allows it to be used in a wide range of temperatures and pressure ranges.
SONIC-PRO® S6A Digital Ultrasonic Flow MeterVolumetric flow meters measure the speed of the flow rather than the actual volumetric rate directly. The volumetric flow rate is calculated by multiplying the measured velocity by the cross-sectional area at which it&#;s installed, accurately representing how much material passes through in a given time period. Flow meter technology has become more advanced, with digital displays becoming more commonplace with improved accuracy due to better calibration technology and new sensing methods.
Ultrasonic flow meters measure flow rate by detecting fluctuations in ultrasonic oscillations. They come in two varieties: time difference and Doppler. Time difference type meters, also called time-of-travel meters or transit meters, measure the time taken for ultrasonic waves to travel from one point to another, while Doppler-type meters measure the frequency shift of soundwaves reflected from the moving particles in the medium. Both are used for accurate flow rate measurement.
Mass flow meters measure the mass of a material that passes through the system in a given period of time. They measure the mass per unit of time, typically expressed in kilograms per second (kg/s). Mass flow meters measure the speed and density of the material as it passes through the device. This data is then used to calculate the mass flow rate. Mass flow meters are typically used to measure the flow of liquids, gases, and solids in industrial processes, such as the chemical, food, and pharmaceutical industries. Coriolis flow meters are the most popular mass flow meters used in industries today.
Flow meters are an incredibly important and versatile tool for measuring the flow of liquids, gases, and solids in a variety of industries. There is an ideal meter for any application, from ultrasonic flow meters to variable area flow meters.
Blue-White has you covered when it comes to fluid control processes. We manufacture industrial-grade flow meters that are accurate and robust, so you can depend on them to keep your processes running smoothly, safely, and cost-effectively. From rotameters / variable area flow meters to paddlewheel flow meters to ultrasonic flow meters, all our products are Made in the USA and ready to ship! Get peace of mind by knowing your flow meters are reliable and of the highest quality. Trust Blue-White for all your flow meter needs.
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This article takes an in-depth look at flow meters
You will learn:
A flow meter is a flow rate measuring device used to determine the linear or nonlinear mass and volumetric flow of a liquid or a gas. The many names of flow meters include flow meter, Flow meters, also known as flow indicators, liquid meters, or flow rate sensors depending on their industrial application, are designed to enhance the precision, accuracy, and resolution of fluid measurement. They improve efficiency, require minimal maintenance, are user-friendly, and offer versatility and durability.
Flow meters can measure the volume, velocity, or mass of a liquid or gas. They use various calculations to provide data on mass flow, absolute pressure, differential pressure, viscosity, and temperature, which can then be used to determine flow rate. The flow rate is calculated by multiplying the velocity (v) by the cross-sectional area (A), expressed as Q = v \times AQ=v×A, with QQ measured in cubic meters per second (m³/s). Mass flow is determined using the formula \dot{m} = Q \times \rhom=Q×ρ, where QQ is the flow rate and \rhoρ is the mass density. Mass measurement is particularly important for gases, chemical reactions, and combustion processes.
The purpose of a flow meter is to measure the quantity of material flowing through it over a specified period. The compressibility of gases and their volume changes under different conditions, such as pressure, temperature, or cooling, affect the measurement. This variability influences the choice of flow meter for gas flow rates. Gas flow rates can be measured in various units, including cubic meters per hour (m³/h), cubic meters per second (m³/s), thousand standard cubic meters per hour (kscm/h), linear feet per minute (LFM), or million standard cubic feet per day (MMSCFD).
The measurement of liquid flow rates varies by application and industry. Common units include gallons per minute, liters per second, liters per square meter per hour, bushels per minute, and cubic meters per second (cumecs). In oceanography, a specialized unit called the volume of transport, measured in Sverdrups (Sv), is used.
Controlling flow is crucial in many industrial applications and requires a diverse range of flow meters tailored to meet specific needs. Flow meters are used for measuring various materials, including water, oil, natural gas, and steam. While these meters perform the same fundamental function, they operate differently depending on the material being measured.
