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Brunel's Atmospheric Railway - could it ever have worked properly?

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Shimbleshanks

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As students of railway history will know, Brunel's bold attempt to build a railway worked by atmospheric power in Devon eventually came to naught. While it did hold out the attractive prospect of a railway without heavy locomotives, able to tackle with ease steeper gradients than locomotive-worked lines of the era, in the end the problems of maintaining an airtight seal in the vacuum pipe with the materials of the time (basically, greased leather flaps) proved too much. The system was prone to frequent breakdowns which were particularly disruptive, because a leak in the pipe brough all trains on the line to a stop.

But if Brunel had access to more modern materials would he have been more successful? A few years later, vulcanised rubber was invented, which might have been more succesful at maintaining the seal than leather.

Eventually, I guess, electric traction would have proved to be more attractive than atmospheric power but in the meantime it would have meant a railway free of expensive, heavy, dirty locomotives. Driving an atmospheric train would, I guess, have been a less skilled, specialsed job and it could of course have been done by one man, not two. Could it have changed the course of railway history?
 
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yorksrob

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I just don't see how it could have worked. Surely the air would have leaked past the leather flap, even if the rats hadn't nibbled it !
 

pdeaves

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As an related aside, the pumping station at Starcross used to house an atmospheric railway museum. It included a short (indoor) demonstration line powered by a vacuum cleaner. Admittedly only a short length and in ideal conditions, it did however show what could have been possible with modern materials.
 

O L Leigh

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Well there is the Aeromovel system used in a cultural theme park (Taman Mini Indonesia Indah) in Jakarta and at the Porto Alegra Airport in Brazil that work by atmospheric pressure. However, these are lightweight driverless metro-style trains rather than powerful locomotive substitutes. That said, they do prove that atmospheric railways can be made to work.

Slightly less conventional is Flight Rail Corp's 1/6 scale demonstrator. This is not physically attached to the piston but rather uses magnets to couple the train to the piston which permits a fully sealed tube. Whether this would be acceptable for a full-sized train is open to debate.
 

John Webb

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The principle limitation in using atmospheric pressure is the relatively small amount of force available as you only have 1bar/14.5psi available at best. If Brunel had used the system to work at a higher pressure by pumping air in rather than sucking it out it's possible he'd have done better, even with the materials of his day?
As trains grew in size and length (and therefore weight) there would have been even more problems, I think.
 

randyrippley

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rats will chew and eat vulcanised rubber, so you'd need to find an environmentally sound way of poisoning them along the whole length of the line
 

edwin_m

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The principle limitation in using atmospheric pressure is the relatively small amount of force available as you only have 1bar/14.5psi available at best. If Brunel had used the system to work at a higher pressure by pumping air in rather than sucking it out it's possible he'd have done better, even with the materials of his day?
As trains grew in size and length (and therefore weight) there would have been even more problems, I think.
Based on various quick web searches:

A 22 inch diameter pipe was proposed for the later extension up the Devon Banks. If this was inside diameter the cross-section area would be roundly 0.25 square metres. The maximum theoretical tractive effort is obtained by multiplying this by atmospheric pressure, the result being about 2.5 tonnes force if I have my figures right.

Tractive effort of "Lion", built in 1838 so a little before the South Devon Railway, was 2160lbf or about 1 tonne. Taking into account the difficulty of achieving anywhere near the theoretical performance, the atmospheric railway probably wasn't much ahead of the locomotives of the time although with the benefits of not having to rely on adhesion or move the weight of the locomotive around. Locomotive technology was of course advancing rapidly, and there was always the option of adding a second locomotive if the train was too heavy.

There were also numerous practical difficulties, not least the impossibility of points. And while station stops could have been done by the operator stopping the pump as he observed the train arriving, how would a train be stopped out of course in emergency?

