Liquid move meter

Measuring liquid move is a important requirement for many industrial plants. In some operations, the ability to make accurate move measurements is so essential that it may possibly make the distinction between a revenue or a loss. In different circumstances, inaccurate circulate measurements or failure to make them can lead to severe (or even catastrophic) results.
For most liquid circulate measurement instruments, flow is set inferentially by measuring the change in velocity or kinetic power of the liquid. The velocity depends on the stress distinction that forces the liquid through the pipe or conduit. Since the cross-sectional space of the pipe is understood and remains constant, the common flow price is an indicator of the flow rate. In this case, the fundamental relationship for determining the move fee of a liquid is

Q = V x A

Q = Flow price of liquid via the pipe

V = Average move rate

A = Cross-sectional area of the pipe

Other factors that affect the flow fee of a liquid include the viscosity and density of the liquid, and the friction of the liquid involved with the pipe.
Liquid circulate could be measured instantly utilizing optimistic displacement circulate meters. These models divide the liquid into particular increments and continue to maneuver. The complete circulate rate is the accumulation of the measured increments and may be counted mechanically or electronically.
Table of Contents

Reynolds number

Types of liquid circulate meters

Differential Pressure move meters

Orifice plate flow meters

Venturi move meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable space circulate meter

Positive displacement flow meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc type meter

Rotary vane gauges

Spiral circulate meter

Velocity meters

Turbine flow meters

Vortex flowmeters

Electromagnetic move meters

Ultrasonic flow meters

Mass flow meter

Coriolis move meters

Thermal mass move meters

Open channel move meter

Select a right liquid circulate meter

Using circulate meters

Calibration

Maintenance

Reynolds number

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

R = 3160 x Q x Gt

D x ต

R = Reynolds quantity

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 rate and particular gravity are the inertial forces, pipe diameter and viscosity are the resistance. For most liquid functions, the pipe diameter and particular gravity remain fixed. At very low velocities or excessive viscosities, R could be very low and the liquid flows in a clean layer with the best velocity at the middle of the pipe, the place viscous forces on the pipe wall restrict it to very low velocities. This kind of move known as laminar move. the R worth is below about 2000. a attribute of laminar flow is the parabolic shape of its velocity distribution.
However, most functions involve turbulent move with R-values above 3000. turbulent circulate happens at excessive speeds or low viscosities. The circulate breaks down into turbulent eddies that move via the pipe with the same average velocity. The fluid velocity is less important and the speed distribution is extra uniform in form. A transition zone exists between turbulent and laminar move. Depending on the pipe configuration and other set up circumstances, the circulate on this zone may be turbulent or laminar.
Types of liquid circulate meters

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

The use of differential stress as an inferred measurement of the circulate price of a liquid is well known. By far, differential pressure circulate meters are essentially the most commonly used unit at present. It is estimated that greater than 50% of all liquid circulate measurement applications use this sort of unit.
The primary operating precept of differential strain move meters relies on the premise that the strain drop throughout the meter is proportional to the square of the circulate price. The flow price is obtained by measuring the differential stress and extracting the sq. root.
Like most move meters, differential pressure flow meters have a primary factor and a secondary element. The primary element causes a change in kinetic power, which creates a differential stress within the pipe. The device must be properly matched to the pipe measurement, flow situations and liquid traits. And, the accuracy of the element measurement must remain good inside cheap limits. The secondary factor measures the differential pressure and supplies a signal or reading that’s converted to an precise flow worth.
Orifice plate circulate meters

Orifice plates are the most popular liquid flow meters in use today. An orifice is just a flat piece of metal with a specific size gap drilled in it. Most orifices are concentric, however eccentric, conical (quadrant) and segmented designs are additionally out there.
In practice, the orifice is installed within the pipe between two flanges. As the first gadget, the orifice restricts the flow of fluid, thereby making a differential stress across the plate. Pressure measurement ports on each side of the plate are used to detect the difference. The major advantages of orifice plates are that they don’t have any moving components and that their value does not improve considerably with the scale of the pipe.
Tapered and quadrant orifices are relatively new. These units have been developed primarily for measuring liquids with low Reynolds numbers. An basically fixed circulate coefficient can be maintained at an R-value beneath 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which must be calculated and machined for every application.
The phase wedge is a variant of the section orifice. It is a throttle orifice designed primarily to measure the flow of liquids containing solids. The gadget is able to measuring circulate at low Reynolds numbers and still maintaining the required square root relationship. Its design is straightforward and the wedge gap has only one crucial dimension. The stress drop through the gadget is simply about half that of a standard orifice plate.
The one-piece wedge meeting combines the wedge element and stress measurement becoming into a one-piece pipe becoming bolted to a traditional stress transmitter. No special piping or fittings are required to install the system in the pipeline.
The metering accuracy of all orifice circulate meters depends on the set up conditions, the orifice plate area ratio, and the bodily traits of the liquid being measured.
Venturi circulate meters

The benefit of a venturi is its capacity to deal with giant flows at low strain drops. A venturi is essentially a bit of pipe with a conical inlet and a straight throat. As the liquid passes through the throat, it will increase in velocity, leading to a strain distinction between the inlet and outlet areas.
Flow meters haven’t any transferring parts. They could be put in in massive diameter pipes using flanged, welded or threaded end connections. The unit is often fitted with 4 or more pressure measuring ports to common the measured pressure. Venturi tubes can be utilized for most liquids, including these with excessive solids content material.
Flow tubes

