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Liquid circulate meter

Measuring liquid flow is a crucial requirement for many industrial vegetation. In some operations, the ability to make accurate flow measurements is so necessary that it might possibly make the distinction between a profit 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 flow measurement devices, move is decided inferentially by measuring the change in velocity or kinetic energy of the liquid. The velocity depends on the pressure distinction that forces the liquid through the pipe or conduit. Since the cross-sectional space of the pipe is understood and stays constant, the typical circulate fee is an indicator of the flow price. In this case, the essential relationship for figuring out the move fee of a liquid is

Q = V x A

Q = Flow rate of liquid via the pipe

V = Average circulate price

A = Cross-sectional area of the pipe

Other components that affect the move rate of a liquid embody the viscosity and density of the liquid, and the friction of the liquid in touch with the pipe.
Liquid circulate can be measured directly utilizing positive displacement move meters. These units divide the liquid into particular increments and continue to move. The complete circulate price is the buildup of the measured increments and can be counted mechanically or electronically.
Table of Contents

Reynolds number

Types of liquid circulate meters

Differential Pressure move meters

Orifice plate move meters

Venturi circulate meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable space move meter

Positive displacement flow meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc type meter

Rotary vane gauges

Spiral move meter

Velocity meters

Turbine move meters

Vortex flowmeters

Electromagnetic circulate meters

Ultrasonic circulate meters

Mass move meter

Coriolis flow meters

Thermal mass circulate meters

Open channel move meter

Select a right liquid circulate meter

Using flow meters

Calibration

Maintenance

Reynolds number

The efficiency of a move meter can also be influenced by the dimensionless unit referred to as Reynolds number. It is outlined as the ratio of the inertial force of a liquid to its resistance.
The formula is

R = 3160 x Q x Gt

D x ต

R = Reynolds quantity

Q = Flow rate 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 applications, the pipe diameter and particular gravity remain fixed. At very low velocities or high viscosities, R could be very low and the liquid flows in a easy layer with the best velocity at the heart of the pipe, where viscous forces on the pipe wall restrict it to very low velocities. This type of circulate is called laminar move. the R worth is below about 2000. a characteristic of laminar circulate is the parabolic form of its velocity distribution.
However, most functions involve turbulent flow with R-values above 3000. turbulent circulate happens at excessive speeds or low viscosities. The flow breaks down into turbulent eddies that move by way of the pipe with the identical 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 other set up conditions, the flow on this zone could additionally be turbulent or laminar.
Types of liquid flow meters

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

The use of differential strain as an inferred measurement of the move price of a liquid is well known. By far, differential stress move meters are probably the most commonly used unit at present. It is estimated that greater than 50% of all liquid circulate measurement purposes use this sort of unit.
The basic working principle of differential stress move meters is predicated on the premise that the strain drop throughout the meter is proportional to the square of the flow price. The circulate rate is obtained by measuring the differential pressure and extracting the sq. root.
Like most flow meters, differential pressure flow meters have a main element and a secondary element. The main element causes a change in kinetic power, which creates a differential pressure within the pipe. The system must be properly matched to the pipe measurement, move circumstances and liquid characteristics. And, the accuracy of the element measurement must remain good inside reasonable limits. The secondary component measures the differential stress and provides a signal or reading that’s transformed to an actual move value.
Orifice plate circulate meters

Orifice plates are the most well-liked liquid circulate meters in use at present. An orifice is just a flat piece of metal with a selected measurement gap drilled in it. Most orifices are concentric, but eccentric, conical (quadrant) and segmented designs are also obtainable.
In apply, the orifice is installed within the pipe between two flanges. As the primary gadget, the orifice restricts the circulate of fluid, thereby making a differential stress throughout the plate. Pressure measurement ports on both sides of the plate are used to detect the distinction. The major advantages of orifice plates are that they haven’t any transferring elements and that their cost doesn’t increase significantly with the size of the pipe.
Tapered and quadrant orifices are relatively new. These items had been developed primarily for measuring liquids with low Reynolds numbers. An basically constant flow coefficient can 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 segment wedge is a variant of the segment 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 sq. root relationship. Its design is straightforward and the wedge hole has just one important dimension. The pressure drop via the system is just about half that of a conventional orifice plate.
The one-piece wedge meeting combines the wedge factor and pressure measurement fitting right into a one-piece pipe becoming bolted to a standard stress transmitter. No particular piping or fittings are required to install the device within the pipeline.
The metering accuracy of all orifice circulate meters is decided by the set up situations, the orifice plate area ratio, and the bodily characteristics of the liquid being measured.
Venturi flow meters

The benefit of a venturi is its capability to handle large flows at low pressure drops. A venturi is basically a section of pipe with a conical inlet and a straight throat. As the liquid passes via the throat, it increases in velocity, resulting in a stress distinction between the inlet and outlet areas.
Flow meters haven’t any moving elements. They could be installed in massive diameter pipes using flanged, welded or threaded end connections. The unit is normally fitted with 4 or extra pressure measuring ports to average the measured pressure. Venturi tubes can be used for most liquids, including those with excessive solids content.
Flow tubes

