An instrument, which measures the volumetric flow rate of the fluid running through a closed conduit, is called a rotameter. The device consists of a float and a tube. Being a kind of a variable-area meter, it analyzes the flow rate by the upward and downward motion of the float in the tapered tube and the measurement provided by the flow meter is directly proportional to the area of flow and the flow rate.

 

Principle Involved in the Operation of the Rotameter

 

Now the question is how to read a rotameter? Rotameter is the most accepted industrial flow meter, which works based on the principle of gravity and variable area. The flow rate increases and decreases the height of the float, which accordingly adjusts the passage of the fluid flow and consequently, the total area between the float and the wall of the tube. Equilibrium is reached when the upward force created by the flowing fluid balances the descending force exerted by the mass of the float, hence maintaining a stable position of the float. The unit of the measurement is in liters or gallons per minute.

 

How to read a Rotameter:

 

Along with the float and tube, a rotameter may come equipped with an adjustment knob, which enables the user to set the flow rate according to their requirement. Let’s summarize the procedure for reading a rotameter:

 

• Connecting the rotameter with the fluid flowing source, to initiate the process.
• The float starts to swim in the middle of the tapered pipe due to the velocity of the fluid.
• The side of the meter has a scale. The lower and upper level of the float is to be measured by that scale, which gives the flow rate.

 

So, this is all about how to read a rotameter, which works in the combined effects of the velocity of the fluid, the gravity of the float, and annular area of the meter.

Instruments that are used for measuring the flow rate of a particular liquid, flowing through a pipe, are called flow meters. The measurements can be done based on either the mass flow rate or the volumetric flow rate and the units in which it is measured are kilogram per second and liters per second respectively. The standard liquid flowmeter is used in various fields and has significant utility. In the medical field, industrial sector, like food processing, semiconductor fabrication, water management, etc. There are various types of flow meters, depending on the principle that administers the application. Ultrasonic, Mechanical, Pressure, and Electromagnetic are the types of liquid flowmeters.

 

Open & Closed Channel Flow

 

The flow of any liquid can be classified into open or closed pipe flow. The open channel in the free-flowing stream is not restricted by any wall and the flow is controlled by the force of gravity. The fluid flow in the closed channel occurs due to the pressure difference in the pipeline.

 

Here are a few types of standard liquid flowmeters discussed:

• Ultrasonic Flowmeters

With the negligible use of the mechanical parts, the maintenance of these flowmeters is very low and has the advantage of measuring any kind of liquid with no hassle. The clamp-on version of these flowmeters is to be snapped outside the pipe, providing a non-intrusive installation. The output is of these meters is generally very accurate.

• Mechanical Flowmeters

These are the conventional devices, with either turbines or wheels inserted in the conduits to calculate the velocity and the volumetric flow with the help of the location of the pipe. They can be categorized into piston meter, single jet meter, and gear meter. Piston meter uses rotating pistons whereas gear meter uses two or more gears, which rotate perpendicular to each other and the single jet meter applies the impellers to measure the flow.

• Pressure Flowmeters

Either differential pressure or dynamic pressure determines the rate of the flow. While using the differential pressure, the pipe is constricted to decrease the pressure, as with the further introduction of liquid, the pressure hikes. The flow rate is concluded by the pressure difference between the inlet and outlet valve.

The dynamic pressure can be determined by finding the difference between the points where the pressure is stagnant and the point where the fluid viscosity is zero. Pilot tubes, dall tubes, cone meters are some examples of this flowmeter.

• Electromagnetic Flowmeters

As the name suggests, the flow rate is determined by the magnetic field created by the magnets in the pipe, which with the help of the conductive components of the fluid alters the voltage. This change in voltage is used to determine the flow rate. These are suitable for water, or water-based liquids like wastewaters. They can’t be used in oil, hydrocarbon, and distilled water.

 

Selection of the appropriate standard liquid flowmeter is essential to avoid any loss due to misapplication, as there are various kinds of flowmeters available. All the devices are not compatible with all types of liquids; the viscosity, quantity of impurity, material, and size of pipe, are some of factors to be considered.