Flow tubes are considerably similar to venturi, except that they don’t have an entrance cone. They have a tapered throat, however the outlet is elongated and clean. The distance between the entrance and the tip is about one-half the diameter of the tube. The stress measurement port is located 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 flow compared to an orifice plate with the same pressure drop. Liquids containing suspended solids can additionally be metered. However, these units usually are not recommended for top viscosity liquids or liquids containing massive quantities of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two forms of pressure simultaneously, shock pressure and static strain. The shock system consists of a tube with one end of the tube bent at proper angles to the path of move. The end of the static tube is closed, however has a small slot in the side of the gadget. These tubes may be put in individually within the pipe or combined in a housing.
Pitot tubes are typically put in by welding a coupling to the pipe and inserting the probe via the coupling. The use of most Pitot tubes is restricted to single point measurements. These devices are prone to clogging by overseas matter in the liquid. The advantages of Pitot tubes are low price, no shifting parts, easy set up and minimal stress drop.
Elbow flowmeter

Elbow move meters work on the precept that centrifugal forces are exerted along the outer edges as the liquid strikes alongside a round path. Thus, as the liquid flows via the pipe elbow, the drive on the internal floor of the elbow is proportional to the density of the liquid multiplied by the square of its velocity. In addition, the pressure is inversely proportional to the radius of the elbow.
Arbitrary ninety levels. Elbows can be used as liquid move meters. All that is required are two small holes placed at the midpoint of the elbow (45 degree point) for the manometer faucet. A stress sensing line could be related to the tap utilizing any handy technique.
Target meter

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

Variable space meters consist primarily of a conical tube and a float. Although categorized as differential stress units, they’re actually constant stress devices. Flange finish connections present a simple approach to set up them within the pipe. Working precept of rotameter is when there isn’t any liquid move, 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 position of the float varies instantly with the flow fee. Its precise position is on the point where the pressure difference between the upper and decrease surfaces balances the weight of the float.
Because the circulate fee can be read directly on a scale mounted subsequent to the tube, there isn’t a want for an auxiliary move reading gadget. However, if desired, an automated sensing device can be utilized to sense the float degree and transmit the move sign. Variable space move meter tubes are made of glass, steel or plastic. Tube diameters range from 1/4 to higher than 6 inches.
Positive displacement circulate meter

The operation of these units consists of separating the liquid into precisely measured increments and persevering with to move. Each phase is counted by a connection register. Because each increment represents a discrete quantity, positive displacement models are well-liked in computerized dosing and accounting functions. Volumetric flow meters are perfect for measuring the move of viscous liquids or where a easy mechanical flow meter system is required.
Reciprocating piston flowmeter

Reciprocating piston flow meters are available in single and multi-piston versions. The specific selection is decided by the vary of circulate rates required in a particular utility. Piston move meters can be utilized to deal with a extensive range of liquids. The fluid never comes in contact with gears or different parts that could clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with intently synchronized teeth. A mounted quantity of fluid passes by way of the meter with every revolution. The shaft rotation may be monitored to acquire a particular flow price.
Disc kind meter

Chapter transferring disc type meters have a movable disc mounted on a concentric sphere that is situated in a spherical sidewall chamber. The pressure of the fluid passing via the measurement chamber causes the disc to oscillate in its circulation path without rotating about its own axis. It is the one transferring part within the measurement chamber.
A pin extending vertically from the disk is linked to a mechanical counter, which screens the oscillating movement of the disk. Each cycle is proportional to a selected move rate. As with all positive displacement meters, modifications in viscosity below a given threshold will have an effect on the measurement accuracy. A big selection of sizes and capacities are available. These models could be made from a wide selection of building materials.
Rotary vane gauges

Rotary vane meters are available in a big selection of designs, but they all operate on the identical precept. The basic unit consists of an equally divided rotating impeller (containing two or more compartments) mounted contained in the instrument housing. The impeller is in fixed contact with the housing. As the impeller rotates, a fixed volume of liquid is swept from each compartment to the outlet of the meter. The variety of impeller revolutions is calculated and recorded in volume units.
Spiral circulate meter

The helical move meter consists of two radially inclined helical rotors which are gear pushed together with minimal clearance between the rotors and the housing. The two rotors transfer the liquid from one finish of the chamber to the other along the axial course.
Velocity meters

These devices function linearly with respect to the volumetric move price. Because there is no sq. root relationship (as with differential strain devices), they have a a lot larger range. Velocity meters are least sensitive to adjustments in viscosity when the Reynolds quantity exceeds 10,000. Most velocity meter housings are outfitted with flanges or fittings to allow them to be linked immediately into the piping.
Turbine circulate meters

Turbine circulate meters have been broadly used for exact liquid measurement purposes. The gadget consists of a multi-bladed rotor mounted in a pipe, perpendicular to the move of the liquid. The rotor rotates as the liquid passes by way of the vanes. Rotational pace is a direct operate of flow price 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 can be added to measure the turbine speed and determine the liquid move fee. A properly specified and put in turbine flow meter has good accuracy, especially for low viscosity liquids.
A major drawback with turbine flowmeters is bearing wear. A “bearingless” design has been developed to keep away from this downside. The liquid getting into the flow meter passes via the spiral vanes of the stator, inflicting the liquid flow to rotate. The flow acts on the spheres, causing them to travel within the house 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 circulate fee.
Vortex flowmeters

