The Newcomen steam engine
newcomen-steam-engine
Newcomen's fire engine
Newcomen's engine raises the water entirely by the pressure of the atmosphere ; for the steam is employed merely as the most expeditious method of displacing the air, and then producing a void, into which the atmospherical pressure may impel the first mover of the machine [1].
On Newcomen's system there is no need of steam of great or dangerous elasticity; for it operates with very moderate heat, and consequently with a much smaller quantity of fuel than Savery's. The power of Newcomen's engine is not bounded by the strength of the boilers, and vessels, to resist internal pressure, but only by the dimensions which it is practicable, and expedient to make boilers, and cylinders, to contain the requisite quantity of steam, of the ordinary pressure, and the strength which can be given to the working lever, chains, and other parts, which communicate the force of the piston, to the rod of the pump. Newcomen's engine can also be applied to other mechanical purposes, besides that of raising water. For instance, to blow air by bellows or pumps, into a furnace ; or, by connecting a crank and fly-wheel with the rod, which is suspended from the extremity of the great lever, the reciprocating motion of the great lever, may be changed into a circular motion. Savery's engine is necessarily restricted to the purpose of raising water, and could not be applied to work mills, except by the intervention of a water-wheel [2].
We see from that historical document that at Newcomens time the technology was not advanced enough to cope with steam pressures much above atmospheric pressure. Savery must have used about 2 atmospheric pressures to push up water, but this caused form time to time problems with the boilers bursting. This set a limit to which height water could be pushed up by steam. Savery had proposed to employ his devices in stages, but it was impractical to have a more then one Savery fire engine deployed in a shaft.
The advantage of the Newcomen engine was that it could operate a chain of mechanical pumps, which could pump water in stages. However, this also came at a price. The design with a sturdy and heavy beam introduced mechanical losses and also each pump added losses. John Farey describes a Newcomen machine that produced 8.03 HP at the piston but the effective power to raise water from a depth of 54 feet was only 2.67 HP [3]. Machine and pumps together introduced losses of 67%. Therfore sometimes it is said that the Newcomen steam engine was less effective than a Savery engine.
Detailed description of the Newcomen engine
The novelty of Newcomen's construction consists in condensing the steam below an air-tight piston in a cylindrical vessel having an open top. [4] The steam is admitted into the part of the vessel below the piston. Initially, the steam was condensed by spraying cold water on the cylinder's exterior, but it quickly became clear that injecting cold water into the inside of the cylinder would be more efficient and result in faster speeds.
In the drawing below a boiler B with its furnace produces steam. With the use of a small steam pipe S a fluid communication is established between the boiler B and the bottom of the cylinder C. A plate p closes up the lower aperture of this pipe S. This plate p, known as the regulator or steam cock, rotates horizontally on an axis that goes through the top of the boiler. It is operated by a handle to open or close the fluid communication between the boiler B and the part of the cylinder C below the piston P.
A packing with a circular edge made of soft rope that is thoroughly packed with tallow to decrease friction is used to secure the piston P to the cylinder and make it airtight. The upper surface of the packing is kept wet to make the piston P steamtight. The working beam, which spins the gudgeon G, is linked to the piston P by a rod A that is hung by a chain from the top extremity D of the lever's arched head.
At the opposite end, this beam bears a similar arched head E for the pump rod H that draws water from the mine. When the water is drawn from a depth where the steam piston P is too heavy for this purpose, counterpoise weights l must be added to the pump rod H until the piston will rise in the steam cylinder at the proper speed.
An injection cistern L, which receives water from a forcing pump R, is located at a certain height above the top of the cylinder. From here, an injection pipe M descends until it reaches N, where it terminates in one or more tiny holes after entering the cylinder through its bottom. A injection cock, which has a handle attached to it, is inserted into the injection pipe M for interrupting the flow of the water from the injection cistern L into the cylinder C. A snifting valve V that turns upward has a little dish around it to store water to maintain it airtight.
Also, a pipe Q emerges from the bottom of the cylinder. This pipe is known as the eduction pipe and has its lower end submerged in a water cistern U known as the hot well. The lower end of the eduction pipe Q, which is in the cistern U, is turned upward and is covered with a valve v. The boiler has a safety valve T to control the strength of the steam, but it is only loaded to a maximum of one or two pounds per square inch (0.07-0.14 atm). It is manufactured and operated in the same way as in a Savery's engine. We note that the pressure of the boiler is lower than in a Savery engine and thus avoids boiler explosions.
The mechanism of functioning is now explained. Close the regulator or steam valve after allowing the piston to descend all the way to the bottom of the steam cylinder. The atmosphere's pressure will then keep the piston there. Add heat to the boiler until steam starts to escape from the safety valve; at that point, open the steam regulator and the piston will rise as a result of the combined action of the steam's strength and the extra weight on the other end of the beam. Close the regulator p when the piston P reaches the top of the cylinder C, then turn the injection cock O to let in a jet of cold water that condenses the steam inside the cylinder C and creates a partial vacuum. The piston P then descends through the pressure of the atmosphere, pumping water up from the mine using the pump rod H. Air introduced into the cylinder by the steam and the injection water is forced out of the snifting valve V by the force of the descenting piston P. Finally, the injection water exits at the eduction pipe Q. The process of raising water is thus accomplished by repeatedly admitting steam and injecting water.
Before a young lad by the name of Humphrey Potter came up with a means to fasten strings and catches to the working beam so that the machine's motions could open and close the valves, these activities were carried out by hand. The engine then moved one step closer to being a self-regulating device when more permanent appendages were added to serve the goal. It was called the Atmospheric Engine when it was in this straightforward and effective stage. Around 1712, it was refined to this level, and such engines were erected in various places in England.