A broad field of fluid media can be minutely audited and detected with the help of the liquid level indicator switches. The level of the fluid is monitored and restricted for different reasons. The liquid level indicators are also used in measuring the liquid flow. There are different operations of the indicator switches which administer various technologies. They are available in a wide range of non-invasive, contact and non-contact liquid level switches.

 

Various Types of Liquid Level Switches

 

The level switch can be distinguished into two categories, solid and liquid. The liquid level switch can be divided into a float level switch, ultrasonic level switch, RF capacitance level switch, and conductivity level switch. A single application can also engage multiple mechanics for the desired result, depending on the consumer choice. Point level detection of fluids and continuous level measurements of liquids are the ways of monitoring the level of the liquid. Point level is the quickest method to detect the level of the liquid, whereas for determining the intermediate levels, the continuous level measurement is recommended.  Point level switch is mandatory for finding the leakage in the pipeline or tank and preventing the overflowing of liquid.

 

Float Level Switch

 

To detect the level of water in the tank, the float switch is used. It can be used in the pumps, along with the alarm, indicator or other devices. Its complexity varies depending on the demand of the application. The most commonly used float switch is the simple rod that rises as the level of the liquid increases resulting in the operation of the microswitch. They can be conveniently handled and quickly installed. It is a very popular technique in the condensate pumps, sump pumps, power plants, shipbuilding, industrial installation, etc.

 

Ultrasonic Level Switch

 

It is used for detecting the level of the bulk slurry. They are the non-contacting liquid level indicator switches. With no mobile parts and low maintenance, it delivers precise and highly satisfactory instant output. These are conventionally used in the chemical manufacturing industry. They are widely accepted for its high flexibility.

 

RF Capacitance Level Switch

 

It provides the reliable and precise output in both conducting and non-conducting liquids, irrespective of the open and closed container or channel. The output of this method is not affected by the properties of the materials involved like corrosiveness or conductivity, or by the temperature and pressure. Remote mounted versions are also available and the time delay can also be administered.

 

Conductivity Level Switch

 

It detects the level of the conducting fluid of the minimum, maximum, or the intermediate level, that is stored in either open or closed container. This switch can control the liquid between the two fixed levels by regulating the pump operation. It provides the dry running and over spilling protection and is easy to maintain as its calibration free. It is applicable with corrosive liquids and can be operated by remote control.

 

Though there are ample varieties of liquid level indicator switches, the selection of the appropriate switch is essential to get an error-free output.

The liquid flow measurement instruments are the devices used to evaluate the flow of water or any liquid in a conduit or an open channel. It is also used to calculate the precise amount of liquid present in the pipeline. These devices not only assess or audit the amount and flow of liquid but also are used to detect any wastage due to leakage. This measurement can be accomplished in various ways and in various mediums like pipelines, tunnels, tanks, natural resources, etc. There are various mechanical and technical instruments, which are used to measure the liquid flow, depending on the applications and type of liquid flowing.

 

Various Categories of Liquid Flow Meter

 

The various designs and technical aspects are responsible for the different designs of the flow meters, which have further variations.

 

Velocity Flow Meters: – This category consists of Vortex Shedding, Turbine, Swirl, Electromagnetic, Ultrasonic Doppler, Pilot Tubes, and Calorimetric.

Differential Pressure Flow Meters: – This flow meter has variations of Venturi Tube, Orifice Plate, Flow Tube, Flow Nozzle, and Rotameter.

Positive Displacement Flow Meter: – This process of liquid measurement includes Nutating Disc, Rotary Vane Meter, Reciprocating Piston Meter, and Oval Gear.

Open Channel Flow Meter: – This flow meter can be divided into two categories- Weirs and Flumes.

Mass Flow Meter: – This flow meter consists of Coriolis and Thermal Flow Meter.

