These devices are used for larger pipe sizes when the fluid (gas, steam or liquid) is clean.
For a pitot tube, the difference between the total (stagnation) pressure at the tip of the pitot tube and the static pressure outside the pitot tube follows the square-root relationship. Flow rates are thus measured.
An annubar is a multiple-ported pitot tube that attempts to provide the average velocity.
A typical pitot tube is shown in Figure 500-12. Figure 500-13 is a schematic of an annubar.