Savery's patent covered all types of engines that used fire to lift water. Because Captain Savery already had a privilege for erecting a fire-machine, Newcomen was unable to obtain any privilege. It is unclear whether Newcomen ever attempted to submit a patent application, which was rejected or if Newcomen was aware of the Savery patent and therfore understood he had no chance.
There are hardly any in-depth accounts of the construction of Newcomen's engines from his contemporaries. The majority of references date from decades later and may not be completely accurate. Mårten Triewald, a Swedish engineer who came to England in 1716 and stayed there for ten years, assisted in the construction of some Newcomen engines. After his return from England, he built the first Newcomen engine in Sweden and he wrote a brief book [20] about it in 1736 that included information from his time in England.
If Mårten Triewald's interpretation of English law is accurate, the Chancellor, to whom all petitions regarding privileges were remitted, took great care to ensure that neither a privilege be granted that was in conflict with an already granted privilege that was still enforceable nor that two privileges be issued for the same thing or invention. A Royal Privilege had never been overthrown or revoked by Parliament in England. Everyone was maintained in the enjoyment of their rights, which were therefore regarded as sacred or unchangeable rights on par with the Magna Charta or the English constitution. [21]
Notwithstanding the fact that the fire engine used by Captain Savery and Mr. Newcomen's innovation were significantly different from one another, Mr. Newcomen and his co-inventor Calley saw no other way out of the troubles but to join Captain Savery and establish a Corporation. In the year 1712, Mr. Newcomen built the first fire-machine in England, which was built at Dudley Castle in Staffordshire [22].
Trievald's accounts are backed up by a note in Stephan Switzer's book about water-works:
“I am well inform’d, that Mr. Newcomen was as early in his Invention, as Mr. Savery was in his, only the latter being nearer the Court, had obtain’d his Patent before the other knew it; on which Account Mr. Newcomen was
glad to come in as a Partner to it." [25]
Double check - Is it all about the condenser?
The use of an exterior condenser to prevent heat losses is claimed to be the principal reason for the improved performance of the Watt steam engine. It is possible to determine if this observation is pertinent. The maximum piston's pressure while raising a column of water is reported for both Watt and Newcomen engines. A maximum of 14.75 psi, or the atmospheric pressure, may be pulled by an atmospheric engine's pistons. Atmospheric engines can counteract with their pistons a maximum pressure of 14.75 psi, which is the pressure of the atmosphere. Due to the steam engine's mechanical losses and the imperfect vacuum, this maximum value is actually lower in real-world applications. According to historical reports, the working cylinder within the Newcomen engine is typically cooled down to a temperature between 140 and 160 degrees Fahrenheit (60°C-71°C). The steam pressure of the steam still present in the cylinder at 152 degrees Fahrenheit (67°C) will be close to 4 psi. [30] The ratio of 4 psi to 14.75 psi, or around 27% of atmospheric pressure, is adopted in exchange for a shorter cycle time and avoiding further heat losses if the inside of the working cylinder would be cooled down to a lower temperature. In the same example, 52% of the maximum pressure (7.8 psi) [31] is ultimately used to raise water, with the remaining 18% going toward mechanical losses (friction, acceleration losses, etc.).
Watt steam engines use typically 68% of the maximum pressure for raising water. So we can see indeed an improvement of 15% of the Watt steam engine over the Newcomen steam engine. A part of this improvement is likely due the improved sealing of the piston. However, we also see that from a mechanical point of view the Newcomen steam engine was already at 52%, so that indeed the most radical improvement could be achieved only by an improvement of heat losses in the steam engine and the boiler.
Historical back ground
Contrary to Watt, who's correspondence with his business partner and friends has been preserved, Newcomen doesn't appear to have any surviving historical documents of this nature. Newcomen tried to keep their knowledge of the steam engine secret and were not even allowing foreigners just to have a look at their machine. Lucky for us, a Swedish engineer, Mårten Triewald , was engaged to assist Samuel C., a son of the co-inventor with the operation of the Newman engine at a client's site. The client thought that Samuel was too young for the job and therefore Mårten Triewald was hired. Triewald stayed 10 years in England and after his return to Sweden wrote a brief book about his experiences and the first steam engine of the Newcomen type he erected in Sweden.
Recent studies [15] looking at historical documents from Newcomen's social environment reveal that he was connected to the Cornwall mining industry through family, friends, and neighbors, as well as through his occupation as an ironmonger.
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[1] John Farey, A treatise on the steam engine : historical, practical, and descriptive, London 1827, page 132 available INTERNET ARCHIVE
[2] Ibid, page 133
[3] Ibid, page 132
[4] Thomas Tredgold, The Steam Engine, Vol. I, London, 1838
[15] James Greener, Thomas Newcomen and his Great Work, October 2015, available on ResearchGate
[20] Mårten Triewald, Mårten Triewald's Short description of the atmospheric engine: published at Stockholm, 1734, Translated from the Swedish [by Are Waerland] with foreword [by Carl Sahlin], introduction [by Rhys Jenkins] and notes [by Are Waerland] https://books.google.ie/books?id=2IWFAAAAIAAJ
[21] Ibid.
[22] Ibid.
[25] Switzer, Stephen (1729) ‘An introduction to a general system of hydrostaticks and hydraulicks’, page 342 available Internet Archive
[30] John Farey, page 132
[31] John Farey, page 131