Measuring liquid flow is a critical requirement for many industrial vegetation. In some operations, the power to make accurate circulate measurements is so necessary that it can make the difference between a profit or a loss. In other instances, inaccurate move measurements or failure to make them can lead to critical (or even catastrophic) outcomes.
For most liquid move measurement devices, flow is set inferentially by measuring the change in velocity or kinetic power of the liquid. The velocity is dependent upon the strain distinction that forces the liquid by way of the pipe or conduit. Since the cross-sectional space of the pipe is known and stays constant, the common move rate is an indicator of the circulate fee. In this case, the fundamental relationship for determining the move price of a liquid is

Q = V x A

Q = Flow rate of liquid via the pipe

V = Average flow rate

A = Cross-sectional space of the pipe

Other elements that affect the move price of a liquid embody the viscosity and density of the liquid, and the friction of the liquid in touch with the pipe.
Liquid flow may be measured immediately using positive displacement flow meters. These models divide the liquid into particular increments and continue to move. The complete move fee is the buildup of the measured increments and may be counted mechanically or electronically.
Table of Contents

Reynolds number

Types of liquid flow meters

Differential Pressure move meters

Orifice plate move meters

Venturi move meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable area circulate meter

Positive displacement circulate meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc kind meter

Rotary vane gauges

Spiral move meter

Velocity meters

Turbine circulate meters

Vortex flowmeters

Electromagnetic move meters

Ultrasonic move meters

Mass move meter

Coriolis circulate meters

Thermal mass move meters

Open channel circulate meter

Select a right liquid flow meter

Using circulate meters

Calibration

Maintenance

Reynolds number

The efficiency of a move meter can be influenced by the dimensionless unit called Reynolds number. It is outlined because the ratio of the inertial pressure of a liquid to its resistance.
The formula is

R = 3160 x Q x Gt

D x ต

R = Reynolds quantity

Q = Flow fee of the liquid, gpm

Gt = Specific gravity of the liquid

D = Internal diameter of the pipe, in.
ต = Viscosity of the liquid, cp

Flow rate and particular gravity are the inertial forces, pipe diameter and viscosity are the resistance. For most liquid applications, the pipe diameter and specific gravity stay constant. At very low velocities or excessive viscosities, R may be very low and the liquid flows in a easy layer with the highest velocity on the middle of the pipe, where viscous forces at the pipe wall restrict it to very low velocities. This sort of flow known as laminar move. the R value is beneath about 2000. a attribute of laminar flow is the parabolic form of its velocity distribution.
However, most functions involve turbulent flow with R-values above 3000. turbulent circulate happens at high speeds or low viscosities. The flow breaks down into turbulent eddies that move via the pipe with the same common velocity. The fluid velocity is much less important and the velocity distribution is extra uniform in form. A transition zone exists between turbulent and laminar move. Depending on the pipe configuration and other installation circumstances, the move on this zone could also be turbulent or laminar.
Types of liquid flow meters

Many types of circulate meters can be found to be used in closed pipe systems. In general, devices can be categorised as differential strain meters, positive displacement meters, velocity meters, and mass meters. Differential stress units (also known as head gauges) embody orifice plates, venturi, move tubes, move nozzles, pitot tubes, elbow type move meters, target type circulate meters and variable area flow meters.
Positive displacement circulate meters include piston, elliptical-gear, chapter-actuated disk and rotary vane types. Velocity meters embody turbine, vortex shedding, electromagnetic, and acoustic designs. Mass meters embody Coriolis and thermal varieties. Measurement of liquid flow in open channels normally entails weirs and flumes.
Differential Pressure circulate meters

The use of differential stress as an inferred measurement of the circulate rate of a liquid is well-known. By far, differential stress circulate meters are essentially the most commonly used unit at present. It is estimated that more than 50% of all liquid move measurement applications use this type of unit.
The basic operating principle of differential stress flow meters relies on the premise that the strain drop throughout the meter is proportional to the square of the move fee. The move price is obtained by measuring the differential pressure and extracting the square root.
Like most move meters, differential strain circulate meters have a major factor and a secondary factor. The primary factor causes a change in kinetic power, which creates a differential strain in the pipe. The system should be properly matched to the pipe measurement, move circumstances and liquid characteristics. And, the accuracy of the factor measurement should stay good within reasonable limits. The secondary component measures the differential stress and provides a signal or reading that is transformed to an actual flow worth.
Orifice plate circulate meters

Orifice plates are the most well-liked liquid move meters in use at present. An orifice is simply a flat piece of steel with a particular size hole drilled in it. Most orifices are concentric, but eccentric, conical (quadrant) and segmented designs are additionally available.
In practice, the orifice is installed in the pipe between two flanges. As the primary system, the orifice restricts the move of fluid, thereby creating a differential pressure across the plate. Pressure measurement ports on both sides of the plate are used to detect the difference. The major benefits of orifice plates are that they haven’t any shifting components and that their cost does not enhance considerably with the scale of the pipe.
Tapered and quadrant orifices are relatively new. These items had been developed primarily for measuring liquids with low Reynolds numbers. An primarily fixed circulate coefficient could be maintained at an R-value below 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which have to be calculated and machined for every software.
The phase wedge is a variant of the phase orifice. It is a throttle orifice designed primarily to measure the flow of liquids containing solids. The system is capable of measuring circulate at low Reynolds numbers and still sustaining the required square root relationship. Its design is simple and the wedge gap has only one important dimension. The stress drop through the system is just about half that of a traditional orifice plate.
The one-piece wedge assembly combines the wedge component and strain measurement becoming right into a one-piece pipe becoming bolted to a conventional pressure transmitter. No particular piping or fittings are required to put in the device within the pipeline.
The metering accuracy of all orifice circulate meters is dependent upon the installation situations, the orifice plate space ratio, and the physical traits of the liquid being measured.
Venturi flow meters

