Liquid circulate meter

Measuring liquid move is a crucial requirement for many industrial crops. In some operations, the ability to make accurate circulate measurements is so necessary that it could possibly make the distinction between a revenue or a loss. In other instances, inaccurate flow measurements or failure to make them can result in critical (or even catastrophic) results.
For most liquid circulate measurement devices, flow is set inferentially by measuring the change in velocity or kinetic vitality of the liquid. The velocity is determined by the stress distinction that forces the liquid via 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 move rate. In this case, the essential relationship for determining the circulate rate of a liquid is

Q = V x A

Q = Flow fee of liquid via the pipe

V = Average move rate

A = Cross-sectional area of the pipe

Other elements that have an result on the circulate fee of a liquid include the viscosity and density of the liquid, and the friction of the liquid involved with the pipe.
Liquid move can be measured immediately utilizing optimistic displacement circulate meters. These units divide the liquid into particular increments and proceed to move. The whole circulate rate is the buildup of the measured increments and can be counted mechanically or electronically.
Table of Contents

Reynolds quantity

Types of liquid circulate meters

Differential Pressure flow meters

Orifice plate move meters

Venturi circulate meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable area move meter

Positive displacement move meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc type meter

Rotary vane gauges

Spiral flow meter

Velocity meters

Turbine circulate meters

Vortex flowmeters

Electromagnetic flow meters

Ultrasonic move meters

Mass circulate meter

Coriolis flow meters

Thermal mass move meters

Open channel flow meter

Select a right liquid flow meter

Using flow meters

Calibration

Maintenance

Reynolds quantity

The performance of a flow meter is also influenced by the dimensionless unit known as Reynolds quantity. It is outlined because the ratio of the inertial force of a liquid to its resistance.
The method 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 fee 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 constant. At very low velocities or high viscosities, R may be very low and the liquid flows in a smooth layer with the very best velocity on the middle of the pipe, the place viscous forces at the pipe wall limit it to very low velocities. This type of circulate is called laminar circulate. the R worth is under about 2000. a characteristic of laminar flow is the parabolic shape of its velocity distribution.
However, most purposes involve turbulent move with R-values above 3000. turbulent circulate occurs at excessive speeds or low viscosities. The move breaks down into turbulent eddies that flow by way of the pipe with the identical common velocity. The fluid velocity is much less vital and the rate distribution is extra uniform in form. A transition zone exists between turbulent and laminar circulate. Depending on the pipe configuration and other installation situations, the circulate on this zone may be turbulent or laminar.
Types of liquid circulate meters

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

The use of differential strain as an inferred measurement of the flow rate of a liquid is well-known. By far, differential strain circulate meters are essentially the most generally used unit today. It is estimated that more than 50% of all liquid circulate measurement applications use this sort of unit.
The primary working precept of differential stress circulate meters relies on the premise that the strain drop throughout the meter is proportional to the sq. of the circulate fee. The flow price is obtained by measuring the differential strain and extracting the sq. root.
Like most circulate meters, differential stress circulate meters have a main element and a secondary element. The primary factor causes a change in kinetic power, which creates a differential pressure in the pipe. The gadget have to be correctly matched to the pipe dimension, circulate circumstances and liquid traits. And, the accuracy of the factor measurement should remain good inside affordable limits. The secondary factor measures the differential strain and supplies a signal or reading that is transformed to an actual move worth.
Orifice plate flow meters

Orifice plates are the most well-liked liquid move meters in use today. An orifice is simply a flat piece of metal with a specific dimension hole drilled in it. Most orifices are concentric, however eccentric, conical (quadrant) and segmented designs are also out there.
In practice, the orifice is put in within the pipe between two flanges. As the first device, the orifice restricts the circulate of fluid, thereby creating a differential strain throughout 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 moving elements and that their price does not enhance considerably with the scale of the pipe.
Tapered and quadrant orifices are relatively new. These units had been developed primarily for measuring liquids with low Reynolds numbers. An primarily fixed flow coefficient may be maintained at an R-value under 5000. Tapered orifice plates have an upstream bevel, the depth and angle of which have to be calculated and machined for each application.
The section wedge is a variant of the segment orifice. It is a throttle orifice designed primarily to measure the circulate of liquids containing solids. The device is capable of measuring flow at low Reynolds numbers and nonetheless sustaining the required square root relationship. Its design is easy and the wedge hole has only one critical dimension. The strain drop by way of the device is just about half that of a standard orifice plate.
The one-piece wedge meeting combines the wedge element and stress measurement fitting into a one-piece pipe becoming bolted to a traditional pressure transmitter. No special piping or fittings are required to put in the device in the pipeline.
The metering accuracy of all orifice move meters depends on the installation circumstances, the orifice plate space ratio, and the bodily characteristics of the liquid being measured.
Venturi flow meters

The advantage of a venturi is its capacity to deal with large flows at low strain drops. A venturi is basically a section of pipe with a conical inlet and a straight throat. As the liquid passes through the throat, it increases in velocity, leading to a strain difference between the inlet and outlet areas.
Flow meters haven’t any shifting components. They can be put in in massive diameter pipes using flanged, welded or threaded finish connections. The unit is normally fitted with four or more stress measuring ports to average the measured stress. Venturi tubes can be utilized for most liquids, together with these with excessive solids content.
Flow tubes

