...
Wrought iron's random weld weakness imposed severe limits on pressure vessels, both boilers and cannon.
... Look up Armstrong's rifled cannon
for more info.
A notable failure of wrought and cast iron: https://en.wikipedia.org/wiki/Tay_Bridge_disaster
The investigation revealed how common foundry practice degraded the
strength of the metal.
Savery's 1698 steam engine used pressure to force water upward, but
the workmanship of the time was inadequate to contain the
stress.
... Newcomen's 1712 engine and others for the next hundred years
avoided pressure for safety reasons.
... Boiler operation was a very
uncertain art until Bourdon introduced a practical pressure gage in
1849.
Trevithick in England and especially Oliver Evans in America advocated
the greater efficiency of high pressure steam in opposition to Watt
who feared the bad publicity of boiler explosions. Being further away,
Evans was less inhibited and created lighter and more efficient high
pressure engines that enabled American river steamboats. Since the
Cornish engine was stationary it could be built of a great mass of
cheap material.
https://en.wikipedia.org/wiki/Oliver_Evans
Evans even experimented with supercharging the firebox but concluded
that it would demand far too much of blacksmiths.
This describes early marine steam engines which needed to be fairly
light weight and fit into confined hull spaces, resulting in some
clever but strange designs. https://www.naval-history.net/WW0Book-Sennett-MarineSteamEngine.htm
-jsw
Hello all
Can you help me understand something about Cornish beam engines?
Studying about Cornish beam engines.
I was working in Cornwall this year, so the interest gripped me.
As you'll be knowing, there's abandoned engine-houses everywhere there
was mining in Cornwall.
I've done a lot of "steam nostalgia", but now as a welder and
technologist, looking at it going forward on then the world leading
edge of engine development.
The mines were hundreds of metres (~ yards) deep chasing the lodes and
there is no coal in Cornwall.
Driving an intense competition for efficiency ("duty") - world leading
edge from 1800 to 1850.
The "Cornish engine" using steam at significantly above atmospheric
pressure - 45psi (3 atmospheres) was daring searing thrilling
technology of its day.
By 1850 advancing technology and accumulated skill had moved the
baseline and 45psi was generally achievable and exceeded. Seems
Cornish beam engines "hit a wall" at about 45psi to 50psi possibly
60psi - apparently literally the walls of the house-built engine can't
take more force. Plus is explained the cast-iron beam of the day was vulnerable to the jerking force of higher-pressure / short cut-off for greater steam expansion. Etc.
So they were stuck about about 45psi.
Yet the use continued and there were even new Cornish beam engines for municipal waterworks up to 1900.
The very last beam engines went out of service in the 1950's - so they couldn't have been that bad even by standards then.
Why?
Higher pressure is usually higher efficiency.
If I estimate right, about 1/3rd of the power came from condensing the
steam and the vacuum it created under the piston.
Given you've got a big slowly-cycling stationary engine where a
condenser can be part of the overall engine concept.
So you are getting that 1/3 "for free" compared to an engine
exhausting to atmosphere...
My conjecture is...
Apart from the efficiency of few parts as the engine directly gave the oscillating motion working the pumps with long pump-rods direct down
the shafts - that the "extra 1/3rd for free" from condensing
compensated for the loss of efficiency from not being able to go above
50psi?
I'm adding detail to this thought that, with this being direct
condensing by water spraying into a chamber with the steam it must
condense - much cheaper and simpler than "indirect condensers" used on
eg. current nuclear power stations - that the mix of water, condensed
steam and some lubricating oil (?) tipped back into the boiler to gain
some fuel economy from heat in the "hotwell" - the oil and
contamination is tolerable in a Cornish boiler at max. 50psi?
Where it would be totally intolerable to the much more sophisticated
"then modern" boilers developing which gave >>50psi and much higher steam-making ("evaporative") capacity...?
Where Cornish boilers with their all-cylindrical shape - a
cutting-edge technology and a huge leap forward in 1800 - had become
very simple by 1850, with their single large furnace/flue tube and no "firetubes" of the later "locomotive" and "marine" boilers - no nooks
and crannies for contaminants to come out doing nasty things?