Just found this interesting post which broadly confirms my calculations: http://www.mrol.com.au/Pages/Vu/AnAtmosphericConspiracy
It also suggests:
Clearly Brunel was a man of exceptional ability but I am led to ask why did he promote the Atmospheric system of propulsion for the South Devon Railway? It was a system which the simplest of arithmetic clearly shows was physically impossible.
...
I suspect that the railway, which was built, together with steam locomotive propulsion, was exactly what was intended from the beginning and that Brunel and the directors of the South Devon Railway conspired to deceive objectors, landowners and Parliament into thinking that the Atmospheric system would avoid noise, smoke and burning cinders from being thrown out across farmland.
 

Shimbleshanks

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rats will chew and eat vulcanised rubber, so you'd need to find an environmentally sound way of poisoning them along the whole length of the line
I thought the rats chewing the flaps was an urban myth?
Based on various quick web searches:



There were also numerous practical difficulties, not least the impossibility of points. And while station stops could have been done by the operator stopping the pump as he observed the train arriving, how would a train be stopped out of course in emergency?
Well, the ever-reliable Wikipedia states: "As well as a brake, the driver had a by-pass valve which admitted air to the partially exhausted traction tube ahead of the piston, reducing the tractive force exerted." Perhaps.
For points, I suppose there could have been breaks in the pipe, analagous to third rail electrification, if there was some way of withdrawing the piston before the break. I think though that the designers of atmospheric lines mostly fudged the issue by using flyovers wherever possible.
 

randyrippley

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I thought the rats chewing the flaps was an urban myth?

Never heard that before, but having seen the damage rats can do to leather balls / gloves / footwear stored outdoors I can well believe the stories of them eating the flaps are true
 

johnnychips

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Never heard that before, but having seen the damage rats can do to leather balls / gloves / footwear stored outdoors I can well believe the stories of them eating the flaps are true
They even eat plastic wiring, so something leather, which might even provide nutrition isn’t too far-fetched.
 

bill1953

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They even eat plastic wiring, so something leather, which might even provide nutrition isn’t too far-fetched.
Yes and they can and will eat even lead piping (which was a considerable nuisance in the days of gas lit homes and offices etc), plaster, wire gauze put there to stop them entering and most other things. Leather would indeed be regarded as a tasty snack. I did hear that the Channel Tunnel has some state of the art way of stopping rats progressing from France to the UK. I am not sure of what exactly it is or even if it is an urban myth. If it really exists and it works it must be the first time humankind has won in the relentless war against rats.
 

edwin_m

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I thought the rats chewing the flaps was an urban myth?

Well, the ever-reliable Wikipedia states: "As well as a brake, the driver had a by-pass valve which admitted air to the partially exhausted traction tube ahead of the piston, reducing the tractive force exerted." Perhaps.
For points, I suppose there could have been breaks in the pipe, analagous to third rail electrification, if there was some way of withdrawing the piston before the break. I think though that the designers of atmospheric lines mostly fudged the issue by using flyovers wherever possible.
How did they even get it past pumping stations? A discontinuous pipe would be necessary if there were any switches and crossings in the vicinity, which would probably have been the case at every station if only the siding that brought in the coal for the pumps. Flyovers are all very well for lines crossing over but connecting to the line in question needs points. I would guess there would be a flap valve on the end of the pipe for incoming trains, normally held closed by atmospheric pressure and as the pump operator saw the train approaching they would stop pumping and possibly vent the pipe to atmosphere so the piston on the train would open the valve with little pressure difference remaining. It could then probably roll through to the next section of pipe.

I guess also the start of the next pipe section would just be open. The electric telegraph didn't exist at the time so there was no way of telling the pump operator at the far end to stop or start, but they could be pumping when a train was expected and as the piston sealed the pipe vacuum would start to be created. The operator might even be able to see the pressure start to fall and increase pumping to maximum.

I was thinking the atmospheric railway also enforced train separation a decade or more before the block telegraph system. But on second thoughts I think if a second train was brought onto a pipe section that already had one train within, the pressure difference might be greater at the second train which would therefore start to catch up the one in front! However, if the pump was running nearly continuously the people at the start of the pipe could probably tell if there was a train "on the block" by the reduced inrush of air.
 

