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Magtube Question

05/20/2018 4:47 AM

I just joined to get some expert advice please.

Magtube would be similar to Hyperloop. Swissmetro and ET3 but instead of vacuum pumps the whole length it would have a 300kw jet compressor evacuating the one tonne of air that enters the 200 kilometre 6m diameter tunnel with every train as it is pushed toward it by the train.

Am I nuts or has nobody thought of eliminating the pressure build up this way.

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#1

Re: Magtube

05/20/2018 8:40 AM

It sounds like you wish to resurrect the Beach Pneumatic Transit system proposed by Alfred Ely Beach.

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#4
In reply to #1

Re: Magtube

05/20/2018 5:55 PM

No mate it would be maglev propulsion

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#20
In reply to #4

Re: Magtube

05/21/2018 11:28 PM

Why not bring more efficiency into the picture by using northbound / southbound air flows to cancel each other out ?

If a pod is creating a pressure zone ahead of it why not use CNC controlled valves to open pathways to the other side so a pod going in the opposite direction creates vacuum to assist the evacuation of that air build up ?

Use of pressure sensors , predictive self learning software to model air flows and optimise efficient transfer or equalisation of air flows could vastly reduce the demands on your proposed 300 kW jet fans.

I have no criticism of the maglev as you described , and in fact the hyperloop is not feasible to me due to the risk of pods becoming depressurised while they are in that vacuum. Instant pink mist would be the outcome .

How do you create redundant layers of safety in that environment ?

If it was a shuttle to mars then sure , you have trained occupants with at least a few layers of backup in a ~ mostly controlled environment but when you introduce the average Joe and their misbehaving kids into public transport the risk factors from damaged equipment become elevated.

Somewhere in your picture you would be considering the equivalent of a hydraulic accumulator , except with low pressure and high flow rates. I can see it being achievable with 20 - 40 cubic meters of air being held in a bellows and transferable in 1 - 3 seconds to smooth out transitions when pods are entering / exiting the relevant zones.

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#29
In reply to #20

Re: Magtube

05/22/2018 5:37 PM

What you are suggesting is what they tried with Swissmetro and even with cruise height density they still had the same problem as Hyperloop with pressure build up but rather than putting compressors on trains or pods they thought cut throughs at stations was the answer but it was still limited to 300kph and they went broke.

Generally as speed increases so does cost but if the 1,000kph Magtube train can get through the 200 kilometre single tunnels in 15 minutes while the other direction is unloading and reloading in the passing stations it brings the tunnel cost between Melbourne and Sydney to only $30b which is doable over 10 years and the gaurenteed $2b per year income would easily cover running costs.

Safety is uppermost in my mind as even one small incident would shake public confidence and it should be regarded as not only cheaper and more reliable than aircraft but safer also.

To achieve this standard I suggest only one train in any tunnel at one time, the train would have to be made of crash proof steel with everything non flammable and enough compressed air, water, food etc. to last four hours until pressure is normalised and help arrives.

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#38
In reply to #29

Re: Magtube

05/23/2018 3:01 AM

There is no “crash proof steel” however collision detection braking systems would be one of at least 4 - 5 layers of safety that such a system would require.

composites would be your construction material , probably over a steel subframe or an aluminium frame reinforced with carbon fibre , however those details are irrelevant , your first hurdle is the method for maintaining a vacuum or partial vacuum to eliminate friction losses .

i don’t think food is required , nor even water but CO2 scrubbers and atmosphere monitoring systems would be a good beginning.

if the system came to a stop then you would activate safety valves which would slowly allow internal vacuum to normalise.

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#39
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Re: Magtube

05/23/2018 4:46 AM

1. Carriages would be thick steel monocoque construction to allow atmospheric pressure inside and would just slide to a stop so as not to hurt anybody.

2. Radio contact would be maintained with a control room at all times as well as electronics for a driverless train.

3. Elon musk said that water pressure is 6 times that of air pressure in tunnels and they can make tunnels waterproof these days.

4. Even though toilets would not be needed between cities it would be good to have an emergency one in each carriage along with some compressed air and water etc.

5. Maintenance/rescue teams would be on hand 24/7 who would allow 200m3/s through regulators to normalise the atmospheric pressure in the tunnel before entering to help.

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#53
In reply to #39

Re: Magtube

05/24/2018 6:14 AM

Composites can be just as strong as steel and could be 1/3 to 1/5 th of the weight .

”thick steel” ?

no.

Radio contact ? No . Each unit would have CCTV and duplicated transponders to monitor its exact location at all times connected with anti collision monitoring , and a whole page full of other big words.

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#54
In reply to #53

Re: Magtube

05/24/2018 8:22 AM

The tunnel could make an effective RF waveguide?

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#56
In reply to #53

Re: Magtube

05/27/2018 5:03 AM

I was mainly thinking about fire resistance and did not think weight was a problem with maglev.

It can have all the bells and whistles you want, the safer the better.

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#2

Re: Magtube

05/20/2018 8:56 AM

Ha ha... surely you jest....

https://en.wikipedia.org/wiki/Hyperloop

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#5
In reply to #2

Re: Magtube

05/20/2018 6:06 PM

Magtube would have the one tonne of air that enters with every train evacuated by a jet compressor as it is pushed towards it by the train instead of the full length like Hyperloop, Swissmatro or ET3

In my opinion Hyperloop would not work.

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#13
In reply to #5

Re: Magtube

05/21/2018 6:28 AM

I doubt it will survive its' first 'pink mist' event. Like the German maglev.

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#14
In reply to #13

Re: Magtube

05/21/2018 10:07 AM

Not sure if you are talking about Hyperloop or Magtube but I agree that one bad accident would be the end of either.