 

Output of the Measurement of the Liquid Flow

 

To achieve the precise and effective measurement of the liquid flow, new technologies are being implemented in the form of digital and analog meters, in the output. To attain the desired result, the meters are attached to the flow meter boards and are placed near the conduits. The digital meters have gained tremendous popularity for its ease of use and accuracy and can be used in commercial as well as domestic fields. The digital devices are widely used in the Magnetic and Ultrasonic Flow Meters. To modify the flow of the liquid, the valve of the pipelines can be conjoined to the data. It is possible because the data obtained from the digital meter can be defined accurately.

 

Applications of the Liquid Flow Meter

 

The liquid flow measurement instruments have a wide range of applications. Many Industrial sectors use this device to measure the quantity and flow of the liquid. Some of them are water research, food & beverage, petrochemical industry, oil industry, the pharmaceutical industry, fire rescue operation, submarine industry, fuel industry, paint industry, etc. The unit used in the flow meters is cubic feet or inches and is altered according to the specifications. It has a huge usage in the domestic purpose as well. It calculates the quantity of the water consumed in a particular area. This not only quantifies but also identifies any leakage, which saves our natural resource to a great extent. Usage, velocity, and level of liquid can also be found out by these instruments. The liquid flow meters are built in a sturdy manner to provide the accurate data in the adverse weather conditions as well.

A flow meter is a device to measure the amount of liquid flowing through a pipe and the quantity of the liquid streaming. It is of utmost importance in any industry as it not only quantifies the liquid but also detects leakages by which the wastage can be avoided. Different kinds of liquid flow meters are used in varied fields and are highly essential for the industrial use. Incorrect data given by an erroneous flow meter can produce disastrous results. With the change in the kinetic energy of the flowing liquid, the flow rate is determined. The velocity, on which the kinetic energy varies, depends on the pressure projection that makes the liquid flow through the pipe. The other influencing factors are density, viscosity and the friction of the liquid with the inner walls of the pipe.

 

Various Categories of the Flow Meter:

 

There are different kinds of liquid flow meters, depending on the circumstances in which the flow meters are used.

• Closed pipe flow meter:

The closed pipe flow meter is a type of flow meter that is used for fluids flowing in a closed conduit like sewer, kitchen pipeline, water pipeline, fuel pipeline, etc. and the open channel includes measuring the flow in a non-constricted area. The meters are placed near the pipelines to get the accurate result and it is displayed on the meters attached to the conduits. The closed pipe flow meter can be divided into differential pressure, positive displacement, velocity, and mass flow meters. And the open channel can be categorized into weir and flumes.

• Differential Pressure Flow Meter:

Being the most common flow meter in use, it has primary and secondary component. The first component changes the kinetic energy and the second one measure the differential pressure, which produces a signal that can be changed to get the flow rate. They can further be divided into Venturi Tube, Orifice Plate, Flow Tube, Flow Nozzle, and Rotameter.

• Velocity Flow Meters:

This flow meter operates directly with the volume flow rate. It translates the data of the velocity of water into its volume. When the flow meter is used with Reynold’s number greater than 10,000, the flow meter becomes insensitive to the viscosity change of the fluid. They can be divided into Vortex Shedding, Turbine, Swirl, Electromagnetic, Ultrasonic Doppler, Pilot Tubes, and Calorimetric.

• Positive Displacement Flow Meter:

The flow of water is measured by correlating it with the number of times the chamber is filled and emptied with water. It includes Nutating Disc, Rotary Vane Meter, Reciprocating Piston Meter, and Oval Gear.

• Mass Flow Meter:

This flow meter measures the mass of fluid flowing through a particular point per unit time. This flow meter consists of Coriolis and Thermal Flow Meter.

• Open Channel Flow Meter:

It refers to the liquid flowing in the free surface and analyzes the flow rate by measuring the water depth. It has two categories- Weirs and Flumes.

 

These flow meters have become an integral part of both the commercial and domestic domain.

