CleaverBrooks 4WI, Operation, Service And Parts Manual

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750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual 2-1
CHAPTER 2
Burner Operation and
Control
2.1 — The Burner
The oil burner is of the low pressure, air atomizing (nozzle) type. The gas burner is of the non-premix orifice type.
The burners are ignited by a spark ignited interrupted type gas pilot and it is extinguished after the main flame is
established.
Burners equipped to burn oil and gas (combination burners) include equip-
ment for each distinct fuel. Since the burner uses only one type of fuel at a
time, a gas/oil selector switch is incorporated.
Regardless of which fuel is used, the burner operates with full modulation
(within its rated operating range). The burner returns to minimum firing posi-
tion for ignition. High pressure boilers (above 15 psi) can be wired for both
low pressure and high pressure modulation, which enables the boiler to oper-
ate at lower pressure during off-load hours, but at a somewhat reduced steam
output, dependent upon lower steam pressure and steam nozzle sizing.
FIGURE 2-1.
Gas/Oil Selector Switch
A flame detector is present to supervise both oil and gas flames, and to shut the burner down in the event of loss of
flame.
The programming portion of the control provides a pre-purging period, proving of the pilot and main flame, and a
period of continued blower operation to post-purge the boiler of all unburned fuel vapor. Other safety controls
shut down the burner under low-water conditions, excess steam pressure, or water temperature.
NOTE: A Series 100 boiler is usually equipped with a light oil pilot, although a gas pilot is also available.