General Description
1-16
750-96 (revised 2010)
Model CB Packaged Boiler Manual
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 (the term “pilot” is used interchangeably).
At the beginning of the ignition cycle, and governed by the program relay, the pilot solenoid valve and ignition
transformer are simultaneously 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 surrounding 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
main flame is ignited and established.
Fuel for the gas pilot is supplied from the utility’s main or from a tank (bottle) supply. Secondary air flows into
and mixes with the pilot gas stream to provide an adequate flame.
Insurance regulations may require two gas pilot solenoids with a normally open vent valve between them. The
vent valve closes when the gas pilot valves open, and opens when the gas pilot valves shut to vent gas should
any be present in the pilot line during 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 flow of oil to the pilot nozzle. This valve is energized simultaneously with the ignition
transformer at the beginning of the ignition cycle and is de-energized after main flame is ignited and established.
1.14 — 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.
Air pressure from the pump also forces sufficient oil from the tank to the pump bearings to lubricate them and
also to provide a seal and lubrication for the pump vanes. As a result the air delivered to the tank contains some
lube oil; however, most of it is recovered through baffles and filters in the tank before the air passes to the burner.
1.15 — Oil Fuel Flow: Light Oil
Fuel oil is delivered into the system by a supply pump which delivers part of its discharge to the oil burner.
Excess oil is returned to the oil storage tank through the fuel oil relief valve and oil return line. Normally the
pump operates only while the burner is in operation, although often a positioning switch is provided so that
either continuous or automatic pump operation can be obtained.
The oil flows through a fuel oil strainer provided to prevent any foreign material from flowing through the control
valves and nozzle. The fuel oil controller contains in a single unit, a metering valve, a regulator, and a gauge
required to regulate the pressure and flow of oil to the burner. The adjustable regulator controls the pressure. To
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