750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
2-3
2.3 — Components Common to All Boilers
Forced Draft Fan Motor Starter Energizes forced draft fan (blower) motor.
Ignition Transformer Provides high voltage spark for ignition of gas pilot or light oil pilot.
Low Fire Switch An internal auxiliary switch, cam actuated by the motor shaft, which
must be closed to indicate that the air damper and fuel metering
valve are in the low fire position before an ignition cycle can occur.
Atomizing Air Proving Switch A pressure sensitive switch actuated by air pressure from the air
pump. Its contacts close to prove presence of atomizing air. The
fuel valves cannot be energized unless this switch is satisfied.
Manual-Automatic Switch When set at “automatic,” subsequent operation is at the command
of the modulating control, which governs the position of the modu-
lating motor in accordance with load demand. When set at “man-
ual,” the modulating motor, through the manual flame control, can
be positioned at a desired burner firing rate. The primary purpose
of the manual position is for testing and setting the air/fuel ratio
through the entire firing range.
Manual Flame Control A manually operated potentiometer that permits the positioning of
the modulating motor to a desired burner firing rate when the man-
ual-automatic switch is set on “manual.” It is used primarily for ini-
tial or subsequent setting of fuel input throughout the firing range.
It has no control over the firing rate when the manual-automatic
switch is set on “automatic.”
Burner Switch A manually operated start-stop switch for directly starting and
stopping burner operation.
Flame Detector Monitors gas or oil pilot and energizes the programmer flame relay
in response to a flame signal. It continues to monitor main flame
(oil or gas) after expiration of pilot providing period. a standardly
equipped boiler has a lead sulfide (infrared sensitive) detector.
Combustion Air Proving Switch A pressure sensitive switch actuated by air pressure from the forced
draft fan. Its contacts close to prove presence of combustion air.
The fuel valves cannot be energized unless this switch is satisfied.
Alarm Sounds to notify the operator of a condition requiring attention.
The alarm is available as optional equipment.
Stack Thermometer Indicates temperature of vented flue gasses.
Diffuser A circular plate, located at the furnace end of the burner drawer,
that imparts a rotary swirling motion to combustion air immediately
prior to its entering the flame, thus providing a thorough and effi-
cient mixture with the fuel.
Rotary Air Damper Provides accurate control of combustion air in proportion to fuel
input for various load demands. It consists of two concentric cylin-
ders 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.
Component Description
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