Article | June 15, .
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Water utilities rely on accurate and dependable flow measurement for critical process controls. Regulatory agencies also require flow monitoring and reporting, with specific accuracy limits.
Flow metering technology is continually improving, and a variety of meter types and styles are available. Each flow meter application is unique, and flow meter selection should not be based on &#;low bid.&#; While cost is always important, other factors carry more weight when it comes to selecting a flow meter.
Here are six important considerations for choosing the best flow meter.
Before specifying a meter, it&#;s important to clearly understand the entire process and where the meter fits in that process. Involve plant operators during design to discuss issues of maintenance, calibration, and access. Does flow need to be totaled? Does information need to be transmitted to a supervisory control and data acquisition (SCADA) system or be available on the Web? Knowing who will be using the meter and specifically how it will be used is the starting point.
The media being measured is one of the most important considerations when choosing a flow meter. Conductivity, temperature, pressure, and viscosity can affect certain types of flow meters. How clean or dirty the water is may also impact the type and style of meter.
So, the next step in choosing a flow meter is to thoroughly understand the characteristics of the flow to be measured. In an existing facility, data on the matrix should be readily available for review. Standard engineering criteria can be used for new facilities if needed.
For example, propeller meters are often used in drinking water systems, especially for measuring well water withdrawal. These velocity meters can measure fluids containing a certain amount of sand, dirt, iron, and other contaminants. However, these meters would not be recommended for raw wastewater containing stringy materials and wipes, which would foul or damage the meter.
On the other hand, electromagnetic &#;mag&#; meters are very accurate when measuring conductive materials like water and wastewater. They have no moving parts to corrode or break. Different styles of mag meters are available for specific fluid measurements, including drinking water, wastewater, and sludges.
How accurate must the flow measurement be? This depends on the meter&#;s purpose. Flow measured to control chemical feed may need greater accuracy than that used for general tracking of water treated. Flow measurement for billing purposes, such as a water supply authority selling water to a utility, must be extremely accurate.
Regulatory conditions may also apply. Most water and wastewater systems have permit limits for maximum flows and must measure and report daily flow totals. Be sure to check all existing permits for flow measurement accuracy requirements.
Measurement range and turndown rates must be considered as well. Engineers often size equipment and pipe for a 20-year growth period, which can lead to problems when current flows are much less than design rates.
Some utilities may require meters to have NSF-61, NSF-372 approvals or ISO certification. Manufacturers may also accredit their calibration laboratories through the National Voluntary Laboratory Accreditation Program (NVLAP). NVLAP provides NIST accreditation to testing and calibration laboratories using management and technical requirements of the international standard ISO/IEC :.
Proper location and installation of flow meters are critical for providing accurate measurement. Even the most sophisticated meter will read erroneously if installed improperly. Improper installation occurs most often when trying to &#;force&#; a flow meter into an existing plant or network or make it fit in a tight site.
Most flow meters require a specific amount of straight run pipe to prevent flow disturbances. Pipe bends, valves, tees, and reducers can create significant flow measurement errors&#;up to 50 percent for certain meters. In a new system, straight runs can usually be designed appropriately. However, sufficient straight runs may be difficult to obtain in existing systems or constrained sites. Flow conditioners may help reduce inaccuracies. Also, some meters can measure more accurately than others under these conditions.
Pipe size, material, and direction are part of the meter selection equation. For instance, downward flow should be avoided when measuring liquid. As noted previously, systems are sometimes overdesigned to accommodate future growth. In most cases, the pipe must be full for accurate measurement.
What information needs to be monitored and recorded, and how? Some applications require continuous recording of the flow, plus total flow readings. Do operators need event notification, such as high flow or zero flow alarms? Data must often be sent to a SCADA system. In some cases, flow meters are located remotely and need battery-powered devices.
During design, determine what type of output is needed. While 4 to 20 milliamp is most common, some facilities may need MODBUS cards or other instrumentation.
Flow meter manufacturers&#; representatives have a great depth of expertise. They know the right questions to ask and can recommend the best solutions for each unique installation. Use them as a trusted technical partner.
Your technical partner can help to make cost-effective decisions as well. Manufacturers can help by outlining lifecycle costs, including installation, maintenance, and calibration in addition to purchase price.
Most of all, your technical partner can help you choose the right meter up front rather than trying to make the wrong meter work after it&#;s installed.
For more information, please visit Gas Flow Meters.
So you&#;ve recognized the need for a flow meter. Whether it's for understanding, controlling, or monitoring a process, a flow meter is essential for visualizing your fluid's behavior and translating it into actionable insights. There are numerous factors to consider when choosing a flow meter, including cost, brand, technology, installation requirements, and application specifics.