The flow meter is a device to measure the quantity and the volume of the fluid flowing through a conduit. Depending on the factors like flow meter material, nature of fluid flowing, and its application, the flow meters are divided into various categories. Differential pressure flow meter, velocity flow meter, positive displacement flow meter, open channel flow meter and mass flow meter. The liquid flow meter with pulse output can be further classified according to its approach of displacement and velocity, both of which use different technology in different fields. The displacement established design has nutating disc meters and oscillating piston, whereas the velocity established design includes single and multi-jet meters turbine meters, paddlewheel and vortex flow meters. Some non-mechanical variations include ultrasonic, which are used in chemical and high purity applications and electromagnetic meters, which can used to measure conductive clean, dirty erosive or viscous liquids and slurries.

 

Specifications of the Pulse Output Flow Meters

 

The magnetically-coupled, nutating disc, positive displacement and the pulse output flow meters are appropriate for the liquid flow rate measurements, which range from low to high flow rate. The nutating disc flow meter can withstand the flow of minor impurities without any obstruction and maintain accurate measurements, whereas the oscillating piston cannot pass impurities without any head loss. The pulse head transmitter is an independent device that is coupled with the body of the flow meter with a turn fitting connection and a bayonet lock, staying completely isolated from the chamber of measuring the liquid. Pulse outputs are available as contact closure or NPN Transistor. The pulse head unit has the same specification for all sizes of the flow meters and the size of the body of the flow meter determines the flow range and the frequency value of the pulse output.

 

Rota Pulse Flow Sensor

 

This flow meter is a paddlewheel insertion type flow meter. It can be inserted directly in any range of pipe that is available in PVC, brass, stainless steel, galvanized iron, or poly pipe material, with standard covering pipe sizes. This enables the liquid flow meter with pulse output to be used in a wide range of liquid flow measurement, and monitoring. With only one mobile part of the flow meter and limited intrusion into the pipe, the flow meter gives precise measurement without any noticeable headloss.  There are four blades in the paddlewheel, which rotates with the flowing liquid and generates a square wave pulse output which is proportional to the flow velocity and pipe diameter. Electrical interference is restricted by constructing the meter with a metal shielding jacket.

 

Application & Maintenance of the Flow Meter

 

The liquid flow meter with pulse output is used for the measurement of recycled as well as fresh water in concrete batch plants, irrigation facilities, measurement of petrol or diesel, and various other low viscosity fluid measurement processes, but it is not suitable for pulsating flows. The pulse output format is appropriate for use with flow rate indicators, preset batch controllers, etc. And the calibration check of the flow meter is a must after maintenance of the device.

Flow meters are used in gas or liquid to signify the mass, quantity, and volumetric rate of flow of the fluid passing through a pipe. Flow measurement techniques are very diverse and each application has its own engineering needs and restraints. It can be referenced by many names, flow indicator, liquid meter, flow gauge, etc. However, the application remains same. When it comes to measuring the fluid in industrial applications, the system demands accuracy, as it directly related to the quality of the end product, which is produced in large quantities. Flow can be classified as open channel flow or closed pipe flow. Open channel refers to the flowing streams and rivers, which are not constrained by any means, whereas the closed pipe flow is the flow in the canal or vented pipelines. There are various types of the liquid cooling flow meters.

 

Application of Cooling Water

 

Cooling water is used in most of the applications in Factory Automation. Due to its property of preventing overheating during the processing, it is widely accepted. Waters from the rivers or ground water reservoirs are pumped in industries for a variety of functions. In the die casting industry, the temperature control of the fluid is required for ensuring the quality of the end product. The liquid flow meters are operated by the oscillations as a result of the flow of the fluid. For the ultimate cooling, it is performed by monitoring the temperature at the outlet and inlet of the conduit and the flow rate of the cooling fluid. This liquid cooling flow meter helps maintain an even temperature throughout the die.