Vortex circulate meters take benefit of the pure phenomenon that occurs when a liquid flows via a blunt object. Vortex or vortex move alternates downstream of the item. The frequency of the vortex shedding is proportional to the velocity of the liquid flowing via the flowmeter.
The three primary 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 circulate price.
Electromagnetic move meters

Magnetic move meters can deal with most liquids and slurries, provided that the material to be metered is electrically conductive. The primary component is the move tube (primary element), which is installed directly in the pipe. The stress drop across the meter is identical as the stress drop by way of the equal length of pipe, since there are no shifting parts or circulate obstructions. The voltmeter may be linked on to the move tube or remotely mounted and related to the circulate tube by way of a shielded cable.
Electromagnetic flow meters work according to Faraday’s regulation of electromagnetic induction, which states that a voltage is induced when a conductor passes by way of a magnetic field. The liquid acts as the conductor; the magnetic field is generated by an energized coil exterior the move tube. The amount of voltage generated is proportional to the move rate. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary element.
Electromagnetic flowmeters offer main benefits: they will measure difficult and corrosive liquids and slurries; they’ll measure ahead and reverse flow with equal accuracy. The disadvantages of early designs had been excessive power consumption and the want to obtain a full tube with no move to set the meter to zero initially. Recent enhancements have eradicated these issues. The pulse-type excitation method reduces power consumption as a outcome of excitation happens solely half the time within the unit. A zero setting is not required.
Ultrasonic flow meters

Ultrasonic flowmeters could be divided into doppler meters and travel time (or transverse) meters. Doppler meters measure the frequency shift brought on by the circulate of a liquid. Two sensors are mounted in a housing related to 1 aspect of the pipe. A signal of known frequency is distributed to the liquid to be measured. Solids, bubbles or any discontinuities within the liquid trigger the heartbeat to be reflected to the receiver element. Since the liquid causing the reflection is transferring, the frequency of the returned pulse is shifted. The frequency shift is proportional to the rate of the liquid.
There is also a conveyable doppler meter that may be run on AC power or a chargeable energy pack. The instrument can be utilized by simply clamping the sensing head to the surface of the pipe. A set of four to twenty mA output terminals permits the unit to be connected 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 permits the sound waves to travel between the gadgets at an angle of 45 levels. angle to the direction of fluid circulate. The pace of the sign propagating between the sensors will increase or decreases with the path of transmission and the pace of the liquid being measured. By transmitting the sign in each instructions 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 should be relatively free of entrained gases or solids to minimize signal scattering and absorption.
Mass flow meter

Mass flowmeters the continued want for extra accurate circulate measurement in mass associated processes (chemical reactions, warmth switch, and so on.) has led to the event of mass flow meters. A variety of designs can be found, but essentially the most generally used for liquid flow purposes is the Coriolis meter. It operates on the idea of a natural phenomenon often identified as the Coriolis force, therefore the identify.
Coriolis flow meters

Coriolis meters are true mass meters that instantly measure mass move as an alternative of quantity move. Since the mass is fixed, the meter is linear and does not must be adjusted for modifications in liquid traits. It also eliminates the necessity to compensate for changing temperature and pressure circumstances. The meter is particularly appropriate for measuring liquids whose viscosity varies with velocity at a given temperature and stress.
Coriolis meters are additionally out there in a selection of designs. A in style unit consists of a U-shaped move tube encapsulated in a sensor housing linked to an electronic unit. The sensing unit can be mounted directly into any process. The electronics unit could be positioned as a lot as 500 ft away from the sensor.
Thermal mass move meters

Thermal mass flowmeters are historically used for gasoline measurements, but are also obtainable in designs for liquid circulate measurements. These mass meters also function unbiased of density, stress and viscosity. Thermal mass meters use a heated sensing factor that is isolated from the fluid circulate path. The flowing stream conducts warmth from the sensing component. The heat transferred is proportional to the mass flow price. The sensor isn’t in direct contact with the fluid. The electronic assembly features a circulate analyzer, temperature compensator, and signal conditioner that gives a linear output proportional to the mass circulate rate.
Open channel move meter

An “open channel” is any pipe in which liquids circulate on a free surface. This consists of tunnels, unpressurized sewers, partially stuffed pipes, canals, streams and rivers. Of the many strategies that can be utilized to monitor circulate in open channels, depth-related methods are the most typical. These methods 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 major units used to measure flow in open channels.
Weirs work on the principle that an obstruction in a channel causes water to flow backwards, making a high water degree (head) behind the obstruction. The head is a perform of the move rate, and subsequently the circulate rate via the system. The weir consists of a vertical plate with a pointed prime. The top of the plate may be straight or notched. Weirs are classified by the shape of the notch. The basic types are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a function of the liquid level, so the gadget should use stage measurement techniques to determine the circulate fee. Staff gauges and floating working models are the best gadgets to make use of for this function. Various digital sensing, totalizing and recording systems are additionally out there.
A latest improvement contains 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 peak of the liquid to a circulate price. A bar graph recorder data the flow fee and a digital totalizer information the total variety of gallons. Another lately introduced microprocessor-based system makes use of ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, management and calibration duties.
Select a right liquid move meter