I'm also seeing that "not simple harmonic motion" of the beam engine -
with a passive slow pumping stoke driven by the weight of the pump rod
and a rapid steam-driven return-stroke - with pumping rate being
controlled by how often you "triggered" the engine to cycle - gave
some efficiency advantage over a rotative engine for pumping...
Added all together...
So I'm conjecturing a status-quo where all advantages of higher
pressure where negated for mine-pumping by inherent advantages
retained by the Cornish engine???
Thanks for indulging me and my interest.
Hoping some of you can offer knowledge, wisdom and guidance on this.
Best wishes,
Rich Smith
PS - I'm hoping to estimate efficiency % for a "duty" of
eg. 100million (the "magic" top figure) - work out what weight of coal
and therefore the energy in Joules was in that "bushel" of coal which
lifted those 100million foot-pounds of water...
When I'm out of Christmas mode and have my technical head back on :-)
On 12/29/2021 1:39 AM, Richard Smith wrote:
...
Perhaps it was just that they knew how to make them and they were
tooled up for it. Perhaps when manufacturing time and costs were
factored in it was cheaper and easier to go with what you know.
As a parallel in my contracting business. When the price of fuel
peaked during the Obamma administration here in the US I looked at
replacing all my 3/4 ton service trucks (except 1) with compact
pickups. When push came to shove the net savings on fuel didn't dent acquisition cost. It was far cheaper even if fuel stayed that price to
keep my 3/4 ton trucks through their normal service life. Load that
compact pickup with tools and materials and the net fuel savings was
even less.
Sometimes its about inertia, but usually its about money.
"Richard Smith" wrote in message news:lyczlf3wdk.fsf@void.com...
Bob La Londe <none@none.com99> writes:
...
Your "expensive" and our "expensive" for fuel are two different
things!
Anyway...
The amount of fuel used by mine pumping engines apparently made an
enormous difference to what was practicable.
Well, I am relying on reading from not many sources.
I'm mainly challenging whether my "condenser" conjecture is correct -
the a "free extra 1/3 of power" compensates for inherently lower
efficiency through low pressure...
----------------------
Watt introduced condensers on atmospheric (no pressure) engines. Their
use depended on availability of cooling water, not steam pressure.
Search for a downloadable .pdf of "Technical Choice, Innovation and
British Steam Engineering, 1800-1850", by Nuvolari_and_Verspagen.
I didn't get it from a quotable link.
"Second, since improvements in designs and operating procedures had
been attained by extrapolation and
guesswork, the actual performance of an engine remained surrounded by
a good deal of uncertainty."
"By the mid 1840s the Cornish engine had probably reached its
practical limits. Carried to the
extreme with pressures reaching 50 p.s.i., the expansion of steam
produced an extremely powerful
shock on the piston and the pitwork. Such an operating cycle increased
the probability of breakages
in the pitwork accelerating the wear and tear of the engine."
The extremely well documented RMS Titanic provides a view of nearly
the ultimate development of coal-fired marine reciprocating steam
engines, before Diesels and turbines took over. Titanic was optimized
for fuel efficiency rather than speed, and consumed only about 70% of
the coal of the slightly faster and considerably smaller Lusitania and Mauretania.
http://www.titanicology.com/Titanica/TitanicsPrimeMover.htm
"Jim Wilkins" <muratlanne@gmail.com> writes:
"Richard Smith" wrote in message news:lyczlf3wdk.fsf@void.com...
Bob La Londe <none@none.com99> writes:
...
Your "expensive" and our "expensive" for fuel are two different
things!
Anyway...
The amount of fuel used by mine pumping engines apparently made an
enormous difference to what was practicable.
Well, I am relying on reading from not many sources.
I'm mainly challenging whether my "condenser" conjecture is correct -
the a "free extra 1/3 of power" compensates for inherently lower
efficiency through low pressure...
----------------------
Watt introduced condensers on atmospheric (no pressure) engines. Their
use depended on availability of cooling water, not steam pressure.
