BY-PASS CIRCUIT:
Slight throttle opening causes a drop in suction at the orifice controlled by volume control screw. While at the same time sufficient suction is not felt at the discharge of the Main spraying Nozzle. It however causes a depression at the By-Pass orifices situated in the body. This depression draws the air and fuel in the same manner as explained under idling, with the only difference that the emulsified fuel is now being discharged through the by-pass orifices also. This permits the engine to accelerate smoothly from idling to normal cruising speed.
THE MAIN JET SPRAYING SYSTEM
We have so far seen how the factors of easy starting in cold, s-low speed running and smooth transition are taken care of Apart from all these factors, emphasis is also given on maximum fuel economy as this is one of the burning problems of the day. Since in city traffic, the normal operating speed of the vehicle is around 40 to so KMPH, carburettors are designed to give optimum fuel economy at this speed. The mixture requirements to obtain fuel economy under normal cruising speed: (i.e. part throttle economy) is usually, leaner than what is required for maximum power. The main jet spraying system takes care of mixture ratios required for fuel economy and performance of engine during cruising speeds. As the throttle valve is progressively opened, air velocity in the choke tube begins to raise, thus creating depression across the spraying orifices. Now the petrol is drawn through the Main Jet and similarly air through the Air correction jet and emulsion tube with literal holes, (which helps emulsification of air and fuel) before the spray starts. Now mixture gets sprayed through the spraying nozzle holes and reaches the engine cylinder along with the air drawn through the main ventury of the carburettor.
THE ACCELERATING PUMP SYSTEM
(PBIC & PAIO carburettors)
This system is used on engines, requiring comparatively large choke-tubes or very weak cruising mixtures, td give optimum performance. A sudden wide opening of the throttle would quickly permit a large amount of air to pass through the choke- tube to the inlet valves without, possibly, creating sufficient depression at the Main spraying orifices to cause petrol to discharge from the Main Spraying well. A lack of petrol at this instant would mean that momentarily, a mixture too weak for proper combustion is fed to the engine, thus creating a condition of hesitancy on the part of the engine to accelerate. This condition is avoided by an injection of metered quantity of petrol at the right moment by the accelerating pump. The pump is actuated by a lever which is attached to the throttle spindle by means of a spring loaded rod. When the throttle is closed the tension of pump spring pushes the diaphragm assembly back, thus drawing petrol to the Pump chamber through the non return valve after getting filtered by a fine filter. Immediately on opening the throttle the lever pushes the diaphragm assembly forward forcing petrol out of the chamber, which is metered by the pump jet and finally into the choke tube via Injector tube. At the same time the ball valve is forced on to its seating, thus preventing the petrol, returning to the float chamber. The travel of lever, adjusted by means of the pump control rod nut, determines the volume of petrol injected and the size of the pump jet controls the rate of flow. Thus the Pump assists the engine to accelerate smoothly in operation. Please note that this comes into operation only on sudden pressing of accelerator and not for a particular position of the same.
PAIO ACCELERATING PUMP SYSTEM:
In 40 PAIO carburettors, an additional feature is given in the Accelerating Pump System, by way of an addition-al pump valve in the Accelerating Pump Assembly. This valve is mechanically operated and actuated by the diaphragm spindle itself and will come into operation only on full load conditions. when the throttle is in part load position, the pump valve is closed so that additional fuel cannot be discharged. when the throttle is in the full load position, the pump valve is opened and additional fuel is discharged to enrichen the mixture to take care of the load.
Slight throttle opening causes a drop in suction at the orifice controlled by volume control screw. While at the same time sufficient suction is not felt at the discharge of the Main spraying Nozzle. It however causes a depression at the By-Pass orifices situated in the body. This depression draws the air and fuel in the same manner as explained under idling, with the only difference that the emulsified fuel is now being discharged through the by-pass orifices also. This permits the engine to accelerate smoothly from idling to normal cruising speed.
THE MAIN JET SPRAYING SYSTEM
We have so far seen how the factors of easy starting in cold, s-low speed running and smooth transition are taken care of Apart from all these factors, emphasis is also given on maximum fuel economy as this is one of the burning problems of the day. Since in city traffic, the normal operating speed of the vehicle is around 40 to so KMPH, carburettors are designed to give optimum fuel economy at this speed. The mixture requirements to obtain fuel economy under normal cruising speed: (i.e. part throttle economy) is usually, leaner than what is required for maximum power. The main jet spraying system takes care of mixture ratios required for fuel economy and performance of engine during cruising speeds. As the throttle valve is progressively opened, air velocity in the choke tube begins to raise, thus creating depression across the spraying orifices. Now the petrol is drawn through the Main Jet and similarly air through the Air correction jet and emulsion tube with literal holes, (which helps emulsification of air and fuel) before the spray starts. Now mixture gets sprayed through the spraying nozzle holes and reaches the engine cylinder along with the air drawn through the main ventury of the carburettor.
THE ACCELERATING PUMP SYSTEM
(PBIC & PAIO carburettors)
This system is used on engines, requiring comparatively large choke-tubes or very weak cruising mixtures, td give optimum performance. A sudden wide opening of the throttle would quickly permit a large amount of air to pass through the choke- tube to the inlet valves without, possibly, creating sufficient depression at the Main spraying orifices to cause petrol to discharge from the Main Spraying well. A lack of petrol at this instant would mean that momentarily, a mixture too weak for proper combustion is fed to the engine, thus creating a condition of hesitancy on the part of the engine to accelerate. This condition is avoided by an injection of metered quantity of petrol at the right moment by the accelerating pump. The pump is actuated by a lever which is attached to the throttle spindle by means of a spring loaded rod. When the throttle is closed the tension of pump spring pushes the diaphragm assembly back, thus drawing petrol to the Pump chamber through the non return valve after getting filtered by a fine filter. Immediately on opening the throttle the lever pushes the diaphragm assembly forward forcing petrol out of the chamber, which is metered by the pump jet and finally into the choke tube via Injector tube. At the same time the ball valve is forced on to its seating, thus preventing the petrol, returning to the float chamber. The travel of lever, adjusted by means of the pump control rod nut, determines the volume of petrol injected and the size of the pump jet controls the rate of flow. Thus the Pump assists the engine to accelerate smoothly in operation. Please note that this comes into operation only on sudden pressing of accelerator and not for a particular position of the same.
PAIO ACCELERATING PUMP SYSTEM:
In 40 PAIO carburettors, an additional feature is given in the Accelerating Pump System, by way of an addition-al pump valve in the Accelerating Pump Assembly. This valve is mechanically operated and actuated by the diaphragm spindle itself and will come into operation only on full load conditions. when the throttle is in part load position, the pump valve is closed so that additional fuel cannot be discharged. when the throttle is in the full load position, the pump valve is opened and additional fuel is discharged to enrichen the mixture to take care of the load.
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