So far as I can tell, they just move air from one place to another; they don't leave a vacuum in place for any substantial amount of time. Sure, you *can* describe that as continuously making a vacuum and filling it, but ISTM that's more simply described as moving air from one place to another. Is it actually a suboptimal description, is there something I'm missing, or am I just wrong about how they work?
-Harry
-Harry