Flow tubes are somewhat 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 pressure measurement port is located about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle

At high velocities, the circulate nozzle can handle roughly 60% of the liquid move in comparability with an orifice plate with the identical stress drop. Liquids containing suspended solids can be metered. However, these units aren’t really helpful for high viscosity liquids or liquids containing giant amounts of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two types of stress simultaneously, shock strain and static strain. The shock gadget consists of a tube with one finish of the tube bent at right angles to the direction of flow. The finish of the static tube is closed, but has a small slot within the aspect of the system. These tubes can 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 via the coupling. The use of most Pitot tubes is restricted to single point measurements. These units 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 stress drop.
Elbow flowmeter

Elbow flow meters work on the principle that centrifugal forces are exerted along the outer edges as the liquid moves alongside a circular path. Thus, because the liquid flows through the pipe elbow, the drive on the inner floor of the elbow is proportional to the density of the liquid multiplied by the square of its velocity. In addition, the force is inversely proportional to the radius of the elbow.
Arbitrary 90 levels. Elbows can be utilized as liquid circulate meters. All that’s required are two small holes placed on the midpoint of the elbow (45 degree point) for the manometer tap. A pressure sensing line can be linked to the faucet using any handy technique.
Target meter

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

Variable space meters consist primarily of a conical tube and a float. Although classified as differential strain devices, they are actually fixed pressure units. Flange finish connections present a simple way to install them within the pipe. Working principle of rotameter is when there is not a liquid move, the float is free to rest at the backside of the pipe. When the liquid enters the underside of the pipe, the float begins to rise. The place of the float varies immediately with the move fee. Its actual place is on the level the place the stress distinction between the higher and decrease surfaces balances the load of the float.
Because the circulate price could be learn instantly on a scale mounted subsequent to the tube, there isn’t any need for an auxiliary flow reading gadget. However, if desired, an automatic sensing system can be utilized to sense the float stage and transmit the move sign. Variable area circulate meter tubes are made from glass, metallic or plastic. Tube diameters vary from 1/4 to higher than 6 inches.
Positive displacement move meter

The operation of those items 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, positive displacement items are in style in automated dosing and accounting purposes. Volumetric flow meters are best for measuring the circulate of viscous liquids or where a easy mechanical flow meter system is required.
Reciprocating piston flowmeter

Reciprocating piston circulate meters can be found in single and multi-piston variations. The specific alternative depends on the range of circulate charges required in a selected software. Piston move meters can be used to handle a broad range of liquids. The fluid by no means comes in contact with gears or other elements that might clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with closely synchronized tooth. A fastened quantity of fluid passes by way of the meter with each revolution. The shaft rotation could be monitored to obtain a particular move fee.
Disc type meter

Chapter moving disc sort meters have a movable disc mounted on a concentric sphere that is positioned 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 half within the measurement chamber.
A pin extending vertically from the disk is related to a mechanical counter, which displays the oscillating motion of the disk. Each cycle is proportional to a selected circulate price. As with all constructive displacement meters, adjustments in viscosity beneath a given threshold will affect the measurement accuracy. A wide selection of sizes and capacities can be found. These units could be created from a wide range of building supplies.
Rotary vane gauges

Rotary vane meters can be found in quite a lot of designs, but all of them operate on the same precept. The primary unit consists of an equally divided rotating impeller (containing two or more compartments) mounted contained in the instrument housing. The impeller is in constant contact with the housing. As the impeller rotates, a fixed quantity 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 circulate meter

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

These instruments function linearly with respect to the volumetric flow price. Because there is not any sq. root relationship (as with differential strain devices), they’ve a a lot bigger range. Velocity meters are least sensitive to changes in viscosity when the Reynolds quantity 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 circulate meters

Turbine circulate meters have been broadly used for exact liquid measurement purposes. The device consists of a multi-bladed rotor mounted in a pipe, perpendicular to the circulate of the liquid. The rotor rotates as the liquid passes via the vanes. Rotational speed is a direct operate of circulate rate and could be sensed by magnetic sensors, photocells or gears. Electrical pulses may be counted and totalized.
The number of electrical pulses counted in a given time interval is proportional to the move price. A tachometer can be added to measure the turbine pace and determine the liquid flow fee. A correctly specified and put in turbine flow meter has good accuracy, especially for low viscosity liquids.
A major problem with turbine flowmeters is bearing wear. A “bearingless” design has been developed to avoid this downside. The liquid getting into the flow meter passes via the spiral vanes of the stator, causing the liquid circulate to rotate. The flow acts on the spheres, causing them to journey in 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 price.
Vortex flowmeters

Vortex circulate meters benefit from the natural phenomenon that happens when a liquid flows by way of a blunt object. Vortex or vortex move alternates downstream of the object. The frequency of the vortex shedding is proportional to the velocity of the liquid flowing via the flowmeter.
The three major parts 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 move fee.
Electromagnetic circulate meters