Flow tubes are considerably just like venturi, besides that they don’t have an entrance cone. They have a tapered throat, but the outlet is elongated and smooth. The distance between the front and the tip is about one-half the diameter of the tube. The stress measurement port is positioned about one-half the diameter of the tube downstream and one diameter upstream.
Flow nozzle

At excessive velocities, the move nozzle can deal with roughly 60% of the liquid move compared to an orifice plate with the same pressure drop. Liquids containing suspended solids can be metered. However, these units aren’t recommended for high viscosity liquids or liquids containing giant quantities of viscous solids.
pressure gauge 10 bar of strain concurrently, shock stress and static stress. The shock gadget consists of a tube with one finish of the tube bent at proper angles to the course of circulate. The end of the static tube is closed, however has a small slot in the aspect of the system. These tubes can be installed individually within the pipe or mixed in a housing.
Pitot tubes are usually installed by welding a coupling to the pipe and inserting the probe by way of the coupling. The use of most Pitot tubes is proscribed to single point measurements. These units are susceptible to clogging by international matter within the liquid. The advantages of Pitot tubes are low value, no moving elements, easy set up and minimal pressure drop.
Elbow flowmeter

Elbow circulate meters work on the precept that centrifugal forces are exerted along the outer edges because the liquid moves alongside a circular path. Thus, because the liquid flows by way of 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 force is inversely proportional to the radius of the elbow.
Arbitrary ninety levels. Elbows can be used as liquid flow meters. All that’s required are two small holes placed at the midpoint of the elbow (45 diploma point) for the manometer faucet. A pressure sensing line may be connected to the faucet using any handy method.
Target meter

The goal meter senses and measures the drive attributable to the liquid putting the target or a drag disk suspended in the liquid stream. By measuring the pressure applied to the target the liquid circulate fee may be directly indicated. In its simplest type, 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 sophisticated variations use refined low-level force sensor sensing elements. The target pressure caused by the liquid move is sensed by a strain gauge. The output sign of the meter indicates the flow rate. The target meter can be used to measure the move rate of dirty or corrosive liquids.
Variable area move meter

Variable space meters consist primarily of a conical tube and a float. Although categorized as differential pressure gadgets, they are truly constant stress units. Flange end connections present a simple way to install them in the pipe. Working principle of rotameter is when there isn’t a liquid flow, the float is free to rest on 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 at the point where the pressure difference between the higher and lower surfaces balances the load of the float.
Because the move fee could be read instantly on a scale mounted next to the tube, there is no want for an auxiliary move reading device. However, if desired, an automatic sensing device can be used to sense the float stage and transmit the flow sign. Variable space circulate meter tubes are manufactured from glass, metal or plastic. Tube diameters range from 1/4 to greater than 6 inches.
Positive displacement move meter

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

Reciprocating piston move meters are available in single and multi-piston versions. The particular choice depends on the vary of flow charges required in a selected utility. Piston circulate meters can be utilized to deal with a wide range of liquids. The fluid never is obtainable 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 through the meter with each revolution. The shaft rotation can be monitored to obtain a particular move price.
Disc kind meter

Chapter transferring disc kind meters have a movable disc mounted on a concentric sphere that’s 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 with out rotating about its personal axis. It is the one transferring part in the measurement chamber.
A pin extending vertically from the disk is related to a mechanical counter, which monitors the oscillating movement of the disk. digital pressure gauge is proportional to a particular circulate price. As with all positive displacement meters, modifications in viscosity below a given threshold will affect the measurement accuracy. A wide selection of sizes and capacities are available. These models could be made from a selection of building supplies.
Rotary vane gauges

Rotary vane meters can be found in a big selection of designs, but all of them operate on the same principle. The primary unit consists of an equally divided rotating impeller (containing two or extra compartments) mounted inside the instrument housing. The impeller is in fixed contact with the housing. As the impeller rotates, a exhausting and fast quantity of liquid is swept from each compartment to the outlet of the meter. The number of impeller revolutions is calculated and recorded in quantity units.
Spiral flow meter

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

These instruments operate linearly with respect to the volumetric flow price. Because there is not a square root relationship (as with differential pressure devices), they have a much bigger vary. Velocity meters are least sensitive to modifications in viscosity when the Reynolds number exceeds 10,000. Most velocity meter housings are geared up with flanges or fittings to allow them to be connected directly into the piping.
Turbine flow meters

Turbine move meters have been extensively used for precise liquid measurement applications. The system consists of a multi-bladed rotor mounted in a pipe, perpendicular to the circulate of the liquid. The rotor rotates because the liquid passes via the vanes. Rotational speed is a direct operate of circulate price 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 flow rate. A tachometer could be added to measure the turbine velocity and decide the liquid flow price. A properly specified and put in turbine flow meter has good accuracy, especially for low viscosity liquids.
A main drawback with turbine flowmeters is bearing put on. A “bearingless” design has been developed to avoid this drawback. The liquid entering the circulate meter passes through the spiral vanes of the stator, causing the liquid circulate to rotate. The flow acts on the spheres, inflicting them to journey within the house between the primary 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 rate.
Vortex flowmeters