The benefit of a venturi is its capability to deal with large flows at low strain drops. A venturi is essentially a piece of pipe with a conical inlet and a straight throat. As the liquid passes through the throat, it increases in velocity, resulting in a stress difference between the inlet and outlet regions.
Flow meters have no shifting elements. They can be put in in large diameter pipes utilizing flanged, welded or threaded end connections. The unit is normally fitted with four or more stress measuring ports to common the measured pressure. Venturi tubes can be utilized for many liquids, together with those with high solids content.
Flow tubes

Flow tubes are considerably similar to venturi, except that they do not have an entrance cone. They have a tapered throat, however the outlet is elongated and smooth. The distance between the front and the tip is about one-half the diameter of the tube. The strain measurement port is situated about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle

At excessive velocities, the circulate nozzle can deal with approximately 60% of the liquid circulate compared to an orifice plate with the identical stress drop. Liquids containing suspended solids can be metered. However, these units are not beneficial for top viscosity liquids or liquids containing large amounts of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two kinds of pressure simultaneously, shock pressure and static strain. The shock system consists of a tube with one finish of the tube bent at proper angles to the course of move. The finish of the static tube is closed, but has a small slot within the side of the gadget. These tubes could be installed individually in the pipe or mixed in a housing.
Pitot tubes are typically installed by welding a coupling to the pipe and inserting the probe through the coupling. The use of most Pitot tubes is restricted to single point measurements. These devices are prone to clogging by international matter in the liquid. The advantages of Pitot tubes are low price, no moving elements, easy installation and minimal strain drop.
Elbow flowmeter

Elbow flow meters work on the principle that centrifugal forces are exerted along the outer edges as the liquid strikes along a circular path. Thus, as the liquid flows via the pipe elbow, the pressure on the inside floor of the elbow is proportional to the density of the liquid multiplied by the sq. of its velocity. In addition, the pressure is inversely proportional to the radius of the elbow.
Arbitrary ninety degrees. Elbows can be used as liquid flow meters. All that is required are two small holes positioned on the midpoint of the elbow (45 diploma point) for the manometer tap. A strain sensing line could be linked to the faucet utilizing any convenient technique.
Target meter

The goal meter senses and measures the pressure attributable to the liquid putting the target or a drag disk suspended in the liquid stream. By measuring the drive utilized to the goal the liquid circulate fee can be immediately indicated. In its simplest kind, the meter consists solely of an articulated oscillating plate that strikes outward with the liquid circulate. In this case, the system is used as a circulate indicator.
More sophisticated variations use subtle low-level force sensor sensing parts. The target pressure brought on by the liquid circulate is sensed by a strain gauge. The output signal of the meter indicates the flow price. The goal meter can be utilized to measure the move rate of soiled or corrosive liquids.
Variable space flow meter

Variable area meters consist primarily of a conical tube and a float. Although classified as differential pressure devices, they’re actually fixed stress gadgets. Flange finish connections provide a simple way to set up them in the pipe. Working principle of rotameter is when there is not a liquid circulate, the float is free to relaxation on the backside of the pipe. When the liquid enters the bottom of the pipe, the float begins to rise. The place of the float varies directly with the move fee. Its exact place is on the level where the strain difference between the upper and decrease surfaces balances the load of the float.
Because the move rate could be learn directly on a scale mounted next to the tube, there is not any want for an auxiliary move studying system. However, if desired, an automated sensing gadget can be utilized to sense the float degree and transmit the circulate signal. Variable area circulate meter tubes are made from glass, metal or plastic. Tube diameters range from 1/4 to higher than 6 inches.
Positive displacement move meter

The operation of these units consists of separating the liquid into precisely measured increments and continuing to move. Each segment is counted by a connection register. Because each increment represents a discrete quantity, optimistic displacement units are well-liked in automatic dosing and accounting purposes. Volumetric flow meters are best for measuring the circulate of viscous liquids or where a easy mechanical move meter system is required.
Reciprocating piston flowmeter

Reciprocating piston move meters are available in single and multi-piston versions. The specific choice is decided by the vary of move charges required in a specific application. Piston circulate meters can be utilized to deal with a extensive range of liquids. The fluid by no means is obtainable in contact with gears or different parts that might clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with carefully synchronized enamel. A fixed amount of fluid passes through the meter with every revolution. The shaft rotation may be monitored to acquire a specific flow price.
Disc sort meter

Chapter moving disc sort meters have a movable disc mounted on a concentric sphere that’s located in a spherical sidewall chamber. The stress of the fluid passing via the measurement chamber causes the disc to oscillate in its circulation path with out rotating about its own axis. It is the only transferring part in the measurement chamber.
A pin extending vertically from the disk is related to a mechanical counter, which displays the oscillating movement of the disk. Each cycle is proportional to a specific circulate price. As with all constructive displacement meters, changes in viscosity beneath a given threshold will affect the measurement accuracy. A wide selection of sizes and capacities can be found. These models can be made from quite lots of construction materials.
Rotary vane gauges

Rotary vane meters are available in a wide selection of designs, but they all function on the identical precept. The basic unit consists of an equally divided rotating impeller (containing two or extra compartments) mounted contained in the instrument housing. The impeller is in constant contact with the housing. As the impeller rotates, a onerous and fast volume of liquid is swept from every compartment to the outlet of the meter. The number of impeller revolutions is calculated and recorded in quantity units.
Spiral move meter

The helical move meter consists of two radially inclined helical rotors which would possibly be gear driven together with minimal clearance between the rotors and the housing. The two rotors switch the liquid from one end of the chamber to the opposite alongside the axial path.
Velocity meters

These instruments function linearly with respect to the volumetric move price. Because there is not any sq. root relationship (as with differential stress devices), they have a a lot larger range. Velocity meters are least delicate to adjustments in viscosity when the Reynolds number exceeds 10,000. Most velocity meter housings are geared up with flanges or fittings to allow them to be connected directly into the piping.
Turbine move meters

