Let me note that thermal expansion and size of the door are just TWO of the many issues with the very concept of Hyperloop design.
Other issues include :
- Airlocks would be needed at start and stop stations. Airlocks that can draw a vacuum in minutes. Has that been tested yet ?
- How do you turn the pods around at start and stop stations ?
- How do you 'split' a Hyperloop track, so trains can go to more than one end station ?
- How do you prevent catastrophic failure of the entire system (killing everyone in any pod in the tube) in the case one pod comes of its tracks and penetrates the tube ?
- What to do if a pod gets stranded off the track in a 600 km long tube, with no way out for the passengers ?
- and so on..
Not even talking about keeping this system all under near vacuum.
People really don't realize that that the hyperloop needs to maintain a 99,9% vacuum in a pressurized atmosphere mainly controlled by mother nature, in space we only keep a small pod sealed and pressurized. That's a huge difference.
I don't know of any tests, yet that would be the first large scale test they would have to do if they ever want to reach at least mach 0.8, IMHO. Personally, I can only compare to HVAC's again, and pros are normally using two stage vacuum pumps there. Amateurs with one stage pumps will have to wait for higher temps if they wish to make a successful installation that (hopefully) will last for decades.
Several factors influence the speed of a high vacuum pump, and thus the time required to attain vacuum and remove all moisture from a refrigerant system. Some of the most important are:
the volume capacity of the system itself
the amount of moisture contained within the system
the ambient temperature present
internal restrictions within the system
external restrictions between the system and the vacuum source
Finally: the size of the pump.
The only factors the service technician controls, are the external restrictions between the system and the vacuum pump. The rest is mother nature.The higher pressure in a system, will flow toward the vacuum pump until it is reduced or equal to the desired pressure. The speed at which it will flow is controlled by the internal dimensions and length of the connecting line. Laboratory tests show that pumpdown time can be significantly reduced by use of larger diameter hoses.
For optimum pumping speed you should then keep access lines as short in length, and as large in diameter, as possible.When reading your gauge, the location of the vacuum gauge tube will affect the reading. The closer to the vacuum source, the lower the reading. When reading the vacuum created in a refrigerant system, you should isolate the vacuum pump with a good vacuum valve and allow the pressure in the system to equalize before taking a final reading.
It sounds like a piece of cake when scaled up to a 600km tube with 20 ton pods at transonic speeds (HTT Mach1 version), right?