Elon's hyperloop under construction:

Originally posted by DeepThought
I had a look at the Wikipedia page about the hyperloop thing and it said they were looking at some sort of magnetic levitation. The problem with the project is that they are trying to build some sort of mass transportation system, but it's more like Concorde. Tony Benn, for perfectly laudable reasons made travel on Concorde as cheap as possible; the pr ...[text shortened]... urbofan and truly dangerous. I hope the room is empty of people while these things are running!

Because ion implanters are always a case within a case within a cases because the voltages run up to a million volts of acceleration voltages and other power supplies with lower voltages, 'only' 25,000 to 50,000 volts, it has very large insulators and literally a case within a case thing so when the pump went, it was all inside the machine. The broken vanes did not penetrate the skin of the pump. Just a lot of metal parts inside the source area (smaller voltages, only 50,000 volts🙂

The 'source' is an assembly that has a gas feed or a solid which is heated to make a gas which is then heated by a tungston filament which brute force ionizes the gas. Then there are electrodes with 25 to 50K on them to accelerate the ions out of the source and the exit is a slit a few mm wide and maybe 20 mm long. The wierd thing I saw when the turbo blew was a piece of the blade had gone out of the throat of the pump, up in the source box, bounced around and ended up INSIDE the source slit itself. That blew my mind more than the pile of junk inside the ravaged pump🙂

Thunderfoot explains some of the risks of the vacuum YouTube

Originally posted by twhitehead
Thunderfoot explains some of the risks of the vacuum [youtube]Z48pSwiDLIM[/youtube]

So the hyperloop will run, if it ever does run, at about 750 millitorr, just within the range of a TC gauge, which cannot make a reading unless you are better than about 1000 millitorr.

So the next step would be in the range of 1E -4 torr, 0.1 millitorr where an ion gauge can start working which can read down to 1E-9 torr. So it won't be at that level, just a high roughing pressure. My rougning pumps and get to 10 millitorr or better.

The question there is, the supports on the milk truck of course were not made to take vacuum so it is a no show, just a demo for shock value. The question is how well are the tubes supported with braces and such. Like I said, the pressure on even a tube 3 meters by 100 meters is 11,000 tons. Better be well braced.

Originally posted by sonhouse
The question is how well are the tubes supported with braces and such.

It can't have braces on the inside.
And he points out that the current tubes they are setting up can't even support their own weight without internal braces. Hilarious.
The other tube was made by spaceX and did hold up to whatever vacuum they put in it, but I don't know what that was.
Still, the tubes will have to be very strong - which means high cost.

Originally posted by sonhouse
Like I said, the pressure on even a tube 3 meters by 100 meters is 11,000 tons. Better be well braced.

I don't think that's how pressure works. The volume is irrelevant. The pressure is approximately 1 Atmosphere.

Originally posted by twhitehead
I don't think that's how pressure works. The volume is irrelevant. The pressure is approximately 1 Atmosphere.

I was just showing the amount of square cm in that hypothetical assembly, total pressure. I still think a real system would have to be half buried and only the top assembly having to take atmosphere pressure. The bottom half could be just concrete a half meter thick or so.
Volume doesn't count, surface area does. My sputtering machine has a door about half meter in diameter with an o ring around the perifery that mates against a 12 mm thick stainless steel plate and when it closes the pressure on the O ring amounts to about 2000 kilograms when most of the air is pumped out.

Originally posted by sonhouse
I was just showing the amount of square cm in that hypothetical assembly, total pressure.

Why? Its a meaningless number.

I still think a real system would have to be half buried and only the top assembly having to take atmosphere pressure. The bottom half could be just concrete a half meter thick or so.
It would still essentially be taking the atmosphere pressure.

Volume doesn't count, surface area does.
Not really, no. What matters is the force per unit area. Doubling the length of the pipe doesn't double the force on any given part of it.

My sputtering machine has a door about half meter in diameter with an o ring around the perifery that mates against a 12 mm thick stainless steel plate and when it closes the pressure on the O ring amounts to about 2000 kilograms when most of the air is pumped out.
Yes, but its flat, not a tube. Not the same thing at all. In the case of the tube, we need only work out the force for a ring of it - and even then, it is the curvature that matters, not the total circumference. All we need to know is the force per unit area vs the strength of the material - which is partly dependent on the circumference, because the curvature gives it strength.
The length is irrelevant. Throwing out massive scary figures based on the length is meaningless.