Data exhibits that more than 75% of the flow meters installed in trade do not carry out nicely. And poor selection accounts for ninety % of these issues. Clearly, flowmeter selection is not a job for amateurs.
The most important requirement is to know exactly what the instrument should do. There are numerous issues to consider right here. Will the measurement be used for course of control (repeatability is the primary 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 start out or stop another device? Is the fluid viscous, clean or slurry? Is it electrically conductive? What is its particular gravity or density? What flow charges are concerned in the application? What is the operating temperature and pressure of the process? Accuracy (see glossary), range, linearity, repeatability, and piping requirements should also be considered.
It is equally important to understand what a circulate meter cannot do in addition to what it can do before making a ultimate selection. Every instrument has strengths and weaknesses, and the diploma of performance satisfaction is immediately associated to how well the instrument’s features and weaknesses match the appliance necessities. Often, the user’s expectations of flowmeter performance don’t match those provided by the provider. Most suppliers are eager to help prospects select the proper flowmeter for a selected job. Many provide questionnaires, checklists and specification sheets designed to obtain the critical information essential to match the correct flowmeter to the job.
Technical enhancements to the flowmeter should even be thought of. For example, a typical mistake is to select the design that was hottest for a given utility a quantity of years in the past and assume that it is still the most effective device for the job. In current years, many adjustments and innovations may have occurred within the development of flowmeters for particular purposes, leading to a wider vary of selections.
Flow meters can be found in a extensive range of costs. Variable space flowmeters are often the least costly, with some smaller models costing less than $90. Mass flow meters are the most costly. They begin at about $3000. However, the whole system cost should at all times be thought-about when selecting a flowmeter. Installation, operation and upkeep prices are additionally important financial elements. For a few of the more complex designs, upkeep costs may be high.
As with many other products, the plant engineer often gets what he pays for when he buys a move meter. But his satisfaction with the product will depend upon the care he uses in selecting and putting in the instrument. It comes back to understanding the process, the product and the circulate metering necessities. It just isn’t unusual to “overbuy”. Plant engineers mustn’t buy extra powerful or complicated flowmeters than they want.
Using move meters

Although suppliers are at all times prepared to offer flowmeter installation companies, it is estimated that about 75% of customers install their very own gear. But installation errors can occur. One of the commonest conditions just isn’t permitting sufficient upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity circumstances in the piping, however all installations require correct piping configurations to operate successfully. Proper piping provides the correct move sample for the system. Without it, accuracy and efficiency can be adversely affected. Flow meters are generally put in backwards (especially orifice plates). Pressure sensing lines can additionally be reversed.
For electrical components, intrinsic security is a crucial consideration in hazardous areas. Most flowmeter suppliers offer intrinsically safe designs for this kind of use.
Stray magnetic fields are present in most industrial plants. Power traces, relays, solenoids, transformers, motors and mills all contribute their share of interference. Users must ensure that the flowmeter they choose just isn’t subject to such disturbances. The drawback happens primarily with the electronics within the secondary parts that should be protected. Strict adherence to the manufacturer’s really helpful set up practices can typically stop such issues.
Calibration

All circulate meters require an preliminary calibration. In most circumstances, the instrument is calibrated by the manufacturer for the desired 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 tremendously on how nicely the meter is matched to the application. Certain fluids that pass via the meter are typically abrasive, aggressive or corrosive. Over time, some components of the system will degrade enough to affect performance. Some designs are more susceptible to damage than others. For instance, put on on particular person turbine blades can cause performance modifications. If the appliance is important, the accuracy of the circulate meter ought to be checked frequently. In different instances, recalibration will not be required for a quantity of years as a end result of the application just isn’t important and wouldn’t in any other case change the meter’s efficiency. Some flowmeters require special equipment for calibration. Most producers will provide such services at their plants or consumer amenities, and they will deliver the gear with them for on-site calibration.
Maintenance

Many factors can have an effect on maintenance necessities and the anticipated life of a circulate meter. The major factor, of course, is matching the right instrument to the particular utility. Poorly selected gear will at all times cause problems early on. Flowmeters with out transferring parts often require less consideration than devices with shifting elements. But all flowmeters will ultimately require some type of upkeep.
The main factor in a differential pressure flowmeter requires lots of piping, valves and fittings when related to the secondary element, so maintenance could be a recurring process in such installations. Pulse strains can become clogged or corroded and have to be cleaned or replaced. And, improperly positioned secondary components can lead to measurement errors. Repositioning elements could be expensive.
Flow meters with shifting components require periodic internal inspection, particularly if the liquid being measured is dirty or viscous. Installing a filter before such gadgets will assist reduce fouling and put on. Accessible instruments corresponding to ultrasonic or electromagnetic meters could have problems with the electronics of their secondary components. Pressure transducers associated with secondary parts should be eliminated and inspected periodically.
Applications the place coatings may happen are additionally potential problems for accessible instruments similar to 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 avoided by common cleansing. With ultrasonic move meters, the refraction angle could change and the acoustic vitality absorbed by the coating could cause the move meter to not work.
More articles on flow meters:
Relation between flow and strain

