The car engine actually burns the mixture of petrol and air, where the petrol is pumped along a pipe from the petrol tank and is then mixed with air in the carburetor from which the engine sucks the mixture. In some engines, fuel injection system is used where the petrol and air are mixed in the inlet manifold. The fuel pump pulls the petrol out of the tank using a pipe connected to carburetor.
To keep the petrol tank safe, it is placed at the opposite end of the car from the engine. A float works an electrical sender unit inside the tank that transmits current to the fuel gauge which signals how much petrol is there in the tank. The tank also has an air vent which allows air inside as the tank empties. Some of the latest model of vehicles also has a carbon filter which stops the fuel fumes from escaping.
- Working of the mechanical pump:
In the mechanical pump, the lever movers up and down pulling the diaphragm down only as needed to refill the pump chamber. The return spring pushes the diaphragm up in order to deliver petrol to the carburetor.
Mechanical fuel pump is driven by a shaft that is driven by the crankshaft. As the shaft turns, a cam passes under the level and forces it up at one end. And the other end of the level goes down and pulls the diaphragm with it. When the level pulls the diaphragm down, it creates suction that which lets the fuel pass through the fuel pipe into the pump. As the revolving cam turns further, the lever is moved back to return spring and relax its pull on the diaphragm. The loose linked lever will not push the diaphragm up. There is a return spring that pushes against it. The petrol is expelled from the chamber when diaphragm moves up. The petrol goes out through carburetor as it needs it, through the needle valve in the float chamber. When the carburetor is full, the needle valve closes and petrol does not leave the pump.
- Working of the electric pump:
An electric pump also has a similar diaphragm mechanism like the mechanical pump. It is worked by a road that is drawn into the switch until it opens a set of contact to turn off the current.
An electric pump also has the diaphragm and valve arrangement. But instead of the cam shaft, a solenoid or electromagnetic switch provides the pull on the diaphragm. The solenoid attracts an iron rod which pulls the diaphragm down, which in turn draws petrol in the chamber. At the end of the travel, the iron rod forces a set of contacts, which breaks the current to the electromagnet. And relax the pull on the diaphragm.
When the diaphragm return spring raises the diaphragm, it pulls the iron rod away from the contacts. Then it closes so that the solenoid pulls the iron rod and diaphragm down again.