HEAD FLOW METERSFlow DetectorsVenturiTubeThe venturi tube, illustrated in Figure 3, is the most accurate flow-sensing element when properlycalibrated. The venturi tube has a converging conical inlet, a cylindrical throat, and a divergingrecovery cone. It has no projections into the fluid, no sharp corners, and no sudden changes incontour.Figure 3 Venturi TubeThe inlet section decreases the area of the fluid stream, causing the velocity to increase and thepressure to decrease. The low pressure is measured in the center of the cylindrical throat sincethe pressure will be at its lowest value, and neither the pressure nor the velocity is changing.The recovery cone allows for the recovery of pressure such that total pressure loss is only 10%to 25%. The high pressure is measured upstream of the entrance cone. The major disadvantagesof this type of flow detection are the high initial costs for installation and difficulty in installationand inspection.IC-04 Page 4 Rev. 0
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