Difference between flow meter and move transmitter

Water level sensor types and works

Solution of water pollutionn
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Measuring liquid circulate is a crucial requirement for many industrial plants. In some operations, the ability to make correct circulate measurements is so essential that it can make the distinction between a profit or a loss. In different cases, inaccurate flow measurements or failure to make them can lead to critical (or even catastrophic) outcomes.
For most liquid flow measurement instruments, flow is set inferentially by measuring the change in velocity or kinetic power of the liquid. The velocity depends on the pressure distinction that forces the liquid via the pipe or conduit. Since the cross-sectional space of the pipe is thought and remains constant, the typical flow fee is an indicator of the move price. In this case, the basic relationship for figuring out the circulate price of a liquid is

Q = V x A

Q = Flow fee of liquid through the pipe

V = Average circulate rate

A = Cross-sectional area of the pipe

Other components that have an result on the move fee of a liquid include the viscosity and density of the liquid, and the friction of the liquid in touch with the pipe.
Liquid move can be measured immediately utilizing constructive displacement flow meters. These items divide the liquid into specific increments and proceed to move. The whole move fee is the buildup of the measured increments and may be counted mechanically or electronically.
Table of Contents

Reynolds quantity

Types of liquid move meters

Differential Pressure flow meters

Orifice plate circulate meters

Venturi flow meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable space flow meter

Positive displacement move meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc kind meter

Rotary vane gauges

Spiral flow meter

Velocity meters

Turbine flow meters

Vortex flowmeters

Electromagnetic move meters

Ultrasonic flow meters

Mass flow meter

Coriolis flow meters

Thermal mass move meters

Open channel move meter

Select a right liquid flow meter

Using move meters

Calibration

Maintenance

Reynolds number

The efficiency of a circulate meter is also influenced by the dimensionless unit known as Reynolds quantity. It is defined as the ratio of the inertial pressure of a liquid to its resistance.
The formulation 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 specific gravity are the inertial forces, pipe diameter and viscosity are the resistance. For most liquid applications, the pipe diameter and particular gravity stay fixed. At very low velocities or high viscosities, R could be very low and the liquid flows in a smooth layer with the best velocity on the heart of the pipe, the place viscous forces at the pipe wall limit it to very low velocities. This kind of move known as laminar move. the R worth is beneath about 2000. a characteristic of laminar move is the parabolic shape of its velocity distribution.
However, most purposes contain turbulent circulate with R-values above 3000. turbulent circulate happens at high speeds or low viscosities. The circulate breaks down into turbulent eddies that flow via the pipe with the same common velocity. The fluid velocity is much less significant and the velocity distribution is more uniform in form. A transition zone exists between turbulent and laminar circulate. Depending on the pipe configuration and different set up situations, the move on this zone may be turbulent or laminar.
Types of liquid flow meters

Many types of flow meters are available for use in closed pipe methods. In common, gadgets may be categorised as differential stress meters, constructive displacement meters, velocity meters, and mass meters. Differential pressure devices (also generally recognized as head gauges) include orifice plates, venturi, move tubes, move nozzles, pitot tubes, elbow kind flow meters, goal sort circulate meters and variable space move meters.
Positive displacement flow meters embrace piston, elliptical-gear, chapter-actuated disk and rotary vane types. Velocity meters embrace turbine, vortex shedding, electromagnetic, and acoustic designs. Mass meters embrace Coriolis and thermal types. Measurement of liquid move in open channels usually entails weirs and flumes.
Differential Pressure flow meters

The use of differential stress as an inferred measurement of the move fee of a liquid is well-known. By far, differential stress flow meters are probably the most generally used unit right now. It is estimated that greater than 50% of all liquid move measurement applications use this kind of unit.
The primary working principle of differential strain circulate meters relies on the premise that the strain drop throughout the meter is proportional to the sq. of the flow rate. The flow price is obtained by measuring the differential stress and extracting the square root.
Like most flow meters, differential stress move meters have a main component and a secondary element. The main factor causes a change in kinetic vitality, which creates a differential pressure in the pipe. The gadget have to be properly matched to the pipe dimension, move situations and liquid characteristics. And, the accuracy of the element measurement must stay good within reasonable limits. The secondary element measures the differential pressure and provides a signal or studying that is transformed to an precise flow worth.
Orifice plate circulate meters

Orifice plates are the most well-liked liquid circulate meters in use right now. An orifice is solely a flat piece of metal with a particular dimension hole drilled in it. Most orifices are concentric, however eccentric, conical (quadrant) and segmented designs are also obtainable.
In follow, the orifice is put in in the pipe between two flanges. As the first system, the orifice restricts the move of fluid, thereby creating a differential strain across the plate. Pressure measurement ports on either side of the plate are used to detect the distinction. The major advantages of orifice plates are that they haven’t any shifting elements and that their cost doesn’t enhance significantly with the size of the pipe.
Tapered and quadrant orifices are comparatively new. These items have been developed primarily for measuring liquids with low Reynolds numbers. An basically constant flow coefficient can be maintained at an R-value under 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which must be calculated and machined for every 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 device is able to measuring move at low Reynolds numbers and still maintaining the required sq. root relationship. Its design is simple and the wedge hole has just one crucial dimension. The strain drop through the system is only about half that of a traditional orifice plate.
The one-piece wedge meeting combines the wedge factor and strain measurement becoming into a one-piece pipe fitting bolted to a traditional stress transmitter. No special piping or fittings are required to install the gadget within the pipeline.
The metering accuracy of all orifice circulate meters is dependent upon the set up situations, the orifice plate area ratio, and the physical characteristics of the liquid being measured.
Venturi flow meters