Magnetic circulate meters can handle most liquids and slurries, offered that the material to be metered is electrically conductive. The major part is the move tube (primary element), which is installed directly in the pipe. The pressure drop across the meter is similar because the stress drop via the equivalent length of pipe, since there are no shifting elements or move obstructions. The voltmeter can be related directly to the circulate tube or remotely mounted and connected to the move tube through a shielded cable.
Electromagnetic move meters work according to Faraday’s legislation of electromagnetic induction, which states that a voltage is induced when a conductor passes by way of a magnetic subject. The liquid acts as the conductor; the magnetic subject is generated by an energized coil outdoors 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 element.
Electromagnetic flowmeters offer main benefits: they’ll measure troublesome and corrosive liquids and slurries; they will measure ahead and reverse move with equal accuracy. The disadvantages of early designs had been excessive power consumption and the want to get hold of a full tube with no move to set the meter to zero initially. Recent improvements have eradicated these problems. The pulse-type excitation approach reduces energy consumption because excitation happens only half the time in the unit. A zero setting is now not required.
Ultrasonic flow 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 connected to 1 facet of the pipe. A signal of recognized frequency is sent to the liquid to be measured. Solids, bubbles or any discontinuities in the liquid cause the heart beat to be mirrored 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 portable doppler meter that can be run on AC power or a rechargeable power pack. The instrument can be utilized by simply clamping the sensing head to the outside of the pipe. A set of four to twenty mA output terminals permits the unit to be connected to a strip chart recorder or other 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 units at an angle of forty five degrees. angle to the path of fluid flow. The pace of the signal propagating between the sensors will increase or decreases with the course of transmission and the pace of the liquid being measured. By transmitting the sign in both instructions alternately, a time-differential relationship proportional to the flow rate may be obtained. A limitation of the travel time meter is that the liquid being measured must be relatively freed from entrained gases or solids to reduce sign scattering and absorption.
Mass circulate meter

Mass flowmeters the continued want for more correct move measurement in mass associated processes (chemical reactions, heat switch, and so on.) has led to the event of mass flow meters. A variety of designs are available, but the most commonly used for liquid circulate purposes is the Coriolis meter. It operates on the premise of a pure phenomenon known as the Coriolis drive, hence the identify.
Coriolis flow meters

Coriolis meters are true mass meters that immediately measure mass flow as an alternative of volume flow. Since the mass is constant, the meter is linear and does not have to be adjusted for adjustments in liquid traits. It also eliminates the necessity to compensate for changing temperature and strain circumstances. The meter is particularly suitable for measuring liquids whose viscosity varies with velocity at a given temperature and strain.
Coriolis meters are also available in quite so much of designs. A well-liked unit consists of a U-shaped move tube encapsulated in a sensor housing related to an electronic unit. The sensing unit can be mounted immediately into any process. The electronics unit can be located as much as 500 ft away from the sensor.
Thermal mass move meters

Thermal mass flowmeters are historically used for gasoline measurements, however are additionally out there in designs for liquid move measurements. These mass meters also function impartial of density, pressure and viscosity. Thermal mass meters use a heated sensing element that is isolated from the fluid flow path. The flowing stream conducts warmth from the sensing component. The heat transferred is proportional to the mass circulate price. The sensor is rarely in direct contact with the fluid. The digital meeting includes a flow analyzer, temperature compensator, and sign conditioner that provides a linear output proportional to the mass move rate.
Open channel circulate meter

An “open channel” is any pipe in which liquids circulate on a free floor. This consists of tunnels, unpressurized sewers, partially filled pipes, canals, streams and rivers. Of the numerous strategies that can be used to watch circulate in open channels, depth-related methods are the most typical. These strategies assume that instantaneous flow can be determined from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used primary gadgets used to measure flow in open channels.
Weirs work on the principle that an obstruction in a channel causes water to flow backwards, creating a excessive water level (head) behind the obstruction. The head is a function of the flow fee, and subsequently the move fee by way of the device. The weir consists of a vertical plate with a pointed top. The high of the plate can be straight or notched. Weirs are categorized by the shape of the notch. The fundamental varieties are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a function of the liquid stage, so the device should use degree measurement methods to discover out the circulate fee. Staff gauges and floating working items are the simplest gadgets to make use of for this function. Various digital sensing, totalizing and recording techniques are also available.
A latest development includes the use of ultrasonic pulses to measure liquid degree. 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 price. A bar graph recorder information the move fee and a digital totalizer information the entire variety 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 shows that greater than 75% of the move meters installed in industry do not carry out properly. And poor choice accounts for 90 percent of those problems. Clearly, flowmeter selection isn’t a job for amateurs.
The most essential requirement is to know exactly what the instrument should do. There are a number of issues to assume about 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 distant sign required? If a remote output is required, is it a proportional sign or a contact closure to start or stop another device? Is the fluid viscous, clear or slurry? Is it electrically conductive? What is its particular gravity or density? What circulate rates are concerned within the application? What is the operating temperature and stress of the process? Accuracy (see glossary), range, linearity, repeatability, and piping requirements should also be thought of.
It is equally important to grasp what a circulate meter can not do as properly as what it could do before making a last selection. Every instrument has strengths and weaknesses, and the degree of efficiency satisfaction is directly associated to how well the instrument’s features and weaknesses match the application necessities. Often, the user’s expectations of flowmeter performance don’t match those supplied by the supplier. Most suppliers are eager to help prospects select the best flowmeter for a specific job. Many provide questionnaires, checklists and specification sheets designed to obtain the critical information essential to match the proper flowmeter to the job.
Technical improvements to the flowmeter must also be thought of. For example, a typical mistake is to select the design that was hottest for a given utility several years in the past and assume that it is nonetheless the most effective device for the job. In latest years, many changes and improvements may have occurred within the improvement of flowmeters for specific applications, resulting in a wider vary of decisions.
Flow meters are available in a variety of costs. Variable space flowmeters are usually the least expensive, with some smaller units costing less than $90. Mass flow meters are the most expensive. They begin at about $3000. However, the entire system cost should all the time be considered when selecting a flowmeter. Installation, operation and upkeep costs are additionally essential economic components. For a few of the extra complicated designs, maintenance prices could be high.
As with many other products, the plant engineer usually gets what he pays for when he buys a flow meter. But his satisfaction with the product will depend upon the care he uses in selecting and putting in the instrument. It comes again to understanding the process, the product and the flow metering necessities. It is not unusual to “overbuy”. Plant engineers should not purchase more powerful or complex flowmeters than they want.
Using move meters

