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OPERATION
The VU fuel unit consists of a pump, solenoid
valve, filter and pressure regulator valve (1) housed
within one casting. The pumping action is obtained
from two spur gears, one of which is connected to
the drive shaft (3). The pump casting provides the
various oil ways, for the suction (6), return (5)
and nozzle ports (9). Pressure (8) and vacuum (7)
gauge ports are also provided.
Under the vacuum gauge is located the rotation
selector (2). See the Installation and Service Section.
The VU unit is supplied in two pipe version (self
priming)
On start up, the rotating gears purge the air from
the suction chamber, through a vent groove in the
piston to the return line in two pipe version, and
through the nozzle line (after the solenoid valve
opening) in one pipe version.
On initial commissioning, it is possible to bleed
the air more quickly, through the pressure gauge
port.
Because a vacuum now exists oil, due to atmospheric
pressure, enters the suction chamber through the
filter.
From the suction side, the gears pass the oil to
the pressure chamber, where it comes up against
the head of the piston. Due to the build up of pressure,
the piston is forced back against the pressure regulating
spring. The flow of pressurized oil is interrupted
by an incorporated solenoid valve, and can, therefore,
be opened following the start of the motor (pre-purge),
or interrupted before stopping the motor itself
(instant shut-off of the flame preventing the nozzle
dripping). The excessive oil discharges to the return
side (or by-passes in the one pipe version). It
will be realized of course that the spring tension,
which is varied by the regulator screw, regulates
the pressure of oil required.
The pump can be converted from the two pipe version
to the single pipe version, removing the by-pass
plug (4) from the return port.
When the unit is converted to the single pipe version,
on initial commissioning the air must be bled through
the pressure gauge port (in this case lift installation
are not recommended).
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