Talk
Tuesday 8th March 2005 2-30pm Field Place, Durrington, Worthing. Steam Power by Ken Wheeler
This is a story about people. Of five engineers in the 18th century whose creativity, entrepreneurship, actions and prejudices changed Britain forever and these were Thomas Savery, Thomas Newcomen, James Watt, Matthew Bolton and Richard Trevithick.
Around the year 1700 Britain was an agrarian economy with a small population of less than 7 million people and where power came from waterwheels or horses. Waterwheels remained an important source of power until around 1840 reaching 100-horse power with an efficiency gain from the beginnings of 21% to 67% in the latter years. Sources of capital for entrepreneurs was restricted being available from wealthy landowners and businessmen willing to risk some capital for a potentially handsome return. Job descriptions were loose. For instance, James Watts who we shall meet later was over his lifetime described and employed as a scientific instrument maker, a merchant dealing in Delf china, a land surveyor and an engineer.
The prime circumstance which made the activities of these five engineers unique was the strong patent protection for inventors at that time. Patent infringement in the 18th century brought dire consequences if proven in court; the journey from a position of relative wealth to the gutter could be swift and unrecoverable. Scientifically inadequate or false paradigms abounded. The strength of a beam in bending based on Galileo’s formulae which was under strength by a factor of 3 was still widely used up to around 1800 a design factor of safety of 4 or more hiding the error. New paradigms correctly describing the theory of bending originated on the continent and were in French. Never the less textbooks in mathematics and natural philosophy, as physics was then called, were available and from 1720 church and grammar taught these subjects particularly Newtonian mechanics a situation peculiar to this country. Anglican churches even preached the virtues of the Newtonian paradigms from the pulpit; the church over the ages being the guardians of scientific and mathematical knowledge particularly among the Baptist and non-conformist movements. Up to1760 no true rudimentary explanation of how heat engines worked existed.
The driving force around 1700, which ultimately resulted in the steam engine in all its forms, the ultimate example of the law of unintended consequences, was the need to raise water by mechanical means to drain deep copper and zinc mines in Cornwall and in the coalfields of the Midlands of England.
In this talk it is best to start with Thomas Newcomen of whom no portrait exists .His ancestors were landed gentry forced to flee and ultimately settle in Dartmouth, Ireland and the USA. Thomas Newcomen in Dartmouth was taught by John Flavell a persecuted non- conformist preacher and eminent scholar who had been given succour by the family in Dartmouth. Newcomen’s occupation is given as ironmonger but he was clearly a merchant of substance being able to employ Jim Calley a smith and plumber for the 10 years it took Newcomen to develop a successful engine. In earlier times Newcomen had done some ironwork for Thomas Savery, a military engineer who in 1698 devised what he called a” fire engine” which he patented as” a device to raise water by the impellent of fire and the condensation of steam”. This, which should have been disallowed, was a master patent, which would encompass Newcomen’s engine and allowed Savery who played no part and his heirs to claim rights over Newcomen until the patent expired in 1733. Newcomen died in 1729.
The Savery Fire Engine which is essentially an egg shaped pressure vessel into which steam at a modest 3psi is introduced causing the water within the vessel to exhaust through a vertical forcing pipe, the height of the water column resulting being limited by the vessel’s steam pressure. A water spray to the outside of the steam filled vessel induces a vacuum thereby replenishing the water level in the vessel from a head of no greater than 30 feet above the free surface of the mine water. Thus, the total lift is the sum of that in the force pipe and the suction head and the Savery engine is a restricted device.
A practical solution requires a minimum lift of some 150 feet and Newcomen’s Atmospheric Engine of 1712 does just that and more. Being also limited to boiler pressures of around 3psi Newcomen utilises the near vacuum pressure of 10psi resulting from condensed steam under the piston in a large brass cylinder with a stroke of some 8 feet to pull up a submerged bucket pump, the attendant weight of the pump rods and the head of water generated by the bucket pump. Thus the bigger the engine the more head it will generate; a facility not shared by the Savery engine.
By placing the pump and the cylinder on opposed sides of a tilting beam both applied tension loads accommodated by the use of chains on each side of the beam.