Turbine circulate meters have been extensively used for precise liquid measurement purposes. The device consists of a multi-bladed rotor mounted in a pipe, perpendicular to the flow of the liquid. The rotor rotates as the liquid passes through the vanes. Rotational velocity is a direct perform of move fee and could be sensed by magnetic sensors, photocells or gears. Electrical pulses could be counted and totalized.
The number of electrical pulses counted in a given time period is proportional to the circulate fee. A tachometer may be added to measure the turbine speed and decide the liquid flow fee. A correctly specified and put in turbine move meter has good accuracy, particularly for low viscosity liquids.
A main downside with turbine flowmeters is bearing put on. A “bearingless” design has been developed to avoid this downside. The liquid getting into the move meter passes by way of the spiral vanes of the stator, causing the liquid flow to rotate. The flow acts on the spheres, inflicting them to journey within the area between the first stator and the spiral-like second stator. The orbital motion of the sphere is detected electronically. The frequency of the generated pulse output is proportional to the flow rate.
Vortex flowmeters

Vortex move meters reap the benefits of the natural phenomenon that happens when a liquid flows via a blunt object. Vortex or vortex flow alternates downstream of the thing. The frequency of the vortex shedding is proportional to the speed of the liquid flowing via the flowmeter.
The three main parts of the move meter are the blunt object strut mounted on the meter bore, the sensor that detects the presence of vortices and generates an electrical pulse, and the sign amplification and conditioning transmitter whose output is proportional to the circulate fee.
Electromagnetic move meters

Magnetic move meters can deal with most liquids and slurries, provided that the material to be metered is electrically conductive. The major part is the flow tube (primary element), which is put in immediately within the pipe. The stress drop across the meter is identical because the strain drop by way of the equal size of pipe, since there are no transferring elements or circulate obstructions. The voltmeter may be linked directly to the move tube or remotely mounted and related to the flow tube via a shielded cable.
Electromagnetic circulate meters work according to Faraday’s law of electromagnetic induction, which states that a voltage is induced when a conductor passes through a magnetic area. The liquid acts because the conductor; the magnetic area is generated by an energized coil exterior the move tube. The quantity of voltage generated is proportional to the move price. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary element.
Electromagnetic flowmeters provide main benefits: they will measure tough and corrosive liquids and slurries; they’ll measure forward and reverse move with equal accuracy. The disadvantages of early designs have been excessive energy consumption and the necessity to get hold of a full tube with no circulate to set the meter to zero initially. Recent enhancements have eradicated these problems. The pulse-type excitation method reduces energy consumption as a outcome of excitation occurs solely half the time within the unit. A zero setting is now not required.
Ultrasonic flow meters

Ultrasonic flowmeters may be divided into doppler meters and journey time (or transverse) meters. Doppler meters measure the frequency shift attributable to the flow of a liquid. Two sensors are mounted in a housing related to at least one aspect of the pipe. A signal of identified frequency is distributed to the liquid to be measured. Solids, bubbles or any discontinuities in the liquid trigger the pulse to be reflected to the receiver component. Since the liquid inflicting the reflection is moving, the frequency of the returned pulse is shifted. The frequency shift is proportional to the rate of the liquid.
There is also a portable doppler meter that could be run on AC energy or a chargeable energy pack. The instrument can be used by merely clamping the sensing head to the skin of the pipe. A set of 4 to 20 mA output terminals allows the unit to be linked to a strip chart recorder or other remote device.
The journey time meter’s sensors are mounted on all sides of the pipe. The configuration allows the sound waves to travel between the devices at an angle of 45 degrees. angle to the path of fluid move. The pace of the sign propagating between the sensors increases or decreases with the course of transmission and the velocity of the liquid being measured. By transmitting the signal in each directions alternately, a time-differential relationship proportional to the flow price can be obtained. A limitation of the travel time meter is that the liquid being measured must be comparatively free of entrained gases or solids to reduce signal scattering and absorption.
Mass flow meter

Mass flowmeters the continued need for extra correct move measurement in mass related processes (chemical reactions, heat transfer, etc.) has led to the development of mass flow meters. A variety of designs are available, however the most commonly used for liquid circulate purposes is the Coriolis meter. It operates on the basis of a pure phenomenon generally identified as the Coriolis force, hence the title.
Coriolis circulate meters

Coriolis meters are true mass meters that instantly measure mass flow instead of volume flow. Since the mass is constant, the meter is linear and does not need to be adjusted for modifications in liquid characteristics. It additionally eliminates the want to compensate for changing temperature and pressure conditions. The meter is especially suitable for measuring liquids whose viscosity varies with velocity at a given temperature and strain.
Coriolis meters are also obtainable in a variety of designs. A popular unit consists of a U-shaped flow tube encapsulated in a sensor housing related to an electronic unit. The sensing unit could be mounted instantly into any process. The electronics unit can be situated up to 500 feet away from the sensor.
Thermal mass flow meters

Thermal mass flowmeters are historically used for gasoline measurements, but are additionally out there in designs for liquid flow measurements. These mass meters also function impartial of density, stress and viscosity. Thermal mass meters use a heated sensing factor that is isolated from the fluid flow path. The flowing stream conducts heat from the sensing element. The warmth transferred is proportional to the mass flow rate. The sensor is never in direct contact with the fluid. The digital meeting includes a circulate analyzer, temperature compensator, and signal conditioner that gives a linear output proportional to the mass move price.
Open channel circulate meter

An “open channel” is any pipe during which liquids move on a free floor. This consists of tunnels, unpressurized sewers, partially crammed pipes, canals, streams and rivers. Of the various techniques that can be used to watch move in open channels, depth-related methods are the most typical. These strategies assume that instantaneous circulate could be determined from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used primary devices used to measure move in open channels.
Weirs work on the principle that an obstruction in a channel causes water to flow backwards, making a excessive water degree (head) behind the obstruction. The head is a perform of the move fee, and therefore the flow fee by way of the gadget. The weir consists of a vertical plate with a pointed prime. The top of the plate could be straight or notched. Weirs are classified by the form of the notch. The fundamental varieties are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a operate of the liquid degree, so the gadget should use degree measurement techniques to determine the circulate rate. Staff gauges and floating operating items are the simplest devices to use for this function. Various digital sensing, totalizing and recording methods are also out there.
A recent growth includes using ultrasonic pulses to measure liquid level. Measurements are made by sending an acoustic pulse from the sensor to the floor of the liquid and timing the return echo. Linearized circuitry converts the height of the liquid to a flow price. A bar graph recorder records the move fee and a digital totalizer information the total variety of gallons. Another just lately introduced microprocessor-based system uses ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, management and calibration duties.
Select a proper liquid move meter