 

Principle of the Flow Meter

 

Thermal dispersion, temperature differential, and capillary tube type flow meter are the types of flow meter. The liquid cooling flow meter measures the fluid flow rate by the process of heat convection from an insulated exterior. In the capillary tube type, the heat is transmitted to the bulk of the liquid that flows through a small heated capillary tube, which is aligned with the main pipe. Temperature differential has two flow conditions. During the high flow, the differential moves to the lower part to decrease the heat and vice versa. And in the thermal dispersion, the heat is transmitted to the border of the pipe, through which the liquid flows. All these types of flow meters have different applications based on their unique standards. The thermal dispersion type is used in industries for gas flow applications in ducts and pipes. The capillary tube, on the other hand, is used for the minor flows of clean fluids.

 

Pros of the Electromagnetic Flow Meter

 

Being an indispensable part of commercial and trading operations, these flow meters are used in the cooling of liquids and operate irrespective of the density, pressure, and viscosity. The precision rate of the flow meter is about 1% to 2%. They are also used in measurement applications such as; fuel usage, water dispensers, industries where cooling of water is required, laboratory testing, water coolers, etc.

Flow meters are the instruments, used to measure the mass and the volumetric flow of liquids and gasses through a pipe. Depending on the material of the flow meter, type of fluid flowing and its application in different fields, the flow meters are divided into different categories, namely differential pressure flow meters, positive displacement flow meters, velocity flow meters, mass flow meters and open channel flow meters. Among these flow meters, the paddlewheel liquid flow meter is a type of velocity flow meter.

 

Types of Velocity flow meters:

 

The velocity flow meter shows the direct proportion of fluid velocity and is related to the volumetric flow rate. When Reynold’s number of fluid is greater than 10000, the flow meter becomes less sensitive. They can further be categorized into turbine, vortex shedding, ultrasonic, electromagnetic, and paddlewheel liquid flow meter.

 

Paddlewheel Type Flow Meter: Classifications & Principles

 

Paddlewheel flow meters are classified into two mechanical groups. First is the tangential-flow paddlewheel flow meter. It has a water wheel structure and second with a windmill structure called axis-flow paddlewheel flow meter. The flow of the fluid is directly proportional to the motion of the paddle wheel. Therefore, revolving the paddle with the help of the flowing liquid enables to measure the rate of the flow from the number of rotations. Impregnated magnets in the revolving axis and on the border of the paddle help derive the pulses as signals and transform the number of rotations in flow-rate.

 

The paddlewheel flow meters are used in water or liquids of its category and need a straight pipe before and after the sensor. It has three components, the controller/display, paddle wheel sensor and the pipe. The sensor has free rotating wheels with encapsulated magnets, perpendicular to the flow which rotates with the flowing liquid. The magnet generates a voltage signal which is directly proportional to the flow rate of the fluid. The faster the fluid flows, higher the frequency and voltage produced. The motor is fitted into the pipeline and is available in a variety of materials like polypropylene, stainless steel, and PVDF. This flow meter is very sensitive because of which it has to be used in clean liquids to avoid clogging of the paddles. And if fluid other than water is used, then the flow meter should be used after checking its compatibility with the chemical composition of the fluid.

 

Benefits of Using Paddlewheel Flow Meters:

 

The paddlewheel liquid flow meter has a very simple structure with superior reproducibility and receptivity, involving easy installation and low maintenance. It has a compact design and can measure a huge quantity of fluid at a very low cost. It has no pressure drop, hence is ideal for gravitational flows.

 

Applications of the Flow Meter:

 

Frequent maintenance is required in order to achieve accurate results in regular course. They are used to regulate the chemical metering pump output, to find the perfect measurement of default fluid volumes in dispensing systems, in irrigation process and notifying the users of the fluctuating flow outside a programmed range.

A liquid flow indicator is used to determine the direction and velocity of the liquid flow. This indicator can be used to detect any leakage, low liquid flow rate, leading to the reduction of water bills and elevation of the efficiency of any system. The accurate liquid flow indicator measures the bidirectional movement of the fluid flow in the smallest unit. The selection of the correct flow meter doesn’t only depend on the flow rate, but various criteria, including technical parameters that have to be analyzed before the selection to obtain the desired result. The indicators work in both conductive as well as non-conductive fluid. The conductive fluid includes electrolytes, liquid metals, saline water, etc. and non-conductive fluid includes heptanes, benzene, toluene, etc.

