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 FIGURE 2-25
Using a Manometer to Measure Velocity Pressure
The relationship between velocity and the velocity pressure is:
V=
where:
V=
velocity, fpm
VP =
velocity pressure, w.c. in inches
Example: Using a water filled manometer, you measured a velocity
pressure of 4.0 inches of w.c. What is the air velocity?
Figure 2-26, air velocity flow charts, tabulates the velocity pressure for
velocities that may be encountered in normal applications.
The formula for velocity pressure given above is actually a
simplification based on the assumption that the air is at 70 F and at
atmospheric pressure. For higher temperature air, the same velocity would
produce a lower velocity pressure due to the reduction in air density. For
air at temperatures other than 70 F, the relationship between velocity and
velocity pressure is:
V=
1,097 x
where:
V=
velocity, fpm
VP =
velocity pressure, in. w.c.
d=
density of air, lb/ft3
2-24
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