A petrol pump works by using a diaphragm that pressurizes gasoline, according to Second Chance Garage. The gas transfers from the pump and through fuel line, until it reaches the carburetor.
The movement of the diaphragm creates a vacuum effect that places more fuel into the chamber, with the help of a siphon mechanism that is already in place. A lever arm is located below the diaphragm that resets the position of the device, and a camshaft is responsible for operating the arm. According to CDXeTextBook.com, the camshaft contains cam lobes that have to be forged into a certain shape to maintain efficient operation of any system. A camshaft from a fuel pump contains an extra cam called an eccentric that is responsible for operating the pump's arm. The fulcrum point of the arm allows it to function with little movement. A 360-degree rotation of the camshaft is responsible for a complete diaphragm cycle.
As the arm sets the diaphragm back into place, valves inside the pump provide an opening that lets fuel be extracted from the petrol tank, while preventing fuel from leaking from the carburetor.
Second Chance Garage also notes that there are puller and pusher pumps. Puller pumps rely on suction to draw fuel from the tank and into the engine. A pusher system pushes the fuel into the line, until it reaches the engine. Electric fuel pumps generally use the pusher method.