 

The function of the Flow Indicator:

 

An accurate liquid flow meter shows the low to moderate flow rate of liquid with minimal back pressure and enhanced accuracy. The flow indicator comprises a cover and a body. Both the halves are fitted around an impeller, leading to the rotation of the impeller when the fluid flows. The velocity of the fluid flowing in the pipe can be increased by using a tapered inlet nozzle. This not only helps the impeller to move freely but also decreases the back pressure. The revolution of the impeller is analyzed electronically and the plenum is used on the inlet and outlet valve to create a platform of consistent pressure irrespective of conduit location and direction. To increase the precision of the flow indicator, the size of the impeller is kept equivalent to the chamber, so that no liquid is able to pass through it without recording its velocity. The blades of the impeller are impregnated with magnets to create an electromagnetic flux when the impeller revolves. A wire coil with an iron core or a Hall-Effect Sensor is used to enhance and detect the magnetic flux generated by the revolving magnet. A microprocessor that has been pre-programmed is installed in the indicator, which records the response of the coil or HE sensor and calculates the appropriate information of the liquid flow and also records the time since the last restore.

 

Selection & Applications of the Flow Indicator:

 

The selection of the indicators should be done on the basis of the few factors which contribute to its maintenance, spare parts availability, installation cost, calibration and failure records. The flow meter should be chosen after the selection of a competent indicator. As the accurate liquid flow indicator will make sure you get a precise result. The re-personification of the indicator can be done with the changing demand, keeping the basic principle of the indicator intact. The use of flow meter indicator in partnership with the water filtration is widely used with no restrictions, as long as the fluid is compatible with the flow meter. The indicator can be used in various fields such as pharmaceutical and chemical processing, food processing, farming, machine tools and robotics application and in any field where the liquid flow needs to be measured.

Calibration is the comparative study made between the readings of a device and a corresponding standard under consideration. Liquid flow meters are devices that have a wide application in the industrial world. Hence, it is important to calibrate such devices so that an accurate and a precise reading are eventually obtained. Thus, this article will tell you that the importance of liquid flow meter calibration.

• Fluid Properties: The flow meters are interactive in nature. This means that the flow meter would interact with the liquid under consideration to establish a valid reading. Now, it is to be noted that the compatibility of the flow meter and the pipeline plays an essential role that gets reflected during calibration. No matter how scientific the method is, the system and the pipeline have to undergo certain changes during the installation process. This leads to the requirement of calibration to establish harmony between them.

• Flow Profile: In simple words, flow profile is the actual flow of the liquid under consideration in the pipeline. No matter how straight the pipe is, you cannot expect the liquid to flow in an even manner. There will be the presence of bends, valves, and viscosity that will alter the velocity gradient of the fluid. In the method of calibration, all these anomalies are kept under consideration before calibrating the liquid flow meter. This helps in obtaining a generalized reading despite the constant changes that actually take place in the velocity gradient of the fluid.

• Traceability, Accuracy, and Uncertainty: Calibrated reading, as mentioned previously, is a comparative study. Therefore, this method actually establishes the relation that the standard of measurement and the quantity to be measured belong to the same category of physical quantities and units. Traceability is the process of comparing a measurement to an unbroken chain of similar national and international standards. Accuracy is the measure of how close the obtained reading is to the true measurement. Besides, the uncertainty is basically a non-negative parameter which features the dispersion of the quantity values attributed to the measurand based on the certain standard information. To establish these three parameters, it is important to calibrate the liquid flow meter. Otherwise, it would not be possible to obtain the specified results.

• Performance Indicators: In order to enable the performance indicators to provide the suitable and the desirable reading, it is important to calibrate the system so that the resultant output is truly satisfactory.

Hence, it can be perceived that the liquid flow meter calibration is an important task for understanding the flow of liquid and taking the correct readings. If the task of obtaining the required measurements remains incomplete then, the entire system would become non-functional. Therefore, it is absolutely necessary to calibrate the device for securing optimum results.