Shimbleshanks

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Yes and they can and will eat even lead piping (which was a considerable nuisance in the days of gas lit homes and offices etc), plaster, wire gauze put there to stop them entering and most other things. Leather would indeed be regarded as a tasty snack. I did hear that the Channel Tunnel has some state of the art way of stopping rats progressing from France to the UK. I am not sure of what exactly it is or even if it is an urban myth. If it really exists and it works it must be the first time humankind has won in the relentless war against rats.
Though if the rats were in the pipe, as opposed to chewing it from outside, pumping the air out for the first train of the day would have been a pretty effective way of getting rid of them...

<< I suspect that the railway, which was built, together with steam locomotive propulsion, was exactly what was intended from the beginning and that Brunel and the directors of the South Devon Railway conspired to deceive objectors, landowners and Parliament into thinking that the Atmospheric system would avoid noise, smoke and burning cinders from being thrown out across farmland.>>

Devising a completely new, untried method of propulsion would be a huge amount of trouble to go to, just to deal with a few stroppy local squires. Surely it would be far less trouble to use the tried and tested methods of overcoming objectors, like buying them out, landscaping the route where it was visible from the Big House or building stations near the landowner's property for his convenience? It might have been a factor in Brunel's enthusiasm for the project but I doubt that it would be the sole motivation.

Slightly less conventional is Flight Rail Corp's 1/6 scale demonstrator. This is not physically attached to the piston but rather uses magnets to couple the train to the piston which permits a fully sealed tube. Whether this would be acceptable for a full-sized train is open to debate.
A neat solution, using today's technology. I don't suppose there would have been powerful enough magnets in Brunel's day to contemplate doing that.
 
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DerekC

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Interesting subject. It all seems to have kicked off from the Dalkey Atmospheric Railway, which operated reasonably successfully from 1843 to 1855. Both the London & Croydon Railway and the South Devon Railway decided to adopt the system in 1844. The London & Croydon started operating atmospheric trains during 1846 and the SDR in 1847, but both abandoned the system within not much more than a year of starting.

Interestingly the system was made even more tasty for rats by the inclusion of a compound made of beeswax and tallow, laid in a slot in the sealing face of the tube. The L&CR seem to have had definite rat trouble, mentioned in contemporary sources, whereas there is no similar evidence for the SDR. Maybe London rats are hungrier!

The L&CR did use the electric telegraph to signal the pumping station when to start up - the GWR had its first telegraph installation in 1838, so the technology was definitely available.
 

bill1953

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Interesting subject. It all seems to have kicked off from the Dalkey Atmospheric Railway, which operated reasonably successfully from 1843 to 1855.
There was an interesting little mishap wasn't there? Where a carriage containing one man was shot off by mistake and completed the journey to Dalkey in seventy five seconds at an average speed of 84mph!
 

edwin_m

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Slightly less conventional is Flight Rail Corp's 1/6 scale demonstrator. This is not physically attached to the piston but rather uses magnets to couple the train to the piston which permits a fully sealed tube. Whether this would be acceptable for a full-sized train is open to debate.
Not sure how that would be to scale up to full size though...

If you multiplied all its dimensions by 6, the pipe cross section and therefore the tractive effort would increase by a factor of 6 squared but the mass potentially by 6 cubed (depending on density). And if you scaled up the speed I think the air resistance would increase by six to the power of about four (six squared for the larger surface and cross section, and the same again because other things being equal air resistance increases by the square of speed). Also pressure wave of the atmosphere behind the piston that pushes the train along will only move at somewhat less than the speed of sound, so if speed gets to a significant proportion of that then the working pressure and hence the tractive effort will start to drop off.

So all in all I'm inclined to think a scale model of an atmospheric railway proves very little about the feasibility of a full size system.
 
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There was an interesting little mishap wasn't there? Where a carriage containing one man was shot off by mistake and completed the journey to Dalkey in seventy five seconds at an average speed of 84mph!
It was a case where someone sent the signal to start without checking that the "piston carriage" (a special vehicle with the piston, which I think was essentially a flat wagon with a seat for the driver/brakeman - the engineers don't seem to have thought of attaching the piston directly to a passenger vehicle, or maybe it was considered undesirable for other reasons) was actually coupled to the rest of the train.

