Problems at the gas pump in Ca.

We have the same spring-loaded vapor recovery nozzles in Sacramento. Not sure about all of CA. I recall having them in Atlanta too, but maybe I have been here too long. It should fill if you push the spring in. I fill up a gas can for my lawn-mower that way. I have read that they cut off when they sense pressure from the back-flow of air out of the filler tube. Can't explain the physics of how that increases as gas reaches the filler tube since you have the same fluid inflow displacing air all the time. I thought the main problem with our pre-"no lead" big filler tubes is that today's pumps don't sense enough back pressure and tend to overflow, as 72bluNblu experiences.