Cornish beam engines - understand continued use

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 :-)

------------------------ Steam engine efficiency could be below 5% for locomotives without condensers, which were too fragile to withstand the engine and track vibration.

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. Despite being a softer and weaker metal, bronze cannon cast in one piece were considered safer. Bessemer steel began replacing wrought iron in

1864, though use of wrought iron continued through the 1887 construction of the Eiffel Tower.

A notable failure of wrought and cast iron:

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.

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.

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?

--------------------------

Spraying water into the cylinder cooled it, so on the next stroke the steam had to first reheat the cylinder. Watt's external condenser eliminated that considerable loss. The tradeoff was cost of fuel versus the skill and wages of the operator, who if good enough could work for the railroads.

Not random - strong in direction of grain, but totally unreliable in any other direction?

You could work around that with plates [in-plane design stresses resulting from boiler pressure] and riveted structures with lapped joints [clamped together and no forces trying to delaminate the metal] ?

There's Woolwich Arsenal (and other?) rifled muzzle loaders all over the place where I am working in Portland. "Effective" range in kilometres compared to a couple of hundred metres (?) with smooth-bore cast-iron canons. Their concentric shrink-fit (?) structure of machined cylinders is totally obvious to see. I'd seen them in books when I was a kid and now for the first time in this job I'm doing I am walking past them all the time. Wrought iron would perform well by reason of stresses in the direction of the grain of the metal given by forging.

I think it was only the cast iron which failed - and the engineer knew and explained the limitations of the then achievable design. I understand there were two things which were the undoing of the Tay bridge

• wind-loadings weren't correctly assessed then (but were after this experience) - not Bouch's fault really

• the railway operators got blase/ and had a flexible relation to the severe speed limits specified

Yes, but it had other limitations - particularly it could not lift more than the about 10 metres of a "Toricelli" (sic.) vacuum with water. As I understand it. So it was a first for applying fossil fuel at a demonstrable level, but didn't have what it took to be a usable device. ?

Yes - Newcomen's engines the boilers had no pressure at all - apparently you could seal leaks with clay.

Boulton and Watt's engines operated at about 5psi - barely any pressure at all.

The Newcomen engine was a "coal guzzler" and almost infeasible in Cornwall, which has no coal. It endured a long time at collieries, where it could consume waste fines of no saleable value. Apparently the "duty" of the generation of engines

• Newcomen - about 4~1/2million, rising to about 12million with vastly improved mechanical detail (precision cylinder boring, etc.)

• Boulton and Watt - maximum about 30million

• "Cornish cycle" - maximum about 100million, but "blunted" back to about 70million to 80million to lower peak forces giving the unfailing reliability needed. All according to "The Cornish Beam Engine" D.B Barton

You only had to have a feedwater water head of a few feet above the boiler to keep it filled, and if it went over pressure it would push water back up into the header and blow off steam - impossible to over-pressurise. However - even that bare puff of pressure was enought to burst boilers as they corroded, with horrible consequences.

Plug for a the book of a friend of a friend - both boilermakers by Trade:

McEwen Historic Steam Boiler Explosions Sledgehammer Engineering Press Limited (his own publishing house)

But come Cornish engine pressures of then "astronomical" 45psi pressure - yes you would do well to have a safety-valve and pressure-gauge...

Trevithick yes. Apparently one of a number of talented Cornish engineers of the time. One interpretation is that the Cornish cycle engine was the combination of a Trevithick high-pressure engine "front-end" feeding a Boulton&Watt separate-condenser "back-end" all on / in one cylinder...

The North American connection / steam-boats is a lead I must follow.

Efficiency - I have found this in the interim time

"Kew Bridge Beam Engines"

"... One important side effect of the Cornish engine’s intermittent action is that each up and down stroke is a separate power entity. So its high efficiency – an 80-inch engine in Cornwall attained 11% overall in 1835, a staggering figure for the time – is virtually unaffected by the pumping rate. Maintaining efficiency over a wide range of load factors is a problem with prime movers even today. ..."

The maximum for a single-stage high-pressure steam engine exhausting to atmosphere peaked at about 12% maximum - if you got everything as optimum as could be ?! - so that 11% 150years before and that maintains over all loadings deserves serious respect.

Best wishes, Rich Smith

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.

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...

Bob La Londe snipped-for-privacy@none.com 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.

Jim - you various links "Titanic" "locomotives 1880's" (a contemporaneous writing) "essay 'Technical Choice, Innovation and British Steam Engineering, 1800-1850'" are amazing.