Data exhibits that greater than 75% of the circulate meters installed in industry don’t carry out nicely. And poor choice accounts for 90 % of these issues. Clearly, flowmeter choice just isn’t a job for amateurs.
The most necessary requirement is to know precisely what the instrument should do. There are a variety of points to think about right here. Will the measurement be used for process management (repeatability is the main concern) or for accounting or trade handover (high accuracy is important)? Is a local indication or a distant signal required? If a distant output is required, is it a proportional sign or a contact closure to start out or stop another device? Is the fluid viscous, clear or slurry? Is it electrically conductive? What is its particular gravity or density? What circulate charges are involved in the application? What is the working temperature and stress of the process? Accuracy (see glossary), vary, linearity, repeatability, and piping requirements must even be thought-about.
It is equally necessary to grasp what a move meter cannot do as properly as what it could possibly do earlier than making a ultimate selection. Every instrument has strengths and weaknesses, and the degree of efficiency satisfaction is instantly related to how properly the instrument’s options and weaknesses match the application necessities. Often, the user’s expectations of flowmeter performance do not match these provided by the provider. Most suppliers are keen to assist clients choose the proper flowmeter for a specific job. ไดอะแฟรม ซีล provide questionnaires, checklists and specification sheets designed to obtain the crucial information necessary to match the correct flowmeter to the job.
Technical improvements to the flowmeter should also be thought of. For example, a typical mistake is to select the design that was hottest for a given application a quantity of years in the past and assume that it’s nonetheless one of the best software for the job. In current years, many adjustments and improvements could have occurred within the improvement of flowmeters for particular functions, resulting in a wider vary of decisions.
Flow meters are available in a broad range of prices. Variable area flowmeters are normally the least expensive, with some smaller units costing less than $90. Mass circulate meters are the most costly. They start at about $3000. However, the entire system cost must always be considered when selecting a flowmeter. Installation, operation and upkeep costs are also necessary economic elements. For a few of the extra complicated designs, maintenance costs may be high.
As with many other products, the plant engineer normally will get what he pays for when he buys a flow meter. But his satisfaction with the product will depend on the care he uses in selecting and installing the instrument. It comes again to understanding the process, the product and the move metering requirements. It is not uncommon to “overbuy”. Plant engineers shouldn’t purchase more powerful or complicated flowmeters than they want.
Using move meters

Although suppliers are all the time prepared to supply flowmeter set up companies, it’s estimated that about 75% of users install their very own equipment. But set up errors can occur. One of the commonest conditions is not allowing enough upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity conditions within the piping, but all installations require correct piping configurations to function effectively. Proper piping offers the proper move pattern for the gadget. Without it, accuracy and efficiency may be adversely affected. Flow meters are generally put in backwards (especially orifice plates). Pressure sensing traces may also be reversed.
For electrical parts, intrinsic safety is a crucial consideration in hazardous areas. Most flowmeter suppliers supply intrinsically protected designs for this type of use.
Stray magnetic fields are present in most industrial crops. Power lines, relays, solenoids, transformers, motors and generators all contribute their share of interference. Users should be positive that the flowmeter they select just isn’t topic to such disturbances. The drawback occurs primarily with the electronics within the secondary elements that must be protected. Strict adherence to the manufacturer’s recommended set up practices can often forestall such problems.
Calibration

All flow meters require an preliminary calibration. In most instances, the instrument is calibrated by the manufacturer for the specified circumstances of use. However, if certified personnel can be found on the factory, the user can perform his own calibration.
The need for recalibration relies upon significantly on how properly the meter is matched to the appliance. Certain fluids that move through the meter are usually abrasive, aggressive or corrosive. Over time, some components of the gadget will degrade enough to affect efficiency. Some designs are more susceptible to break than others. For example, wear on individual turbine blades may cause performance modifications. If the applying is critical, the accuracy of the circulate meter must be checked regularly. In other circumstances, recalibration will not be required for many years as a end result of the appliance is not critical and would not otherwise change the meter’s efficiency. Some flowmeters require particular equipment for calibration. Most producers will present such companies at their plants or user amenities, and they’re going to bring the equipment with them for on-site calibration.
Maintenance

Many elements can affect maintenance requirements and the expected life of a move meter. The major issue, in fact, is matching the right instrument to the particular software. Poorly chosen equipment will at all times trigger issues early on. Flowmeters with out transferring components normally require much less consideration than gadgets with transferring parts. But all flowmeters will ultimately require some type of maintenance.
The major element in a differential strain flowmeter requires a lot of piping, valves and fittings when connected to the secondary element, so upkeep is usually a recurring process in such installations. Pulse lines can turn into clogged or corroded and must be cleaned or changed. And, improperly positioned secondary elements can result in measurement errors. Repositioning parts could be expensive.
Flow meters with transferring elements require periodic inner inspection, particularly if the liquid being measured is soiled or viscous. Installing a filter earlier than such devices will assist reduce fouling and wear. Accessible instruments such as ultrasonic or electromagnetic meters may have issues with the electronics of their secondary components. Pressure transducers related to secondary components should be eliminated and inspected periodically.
Applications where coatings might occur are also potential issues for accessible instruments such as magnetic or ultrasonic units. If the coating is insulated, the operation of the magnetic move meter can eventually be impaired if the electrodes are insulated from the liquid. This scenario could be prevented by common cleaning. With ultrasonic move meters, the refraction angle could change and the acoustic power absorbed by the coating may cause the flow meter to not work.
More articles on circulate meters:
Relation between flow and strain