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#23
In reply to #14

Re: Magtube

05/22/2018 12:20 AM

Transrapid

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#36
In reply to #23

Re: Magtube

05/23/2018 1:06 AM

Yes I know about the Transrapid accident but I was not sure if you meant Hyperloop or Magtube but I think you meant Magtube

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#3

Re: Magtube Question

05/20/2018 1:28 PM

Welcome.

"Elon Musk's version of the concept, first publicly mentioned in 2012,[2] incorporates reduced-pressure tubes in which pressurized capsules ride on air bearings driven by linear induction motors and air compressors."

Personally, I'd rather have more, smaller sections controlled by smaller pumps, which would be easier to replace in case one failed.

Also. the concept of having the entire tube evacuated by a single mega pump makes me wonder what would happen in case a tube/capsule were stuck in the middle. How do these folks get oxygen?

Also the concept of building a tunnel through earthquake alley makes me fearful.

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#6
In reply to #3

Re: Magtube Question

05/20/2018 6:37 PM

Thanks for taking me seriously.

As it is very hard to get a deep vacuum with a single stage compressor there is the problem of pressure build up with Hyperloop, Swissmetro and ET3

Hyperloop address this by having a compressor on each pod.

Swissmetro want to have cut throughs near stations to recycle any air and at a slower speed.

ET3 think somehow they will be able to achieve high vacuum with single stage compressors and tiny tubes

None would be able to achieve the desired vacuum to go 1,000kph but using the train as the primary pump with a 300kw jet compressor to evacuate any air as it is pushed towards it would

A single jet motor on a passenger plane sucks in 2.5 tonnes of air per second and you could easily have a second one with back up power.

With it being a tunnel it cannot fall out the sky or off the elevated track and as it would have to be airtight people would stay put like in a tall building for four hours until pressure was normalized and help arrived.

Magtube would be three single tunnels Between Melbourne and Sydney with passing stations at Albury and Canberra costing $35b to build with $2b per year income and although around Canberra is mountainous I believe tunnels in that area would be safe.

.

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#7
In reply to #6

Re: Magtube Question

05/20/2018 7:28 PM

Take a look at these:

Pneumatic Vacuum Elevators: Home Elevator Manufacturers

Assuming the tunnel is close to sea level, -14.7 PSI is all the force you can generate. Not enough to achieve 1,000 kph without some other form of propulsion (is this the maglev to which you referred?) to push your system.

If maglev is in play, you don't need a hard vacuum.

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#8
In reply to #7

Re: Magtube Question

05/20/2018 8:16 PM

Even with maglev you need a deeper vacuum than 1 torr to prevent pressure build up and that is why Hyperloop need compressors on the pods and the only way to get this is with primary and secondary compressors.

With Magtube the tunnel would be 6m diameter with the train 5.6m so it would act as the primary compressor pushing any air towards the jet fan to evacuate it.

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#9
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Re: Magtube Question

05/20/2018 9:51 PM

"... need a deeper vacuum than 1 torr to prevent pressure build up ..."

By 'pressure build up', what precisely do you mean?

Are you describing a result of a decrease in volume of the tube on the side toward which the car/capsule is advancing? That would mean the car/capsule would be acting as a piston with very restricted flow around.

If

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#10
In reply to #9

Re: Magtube Question

05/20/2018 9:58 PM

yep

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#11
In reply to #10

Re: Magtube Question

05/21/2018 3:01 AM

You mention an engine off of a commercial passenger plane. While using off the shelf technology would be great for reducing development costs, that is probably unlikely.

Your target of reaching 1 torr is equivalent to an altitude somewhere around 125,000 ft. That isn't a height that jets typically run. The changes necesary to get a jet engine to run reliably and efficiently at those reduced pressures could be significant.

While some jet engines may be ingesting the tonnage of air desired when flying at 35,000 ft, the air is hundreds of times more dense at that altitude than at your 1 torr goal. Mass ingested near 1 torr should be far less.

Does the jet engine exhaust behind the car? This is going to cause problems with sufficiently ventilating the tube to maintain fresh air if for no other reason than subsequent cars coming through the tube.

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#12
In reply to #11

Re: Magtube Question

05/21/2018 3:59 AM

Sorry if I was a bit brief before.

Firstly it is a 5.6m wide train with ten seats per row as it has to have sufficient capacity to kill air travel on the Sydney to Melbourne route with immediate $2b per year income.

I only used the jet compressor as an example but perhaps it would not be too hard to drive one with a 300 kw electric motor.

The 2.5 tonne per second is on the airstrip taking off and even though the vacuum in the tunnel would be as low as possible to reduce power consumption by the maglev train I would expect the air at the jet compressor would be far greater than that in the tunnels but I do not see any problem if is lower than cruise density.

At 1,000kph the northbound trains would only take 15 minutes to clear the single tunnels while the southbound are in the passing stations and that should be ample time for the axial compressor to expel the one tonne that enters with every train through the double doors.

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#15
In reply to #12

Re: Magtube Question

05/21/2018 2:11 PM

1000 kmhr = 277 m/s

6m diameter is about 28 m2 area. That leads to a little over 7750 m3/s at stp

Instead of trying to get down to 1 torr, use a figure in the ballpark of pressure at cruise altitude for commercial airliners. Fot convenience lets use 152 torr as it is about 1/5th of sealevel atmosphere. For ease of estimate an isothermal pressure to 1/5 initial leads to 5 times the volume so 38,750 m3 /s

Compressing back to sea level pressure is a change in volume of 31,000 m3 /s or 31,000,000 l/s

Assume a very efficient compressor is using an average pressure 0.4 atm for the volume reduction so roughly 300 torr.

