Page 7 - Webster Service Manual

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used where the fuel supply tank is above the burner or
where the inlet vacuum is limited to 10” Hg or less when
measured at an unused inlet port.
A two-stage fuel unit has two sets of gears. The suction
gearset creates a vacuum within the fuel unit which
draws oil from a submerged tank or a tank located
below the oil burner and discharges it into an intermedi-
ate chamber or reservoir which supplies the pressure
gears. The pressure gearset delivers oil under pressure
to the burner nozzle. Thus, the pressure gears do none
of the lifting.
2.
Clean the Oil.
Clean oil is
essential for the ef ficient
operation of any oil burner .
The purpose of the filter is to
protect the nozzle from for-
eign particles or any other
matter that might clog the
minute nozzle opening.
Webster fuel units utilize our
exclusive rotary filter which
reduces the need for trouble-
some periodic cleaning. The
rotary filter's blades rotate at motor speed with constant
cleaning action to minimize clogging, compared to
strainer type filters. For maximum protection, an addi-
tional line filter should be u sed, in accordance with rec-
ommended standard practice.
3.
Build Pressure and Provide Clean Fuel Cutoff
Probably the most important functions of the fuel unit
are to build pressure to properly atomize the fuel oil and
to provide clean cutof f of oil when the burner shuts
down. These functions are primarily performed by the
valve assembly consisting of a pressure regulating
spring, pressure adjusting screw, valve and valve seat,
working in conjunction to the gearsets.
The pressure regulating spring and the pressure adjust-
ing screw determine the pressure at which oil is deliv-
ered to the nozzle. For example, when the spring in a
valve assembly is set for 100 pounds per square inch
pressure the valve will not open until the pressure gears
have built up enough pressure in the valve chamber to
raise the piston from its seat. This prevents oil from
reaching the nozzle while under too low a pressure for
correct atomization. The valve and valve seat control
the flow of oil. They also are responsible for a sharp
clean cutoff when the pressure within the fuel unit drops
below the setting of the valve spring. W ebster's
M34DK-3 fuel unit has exceptionally fast fuel cutof
f
through the additional use of an internal flow control
device.