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A fuel pump draws petrol out of the tank through a pipe to the carburettor .

The pump may be mechanical worked by the engine - or it may be electric, in which case it is usually next to or even inside the fuel tank .

Keeping the petrol tank safe

How a mechanical pump works

A mechanical fuel pump is driven by the camshaft , or by a special shaft driven by the crankshaft . As the shaft turns, a cam passes under a pivoted lever and forces it up at one end.

The other end of the lever, which is linked loosely to a rubber diaphragm forming the floor of a chamber in the pump, goes down and pulls the diaphragm with it.

How an electric car fuel pump works

An electric pump has a similar diaphragm-and-valve arrangement, but instead of the camshaft, a solenoid (an electromagnetic switch ) provides the pull on the diaphragm.

Circulating petrol continuously

Most mechanical and electrical systems pump fuel only when the carburettor needs it, such as motorcycle fuel pump injector. An alternative system has a complete circuit of pipes, from the tank to the carburettor and back again. The pump sends petrol continuously round this circuit, from which the carburettor draws petrol as it needs it.

Filtering petrol and air

Both petrol and air are filtered before passing into the carburettor.

The petrol filter may be a replaceable paper one inside a plastic housing in the fuel line . A pump, like a motorcycle fuel pump, may include a wire or plastic gauze filter, and sometimes a bowl to catch sediment .