Search for a downloadable .pdf of "Technical Choice, Innovation and
British Steam Engineering, 1800-1850", by Nuvolari_and_Verspagen.
I didn't get it from a quotable link.
"Second, since improvements in designs and operating procedures had
been attained by extrapolation and
guesswork, the actual performance of an engine remained surrounded by
a good deal of uncertainty."
"By the mid 1840s the Cornish engine had probably reached its
practical limits. Carried to the
extreme with pressures reaching 50 p.s.i., the expansion of steam
produced an extremely powerful
shock on the piston and the pitwork. Such an operating cycle increased
the probability of breakages
in the pitwork accelerating the wear and tear of the engine."
The extremely well documented RMS Titanic provides a view of nearly
the ultimate development of coal-fired marine reciprocating steam
engines, before Diesels and turbines took over. Titanic was optimized
for fuel efficiency rather than speed, and consumed only about 70% of
the coal of the slightly faster and considerably smaller Lusitania and
Mauretania.
http://www.titanicology.com/Titanica/TitanicsPrimeMover.htm
I've calculated thermal efficiency for a Cornish beam engine.
The best was a "duty" of about 100Million - foot-pounds of work
to a bushel of coal.
For a "duty" of 100million - ft-lb to a bushel of coal
94lb of coal per bushel
0.4536 kg per lb (pound)
30e6 J/kg calorific value of coal
9.81 Earth's gravity, N/kg
12 inches per foot
25.4 mm per inch
1e-3 mm to m (convert to SI units)
(/
(* 94 0.4536 30e6) ;; 1279152000.0
(* 100e6 0.4536 9.81 12 25.4 1e-3) ;; 135630391.68
)
9.431160554471974
9.4% efficiency
That is quite remarkable.
More than 100 years later by 1950 steam railway locomotives couldn't realistically match that (?).
That "work" in the "duty" is a measure of the amount and height of
water lifted from the mine? (what else could they be measuring?!
What else would be possible to measure!!)
If so, that answer is very "final".
Comment is made in well-regarded books that that efficiency does not
change over all intended pumping rates.
Which is the cause of envy, to this day.
With the amount of water being adjusted by how many strokes per minute
the engine performed.
"Richard Smith" wrote in message news:lyczkos0rn.fsf@void.com...
....
------------------
The Cornish engine is an example of maximizing efficiency at the
expense of size and weight, which were more important in other
applications. Particularly in Britain the "loading gauge" or bridge
and tunnel clearance restricted the dimensions of steam locomotives. https://en.wikipedia.org/wiki/Loading_gauge
"Great Britain has (in general) the most restrictive loading gauge
(relative to track gauge) in the world."
"David Billington" wrote in message
news:ss96k0$snd$1@dont-email.me...
...My neighbour does miniature steam locos and many of his drawings
I've seen have the loading gauge shown for various rail companies and
yes as you mention the clearance is minimal in many cases.
Why did Britain change from inside to outside cylinders?
"Richard Smith" wrote in message news:lyczkos0rn.fsf@void.com...
....
------------------
The Cornish engine is an example of maximizing efficiency at the
expense of size and weight, which were more important in other
applications. Particularly in Britain the "loading gauge" or bridge
and tunnel clearance restricted the dimensions of steam locomotives. https://en.wikipedia.org/wiki/Loading_gauge
"Great Britain has (in general) the most restrictive loading gauge
(relative to track gauge) in the world."
"David Billington" wrote in message
news:ss96k0$snd$1@dont-email.me...
...My neighbour does miniature steam locos and many of his drawings
I've seen have the loading gauge shown for various rail companies and
yes as you mention the clearance is minimal in many cases.
Why did Britain change from inside to outside cylinders?
The power-to-weight of some good British locos - eg. the Stanier 8F's,
the Great Western Railway "Castles", etc - all with tapered boilers
and other features which are hard work to make and not normally worth
it but allow it to "pack a punch" when size is limited.
In most countries you would not make an engine more powerful that
would break traction on the rails if unskillfully driven.
In Britain with the good locos - skilled driving needed to know how
much punch to apply...