1 l*atm requires a little over 100J

12,400,000 l*atm/s is about 12,400,000,000 J/s or watts.

That is just a ballpark, but 12 million kilowatts is a ginormous ball park. Even if the estimate is hifh by several orders of magnitude, it is still daunting at best.

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#17
In reply to #15

Re: Magtube Question

05/21/2018 4:26 PM

I may have misunderstood you but this is what I was thinking.

If a jet uses about 300kw just to turn the compressor then if the air pressure is lower than that, which it would be, then the axial compressor would use less and as you would only have three operating at any time 24/7 I worked it out at $1m worth of electricity per year plus a some for the maglev train.

Basically I moved away from m3 and into tonnes of air with my thinking.

The axial compressor would not have to create a vacuum but just evacuate any residual air that is pushed towards it by the train to prevent any pressure build up.

I am not sure if I have answered you properly but thanks for the discussion.

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#24
In reply to #17

Re: Magtube Question

05/22/2018 1:09 AM

I thought you were suggesting using a turbine to evacuate air in front of the tube vehicle quickly enough to draw a significant vacuum and pressurize it back up to starting point which I presumed was ambient. I thought you were proposing using a turbocompressor on each vehicle instead of evacuating the entire tube.

The reason so much power was required is because (I mistakenly understood) the compressor needed to move a huge volume quickly to a higher pressure. If the change in pressure is much less, then much less energy and therefore power would be required for the scenario.

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#25
In reply to #15

Re: Magtube Question

05/22/2018 1:25 AM

if the system is Mag-Lev, and we're talking about 120 to 250 mph, which is a reasonable speed, and still provide a comfortable ride in a reasonable trip time, at a relatively safe speed and very doable within the world of Mag Lev engineering, why do you need a vacuum in the tube anyway?

A simple 'flap-valve' or spring controlled system could easily be engineered to both relieve air pressure before the vehicle and accommodate the vacuum created after the vehicle, forgive the pun, but a more 'passive' and responsive air venting system. Not requiring highly expensive pressurized control engineering or 'motorized' support systems in need of constant maintenance oversight.

Why not start with a comparatively simple and very functionally engineered system that ( relative to what has been discussed here) works, makes money, has acceptable speed between destinations and makes money, with financial return ratios providing a faster investment/cost recovery. From that beginning, 'gear heads' can propose and design more sophisticated systems, over time and insuring better safety and functionality, not to mention better investment returns.

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#32
In reply to #25

Re: Magtube Question

05/22/2018 6:21 PM

The NWRL tunnels cost AU$1.15b for 15 kilometres of twin tunnel which works out at $38m per kilometre so as each of the three single tunnels between Melbourne, Albury, Canberra and Sydney are around 200 kilometres they would cost $7.6b each and if the trains can go 1,000kph you can save half the cost of twin tunnels.

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#65
In reply to #25

Re: Magtube Question

05/27/2018 11:49 PM

".... why do you need a vacuum in the tube anyway?...."

If you don't need a vacuum then you don't need a tube. The project could be much less expensive without the tube and without having to dig a hole. It will also take less power to push the train without a tube if no vacuum is used ib either case.

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#66
In reply to #65

Re: Magtube Question

05/28/2018 1:56 AM

No, takes it 27 times more power to push an atmospheric train along at 500kph than 100kph and there is no point in just competing with planes you need to be cheaper, faster, more reliable and comfortable than them on a very busy route to guarantee a monopoly.

The Japanese Maglev is limited to 500kph by the atmosphere even with the huge tunnels and tiny trains and even it has to have 86% tunnels to maintain a straight line.

The three axial compressors would use 1MWh between them 24/7 so over a year at $100 per MWh it is 8,760 x $100 = $866,000 per year plus a tiny bit to run the maglev with deep vacuum and Sydney/Melbourne income $2b and $30b to build over ten years because with it able to go 1,000kph there is only a need for single tunnels.

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#67
In reply to #66

Re: Magtube Question

05/29/2018 8:10 AM

Your estimate for pumping down is low, significantly.

Jets on airplanes move high volumes of air from one point to another point that is at roughly the same pressure. it takes much more work to move large volumes of air from one point to a point at higher pressure. If the process is to be completed iin a short amount of time then the power required is similarly much more.

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#16
In reply to #12

Re: Magtube Question

05/21/2018 2:21 PM

The other big problems:

It would be exteremly difficult to pull air in so fast as to draw just a vacuum just locally. It will just have to pump down the whole tube. having a local low pressure woulds require somerhibg akin to a shockwave.

Also, as air i drawn towards ths car, the relative speed between car and air increases so drag does as well.

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#18
In reply to #16

Re: Magtube Question

05/21/2018 4:32 PM

The residual air would be pushed away from the train towards the axial compressor which would then act like a second stage evacuating it so at no time is it required to create a vacuum.

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#58
In reply to #7

Re: Magtube Question

05/27/2018 5:34 AM

If you want to go 1,000 kph you do.

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#19

Re: Magtube Question

05/21/2018 11:16 PM

Will it be possible to have concentric tubes, the outer one having openings at intervals, may be for every the length of the train, or even like windows, so that the air pushed out by the train, could get back to the back of the train, where vacuum is created, so that the problem of high vacuum, creating it, sealing it from the inside of the train ?

May be crazy, but it would be a one time investment .

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#21
In reply to #19

Re: Magtube Question

05/21/2018 11:32 PM

Unlike Hyperloop or Swissmetro The Magtube concept is to have such a deep vacuum there would almost no resistance to the train like ET3 but where they want to have single stage compressors the whole length Magtube would have a 300kw axial compressor evacuating any build up of air in front of the train as it approaches it.