Although suppliers are always ready to offer flowmeter installation companies, it’s estimated that about 75% of customers set up their own tools. But set up errors can occur. One of the most typical conditions just isn’t permitting enough upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity situations in the piping, however all installations require correct piping configurations to operate effectively. Proper piping provides the correct flow pattern for the device. Without it, accuracy and performance could be adversely affected. Flow meters are generally put in backwards (especially orifice plates). Pressure sensing strains may also be reversed.
For electrical components, intrinsic security is an important consideration in hazardous areas. Most flowmeter suppliers supply intrinsically protected designs for this sort of use.
Stray magnetic fields are current in most industrial vegetation. Power traces, relays, solenoids, transformers, motors and generators all contribute their share of interference. Users should ensure that the flowmeter they choose just isn’t subject to such disturbances. The problem happens primarily with the electronics in the secondary elements that should be protected. Strict adherence to the manufacturer’s beneficial set up practices can often prevent such problems.
Calibration

All circulate meters require an initial calibration. In most cases, the instrument is calibrated by the producer for the specified conditions of use. However, if certified personnel are available on the factory, the user can carry out his personal calibration.
The need for recalibration relies upon tremendously on how properly the meter is matched to the appliance. Certain fluids that pass through the meter are usually abrasive, aggressive or corrosive. Over time, some components of the device will degrade enough to have an result on performance. Some designs are more prone to wreck than others. For instance, put on on individual turbine blades can cause performance changes. If the appliance is crucial, the accuracy of the flow meter must be checked frequently. In different cases, recalibration may not be required for many years because the appliance just isn’t critical and would not in any other case change the meter’s efficiency. Some flowmeters require special equipment for calibration. Most manufacturers will present such providers at their plants or person services, and they will deliver the tools with them for on-site calibration.
Maintenance

Many components can affect maintenance requirements and the anticipated life of a flow meter. The primary factor, of course, is matching the right instrument to the precise utility. Poorly selected equipment will always cause issues early on. Flowmeters without shifting components usually require less attention than devices with moving components. But all flowmeters will ultimately require some sort of maintenance.
The major component in a differential pressure flowmeter requires a lot of piping, valves and fittings when connected to the secondary factor, so maintenance is normally a recurring task in such installations. Pulse lines can turn out to be clogged or corroded and have to be cleaned or changed. And, improperly positioned secondary parts can result in measurement errors. Repositioning components may be costly.
Flow meters with shifting elements require periodic inside inspection, especially if the liquid being measured is soiled or viscous. Installing a filter before such gadgets will assist scale back fouling and put on. Accessible devices similar to ultrasonic or electromagnetic meters might have issues with the electronics of their secondary components. Pressure transducers associated with secondary components ought to be eliminated and inspected periodically.
Applications where coatings could occur are additionally potential issues for accessible devices similar to magnetic or ultrasonic units. 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 state of affairs can be avoided by common cleansing. With ultrasonic move meters, the refraction angle might change and the acoustic energy absorbed by the coating could cause the circulate meter to not work.
More articles on circulate meters:
Relation between flow and pressure

Difference between move meter and move transmitter

Water level sensor types and works

Solution of water pollutionn
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Measuring liquid flow is a critical requirement for many industrial crops. In some operations, the ability to make correct flow measurements is so necessary that it can make the distinction between a profit or a loss. In other circumstances, inaccurate move measurements or failure to make them can result in critical (or even catastrophic) outcomes.
For most liquid move measurement devices, circulate is set inferentially by measuring the change in velocity or kinetic power of the liquid. The velocity depends on the pressure difference that forces the liquid through the pipe or conduit. Since the cross-sectional space of the pipe is known and stays fixed, the common flow rate is an indicator of the circulate rate. In this case, the essential relationship for determining the circulate price of a liquid is

