CHAPTER I
GENERAL DESCRIPTION AND PRINCIPLES OF OPERATION
J.
CONTROLS
FOR
COMBINATION
BURNERS
ONLY
(1) Gas-Oil Switch (Fig. 1-7): Burners equipped
to
bum
either oil
or
gas include equipment for
each
~el..
The selector switch engages the ap-
propnate Interlocks and controls for gas
or
oil
operation.
Chapter
4
details
the
required
mechanical functions
of
each fuel system.
K.
COMBUSTION
AIR
Air for combustion
of
fuel (often referred to
as
"secondary" air)
is
furnished by the forced draft
fan (Fig.
1-1 0) mounted in the boiler head. In
operation, air pressure
is
built up
in
the entire
· head and
is
forced through a diffuser plate for a
thorough mixture with the fuel for proper
com-
bustion. The supply
of
secondary air to the burner
is
governed by automatically throttling the out-
put
of
the fan by regulating the rotary air damper.
This furnishes the proper amount
of
air for the
correct ratio
of
air to fuel for efficient combustion
at all firing rates.
L.
AUTOMATIC
IGNITION
Oil
or
gas burners are ignited by an interrupted
type
pilot..
The pilot flame is ignited automat-
ically by an electric spark.
A series
100 burner usually
is
equipped with a
pilot fired with light oil fuel. All
other
burners,
as
well
as
a series 100 burner complying with
insurance
underwriters
requirements,
are
equipped with a gas burning pilot. In the case
of
a combination burner, the gas pilot
is
used
to
ignite either the main gas flame
or
the oil flame.
Either pilot serves the same function and unless
exception
is
taken
in
the text, the term pilot
is
used interchangeably.
CHAPTER 1-16
At
the beginning
of
the ignition cycle, and
governed by the program relay, the pilot solenoid
valve and ignition transformer are
simultaneous-
ly
energized.
The ignition transformer supplies high voltage
current for the igniting spark. A gas pilot has a
single electrode and a spark arcs between the tip
of
the electrode and the wall
of
the tube surround-
ing
it..
A light oil pilot has two electrodes and the
arc
is between their tips. The pilot solenoid valve
and the transformer are de-energized after the
main flame
is
ignited and established.
Fuel for the gas pilot
is
supplied from the utility's
~ain
or
~om
a
ta~
(bott~e)
supply. Secondary
a1r
flows
10to
and
m1xes
w1th
the pilot gas stream
to provide an adequate flame.
Insurance regulations may require two gas pilot
solenoids with a normally open vent valve
be-
~een
them. The vent valve closes when the gas
ptlot valves open, and opens when the gas pilot
valv~
sh~t
to
ve~t
gas should any be present
in
the pilot hoe
dunng
the de-energized period
of
the gas pilot valves.
Fuel for a light oil pilot
is
provided from the line
that supplies oil under pressure for the main
flame. A solenoid actuated valve controls the
flow
of
oil to the pilot nozzle. This valve
is
energized simultaneously with the ignition trans-
~ormer
at the beginning
of
the ignition cycle and
IS
de-energized after the main flame
is
ignited
and established.
M
ATOMIZING
AIR
Air for atomizing the fuel oil (often referred
to
as
"primary
air") is pumped by the air pump into the
air-oil receiver tank and delivered under pressure
through a manifold block to the oil burner nozzle.
The atomizing air mixes with the fuel oil just
prior to the oil leaving the nozzle.
Atomizing air pressure
is
indicated by the air
pressure gauge on the burner gun.
750-150
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