Difference between flow meter and circulate transmitter

Water degree sensor sorts and works

Solution of water air pollutionn
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Measuring liquid flow is a important requirement for lots of industrial vegetation. In some operations, the ability to make accurate flow measurements is so important that it could possibly make the distinction between a revenue or a loss. In different instances, inaccurate flow measurements or failure to make them can lead to critical (or even catastrophic) outcomes.
For most liquid move measurement devices, flow is decided inferentially by measuring the change in velocity or kinetic energy of the liquid. The velocity is dependent upon the stress distinction that forces the liquid via the pipe or conduit. Since the cross-sectional space of the pipe is known and remains constant, the average circulate fee is an indicator of the move price. In this case, the fundamental relationship for figuring out the move fee of a liquid is

Q = V x A

Q = Flow price of liquid through the pipe

V = Average move price

A = Cross-sectional area of the pipe

Other elements that affect the flow price of a liquid embody the viscosity and density of the liquid, and the friction of the liquid in contact with the pipe.
Liquid flow could be measured instantly using positive displacement move meters. These models divide the liquid into particular increments and continue to maneuver. The whole flow fee is the buildup of the measured increments and may be counted mechanically or electronically.
Table of Contents

Reynolds quantity

Types of liquid flow meters

Differential Pressure move meters

Orifice plate circulate meters

Venturi flow meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable area move meter

Positive displacement move meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc type meter

Rotary vane gauges

Spiral circulate meter

Velocity meters

Turbine move meters

Vortex flowmeters

Electromagnetic circulate meters

Ultrasonic move meters

Mass move meter

Coriolis move meters

Thermal mass circulate meters

Open channel circulate meter

Select a proper liquid circulate meter

Using move meters

Calibration

Maintenance

Reynolds number

The performance of a circulate meter can be influenced by the dimensionless unit called Reynolds number. It is defined as the ratio of the inertial drive of a liquid to its resistance.
The formula is

R = 3160 x Q x Gt

D x ต

R = Reynolds number

Q = Flow price of the liquid, gpm

Gt = Specific gravity of the liquid

D = Internal diameter of the pipe, in.
ต = Viscosity of the liquid, cp

Flow price and particular gravity are the inertial forces, pipe diameter and viscosity are the resistance. For most liquid purposes, the pipe diameter and particular gravity remain constant. At very low velocities or high viscosities, R could be very low and the liquid flows in a clean layer with the very best velocity at the heart of the pipe, where viscous forces on the pipe wall restrict it to very low velocities. This type of flow is known as laminar flow. the R worth is beneath about 2000. a attribute of laminar circulate is the parabolic form of its velocity distribution.
However, most applications contain turbulent move with R-values above 3000. turbulent move occurs at excessive speeds or low viscosities. The move breaks down into turbulent eddies that flow by way of the pipe with the identical common velocity. The fluid velocity is less important and the speed distribution is more uniform in form. A transition zone exists between turbulent and laminar circulate. Depending on the pipe configuration and other installation conditions, the circulate on this zone may be turbulent or laminar.
Types of liquid circulate meters

Many types of circulate meters can be found to be used in closed pipe methods. In basic, devices may be classified as differential strain meters, optimistic displacement meters, velocity meters, and mass meters. Differential strain units (also known as head gauges) embrace orifice plates, venturi, circulate tubes, flow nozzles, pitot tubes, elbow type move meters, target kind flow meters and variable area flow meters.
Positive displacement circulate meters include piston, elliptical-gear, chapter-actuated disk and rotary vane sorts. Velocity meters embody turbine, vortex shedding, electromagnetic, and acoustic designs. Mass meters embrace Coriolis and thermal types. Measurement of liquid flow in open channels normally entails weirs and flumes.
Differential Pressure move meters

The use of differential strain as an inferred measurement of the circulate rate of a liquid is well known. By far, differential stress circulate meters are essentially the most generally used unit at present. It is estimated that greater than 50% of all liquid circulate measurement applications use this type of unit.
The fundamental operating principle of differential strain circulate meters relies on the premise that the stress drop throughout the meter is proportional to the sq. of the circulate rate. The circulate price is obtained by measuring the differential strain and extracting the square root.
Like most circulate meters, differential strain move meters have a major element and a secondary element. The primary factor causes a change in kinetic power, which creates a differential stress in the pipe. The gadget should be correctly matched to the pipe size, flow situations and liquid traits. And, the accuracy of the factor measurement should remain good inside cheap limits. The secondary factor measures the differential stress and provides a signal or studying that’s converted to an actual circulate worth.
Orifice plate move meters

Orifice plates are the most well-liked liquid flow meters in use today. An orifice is simply a flat piece of metal with a specific dimension gap drilled in it. Most orifices are concentric, however eccentric, conical (quadrant) and segmented designs are additionally out there.
In practice, the orifice is put in within the pipe between two flanges. As the primary gadget, the orifice restricts the flow of fluid, thereby making a differential strain throughout the plate. Pressure measurement ports on each side of the plate are used to detect the difference. The main advantages of orifice plates are that they haven’t any shifting parts and that their price doesn’t improve significantly with the scale of the pipe.
Tapered and quadrant orifices are comparatively new. These items had been developed primarily for measuring liquids with low Reynolds numbers. An basically fixed flow coefficient may be maintained at an R-value beneath 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which have to be calculated and machined for each application.
The segment wedge is a variant of the section orifice. It is a throttle orifice designed primarily to measure the circulate of liquids containing solids. The system is able to measuring circulate at low Reynolds numbers and still maintaining the required square root relationship. Its design is easy and the wedge hole has only one important dimension. The strain drop via the system is only about half that of a traditional orifice plate.
The one-piece wedge assembly combines the wedge element and pressure measurement becoming right into a one-piece pipe fitting bolted to a standard pressure transmitter. No particular piping or fittings are required to put in the system within the pipeline.
The metering accuracy of all orifice move meters is dependent upon the set up circumstances, the orifice plate space ratio, and the bodily characteristics of the liquid being measured.
Venturi move meters