More generally, I think the Dalkey line lasted a relatively long time (in comparison to other atmospheric lines) because it was a very simple short-distance, self-contained shuttle with a single pumping station; the journey from Dalkey was made by gravity, too, so there was no need to worry about pumping arrangements for two directions. Extension of the line sealed the fate of the atmospheric system, particularly given that there had already been a period of temporary locomotive operation (I believe the loco had to have the cab cut down to fit the clearances of the atmospheric line) due to technical problems.
 

O L Leigh

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A neat solution, using today's technology. I don't suppose there would have been powerful enough magnets in Brunel's day to contemplate doing that.

No, of course not. I simply mentioned this (together with Aeromovel) to highlight that atmospheric railways can and have been made to work and that they still receive the attention of engineers today.

Not sure how that would be to scale up to full size though...

If you multiplied all its dimensions by 6, the pipe cross section and therefore the tractive effort would increase by a factor of 6 squared but the mass potentially by 6 cubed (depending on density). And if you scaled up the speed I think the air resistance would increase by six to the power of about four (six squared for the larger surface and cross section, and the same again because other things being equal air resistance increases by the square of speed). Also pressure wave of the atmosphere behind the piston that pushes the train along will only move at somewhat less than the speed of sound, so if speed gets to a significant proportion of that then the working pressure and hence the tractive effort will start to drop off.

So all in all I'm inclined to think a scale model of an atmospheric railway proves very little about the feasibility of a full size system.

The scaling is purely with regard to the demonstrator vehicles; I'm not suggesting that they are simply going to take the dimensions of the demonstrator and times them all by six to arrive at a full-size system. I would imagine that all of these considerations (and more) will have been taken into account by the engineers.
 

thenorthern

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As others have said the leather would have been difficult to use as a seal. Modern synthetic materials are much better to use as a sealant.

Like most technology it's possible to build an atmospheric railway however it's just easier and cheaper to use the most common type of technology at the time which was Steam.

Over the years there have been many technologies that have been tried and failed such as petrol engined trains, gas turbine trains, hydrogen powered trains, Flywheel energy storage with an LPG engine (The Parry People Movers haven't really been a success) and many others.

In the end the best option was either electrification or an internal combustion diesel engine.
 

bill1953

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With the present level of government 'think tanking' letting the Impulsoria have another fling must surely be just around the corner?
 

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Shimbleshanks

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With the present level of government 'think tanking' letting the Impulsoria have another fling must surely be just around the corner?
What were they thinking of? Did that thing have ANY advantages over just letting the horse pull the train?

No, of course not. I simply mentioned this (together with Aeromovel) to highlight that atmospheric railways can and have been made to work and that they still receive the attention of engineers today.
I wonder what advantages does it have over, say, electrification?
 

O L Leigh

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I wonder what advantages does it have over, say, electrification?

The immediate ones I can think of are no 'wires down' risk and no zapping animals/trespassers/etc. That's not to say there aren't commensurate disadvantages, too.

Well the website talks expansively about the environmental benefits of the system, from it's construction to it's operation. I can see how it could be a more energy-efficient alternative to electric traction and provide the basis for a self-contained high speed network, but it's not a realistic alternative to conventional means of traction for an existing, complex and busy network like our own. But then that's not really the market that they're targeting. I think they'd rather be considered as an alternative to Maglev and the like.
 

mark-h

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Slightly less conventional is Flight Rail Corp's 1/6 scale demonstrator. This is not physically attached to the piston but rather uses magnets to couple the train to the piston which permits a fully sealed tube. Whether this would be acceptable for a full-sized train is open to debate.

I suspect that there would be issues with the train and magnet becoming uncoupled leaving the train without any power or control. I doubt that there could be more than one train (magnet) per section of pipe as they would both move at the same time.