Vortex move meters reap the advantages of the pure phenomenon that happens when a liquid flows via a blunt object. Vortex or vortex circulate alternates downstream of the thing. The frequency of the vortex shedding is proportional to the speed of the liquid flowing through the flowmeter.
The three main components 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 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 circulate tube (primary element), which is installed immediately within the pipe. The stress drop across the meter is similar as the stress drop via the equivalent size of pipe, since there are not any moving elements or move obstructions. The voltmeter can be related directly to the flow tube or remotely mounted and connected to the circulate tube via a shielded cable.
Electromagnetic flow meters work in accordance with Faraday’s legislation of electromagnetic induction, which states that a voltage is induced when a conductor passes through a magnetic subject. The liquid acts as the conductor; the magnetic subject is generated by an energized coil outdoors the move tube. The amount of voltage generated is proportional to the move fee. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary element.
Electromagnetic flowmeters supply major benefits: they’ll measure tough and corrosive liquids and slurries; they will measure forward and reverse flow with equal accuracy. The disadvantages of early designs were high energy consumption and the necessity to obtain a full tube with no move to set the meter to zero initially. Recent improvements have eradicated these problems. The pulse-type excitation technique reduces power consumption as a result of excitation happens solely half the time in the unit. A zero setting is now not required.
Ultrasonic flow meters

Ultrasonic flowmeters may be divided into doppler meters and journey time (or transverse) meters. Doppler meters measure the frequency shift caused by the circulate of a liquid. Two sensors are mounted in a housing linked to at least one facet of the pipe. A sign of recognized frequency is shipped to the liquid to be measured. Solids, bubbles or any discontinuities in the liquid trigger the coronary heart beat 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 is also a transportable doppler meter that could be run on AC power or a chargeable energy pack. The instrument can be utilized by merely clamping the sensing head to the outside of the pipe. A set of four to 20 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 each side of the pipe. The configuration allows the sound waves to journey between the units at an angle of 45 levels. angle to the direction of fluid flow. The pace of the sign propagating between the sensors will increase or decreases with the course of transmission and the velocity of the liquid being measured. By transmitting the signal in each directions alternately, a time-differential relationship proportional to the circulate price can be obtained. A limitation of the journey time meter is that the liquid being measured must be relatively free of entrained gases or solids to minimize signal scattering and absorption.
Mass move meter

Mass flowmeters the continued want for more correct move measurement in mass associated processes (chemical reactions, warmth transfer, etc.) has led to the event of mass move meters. A variety of designs can be found, however probably the most generally used for liquid move purposes is the Coriolis meter. It operates on the basis of a pure phenomenon often recognized as the Coriolis pressure, hence the identify.
Coriolis move meters

Coriolis meters are true mass meters that instantly measure mass circulate as an alternative of volume move. Since the mass is fixed, the meter is linear and does not must be adjusted for modifications in liquid characteristics. It additionally 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 available in quite a lot of designs. A popular unit consists of a U-shaped flow tube encapsulated in a sensor housing related to an digital unit. The sensing unit could be mounted instantly into any course of. The electronics unit may be positioned as much as 500 ft away from the sensor.
Thermal mass circulate meters

Thermal mass flowmeters are traditionally used for fuel measurements, but are additionally obtainable in designs for liquid flow measurements. These mass meters also function impartial of density, pressure 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 warmth transferred is proportional to the mass flow rate. The sensor is rarely in direct contact with the fluid. The digital meeting includes a circulate analyzer, temperature compensator, and signal conditioner that provides a linear output proportional to the mass flow fee.
Open channel circulate meter

An “open channel” is any pipe during which liquids move on a free floor. This includes tunnels, unpressurized sewers, partially stuffed pipes, canals, streams and rivers. Of the many methods that can be used to watch circulate in open channels, depth-related strategies are the commonest. These methods assume that instantaneous flow could be determined from a measurement of water depth or head. Weirs and flumes are the oldest and most generally used major gadgets used to measure flow in open channels.
Weirs work on the principle that an obstruction in a channel causes water to move backwards, making a excessive water level (head) behind the obstruction. The head is a perform of the circulate fee, and due to this fact the circulate fee by way of the gadget. The weir consists of a vertical plate with a pointed high. The high of the plate may be straight or notched. Weirs are categorised by the form of the notch. The basic types are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a perform of the liquid degree, so the system must use degree measurement strategies to determine the circulate rate. Staff gauges and floating operating items are the only gadgets to use for this purpose. Various digital sensing, totalizing and recording techniques are additionally available.
A latest growth consists of the use 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 height of the liquid to a move fee. A bar graph recorder data the circulate fee and a digital totalizer information the entire number of gallons. Another just lately launched microprocessor-based system uses ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, control and calibration tasks.
Select a proper liquid circulate meter