The advantage of a venturi is its ability to deal with massive flows at low stress drops. A venturi is basically a section of pipe with a conical inlet and a straight throat. As the liquid passes by way of the throat, it increases in velocity, resulting in a pressure difference between the inlet and outlet regions.
Flow meters don’t have any moving parts. They may be installed in massive diameter pipes utilizing flanged, welded or threaded end connections. The unit is usually fitted with four or extra stress measuring ports to average the measured strain. Venturi tubes can be used for many liquids, including these with high solids content material.
Flow tubes

Flow tubes are considerably much like venturi, besides that they do not have an entrance cone. They have a tapered throat, however the outlet is elongated and smooth. The distance between the front and the tip is about one-half the diameter of the tube. The strain measurement port is situated about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle

At excessive velocities, the move nozzle can handle roughly 60% of the liquid circulate in comparison with an orifice plate with the same strain drop. Liquids containing suspended solids may additionally be metered. However, these gadgets are not really helpful for high viscosity liquids or liquids containing large amounts of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two kinds of pressure concurrently, shock strain and static pressure. The shock device consists of a tube with one end of the tube bent at proper angles to the path of circulate. The end of the static tube is closed, but has a small slot within the aspect of the device. These tubes may be installed individually in the pipe or mixed in a housing.
Pitot tubes are usually installed by welding a coupling to the pipe and inserting the probe through the coupling. The use of most Pitot tubes is restricted to single point measurements. These devices are vulnerable to clogging by overseas matter within the liquid. The advantages of Pitot tubes are low price, no moving parts, simple set up and minimal pressure drop.
Elbow flowmeter

Elbow circulate meters work on the precept that centrifugal forces are exerted along the outer edges as the liquid strikes along a circular path. Thus, as the liquid flows via the pipe elbow, the force on the inner floor of the elbow is proportional to the density of the liquid multiplied by the sq. of its velocity. In addition, the drive is inversely proportional to the radius of the elbow.
Arbitrary ninety levels. Elbows can be used as liquid flow meters. All that is required are two small holes placed at the midpoint of the elbow (45 diploma point) for the manometer tap. A strain sensing line may be connected to the tap utilizing any convenient method.
Target meter

The goal meter senses and measures the force caused by the liquid striking the goal or a drag disk suspended in the liquid stream. By measuring the force utilized to the target the liquid flow fee can be immediately indicated. In its simplest type, the meter consists solely of an articulated oscillating plate that moves outward with the liquid flow. In this case, the system is used as a flow indicator.
More sophisticated versions use subtle low-level pressure sensor sensing elements. The goal drive caused by the liquid flow is sensed by a strain gauge. The output sign of the meter indicates the move rate. The goal meter can be utilized to measure the circulate price of soiled or corrosive liquids.
Variable space flow meter

Variable space meters consist primarily of a conical tube and a float. Although classified as differential pressure units, they are actually constant stress devices. Flange end connections provide a simple way to set up them in the pipe. Working principle of rotameter is when there is not a liquid flow, the float is free to relaxation on the bottom of the pipe. When the liquid enters the bottom of the pipe, the float begins to rise. The place of the float varies directly with the move price. Its actual place is at the level where the strain distinction between the higher and decrease surfaces balances the weight of the float.
Because the move fee may be read instantly on a scale mounted subsequent to the tube, there isn’t a need for an auxiliary move studying device. However, if desired, an computerized sensing gadget can be utilized to sense the float degree and transmit the flow sign. Variable area circulate meter tubes are made from glass, steel or plastic. Tube diameters vary from 1/4 to higher than 6 inches.
Positive displacement circulate meter

The operation of those models consists of separating the liquid into exactly measured increments and continuing to maneuver. Each phase is counted by a connection register. Because every increment represents a discrete quantity, optimistic displacement models are popular in computerized dosing and accounting functions. Volumetric flow meters are perfect for measuring the circulate of viscous liquids or where a simple mechanical circulate meter system is required.
Reciprocating piston flowmeter

Reciprocating piston circulate meters are available in single and multi-piston variations. The specific selection depends on the range of circulate charges required in a particular application. Piston circulate meters can be utilized to handle a broad range of liquids. The fluid never comes in contact with gears or other components that would clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with carefully synchronized teeth. A fixed amount of fluid passes by way of the meter with each revolution. The shaft rotation could be monitored to obtain a selected flow fee.
Disc sort meter

Chapter moving disc sort meters have a movable disc mounted on a concentric sphere that is situated in a spherical sidewall chamber. The stress of the fluid passing through the measurement chamber causes the disc to oscillate in its circulation path with out rotating about its own axis. It is the only moving half in the measurement chamber.
A pin extending vertically from the disk is related to a mechanical counter, which monitors the oscillating motion of the disk. Each cycle is proportional to a particular circulate rate. As with all optimistic displacement meters, adjustments in viscosity beneath a given threshold will affect the measurement accuracy. A big selection of sizes and capacities can be found. These items can be made from a variety of building materials.
Rotary vane gauges

Rotary vane meters can be found in a big selection of designs, but all of them function on the same precept. The fundamental unit consists of an equally divided rotating impeller (containing two or extra compartments) mounted contained in the instrument housing. The impeller is in constant contact with the housing. As the impeller rotates, a fixed volume of liquid is swept from every compartment to the outlet of the meter. The number of impeller revolutions is calculated and recorded in volume units.
Spiral flow meter

The helical move meter consists of two radially inclined helical rotors which might be gear pushed together with minimal clearance between the rotors and the housing. The two rotors switch the liquid from one finish of the chamber to the opposite alongside the axial course.
Velocity meters

These instruments operate linearly with respect to the volumetric flow price. Because there is no square root relationship (as with differential strain devices), they’ve a much larger range. Velocity meters are least delicate to modifications in viscosity when the Reynolds quantity exceeds 10,000. Most velocity meter housings are outfitted with flanges or fittings to permit them to be connected instantly into the piping.
Turbine circulate meters

