The total impact pressure (P T) is the sum of the static and kinetic pressures and is detected as the flowing stream impacts on the pitot opening. It is measured at right angles to the flow direction, preferably in a low turbulence location (Figure 1).įigure 1: Pitot Tubes Measure Two Pressures The static pressure is the operating pressure in the pipe, duct, or the environment, upstream to the pitot tube.
Basically a differential pressure (d/p) flow meter, a pitot tube measures two pressures: the static and the total impact pressure. Pitot tubes were invented by Henri Pitot in 1732 to measure the flowing velocity of fluids. An advantage of the slender pitot tube is that it can be inserted into existing and pressurized pipelines (called hot tapping) without requiring a shutdown and causing unwanted downtime.
EQUATIONS FOR VELOCITY USING A PITOT TUBE FULL
The main difference between pitot tubes and orifice plates is that, while an orifice measures the full flow stream, the pitot tube detects the flow velocity at only one point in the flow stream. Pitot tubes, like orifice plates and other differential pressure flow meters, function on the principles of the Bernoulli equation – which states that as the flow of a fluid increases, pressure loss occurs. Its flow rangeability of 3:1 (some operate at 4:1) is also similar to the capability of the orifice plate. The pitot tube is an inexpensive alternative to an orifice plate, and its accuracy ranges from 0.5% to 5% FS – which is comparable to that of an orifice. While accuracy and rangeability are relatively low, pitot tubes are simple, reliable, inexpensive, and suited for a variety of environmental conditions, including extremely high temperatures and a wide range of pressures. In industrial applications, pitot tubes are used for air flow measurement in pipes, ducts, and stacks, as well as for liquid flow measurement in pipes, weirs, and open channels. Although the pitot tube is one of the simplest flow sensors, it is used in a wide range of flow measurement applications, such as air speed in racing cars and Air Force fighter jets.
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