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 2.16 PITOT TUBE. The pitot (pronounced pee-toe) tube is a device that
senses both velocity and static pressure. It is inserted into a moving air
stream and connected to a manometer. The inside of the pitot tube is shown
in Figure 2-29. It is actually a tube within a tube. The inside tube
senses pressure at the end of the tube facing in the direction of airflow.
It senses the total pressure within the duct; that is, it senses velocity
plus static pressure. The hose connection to send this pressure to the
manometer is at the bottom of the pitot tube. A second hose is connected to
the fitting on the side of the pitot tube and reads pressure in the area
between the two tubes. This pressure is created by a series of small holes
around the circumference of the outer tube. As each of these holes is
perpendicular to the direction of airflow, they will sense static pressure
FIGURE 2-29
Pitot Tube Internals
The pitot tube may be used with a manometer to measure velocity pressure
or the static pressure in a duct by hooking it up as in Figure 2-30.
It
does not matter if the static pressure within the duct is positive or
negative.
2-28
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