Turbine circulate meters have been extensively used for exact liquid measurement functions. The gadget consists of a multi-bladed rotor mounted in a pipe, perpendicular to the flow of the liquid. The rotor rotates as the liquid passes through the vanes. Rotational velocity is a direct operate of flow price and may be sensed by magnetic sensors, photocells or gears. Electrical pulses can be counted and totalized.
The number of electrical pulses counted in a given time interval is proportional to the circulate rate. A tachometer could be added to measure the turbine velocity and determine the liquid flow price. A properly specified and installed turbine move meter has good accuracy, especially for low viscosity liquids.
A major problem with turbine flowmeters is bearing put on. A “bearingless” design has been developed to avoid this drawback. The liquid getting into the flow meter passes via the spiral vanes of the stator, causing the liquid flow to rotate. The move acts on the spheres, inflicting them to travel within the area between the primary stator and the spiral-like second stator. The orbital movement of the sphere is detected electronically. The frequency of the generated pulse output is proportional to the circulate price.
Vortex flowmeters

Vortex flow meters benefit from the pure phenomenon that happens when a liquid flows by way of a blunt object. Vortex or vortex flow alternates downstream of the object. The frequency of the vortex shedding is proportional to the velocity of the liquid flowing through the flowmeter.
The three main parts of the flow meter are the blunt object strut mounted on the meter bore, the sensor that detects the presence of vortices and generates an electrical pulse, and the signal amplification and conditioning transmitter whose output is proportional to the flow fee.
Electromagnetic flow meters

Magnetic circulate meters can handle most liquids and slurries, provided that the fabric to be metered is electrically conductive. The major component is the flow tube (primary element), which is installed immediately in the pipe. The pressure drop across the meter is similar because the pressure drop by way of the equal length of pipe, since there are not any shifting components or flow obstructions. The voltmeter can be related on to the circulate tube or remotely mounted and related to the flow tube by way of a shielded cable.
Electromagnetic flow meters work in accordance with Faraday’s regulation of electromagnetic induction, which states that a voltage is induced when a conductor passes through a magnetic field. The liquid acts as the conductor; the magnetic area is generated by an energized coil exterior the flow tube. The amount of voltage generated is proportional to the flow fee. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary factor.
Electromagnetic flowmeters provide major advantages: they will measure troublesome and corrosive liquids and slurries; they can measure forward and reverse flow with equal accuracy. The disadvantages of early designs had been high energy consumption and the want to acquire a full tube with no flow to set the meter to zero initially. Recent improvements have eradicated these problems. The pulse-type excitation method reduces power consumption because excitation occurs solely half the time in the unit. A zero setting is now not required.
Ultrasonic flow meters

Ultrasonic flowmeters may be divided into doppler meters and travel time (or transverse) meters. Doppler meters measure the frequency shift attributable to the flow of a liquid. Two sensors are mounted in a housing linked to at least one aspect of the pipe. A signal of known frequency is shipped to the liquid to be measured. Solids, bubbles or any discontinuities within the liquid cause the coronary heart beat to be mirrored to the receiver factor. Since the liquid causing the reflection is moving, the frequency of the returned pulse is shifted. The frequency shift is proportional to the rate of the liquid.
There can be a transportable doppler meter that can be run on AC energy or a chargeable energy pack. The instrument can be used by merely clamping the sensing head to the outside of the pipe. A set of 4 to 20 mA output terminals permits the unit to be related to a strip chart recorder or different remote gadget.
The travel time meter’s sensors are mounted on both sides of the pipe. The configuration allows the sound waves to travel between the gadgets at an angle of 45 levels. angle to the course of fluid move. The pace of the signal propagating between the sensors increases or decreases with the path of transmission and the pace of the liquid being measured. By transmitting the signal in both directions alternately, a time-differential relationship proportional to the circulate price may be obtained. A limitation of the travel time meter is that the liquid being measured should be comparatively freed from entrained gases or solids to minimize sign scattering and absorption.
Mass flow meter

Mass flowmeters the continued want for extra accurate flow measurement in mass related processes (chemical reactions, heat switch, etc.) has led to the development of mass move meters. A variety of designs can be found, but essentially the most generally used for liquid move applications is the Coriolis meter. It operates on the idea of a pure phenomenon generally known as the Coriolis drive, therefore the identify.
Coriolis flow meters

Coriolis meters are true mass meters that immediately measure mass circulate instead of volume circulate. Since the mass is constant, the meter is linear and doesn’t have to be adjusted for modifications in liquid characteristics. It additionally eliminates the want to compensate for altering temperature and pressure circumstances. The meter is especially suitable for measuring liquids whose viscosity varies with velocity at a given temperature and stress.
Coriolis meters are additionally out there in a wide selection of designs. A well-liked unit consists of a U-shaped flow tube encapsulated in a sensor housing connected to an digital unit. The sensing unit could be mounted immediately into any process. The electronics unit could be located as much as 500 ft away from the sensor.
Thermal mass circulate meters

Thermal mass flowmeters are historically used for gasoline measurements, however are additionally out there in designs for liquid flow measurements. These mass meters also operate impartial of density, strain and viscosity. Thermal mass meters use a heated sensing factor that’s isolated from the fluid flow path. The flowing stream conducts heat from the sensing factor. The warmth transferred is proportional to the mass move fee. The sensor isn’t in direct contact with the fluid. The digital meeting includes a circulate analyzer, temperature compensator, and signal conditioner that gives a linear output proportional to the mass flow fee.
Open channel flow meter

An “open channel” is any pipe during which liquids circulate on a free floor. This consists of tunnels, unpressurized sewers, partially crammed pipes, canals, streams and rivers. Of the various methods that can be utilized to monitor flow in open channels, depth-related strategies are the most typical. These techniques assume that instantaneous flow may be decided from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used main gadgets used to measure flow in open channels.
Weirs work on the precept that an obstruction in a channel causes water to flow backwards, creating a excessive water level (head) behind the obstruction. The head is a perform of the circulate rate, and therefore the move fee by way of the device. The weir consists of a vertical plate with a pointed top. The prime of the plate can be straight or notched. Weirs are categorized by the form of the notch. The fundamental varieties are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a perform of the liquid degree, so the gadget must use degree measurement methods to determine the flow price. Staff gauges and floating operating items are the simplest units to make use of for this objective. Various electronic sensing, totalizing and recording techniques are additionally out there.
A current growth includes the use of ultrasonic pulses to measure liquid stage. Measurements are made by sending an acoustic pulse from the sensor to the floor of the liquid and timing the return echo. Linearized circuitry converts the height of the liquid to a circulate price. A bar graph recorder information the flow price and a digital totalizer data the total number of gallons. Another just lately launched microprocessor-based system makes use of ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, control and calibration duties.
Select a right liquid circulate meter

