C. COMPONENTS COMMON TO ALL
BOILERS
1. Forced Draft Fan Motor (Figure 2-5, 2-7): Drives forced
draft fan directly to provide combustion air. Also referred
to as a blower motor.
2. Forced Draft Fan (Figure 2-6): Provides all air, under
pressure, for combustion of pilot fuel and main fuel, and
for purging.
3. Modulating Motor (Figure 2-7): Operates the rotary air
damper and fuel metering valves through a cam and
linkage system to provide proper air/fuel ratios under all
boiler load conditions.
4. Modulating Motor Transformer (Figure 2-7) (located in
the mod motor): Reduces control circuit voltage (115
Vac) to required voltage (24Vac) for operation of the
modulating motor.
5. Forced Draft Fan Motor Starter (Figure 2-7 & 2-8):
Energizes forced draft fan (blower) motor.
6. Ignition Transformer (Figure 2-7): Provides high voltage
spark for ignition of gas pilot or light oil pilot.
7. Low Fire Switch (Not Shown, located in the mod motor):
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.
8. Atomizing Air Proving Switch (Figure 2-7): A pressuresensitive
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.
9. Manual-Automatic Switch (Figure 2-7): When set at
“automatic,” subsequent operation is at the command of
the modulating control, which governs the position of the
modulating motor in accordance with load demand.
When set at “manual,” 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.
10. Manual Flame Control (Figure 2-7): A manually
operated potentiometer that permits the positioning of
the modulating motor to a desired burner firing rate when
the manual-automatic switch is set on “manual“. It is
used primarily for initial 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.”
11. Burner Switch (Figure 2-7 & 2-8): A manually operated
start-stop switch for directly starting and stopping
operation of burner.