Page 113 - Mechanic Diesel - TT
P. 113
MECHANIC DIESEL - CITS
In the power jet, instead of the piston and needle valve, a diaphragm type disc valve is fitted. When the vacuum
is high in this valve, it keeps the jet closed through the seat. And as soon as the accelerator is pressed and the
throttle opens by pressing the accelerator, the effect of vacuum on the diaphragm reduces and it rises from its
seat by pressing the spring, which opens the way for petrol and it can go more into the carburetor through the jet.
A disc valve is fitted in the middle of such a diaphragm.
Metering rod: In many carburetors, a metering rod is fitted like a vacuum type power jet. It is in the shape of
a needle and steps are made in its lower part. The upper part of this rod is connected to the accelerator lever
through a lever. When the driver presses the accelerator, this rod is raised by the lever, which opens the mouth of
the high speed jet and a large amount of petrol can go into the carburetor. As soon as the pressure of the foot is
removed from the pedal, the metering rod keeps coming down and the path of petrol keeps closing.
Accelerating Pump Circuit: When the engine is accelerated, the main jet supplies the same amount of petrol to
the carburetor, whereas the engine needs a little more petrol to pick up speed quickly. Until the power jet starts its
work, the carburetor circuit fulfills this requirement.
A small pump is fitted in the accelerator whose plunger is connected to the accelerator links. On pressing the
accelerator, this plunger pumps the petrol coming inside the cylinder and puts it in the carburetor through the jet,
due to which the engine is able to pick up speed on accelerating. There is another reason for installing such a
pump circuit.
When the throttle is opened quickly, a large amount of air enters the carburetor quickly. Before the power jet starts
its work, it reaches the manifold without taking petrol vapor because it is lighter than petrol. The accelerator jet
sprays petrol into the fast incoming air, which makes the engine pick up speed quickly.
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CITS : Automotive - Mechanic Diesel - Lesson 29 & 30