Data exhibits that more than 75% of the circulate meters installed in business don’t perform well. And poor choice accounts for ninety p.c of those issues. Clearly, flowmeter choice just isn’t a job for amateurs.
The most essential requirement is to know precisely what the instrument should do. There are a number of issues to contemplate right here. Will the measurement be used for course of management (repeatability is the principle concern) or for accounting or trade handover (high accuracy is important)? Is a local indication or a distant sign required? If a distant output is required, is it a proportional signal or a contact closure to begin or cease one other device? Is the fluid viscous, clean or slurry? Is it electrically conductive? What is its particular gravity or density? What move rates are involved in the application? What is the working temperature and pressure of the process? Accuracy (see glossary), range, linearity, repeatability, and piping necessities should even be thought-about.
It is equally important to grasp what a flow meter can not do in addition to what it may possibly do earlier than making a last alternative. Every instrument has strengths and weaknesses, and the diploma of efficiency satisfaction is instantly associated to how well the instrument’s features and weaknesses match the applying necessities. Often, the user’s expectations of flowmeter efficiency don’t match those provided by the supplier. Most suppliers are eager to assist clients choose the right flowmeter for a particular job. Many present questionnaires, checklists and specification sheets designed to obtain the critical info necessary to match the right flowmeter to the job.
Technical improvements to the flowmeter must also be thought-about. For instance, a typical mistake is to decide out the design that was most popular for a given application a number of years ago and assume that it is still one of the best software for the job. In latest years, many modifications and improvements might have occurred in the growth of flowmeters for particular purposes, leading to a wider range of choices.
Flow meters are available in a wide range of costs. Variable area flowmeters are usually the least costly, with some smaller units costing less than $90. Mass move meters are the most costly. They start at about $3000. However, the entire system price should always be considered when deciding on a flowmeter. Installation, operation and maintenance prices are additionally necessary financial factors. For a few of the extra complicated designs, maintenance costs can be high.
As with many other products, the plant engineer normally gets 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 deciding on and putting in the instrument. It comes back to understanding the method, the product and the move metering requirements. It isn’t uncommon to “overbuy”. Plant engineers should not purchase extra highly effective or complex flowmeters than they need.
Using circulate meters

Although suppliers are all the time ready to offer flowmeter set up providers, it is estimated that about 75% of customers set up their very own gear. But installation errors can happen. One of the most common situations is not allowing adequate upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity situations within the piping, however all installations require correct piping configurations to function effectively. Proper piping provides the right flow pattern for the system. Without it, accuracy and performance may be adversely affected. Flow meters are typically installed backwards (especially orifice plates). Pressure sensing strains can also be reversed.
For electrical parts, intrinsic safety is an important consideration in hazardous areas. Most flowmeter suppliers provide 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 must be positive that the flowmeter they select just isn’t subject 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 really helpful set up practices can often prevent such issues.
Calibration

All move meters require an preliminary calibration. In most circumstances, the instrument is calibrated by the producer for the desired conditions of use. However, if qualified personnel are available at the factory, the consumer can perform his own calibration.
The need for recalibration relies upon significantly on how properly the meter is matched to the appliance. Certain fluids that move via the meter tend to be abrasive, aggressive or corrosive. Over time, some elements of the gadget will degrade enough to affect efficiency. Some designs are more vulnerable to wreck than others. For example, wear on particular person turbine blades could cause efficiency changes. If the applying is important, the accuracy of the move meter ought to be checked incessantly. In different circumstances, recalibration may not be required for a number of years as a end result of the appliance is not crucial and wouldn’t in any other case change the meter’s efficiency. Some flowmeters require special gear for calibration. Most producers will provide such companies at their plants or user services, and they will convey the tools with them for on-site calibration.
Maintenance

Many components can affect upkeep necessities and the expected life of a move meter. The main factor, of course, is matching the correct instrument to the specific utility. Poorly chosen tools will at all times trigger problems early on. Flowmeters with out transferring elements usually require much less consideration than gadgets with transferring components. But all flowmeters will finally require some kind of upkeep.
The primary factor in a differential stress flowmeter requires a lot of piping, valves and fittings when linked to the secondary element, so maintenance could be a recurring task in such installations. Pulse lines can turn into clogged or corroded and have to be cleaned or replaced. And, improperly positioned secondary components can result in measurement errors. Repositioning elements can be costly.
Flow meters with shifting parts require periodic inner inspection, especially if the liquid being measured is soiled or viscous. Installing a filter earlier than such devices will assist cut back fouling and put on. Accessible instruments corresponding to ultrasonic or electromagnetic meters might have issues with the electronics of their secondary components. Pressure transducers related to secondary parts ought to be removed and inspected periodically.
Applications the place coatings could happen are also potential issues for accessible devices similar to magnetic or ultrasonic devices. If the coating is insulated, the operation of the magnetic flow meter can ultimately be impaired if the electrodes are insulated from the liquid. This state of affairs could be averted by regular cleansing. With ultrasonic flow meters, the refraction angle could change and the acoustic vitality absorbed by the coating can cause the move meter to not work.
More articles on move meters:
Relation between circulate and stress

Difference between flow meter and move transmitter

Water level sensor varieties and works

Solution of water pollutionn
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Measuring liquid circulate is a critical requirement for a lot of industrial vegetation. In some operations, the power to make accurate flow measurements is so essential that it could make the difference between a profit or a loss. In different instances, inaccurate move measurements or failure to make them can result in serious (or even catastrophic) results.
For most liquid circulate measurement devices, move is decided inferentially by measuring the change in velocity or kinetic power of the liquid. The velocity depends on the strain distinction that forces the liquid via the pipe or conduit. Since the cross-sectional space of the pipe is understood and stays fixed, the common circulate rate is an indicator of the circulate fee. In this case, the essential relationship for determining the flow rate of a liquid is

