Flow meters are instruments used to measure the volume or mass of a fluid. Flow meters are referred to by many names such as flow sensor, flow indicator, flow gauge or simply a meter.
Metering technology has improved significantly over the past few years increasing the number of options available for every kind of application. The right flow meter is essential for accurate & reliable data collection while the wrong flow meter can result in costly losses and inaccuracies. It is important to realize that no two flow meters are the same and every application is unique. The ideal meter depends on the application and the precision you require, among other things. Continue reading to understand how you can select the ideal flow meter for your application and system.
Meter Types
There are two basic ways to measure fluids, by volume or by mass, so a flow meter is either a volumetric flow meter or a mass flow meter. Whether a volumetric flow meter or mass flow meter is the best depends on the application, its components and the purpose of measurement.
There are several different types of flow meters on the market. Positive displacement (PD), turbine, electromagnetic and Coriolis, to name a few. Each type of flow meter is best suited for a specific type of application or fluid.
Choosing the right type of meter is critical because the accuracy of measurement depends heavily on this factor. Some flow meters simply will not work for certain applications. For example, electromagnetic flow meters require a conductive fluid to function and therefore will not work with hydrocarbons.
Some flow meters cannot measure slurries, vapors or gases.
Positive Displacement, Electromagnetic and Turbine meters are liquid and gas flow measurement devices that measure in volumetric units, such as liters, imperial gallons, etc. These meters are ideal for a wide range of industrial applications including custody transfer, blending, flow control and batch processing. For the lowest uncertainty of measurement, positive displacement meters are generally the most accurate meters. Electromagnetic meters allow for the widest of flow ranges while turbine meters are the ultimate choice for high short-term repeatability.
Coriolis Mass flow meters are liquid and gas flow measurement devices that measure in mass units, such as pounds, kilograms, tons, etc. These meters are expensive but ideal for measuring thick, viscous products or when measurement of the product and/or formula is based on weight. Dosing (i.e., additive injection), filling machines, process control, crude oil production, multi-phase liquid and gas measurement, and highly corrosive applications are ideal for this meter.
Fluid Properties
Where accuracy is concerned, it is important to remember that all flowmeters may be affected to some extent by the fluid they are metering and by the way they are installed. It is therefore important to know the properties of the fluid being measured.
Below are some of the properties of fluids that are to be taken into consideration when selecting a meter.
Type of fluid – liquid, vapor, gas or slurry
Temperature – high temperature applications sometimes require a special type of flow meter
Viscosity – affects accuracy of measurement
Pressure – high-pressure processes sometimes require a certain flow meter
Density – this is important in case of mass flow meters
Fluid Condition – foreign objects in it, suspended particles, air bubbles,
Flow consistency – consistent or breaks in flow will affect accuracy, hence it is usually recommended to always run the meter full of product
Flow range – the minimum and maximum flow required determines the sizing of the meter
Corrosive nature of the material – corrosive liquid or gas can deteriorate seals and other parts, causing the meter to lose accuracy.
Let us look at some of the best meter technologies for each of these fluids:
When it comes to selecting a flow meter, cheapest certainly does not mean best. Although it may seem like the best way to save money in the short term, it could potentially result in a disaster down the road. If the flow meter and its accessories require frequent repair, what seemed like a low cost solution will quickly turn into a budget nightmare. Similarly, a flow meter with a higher initial investment can make up for it by providing accurate measurement and costing less to operate and maintain. It is important to think about the cost of ownership of a few meter as opposed to price. This should include installation, maintenance and repairs over time. How much the meter costs to operate, like its electrical demands, can also increase the overall cost of the flow meter.
Be particularly careful when price reductions have been achieved by compromises in supplier support and expertise. Ultimately, the most cost-effective installation will be the one in which the supplier can offer good technical support, reliable test & repair facilities and an established track record for high-reliability products based on sound research and development.
While it is good to research which meters are commonly used in your industry, simply selecting a popular meter can also lead to problems. If the flow meter is not appropriate for the application, inaccurate measurements can lead to costly losses in material, revenue and reputation.
Accessories and Options
A wide variety of accessories is available to complete your meter. These include:
Meter Registers: A mechanical register is ideal when no power is available while an electronic register can provide simplicity and increased functionality.
Pulse Output Devices converts the rotary motion created during the process of measuring fluid through a positive displacement meter into a high-res pulse stream.
Differential pressure sensors are typically used in aviation fueling applications and measures the pressure differential across the filter separator.
Air & Vapor Eliminators eliminate air and vapor from the metering system and therefore increase accuracy.
Strainers prolong the life of your meter by preventing solid particles from entering and affecting the meter operation
Printers allow you to print a ticket / receipt when delivering or receiving a fluid.
Check valves provides backpressure to increase air/vapor eliminator efficiency and to prevent reverse flow.
Flow Measurement Goals
Every user has different requirements that need to be taken into consideration when selecting the right flow meter.
Accuracy is the most important factor in selecting a flow meter. Not all flow meters have the same accuracy; some applications do not even require high precision. The accuracy of measurement can depend on several factors. A low cost, low-quality flow meter is likely to provide less accurate measurements while a quality meter from a reputable manufacturer will provide a high accuracy measurement. It is important to select a flow meter depending on your application’s tolerance for error.
Repeatability means the percentage of times you get the same result running the same test or measurement under the same conditions. Accuracy requires repeatability; however, repeatability does not necessarily require accuracy. It simply needs consistency. Therefore, repeatability of a flow meter is often as important as its accuracy.
Rangeability or Turndown Ratio is simply the range that a flow meter can accurately measure the fluid. Typically, it is best to choose a meter that can handle a wide range of flow rates accurately, without compromising other critical components. Calculating the minimum, maximum and optimal flow range can help to pinpoint the right size meter for your application.
Installation
It is important to know exactly where and how the flow meter will be installed, as this can considerably affect accuracy and efficiency. Obstructions in the pipeline such as elbows, reducers, valves, etc. close to the meter can cause distortions in flow, affecting accuracy of the meter. To ensure best results, flowmeters should be installed in locations where there are several straight lengths of unobstructed pipeline both upstream and downstream of the meter.
Knowing the pipeline size as well as other information will help us determine whether a flow meter of the same size will work or whether a smaller one is needed. In some cases, the meter can be smaller than the pipeline, however, it is important to know the pressure drop limit of the process. It is therefore critical to find out the manufacturer’s installation & operation recommendations before buying a meter, particularly when space is limited.
Use the Same Supplier for your Complete Metering System
A flow meter is often only as reliable as the equipment that sits alongside it. For example, a mechanical or electronic register or batch controller is needed to accurately process data from the metering element.
Although there are many suppliers offering flow equipment, the best way to ensure a perfectly matched system, where all components are completely compatible is to specify everything from a single reputable supplier. This will ensure all equipment has the same quality and manufacturing standards. It will also ensure support is available (and you know who to catch) in case something goes wrong with your system.
In Conclusion
As you can see, there are many variables in finding the ideal flow meter and the ones we have explored only scratch the surface. The best way to get the right flow meter is to team up with experts in the field. It is important to get your information from people who know these complex and important equipment. Experience matters! Ali Yaqoob Trading Co. L.L.C. is always here for you if you need help. We have available for you a tremendous variety of flow meters and related flow equipment. Our application engineers are factory trained to select the right flow meter for your application or system. Get in touch or come by for a cup of coffee and we will be glad to assist you!
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