RVL Series Vortex Flowmeters
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CLARK SOLUTIONS RVL Vortex Flowmeters Technical Bulletin: Application, Design, Installation INTRODUCTION Slection of the best flow meter for your spcifie application is a critical step, one that will affect the quality of your process for years. Choosing the wrong meter can lead to inaccurate readings, high mainte驭nance costs, and expensive downtime. The following section is designed to explain the technology of vortex flow meters and the specifications of the Clark Solutions vortex product line. Our goal is to ensure that the vortex meter you select meets the requirements of your specific application. HOW VORTEX FLOW METERS WORK The operation of the RVL vortex flow meter is based on the vortex shedding principle. As fluid moves around a body, vortices (eddies) are formed and move downstream. They form alternately, from one side to the other, causing pressure fluctuations. These are sensed by a piezoelectric crystal in the sensor tube, and are converted to a 4-20 mA or pulse signal. The frequency of the vortices is directly proportional to the flow. This results in extremely accurate and repeatable measurements with no troublesome moving parts. MATERIAL SELECTION When choosing the best pipe material for your process, it is necessary to review the fluid to be trans-ported, its concentration, the minimum and maximum operating temperatures, and the pressures to be accommodated. Choosing a flow meter is a similar process, but it is necessary to review a few additional considerations, such as fluid viscosity, suspended parti-cles, density of the fluid and, most importantly, expected flow range. One advantage of utilizing a Universal vortex flow meter is that there are no gas-kets or elastomers in the meter. Therefore, you only need to be concerned with the thermoplastic material used for the body construction. In a thermoplastic piping system, the material chosen for the flow meter should match that of the pipe if at all possible. If you are planning to install a meter in a metal pipe system, you must consider three operating conditions: temͭperature, media, and pressure. Chemical resistance data is available on request from Clark. FLOW RATE AND RANGE REQUIREMENTS When choosing a flow meter, it is necessary to verify with the supplier that the unit selected is suited for your specific flow range needs. Most manufacturers state flow range capabilities by publishing maximum allowed flow rates. Then they provide a turndown ratio to determine minimum flow rate. To use the turndown ratio, simply divide the maximum rate by the ratio to determine the minimum rate. RVL vortex flow meters offered by Clark have a 12:1 turndown ratio (exceptions: RVL025 1/4" unit and RVL050L 1/2" unit; 8:1). LINE FLUIDS Many factors may affect the capability of a meter to accurately measure the flow of specific fluids. Different solutions have varying effects on meters. For instance, heavy particle suspension will wear down internal parts on some meters or cause sensing inaccuracies for non-obtrusive metering systems. For vortex flow meters, high viscosities tend to dampen the formation of vortices and reduce the effective range. Particles and internal bubbles do not usually affect vortex meters. PVDF models work very well in slurry services. However, slurries containing grit will wear down the bluff body, although it can withstand a 5% reduction before accuracy is affected. Also, long fibers will catch and build up on the bluff, decreasing accuracy. Stanͭdard factory calibration is for 32 SSU (1 CST) viscos-ity liquid. Viscosity above 1 CST will raise the minimum readable flow rate, reducing rangeability. The effect is linear to viscosity. No adjustments are required for specific gravities up to 2.0. Liquids with high specific gravities will adversely affect the permissible amount and duration of overrange flow. The following chart indicates the reduction of range based on viscosity. Viscosity Min. Max. Flow Range 1 CST 1 12 12:1 2 CST 2 12 6:1 3 CST 3 12 4:1 4 CST 4 12 3:1 5 CST 5 12 2.4:1 6 CST 6 12 2:1 E. Clark & Associates 10 Brent Drive Օ Hudson, MA 01749 Tel. 978 / 568 3400 Օ Fax 978 / 568 0060

ACCURACY AND REPEATABILITY Depending on your application, accuracy and repeatability may be critical. Accuracy is measured as a percentage by which the meter reading could vary from the actual flow. Repeatability is the percentage by which the meter may vary for a specific flow rate from reading to reading. In other words, if you are operating at a flow rate of 50 gpm and the rate increases to 75 gpm and then returns to 50 gpm, repeatability indicates the percentage within which you will now read the 50 gpm flow rate versus the original reading. Accuracy is normally published by the...

For optimum accuracy, we recommend at least 20 PD upstream and 5 PD downstream for Universal vortex flow meters. If an upstream elbow is closely coupled to another elbow, 27 PD may be required upstream and 10 PD may be required downstream between the meter and a valve. When the diameter of the meter is smaller than the pipe line, you need at least 15 PD of pipe with the same diameter as the meter upstream, and 5 PD downstream. Overall, 25 PD of straight run prior to the meter is required. If there is a plane change in the installation, this requirement increases to 30 PD upstream. The...