No machine tools were available to prepare the cylinder bore so a cup seal was arranged around the piston diameter with a well of water above the piston forming the seal to prevent vertical escape of steam past the piston. The Newcomen engine required that the cylinder walls be cooled to help with the condensation of the steam and he tried a cold water jacket. A lucky incident due to a small hole breaking through into the cylinder during test caused cold water to enter from the jacket and cause rapid condensation within producing exactly the effect required. A post mortem decided that a means of regulated water injection into the cylinder should be used during the operating cycle of the engine. One problem remained; how to make the engine operate automatically. Newcomen would have been unaware that on history’s subsequent internal combustion engines where power was transmitted by a rotating shaft, it is necessary to get the shaft rotating at some minimum speed for rotary inertia to ensure that the ignition cycle ensures continuous operation. The Newcomen engine had a vertical rod (plug rod) attached to and hanging down from the beam for purposes of control and this triggered a tumbling bob to produce a rapid opening and shutting of the steam valve from the boiler at the extremes of plug rod travel where the bob was caused to over balance from top dead centre. The Newcomen engine had other triggers on the plug rod such as water injection valve operation to make it function in total. The concept of this engine and its enactment can never be underestimated in the annuals of technology, producing the world’s first automatic machine, which remained practically unchanged for the next 53 years. Newcomen engines were very inefficient using large quantities of coal. This was no problem where engines were sited in coalfields but for mining in Cornwall the coal had to be imported by sea from Wales and successive generations of engineers were unable to effect much improvement on fuel consumption using the basic Newcomen design.
James Watt realised some 50 years after Newcomen that the high fuel consumption of the Newcomen engine was due to the need to reheat the piston cylinder with new steam before applying a water injection to induce a near vacuum below the piston and hence achieve a power stroke and thereafter heat the cylinder again to repeat the cycle. By venting the steam to a separate cylinder containing the water injection feature he thereby maintained the piston cylinder a high temperature with the steam exhausting to the lower colder cylinder, which he called a “separate condenser” in his patent. At the same time he patented the use of a gland around the top of the piston rod to enable steam pressure to be applied above the piston. Therefore in the power stroke the piston reacted to the pressure of steam on top of the piston concurrent with near vacuum conditions below the piston. The success of the Watt engine depended on the ability to produce a cylinder whose bore was both straight and truly circular with a good surface finish and in cheaper cast iron, rather than the brass previously used and this had depended on the unrelated development of a water wheel driven boring mill capable of the task. All early Watt engines used cylinders cast and machined by Wilkinson. Watt was prevented from proceeding with his prototype engine due to lack of money. His efforts came to the attention of Matthew Boulton who initially sought to buy a Savery engine but was so impressed by Watt’s engine that he entered into partnership with Watt to develop the engine and initially sell it to the Cornish miners to resolve the problem of deep mine drainage. Boulton was a man of confidence and of substance and Watt remained in awe of him throughout his life. Watt, highly inventive, but reluctant to enter into negotiations with such as the mine owners left this to Boulton. Watt was also highly touchy about any of his inventions often taking criticism as a personal insult but never to or in the presence of Boulton who left primary design to Watt although Boulton was an engineer of considerable merit himself. In later times Boulton was commissioned by the government to design new machines and oversee the manufacture of new coinage, which meant his
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contribution was in determining policy and policy for the partnership and pushing Watt along.
The B&W partnership in the early days when devoted to mining engines gained their profits not from making the engines but from a certain proportion of the savings in fuel compared with the Newcomen engine (about a quarter of that used by the Newcomen engine). They entered into agreements with the mine owners for one-third part of the savings made to be paid annually to B&W for a term of twenty-five years. Alternatively, the mine owners could purchase the indemnity at ten years price in ready cash. Utilisation of the engine was determined by examination of a pendulum mechanism attached to the beam and secured within a padlocked box (A Boulton invention). Determining comparative economy for pumping engines was by measuring the DUTY. This is the number of pounds of water raised one foot in height for the consumption of one bushel of coal (84 lbs). The average duty for Newcomen engines was 5,590,000lb and for original Watt engines was 21,600,000 lbs.
Prospective customers wanted to know how many horses a Watt engine could supplant. Watt determined this by an experiment with a mine horse tethered to walk around a 24 feet diameter 2 and BD times in one minute against an average pull of 172lbs (32425 foot lbs/minute). Watt rounded this up to 33000-foot lbs/min and called this one HORSE POWER. As the duty as expressed above was independent of speed the notion of horsepower only came into its own with the advent of the rotative engine.
