Chapter 2 — Burner Operation and Control
2-18 Part No. 750-184
L. OIL FUEL FLOW - HEAVY OIL
The oil fuel flow and circulating system is shown in schematic
diagram form in Figure 2-17. The pertinent controls are called out
and the oil flow is indicated by arrows.
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.
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 deenergizes the solenoid oil valve to
permit or cut off oil flow to the burner. The oil solenoid is closed
when deenergized. 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.
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