Its diaphragm functions with the electric magnet and spring. When the electric circuit is complete, its winding becomes magnetic which pulls up the armature and diaphragm. As a result petrol comes into the pump. At this moment C.B. points open up and the electric circuit breaks. With this the magnetic effect is over. As soon as the magnet ends, diaphragm spring lowers the diaphragm and the petrol that came into the pump goes into the float chamber of the carburettor.