Although all flow meters serve the same basic function, each type is designed to meet specific application requirements. The two primary categories of flow meters are volumetric flow meters and mass flow meters. Volumetric flow meters measure the volume of fluid, while mass flow meters measure the mass. Volumetric flow rates can be affected by temperature and pressure, whereas mass flow rates are influenced by the density of the fluid. Various types of flow meters include differential pressure, velocity, and others. positive displacement, mass flow, and open channel flow meters.
Volumetric flow meters operate linearly and measure flow by assessing the velocity of the fluid. Unlike mass flow meters, they are less sensitive to changes in viscosity and are typically connected directly to pipelines. Types of volumetric flow meters include positive displacement flow meters, turbine flow meters, electromagnetic flow meters, ultrasonic flow meters, and vortex flow meters.
Differential pressure flow meters utilize the Bernoulli Equation, which indicates that fluid speed increases as pressure decreases. To measure flow, these meters introduce a constriction or obstruction within a pipe, creating a pressure drop across the flow. As the flow rate increases, the pressure drop also increases, with the drop being proportional to the square of the flow rate.
In a differential pressure flow meter, pressure sensors are positioned before and after the constriction to accurately measure the flow rate. The constriction alters the kinetic energy of the flow, which is then detected by a second sensor. Differential pressure flow meters often use a Venturi tube to constrict and slow the flow. Common sub-types of differential pressure flow meters include orifice plates, flow nozzles, Venturi flow meters, and rotameters.
Velocity flow meters are volumetric flow meters that are used to calculate the flow rate by computing the speed of the flow using sensors located along the flow. The accuracy of velocity flow meters depends on the density, cross sectional area of piping, and the velocity of a fluid remaining constant. Any type of device that can directly measure fluid velocity is able to measure the volumetric flow rate of a fluid in a pipe that has a set cross sectional area. The types of velocity flow meters include turbine and vortex flow meters.
Pitot Tube Flow Meters - A pitot tube flow meter has two pipes to measure fluid pressure with the difference between the pressure in the tubes being proportional to the velocity of the flow. One tube measures the impact pressure while the other tube measures the static pressure. The tubes are mounted separately or in a casing as a single unit and are at right angles to the flow.
The total impact pressure tube is L shaped with an opening that faces the flow. The static tube&#;s pressure is the operating pressure of the piping upstream from the total impact tube and at right angles to the flow. The dynamic pressure is the difference between the total pressure and static pressure from the tubes multiplied by the ratio of the dimensional constant and density. As the velocity rises, the profile in the pipe changes from elongated to turbulent or flat.
Turbine Flow Meters - Turbine flow meters use the mechanical rotation of a rotor that is placed in the flow to determine the flow rate with the rotation of the rotor being proportional to the velocity of the flow. They are used with clean and viscous liquids and have an accuracy of 0.5%.
Turbine flow meters are classified as rotating vane flow meters that include paddle wheel flow meters and Pelton wheel flow meters, each version of which has a different shaped rotor. The angled, twisted, or blade rotor is parallel to the flow and faces it straight on. As the flow moves through the pipe, the turbine spins, the motion of which is electronically detected by a magnetic pickup. The frequency output from the pickup is used directly or converted to an analog signal.
Vortex Flow Meters - Vortex flow meters measure fluid velocity using the von Kármán effect, which states that when a flow passes a body, a pattern of swirling votives is generated. In a vortex flow meter, a shredder bar is placed in the flow that causes the fluid to separate and form alternating differential pressure or vortices on the back side of the bar. The vortices cause a sensor to oscillate at a frequency that is proportional to the velocity of the fluid. The sensing element converts the rate of oscillation into an electrical signal that is converted to a velocity reading.
Ultrasonic Flow Meters - An ultrasonic flow meter measures fluid velocity by sending ultrasonic waves across the flow in the direction of the flow and in the opposite direction of the flow. The ultrasonic waves and the velocity of the flow are combined to calculate the flow rate. The structure of an ultrasonic flow meter includes two transmitters and two receivers with one of each on opposite sides of the pipe at a measured distance from each other.
