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# Hyperloop Evacuation

Use the trains as pistons in a pump
 (+3, -1) [vote for, against]

A long-time science-fictional notion, a high-speed train inside an evacuated tunnel, is attracting support in the form of "we intend to build it" projects. It is being called a "hyperloop". See the link for more details.

The main detail is that the degree to which the tunnel has its air removed by normal vacuum pumps, 99.9%, is still associated with significant air resistance when the speed of the train approaches 1000 km/hr. I've seen some different ways to deal with it, like compressing it at the front of the train and letting it loose behind the train (see second link, hah!).

This Idea is about something else. If a small amount of air pressure in the tunnel is a problem, and cannot be removed easily by normal vacuum pumps, then what about an abnormal vacuum pump? Let the train be the pump!

Let us suppose that at 600 kph, the train stars encountering air resistance such that you have to start worrying about aerodynamics and stuff like that, to minimize the problem. Suppose instead there was a normal vacuum pump at the front of the train? It could capture some of that air pressure building up in front of the train, and store it on-board.

When the train docks at a passenger terminal, there will be air- lock connections for boarding and disembarking. The train could now extend an umbilical to the wall of the tunnel, and pump out the stored air. Now the overall tunnel is slightly more evacuated than it was before.

As all the trains in the tunnel do that simple thing, over and over again, the maximum speed in the tunnel can go up and up and up, with air resistance no longer being a problem.

 — Vernon, Jul 20 2015

Hyperloop https://en.wikipedia.org/wiki/Hyperloop
As mentioned in the main text. [Vernon, Jul 20 2015]

Passing air through Cylindrical_20Aircraft_20Body
As mentioned in the main text. [Vernon, Jul 20 2015]

Rescue Party https://en.wikipedi...g/wiki/Rescue_Party
This short story was written about 1945, and includes a train in an evacuated tunnel travelling under the ocean between continents. The idea is even older, however. [Vernon, Jul 20 2015]

I should note there are different notions for supporting the weight of the train inside the tunnel. My personal preference is magnetic levitation, which means it works best if the tunnel is fully evacuated. The linked article talks about how the train could in-essence fly inside the tunnel, using that small remaining amount of air in the tunnel --you would not want to remove that air, even though the max speed is limited.
 — Vernon, Jul 20 2015

I still think H2 is the best option: you'd just need the tunnel be big enough that "ground effect" wouldn't interfere with the trains' passing. The tunnel could then just be a plastic bag... no ?
 — FlyingToaster, Jul 20 2015

/hyperloop evacuation/ the name reminds me of a terrible roller coaster event I heard about.
 — bungston, Jul 20 2015

640 kph should be fast enough for anyone.
 — Cuit_au_Four, Jul 20 2015

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