... while the Mustang could stay
up for eight and protect the bombers to Berlin, Prague or
Vienna. German fighters also had relatively little endurance.
Shays - "Iron Dinosaurs" Colin Garratt - journey of the imagination as kid
...
We aren't bothered at all that the computer chip in our cell phones is
a British ARM instead of a US product.
... while the Mustang could stay
up for eight and protect the bombers to Berlin, Prague or
Vienna. German fighters also had relatively little endurance.
"Richard Smith" wrote in message news:ly5yps5m5n.fsf@void.com...
...
-----------------------
...
If you care enough the flow rate can be measured by timing the filling
of a measured volume, perhaps the cistern that stores water for the
steam engine boiler. ...
...
"Richard Smith" wrote in message news:ly5yps5m5n.fsf@void.com...
...
-----------------------
...
If you care enough the flow rate can be measured by timing the filling
of a measured volume, perhaps the cistern that stores water for the
steam engine boiler. ...
...
"Richard Smith" wrote in message news:lya6f35jom.fsf@void.com...
"Jim Wilkins" <muratlanne@gmail.com> writes:
"Richard Smith" wrote in message news:ly5yps5m5n.fsf@void.com...
...
-----------------------
...
If you care enough the flow rate can be measured by timing the filling
of a measured volume, perhaps the cistern that stores water for the
steam engine boiler. ...
...
The water from the mines was is too full of minerals to be much use...
---------------------
It was technically possible for them to measure flow rate though
probably not worth the effort if the results wouldn't lead to
cost-effective improvements.
https://proteusind.com/history-of-flow-meters/
...
"Richard Smith" wrote in message news:ly4k5ae5ep.fsf@void.com...
"Jim Wilkins" <muratlanne@gmail.com> writes:
"Not worth the effort" is surely the answer.
The pump's swept-volume (piston-area x stroke) will give a very
accurate estimate of water volume pumped.
Measuring water flow directly - at each mine you'd have to get down to
the adit carrying your equipment down a small twisting shaft then have
some space to deploy it - big "ask".
The readings would have to be the same for the same water-flow at
each mine - so whatever direct measurement you use would have to be
very consistent.
Rich Smith
-----------------
Accurate measurement wasn't a priority until recently. Consider that the >steam engine had been in use for 150 years before someone bothered to invent >the boiler pressure gauge. Previously stokers shoveled in coal until the >weighted safety valve opened.
When I was a kid learning to use a lathe the size measurement tool was still >friction calipers, set by eye to a wooden ruler.
"Richard Smith" wrote in message news:ly4k5ae5ep.fsf@void.com...
"Jim Wilkins" <muratlanne@gmail.com> writes:
...
Accurate measurement wasn't a priority until recently. Consider that
the steam engine had been in use for 150 years before someone bothered
to invent the boiler pressure gauge. Previously stokers shoveled in
coal until the weighted safety valve opened.
...
When I was a kid learning to use a lathe the size measurement tool was
still friction calipers, set by eye to a wooden ruler.
"Richard Smith" wrote in message news:ly4k5ae5ep.fsf@void.com...
"Jim Wilkins" <muratlanne@gmail.com> writes:
"Not worth the effort" is surely the answer.
The pump's swept-volume (piston-area x stroke) will give a very
accurate estimate of water volume pumped.
Measuring water flow directly - at each mine you'd have to get down to
the adit carrying your equipment down a small twisting shaft then have
some space to deploy it - big "ask".
The readings would have to be the same for the same water-flow at
each mine - so whatever direct measurement you use would have to be
very consistent.
Rich Smith
-----------------
Accurate measurement wasn't a priority until recently. Consider that the >steam engine had been in use for 150 years before someone bothered to
invent
the boiler pressure gauge. Previously stokers shoveled in coal until the >weighted safety valve opened.
When I was a kid learning to use a lathe the size measurement tool was
still
friction calipers, set by eye to a wooden ruler.
...
When I was a kid learning to use a lathe the size measurement tool was
still friction calipers, set by eye to a wooden ruler.
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