Q = V x A

Q = Flow rate of liquid by way of the pipe

V = Average flow rate

A = Cross-sectional space of the pipe

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

Reynolds quantity

Types of liquid circulate meters

Differential Pressure flow meters

Orifice plate flow meters

Venturi circulate meters

Flow tubes

Flow nozzle

Pitot tube flowmeter

Elbow flowmeter

Target meter

Variable area move meter

Positive displacement move meter

Reciprocating piston flowmeter

Oval Gear Flow Meters

Disc type meter

Rotary vane gauges

Spiral move meter

Velocity meters

Turbine flow meters

Vortex flowmeters

Electromagnetic circulate meters

Ultrasonic circulate meters

Mass circulate meter

Coriolis circulate meters

Thermal mass flow meters

Open channel circulate meter

Select a right liquid flow meter

Using circulate meters

Calibration

Maintenance

Reynolds number

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

R = 3160 x Q x Gt

D x ต

R = Reynolds number

Q = Flow 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 purposes, the pipe diameter and particular gravity stay constant. At very low velocities or excessive viscosities, R may be very low and the liquid flows in a easy layer with the best velocity at the middle of the pipe, where viscous forces at the pipe wall limit it to very low velocities. เกจวัดแรงดัน of circulate known as laminar move. the R worth is beneath about 2000. a characteristic of laminar circulate is the parabolic form of its velocity distribution.
However, most purposes contain turbulent flow with R-values above 3000. turbulent flow happens at high speeds or low viscosities. The flow breaks down into turbulent eddies that move by way of the pipe with the identical average velocity. The fluid velocity is much less vital and the velocity distribution is extra uniform in form. A transition zone exists between turbulent and laminar flow. Depending on the pipe configuration and other installation circumstances, the flow on this zone may be turbulent or laminar.
Types of liquid move meters

Many kinds of flow meters are available to be used in closed pipe systems. In basic, gadgets could be categorized as differential pressure meters, constructive displacement meters, velocity meters, and mass meters. Differential pressure devices (also often recognized as head gauges) embody orifice plates, venturi, circulate tubes, circulate nozzles, pitot tubes, elbow type circulate meters, goal kind flow meters and variable space circulate meters.
Positive displacement flow meters embody 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 flow in open channels often involves weirs and flumes.
Differential Pressure move meters

The use of differential strain as an inferred measurement of the circulate fee of a liquid is well known. By far, differential pressure flow meters are the most commonly used unit right now. It is estimated that more than 50% of all liquid move measurement functions use this kind of unit.
The primary working principle of differential stress flow meters is predicated on the premise that the strain drop across the meter is proportional to the square of the move price. The flow rate is obtained by measuring the differential pressure and extracting the square root.
Like most move meters, differential stress move meters have a main element and a secondary element. The main element causes a change in kinetic energy, which creates a differential stress within the pipe. The gadget must be correctly matched to the pipe size, move situations and liquid traits. And, the accuracy of the element measurement should remain good within cheap limits. The secondary component measures the differential pressure and supplies a signal or studying that is transformed to an precise circulate value.
Orifice plate circulate meters

Orifice plates are the most well-liked liquid flow meters in use right now. An orifice is simply a flat piece of steel with a specific dimension gap drilled in it. Most orifices are concentric, but eccentric, conical (quadrant) and segmented designs are additionally available.
In follow, the orifice is installed within the pipe between two flanges. As the first device, the orifice restricts the move of fluid, thereby making a differential strain throughout the plate. Pressure measurement ports on both sides of the plate are used to detect the distinction. The primary advantages of orifice plates are that they haven’t any shifting components and that their cost doesn’t increase significantly with the scale of the pipe.
Tapered and quadrant orifices are relatively new. These items had been developed primarily for measuring liquids with low Reynolds numbers. An primarily constant flow coefficient may be maintained at an R-value below 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 phase orifice. It is a throttle orifice designed primarily to measure the flow of liquids containing solids. The gadget is able to measuring flow at low Reynolds numbers and still maintaining the required sq. root relationship. Its design is simple and the wedge gap has just one crucial dimension. The pressure drop through the system is only about half that of a traditional orifice plate.
The one-piece wedge assembly combines the wedge element and stress measurement becoming right into a one-piece pipe fitting bolted to a standard strain transmitter. No particular piping or fittings are required to put in the gadget in the pipeline.
The metering accuracy of all orifice circulate meters depends on the set up circumstances, the orifice plate area ratio, and the physical characteristics of the liquid being measured.
Venturi move meters

The advantage of a venturi is its capacity to deal with massive flows at low stress drops. A venturi is basically a piece of pipe with a conical inlet and a straight throat. As the liquid passes via the throat, it will increase in velocity, resulting in a stress distinction between the inlet and outlet areas.
Flow meters have no shifting components. They can be put in in large diameter pipes using flanged, welded or threaded finish connections. The unit is normally fitted with four or extra pressure measuring ports to common the measured strain. Venturi tubes can be utilized for many liquids, including these with excessive solids content.
Flow tubes

