Accuracy in the measurement of your flow rate is important for any business application that involves liquid flow meters. Knowing the strengths and weaknesses of the flow rate throughout your system can help you address needs or troubleshoot issues.
Depending on your application, you may need either a high or low flow rate meter. In speaking with customers, we often hear that there is confusion over these two water meter types. In this article, we discuss the differences between high and low flow rate meters.
Turndown Ratio In Flow Meters
One of the governing principles of any flow meter is going to be the turndown ratio. Whether you have a high-pressure flow meter or a low-pressure flow meter, mechanical or digital, volumetric or velocity, all water meter types have a turndown ratio.
The turndown ratio is a liquid flow meter's rangeability, represented by the ratio of its maximum flow divided by its minimum flow. For example, if a flow meter has a turndown ratio of 10:1 and a maximum flow rate of 100 GPM, then its minimum flow capability would be 10 GPM.
The turndown ratio partially governs a flow meter's effectiveness at accurately measuring the flow of the media through the meter. For a high-pressure flow meter, accuracy will suffer at lower velocities of the media, and if it drops below the effective rangeability, readings may not be possible at all.
Flow Meter Accuracy Statements
Each flow meter will have an accuracy statement. Most are listed somewhere between 0.1% to 1.5% of the measured value, depending on the type of flow meter you are using. What this means is that the accuracy within a liquid flow meter's specified range will be plus or minus the percent listed on the accuracy statement.
A measured flow rate of 100 GPM with a 0.5% accuracy statement means that the actual flow rate is 100 GPM +/- 0.5% (99.5 to 101.5 GPM). If the measured flow rate of the meter at a different time is 50 GPM, then its true flow rate is 50 GPM +/- 0.5% (49.75 to 50.25 GPM).
Accuracy is important in water flow rate meters for many reasons. For water departments, accuracy in water consumption reporting allows them to maintain integrity in billing customers for the water they use. In certain industrial applications, continuous and even flow is a vital necessity that requires precise monitoring.
High-Pressure Flow Meters
Water flow rate meters that measure high velocities will often have wide operable ranges (high turndown ratios) but may be less accurate overall. Since fluid flow meters are rated as being able to measure high GPM, it is generally assumed that they will be operating at a moderate flow rate below their maximum but well above their minimum.
If a high-pressure flow meter has a maximum flow rate of 400 GPM with a 100:1 turndown ratio, it can measure between 4-400 GPM. However, it is expected that the operational flow rate for such a meter would consistently be between 150-250 GPM.
Low-Pressure Flow Meters
Fluid flow meters that are not intended to measure high-velocity media applications have lower operable ranges but tend to be more accurate with regard to flow measurement. Such flow meters may have accuracy statements as narrow as 0.1%, giving them a high degree of accuracy. As an example, a low-pressure flow meter with a maximum flow rate of 40 GPM and a 100:1 turndown would be able to measure flow rates as low as 0.4 GPM.
Buy Fluid Flow Meters From GPImeters
GPI carries the full line of digital and mechanical flow meters from FLOMEC and Great Plains Industries, a leading manufacturer of liquid flow meters. GPI provides the best value and quality of flow meter for any application. Whether you need high-pressure water flow rate meters or low-pressure flow meters for mixed media, you can find them in our online store.
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