Q = V x A

Q = Flow rate of liquid via the pipe

V = Average flow price

A = Cross-sectional area of the pipe

Other components that affect the circulate fee of a liquid include the viscosity and density of the liquid, and the friction of the liquid in contact with the pipe.
Liquid move may be measured instantly utilizing positive displacement circulate meters. These models divide the liquid into specific increments and continue to move. The whole move price is the accumulation 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 circulate meter

Positive displacement circulate meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc sort meter

Rotary vane gauges

Spiral move meter

Velocity meters

Turbine flow meters

Vortex flowmeters

Electromagnetic move meters

Ultrasonic circulate meters

Mass move meter

Coriolis flow meters

Thermal mass move meters

Open channel move meter

Select a right liquid move meter

Using flow meters

Calibration

Maintenance

Reynolds quantity

The efficiency of a move meter can also 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 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 particular gravity remain 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, the place viscous forces at the pipe wall restrict it to very low velocities. This kind of circulate is recognized as laminar move. the R value is below about 2000. a attribute of laminar move is the parabolic form of its velocity distribution.
However, most functions contain turbulent flow with R-values above 3000. turbulent flow happens at excessive speeds or low viscosities. The circulate breaks down into turbulent eddies that move through the pipe with the same average velocity. The fluid velocity is much less significant 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 circulate on this zone could also be turbulent or laminar.
Types of liquid flow meters

Many types of circulate meters are available to be used in closed pipe systems. In basic, devices can be categorized as differential stress meters, constructive displacement meters, velocity meters, and mass meters. Differential pressure devices (also generally identified as head gauges) include orifice plates, venturi, move tubes, flow nozzles, pitot tubes, elbow type move meters, target type move meters and variable space move meters.
Positive displacement circulate meters embody piston, elliptical-gear, chapter-actuated disk and rotary vane types. Velocity meters include turbine, vortex shedding, electromagnetic, and acoustic designs. Mass meters include Coriolis and thermal types. Measurement of liquid circulate in open channels usually involves weirs and flumes.
Differential Pressure circulate meters

The use of differential pressure as an inferred measurement of the flow rate of a liquid is well-known. By far, differential pressure move meters are essentially the most commonly used unit today. It is estimated that more than 50% of all liquid flow measurement applications use this type of unit.
The basic operating principle of differential pressure move meters is based on the premise that the pressure drop throughout the meter is proportional to the sq. of the circulate price. The move rate is obtained by measuring the differential stress and extracting the square root.
Like most flow meters, differential stress circulate meters have a major element and a secondary element. The primary component causes a change in kinetic power, which creates a differential strain in the pipe. The device must be properly matched to the pipe dimension, circulate conditions and liquid characteristics. And, the accuracy of the component measurement should stay good inside reasonable limits. The secondary element measures the differential pressure and offers a sign or studying that is transformed to an precise flow worth.
Orifice plate move meters

Orifice plates are the most popular liquid flow meters in use today. An orifice is simply a flat piece of metallic with a specific size hole drilled in it. Most orifices are concentric, but eccentric, conical (quadrant) and segmented designs are additionally obtainable.
In apply, the orifice is put in within the pipe between two flanges. As the primary system, the orifice restricts the move of fluid, thereby creating a differential pressure throughout the plate. Pressure measurement ports on each side of the plate are used to detect the difference. The primary benefits of orifice plates are that they don’t have any shifting elements and that their cost doesn’t improve considerably with the dimensions of the pipe.
Tapered and quadrant orifices are comparatively new. These units were developed primarily for measuring liquids with low Reynolds numbers. An basically fixed circulate coefficient may 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 each software.
The segment wedge is a variant of the section orifice. It is a throttle orifice designed primarily to measure the flow of liquids containing solids. The system is capable of measuring flow at low Reynolds numbers and nonetheless maintaining the required sq. root relationship. Its design is easy and the wedge gap has just one important dimension. The stress drop by way of the device is just about half that of a traditional orifice plate.
The one-piece wedge meeting combines the wedge element and stress measurement fitting right into a one-piece pipe fitting bolted to a standard pressure transmitter. No special piping or fittings are required to install the device in the pipeline.
The metering accuracy of all orifice flow meters depends on the installation conditions, the orifice plate space ratio, and the physical characteristics of the liquid being measured.
Venturi move meters

The benefit of a venturi is its ability to deal with massive flows at low pressure drops. A venturi is essentially a section 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 pressure difference between the inlet and outlet areas.
Flow meters haven’t any moving elements. They may be put in in massive diameter pipes using flanged, welded or threaded end connections. The unit is usually fitted with four or extra stress measuring ports to common the measured strain. Venturi tubes can be utilized for most liquids, together with those with high solids content.
Flow tubes

