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Page S5.
Fuel lniection System-continued
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in the fifth sketch of Fig. S.2, the "no Cue!" position
tion.
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Contro1ling the Idllng Speed.
An important function of this pneumatic
govemor is that of controlling the idling speed
of the engine.
Tbat is the speed at which it rotates when the
butterfly is in its nearly closed position.
That
position is detennined and limited by an adjust-
able stop mounted on the body of the venturi.
With the butterfly valve con trol lever in this
limiting position the vacuum in the airtight
chamber is at a maximum and the diaphragm
together with the fuel pump control rad, is as
far to the right as the damping spring, des~ribed
below, will allow it to go. Tbe minimum quantity
of fuel, just sufficient to .. idle" the engine, is
then being delivered.
Vader these conditions there is a tendency for
the engine to .. hunt," that is, for its speed to
fluctuate.
It is to eliminate .. hunting" and to ensure a
oteady idling speed, that the .. damping" mechan-
ism shown on the extreme right of the pneumatic
govemor is provided. Refer agam to FIg. S.ll.
Tbe idling control spindle, 33, which is under
the control of a small strong spring, 32, contacts
the centre of the diaphragm when the latter is in
the extreme right or .. idling " position and steadies
it.
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Atomisers.
Af ter leaving the fuel pump the fuel passes
through short steel pipcs, 35, to the atomisers.
Atomisers perform the function of injecting the
fue!, in the form of fine sprays, into the cylinders,
at the moment when the air in the cylinder has
been comprcssed and, as the result of the com-
prcssion, is at a temperature sufficient to ignite
the incoming fuel.
An atomiser compriscs two principal parts:
the nozzle, 45, with its valve, 44, and the atomiser
body, 41.
The atomiser nozzle and nozzle valves are the
important parts. They are shown in Fig. S.8.
Fuel is fed to tbc upper channel in the nozzle
from the atomiser body and travels thence along a
number of drilled.holcs to the lower circumfer-
ential channel. The outlet from the Iatter is
normally closed by the valve as shown.
The atorniser body, complete with nozzle and
nozzle valve lis shown in Fig. S.ll. The nozzle is
held in place by the nozzle holder cap nut, 43.
This holds the upper face of the nozzle in close
contact with the corrcsponding lower face of the
atomiser body. A metal to metal joint is made
here.
Fuel is supplied thrOUgh the fue! inlet con-
nection, 36, and passes thrOUgh the drilled holes
down to the channel in the face of the nozzle.
In the centre of the atomiser body is the spindle,
42, surmounted by the valve spring, 40, and
washer, on the top of which bears the compIession
screw, 38. There is a lock nut on this screw. A
covering nut protects the upper part of the :I tomiser
body and the comprcssion screw.
The small quantity of fuel wbich by-passes
the nozzle valve and accumulatcs within thc
atomiser body, lubricatcs the mcchanism and is
led away by a pipe, 37, connected to the teak-alT
nipp!e stud. At the start of injection the fue!
pump delivels fue! at a bigh prcssure into th~
channe! round the lower end of the nozzle. Tbe
prcssure of this fue! on the end surface of the cone
of the valve lifts it against the tension of the
spring and fuel passes through two small bo!cs in
the end of tbc nozzle as two fine sprays.
Adjustment is provided for the positioo of this
spin die.
Screwing the adjustment in drives the spindie
further io and increases the idling speed.
Adjustmeot of the idliog speed is etfectcd by
altemate manipulation of the screw 00 the end
of the poeumatic governor and the stop foT the
venturi lever.
This is a very delicate operation, ooly to be
attempted by experts. Tt is complcted at the
works for every cngine.
There is another adjustable stop 00 the venturi
to limit the maximum speed of the engine, which
is sealed. Disturbance of this seal may iovolve
forfeiture of the manufacturer's guarantee.
Tostop the cngine the stop lever, 34, is moved
clockwisc, carrying the control rack with it and
tuming the pump plungcr into the position shown
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