An automatic fuel nozzle turns off a gas pump during refueling when the tank is full or near full. These devices are a safety mechanism so the fuel pumper does not over-pump gasoline into the car.
Automatic fuel nozzles utilize a vacuum pressure gauge on the pump to determine if a car tank is full. Once the gauge registers that a car's tank is almost full, the nozzle shuts off the flow of gas.
Without this mechanism, gasoline could spill outside the motor vehicle, creating a fire or environmental risk to the driver and other consumers.
The standard type of fuel nozzle has pressure within it so the driver can immediately pump gas. A pressure activated fuel nozzle needs pressure to be filled into the pump before the driver can pump gas. An interlock fuel nozzle attaches to the fuel line before fuel is pumped into the vehicle.
Gas stations usually employ pressure activated pumps. With pressure activated pumps, the gas nozzle cannot pump gas until the attendant allows pressure to build up in the fuel station. The attendant allows pressure to go into the gas tank once the driver confirms payment.