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

At excessive velocities, the flow nozzle can deal with approximately 60% of the liquid move compared to an orifice plate with the same pressure drop. Liquids containing suspended solids can be metered. However, these devices aren’t beneficial for high viscosity liquids or liquids containing large quantities of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two forms of strain concurrently, shock stress and static strain. The shock system consists of a tube with one finish of the tube bent at proper angles to the path of circulate. The finish of the static tube is closed, however has a small slot in the aspect of the gadget. These tubes could be installed individually in the pipe or combined in a housing.
Pitot tubes are sometimes 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 level measurements. These units are susceptible to clogging by international matter within the liquid. The advantages of Pitot tubes are low value, no shifting parts, simple installation and minimal strain drop.
Elbow flowmeter

Elbow move meters work on the principle that centrifugal forces are exerted alongside the outer edges as the liquid strikes along a round 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 ninety levels. Elbows can be utilized as liquid circulate meters. All that is required are two small holes positioned at the midpoint of the elbow (45 diploma point) for the manometer faucet. A strain sensing line can be connected to the tap using any handy technique.
Target meter

The goal meter senses and measures the force brought on by the liquid putting the goal or a drag disk suspended within the liquid stream. By measuring the drive applied to the target the liquid flow fee could be instantly indicated. In its simplest kind, the meter consists solely of an articulated oscillating plate that moves outward with the liquid circulate. In this case, the gadget is used as a flow indicator.
More refined versions use refined low-level drive sensor sensing elements. The target force caused by the liquid circulate is sensed by a strain gauge. The output sign of the meter signifies the circulate price. The target meter can be used to measure the circulate price of dirty or corrosive liquids.
Variable area move meter

Variable area meters consist primarily of a conical tube and a float. Although classified as differential pressure units, they’re actually fixed stress gadgets. Flange finish connections provide a simple approach to set up them in the pipe. Working principle of rotameter is when there is no liquid flow, the float is free to relaxation 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 flow fee. Its precise place is on the point the place the stress difference between the upper and decrease surfaces balances the load of the float.
Because the move fee could be learn instantly on a scale mounted subsequent to the tube, there isn’t a need for an auxiliary move studying system. However, if desired, an automatic sensing system can be used to sense the float degree and transmit the flow sign. Variable space flow meter tubes are manufactured from glass, steel or plastic. Tube diameters range from 1/4 to greater than 6 inches.
Positive displacement move meter

The operation of those units consists of separating the liquid into precisely measured increments and continuing to move. Each phase is counted by a connection register. Because each increment represents a discrete volume, positive displacement models are in style in automatic dosing and accounting purposes. Volumetric move 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 flow meters are available in single and multi-piston variations. The specific alternative is dependent upon the vary of move rates required in a specific application. Piston flow meters can be used to deal with a broad range of liquids. The fluid never comes in contact with gears or different parts that would clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with intently synchronized tooth. A fixed quantity of fluid passes via the meter with each revolution. The shaft rotation can be monitored to acquire a particular move rate.
Disc sort meter

Chapter shifting disc kind meters have a movable disc mounted on a concentric sphere that is situated in a spherical sidewall chamber. The pressure of the fluid passing by way of the measurement chamber causes the disc to oscillate in its circulation path without rotating about its own axis. It is the one transferring half in the measurement chamber.
A pin extending vertically from the disk is connected to a mechanical counter, which monitors the oscillating movement of the disk. Each cycle is proportional to a particular flow fee. As with all optimistic displacement meters, modifications in viscosity below a given threshold will have an effect on the measurement accuracy. A wide range of sizes and capacities can be found. These items could be created from quite lots of building materials.
Rotary vane gauges

Rotary vane meters can be found in quite so much of designs, however they all function on the identical principle. The primary 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 set quantity of liquid is swept from each compartment to the outlet of the meter. The variety of impeller revolutions is calculated and recorded in volume models.
Spiral flow meter

The helical circulate 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 end of the chamber to the opposite along the axial path.
Velocity meters

These instruments function linearly with respect to the volumetric flow fee. Because there isn’t any sq. root relationship (as with differential strain devices), they’ve a much bigger vary. Velocity meters are least delicate to modifications in viscosity when the Reynolds number exceeds 10,000. Most velocity meter housings are equipped with flanges or fittings to allow them to be linked instantly into the piping.
Turbine move meters

Turbine move meters have been widely used for exact 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 via the vanes. Rotational pace is a direct function of move fee and can be sensed by magnetic sensors, photocells or gears. Electrical pulses may be counted and totalized.
The variety of electrical pulses counted in a given time period is proportional to the circulate price. A tachometer can be added to measure the turbine pace and decide the liquid move rate. A correctly specified and put in turbine flow meter has good accuracy, particularly for low viscosity liquids.
A main downside with turbine flowmeters is bearing wear. A “bearingless” design has been developed to keep away from this problem. The liquid entering the flow meter passes through the spiral vanes of the stator, inflicting the liquid move to rotate. The move acts on the spheres, inflicting them to travel within the space 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 move fee.
Vortex flowmeters

Vortex flow meters take advantage of the natural phenomenon that occurs when a liquid flows through a blunt object. Vortex or vortex circulate 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 components 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 signal amplification and conditioning transmitter whose output is proportional to the circulate rate.
Electromagnetic circulate meters

