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4 TRG-TRC013-EN
notes
period one
Fan Performance
Since some of the pressures observed in air conditioning systems are very
small, the U-tube has been modified to improve the ability to read such small
differences in water levels. The modification replaces one leg of the tube with a
liquid reservoir and the other leg with an inclined tube. This instrument is called
an inclined manometer.
Knowing the slope of the tube to be 10:1, a pressure applied to the reservoir
causes the liquid to travel ten times further up the inclined tube to achieve the
liquid level difference between the tube and the reservoir. This allows the
pressure difference to be read with greater accuracy.
For example, a 0.5 in. [12.7 mm] H
2
O pressure applied to the reservoir end of
the device causes the water to travel 5 in. [127 mm] up the inclined leg.
Other instruments commonly used to measure pressures related to fans
include the electronic manometer and mechanical gages.
Inclined Manometer
reservoir
reservoir
duct
duct
pressure
pressure
atmospheric
atmospheric
pressure
pressure
Figure 6