Weifang 495 Operation And Maintenance Manual page 83

T"he fuel from t11e feed pump flows, after being· filtered, into
the upper housing of the injection pUlnp through the:inlet banjo
.
.
connection bolt
an~
fills up the space above the pluqget. When the
fuel pressure reaches 49kpa, the checkvalve opensa~athe exces-
sive fuel flows hackto
the
:deIivery pump via returppipe.
As the plunger moves upward to cover the rPo~ hpleson the
barrel thouroghly, the ·ftiel is compressed. The plun¥er;~()e~:on to
mOve up until the increased fuel pressure
canovei.cPni~,th~force
of
the delivery. valve spring,tne deliveryvalve
l~~s:iio~;:it~s;arand
the fl:lel flows
into.the.injec:~or
through the fuel injeCtion' pipe.
The plunger moves . . . upward continuously, 'the' helical groove
on it is connected with the spill- port on the bareel, the 'residual
compressed fuel above the plunger top flows back to the low pres-
sure chamber within the
p~urrlp
hOllsing along the vertical passage
and helical groove on .the ,plunger a.nd thro:ugh the apill- port on
the barrel. ThJ;1s ,-fuel ·press\l:re within thespace.above the plunger
drops ,the deliv:eryvalve returns to its seat-under· the action of
~-its
spring and the 'ftiel delivery ceases.
During the end of the
fuel
injectiorl' the relief'piston of the de-
livery valve makes the fuel pres.sure within
tpe
injection pipe dn;>p
rapidly to make the nozzle terminate the fuel injection insta.nta-
neously and
t.her~by
avoid
"dribbling~'after
injection of
th~
fuel.
Theq~antit}1'of
fuel delivered by the pump varies with the en-
gine load and its variation
is~.arried
,o·ut by turning the plunger of
the pump which is achieved by the movement o.f the· control rod"
cqntrol fork and the adjucting.arm. The axial ffi.ovem.ent of the
~on­
trol rod is governed by the governor.
The injection pump is provided with a
~entrifugal
\laria.ble
speed type governor (Fig. 21) mounted on pump's rear end. The
48