Dall Flow Tube:
The dall flow tube, described in Figure, has a higher ratio of pressure build to pressure lost than the venturi flow tube. It is more compact and is generally used in huge flow applications. A tube consists of a short, straight inlet section followed through an abrupt decrease in the within diameter of the tube. This section, known the inlet shoulder, is followed through the converging inlet cone and a diverging exit cone. The two cones are separated through a slot or gap among the two cones. The low pressure is measured at the slotted throat (area between the two cones). A high pressure is measured at the upstream edge of the inlet shoulder.
The dall flow tube is available in medium to extremely large sizes. Within the large sizes, the cost is normally less than that of a venturi flow tube. This category of flow tube has a pressure loss of about 5%. Flow rate and pressure drop are related as shown in Equation 1.
Figure: Dall Flow Tube
v =K√?P .... (1)
where
v = volumetric flow rate
K = denotes constant derived from the mechanical parameters of the primary elements
P = differential pressure