Design .....here is some information from Wikipedia .....
A modern fuel dispenser is logically divided into two main parts — an electronic "head" containing an embedded computer to control the action of the pump, drive the pump's displays, and communicate to an indoor sales system; and secondly, the mechanical section which in a ‘self contained’ unit has an electric motor, pumping unit, meters, pulsers and valves to physically pump and control the fuel flow.
In some cases the actual pump may be sealed and immersed inside the fuel tanks on a site, in which case it is known as a submersible pump. In general submersible solutions in Europe are installed in hotter countries, where suction pumps may have problems overcoming cavitation with warm fuels or when the distance from tank to pump is longer than a suction pump can manage.
In modern pumps, the major variations are in the number of hoses or grades they can dispense, the physical shape, and the addition of extra devices such as pay at the pump devices and attendant "tag" readers.
Flow rate is typically 40+ liters per minute and is higher for high-speed pumps serving trucks and other large vehicles. In the USA flow rate is limited to 10 gallons per minute (37.8 liters per minute) except "Any dispensing pump that is dedicated exclusively to heavy-duty vehicles, boats, or airplanes is exempt from this requirement.
Historically, fuel dispensers had a very wide range of designs to solve the mechanical problems of mechanical pumping, reliable measurement, safety, and aesthetics. This has led to some popularity in collecting antique dispensers, especially in the USA.
And next time you visit your station, kindly take full tank because it will save money and time + you will save your engine from any petrol tank deposits.......regards