petrol from the fueltank has to be filled to carborator so that it can be mixed with air for onward feeding two cylinder fuel is feet to the carburettor by two ways namely :
(A) Gravity feed system and
(B) Forced feed system.
(A) Gravity feed system
Hindi system fueltank is placed above the level of carburettor and is connected to it with the help of pipe fuel flows to the carburettor due to its own Gravity.
Such system is not used in motor vehicle as there is no place to keep the tank at a higher level however this system is used in almost all the motorcycle and scooters being it very cheap.
(B) Forced feed system
In this system tank is placed at a distance and also under the level of carburettor to pump the fuel from low level and feed it to carburettor fuelpump is used. In almost all the vehicle this system is used.
Main parts of fuelfeed system
The main part of fuelfeed system is employed in motor vehicle are shown in below:
(●) Fuel tank
(●) Fuel pump
(●) Fuel filter
now let us discuss the construction and working of these units.
(●) Fuel tank
It is made of galvanized MS sheet and is fast and under the chassis with straps nuts and bolts with rubber packing in between.
Petrol connection is taken at the bottom sometimes a fine wire gauge strainer is also fitted in it so that petrol leaving the tank is free from coarse suspended impurities.
Drain plug is fitted at the lowest portion of tank sometimes plug position of the tank is dished so that condenser water being heavier than petrol can settle here.
In a rainy season this condensed water should be drained by opening the drain plug at regular intervals the fueltank has 2/3 compartments interconnected with each other.
This compartments are made in the bank so that fuel does not strike with walls of the tank when the vehicle is moving on rough road.
Fueltank has a neck made on its top where tank cap is placed on the neck a small air bleed pipe is also welded so that when fuel is being consumed by the engine space vacated by the fuel is fill up by air.
In some of the vehicle instead of providing an air bleed pipe in air bleed hole is drilled in the cap itself.
(●) Fuel pump
The function of fuelpump is to pump fuel from the tank and feed it to the carburettor.
These pump are designed to pump sufficient quantity of fuel at all working condition so that the pipeline always remains filled up with fuel at all working condition failing which these are chances of paper Lok usually called airlock in the pipeline
There are two types of pump used these are :
(A) Mechanical fuel pump
(B) Electrical fuel pump.
(●) Fuel filter
In some of the fuelpumps trainer is placed in the glass bowl it requires cleaning at each service.
In some of the vehicle a separate fuelfilter is connected between carburettor and fuelpump this glass bowl and the filter element should be cleaned and each service.
While in some other makes inline type of filter this type of filter is not cleanable and has to be replace when found dirty.
Fuelfilter fitted to Maruti engine is not cleanable type hence complete assembly has to be changed at 40,000 kilometre.
While fitting the filter and sure that outlet coming on top and inlet is at the lower end of body.
Electric fuel pump
In some of the vehicles instead of mechanical fuelpump electrical fuel pump is fitted which is connected through ignition key there are two types of pump available these are :
(A) Diaphragm type
A diaphragm pump (also known as a Membrane pump) is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable valves on either side of the diaphragm (check valve, butterfly valves, flap valves, or any other form of shut-off valves) to pump a fluid.
When the volume of a chamber of either type of pump is increased (the diaphragm moving up), the pressure decreases, and fluid is drawn into the chamber.
When the chamber pressure later increases from decreased volume (the diaphragm moving down), the fluid previously drawn in is forced out.
Finally, the diaphragm moving up once again draws fluid into the chamber, completing the cycle. This action is similar to that of the cylinder in an internal combustion engine.
Diaphragm Pumps deliver a hermetic seal between the drive mechanism and the compression chamber, allowing the pump to transfer, compress, and evacuate the medium without a lubricant.
An elastomeric diaphragm can be used as a versatile dynamic seal that removes many of the limitations found with other sealing methods.
They do not leak, offer little friction, and can be constructed for low pressure sensitivity.
With the right material consideration, diaphragms can seal over a wide range of pressures and temperatures without needing lubrication or maintenance.
(B) Bellow type
In this pump instead of diaphragm flexible metal below is used the pump work in the same way as stated for diaphragm type.
Precautions to be taken for the electric fuel pump :
(1) do not connect the battery in Reverse polarity.
(2) do not drop the pump.
(3) do not apply overvoltage.
(4) do not install the pump near high temperature.
(5) make correct electrical connection on fuel pump.
(6) never keep the terminal loose.
(7) keep fuel line joint fully tight and there should be no leakage.
Fuel pump troubleshooting
Note :- if your vehicles fuelpump supplies less fuel, so read carefully these table below.
|blocked vent screw on fuel tank.||Clean the vent hole.|
|choked or bent fuel pipe from tank to fuel pump or fuel pump to carburettor.||Clean the pipe remove sharp bend or replace squeezed pipe.|
|loose petrol pipe connection.||Tighten the unions.|
|Choked petrol strainer in fuel pump or tank.||Clean the strainer.|
|loose filter housing on fuel pump.||Tighten it fully.|
|broken or pressed filter housing packaging.||Replace with new one.|
|leaky diaphragm.||Replace diaphragm.|
|Valve holding clip loose.||Tighten it fully.|
|leaky valve.||reface if split valve otherwise change.|
|rocker arm pin moved out of its place or worn out pin.||Reposition the pin and lock it;if worn out replace.|
|worn out rocker arm.||rebuild or replace.|
|loose body screw||Tighten it fully.|
|thick gasket used for mounting fuel pump to block.||use thinner gasket|