The advantage of a venturi is its ability to deal with massive flows at low stress drops. A venturi is actually a bit of pipe with a conical inlet and a straight throat. As the liquid passes through the throat, it will increase in velocity, resulting in a stress difference between the inlet and outlet areas.
Flow meters have no transferring parts. They may be put in in massive diameter pipes utilizing flanged, welded or threaded finish connections. The unit is usually fitted with 4 or extra stress measuring ports to common the measured stress. Venturi tubes can be used for most liquids, including these with high solids content material.
Flow tubes

Flow tubes are somewhat similar to venturi, except that they don’t have an entrance cone. They have a tapered throat, but the outlet is elongated and clean. The distance between the front and the tip is about one-half the diameter of the tube. The stress measurement port is situated about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle

At excessive velocities, the flow nozzle can handle roughly 60% of the liquid circulate compared to an orifice plate with the identical pressure drop. Liquids containing suspended solids can additionally be metered. However, these units are not really helpful for high viscosity liquids or liquids containing massive quantities of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two kinds of pressure simultaneously, shock pressure and static pressure. The shock system consists of a tube with one finish of the tube bent at proper angles to the course of move. The end of the static tube is closed, but has a small slot in the side of the system. These tubes may be installed individually within the pipe or mixed in a housing.
Pitot tubes are typically put in by welding a coupling to the pipe and inserting the probe by way of the coupling. The use of most Pitot tubes is restricted to single point measurements. These gadgets are vulnerable to clogging by foreign matter within the liquid. The benefits of Pitot tubes are low price, no moving parts, simple installation and minimal pressure drop.
Elbow flowmeter

Elbow move meters work on the precept that centrifugal forces are exerted alongside the outer edges as the liquid moves alongside a circular path. Thus, as the liquid flows via the pipe elbow, the pressure on the internal 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 90 levels. Elbows can be utilized as liquid move meters. All that’s required are two small holes positioned on the midpoint of the elbow (45 diploma point) for the manometer faucet. A pressure sensing line can be related to the faucet using any handy technique.
Target meter

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

Variable area meters consist primarily of a conical tube and a float. Although classified as differential strain devices, they’re really fixed pressure devices. Flange finish connections present a simple method to install them within the pipe. Working precept of rotameter is when there is no liquid move, the float is free to rest at the bottom of the pipe. When the liquid enters the underside of the pipe, the float begins to rise. The position of the float varies directly with the circulate price. Its precise place is at the point the place the stress distinction between the higher and decrease surfaces balances the burden of the float.
Because the circulate rate may be read immediately on a scale mounted subsequent to the tube, there is no want for an auxiliary circulate studying device. However, if desired, an automatic sensing device can be utilized to sense the float level and transmit the flow sign. Variable area flow meter tubes are made from glass, metallic or plastic. Tube diameters range 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 persevering with to move. Each phase is counted by a connection register. Because every increment represents a discrete volume, positive displacement items are popular in computerized dosing and accounting purposes. Volumetric circulate meters are perfect for measuring the circulate of viscous liquids or the place a easy mechanical circulate meter system is required.
Reciprocating piston flowmeter

Reciprocating piston move meters can be found in single and multi-piston variations. The particular alternative is dependent upon the vary of move charges required in a particular application. Piston move meters can be utilized to deal with a variety of liquids. The fluid by no means is out there in contact with gears or different parts that could clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with intently synchronized enamel. A mounted quantity of fluid passes through the meter with each revolution. The shaft rotation may be monitored to obtain a specific circulate rate.
Disc type meter

Chapter moving disc kind meters have a movable disc mounted on a concentric sphere that’s located 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 one shifting half 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 particular circulate fee. As with all constructive displacement meters, changes in viscosity under a given threshold will affect the measurement accuracy. A big selection of sizes and capacities can be found. These models may be made from a variety of construction materials.
Rotary vane gauges

Rotary vane meters are available in a selection of designs, however they all function on the identical precept. The fundamental unit consists of an equally divided rotating impeller (containing two or more compartments) mounted inside the instrument housing. The impeller is in fixed contact with the housing. As the impeller rotates, a onerous and fast volume of liquid is swept from each compartment to the outlet of the meter. The variety of impeller revolutions is calculated and recorded in volume items.
Spiral flow meter

The helical move meter consists of two radially inclined helical rotors which are gear pushed along with minimal clearance between the rotors and the housing. The two rotors transfer the liquid from one finish of the chamber to the other alongside the axial direction.
Velocity meters

These instruments operate linearly with respect to the volumetric move rate. Because there is no sq. root relationship (as with differential strain devices), they’ve a much bigger range. Velocity meters are least sensitive to adjustments in viscosity when the Reynolds quantity exceeds 10,000. Most velocity meter housings are equipped with flanges or fittings to allow them to be connected directly into the piping.
Turbine circulate meters

Turbine circulate meters have been widely used for precise liquid measurement functions. The device consists of a multi-bladed rotor mounted in a pipe, perpendicular to the flow of the liquid. The rotor rotates because the liquid passes by way of the vanes. Rotational speed is a direct function of flow price and could 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 flow rate. A tachometer can be added to measure the turbine velocity and decide the liquid flow fee. A correctly specified and put in turbine circulate meter has good accuracy, especially for low viscosity liquids.
A major drawback with turbine flowmeters is bearing wear. A “bearingless” design has been developed to keep away from this drawback. The liquid entering the flow meter passes through the spiral vanes of the stator, causing the liquid flow to rotate. The move acts on the spheres, inflicting them to journey within the space between the first 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 rate.
Vortex flowmeters