Flow tubes are considerably just like venturi, besides that they don’t have an entrance cone. They have a tapered throat, but the outlet is elongated and easy. The distance between the front 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 high velocities, the circulate nozzle can handle roughly 60% of the liquid move compared to an orifice plate with the same pressure drop. Liquids containing suspended solids can additionally be metered. However, these gadgets are not beneficial for prime viscosity liquids or liquids containing massive amounts of viscous solids.
Pitot tube flowmeter

The Pitot tube senses two types of stress simultaneously, shock stress and static strain. The shock system consists of a tube with one finish of the tube bent at proper angles to the course of flow. The finish of the static tube is closed, however has a small slot in the aspect of the system. These tubes may be put in individually within the pipe or combined in a housing.
Pitot tubes are sometimes put in by welding a coupling to the pipe and inserting the probe via the coupling. The use of most Pitot tubes is limited to single point measurements. These gadgets are vulnerable to clogging by international matter in the liquid. The benefits of Pitot tubes are low value, no moving components, easy set up and minimal strain drop.
Elbow flowmeter

Elbow flow meters work on the precept that centrifugal forces are exerted alongside the outer edges because the liquid moves alongside a round path. Thus, as the liquid flows by way of the pipe elbow, the force on the internal surface of the elbow is proportional to the density of the liquid multiplied by the square of its velocity. In addition, the drive is inversely proportional to the radius of the elbow.
Arbitrary 90 degrees. Elbows can be used as liquid circulate meters. All that’s required are two small holes positioned at the midpoint of the elbow (45 diploma point) for the manometer faucet. A pressure sensing line could be related to the tap utilizing any convenient methodology.
Target meter

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

Variable space meters consist primarily of a conical tube and a float. Although classified as differential stress devices, they’re actually constant stress units. Flange end connections present a easy approach to set up them within the pipe. Working principle of rotameter is when there is no liquid move, the float is free to relaxation on the bottom of the pipe. When the liquid enters the bottom of the pipe, the float begins to rise. The place of the float varies instantly with the flow rate. Its precise place is on the point the place the stress distinction between the higher and lower surfaces balances the burden of the float.
Because the circulate rate could be read immediately on a scale mounted subsequent to the tube, there is not a need for an auxiliary move studying system. However, if desired, an automatic sensing gadget can be utilized to sense the float stage and transmit the flow signal. Variable area move meter tubes are made of glass, metal or plastic. Tube diameters vary from 1/4 to greater than 6 inches.
Positive displacement circulate meter

The operation of these models consists of separating the liquid into precisely measured increments and continuing to maneuver. Each section is counted by a connection register. Because every increment represents a discrete quantity, constructive displacement units are well-liked in automated dosing and accounting applications. Volumetric circulate meters are best for measuring the move of viscous liquids or the place a easy mechanical move meter system is required.
Reciprocating piston flowmeter

Reciprocating piston flow meters can be found in single and multi-piston variations. The particular choice is dependent upon the range of circulate rates required in a particular software. Piston move meters can be used to deal with a variety of liquids. The fluid by no means is obtainable in contact with gears or different components that would clog or corrode.
Oval Gear Flow Meters

Oval gear flowmeters have two rotating oval gears with carefully synchronized tooth. A fastened quantity of fluid passes through the meter with every revolution. The shaft rotation could be monitored to obtain a particular flow fee.
Disc sort meter

Chapter transferring disc type meters have a movable disc mounted on a concentric sphere that is positioned in a spherical sidewall chamber. The strain of the fluid passing through the measurement chamber causes the disc to oscillate in its circulation path without rotating about its personal axis. It is the only transferring part in the measurement chamber.
A pin extending vertically from the disk is linked to a mechanical counter, which monitors the oscillating movement of the disk. Each cycle is proportional to a selected circulate fee. As with all positive displacement meters, adjustments in viscosity below a given threshold will affect the measurement accuracy. A wide selection of sizes and capacities can be found. These units can be made from quite so much of development materials.
Rotary vane gauges

Rotary vane meters can be found in quite lots of designs, but they all operate on the same principle. The fundamental 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 number of impeller revolutions is calculated and recorded in volume units.
Spiral circulate meter

The helical circulate meter consists of two radially inclined helical rotors which may be 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 course.
Velocity meters

These instruments function linearly with respect to the volumetric flow price. Because there is not a square 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 permit them to be connected instantly into the piping.
Turbine flow meters

Turbine move meters have been widely used for precise liquid measurement purposes. The system consists of a multi-bladed rotor mounted in a pipe, perpendicular to the circulate of the liquid. The rotor rotates as the liquid passes through the vanes. Rotational velocity is a direct perform of move fee and can be sensed by magnetic sensors, photocells or gears. Electrical pulses can be counted and totalized.
The variety of electrical pulses counted in a given time period is proportional to the circulate fee. A tachometer may be added to measure the turbine pace and decide the liquid flow price. A correctly specified and installed turbine flow meter has good accuracy, especially for low viscosity liquids.
A major downside with turbine flowmeters is bearing put on. A “bearingless” design has been developed to keep away from this drawback. The liquid coming into the circulate meter passes via the spiral vanes of the stator, inflicting the liquid circulate to rotate. The circulate acts on the spheres, inflicting them to travel in 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 flow fee.
Vortex flowmeters