With an ultrasonic flow meter, sound waves are sent into the flow using transducers that make direct contact with the flow or uses clamp on transducers that are connected to the exterior of the pipe. Alternating bursts of ultrasounds are measured to determine the time it takes for sound to travel between the transducers. The difference in the transit times is proportional to the velocity of the flow.
The two types of ultrasonic flow meters are in-line and clamp-on flow meters. In-line ultrasonic meters are the insertion type with two sets of ultrasonic transducers aligned opposite each other. Clamp-on ultrasonic flow meters are connected to the exterior of the pipe.
Hydraulic Flow Meters - The term hydraulic flow meter is a generic term that refers to flow meters that measure and monitor the flow of hydraulic fluid. Several different types of flow meters are used to monitor hydraulic fluid due to the different viscosities and flow rates of each type of hydraulic fluid. They are made of resilient material that is capable of withstanding the stress and pressure associated with hydraulic fluids.
The main parts of a hydraulic flow meter are a transducer and transmitter, which are positioned in various locations along the hydraulic line. The transducer measures the velocity of the liquid and calculates the flow level. It senses the movement of flow through the line and sends a signal to the transmitter. The three types of hydraulic flow meters are orifice, gear, and turbine. Hydraulic flow meters help to determine how efficiently and effectively the hydraulic system is running and warn of any problems.
Positive displacement flow meters pass fluids through a series of gears or gears in a chamber. They are a type of mechanical flow meter where fluids displace components in the meter, which is used for flow measurement. They consist of a chamber that is placed in the flow that blocks the movement of a fluid. In the chamber are rotating mechanisms that permit passage of a fixed amount of a fluid. The number of fixed amounts that pass through the chamber helps determine the volume of the fluid with the rate at which the mechanism turns being the flow rate. Positive displacement flow meters are used for measurements when straight pipe is not available or as a replacement for turbine flow meters and paddle wheel sensors when there is too much turbulence in the flow.
Unlike gear type positive displacement flow meters, screw flow meters have a set of screws called spindles that rotate from one end of the chamber to the other end of the chamber as a fluid passes through. The rotation of the screws by the fluid causes a pressure drop. The rotation of the screw is recorded by a sensor to deliver a measurement that is determined by the flow rate, viscosity of the fluid, and the size of the chamber.
Other types of positive displacement flow meters include oval gear, helical gear, nutating disk, rotary vane, and diaphragm. The popular use of positive displacement flow meters is due to their accuracy and ability to measure viscous, dirty, and corrosive media. The one issue with the measurements of positive displacement flow meters is the pressure drop.
While volumetric flow meters measure the velocity of the flow of gases and liquids, mass flow meters determine the flow rate by measuring the convective transfer of heat on the surface of the flow using temperature sensors in the flow or attached to the piping. They are direct measurement devices capable of measuring a wide range of temperatures with precision and accuracy. Mass flow meters are suitable for use with a variety of fluids including slurries and other viscous materials, non-conductive fluids, and other mass fluids by their density. Two common types of mass flow meters are coriolis and thermal mass.
A mass flow meter measures the mass of a fluid by its inertia as it passes through a vibrating tube equipped with sensors at the inlet and outlet. The vibration of the tube causes oscillation that is proportional to the mass of the fluid. The principle of mass flow meters is based on the Coriolis effect that states that any body moving on the earth&#;s surface tends to drift sideways from its course due to the earth&#;s rotation. The movement of the tubes twist when fluids flow through, which represents the sideways drift caused by the rotation of the earth.
Coriolis flow meters - Coriolis flow meters work on the principle of the Coriolis principle, which states that a moving mass in a rotating system experiences a force that acts perpendicular to the motion and axis of the rotation. When a fluid is flowing in a pipe, it experiences Coriolis acceleration from the introduction of rotation in the pipe. The force generated by the Coriolis inertial effect is the flow rate of a fluid. The generated inertial force is at right angles to the direction of the flow, which is used by a Coriolis flow meter to measure mass and determine the flow rate.