Data exhibits that greater than 75% of the flow meters installed in business do not perform properly. And poor selection accounts for 90 % of these problems. Clearly, flowmeter selection isn’t a job for amateurs.
The most important requirement is to know exactly what the instrument ought to do. There are a selection of points to consider right here. Will the measurement be used for process management (repeatability is the main concern) or for accounting or trade handover (high accuracy is important)? Is a local indication or a remote signal required? If a distant output is required, is it a proportional sign or a contact closure to begin out or stop one other device? Is the fluid viscous, clear or slurry? Is it electrically conductive? What is its specific gravity or density? What flow charges are involved in the application? What is the operating temperature and stress of the process? Accuracy (see glossary), vary, linearity, repeatability, and piping requirements should even be considered.
It is equally important to grasp what a move meter can not do as properly as what it might possibly do earlier than making a final choice. Every instrument has strengths and weaknesses, and the degree of performance satisfaction is instantly associated to how nicely the instrument’s features and weaknesses match the application necessities. Often, the user’s expectations of flowmeter efficiency do not match those provided by the supplier. Most suppliers are keen to assist clients select the proper flowmeter for a selected job. Many present questionnaires, checklists and specification sheets designed to acquire the crucial information necessary to match the right flowmeter to the job.
Technical enhancements to the flowmeter should also be thought of. For example, a common mistake is to pick out the design that was hottest for a given utility several years ago and assume that it’s nonetheless the most effective tool for the job. In recent years, many adjustments and innovations could have occurred within the development of flowmeters for specific functions, leading to a wider vary of decisions.
Flow meters are available in a broad range of prices. Variable area flowmeters are normally the least expensive, with some smaller models costing less than $90. Mass flow meters are the most costly. They start at about $3000. However, the whole system price should always be considered when deciding on a flowmeter. Installation, operation and maintenance prices are additionally necessary economic factors. For a few of the more advanced designs, maintenance prices may be high.
As with many other merchandise, the plant engineer usually will get what he pays for when he buys a flow meter. But his satisfaction with the product will rely upon the care he makes use of in choosing and installing the instrument. It comes back to understanding the method, the product and the move metering necessities. It just isn’t uncommon to “overbuy”. Plant engineers should not purchase extra powerful or complex flowmeters than they want.
Using flow meters

Although suppliers are at all times prepared to offer flowmeter set up companies, it is estimated that about 75% of users set up their own tools. But set up errors can happen. One of the commonest conditions just isn’t allowing enough upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity conditions in the piping, however all installations require proper piping configurations to operate effectively. Proper piping provides the right circulate sample for the gadget. Without it, accuracy and performance may be adversely affected. Flow meters are sometimes put in backwards (especially orifice plates). Pressure sensing lines can also be reversed.
For electrical components, intrinsic security is an important consideration in hazardous areas. Most flowmeter suppliers supply intrinsically protected designs for this kind of use.
Stray magnetic fields are current in most industrial vegetation. Power lines, relays, solenoids, transformers, motors and mills all contribute their share of interference. Users must be sure that the flowmeter they choose isn’t topic to such disturbances. The downside occurs primarily with the electronics in the secondary elements that must be protected. Strict adherence to the manufacturer’s beneficial installation practices can typically stop such problems.
Calibration

All flow meters require an initial calibration. In most circumstances, the instrument is calibrated by the producer for the desired situations of use. However, if certified personnel are available on the factory, the person can perform his own calibration.
The want for recalibration relies upon significantly on how properly the meter is matched to the appliance. Certain fluids that cross through the meter are usually abrasive, aggressive or corrosive. Over time, some parts of the device will degrade sufficient to have an effect on efficiency. Some designs are more susceptible to break than others. For example, wear on individual turbine blades can cause efficiency changes. If the appliance is crucial, the accuracy of the circulate meter should be checked frequently. In other instances, recalibration may not be required for a number of years as a result of the application isn’t important and wouldn’t otherwise change the meter’s efficiency. Some flowmeters require particular equipment for calibration. Most producers will provide such services at their vegetation or person facilities, and they will deliver the tools with them for on-site calibration.
Maintenance

Many components can affect upkeep necessities and the anticipated life of a flow meter. The primary factor, after all, is matching the right instrument to the precise application. Poorly chosen equipment will all the time cause problems early on. Flowmeters without shifting elements usually require much less consideration than devices with moving components. But all flowmeters will eventually require some kind of upkeep.
The primary component in a differential pressure flowmeter requires a lot of piping, valves and fittings when related to the secondary factor, so upkeep could be a recurring task in such installations. Pulse lines can turn out to be clogged or corroded and must be cleaned or replaced. And, improperly positioned secondary parts can lead to measurement errors. Repositioning components can be expensive.
Flow meters with shifting parts require periodic internal inspection, particularly if the liquid being measured is soiled or viscous. Installing a filter before such gadgets will assist scale back fouling and wear. Accessible devices such as ultrasonic or electromagnetic meters might have problems with the electronics of their secondary parts. Pressure transducers associated with secondary parts should be eliminated and inspected periodically.
Applications the place coatings might happen are additionally potential issues for accessible instruments such as magnetic or ultrasonic devices. If the coating is insulated, the operation of the magnetic move meter can finally be impaired if the electrodes are insulated from the liquid. This situation can be avoided by regular cleansing. With ultrasonic flow meters, the refraction angle could change and the acoustic power absorbed by the coating could cause the flow meter to not work.
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Difference between flow meter and circulate transmitter

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