Magnetic move meters can deal with most liquids and slurries, offered that the material to be metered is electrically conductive. The major element is the circulate tube (primary element), which is put in immediately in the pipe. The strain drop across the meter is the same because the stress drop by way of the equal size of pipe, since there aren’t any transferring elements or flow obstructions. The voltmeter may be linked directly to the move tube or remotely mounted and linked to the move tube through a shielded cable.
Electromagnetic move meters work according to Faraday’s regulation of electromagnetic induction, which states that a voltage is induced when a conductor passes via a magnetic area. The liquid acts because the conductor; the magnetic area is generated by an energized coil outdoors the circulate tube. The amount 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 component.
Electromagnetic flowmeters supply major advantages: they can measure troublesome and corrosive liquids and slurries; they can measure ahead and reverse move with equal accuracy. The disadvantages of early designs had been high energy consumption and the necessity to get hold of a full tube with no flow to set the meter to zero initially. Recent enhancements have eliminated these issues. The pulse-type excitation technique reduces power consumption as a outcome of excitation occurs 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 journey time (or transverse) meters. Doppler meters measure the frequency shift attributable to the circulate of a liquid. Two sensors are mounted in a housing linked to 1 facet of the pipe. A sign of recognized frequency is distributed to the liquid to be measured. Solids, bubbles or any discontinuities in the liquid trigger the heartbeat to be mirrored 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 can also be a conveyable doppler meter that might be run on AC energy or a chargeable energy pack. The instrument can be utilized by simply clamping the sensing head to the skin of the pipe. A set of four to 20 mA output terminals allows the unit to be related to a strip chart recorder or other distant system.
The journey time meter’s sensors are mounted on each side of the pipe. The configuration permits the sound waves to journey between the units at an angle of 45 levels. angle to the direction of fluid flow. The velocity of the sign propagating between the sensors will increase or decreases with the course 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 rate may be obtained. A limitation of the travel time meter is that the liquid being measured have to be comparatively freed from entrained gases or solids to reduce sign scattering and absorption.
Mass flow meter

Mass flowmeters the continued want for more correct move measurement in mass associated processes (chemical reactions, heat transfer, and so on.) has led to the development of mass move meters. A variety of designs can be found, however essentially the most generally used for liquid flow functions is the Coriolis meter. It operates on the idea of a natural phenomenon generally recognized as the Coriolis force, hence the title.
Coriolis flow meters

Coriolis meters are true mass meters that directly measure mass flow as a substitute of quantity flow. Since the mass is fixed, the meter is linear and doesn’t need to be adjusted for adjustments in liquid traits. It also eliminates the necessity to compensate for altering temperature and pressure situations. The meter is particularly appropriate for measuring liquids whose viscosity varies with velocity at a given temperature and strain.
Coriolis meters are also obtainable in quite a lot of designs. A popular unit consists of a U-shaped circulate tube encapsulated in a sensor housing linked to an electronic unit. The sensing unit may be mounted immediately into any course of. The electronics unit may be positioned up to 500 feet away from the sensor.
Thermal mass flow meters

Thermal mass flowmeters are historically used for fuel measurements, however are additionally out there in designs for liquid move measurements. These mass meters additionally function impartial of density, pressure and viscosity. Thermal mass meters use a heated sensing component that is isolated from the fluid flow path. The flowing stream conducts heat from the sensing component. The warmth transferred is proportional to the mass flow fee. The sensor is never in direct contact with the fluid. The digital meeting features a flow 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 by which liquids flow on a free surface. This consists of tunnels, unpressurized sewers, partially crammed pipes, canals, streams and rivers. Of the numerous methods that can be used to monitor flow in open channels, depth-related methods are the most common. These techniques 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 devices used to measure move in open channels.
Weirs work on the principle that an obstruction in a channel causes water to flow backwards, creating a high water degree (head) behind the obstruction. The head is a function of the move rate, and therefore the move rate by way of the gadget. The weir consists of a vertical plate with a pointed high. The top of the plate could be straight or notched. Weirs are categorized by the form of the notch. The primary varieties are V-notched, rectangular and trapezoidal.
The discharge through the weir and flume is a perform of the liquid level, so the device must use degree measurement techniques to discover out the flow rate. Staff gauges and floating working items are the best devices to make use of for this purpose. Various digital sensing, totalizing and recording systems are also available.
A latest improvement includes the usage of ultrasonic pulses to measure liquid degree. 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 move rate. A bar graph recorder records the circulate fee and a digital totalizer records the entire variety of gallons. Another just lately launched microprocessor-based system uses ultrasonic or float sensors. pressure gauge 10 bar keypad with an interactive LCD show simplifies programming, management and calibration duties.
Select a right liquid circulate meter