As a liquid or gas flows through a tube or tubes of a Coriolis flow meter, an actuator vibrates the tube, which artificially causes a Coriolis acceleration in the flow that produces a twisting force that causes a phase shift. The amount of twisting force is proportional to the mass that a meter uses to measure mass flow by detecting the angular momentum. A Coriolis flow meter can measure the flow rate in a forward or reversed direction and is used for leak testing and low flow measurements.
Open Channel Flow Meters - Open channel flow meters are non-contact flow meters that use level sensors that detect the level of a liquid, usually water, in a channel, flume, weir, or partially filled pipe. The flow rate is determined using the level of the liquid and its volume and the Manning equation, which requires uniform flow with the bottom slope and surface slope being the same to calculate the flow rate. A key factor in the use of Manning&#;s equation is the roughness or friction that is being applied to the flow by the channel, which is calculated or taken from a table. The flow rate (Q) is equal to the velocity (v) of the flow multiplied by the flow area (A), all of which are equal to the calculated roughness coefficient multiplied by the hydraulic radius (R), the area (A), and the square root of the slope (&#; &#;S).
Spring and piston flow meters are an easy view flow meter that uses a piston and spring to calculate the flow rate. As the flow enters the flow meter, it creates a pressure differential that moves the piston against the spring, which moves in direct proportion to the rate of the flow. The flow rate is viewed in the same manner as a rotameter and has a red indicator line on the piston that moves along a pre-calibrated numerical scale that is mounted on a transparent section of the body of the flow meter.
Spring and piston flow meters measure the annular flow, which is a type of fluid flow that is lighter in the center of a pipe and heavier along the pipe walls. The scales for a spring and piston flow meter are based on the gravities of fluids with oil being 0.84, and water being 1.0. Spring and piston flow meters, like rotameters, have a simple design and are an alternative to rotameters since they can be configured to transmit electrical signals.
Digital flow meters are high tech flow meters that have four components that act like sensors. Included are anemometers, thermistors, and pressure gauge transducers, all of which have direct contact with the flow and measure mass flow, gas temperature, and gas/back pressure. The one external sensor of a digital flow meter is the absolute pressure transducer that produces pressure readings without the influence of atmospheric pressure.
The readings that are accumulated by the four sensors of a digital flow meter measure mass flow, which is converted to volumetric flow according to flow density and the system&#;s backpressure.
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There are several forms of water flow meters, each of which is designed to meet the needs of an application, maintenance requirements, and cost. They measure the volume of slurries, water, and closed pipe fluids. The types of water flow meters include mechanical flow meters, vortex flow meters, ultrasonic flow meters, and magnetic flow meters with mechanical flow meters being the most used and most economical. Each type of water flow meter is designed to measure, monitor, and control the flow of water in a pipe, hose, and other conveyance.
Water flow meters operate under the same principles of other flow meters but are designed to measure the flow of water. They are a subset and special form of flow meter that works only with water although some flow meters are water flow meters but are capable of measuring other liquids and gases.
Fuel Flow Meters measure the amount of fluid being transferred using a digital or mechanical visual display to show how much fuel has been transferred during a transaction. There are several types of flow meters that are used to monitor fuel transfer. How they complete the measurement varies between the different types.
A nutating disk fuel flow meter has a disk that the fuel makes contact with as it enters the flow meter. The disk nutates, moves back and forth, along its vertical axis as the fuel passes through. The back and forth movement of the disk provides an indication of the amount of fluid being transferred through the meter.
Oval gear fuel flow meters have gears that rotate at right angles to each other creating a T shape. The gears mesh in the center of the flow to prevent the passage of fuel. When flow enters the flow meter, it pushes against the gears and makes them rotate and moves out of the flow meter. Magnets in the gears send signals to an electronic reed switch that provides a fuel transport reading.
Turbine fuel flow meters use a rotating turbine that rotates in the fuel around an axis. The mechanical action of the rotating turbine is converted into a flow rate. As the fuel impacts the blades of the turbine, the blades rotate at a steady speed that is proportional to the fuel&#;s velocity.