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#27
In reply to #21

Re: Magtube Question

05/22/2018 8:25 AM

I don't think you have any experience in vacuum technology. Vacuum pump theory will prevent any time saving due to the large volume of space in front of the passenger capsule and entering the Magtube. Achieving the proposed medium vacuum level (2.65*10^15 molecules/cm3 at 1 mbar) can take hours when things seal properly.

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#28
In reply to #27

Re: Magtube Question

05/22/2018 9:57 AM

{I ran out of time to finish. }

Turning your rail system into a contained tube instead of an open rail does mitigate collisions with unsuspecting fauna. It also immediately poses the problem of what to do with the air in front of and behind this speeding rail car. Evacuating the air before and after the rail car mitigates this problem but at considerable engineering and passenger time expense. An active blower either on the rail car itself or along the tube length might reduce some aerodynamic drag on the rail car but at what cost?

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#30
In reply to #28

Re: Magtube Question

05/22/2018 5:50 PM

The closer you get to perfect vacuum the less energy use by the train but then like you say you have to consider the cost of evacuating the residual air for which Magtube would be around $1 million per year.

To get very deep vacuum you need a two stage compressor and using a 5.6m diameter train in a 6m diameter tunnel not only allows the train to act as the primary compressor but allows ten seats per row allowing the capacity needed to kill air travel on that route as everybody wants to travel around the same time.

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#34
In reply to #30

Re: Magtube Question

05/22/2018 9:20 PM

The less energy used by the train but at what energy and time cost to achieve the vacuum.

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#35
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Re: Magtube Question

05/23/2018 1:01 AM

Then there is the logistics of trying to send a train faster along a track. Going fast means pushing air out of the way, which also requires a lot of power. A train travelling at 300mph (480km/h) uses roughly 27 times more power than one travelling at 100mph (160km/h). And at ground level the air is a lot denser than it is at 35,000ft (10,600m) where airliners regularly cruise. That means more resistance, and therefore more vibrations. http://www.bbc.com/future/story/20140813-the-challenge-to-make-trains-fast

Many people have known for a long time that it is mainly the air resistance that uses most energy when a train goes fast but until now there have not been the Tunnel Boring Machines or Axial compressors to make a vacuum train and until one is made I do not believe we will know what level of vacuum can be achieved therefore the energy use by a maglev train cannot be worked out by computers in my opinion.

Although there would be six 300kw axial compressors removing the one tonne of air that is pushed towards it by the Magtube train there would only be three operating at once 24/7 so 900kw x 8,760 hours per year = 7,884,000kwh = 7.884MWh @$100 per MWh = $784.4 per year, please pick me up if I have made a mistake here.

Initially it would need the train to go back and forward pushing the air out the tunnel at increasing speed but once vacuum was established there would only be the one tonne that enters the tunnel through the double doors with every train and the train could go immediately the tunnel was clear.

Sydney would leave at 5, 5.30, 6, 6.30 etc. waiting at the passing stations at Canberra and Albury 15 minutes

Melbourne would leave 5.15, 5.45, 6.15, 6.45 etc. waiting at the passing stations at Albury and Canberra 15 minutes.

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#37
In reply to #35

Re: Magtube Question

05/23/2018 1:50 AM

I think it’s a significant attraction to have a system where these high speed trains would leave major cities on the hour , every hour.

To me , it adds a perception of reliability when you don’t need to look up timetables because you just know they are punctual on the hour. As you say , half hourly might become necessary but at the beginning , perceptions are important .

intermediate stops like Albury / Goulburn etc don’t matter so much if they have that waiting time in my opinion.

good luck with finding simple elegant safe reliable systems to achieve the numbers on resistance versus speed.

getting the engineering right is one thing however this country has a reputation with our politicians buying the wrong s**t at the wrong time and paying 30 x more for it than what it should have been :(

dont let that discourage you though.

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#40
In reply to #35

Re: Magtube Question

05/23/2018 4:57 PM

"Initially it would need the train to go back and forward pushing the air out the tunnel at increasing speed but once vacuum was established ..."

This sounds magical. How is a train, with compressor aboard, traveling down a sealed tube removing gas from the tube? Is it filling compressed air tanker cars in tow? If so, the time to reduce pressure significantly will be very very long with only 300 kw, or more than 300 kw will be needed.

.

"... there would only be the one tonne that enters the tunnel through the double doors with every train ..."

Where is this one ton figure coming from? How long is the imagined train? How quickly does it move through and how big is the gap?

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#41
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Re: Magtube Question

05/23/2018 5:39 PM

Only some magic fairy dust enters when the doors opens.

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#43
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Re: Magtube Question

05/23/2018 5:46 PM

No, the double doors would be hydraulically operated and tightly sealed when closed

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#44
In reply to #43

Re: Magtube Question

05/23/2018 9:21 PM

And when opened these doors are not sealed. Since your train levitates (magLEV) then where is the seal?

I can tell, you've never actually worked with vacuum of any better quality than an engine intake manifold.

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#47
In reply to #44

Re: Magtube Question

05/23/2018 9:38 PM

Double doors have been used for many years in mines etc. and as long as you do not open them both at the same time there is no problem but if however they are both left open at the same time they would be very difficult to close and they accidently left both open with the Brooklyn bridge caissons where they almost drowned in 1869.

I have worked in an underground coal mine 25 years and have much experience with double doors.

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#48
In reply to #47

Re: Magtube Question

05/23/2018 9:44 PM

Theoretically, not necessary that any air enter with loading and unloading.

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#50
In reply to #48

Re: Magtube Question

05/23/2018 9:51 PM

I am after simplicity, economy and reliability.

