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[Instrumentation Table of Contents]
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The pitot tube, illustrated in Figure F1, is
another primary flow element used to produce a differential
pressure for flow detection. In its simplest form, it
consists of a tube with an opening at the end. The small hole
in the end is positioned such that it faces the flowing
fluid. The velocity of the fluid at the opening of the tube
decreases to zero. This provides for the high pressure input
to a differential pressure detector. A pressure tap provides
the low pressure input.
Figure F1
The pitot tube actually measures fluid
velocity instead of fluid flow rate. However, volumetric flow
rate can be obtained using Equation E1.
E1
Pitot tubes must be calibrated for each
specific application, as there is no standardization. This
type of instrument can be used even when the fluid is not
enclosed in a pipe or duct.
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