Peak Flow Meters measure how fast a person can push air out of their lungs to determine how open the airways of the lungs are. They help determine what causes a drop in lung efficiency and help decide what medications to use or if there is a need for emergency care. Peak flow meters are a portable, inexpensive tool that measures air flow.
The two ranges of peak flow meters are low range peak flow meters for small children and standard range peak flow meters for older children and adults with the standard range peak flow meter having a larger airway. The three zones of a peak flow meter are green, yellow, and red.
Green Zone - 80% to 100% peak flow rate. Asthma is under control.
Yellow Zone - 50% to 80% peak flow rate signals caution due to airways narrowing and action is needed.
Red Zone - Less than 50% means medical alert. There is severe airway narrowing and a medical professional needs to be contacted.
One of the considerations regarding the use of a flow meter is the type of flow, which can be open channel or closed conduit. Open channel flow is open to the atmosphere and is a channel, weir, or flume while closed conduit flow is in a tube or pipe. There are various features that need to be evaluated when determining the effectiveness of a flow meter. Remote monitoring, types of data, and the frequency of collection are a few of those factors.
The technology of flow meters is constantly evolving as new and more technologically advanced flow meters are introduced to the market. The applications for each type of flow meter is unique with cost being the least important factor in the selection process.
The reason a flow meter is being selected is due to the application for which it will be used. During an evaluation of a process, it has become clear that a flow meter is needed for safety, monitoring, and control of a flow. This knowledge indicates that engineers and designers have studied every detail of a process to determine where to place a flow meter. What may be overlooked in their assessment is an understanding of the issues of maintenance, calibration, and access to the flow meter, which are necessary considerations as part of the selection process.
It is important to understand the pressure, temperature, allowable pressure drop, density or specific gravity, conductivity, viscosity, and vapor pressure of the flow, which are displayed as a single reading. Flow meters monitor the toxicity, bubbles, presence of abrasives, and transmission qualities of a material to ensure the safety of workers and equipment. With gas flow, gas density changes as pressure and temperature change, common factors of a gas flow meter that have to be closely monitored to ensure accuracy.
The most important consideration when choosing a flow meter is the media to be measured, which can vary in conductivity, temperature, pressure, and viscosity. Additional factors are how clean or dirty the media is since certain flow meters are incapable of withstanding the impact of such media. Engineers and designers normally have a clear understanding of the media that will be transferred from the data collected on their matrix.
As an example, a propeller flow meter is normally used for measuring the flow of drinking water but is not capable of measuring the flow of water that has sand, dirt, iron or contains contaminants. Magnetic meters are ideal for measuring conductive materials and have no moving parts to corrode or break.
The process of flow measurement is a method of quantifying the flow rate of a medium and is based on fluid dynamics or fluid characteristics, such as thermal, acoustic, and electromagnetic properties. Flow rates are taken directly using a mechanical flow meter or indirectly calculated. The different physical properties of gases and fluids requires that they be measured separately using different flow measurement methods with a distinction made between volume flow measurement and mass flow measurement.
Gases have weak intermolecular bonds that cause their density to be influenced by temperature and pressure variations, which influences their volumetric measurement and requires adjustments and compensation in a gas flow meter to ensure accurate readings. With mass gas flow meters, compensation is not required.
The types of measurements for liquids vary according to the application and industry with gallons per minute, liters per second, bushels per minute, and cubic meters per second being the most common units of measure used. In some conditions, the flow rate of liquids can be measured in terms of energy flow in gigajoules per hour or BTUs per day.
Any mass needs force to move, which is part of Newton&#;s Second Law of Motion. In the case of fluids, in a confined pipe, the force that is applied to move the liquid is pressure. The density of the liquid determines the amount of necessary pressure, which indicates the flow rate. When a flow meter is measuring density and pressure, it uses that data to calculate flow rate.
Flow pressure is force that is measured in pounds per square inch (PSI) or kilopascals (KPa). Pressure varies depending on the type of system, the size of the pipes, and the kind of gas or liquid and can increase or decrease with the change of pipes, the addition of fittings, and the pumping mechanism.
