Figure 1-6.Boiler fittings.
or device not covered in this text, check the manu-
facturer's manual for information on details of its
construction and method of operation.
The term fittings include various control devices on
the boiler. Fittings are vitally important to the economy
of operation and safety of personnel and equipment. You
must understand fittings if you are to acquire skill in the
installation, operation, and servicing of steam boilers.
All boilers require boiler fittings to operate safely.
The American Society of Mechanical Engineers (ASME)
requires all boiler fittings to be made of materials that
withstand the pressure and temperatures that boilers are
All of the boiler fittings discussed are
important and must be operated and maintained properly
to operate a boiler safely.
An air cock is located in the uppermost steam space
of a boiler, as shown in item 7 in figure 1-6. This design
allows for air to enter and escape during filling and
draining of the boiler. Before firing a cold boiler with no
steam pressure, the air cock is opened to allow air to
escape during the heating of the water. When steam
begins to come out of the air cock piping, close the valve.
CHIMNEYS, DRAFT FANS, AND
Chimneys are necessary for discharging the products
of combustion at an elevation high enough to comply
with health requirements and to prevent a nuisance
because of low-flying smoke, soot, and ash. A boiler
needs a draft to mix air correctly with the fuel supply and
to conduct the flue gases through the complete setting.
The air necessary for combustion of fuel cannot be
supplied normally by a natural draft. Therefore, draft
fans may be used to ensure that the air requirements are
properly attained. Two types of draft fans used on boilers
are forced-draft and induced-draft fans. They are damper
controlled and usually are driven by an electric motor.
The FORCED-DRAFT fan forces air through the
fuel bed, or fuel oil burner, and into the furnace to supply
air for combustion. The INDUCED-DRAFT fan draws
gases through the setting, thus facilitating their removal
through the stack. Breechings (see item 1 in fig. 1-6) are
used to connect the boiler to the stack. They are usually
made of sheet steel with provision for expansion and
The breaching may be carried over the
boilers, in back of the setting, or even under the boiler
room floor. Keep breechings as short as possible and free
from sharp bends and abrupt changes in area. The
cross-sectional area should be approximately 20 percent
greater than that of the stack to keep draft loss to a
A breaching with a circular cross section
causes less draft loss than one with a rectangular or
square cross section.
Blowdown valves on boilers are located on the water
column and on the lowest point of the water spaces of the
boiler (see items 2, 5, 10, and 11 in fig. 1-6). The blowdown
valves on a boiler installed at the bottom of each water