To simplify the decision-making process, we've compiled a list of the Top 7 Key Factors to Consider when Choosing a Flow Meter. Understanding these factors will clarify your requirements and streamline the product selection process.
1. FLUID
WHAT ARE YOU MEASURING?
Identifying the type and state of the fluid being measured is crucial for selecting the appropriate flow meter. Gases and liquids have different measurement requirements, with gases being compressible and requiring specialized meters. This article focuses on selecting a meter for liquid measurement. Once the fluid is identified, its cleanliness and compatibility with meter materials should be assessed to ensure accurate and reliable measurement.
Once the type of fluid has been identified, it's crucial to determine its cleanliness. A contaminated fluid, often referred to as a slurry, contains solid particles, whereas a clean fluid is particle-free. For instance, flow meters equipped with wetted moving parts, such as positive displacement (volumetric flow meter) or turbine (velocity flow meter), are unsuitable for handling dirty fluids. This is because they are more prone to mechanical wear, clogging, or erosion when exposed to solid particles. Therefore, flow meters with wetted moving parts are primarily suited for clean fluids. Conversely, dirty fluids are better suited for non-contact meters such as electromagnetic (velocity meter), ultrasonic (velocity meter), or Coriolis (mass meter). Although these meters also have limitations, they handle particles more effectively.
2. VISCOSITY AND FLOW PROFILE
HOW THICK OR THIN IS THE LIQUID?
Viscosity, or fluid thickness, plays a significant role in flow measurement. Different flow profiles, such as laminar and turbulent flow, require different metering techniques. Understanding the viscosity of the fluid allows for the selection of the most suitable flow meter technology, whether it's positive displacement meters for high-viscosity fluids or velocity meters for low-viscosity fluids.
It's important to note that viscosity is affected by temperature. In liquids, viscosity decreases as temperature increases, following an inverse relationship. Therefore, considering the operating temperature of the system or application is crucial to understanding how fluid flow will be influenced by viscosity changes.
3. FLOW RATE INFORMATION
WHAT IS THE MAXIMUM AND MINIMUM FLOW RATE?
Determining the flow rate range is essential for selecting the right-sized meter. Flow rate directly impacts meter performance and durability. Selecting a meter with a flow rate range that encompasses the application's requirements ensures optimal performance and longevity.
At FLOMEC, when sizing flow meters, we adhere to a practical guideline: aim for flow rates between 20% and 80% of the maximum capacity to determine the appropriate meter size. This range should encompass the minimum and maximum flow rates expected in the application. For instance, if a meter has a flow rate range of 1-40 L/min, it's recommended to operate it within the range of 8-32 L/min. This strategy optimizes meter performance and enhances its durability and longevity. Operating within this range allows the meter to handle both peak flows, which could otherwise damage the meter, and lower-than-normal flows caused by line obstructions or blockages that might go unnoticed if the meter is operating at its limits.
4. TEMPERATURE AND PRESSURE RATING
WHAT IS THE MAXIMUM ALLOWABLE?
Temperature and pressure ratings are critical parameters for meter selection. Meter materials must withstand the fluid's temperature and pressure to prevent inaccuracies and hazards. Operating within the meter's allowable temperature and pressure limits ensures reliable measurement and prevents meter failure.
Ensuring that the system's temperature and pressure do not surpass the flow meter's allowable limits is crucial to avoid measurement inaccuracies and potential hazards. Elevated temperatures can impact the pressure capacity of the meter, causing metals to become more ductile and prone to stretching. Maximum pressure ratings are designed to accommodate the highest temperature rating of a meter, thus maintaining its integrity and accuracy under varying operating conditions.
5. ACCURACY / REPEATABILITY / LINEARITY
HOW ACCURATE AND PRECISE?
Accuracy, repeatability, and linearity are essential performance factors for flow meters. High accuracy meters are necessary for applications requiring precise measurement, such as dosing or custody transfer. Understanding these performance parameters ensures the selected meter meets the application's requirements.
6. INSTALLATION
WHAT ARE THE INSTALLATION PARAMETERS?
Proper meter installation is vital for optimal performance. Considerations such as piping configuration, flow direction, and straight run pipe requirements impact meter accuracy and reliability. Following manufacturer guidelines for installation ensures accurate measurement and prevents operational issues.
7. OUTPUT/INDICATION
DO YOU REQUIRE A DISPLAY OR A SIGNAL OUTPUT?
Choosing the right output options for the meter is essential for data collection and analysis. Whether it's local display, analog, or digital signal output, selecting the appropriate output option ensures compatibility with the application's monitoring or control system. Additionally, certifications may be required for specific applications, such as hazardous area certifications or industry-specific approvals.
Understanding these key considerations and their importance will guide you in selecting the optimal flow meter for your application. For further assistance or information: complete our flow meter specification request for quote form or contact sales support via or .
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