A carburettor is a device used in petrol or similar liquid fuel engines by means of which the fuel mixed with Air ,is supplied into the induction manifold of the engine .The main object of the carburettor is to supply the required quantity of fuel and air mixture of the correct strength as dedicated by the load condition of the engine.
For this purpose different types of carburettors are available in the market.Out of that,you will find here the details of Zenith Carburettor,as below.
Zenith carburettor is also known as "British Carburettor" and used by various famous car manufacturer.This carburettor has also number of designs available for different purposes.
Construction And Working Of Zenith Carburettor:-
Construction:-In this,float chamber is supplied with fuel from the fuel tank through a pipe.Whenever the float chamber falls short of fuel,the fuel from the fuel tank flows into the chamber at a fastest speed than is consumed by the engine with the result that,the float rises up,till it reaches a certain level.At this time,a needle valve moves down and rest against the seat,resulting the stoppage of fuel supply from fuel tank.
The main jet is directly connected to the float chamber while the auxiliary jet which is also called as compensating jet draws fuel from auxiliary chamber (Reservoir).This auxiliary chamber is connected to the float chamber through an orifice.Both,main and auxiliary jet are opened up in the venturi.
The air to the carburettor is supplied through the passage.The throttle valve is located at the end of the carburettor and connected to the engine suction pipe.The opening and the closing of the throttle valve controls the quantity of air-fuel mixture supplied to the engine suction manifold.
An auxiliary nozzle from auxiliary chamber (Reservoir) is located at one end of the by-pass and the other end of this nozzle,opens up near the throttle valve.
Working At Starting And Low Speed Running:-
Because of lower Velocity of air at the time of starting or slow speed of the engine,the suction produced at the venturi is quite insufficient to operate the main and the auxiliary jet in nozzle.To improve the velocity of air,the throttle valve is closed to such an extent that there is only a small contracted passage is provided near the end of by-pass.By this,the velocity of air,passing through the region increases,producing the high suction,which operates the nozzle at auxiliary chamber and the air-fuel mixture supplied through the holes.
There is starting and slow running device is fitted in reservoir (Auxiliary Chamber).To vary the supply of air to the nozzle,the set screw given is slackened and whole assembly is taken out.By the suitable number of rotation of screw joint,the position of auxiliary nozzle is set.The whole device is then again fitted to the carburettor and tightened the screw.
Working At Normal Running:-
At this condition,the throttle valve is opened about 66% and as the air entering through the passage,passes through the venturi,its velocity increases due to smaller area consequently its pressure drops,resulting the suction effect.The fuel is sprayed in the venturi by main and auxiliary nozzle.As the speed of engine increases,there by producing the greater suction.Due to this,greater fuel being supplied by the main nozzle.Since the compensating jet (Auxiliary Jet) draws fuel from reservoir (Auxiliary Chamber),which is subjected to atmosphere pressure,through the air,the quantity of fuel supplied by it to the venturi does not change to an appreciable extent.This has the effect of supplying a weaker solution than if only one jet were provide in which case,the air-fuel mixture supplied at high speed will be richer then desired.
Thus the compensating jet enables the air-fuel mixture of the desirable strength to be supplied.In fact with correctly proportioned design of various parts of this carburettor,the fuel supplied by the main and compensating nozzle can be made to bear almost a constant ratio to the air supplied.
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