| Vol.2 No.4 Subject: Flow Measurement News Date: 4-7-00 From: McCrometer, "The Flow Measurement Specialists" ........ http://www.mccrometer.com ........ ******************************************* This newsletter is e-mailed by McCrometer monthly to subscribers worldwide. It consists of flow measurement information of interest for professionals in this field. For More information on our complete line of flowmeters go to: http://www.mccrometer.com ******************************************* Ask The Experts... Focus on Flowmeter Selection for Water & Wastewater Industries: Part II Continuing with our series on flowmeter selection, we will next take a look at three of the most critical factors to consider - flow rate, flow variability and fluid characteristics. In some applications, there can be huge daily, hourly, or even minute-to-minute variations in the volume of water being measured. If such widely varying flow conditions are anticipated, the designer must specify a meter that is accurate over the entire anticipated flow range. Many times this is referred to as the flowmeter's rangeability and is specified in terms of a ratio, e.g. 10:1. In other scenarios, flow rates remain relatively constant, so rangeability is less critical. Typically, magmeters offer the best rangeability for varying flow rates, with the ability to measure flows from as low as 0.2 fps up to 34 fps, or a ratio of 170:1. Propeller meters, on the other hand, are more suited to fairly constant flow rates, and are normally sized for a maximum of 10 to 12 fps, maintaining their accuracy down to 1 fps, or a ratio of up to 12:1. Once rangeability has been taken into account, the designer should next consider the water content and consistency. Drinking water is clean and free of debris; irrigation water can contain abrasives like sand or twigs; and industrial wastewater and sewerage can be thick and sludge-like. These are major factors that determine the life and efficiency of a flowmeter. A rough guide is to use a magmeter for dirty water conditions with large amounts of suspended solids where its non-invasive operation makes for low maintenance. A propeller meter is typically used for cleaner water flows such as water well discharge or final effluent where its mechanical design is best suited. Next month's newsletter will examine the effect of location and power supply on flowmeter selection, and look at what to do when things go wrong. If you have any questions in the meantime, please contact your nearest McCrometer flowmeter expert at 951-652-6811 or visit our web-site www.mccrometer.com. ******************************************* |