Most curious, the resender seems to have applied a random rearrangement
to my line lengths. Let's see if I can straighten them out...
On Mon, 26 Dec 2011, pete wrote:
An odd synchronicity, I stumbled upon this story just this summer, and
had an entertaining time reading about the whole adventure. The
invention was not initially Brunel's, but rather had been proposed as
early as 1799, and developed by a group of engineers who built the
first example in Dublin. It is thought Brunel's attention was drawn to
this example after an unintended incident during an early
demonstration of the new line, when the steam pump built up the
pressure to drive a full line of cars up the hill on which the line
was constructed, but only one car had been placed on the line, with a
single passenger, a young worker who volunteered. The over-pressure
drove the car up the hill at something over 65 mph, an unheard of
speed for 1844, and I expect that the young man held the land speed
record for a couple of decades, though no one was keeping track of
such things in those days.
The main advantage of the remote pressure driven line is that you
don't have to move the engine nor the fuel, so the cars can be much
lighter, and everything is much more efficient. That was a big concern
in the 19th century, when power came from heavy cast iron steam
engines burning mountains of coal. The development of the electric
locomotive engine freed the vehicles from the need to transport fuel,
though some still do (all locomotives are electric driven - the
diesels are diesel-electric, with the diesel engine powering an
electric generator which then powers an electric motor which drives
the wheels, for the same reasons of efficiency that hybrid cars use a
gasoline engine to drive an electric motor), so the strong impetus for
the use of remote power is considerably reduced. In north america, the
distances make electric power lines less economical than carrying the
diesel fuel, but tht is not the case in europe, so electric lines are
common there.
Another problem with the remote power pneumatic system is the
limitations on the power which can be delivered, being constrained by
the strength of the pneumatic pipe. The problem is also present with
electric rail lines, though not in such severe form, as you can put a
large amount of electric power down a fairly inexpensive line by just
using a higher voltage. With diesel electrics, more power is just a
matter of inserting more engines in the line of cars. Typical freight
trains in western Canada can have many engines, and an immense load,
being as much as 4km long and weighing 18kt, with seven or more
engines distributed along the length.
-Pete
On Mon, 26 Dec 2011, Keith Hudson wrote:
One of the greatest inventions of the 19th century, and of all man's time,
has yet to be developed. It failed initially for a trivial reason which,
today, could be easily overcome. When it is finally embarked upon, it will
change the physical infrastructure of many countries to such an enormous
extent that we can't possibly imagine all its ramifications. Its
development may still lie a century in the future, though there's no reason
why a particularly enterprising culture such as Singapore or Switzerland or
Israel shouldn't start planning it tomorrow.
I'm reminded of the invention every day as I sit at my keyboard and look
out of the window. Yet, to my complete surprise this morning, I realize
that I have never written about it before now. A group of trees about 100
yards ahead of me is the prompt. This at is the beginning of one of the
first tunnels of the Great Western Railway built by the engineering genius,
Isambard Kingdom Brunel in 1833. It's still in use today. If I listen
carefully at various times in the day I can hear the low rumble of a
London-destined train approaching along a deep tree-lined cutting. The
sound then vanishes. If I walk to my back garden quickly I can hear the
sound again as the train emerges from the tunnel about 200 yards away to
the east. (My house doesn't actually sit over the tunnel, thank goodness!)
Brunel's first idea was that his Great Western Railway should be pneumatic
-- that is, driven by air pressure. It would be so much more efficient than
the locomotive system than was then being used to pull carriages and
freight trucks along. Instead, in Brunel's experimental version, the
leading carriage or truck had a short downward extension on which there was
a circular piston which snugly fitted inside a 12 inch wide tube with a
slit along the top to allow forward motion. A steam-driven pumping engine a
mile or two ahead pumped out the air ahead of the train. The air pressure
behind the train would then push the piston forward -- and at very high
speed, too. The slit in the tube was was covered by a continuous leather
strap which slid aside briefly as the piston-arm moved along the tube and
then sealed over again when the train was past. Brunel tried it out. He
demonstrated conclusively that a pneumatic railway was, indeed, much more
efficient than a locomotive driven railway (in which heavy steam engines)
have to travel almong as well as the freight.
The problem with this experimental model -- which Brunel hadn't foreseen --
emerged within weeks. This was that countryside rats took a liking to the
leather valve, nibbled away at it and thus rendered the tube less than
air-tight. This dashed the whole project. There were no rubber-like or
plastic materials available in those days which were rat-proof and could
have been used instead of leather. Thus, Brunel had to revert to the
conventional method of mobile steam-engines pulling the train for his Great
Western Railway. Another way of overcoming the problem was theoretically
possible. This was to construct a much larger tube so that it fitted snugly
around the whole front of the leading carriage or truck. This would be even
more efficient. But the cost of building a tunnel for the whole distance of
110 miles between Bristol and London was far beyond the pockets of the GWR
Board of Directors.
However, to show that this method was feasible, a full-tunnel short-length
fun version was built in the grounds of Crystal Palace in 1864 to the
delight of hundreds of people who tried it. Also a short-length passenger
railway (with serious intent this time!) was constructed under Broadway in
New York. Once again, however, this proved to be unfeasible because of lack
of suitable sealing materials. In the 1960s, some Lockheed engineers
designed a pneumatic system for a Boston-Washington commuter route. At the
same time, the Swiss were considering a pneumatic metro system between
their major cities. But in both cases it was cost, not method, that stopped
further consideration.
However, the cost could be much further reduced by a cut-and-cover method
of construction whereby, for most of its length, the top soil is replaced
over the top of the tube and the normal amenity or agricultural value of
the countryside is resumed. The overall cost would also be reduced
substantially if large factories and warehouses (both increasingly
automated with smaller numbers of personnel) were integrated with pneumatic
railways with countryside above them all. Freight containers could be
rolled on and off vessels at the ports and imports delivered at regional
warehouses within an hour or two even in large countries. The cost of
land-freight could be reduced to levels scarcely more than those of sea
transport today. Countries without coastlines would not be as disbenefited
as they are now. As for commuters, the time spent every day could be
reduced to a fraction of that by car or existing railways.
I gave a talk about this to the Bath Royal Literary and Scientific Society
about 20 years ago. A friend told me afterwards that I'd given the talk in
a flat, unexciting way. That surprised me but perhaps I did. If so, the
reason was probably due to the fact that I then still considered Brunel's
invention to be premature. If the Swiss had decided against it for cost
reasons in the 1960s then it was still probably not the time for it to be
taken up in the 1990s. But there is a difference today which is beginning
to be discernible as part of our credit-crunch problem and forthcoming
recession. This is that there is no great chain of new consumer products
ahead of us which existed all through the past 300 years and served stimuli
for economic growth. If there is to be economic development (measure in
conventional terms) then it's going to come via new efficiencies on the
production side and not new consumer gew-gaws. Also, if we add in the
desirable restoration of a great deal of our countryside, then Brunel's
invention is surely going to be one of the answers one day.
Keith
Keith Hudson, Saltford, England http://allisstatus.wordpress.com
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