Data exhibits that more than 75% of the move meters installed in trade don’t perform well. And poor choice accounts for ninety percent of these issues. Clearly, flowmeter choice isn’t a job for amateurs.
The most necessary requirement is to know exactly what the instrument should do. There are numerous issues to suppose about here. Will the measurement be used for course of control (repeatability is the principle concern) or for accounting or commerce handover (high accuracy is important)? Is a neighborhood indication or a remote sign required? If a distant output is required, is it a proportional sign or a contact closure to start or cease another device? Is the fluid viscous, clear or slurry? Is it electrically conductive? What is its particular gravity or density? What flow charges are concerned within the application? What is the working temperature and strain of the process? Accuracy (see glossary), range, linearity, repeatability, and piping requirements should even be considered.
It is equally necessary to understand what a circulate meter can’t do in addition to what it can do before making a last alternative. Every instrument has strengths and weaknesses, and the degree of efficiency satisfaction is immediately related to how nicely the instrument’s features and weaknesses match the application necessities. Often, the user’s expectations of flowmeter performance do not match those offered by the provider. Most suppliers are eager to help clients select the right flowmeter for a selected job. Many present questionnaires, checklists and specification sheets designed to acquire the important information necessary to match the proper flowmeter to the job.
Technical improvements to the flowmeter must even be thought of. For instance, a common mistake is to pick the design that was most popular for a given utility a quantity of years in the past and assume that it’s still the best device for the job. In latest years, many modifications and improvements could have occurred in the improvement of flowmeters for particular applications, leading to a wider range of choices.
Flow meters are available in a extensive range of prices. Variable area flowmeters are often the least costly, with some smaller units costing less than $90. Mass move meters are the most expensive. They start at about $3000. However, the total system cost should all the time be thought-about when selecting a flowmeter. Installation, operation and upkeep costs are also essential financial elements. For a number of the extra advanced designs, maintenance prices may be excessive.
As with many different products, the plant engineer often will get what he pays for when he buys a move meter. But his satisfaction with the product will depend on the care he makes use of in selecting and installing the instrument. It comes back to understanding the method, the product and the circulate metering necessities. It isn’t unusual to “overbuy”. Plant engineers mustn’t buy extra highly effective or advanced flowmeters than they need.
Using flow meters

Although suppliers are always ready to supply flowmeter set up services, it’s estimated that about 75% of users install their very own tools. But installation errors can occur. One of the most common conditions is not permitting 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 successfully. Proper piping offers the right circulate sample for the system. Without it, accuracy and performance can be adversely affected. Flow meters are sometimes put in backwards (especially orifice plates). Pressure sensing lines can also be reversed.
For electrical parts, intrinsic security is an important consideration in hazardous areas. Most flowmeter suppliers supply intrinsically protected designs for this type of use.
Stray magnetic fields are current in most industrial plants. Power lines, relays, solenoids, transformers, motors and generators all contribute their share of interference. Users should be certain that the flowmeter they choose just isn’t subject to such disturbances. The drawback occurs primarily with the electronics within the secondary components that have to be protected. Strict adherence to the manufacturer’s really helpful set up practices can often forestall such problems.
Calibration

All circulate meters require an initial calibration. In most cases, the instrument is calibrated by the manufacturer for the desired situations of use. However, if qualified personnel can be found on the factory, the consumer can perform his own calibration.
The need for recalibration depends greatly on how properly the meter is matched to the applying. Certain fluids that pass by way of the meter are usually abrasive, aggressive or corrosive. Over time, some components of the device will degrade sufficient to affect performance. Some designs are extra vulnerable to wreck than others. For instance, put on on particular person turbine blades can cause efficiency modifications. If the application is critical, the accuracy of the circulate meter should be checked regularly. In different circumstances, recalibration may not be required for a number of years as a result of the applying just isn’t critical and would not otherwise change the meter’s performance. Some flowmeters require special tools for calibration. Most producers will provide such services at their vegetation or user facilities, and they are going to deliver the tools with them for on-site calibration.
Maintenance

Many components can affect upkeep requirements and the expected life of a move meter. The primary issue, in fact, is matching the right instrument to the specific utility. Poorly chosen equipment will all the time cause problems early on. Flowmeters with out moving elements normally require less attention than units with shifting components. But all flowmeters will finally require some sort of maintenance.
The primary component in a differential strain flowmeter requires a lot of piping, valves and fittings when related to the secondary component, so maintenance can be a recurring task in such installations. Pulse strains can turn out to be clogged or corroded and must be cleaned or replaced. And, improperly positioned secondary components can lead to measurement errors. Repositioning components may be expensive.
Flow meters with moving elements require periodic inner inspection, especially if the liquid being measured is dirty or viscous. Installing a filter before such units will help scale back fouling and put on. Accessible instruments similar to ultrasonic or electromagnetic meters may have issues with the electronics of their secondary components. Pressure transducers associated with secondary elements should be eliminated and inspected periodically.
Applications where coatings could happen are also potential problems for accessible devices 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 state of affairs can be prevented by common cleansing. With ultrasonic circulate meters, the refraction angle may change and the acoustic power absorbed by the coating could cause the circulate meter to not work.
More articles on flow meters:
Relation between circulate and stress

Difference between move meter and move transmitter

Water degree sensor sorts and works

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