Ok so i read the other posts and i understand the concept but as you all have different approaches i figured i would reply to you @kryzsec. As yours centers around the general mathematics of the issue i wanted to address that. As temperature and pressure are linked, pump stations (as suggested in this entire theory) would be following the length of the tunnel. As its being built above ground the tubes would be subjected to environmental stress and temperatures, some sections may be warmer than others and therefore would have different air pressures and densities inside the tube. Ok you may ask WHY is this being built above ground?? Well 2 issues, California's governor has a pet project of high speed rail and is draining the tax coffers to cover that, on the other hand the hyperloop is payed for by Elon. So the hyperloop project has no backing from local government. Secondly i think its being built above ground to allow for fault movement. Underground tunnels have less flex, but the hyperloop could be built upon supports that may have dampeners. the problem is this becomes one giant long target for anyone wanting to cause chaos, so i would assume an outer "shell " would be needed to prevent sabotage. I hope im on the right track in my theories.