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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