Thermal flow meters use heat sensing elements that are isolated from the path of the flow. As liquids or gases pass through a pipe, they generate heat that is proportional to the mass flow rate. These types of flow meters have sensors that measure the flow rate of liquids or gases by recording the temperature from the heat transfer that is produced by the flow. The typical temperature ranges are -40°F to 400°F (-40°C to 204°C). Thermal flow measurement is a reading of the amount of heat that is transferred as a gas or liquid passes over the surface of a pipe.
Heat transfer is a common aspect of piping systems and is a necessary part of fluid flow analysis and the determination of the density, viscosity, and surface tension of a fluid. The three ways that heat transfer happens is convection, conduction, and radiation. Convection refers to the heat energy produced by the movement of a liquid or gas. Conduction is the exchange of heat between the material and the pipe. Radiation is the least common method of heat transfer and mainly happens in gas and oil lines. It refers to the transfer of heat between a hot surface and a cold surface.
The two basic configurations of thermal flow sensors rely on a fluid&#;s predisposition to absorb thermal energy, which can be measured by a thermal flow meter. With the heating element method, fluid flow passes across the heating element that is connected to a thermal sensor where the fluid absorbs heat from the heating element. The sensor measures how much heat was absorbed. The velocity of the fluid is directly related to the amount of energy it absorbs.
With the single heating element process, the heating element works to maintain a fixed temperature. The fluid absorbs heat from the heating element, which requires more energy to keep its fixed temperature. The mass flow is determined by the amount of energy needed.
The location of a flow meter is a major factor in providing accurate and reliable data. The best flow meter will be inaccurate if installed incorrectly. Errors in installation occur when the wrong flow meter is forced into a location, position, or flow. This determination can be damaging to the flow meter, produce incorrect data, be unsafe, and cause damage to equipment or processes.
Flow meters are normally installed on a straight pipe to avoid flow disturbances since bends, valves, tees, and reducers produce flow measurement errors. When straight pipes are not accessible, flow conditioners are used to reduce inaccuracies with a select few flow meters being able to perform under those conditions.
The size of the pipe, its material, and the direction of the flow are essential parts of the selection process. In most cases, downward flow should be avoided, and the piping should be full for accurate measurement.
The need for reporting varies between applications with some applications requiring constant and continual flow reporting and flow readouts. Data from flow meters is sent to a Supervisory Control and Data Acquisition (SCADA) system that is used for controlling, monitoring, and analyzing flow meter data and devices and can be accessed on site or remotely using specially designed software and hardware. The type of output is decided during the selection process and is normally 4 to 20 milliamp (mA).
The design of a flow meter begins with the collection of data, which is used to determine the dimensions, thickness, requirements, and bore of the meter. Flow calculations are based on flow conditions, physical properties of the meter, and the results that include discharge coefficient, beta ratio, flow velocity, pressure differential, and total pressure loss. All of the various calculations are processed and included in an engineering design drawing that is used to manufacture a flow meter.
The design of digital flow meters includes the flow meter body, transducers, and transmitters that are combined into a single instrument. Positive flow meters give precise real-time output and accurate measurements with a signal directly connected to the force of the gas or fluid. The output signal is connected to the flow meter system of a turbine or rotator wheel, plate, channel, nozzle, laminar, and pilot table system.
Basic flow meters or mechanical flow meters are designed to provide readings by the movement of a piston or turbine that moves up or down in a clear plastic tube where it registers a reading on a scale placed on the walls of the tube. They are the least sophisticated of the flow meters and have been used for many years to record flow rates.
Flow meters are made from stainless steel plates, brass, aluminum, PVC, PVDF, and nylon. Their design depends on the viscosity of the measured substance, cleanliness of the flow, pressure, temperature, and pipe size. Most recently, flow meters are being custom manufactured to meet the needs of unique and unusual media.
Flow switches and flow meters differ in how they function and monitor media flow. The main purpose of flow meters is to record and report data that is used to determine the flow rate, mass, and velocity of the flow. Users regularly check the readings and monitor the flow stream using a flow meter.