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

Magnetic circulate meters can handle most liquids and slurries, offered that the fabric to be metered is electrically conductive. The main component is the circulate tube (primary element), which is installed directly within the pipe. The stress drop across the meter is the same because the pressure drop by way of the equivalent length of pipe, since there are not any shifting elements or move obstructions. The voltmeter can be connected on to the circulate tube or remotely mounted and related to the move tube by way of a shielded cable.
Electromagnetic flow meters work based on Faraday’s regulation of electromagnetic induction, which states that a voltage is induced when a conductor passes through a magnetic subject. The liquid acts as the conductor; the magnetic area is generated by an energized coil outside the circulate tube. The quantity of voltage generated is proportional to the move price. Two electrodes mounted on the wall of the tube detect the voltage measured by the secondary element.
Electromagnetic flowmeters provide main benefits: they’ll measure difficult and corrosive liquids and slurries; they can measure ahead and reverse circulate with equal accuracy. The disadvantages of early designs have been excessive energy consumption and the necessity to obtain a full tube with no move to set the meter to zero initially. Recent improvements have eliminated these issues. The pulse-type excitation approach reduces power consumption as a end result of excitation happens only half the time in the unit. A zero setting is no longer required.
Ultrasonic circulate meters

Ultrasonic flowmeters may be divided into doppler meters and journey time (or transverse) meters. Doppler meters measure the frequency shift attributable to the flow of a liquid. Two sensors are mounted in a housing related to 1 side of the pipe. A signal of known frequency is shipped to the liquid to be measured. Solids, bubbles or any discontinuities in the liquid cause the pulse to be reflected to the receiver element. Since the liquid inflicting the reflection is moving, the frequency of the returned pulse is shifted. The frequency shift is proportional to the speed of the liquid.
There can additionally be a conveyable doppler meter that might be run on AC energy or a chargeable power pack. The instrument can be used by merely clamping the sensing head to the outside of the pipe. A set of 4 to twenty mA output terminals allows the unit to be related to a strip chart recorder or different distant device.
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 forty five levels. angle to the path of fluid circulate. The speed of the signal propagating between the sensors will increase or decreases with the direction 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 move price may be obtained. A limitation of the journey time meter is that the liquid being measured should be comparatively free of entrained gases or solids to minimize sign scattering and absorption.
Mass flow meter

Mass flowmeters the continued need for more correct circulate measurement in mass related processes (chemical reactions, warmth switch, and so on.) has led to the development of mass circulate meters. A variety of designs are available, however the most generally used for liquid flow functions is the Coriolis meter. It operates on the idea of a natural phenomenon known as the Coriolis force, therefore the identify.
Coriolis move meters

Coriolis meters are true mass meters that directly measure mass move as an alternative of volume move. Since the mass is constant, the meter is linear and doesn’t need to be adjusted for changes in liquid characteristics. It additionally eliminates the necessity to compensate for changing temperature and pressure situations. The meter is especially suitable for measuring liquids whose viscosity varies with velocity at a given temperature and stress.
Coriolis meters are also out there in a selection of designs. A well-liked unit consists of a U-shaped circulate tube encapsulated in a sensor housing connected to an digital unit. The sensing unit could be mounted immediately into any course of. The electronics unit can be located as a lot as 500 feet away from the sensor.
Thermal mass circulate meters

Thermal mass flowmeters are traditionally used for fuel measurements, however are also out there in designs for liquid circulate measurements. These mass meters also operate independent of density, strain and viscosity. Thermal mass meters use a heated sensing component that’s isolated from the fluid circulate path. The flowing stream conducts warmth from the sensing factor. The heat transferred is proportional to the mass flow price. The sensor is never in direct contact with the fluid. The digital meeting features a circulate 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 during which liquids circulate on a free surface. This consists of tunnels, unpressurized sewers, partially stuffed pipes, canals, streams and rivers. Of the various methods that can be utilized to watch flow in open channels, depth-related strategies are the most typical. These methods assume that instantaneous flow may be determined from a measurement of water depth or head. Weirs and flumes are the oldest and most widely used major gadgets used to measure move in open channels.
Weirs work on the principle that an obstruction in a channel causes water to circulate backwards, making a excessive water level (head) behind the obstruction. The head is a function of the move price, and subsequently the circulate price through the device. The weir consists of a vertical plate with a pointed top. The prime of the plate can be straight or notched. Weirs are categorised by the form of the notch. The basic sorts are V-notched, rectangular and trapezoidal.
The discharge via the weir and flume is a function of the liquid stage, so the system must use degree measurement strategies to find out the circulate rate. Staff gauges and floating working items are the only gadgets to use for this purpose. Various digital sensing, totalizing and recording methods are additionally available.
A current improvement consists of 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 flow rate. A bar graph recorder data the circulate rate and a digital totalizer data the total number of gallons. Another lately launched microprocessor-based system uses ultrasonic or float sensors. A keypad with an interactive LCD show simplifies programming, control and calibration duties.
Select a right liquid move meter

