there was another issue left open in this thread, concerning fuel pumps. it came up, before all of the EVAP discussion started.
the main crux of that part of the discussion was concerning why some vehicles had pumps in the fuel tank, and other didn't.
as i mentioned before, it was/is to do with cooling the pump. as you can see from the following picture, the intank pump is very small. it spins at a much higher rpm, creating more heat to create enough pressure, and volume. it doesn't have enough mass to shed any of its heat if only exposed to air, thus it is stuck inside the fuel tank.
i hadn't realized that the text was gonna be so small on this picture.
the pump on the left is from a ford pickup truck. these trucks, can have up to 3 fuel pumps, depending on how many fuel tanks it has. this system uses a low pressure "feed" pump in the tank(it looks like the pump all the way to the right of the picture) to supply fuel to the high pressure pump, mounted on the frame rail. notice it is larger? it doesn't make any more pressure than the other pumps in the picture....but it is designed to be mounted externally.
the one in the middle is out of a mercedes benz, although i forget the year and model. it mounts underneath the rear of the car next to the fuel filter. again, large pump, mounted externally. the one far right is from a 96 buick roadmaster estate wagon. this one is in the tank.
another picture.......