or a bellows. The liquids used are oil, water, or mercury.
The gauge shown in figure 1-26 is an indicating type that
operates on the same principle as the U tube (difference
between the levels of the liquid in the two legs is a
measure of the draft).
The bottom of the inverted bell is sealed with oil or
mercury, depending on the magnitude of the draft or
pressure to be measured. It is supported by knife-edges
on the beam to reduce friction as much as possible. The
weights counterbalance the weight of the bell. and the
pointer is returned to zero. The source of draft is
connected to the tube, which projects into the inverted
bell, so an increase in draft causes the pointer to move
CO2 METERS (ANALYZERS)
Figure 1-27 shows one type of carbon dioxide meter.
The meters are also known as analyzers and are designed
for determining, indicating, and recording the percentage
of CO2 (carbon dioxide) in the products of combustion.
The principle of this instrument is based on the fact that
the specific weight of flue gas varies in proportion to its
CO2 content (CO2 being considerably heavier than the
remaining parts of the flue gas).
Q20. Meters are divided into what two general
Q21. In reference to boiler operations, what does the
term "draft" mean?
BOILER WATER TREATMENT AND
Learning Objective: Describe the methods and
procedures for the testing of and treatment of boiler
A Utilitiesman must understand the methods, tests,
and safety precautions involved in boiler water treatment
and the procedures for cleaning boiler firesides and
watersides. To ensure a boiler operates at peak
efficiency, you must treat and clean it. Water testing,
treatment. and cleaning go hand-in-hand. The reason for
this is because the effect of the impurities in the water on
interior surfaces determines the method and frequency of
boiler cleaning. In this section, we will discuss the
relationships between water testing. treatment. and
cleaning and the procedures for each.
All natural waters contain acid materials and
scale-forming compounds of calcium and magnesium
that attack ferrous metals. Some water sources contain
more scale-forming compounds than others; therefore,
some waters are more corrosive than others. Subsurface
or well waters are generally more scale-forming, while
surface waters are usually more corrosive. To prevent
scale formation on the internal water-contacted surfaces
of a boiler and to prevent destruction of the boiler metal
by corrosion, chemically treat feedwater and boiler
Figure 1-26.Liquid-sealed draft gauge.