The FEP is pulled taught and sandwiched in place. There is constant air flow, in and out, so there is no pressure build up for inflating or deflating of the FEP surface. As for why there are no air bubbles, its very little air passing through, just enough to negate a vacuum. That's also why you don't see resin leaking out. I had wondered the same but after talking with folks that have seen/used the Solidator, that's how it is apparently. SCIENCE!
![Smile :)](./images/smilies/icon_e_smile.gif)
The gap is also very small, apparently 1mm.
As for the liquid pump and inflating method, wouldn't you get optical distortion when the light tries to pass through?