Figure 1-24.Airflow mechanism of a boiler air flowmeter.
a close look at figure 1-25 that shows a comparison of an
inclined-draft gauge and a U-tube gauge.
When one leg of the U tube is arranged on an incline,
the distance moved by the liquid in the inclined portion is
increased for a given draft change which makes more
accurate reading possible.
Two or more draft gauges are required for
economical boiler operation. The gauges inform the
operator of the relative amount of air being supplied to
burn the fuel and the condition of the gas passages. Draft
gauges are made as indicators, recorders, or both. The
measuring element uses a column of liquid, a diaphragm,
Figure 1-25.Comparison of inclined-draft gauge and U-tube gauge.