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#51
In reply to #47

Re: Magtube Question

05/23/2018 10:42 PM

Double doors:

Air lock:

Except in your proposal one of the two walls with a door must be able to move for it will be your train door. Now the size of the airlock region does not have to be deep enough for a person to stand between airlock doors. However you will still have difficulty sealing the walls to minimize leaks at one torr (~ one mbar) with most flexible seals.

Your proposal will also dwarf the volume of the largest vacuum chamber in the world. You do not understand vacuum systems.

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#57
In reply to #51

Re: Magtube Question

05/27/2018 5:30 AM

Sorry about using the old mining term “double doors” when I should have said a 200m long airlock.

One door would open allowing the train to enter then it would be completely closed before the other one opens allowing about one tonne of air to enter the tunnel.

When it reaches the next station the tunnel door would open allowing the train to enter and when closed it would open the station door to allow the train into the station and the waiting train to then enter the airlock.

These doors would be made of substantial steel and such an angle so as the extreme air pressure would make a complete seal.

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#61
In reply to #57

Re: Magtube Question

05/27/2018 6:26 AM

This implies your train, tunnel door clearance cross sectional area will be less than 4.4 m2 . I still say you don't understand vacuum.

Your proposal and the Hyperloop will have similar vacuum problems but SpaceX is properly attempting to solve this and other problems with experimental prototypes. If you think you have a better idea, build it.

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#62
In reply to #61

Re: Magtube Question

05/27/2018 7:05 AM

Magtube is for people who want to travel between 200 to 1,000 kilometres and SpaceX I thought was to get people from one side of the world to the other in rockets.

The roadheader used for the station would make the excavation for the air lock and double doors as big as required but at least 30m2 so I don’t understand your 4.4m2

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#63
In reply to #62

Re: Magtube Question

05/27/2018 7:18 AM

SpaceX is the company building Hyperloop. It seems you don't even know who you are trying to copy.

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#64
In reply to #63

Re: Magtube Question

05/27/2018 7:26 AM

I am not trying to copy anyone.

A train in a vacuum tube has been talked about for years but it is only now we have the TBM for the straight tunnel required and the axial compressors available.

I think Hyperloop would not even work even in a flat desert let alone where you have mountains.

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#45
In reply to #43

Re: Magtube Question

05/23/2018 9:26 PM

That does not explain how a train with a compressor aboard removes air from a sealed tube in which it travels back and forth.

Are you imagining air being compressed into tanks?

The energy required to move a mass of air from one location quickly to another location that is roughly at the same pressure is not a good reference for estimating how much energy is required to move a mass of air from one location to anothet location that is at a much higher pressure than the first. Basing your idea of energy consumption on a turbine used aboard an aircraft is leading you to a fanciful conclusion.

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#42
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Re: Magtube Question

05/23/2018 5:44 PM

Many people do not get it so I will try to be more explicit.

The Magtube train is Japanese maglev with ten carriages 20m long by 5.6m in a 6m by 200km tunnel and at 1,000kph would push any residual air towards the axial compressor to evacuate it.

Initially the tunnel would have atmospheric pressure so the maglev train would be unable to attain top speed due to air resistance but as the air was evacuated and pressure reduced it could go faster until it reached peak vacuum.

The compressed air I mentioned would only be a reserve to replenish air in the carriages in case of breakdown.

Volume between the double doors is 200m x 6m = 5,654m3 less train 200m x 5.6m = 4,926m3 = 728m3 @ atmospheric pressure = 728 x 1.2754 kg = 928.4912kg or one tonne.

Do not hesitate to ask if I have not explained sufficiently.

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#46
In reply to #42

Re: Magtube Question

05/23/2018 9:32 PM

".... push any residual air towards the axial compressor to evacuate it...."

Evacuate it to where? How is the compressor onboard the train connected to the outside...if that is where it is evacuating to?

Do you imagine this evacuation to take place within each single trip or to build over many trips?

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#49
In reply to #46

Re: Magtube Question

05/23/2018 9:49 PM

There is NO compressor on the Magtube train.

Air would be evacuated to the atmosphere by the axial compressor adjacent to the next station as it is pushed towards it by the Magtube train.

Assuming the train had created the initial vacuum then there would only be the one tonne to evacuate every trip and that would be easily done with the axial compressor over the 15 minutes the train is in the tunnel.

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#52
In reply to #49

Re: Magtube Question

05/23/2018 11:32 PM

It sounded like you had the compressor on the train.

Pumping down that ton of air will not really be that easy. It will be even harder if you release it to the main volume instead of pumping it out when locked in your airlock.

Even behind your airlock, if you want to get down to 1 torr in say 15 minutes, your 300 kw estimate is low by somewhere around a factor of at least 20.

Think about it this way. The volume you estimate between train and airlock was what 728 m3 ? To get down to 1 torr is like having a cylinder with a crossectional area 728 m2 with a piston 1 m off the bottom then raising that piston to a height of 760 m in the cylinder without leaks against atmospheric pressure.

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#59
In reply to #52

Re: Magtube Question

05/27/2018 5:58 AM

No sorry, I meant that it would be good to have a cylinder of compressed air in each carriage to maintain the atmosphere within the carriage in case they had to wait four hours for help.

The one tonne of air that enters with every train would have a negligible effect on the volume of the 200 kilometre x 6 m diameter tunnel and given it would take 15 minutes for the train to travel to the next station the axial compressor would have plenty of time to evacuate it as it is pushed by the train.

If a commercial jet uses about 300kw for the compressor and can suck up to 2.5 tonne per second it should easily evacuate one tonne in 15 minutes.