The length comes into play if you have a catastrophic failure and you want to know the total energy released by the air rushing it. Again, tons is totally the wrong unit of measure.

Originally posted by twhitehead
Why? Its a meaningless number.

[b]I still think a real system would have to be half buried and only the top assembly having to take atmosphere pressure. The bottom half could be just concrete a half meter thick or so.
It would still essentially be taking the atmosphere pressure.

Volume doesn't count, surface area does.
Not really, no. W ...[text shortened]... e total energy released by the air rushing it. Again, tons is totally the wrong unit of measure.[/b]

At least, if half buried the stress would not be on the whole circumferance and I think it would be easier to reinforce the top hemicircle of the tubing. Supports don't have to be inside the tube as long as the support structure is welded or rivited to the tube itself.

My guess is it could be built, but like you say, at what expense. If it cost a billion dollars for a few kilometers, it wouldn't work.

Originally posted by sonhouse
At least, if half buried the stress would not be on the whole circumferance ....

Yes it would. It would just be that the stress is borne by concrete not steel. But the stress is still there.

Originally posted by twhitehead
Yes it would. It would just be that the stress is borne by concrete not steel. But the stress is still there.

My point is, concrete is a LOT cheaper than steel. I have no doubt a tube a few meters in diameter and kilometers long can be built and with maglev drives but will it be economically viable? Only time will tell. One thing that would help, if they don't use steel but come up with a carbon nanotube kind of structure that does the same job but cost at one third or some such.

Originally posted by sonhouse
My point is, concrete is a LOT cheaper than steel.

I would be concerned about getting a strong airtight seal between the two. But if concrete is so much cheaper and can be made airtight, then forget steel altogether and just bury the whole thing or make it in concrete even overground. Certainly underground would have fewer problems with temperature fluctuations and the need for expansion gaps has been cited as one difficulty with the steel tubes.

The reason most pictures show it overground is quite simply look. Its a marketing thing not an engineering one. And if you make it look like its made of glass - even better.

Ultimately, I think that the extra speed vs high speed trains is not worth it, so the question is whether high speed trains use that much more power trying to over come air resistance. If the power savings make up for the construction cost then it might make sense.

Originally posted by twhitehead
I would be concerned about getting a strong airtight seal between the two. But if concrete is so much cheaper and can be made airtight, then forget steel altogether and just bury the whole thing or make it in concrete even overground. Certainly underground would have fewer problems with temperature fluctuations and the need for expansion gaps has been cited as one difficulty with the steel tubes.

Didn't think of expansion gaps, so do the whole thing in concrete, but even concrete expands in the heat so like you say, put it underground.

It just gets more and more unfeasible doesn't it.

Just a thought;

Have they even BEGAN to think of the nightmare of what would happen during a major earthquake with the tube suspended on vertical supports while a train is moving through it at massive spread?

I bet they haven't even BEGAN to think of that problem let alone solve it!
And to make it Earthquake proof would add to its cost and make it even less economically feasible.

Originally posted by humy
Have they even BEGAN to think of the nightmare of what would happen during a major earthquake with the tube suspended on vertical supports while a train is moving through it at massive spread?

I would expect that it would be no different for high speed rail. Stop as soon as possible.

Originally posted by twhitehead
I would expect that it would be no different for high speed rail. Stop as soon as possible.

But the passengers will still be in big trouble if the vertical supports for the tube fail in an earthquake which a assume would result in breakage of tube and then, to make matters worse, air rushing in at unimaginable speeds and force, a serious problem that conventional high speed rail wouldn't have. Then there is the possibility that if the tube collapses, even if the train is stationary, the collapse could cause breakage of the train and sudden decompression for the passengers.
In fact, if that even happened just once for real, it wouldn't surprise me if the governments banned the hyperloop purely on safety grounds (and I think rightly so) which would then render the whole thing a huge terrible waste of money; I bet they also haven't given that dreadful possibility much thought either!

Although I find the hyperloop a pretty interesting idea, the more I think about the problems with the hyperloop, the more I think the whole thing is both a safety nightmare and probably will never be cost effective and personally think the whole thing is SO problematic that its not worth any investment in it and any money spent on its development is wasted money that could be better spent on other things. Well, that's my opinion anyway.