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Venturi Tube
Pitot Tube

Instrumentation and Control Volume 1 of 2
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Flow Detectors HEAD FLOW METERS Dall Flow Tube The dall flow tube, illustrated in Figure 4, Figure 4   Dall Flow Tube has a higher ratio of pressure developed to pressure  lost  than  the  venturi  flow  tube. It is more compact and is commonly used in   large   flow   applications. The   tube consists  of  a  short,  straight  inlet  section followed  by  an  abrupt  decrease  in  the inside diameter of the tube.   This section, called  the  inlet  shoulder,  is  followed  by the converging inlet cone and a diverging exit  cone.    The  two  cones  are  separated by  a  slot  or  gap  between  the  two  cones. The   low   pressure   is   measured   at   the slotted   throat   (area   between   the   two cones).   The high pressure is measured at the upstream edge of the inlet shoulder. The dall flow tube is available in medium to very large sizes.   In the large sizes, the cost is normally less than that of a venturi flow tube.  This type of flow tube has a pressure loss of about 5%.   Flow rate and pressure drop are related as shown in Equation 4-3. (4-3) V K  DP where = volumetric flow rate K     = constant derived from the mechanical parameters of the primary elements DP   = differential pressure Rev. 0 Page 5 IC-04







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