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#68
In reply to #59

Re: Magtube Question

05/29/2018 12:44 PM

To release the amount of air at atmospheric pressure you describe in the airlock into 200km of tubing will raise the pressure to roughly 1.01 torr. To pump down 200km by 6m diameter from 1.01 torr to 1.00 torr is, at best, the same as sliding a frictionless leak-free 6m diameter piston against atmospheric pressure 1% of the 200km.

9π m2 × 101325 N/m2 x 2000 m = ~5.7 billion jules.

Completed over 900 seconds requires 6.36 million watts. So 6360 Kilowatts. That's neglecting a minute amount of pressure of less than 2 torr helping, which is dwarfed by the exception of assuming everything is running at 100% efficiency and there are no leaks.

Your power bill will be at least 21 times your initial estimate at best.

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#69
In reply to #68

Re: Magtube Question

05/29/2018 2:33 PM

As I said, he knows nothing about vacuum systems.

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#71
In reply to #69

Re: Magtube Question

05/31/2018 2:40 AM

Maybe you could help?

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#72
In reply to #71

Re: Magtube Question

05/31/2018 5:17 AM

Vacuum technology is an esoteric field of its own. Here is a nice introductory article designed to also sell this company's pumps. (Warning: Units of vacuum pressure are not well standardized and baffling. Even this introductory paper switches between units without an explanation.)

First you have to understand the implication that a gas is an expandable fluid. On average each molecule has enough kinetic energy to overcome the attractive forces of adhesion and cohesion with all other molecules in proximity. A gas molecule is constantly moving (kinetic energy) in any direction until it's electron cloud "collides" with the cloud of another molecule. When these gas molecules are dense enough (rough vacuum {inches of H2O}) opening a valve will allow higher pressure gas to flow to a lower pressure region. This is how mechanical roughing pumps work. Eventually the molecules in the region to be pumped down become sparse enough that they don't rush into the valve opening before the valve closes. This is when a secondary (turbo) pump (usually with a much larger entry opening) adds energy to molecules that pass through it to raise the pressure for entry into the roughing pump.

The rate this all happens depends on the differential pressure difference between each region. Thus the rate of pressure drop will be an exponential curve. The amount of time it takes to pump down the first half of the molecules removed will be the same amount of time to remove the next quarter of the original molecules.

Then there is the complication of outgassing. During the pump down cycle many liquids and solids (water droplets, pollen, dust, etc.) now succeed in becoming a gas. So while you are expecting five time constants of your pumping capacity to drop pressure to expected levels, more molecules are becoming a gas.

Then there is the fun of a small leak. Often such a leak will be hard to notice for the first one or two pumping time constants.

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#79
In reply to #72

Re: Magtube Question

05/31/2018 5:22 PM

Thanks for that.

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#70
In reply to #68

Re: Magtube Question

05/31/2018 2:36 AM

Thanks for your expertise as like redfred says I am not an expert on vacuum.

Here is my working out

The airlock would be 200m x 6m = 5,654 m3 less train (200m x 5.6 = 4,926 m3) =728m3

The tunnel at 200km x 6m = 5,654,866 m3

728 divided by 5,654,866 = 0.00012874 of one atmosphere = 0.0978414 Torr after the one tonne enters the tunnel.

It is a bit beyond me to know exactly what power they would use 24/7 because most of the time they would have almost no load until the pressure built up in front of the train perhaps you could help me here.

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#73
In reply to #70

Re: Magtube Question

05/31/2018 7:55 AM

Your units are wrong. Multiplying two linear measurements (meters) produces an area result (meters^2). To achieve a volume (meters^3) there must be a third linear value.

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#74
In reply to #73

Re: Magtube Question

05/31/2018 9:52 AM

Sorry if I misled you I was using the volume calculator http://www.calculator.net/volume-calculator.html

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#75
In reply to #70

Re: Magtube Question

05/31/2018 10:54 AM

The rough estimate I made was based on your numbers (That is quite a blunt nose for a highspeed train. Also, there needs to be clearance allowing the airlock door to function. A door sealing a decent vacuum shouldn't have to accomodate thermal expansion of a 200m train.)

There are countless ways with a range of possible efficiencies the tube could be pumped down. The process or combination used will always require more energy than the calculated estimate.

So even with the train behaving like a first stage and then another pump continuing the process, you can know that the energy used to pump the tube down being a combination of energy used ny the pump and additional energy used by the train to attain a certain speed due to pumping action will always be greater than the perfect efficiency calculation.

.

One way to slightly reduce the energy required would be to avoid releasing the air in the airlock to the main tube by pumping down the airlock prior to opening the airlock doors. This will also help maintain airlock door integrity and seal. Additionally when bringing the airlock uo to atmospheric pressure, energy could be recovered from the dp and inflow of air offsetting a little of the pump down .

The problem witg pumping down the airlock is it takes time, so extends travel time. Reducing the time required higher capacity pumps that use more power. So instead of say 20MW running continuously on a track that opened its airlock every 15 minutes, you might need 200MW that ran for 1.6 minutes every 15.

The problem with things like leaks, adsorption, bake out, etc still are concerns.

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#78
In reply to #75

Re: Magtube Question

05/31/2018 5:16 PM

Not only does a straight tunnel allow a faster train but it avoids expansion joints, farmers and houses so the only leaks, if any, would be at the airlock doors.

The airlock would of coarse be sufficiently longer than the train but as it would not make much difference for simplicity sake I just rounded it off.

The more piston effect the better to get a deeper vacuum and with the train as the primary pump it allows the deep vacuum of 0.0978414 Torr ( I had used the volume calculator http://www.calculator.net/volume-calculator.html when working out volumes) and confused redfred.

