CHAPTER!
GENERAL DESCRIPTION AND PRINCIPLES OF OPERATION
(10) Modulating Motor Transformer (located in
the mod motor): Reduces control circuit voltage
(115V
Aq
to required voltage (24V
Aq
for
operation
of
the modulating motor.
(11) Indicator Lights (Fig. 1-7): Provide visual
information on operation
of
the boiler
as
follows:
Flame Failure
Load Demand
Fuel Valve (valve open)
Low Water
(12) Program Relay and
Flame Safe Guard Con-
trol (Fig.
1~
7): Automatically programs each
starting, operating and shutdown period
in
con-
junction
with
operating limit and interloc,k
devices. This includes,
in
a timed and proper
sequence, the operation
of
the blower motor,
ignition system, fuel valve(s), and the damper
motor. The sequence includes air purge periods
prior to ignition and upon burner shutdown.
The flame
detector
portion
of
this control
monitors both oil and gas flames and provides
protection
in
the event
of
the loss
of
a flame
signal.
The control
re~ycles
automatically during nor-
mal operation
or
following a power interruption.
It
must be manually reset following a safety
shut~own
caused by a loss
of
flame. lncor·
porated
is
an internal checking circuit, effective
on every start that will prevent burner operation
in
the event anything causes the flame relay to
h~ld
in during this period.
(13) Flame Detector (Fig. 1-1): Monitors gas
or
oil pilot and energizes the programmer's flame
relay in response
to
a flame signal. It continues
to monitor main flame (oil
or
gas) after expiration
CHAPTER 1-6
of
pilot proving period. A standard equipped
boiler has a
·lead sulfide (infrared sensitive)
detector.
(14) Combustion Air
Proving Switch (Fig. 1-1):
A pressure sensitive switch actuated
by
air pres-
sure from the forced draft fan. Its contacts close
to
prove the presence
of
combustion air. The fuel
valves cannot
be energized unless this switch is
satisfied.
(15) Alarm (Not
Shown): Sounds
to
notify the
operator
of
a condition requiring attention. The
alarm
is
available
as
optional equipment.
(16)
Stack Thennometer (Fig. 1-1): Indicates the
temperature
of
the vented flue gases.
(17) Diffuser (Figs.
1-4 and 1-10): This
is
a
circular plate located at the furnace end
of
the
burner drawer, which imparts a rotary swirling
motion to combustion air immediately prior to its
entering· the furnace, thus providing for thorough
and efficient mixing with the fuel.
(18) Rotary Air Damper (Figs.
1-4 and 1-10):
This damper provides accurate control
of
com-
bustion air
in
proportion to fuel input for various
load demands.
It
consists
of
two concentric
cylinders with openings. The outer
is
stationary.
The
inner is rotated,
under
control
of
the
modulating motor,
to vary the effective size
of
the openings where they overlap.
E.
STEAM
CONTROLS
(ALL
FUELS)
(1) Steam Pressure Gauge (Fig. 1-1): Indicates
the pressure
in
the boiler.
(2) Operating Limit Pressure Control (Fig. 1-1):
Breaks a circuit
to
stop the burner operation on a
rise
of
boiler pressure above a selected setting.
It
is
adjusted to stop
or
start the burner at a
preselected pressure setting.
750-150
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