Flow Switches are mechanical devices used to control the flow of air, steam, gases, and liquids. They send messages or signals to another device, such as a pump, to tell it to shut off or turn on to protect a system from damage and warn of the need for cooling protection. Flow switches are set to be able to determine if the flow is above or below a preset rate or set point, which can be adjustable or fixed. When the set point is reached, an electrical circuit is activated and remains activated until the flow falls below the set point.
Flow switches are constructed to make or break an electrical circuit and are configured to be normally open (NO) or normally closed (NC), which are the default states of the switch. With a NO switch, the circuit is open until triggered while a NC switch is closed until triggered.
A flow switch is made up of a paddle system, permanent magnet, reed contact, and a second magnet. The flow pushes the paddle that is connected to a permanent magnet attached to the reed switch that is above the flow and outside the fluid. The paddle is always connected to an electronic circuit. The paddle turns as the gas or fluid passes into the switch, which sends a signal to a transducer like device that receives the signal and sends it to a transmitter that takes readings.
When the flow rate hits the set point, the circuit closes or opens and turns the pump on or off. In another scenario, when the set point is reached, an alarm can sound and send a warning to users.
Paddle flow switches have a hinged or spring loaded paddle that makes contact with the media. The paddle remains in place as the media flows through. When there is a change in the flow rate, the paddle will deviate from its set point and cause a switch to be thrown.
Unlike a paddle flow switch, in a piston flow switch, a piston reacts to the change in the flow rate. Its movement activates a reed switch that requires action or activates a pump until the flow rate increases or decreases to reach the set point.
Variable area flow switches have a plastic, metal, or glass tube that floats inside the flow. The tube is moved as the flow increases and continues to float until the set point is reached. At that time, a switch is triggered that requires further action and intervention.
With a thermal flow switch, a heated probe is inserted into the pipe that includes a housing that is located outside the piping. As the media passes the heated probe and dissipates its heat, a temperature drop occurs that is converted by electronics in the switch to create a switch point value.
The few flow switches listed above are a very small sampling of the many types of flow switches that are available and include ones for HVAC systems, fire systems, boilers, chillers, pumps, and air flow. They are an ideal safety device that can enhance the efficiency and performance of flow transport and transfer.
A flow indicator is a device that is designed to provide an indication that flow is occurring. Unlike a flow switch or flow meter, flow indicators do not provide data or monitor and control flow. They let operators know that flow is happening. As sight flow indicators, they provide an inside look at the flow inside a pipe. Flow indicators are also known as plain sight indicators and are the simplest form of flow monitoring device.
How a flow indicator works is dependent on its manner of providing an indication. In most instances, something is moved by the flow or a sight glass is provided to observe the flow. For indicators with devices in them, the flow moves a ball, spins a paddle, flaps, or chains. Flow indicators with a mechanism enclosed can be seen from a distance, which makes them more efficient and convenient.
Flow meters are selected to meet the needs of the media, the type of piping, and the requirements of an application. The over 200 types flow meters makes it possible to choose the correct flow meter to meet the need of an application as well as provide valuable data regarding the movement of gases and fluids. Flow meters have become an integral part of industrial processes as an important safety tool and monitoring device.
Flow meters provide accurate measurement of fluid flow rates, which makes it possible for businesses to monitor processes and identify issues that can damage processes, employees, or equipment. They help management develop methods to improve product quality, eliminate waste, and enhance manufacturing processes.
A major selling point for an investment in flow meters is their low cost, which makes it possible to make a small investment to gain precise measurement data to help improve efficiencies, minimize waste, and lower labor costs. Additionally, flow meters require little maintenance, are long lasting, and do not necessitate any upkeep.
It can easily be said that there is a flow meter for any type of application that has a volumetric transfer or transport of air, gas, water, or liquids. This versatility makes it possible to find a flow meter that can provide protection, monitor flow, and collect data for any application or condition. They can be mounted on pipes, placed above channels, and be placed in the flow or on the walls of pipes and not prohibit or interfere with the flow.