Boulton was incensed to find that a James Pickard had adapted a Newcomen type engine with a crank which in conjunction with a Matthew Wasborough’s fly (later called a flywheel) became a rotative engine suitable for driving rotating mill drive shafts and in 1781 pressed Watt to patent methods of producing rotary motion from the Watt engine. He pressed Watt repeatedly about the matter pointing out the mine pump market was all but satisfied and mills were the future. Indeed, they should set up a manufactory to make these rotative engines forthwith and Watt had better come up with this new engine design with appropriate patent protection as a matter of urgency. (It was to take some six years).
Watt was beset with three problems. No way was he going to use Pickard/Wasbrough patent in spite of a reciprocal offer for the use of the Watt separate condenser. Watt devised a complicated sun and planet drive to rotate the output shaft. He determined that a double acting piston/cylinder was necessary to ensure smooth transmission duty each cycle of the output shaft and that long term fluctuations of power could be overcome by monitoring steam input with a rotating ball assembly using centrifugal force to adjust the steam valve.
The use of a double acting cylinder presented the most serious problem. The beam in rotating about a fulcrum produced a radial locus at the end to be connected to the piston rod whose up and down stroke is in a straight line. The single acting cylinder going back to Newcomen always applied a tension load between beam end and piston rod and was accommodated by a chain drive Certain ideas such as a rack and gear design were tried but the friction load engendered by gear pressure angle and reacted by crude slides reduced life and efficiency dramatically. All subsequent beam engines made thereafter after used the straight line motion devised by Watt which comprised a series of rods with a bearing at each end such that each when connected into a five bar chain acted as either a strut or tie with no induced bending moment in any link Watt considered his parallel motion to have been his finest invention. Boulton and Watt went into series production (around 1789) of their rotative engine with developed about 10-horse power.
Richard Trevithick, a tall, well-built and extremely intelligent Cornishman has a place in history far beyond his presence in this story. The Cornish mine owners were seeking a pumping engine far superior to the Watt engine in terms of duty, for coal was expensive and had to be shipped by sea from Wales. A Joshua Hornblower had earlier tried to defeat the Watt patent by using two cylinders at the same end of the beam as a compound combination whereby steam from one cylinder was exhausted to the other in an effort to improve efficiency. Hornblower was sued for infringement by B&W and he lost the case. Trevithick formed a lasting friend ship with Davies Gilbert who eventually became President of the Royal Society and used him to check the feasibility of various ideas. Trevithick had determined that “strong steam” was necessary (50psi) to improve the efficiency of the steam engine. That the valve admitting steam to the cylinder during the power stroke should be cut off early allowing the steam to expand and complete the working stroke. Double acting cylinders could be used without a separate condenser and what was needed was a high- pressure boiler. Trevithick invented what became known a the Cornish boiler where the boiler shell containing the water feedstock was in the form of a large tube with the furnace and grate provided by another smaller tube running down the bore of the boiler shell. Robust end plates carrying the furnace door at one end resisted the pressure end loads. Watt was well aware of the efficacy of using strong steam, the early cut off of steam to the cylinder, that a separate condenser was not necessary with a double acting strong steam engine. He devoted considerable time to discrediting Trevithicks’s strong steam as it would damage the powerful market position of B&W. Patent law had restricted development of the steam engine until 1800 to B&W’s advantage. However, he had been advised that as the Watt patents could be disallowed and the patents were due to expire in a few years 1800 anyway he should devote his energises to maximising the production on the rotative engines and the collection of the royalties due from the mine owners, much of which was overdue; it is certain that Boulton concurred in this.
Meanwhile Trevithick who cared little for Watts patents and was protected by his isolation in Cornwall and the connivance of mine owners seeking a better pumping engine went ahead with what became the ultimate in beam pumping engines. Early versions of the Cornish Beam Engine as it become known, as had an average duty of 43,350,000 lbs. After 1820 around 100,000,000 lbs duty was achieved on larger engines.
The Cornish beam engine as a pumping engine has a Watt linkage at each end of the beam. At one end is a counterweighted plunger (ram) pump, at the other is a steam jacketed single acting piston/cylinder working at around 50 psi fitted with a separate condenser and is valved for expansive working during the power stroke. The installation at the Kew Bridge Water Pumping Station built around 1846 is a typical example. The plunger pump has a counter weight of 36 tons, which is lifted via a cast iron beam weighing 35 tons by a 90inch diameter cylinder with a 132-inch stroke. The ram pump which has a 38-inch diameter shaft pumps 6.5 million gallons of water from the river Thames at 4 strokes a minute.
Ken Wheeler