I strongly oppose vacuum pumps all the way because to me it would pull the train back rather than in the direction of travel and as I said to redfred most of the time the axial compressors would have no load so it is very hard to work out how much energy they would use 24/7

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#80
In reply to #78

Re: Magtube Question

05/31/2018 5:26 PM

It isn't hard to work out a minimum energy/power required to pump down the volume to offset an introduction of a certain amount of gas with each cycling of the airlock/repeated in a certain time frame.

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#81
In reply to #80

Re: Magtube Question

05/31/2018 6:20 PM

I gotta go now but perhaps you may give me a clue as the axial compressor in my opinion would have no load at all for the first 100 kilometers or 7 minutes.

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#83
In reply to #81

Re: Magtube Question

05/31/2018 9:38 PM

No, you ... Your compressor will be working hard to keep the atmosphere from roaring back through the pumping mechanism into the tube thus filling the tube with one atmosphere of air. It's easy to maintain a good vacuum in geostationary orbit. Here at altitudes that will sustain the lives of your passengers one must work very hard or smart to maintain a vacuum.

Ignorance is curable...

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#85
In reply to #83

Re: Magtube Question

06/02/2018 3:02 PM

What confused me was the domestic vacuum cleaner increased revs when suction was blocked but yes you are right.

Bear with me as I am no expert on maglev or vacuum or anything for that matter but I see the problem is the pressure build up in front of the train once you reach the Kantrowitz limit so I suggest using the train to push the residual air towards the evacuation compressor which is closed to the outside atmosphere only to open and start once the build up was sufficiently high.

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#60
In reply to #52

Re: Magtube Question

05/27/2018 6:04 AM

No sorry, I meant that it would be good to have a cylinder of compressed air in each carriage to maintain the atmosphere within the carriage in case they had to wait four hours for help.

The one tonne of air that enters with every train would have a negligible effect on the volume of the 200 kilometre x 6 m diameter tunnel and given it would take 15 minutes for the train to travel to the next station the axial compressor would have plenty of time to evacuate it as it is pushed by the train.

If a commercial jet uses about 300kw for the compressor and can suck up to 2.5 tonne per second it should easily evacuate one tonne in 15 minutes.

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#55
In reply to #35

Re: Magtube Question

05/27/2018 4:54 AM

Previously I had worked it out at about $1m per year so this is a simpler way to work it out.

As only 3 axial fans would be operating at any one time that is 900 kw per hour for each hour 24/7

Rounding this to 1MWh @$100 per MWh for 8,760 hours per year=$876,000 per year.

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#22

Re: Magtube Question

05/21/2018 11:44 PM

wouldn't the minimal air design within the chamber, flow over and around the 'train' as it moved though the tunnel? One would expect such a 'missile' to be somewhat designed to facilitate maxi movement in that environment. Personally I like the idea that solar energy could support the high demands of a mag-Lev system that would function during supportive daylight hours....Nat gas could cover the balance of the 24 hours if needed. (not an engineer, just an observer )

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#33
In reply to #22

Re: Magtube Question

05/22/2018 6:41 PM

I am in favour of renewable energy also not wasting it by pushing heaps of air with trains so if it is possible to create a near vacuum for a little over $1m per year electricity cost then the only problem is the cost of building Magtube.

Regarding movement in the tunnel I believe the air over 500kph can cause movement in atmospheric trains but as Magtube would be a 5.6m diameter train in a 6m diameter tunnel with very little air I see no problem.

There may be some very small amount of air going around the 1,000kph train but insufficient to cause any problem.

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#26

Re: Magtube Question

05/22/2018 3:46 AM

There is, I imagine, a question as to whether the entire column of air will travel at a uniform velocity,

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#31
In reply to #26

Re: Magtube Question

05/22/2018 6:02 PM

I think by having the tunnel 6m diameter it would be far more likely to have a more uniform velocity of residual air than ET3 which uses very small elevated tubes

Single compressors along the entire length instead of in the direction of travel would in my opinion actually restrict the movement of any air.

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#76

Re: Magtube Question

05/31/2018 11:05 AM

With all of the discussion about vacuum levels, I see one additional problem that hasn't been brought up until now.

The point of magnetic levitation and moving in a vacuum is to get as close to zero friction as possible. In a low friction environment how does one apply a force to the train to get it to move or stop? Remember, you have to do this without using a patented process.

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#77
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Re: Magtube Question

05/31/2018 4:50 PM

The Japanese maglev can accelerate and slow faster than a conventional train and their government is so keen to sell the technology they will give any country an interest free loan to build it.

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#82
In reply to #77

Re: Magtube Question

05/31/2018 9:27 PM

It's not a Japanese design. The Japanese government nor any of their companies do not own this patent. I worked in a different department of one of the two inventors. He is probably spinning in his grave. He and his co-inventor were both very generous in the use of their technology but you obviously also know little about maglev.

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#84
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Re: Magtube Question

06/02/2018 2:36 PM

The Japanese EDS system seems the simplest to me and as their government is prepared to loan the money cheaply to any country to showcase it I think it only fair to buy the technology off them.

I find it very hard to guess how much the track would be over a long distance with all the material mined here in Australia and the reduction in cost with mass production.

It may be right for Japan to use 500kph atmospheric trains but here in Australia with greater distances a smaller cheaper tunnel with a bigger faster train would be worth the effort of reduced atmosphere I think.

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#86

Re: Magtube Question

06/04/2018 10:02 PM

Thought I may get a bit more assistance with Magtube from Fuser Forums but the question they ask to register is beyond me.

N4me 7h3 gas usseed 1n amateur n3utron pr0duclng fus0rs f0llowed buy the3\ n0mb3r of n3utr0ns it c0ntalns. No spaces and all lower case.:

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#87
In reply to #86

Re: Magtube Question

06/05/2018 12:29 PM

deuterium1

If not then

tritium2

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#88
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Re: Magtube Question

06/05/2018 4:10 PM

Thanks mate I worked it out and am on the new starters part, 42 views but no comments yet maybe wrong forum.

