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Page S3
Fue/ lnjection System-continued
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The upper, and helical edge of the annular
groove thus
serves
as a valve. The higher that
edge is in relation to the top of the plunger the
sooner the cut-oir and the less quantity of oil
supplied to the atomiser per stroke.
By varying the level of that edge the quantity
of oil supplied is controlled.
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To alter that level, so that it uncovers the port
in the pump barrel to vary the quantity of fuel
delivered, the plunger is turned in its barre! by a
simple means to he described shortly.
In the
first
and
second
sketches
of
Fig.
S.2,
the
plunger
is tumed
to one extreme
position
with
the
vertical
groove
just
clear
of
anc
of
the
two
port
holes
in
the
pump
barrel.
In
that
position
the
helical
edge
of the
circular
groove
is at its lowest
point
and,
so
far
as
the
port
in
tbc
barrel
is
concemed
the
maximum
quantity
of oil is delivered.
That
is the
setting
of the
plunger
for
starting
tbc
engine.
In the third
and
fourth
sketches
the
plunger
is
shown
set
fot
normal
running.
The
precise
position
is
varied
by
tuming
the
plunger
so
that
a
greater
or
lesser
quantity
of
oil
is
de-
livered
to
conform
with
the
demand
for
power.
The
otber
extreme
position
of
the
plunger
FIG. SJ.
Pump
element
is
shown
in
the
fifth
shown in section.
sketch.
This
is the"
stop .,
position : the vertical groove is now in line with
the delivery port to the fuel pump gallery, whicb
is thus put into communication with the top of
the plunger, and oil therefore, merely passes down
this vertical groove as the pump plunger rises.
It is not delivered to the atomisers.
Rotation of the. plunger into these different
positions is brought about in this war. Near the
lower end of each plunger are two lugs (see Fig.
5.3). The lugs are held in a slot on the actuating
sleeve which is mounted on the outside of the
pump barrel and can be rotated. Clamped to the
upper end of each sleeve is a toothed quadrant.
The teeth of the quadrant are engaged by a rack
on the control rad (Fig. 5.11). To and fro move-
ment of the rack turns the quadrants, the sleeves
and the plungers.
Between the fuel pump and the atomisers are
delivery valves, 21, one to each pump plunger,
these serve the important purpose of preventing
dribble at the atomisers. They do that by causing
a sharp cut off in the oil supply at the end of
each injection.
Fig. 5.4 shows a delivery valve. It is at one and
the same time a poppet valve and a piston valve.
The head is poppet valve shaped and below that
is a cylindrical portion which serves as a piston
valve. In the left-hand sketch of Fig. 5.4, the
valve is shown closed.
This valve bas a high lift, so that, as shown in
Fig. 5.4 the cylindrical part of the valve rises clear
of the valve scat when the valve is fully open.
The war in which this valve operates to prevent
dribble at the atomiser is as follows :-
50 long as the fuel pump is delivering fuel oil
the pressure of that oil on the underside of the
valve keeps it wide open as in the third sketch
of Fig. 5.4.
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