Vortex move meters benefit from the pure phenomenon that occurs when a liquid flows by way of a blunt object. Vortex or vortex circulate 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 primary elements of the circulate 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 flow fee.
Electromagnetic flow meters

Magnetic flow meters can deal with most liquids and slurries, offered that the material to be metered is electrically conductive. The main part is the move tube (primary element), which is installed instantly within the pipe. The pressure drop across the meter is the same as the pressure drop by way of the equal length of pipe, since there aren’t any shifting parts or flow obstructions. The voltmeter can be linked directly to the flow tube or remotely mounted and related to the flow tube via a shielded cable.
Electromagnetic circulate meters work according to Faraday’s regulation of electromagnetic induction, which states that a voltage is induced when a conductor passes through a magnetic subject. The liquid acts because the conductor; the magnetic subject is generated by an energized coil outside the circulate tube. The quantity of voltage generated is proportional to the flow rate. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary factor.
Electromagnetic flowmeters provide main advantages: they can measure difficult and corrosive liquids and slurries; they’ll measure ahead and reverse move with equal accuracy. The disadvantages of early designs were excessive energy consumption and the necessity to acquire a full tube with no flow to set the meter to zero initially. Recent improvements have eliminated these problems. The pulse-type excitation method reduces power consumption because excitation occurs only half the time within the unit. A zero setting is now not required.
Ultrasonic move meters

Ultrasonic flowmeters can be divided into doppler meters and journey time (or transverse) meters. Doppler meters measure the frequency shift brought on by the move of a liquid. Two sensors are mounted in a housing linked to a minimal of one aspect of the pipe. A signal of identified frequency is distributed to the liquid to be measured. Solids, bubbles or any discontinuities within the liquid cause the heartbeat to be reflected to the receiver element. Since the liquid causing the reflection is shifting, the frequency of the returned pulse is shifted. The frequency shift is proportional to the rate of the liquid.
There can also be a conveyable doppler meter that can be run on AC energy or a rechargeable power pack. The instrument can be used by merely clamping the sensing head to the surface of the pipe. A set of 4 to twenty mA output terminals permits the unit to be linked to a strip chart recorder or other remote system.
The journey time meter’s sensors are mounted on each side of the pipe. The configuration allows the sound waves to travel between the units at an angle of forty five degrees. angle to the direction of fluid move. The velocity of the sign propagating between the sensors will increase or decreases with the direction of transmission and the speed of the liquid being measured. By transmitting pressure gauge octa in both instructions alternately, a time-differential relationship proportional to the circulate price could be obtained. A limitation of the journey time meter is that the liquid being measured have to be comparatively freed from entrained gases or solids to reduce signal scattering and absorption.
Mass move meter

Mass flowmeters the continued want for extra accurate circulate measurement in mass associated processes (chemical reactions, warmth switch, and so on.) has led to the development of mass circulate meters. A number of designs can be found, but the most generally used for liquid flow functions is the Coriolis meter. It operates on the basis of a pure phenomenon often recognized as the Coriolis drive, hence the name.
Coriolis flow meters

Coriolis meters are true mass meters that instantly measure mass flow as a substitute of volume move. Since the mass is fixed, the meter is linear and doesn’t must be adjusted for adjustments in liquid characteristics. It also eliminates the need to compensate for altering temperature and strain conditions. The meter is especially suitable for measuring liquids whose viscosity varies with velocity at a given temperature and strain.
Coriolis meters are also out there in a big selection of designs. A in style unit consists of a U-shaped circulate tube encapsulated in a sensor housing linked to an electronic unit. The sensing unit can be mounted instantly into any process. The electronics unit could be located as much as 500 feet away from the sensor.
Thermal mass flow meters

Thermal mass flowmeters are traditionally used for fuel measurements, however are additionally out there in designs for liquid move measurements. These mass meters additionally function 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 element. The heat transferred is proportional to the mass flow fee. The sensor is never in direct contact with the fluid. The electronic meeting features a move analyzer, temperature compensator, and sign conditioner that provides a linear output proportional to the mass circulate rate.
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 many techniques that can be used to observe circulate in open channels, depth-related strategies are the most common. These methods assume that instantaneous circulate may be decided from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used main units used to measure move in open channels.
Weirs work on the precept that an obstruction in a channel causes water to circulate backwards, making a high water stage (head) behind the obstruction. The head is a function of the circulate fee, and due to this fact the move rate through the system. The weir consists of a vertical plate with a pointed high. The top of the plate may be straight or notched. Weirs are categorised by the shape 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 should use degree measurement strategies to determine the move rate. Staff gauges and floating working items are the simplest gadgets to use for this function. Various digital sensing, totalizing and recording methods are also obtainable.
A current growth contains the usage of ultrasonic pulses to measure liquid level. Measurements are made by sending an acoustic pulse from the sensor to the surface of the liquid and timing the return echo. Linearized circuitry converts the peak of the liquid to a circulate fee. A bar graph recorder data the flow fee and a digital totalizer records the total number of gallons. Another recently launched microprocessor-based system uses ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, management and calibration tasks.
Select a proper liquid move meter