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#115
In reply to #86

Re: Magtube Question

11/18/2019 1:30 AM

I just registered this Fusor Forum, and the question is hard for me, could you tell me the answer?

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#89

Re: Magtube Question

06/29/2018 6:48 PM

After talking with a mate I now believe it will be possible to use only the train as the vacuum pump.

The proposed demonstration would consist of a weighted loose fitting piston within a long tube with a ball valve at either end so when the piston is released from the top end air would be forced out the bottom until bubbles stopped in the water bucket at which point the tap would be quickly shut, piston securing magnet applied and tube inverted so when the securing magnet is released the process is repeated.

As the vacuum is increased in the tube the time for the piston to travel to the bottom would become shorter demonstrating it only needs the train, an airlock that can accommodate the train and an exhaust valve both ends to push the one tonne of air that enters with every train out the tunnel exhaust valve adjacent to the next station.

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#90
In reply to #89

Re: Magtube Question

06/29/2018 8:57 PM

".... a weighted loose fitting piston within a long tube with a ball valve at either end so when the piston is released from the top end air would be forced out the bottom until bubbles stopped in the water bucket at which point the tap would be quickly shut, piston securing magnet applied and tube inverted so when the securing magnet is released the process is repeated. ...."

.

Yes, you definitely need to do this. It should help clear up (or at the very least, make it much more difficult to ignore) some of the fundamental misconceptions of which you so far seem unable to be discouraged.

Just a suggestion, rather than trying to operate a ball valve at just the right time, you might use a check valve (or two on series).

Regardless, you will find very quickly that the loose fitting piston will develop most of its travel related the leakage past inherent with its loose fitting nature. The more snug fitting piston will very quickly reach a point where air expelled from each inversion is negligible.

Please, don't take my word for it. This experiment is easy and cheap and worth countless explanations.

Oh, one more thing, if you do insist on having the tube ends expell gas under water for proof, the shallower the water, the less backpressure you will have to fight against. If you try this trick with a gravity only inverting cylinder and piston against even the mild back pressure of a foot deep bucket, depending on the set up, you might not even obtain any vacuum relative to local atmosphere at all.

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#91
In reply to #90

Re: Magtube Question

06/29/2018 9:51 PM

Thanks heaps for your interest

When I spoke to my mate I suggested a good seal piston but he said if you did that it could only go so far and the vacuum above would prevent it going any further until I allowed more air in the top of the pipe which would then defeat the purpose of the piston.

After a good nights sleep I thought that the trick is to allow some air to get past the piston just as would happen with a 1,000kph 5.6 metre diameter train in a 6 metre diameter tunnel.

At present I am thinking about 10 metre of 100mm diameter plastic pipe with a one metre piston and just exhaust check valves while standing on my brothers patio to invert it.

Off to the shops now and will get back with any results.

Here is hoping Eddy

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#92
In reply to #90

Re: Magtube Question

06/30/2018 12:09 PM

I agree that experimental data should reveal some of the misunderstandings but I'm leery of using water for a gas bubbling valve system. Such a water trapping system is actually making a water barometer. Atmospheric pressure levels on the water surface will change the actual pressure internally.

On second thought, this approach can provide very good, repeatable data on precisely the question I believe should be explored. Set up the tube in the water to allow a difference measurement of in water levels, both inside and outside the tube. This difference will reflect the vacuum level in the tube. After a drop you will have to wait for water levels to settle and observe that air did not return back to the tube. To repeat with a partial vacuum to simulate a second mass pushing gas out just make the difference in water levels the same as the previous difference. Raising the tube or adding a vacuum pump tap will work.

The drawback of this experiment is the maximum acceleration will be only due to the very modest but constant force of gravity until one approaches the terminal velocity of this fluid dynamics of this system. Speaking of terminal velocity, increasing the terminal velocity is precisely the effect evacuating a chamber will provide. So if Edward wishes to time the transit time (opto-coupler sensors?) of falling under different vacuum levels he can then extrapolate from the data of many tests what is the terminal velocity and therefore back pressure resistance for a body falling in a tube.

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#93
In reply to #92

Re: Magtube Question

06/30/2018 6:54 PM

For simplicity I will now have exhaust valves both ends rather than messing about with water.

It will be a very simple demonstration and I was encouraged by dropping one end of the piston through a short pipe hard on the carpet that took 3 seconds where lifting the pipe up 100mm the piston dropped as it would outside the pipe.

Another encouraging video was Brian Cox video https://www.youtube.com/watch?v=E43-CfukEgs that demonstrated the resistance of air.

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#94

Re: Magtube Question

07/22/2019 2:31 AM

Which glasses are suitable for reading?

i am truly an issue for this question please help me

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#95
In reply to #94

Re: Magtube Question

07/22/2019 6:30 PM

Reading glasses.

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#98
In reply to #95

Re: Magtube Question

07/23/2019 4:44 AM

Thank you so much

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#96

Re: Magtube Question

07/22/2019 6:52 PM

Getting back to the real world

I realised that if 30% of Chinese Magtube would be in tunnels then they would have to use the train as the compressor because it would be very difficult to have vacuum pumps every so often along them.

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#97

Re: Magtube Question

07/23/2019 4:43 AM

Multiply the number of lowercase letters by the number of uppercase letters from the following text: 74 "3J! GhZ & üK8VGz6j Write the result as a word !:

Please Answers this question from forum site big error

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#102
In reply to #97

Re: Magtube Question

07/29/2019 10:58 AM

twenty-four

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