HEAD FLOW METERS
Flow Detectors
Venturi Tube
The venturi tube, illustrated in Figure 3, is the most accurate flow-sensing element when properly
calibrated. The venturi tube has a converging conical inlet, a cylindrical throat, and a diverging
recovery cone. It has no projections into the fluid, no sharp corners, and no sudden changes in
contour.
Figure 3 Venturi Tube
The inlet section decreases the area of the fluid stream, causing the velocity to increase and the
pressure to decrease. The low pressure is measured in the center of the cylindrical throat since
the 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 disadvantages
of this type of flow detection are the high initial costs for installation and difficulty in installation
and inspection.
IC-04
Page 4
Rev. 0
