How does a gas pump know when to shut off?

(WHTM) -- Pumping gas is an act so routine, drivers can do it on autopilot, zoning out while the gallons add up. But have you ever stopped to wonder just how that pump works? Or why your tank doesn't overflow while you're daydreaming?There are large gas tanks underneath all the service pumps at a gas station. Gas stations have two or three of these large tanks, which can hold several thousand gallons of gasoline.
In order for the gas to come up from these tanks into the actual pump, it has to de