Data exhibits that more than 75% of the move meters put in in trade don’t carry out well. And poor choice accounts for ninety p.c of these issues. Clearly, flowmeter selection just isn’t a job for amateurs.
The most necessary requirement is to know exactly what the instrument ought to do. There are numerous points to consider right here. Will the measurement be used for process control (repeatability is the principle concern) or for accounting or commerce handover (high accuracy is important)? Is a neighborhood indication or a remote signal required? If a distant output is required, is it a proportional signal or a contact closure to start or stop one other device? Is the fluid viscous, clear or slurry? Is it electrically conductive? What is its particular gravity or density? What move rates are concerned within the application? What is the operating temperature and pressure of the process? Accuracy (see glossary), range, linearity, repeatability, and piping requirements must even be considered.
It is equally essential to grasp what a flow meter cannot do as nicely as what it might possibly do before making a ultimate selection. 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 appliance requirements. Often, the user’s expectations of flowmeter efficiency don’t match these supplied by the provider. Most suppliers are eager to assist clients select the best flowmeter for a particular job. Many present questionnaires, checklists and specification sheets designed to obtain the important information essential to match the proper flowmeter to the job.
Technical improvements to the flowmeter must even be considered. For example, a standard mistake is to pick the design that was hottest for a given software a quantity of years in the past and assume that it’s nonetheless the most effective software for the job. In current years, many modifications and improvements might have occurred within the development of flowmeters for specific purposes, resulting in a wider vary of choices.
Flow meters are available in a extensive range of costs. Variable space flowmeters are often the least costly, with some smaller items costing lower than $90. Mass flow meters are the most costly. They begin at about $3000. However, the whole system cost must always be thought-about when selecting a flowmeter. Installation, operation and upkeep costs are additionally essential financial elements. For a variety of the extra complicated designs, maintenance prices may be excessive.
As with many other merchandise, the plant engineer normally gets 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 process, the product and the circulate metering requirements. It just isn’t uncommon to “overbuy”. Plant engineers should not buy more powerful or complicated flowmeters than they need.
Using move meters

Although suppliers are always ready to provide flowmeter installation providers, it’s estimated that about 75% of users install their own gear. But installation errors can occur. One of the most typical conditions is not allowing adequate 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 function effectively. Proper piping offers the right circulate sample for the system. Without it, accuracy and performance may be adversely affected. Flow meters are sometimes put in backwards (especially orifice plates). Pressure sensing strains can be reversed.
For electrical components, intrinsic safety is an important consideration in hazardous areas. Most flowmeter suppliers provide intrinsically safe designs for this sort of use.
Stray magnetic fields are current in most industrial crops. Power strains, relays, solenoids, transformers, motors and turbines all contribute their share of interference. Users must ensure that the flowmeter they choose isn’t topic to such disturbances. The drawback occurs primarily with the electronics in the secondary components that have to be protected. Strict adherence to the manufacturer’s recommended installation practices can usually prevent such issues.
Calibration

All flow meters require an initial calibration. In most cases, the instrument is calibrated by the manufacturer for the specified conditions of use. However, if qualified personnel can be found on the manufacturing facility, the user can carry out his own calibration.
The want for recalibration depends greatly on how well the meter is matched to the appliance. Certain fluids that pass via the meter are usually abrasive, aggressive or corrosive. Over time, some components of the gadget will degrade sufficient to have an effect on efficiency. Some designs are extra vulnerable to wreck than others. For example, put on on particular person turbine blades could cause efficiency modifications. If the applying is critical, the accuracy of the flow meter must be checked incessantly. In different cases, recalibration may not be required for many years because the application isn’t important and wouldn’t in any other case change the meter’s performance. Some flowmeters require special tools for calibration. Most producers will provide such services at their crops or consumer services, and they’ll bring the equipment with them for on-site calibration.
Maintenance

Many elements can affect maintenance requirements and the anticipated lifetime of a circulate meter. The main factor, in fact, is matching the correct instrument to the specific software. Poorly selected equipment will always cause issues early on. Flowmeters without shifting elements often require less attention than gadgets with moving components. But all flowmeters will finally require some kind of upkeep.
The major factor in a differential pressure flowmeter requires a lot of piping, valves and fittings when linked to the secondary factor, so upkeep could be a recurring process in such installations. Pulse lines can turn into clogged or corroded and have to be cleaned or replaced. And, improperly positioned secondary elements can lead to measurement errors. Repositioning parts can be costly.
Flow meters with moving elements require periodic inner inspection, especially if the liquid being measured is soiled or viscous. Installing a filter before such gadgets will help scale back fouling and put on. Accessible instruments similar to ultrasonic or electromagnetic meters might have issues with the electronics of their secondary components. Pressure transducers related to secondary elements must be eliminated and inspected periodically.
Applications the place coatings may happen are also potential problems for accessible devices such as magnetic or ultrasonic devices. If the coating is insulated, the operation of the magnetic flow meter can eventually be impaired if the electrodes are insulated from the liquid. This scenario can be prevented by common cleansing. With ultrasonic flow meters, the refraction angle might change and the acoustic power absorbed by the coating could cause the flow meter to not work.
More articles on flow meters:
Relation between flow and strain

Difference between flow meter and circulate transmitter

Water stage sensor varieties and works

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