Aeromovel system used in a cultural theme park (Taman Mini Indonesia Indah) in Jakarta and at the Porto Alegra Airport in Brazil that work by atmospheric pressure.
They have sold 3 systems in 30 years so which is not a great endorsement of their system (although it does seem to function). It would be interesting to see a cost comparison with more conventional people mover systems (electric, cable etc.); the full system cost is not directly comparable as it includes other aspects of construction.
 

edwin_m

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Well the website talks expansively about the environmental benefits of the system, from it's construction to it's operation. I can see how it could be a more energy-efficient alternative to electric traction and provide the basis for a self-contained high speed network, but it's not a realistic alternative to conventional means of traction for an existing, complex and busy network like our own. But then that's not really the market that they're targeting. I think they'd rather be considered as an alternative to Maglev and the like.
It wouldn't be either energy-efficient or high speed. Electric traction is about 80% efficient and anything that involves repeatedly changing the pressure in pipes by enough to produce a decent tractive effort is going to dissipate a lot of heat. And as I posted above, the effectiveness will fall off rapidly as the speed gets to a significant fraction of the speed of sound. The laws of physics and thermodynamics are decidedly against this one.
 

O L Leigh

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I suspect that there would be issues with the train and magnet becoming uncoupled leaving the train without any power or control. I doubt that there could be more than one train (magnet) per section of pipe as they would both move at the same time.

Oh, I don't think that there's any question that magnetic coupling would fail regulatory scrutiny. However, assuming that it was allowed to pass, I don't think it would be beyond the wit of man to deal with a situation where the train falls off the magnet. The demonstrator vehicles (14 metres, around 2200 lbs) currently have no wheel brakes, but I would expect a full-size train would and that losing the magnet would be enough to trigger an emergency stop. With some electrickery I'm sure the train could be put back on the magnet quite easily. As for pipe sectioning, I'm sure that too would not be impossible to achieve using a system of valves at strategic points.

They have sold 3 systems in 30 years so which is not a great endorsement of their system (although it does seem to function). It would be interesting to see a cost comparison with more conventional people mover systems (electric, cable etc.); the full system cost is not directly comparable as it includes other aspects of construction.

So taking sales and longevity as defining factors for success, they've done about as well as the Victorians then. Not bad for a small company in Brazil. :lol:

It wouldn't be either energy-efficient or high speed. Electric traction is about 80% efficient and anything that involves repeatedly changing the pressure in pipes by enough to produce a decent tractive effort is going to dissipate a lot of heat. And as I posted above, the effectiveness will fall off rapidly as the speed gets to a significant fraction of the speed of sound. The laws of physics and thermodynamics are decidedly against this one.

Have you seen the details on their website?

I don't expect that the engineers behind this scheme are ignorant of the various physical problems with this scheme and have made what they feel to be realistic claims (although whether they turn out to be correct will only be established if a full-size vehicle is built and tested). Clearly they think their idea has legs and I wish them good luck with it. I don't expect that we'll ever see it in large-scale use for the purposes envisaged, but I think it's an interesting engineering exercise and shows that just maybe the ideas discarded by the past were not always terrible but maybe just a little before their time. As such, I think that it fits perfectly within the ambit of this thread.

There was an interesting little mishap wasn't there? Where a carriage containing one man was shot off by mistake and completed the journey to Dalkey in seventy five seconds at an average speed of 84mph!

Just spotted this. I wonder if this is true. If it is the gentleman in question would have been the fastest human being on the planet, probably at least until the First World War.
 
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edwin_m

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Have you seen the details on their website?

I don't expect that the engineers behind this scheme are ignorant of the various physical problems with this scheme and have made what they feel to be realistic claims (although whether they turn out to be correct will only be established if a full-size vehicle is built and tested). Clearly they think their idea has legs and I wish them good luck with it. I don't expect that we'll ever see it in large-scale use for the purposes envisaged, but I think it's an interesting engineering exercise and shows that just maybe the ideas discarded by the past were not always terrible but maybe just a little before their time. As such, I think that it fits perfectly within the ambit of this thread.
In 33 years on the railway I've seen enough crackpot schemes to recognize a solution that's in need of a problem. I've read that link and it doesn't answer either of the points I made.
 
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