[2] Without either of these two systems, fuel vapors trapped inside gas tanks would be released into the atmosphere, each time refueling of the vehicle occurred.
[4] According to Freda Fung and Bob Maxwell, the Environmental Protection Agency (EPA) has been controlling emissions among the United States since the 1970s.
[5] They implemented regulations which would limit the amount of fuel vapor released into the atmosphere during the refueling of a motor vehicle.
Before any EPA mandate was put into action, California devised its own regulations, ahead of every other state, by 16 years, when it required the implementation of the Stage II vapor recovery system.
That frustrates the purpose of the Stage II nozzle, which was designed to vacuum away any fuel vapors that come up that fill pipe during the refueling process.
If the car's own vapor recovery system is working properly, then the Stage II nozzle will only be vacuuming normal fresh air and depositing that into the gas station's underground fuel storage tanks.
[8][dead link] The vent/rollover valve provides a method of controlled escape for gasoline vapors during the refueling process.
It has a mechanism which closes the vent in the event the vehicle rolls over, to prevent spilling of VOCs or fuel in general.