CHAPTER I
GENERAL DESCRIPTION AND PRINCIPLES OF OPERATION
Regardless
of
which fuel is used, the burner
operates with full modulation (within
its
rated
operating range) through potentiometer-type
positioning controls, and the burner returns to
minimum firing position for ignition. High pres-
sure boilers (above 15 psi) can be
wired for both
low pressure and high pressure modulation
as
optional equipment. This enables the boiler to
operate at lower pressure during off-load hours,
but at a somewhat reduced steam output
depend-
ent upon lower steam pressure and steam nozzle
sizing.
The flame safeguard and program relay include
a flame detector
to supervise both oil· and gas
flames and to shut the burner down
in
the event
ofloss
of
flame signal. The programming portion
of
the control provides a . pre-purging period,
proving
of
the pilot and main flame, and a period
of
continued blower operation to postpurge the
boiler
of
all unburned fuel vapors. Other safety
controls shut down the burner under low water
conditions, excess steam pressure or high water
tern
perature.
The safety interlock controls include combustion
and atomizing air proving switches and,
depend-·
ing upon the fuel and insurance carrier require-
ments, controls that prove the presence
of
adequate fuel pressure plus temperature proving
controls when
heated fuel oil
is
used.
The sequence
of
burner operatiop from start-up
through shut-down
is
governed
by
the program
relay
in
conjunction with the operating, limit and
interlock devices, which are
wired into the cir-
cuitry to provide safe operation and help to
protect against incorrect operating techniques.
All "CBW" model boilers
·have the burner as-
sembly attached
to
the front head. The entire head
may be swung open for inspection and
main-
tenance.
Combustion air
is
provided
by
a centrifugal
blower located
in
the front head. Combustion air
delivery
to
the burner
is
under the control
of
the
damper motor. This same motor regulates the
flow
of
gas fuel through a linkage system con-
nected to the gas butterfly valve and the flow
of
750-150
fuel oil through a cam operated metering valve.
Fuel input and air are thus properly proportioned
for most efficient combustion.
Filtered primary air for atomizing fuel oil
is
furnished independently
of
combustion air
by
an
air pump. The burner control circuit operates on
115 volt, single phase
60 hertz (or
SO
hertz when
so equipped) alternating current. The forced draft
fan motor
is
generally operated on 3 phase ser-
vice at the available main power supply voltage.
Indicator lights signaling load demand, fuel
valve, low water, and flame failure conditions are
standard equipment.
In addition to the standard basic controls
sup-
plied,
other devices may be required to meet
specific requirements
of
an insurance carrier or
local code. Refer
to the Wiring Wiagram (WD)
prepared by Cleaver-Brooks for your specific
installation to determine the specific controls
in
the burner and limit control circuits. The function
of
individual components
is
outlined
in
this chap-
ter and the electrical sequence
is
covered
in
Chapter
3.
C.
CONTROL
AND
COMPONENT
FUNCTION
The term "control" covers the more important
valves and components, including but not limited
to electrical controls or those monitored by the
program relay.
The
operator
must become
familiar with the individual functioning
of
all
controls before he can understand the boiler's
operation and procedures outlined
in
the manual.
Identify and locate each item using the figure
callout.
The actual controls furnished with any given
boiler will depend upon the type
of
fuel for which
it
is
equipped and whether
it
is
a hot water or
steam boiler. Refer to the applicable group or
groups listed which apply to the particular boiler.
CHAPTER
1--3
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