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Fue/ fn;ection System-conttnued
Page 52
Oil is supplied from the lift pump through the
fuel inlet connection, 25, and entirely fills the
fuel pump gallery, 23. That is a tubular passage
running the fuillength of the Cue! pump and closed
at lhe end opposite to the inlet by the vent
plug. This fuel pump gallery is connected through
small ports with all the pump barrels, 19.
In the base of the body of the pump is a cam-
shaft. In contact with each cam is a cam roller,
14.
the port. When that happens communication is
established between the oil above the plunger and
that in the gallery via la) lhe vertIcal Sroove.
(b) the annular groove. (c) the port in the pump
barrel. (See Fig. S.2).
11lat is the position shown in the second sketch
of Fig. S.2.
Tbe Dil then ceases to flow to the atomisers and
is merely by-passed through these passages to tbe
fuel pump gallery.
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FIG. SI
FuEL LIFT PUMP.
(Tbe preliminary fiJler
is not always supplied).
B
Tappet Roller.
S.
Packing Washer.
E.
FuelOutlet.
T.
Valve Plugs.
F.
Outlet Valve.
U.
Copper-Asbestos
G.
Plunger Spring
Sealing Washen
H.
Inlet Valve.
V.
Spring Chamber Caps
J.
Inlet.
W.
Lift Pump Body.
L.
Plunger.
X.
Preliminary Filter
N.
Guide SpindIe.
Gauze Container.
P.
Preliminary Filter
Y.
SpindIe Guide.
Gauze.
Z.
Primer.
Q.
Clamping Nut.
AC. Inlet Plug Filter
R
Fir;na S'm"
G"117~
~
The roller is held in close contact with the
cam by the spring, 15. The top of this tappet
is in close contact with the lower end of the pump
plunger, 20, contact being maintained between
plunger and tappet by the pressure of the oU above
the plunger.
As the pump plunger falls, oil fiows into the
barrel through the port. As the plunger rises it
closes the port and propels the oil past the delivery
valve, 21, into the pipe leading to the atomiser.
Fig. S.2 shows how the upper part of the pump
plunger is formed. Observe that an annular
groove is cut in the plunger. The lower edge of
this groove is level, or horizontal, the upper edge
B, is helical. In addition there is avertical groove
cut right to the top of the plunger and running
into the annular groove.
This groove is the means of varying the quantity
of Cuel delivered per stroke. (See below).
The first sketch in Fig. S.3, shows the working
end of the plunger and barrel with the fuel port
in the latter, which, it should be remembered, is
in communication with the fuel gallery, 23, of
the pump (Fig. S.lI). The plunger is shown at
the bottom of its stroke with the cam at its bottom
dead centre.
As the camshaft turns the plunger rises, but
nothing happens until the top end of the plunger
bas reached the upper edge of the port in the
barrel and closes it. Then the oU is propelled
past the delivery valve and injection commences.
The camshaft of the fuel pump is direct driven
from the engine timing gear at half engine speed.
It is .. timed" like the magneto or distributor
of a petrol engine, so that the closing of the port
and commencing of fuel delivery to the engine,
that is, injection, comes at a predetermined point
in the compression stroke. The timing, of course,
is precisely the same Cor each cylinder.
Oil continues to fiow until the helical upper
edge B of the groove in the pump plunger uncovers
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