The locomotives 1880 by Angus Sinclair is notable for being contemporaneous by someone involved in the then experience of running locomotives.

Best wishes,

Jim - you various links "Titanic" "locomotives 1880's" (a contemporaneous writing) "essay 'Technical Choice, Innovation and British Steam Engineering,

1800-1850'" are amazing.

The locomotives 1880 by Angus Sinclair is notable for being contemporaneous by someone involved in the then experience of running locomotives.

Best wishes,

----------------------

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.

Belay this - I got the maths the wrong way around. Sorry - I was wilting by then. Had quite a day at work welding in the void spaces in an aluminum boat...

It's

work-done

----------- energy-used

and answer is a fraction of 1

I will leave it for now. The answer could be 10.6% efficient...

---------------------

Locomotives couldn't realistically employ bulky and fragile condensers or tall smokestacks to improve draft, so they used the cylinder exhaust steam to increase air flow through the firebox.

When condensing the steam was required they usually lost overall efficiency.

Hi there

I think this is the correct calculation for the thermal efficiency of a Cornish beam engine.

For a "duty" of 100million - ft-lb to a bushel of coal

94lb of coal per bushel 0.4536kg per lb (pound) 30e6 J/kg calorific value of coal (used good Welsh 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)

Work done (* 100e6 0.4536 9.81 12 25.4 1e-3) ;; 135630391.68 (message "%e" (* 100e6 0.4536 9.81 12 25.4 1e-3)) ;; "1.356304e+08" ;; J

Energy used (* 94 0.4536 30e6) ;; 1279152000.0 (message "%e" (* 94 0.4536 30e6)) ;; "1.279152e+09" ;; J

(/ (* 100e6 0.4536 9.81 12 25.4 1e-3) (* 94 0.4536 30e6) )

0.10603148936170213

Efficiency of 0.106 = 10.6%

Comment as from previous message:

That is quite remarkable.

More than 100 years later by 1950 steam railway locomotives couldn't realistically match that (?).

It's the condenser on this slow-cycling stationary engine which makes the difference, it seems. Boiler pressures approaching 20Bar (300psi) but exhausting to atmosphere could not overcome the advantage of condensing despite the Cornish engine hitting a practical limit at 50psi (just over 3Bar). Unimaginably high when first done in around 1800, but "left behind" after 1850.

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.

------------------ 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.

"Great Britain has (in general) the most restrictive loading gauge (relative to track gauge) in the world."

I think much of that was down to penny pinching investors that didn't want to pay for the larger loading gauge costs. I live less than a mile from a GWR branch line that was originally broad gauge and the loading gauge is huge in comparison to many other locations, Brunel had some foresight, you could probably double the width and height of the current trains and they would still pass through. 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.

...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?

Yes, small crowded island. Lots of convoluted routes.

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.

Videos of 8F's in Turkey - they snort along with a fiesty blast despite being half the size of "Continental loading gauge" main-route engines. It's quite a sight to see. Apparently the Turks called the

8F's "Churchills" and it part influenced them to stay strictly neutral in the WW2 - sense of be careful juding how much strength-in-depth Britain might have...

Good question. Well informed answers looked forward to. I conjecture that inside cylinders gave smoother running - but the simplicity and easy maintainability of outside cylinders and motion became the rational choice as technology developed and labour became more expensive. Anyone???

Good question. Well informed answers looked forward to. I conjecture that inside cylinders gave smoother running - but the simplicity and easy maintainability of outside cylinders and motion became the rational choice as technology developed and labour became more expensive. Anyone???

-------------------- One explanation that I read for retaining inside cylinders amounted to NOT being like the USA, where locos rudely exposed their private parts.

------------------------

British resentment of US advances appeared strongly during WW2, largely in the differing capabilities in air power. The RAF firmly advised us that daylight bombing was impossible, then fumed and sputtered when we forged ahead and succeeded with heavily armed bombers and long range escort fighters. Though an excellent dogfighter, the Spitfire had an endurance of barely two hours, even less for the otherwise superb XIV model, while the Mustang could stay up for eight and protect the bombers to Berlin, Prague or Vienna. German fighters also had relatively little endurance.

British designers tended to maximize performance in one area at the expense of others while US ones sought a wider balance with no exploitable weaknesses. An example is the 17-pounder gun fitted to British Sherman "Firefly" tanks. It was a superior antitank gun but inferior against infantry, so we kept our 75mm gun for most of our tanks.

We aren't bothered at all that the computer chip in our cell phones is a British ARM instead of a US product.