CleaverBrooks CBLE, Operation And Maintenance Manual

Page: 44 / 194

Burner Operation and Control
2-18 750-91 (revised 2009)
Model CB-LE Packaged Boiler Manual
2.12 — Oil Fuel Flow: Heavy Oil
Fuel oil is delivered into the system by the fuel oil supply pump which delivers part of its discharge to the oil heater.
The remainder of the fuel oil returns to the oil storage tank through a fuel oil relief valve and oil return line (see
Figure 2-11).
The combination electric and steam oil preheater is controlled by thermostats. The electric oil heater thermostat
energizes the electric heater, which is provided to supply heated oil on cold starts. The steam heater thermostat
controls operation of the steam solenoid valve to permit a flow of steam to the heater when steam is available.
A hot water boiler is equipped to heat the oil with hot water from the boiler, unless other preheating equipment is
utilized. The electric heater, which is housed separately, is sized to provide heated oil on a cold start. The hot water
thermostat controls the operation of a pump that supplies hot water to the oil heater when hot water is available.
The heated oil flows through a fuel oil strainer to prevent any foreign matter from entering the control valves and
nozzle.
The fuel oil controller contains, in a single unit, the necessary valves, regulators and gauges to regulate the pressure
and flow of oil to the burner.
The program relay energizes or de-energizes the solenoid oil valve to permit or cut off oil flow to the burner. The
oil solenoid is closed when de-energized. It cannot be opened (energized) unless the combustion air proving
switch, the atomizing air proving switch, and the low oil temperature and any pressure switches are closed. They
are satisfied, respectively, by sufficient combustion air pressure from the forced draft fan, pressurized air from the
air pump, and sufficient oil temperature and pressure.
Oil flow to the burner is controlled by the movement of the metering stem of the oil metering valve, which varies
the flow to meet load demands. The metering valve and the air damper are controlled simultaneously at all times by
the modulating motor to proportion combustion air and fuel for changes in load demand.
Oil is purged from the burner gun upon each burner shutdown. The air purge solenoid valve opens as the fuel
valve closes, diverting atomizing air through the oil line. The air assures a clean nozzle and line for subsequent
restart.