How will you keep/maintain the vacuumed tubes? will you build the system then vacuum the air out?

Yes the tubes will be built along a route, and then as a last step of construction almost all the air will be removed.  It will take about 5 gallons of gasoline equivalent worth of electrical energy to evacuate a mile.  It will take a few days before the water dries out, and the materials stop out gassing.  Vacuum pumps will be at least every couple miles, they will be capable of overlap so if one pump fails the other pumps can keep the vacuum consistent.   Depending on the type of pumps used they may run all the time (maglev turbo pumps have ultra low energy use unless there they are moving a lot of air) or infrequently.  The energy use is a function of how much air leaks in, and this will be minimal.  If the pumps start drawing more power, or turn on frequently it indicates a leak in the area.  The pumps can keep up with small leaks, and the leaks can be repaired without stopping service. 

Airlocks at access portals allow the capsules to enter or leave the tubes without letting much air in.  It will take a few cents worth of energy per air lock cycle.  The optimum vacuum level will likely be in the range of 10ee-3 to 10ee-4 Torr.  If the vacuum quality is too great it will take more energy to maintain than the energy saved from drag reduction. If the vacuum not good enough the propulsion energy loss from drag increases more than the energy savings from lower quality vacuum.

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