One of the primary reasons that flow meters are so widely used is due to how easily they can be installed and adapted to an existing system. This aspect of flow meters makes it possible for organizations to use a flow meter for collecting data, monitoring flow movement, and determining gas and liquid use. The assessment of the data assists in decisions regarding the viability of a product and the amount of an asset that is necessary to manufacture the product.
Unlike other tools in the manufacturing process, flow meters operate continuously providing a constant flow of real time data. Calculations of flow and mass are immediately available without the need for special procedures or actions. Management can minutely monitor hourly flow to determine the use of gases or liquids.
For safety reasons, there are areas of the United States that have enacted laws regarding the movement of fluids, gases, and liquids. The requirements of these laws demand that companies closely monitor the movement of media to ensure that the transport and transmission of the media is controlled, monitored, and completed safely. Flow meters help companies avoid penalties, fines, and business shutdowns for lack of compliance with local regulations.
For many years, going back to ancient times, flow meters have been used to measure the flow of liquids. They were placed in channels when water was being shared for irrigation and at the openings of pipes to measure flow. These types of flow meters were mechanical and did not depend on computers and electronics to complete their readings. Unfortunately, due to the crude design of the ancient flow meters, the collected information was approximate and an estimate.
Modern flow meters that had scales and provided numerical readings were introduced in the 16th century with the introduction of a tool designed to measure differential pressure and the Venturi tube. At the beginning of the 20th century, various experiments were conducted to improve the Venturi tube and improve its accuracy, which was followed in the s by the introduction of ultrasonic flow meters that were capable of measuring the velocity of liquid flow.
The event that changed the world of flow meters was the introduction of the computer age, which made it possible to produce miniaturized flow meters that had the precision and accuracy required by modern industry. Although technology has advanced flow meters from the estimates produced by the ancient flow meters of China and Egypt, mechanical flow meters still exist due to their low cost, ease of installation, and accuracy for certain applications.
Mechanical flow meters have gears, rotors, impellers, and turbines to measure media flow. They indicate the total flow rate and operate without the use of any source of power. The function of a mechanical flow meter is dependent on constant flow that moves an impeller, rotor, or other mechanical part. There are several types of mechanical flow meters with positive displacement flow meters, turbine flow meters, and rotameters being the most commonly used.
Digital flow meters are flow meters for the modern era. They include a digital computer display that provides data about many aspects of the flow depending on the type of software and hardware used to construct the flow meter. As sensors and transmitters collect data from components placed in the media stream or on the walls of piping, the data is calculated using computer software and projected in an easily readable display. Digital flow meters are more reliable, accurate, and robust than traditional mechanical flow meters and make it possible to send data to computer terminals and laptops.
The structure of a digital flow meter includes impellers to determine flow that are connected to electrode sensors that measure the induced voltage created by the rotation of the impeller to measure velocity and flow rate. Digital flow meters are easy to install, have a long life span, and require very minimal maintenance. They are not susceptible to jamming or breaking since they have no moving parts.
There are several factors to consider when installing a flow meter with the most essential part of the process being the location of a flow meter. In the majority of cases, and to ensure proper readings, flow meters are installed on a straight length of pipe away from elbows, tees, valves, fans, and pumps, which are common causes of turbulence in piping systems.
The fluid or gas that is to be measured must be a single phase media, meaning it is a gas or liquid. Two phase media are difficult to measure and provide inaccurate readings.
The orientation of a flow meter affects the precision of its readings, its accuracy, and overall performance. Flow meters are installed on straight pipes in any direction with 10 diameters upstream and 5 diameters downstream. For their most efficient operation, they are placed away from magnetic fields and vibrations, which can affect their readings. There are a wide variety of installation configurations with ones that are connected to piping such that the flow goes through the flow meter while other installations are merely sensors that are attached to the walls of the piping.
A flow meter, whether it is for gas or liquid, must always be placed such that it is always filled with fluid with an escape for the removal of second phase media. For gas and steam flow meters in horizontal piping, the flow meter should be placed at a high point to enable any condensation to drain out of the piping.
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