Data reveals that greater than 75% of the circulate meters put in in industry do not carry out nicely. And poor selection accounts for ninety % of those issues. Clearly, flowmeter selection is not a job for amateurs.
The most essential requirement is to know precisely what the instrument should do. There are a number of points to contemplate right here. Will the measurement be used for process management (repeatability is the primary concern) or for accounting or commerce handover (high accuracy is important)? Is a neighborhood indication or a remote signal required? If a remote output is required, is it a proportional signal or a contact closure to start out or cease another device? Is the fluid viscous, clean or slurry? Is it electrically conductive? What is its particular gravity or density? What move charges are concerned in the application? What is the operating temperature and stress of the process? Accuracy (see glossary), vary, linearity, repeatability, and piping requirements must even be considered.
It is equally important to know what a circulate meter can’t do in addition to what it can do before making a last selection. Every instrument has strengths and weaknesses, and the degree of performance satisfaction is immediately related to how well the instrument’s features and weaknesses match the appliance requirements. Often, the user’s expectations of flowmeter efficiency do not match those provided by the supplier. Most suppliers are eager to assist customers select the right flowmeter for a specific job. Many present questionnaires, checklists and specification sheets designed to obtain the critical information essential to match the right flowmeter to the job.
Technical enhancements to the flowmeter should also be considered. For example, a typical mistake is to pick out the design that was most popular for a given software several years ago and assume that it is still the best software for the job. In current years, many changes and improvements might have occurred within the development of flowmeters for particular functions, leading to a wider vary of decisions.
Flow meters are available in a variety of costs. Variable area flowmeters are usually the least costly, with some smaller items costing lower than $90. Mass move meters are the costliest. They begin at about $3000. However, the entire system cost must at all times be considered when choosing a flowmeter. Installation, operation and maintenance costs are also important economic elements. For some of the more complex designs, maintenance costs can be excessive.
As with many other products, 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 uses in choosing and putting in the instrument. It comes again to understanding the method, the product and the move metering necessities. It just isn’t unusual to “overbuy”. Plant engineers should not purchase extra highly effective or complicated flowmeters than they want.
Using move meters

Although suppliers are always ready to provide flowmeter installation companies, it is estimated that about 75% of users install their very own tools. But installation errors can happen. One of the most common situations isn’t permitting sufficient upstream and downstream straight pipe for the flowmeter.
Each design has some tolerance for erratic velocity situations within the piping, but all installations require correct piping configurations to operate successfully. Proper piping provides the correct move sample for the device. Without it, accuracy and efficiency could be adversely affected. Flow meters are typically put in backwards (especially orifice plates). Pressure sensing lines can additionally be reversed.
For electrical elements, intrinsic security is an important consideration in hazardous areas. Most flowmeter suppliers offer intrinsically protected designs for this type of use.
Stray magnetic fields are current in most industrial plants. Power lines, relays, solenoids, transformers, motors and turbines all contribute their share of interference. Users must be sure that the flowmeter they select just isn’t subject to such disturbances. The drawback happens primarily with the electronics within the secondary parts that must be protected. Strict adherence to the manufacturer’s beneficial set up practices can often stop such issues.
Calibration

All flow meters require an initial calibration. In most circumstances, the instrument is calibrated by the producer for the required circumstances of use. However, if certified personnel can be found at the manufacturing unit, the consumer can perform his own calibration.
The need for recalibration relies upon significantly on how well the meter is matched to the application. Certain fluids that move via the meter tend to be abrasive, aggressive or corrosive. Over time, some elements of the gadget will degrade sufficient to have an effect on efficiency. Some designs are more susceptible to damage than others. For example, wear on particular person turbine blades could cause performance modifications. If the appliance is important, the accuracy of the circulate meter ought to be checked frequently. In different instances, recalibration is probably not required for a couple of years because the applying just isn’t critical and would not otherwise change the meter’s performance. Some flowmeters require special gear for calibration. Most producers will present such providers at their plants or consumer amenities, and they’ll bring the tools with them for on-site calibration.
Maintenance

Many components can affect maintenance necessities and the anticipated lifetime of a move meter. The major factor, after all, is matching the proper instrument to the precise utility. Poorly selected tools will always cause problems early on. Flowmeters with out transferring components usually require less consideration than gadgets with shifting elements. But all flowmeters will ultimately require some sort of maintenance.
The main factor in a differential pressure flowmeter requires lots of piping, valves and fittings when linked to the secondary element, so upkeep could be a recurring activity in such installations. Pulse strains can turn into clogged or corroded and have to be cleaned or changed. And, improperly positioned secondary components can result in measurement errors. Repositioning parts could 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 units will assist cut back fouling and wear. Accessible devices similar to ultrasonic or electromagnetic meters could have problems with the electronics of their secondary parts. Pressure transducers related to secondary parts ought to be removed and inspected periodically.
Applications where coatings could happen are additionally 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 could be avoided by regular cleaning. With ultrasonic flow meters, the refraction angle might change and the acoustic vitality absorbed by the coating could cause the move meter to not work.
More articles on circulate meters:
Relation between flow and pressure

Difference between move meter and move transmitter

Water degree sensor sorts and works

Solution of water air pollutionn

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