Editing Newcomen atmospheric engine (section)

==Technical details==

===Components===
Although based on simple principles, Newcomen's engine was rather complex and showed signs of incremental development, problems being [[empirical]]ly addressed as they arose. It consisted of a [[boiler]] '''A''', usually a haystack boiler, situated directly below the cylinder. This produced large quantities of very low pressure steam, no more than {{convert|1|-|2|psi|bar|2|abbr=on}} – the maximum allowable pressure for a boiler that in earlier versions was made of copper with a domed top of lead and later entirely assembled from small riveted iron plates. The action of the engine was transmitted through a rocking [[beam engine|"Great balanced Beam"]], the [[Lever|fulcrum]] '''E''' of which rested on the very solid end-gable wall of the purpose-built engine house with the pump side projecting outside of the building, the engine being located ''in-house''. The pump rods were slung by a chain from the arch-head '''F''' of the great beam. From the in-house arch-head '''D''' was suspended a piston '''P''' working in a [[cylinder (engine)|cylinder]] '''B''', the top end of which was open to the atmosphere above the [[piston]] and the bottom end closed, apart from the short admission pipe connecting the cylinder to the boiler; early cylinders were made of cast brass, but cast iron was soon found more effective and much cheaper to produce. The piston was surrounded by a seal in the form of a leather ring, but as the cylinder bore was finished by hand and not absolutely true, a layer of water had to be constantly maintained on top of the piston. Installed high up in the engine house was a water tank '''C''' (or ''header tank'') fed by a small in-house pump slung from a smaller arch-head. The header tank supplied cold water under pressure via a ''stand-pipe'' for condensing the steam in the cylinder with a small branch supplying the cylinder-sealing water; at each top stroke of the piston excess warm sealing water overflowed down two pipes, one to the in-house well and the other to feed the boiler by gravity.

===Operation===
The pump equipment was heavier than the steam piston, so that the position of the beam at rest was pump-side down/engine-side up, which was called "out of the house".

To start the engine, the regulator [[valve]] '''V''' was opened and steam admitted into the cylinder from the boiler, filling the space beneath the piston. The regulator valve was then closed and the water injection valve '''V'''' briefly snapped open and shut, sending a spray of cold water into the cylinder. This [[Condenser (heat transfer)|condensed]] the steam and created a partial vacuum under the piston. Pressure differential between the atmosphere above the piston and the partial vacuum below then drove the piston down making the [[Stroke (engine)|power stroke]], bringing the beam "into the house" and raising the pump gear.

Steam was then readmitted to the cylinder, destroying the vacuum and driving the condensate down the sinking or "eduction" pipe. As the low pressure steam from the boiler flowed into the cylinder, the weight of the pump and gear returned the beam to its initial position whilst at the same time driving the water up from the mine.

This cycle was repeated around 12 times per minute.

====Snifting valve====
Newcomen found that his first engine would stop working after a while, and eventually discovered that this was due to small amounts of air being admitted to the cylinder with the steam. Water usually contains some dissolved air, and boiling the water released this with the steam. This air could not be condensed by the water spray and gradually accumulated until the engine became "wind logged". To prevent this, a release valve called a "snifting clack" or snifter valve was included near the bottom of the cylinder. This opened briefly when steam was first introduced, and non-condensable gas was driven from the cylinder. Its name was derived from the noise it made when it operated to release the air and steam "like a Man snifting with a Cold".<ref>"A Course of Experimental Philosophy", John Theophilus Desaguliers, 1744, Vol II p. 474.</ref>

===Automation {{anchor|Humphrey Potter}}===
[[File:Humphrey Potter.png|thumb|Humphry Potter tying his strings.]]
In early versions, the [[valve]]s or ''plugs'' as they were then called, were operated manually by the ''plug man'' but the repetitive action demanded precise timing, making automatic action desirable. This was obtained by means of a ''plug tree'' which was a beam suspended vertically alongside the cylinder from a small arch head by crossed chains, its function being to open and close the valves automatically when the beam reached certain positions, by means of tappets and [[escapement]] mechanisms using weights. On the 1712 engine, the water feed pump was attached to the bottom of the plug tree, but later engines had the pump outside suspended from a separate small arch-head. There is a common legend that in 1713 a ''cock boy'' named Humphrey Potter,<ref>{{Cite web|url=https://archive.org/details/steamenginefami00lardgoog/page/n71|title=The steam engine familiarly explained and illustrated; with an historical sketch of its ...|date=6 May 1851|via=Internet Archive}}</ref> whose duty it was to open and shut the valves of an engine he attended, made the engine self-acting by causing the beam itself to open and close the valves by suitable cords and catches<ref name=EB1911>{{EB1911 |wstitle=Steam Engine |volume=25 |pages=818–850 |first=James Alfred |last=Ewing |inline=1}}</ref> (known as the "potter cord");<ref>
{{cite web
 |url         = http://www.history.rochester.edu/steam/carnegie/ch7.html
 |title       = Chapter 7: Second Patent
 |publisher   = www.history.rochester.edu
 |access-date  = 6 July 2009
 |url-status     = dead
 |archive-url  = http://arquivo.pt/wayback/20090708035343/http://www.history.rochester.edu/steam/carnegie/ch7.html
 |archive-date = 8 July 2009
 |df          = dmy-all
}}
</ref> however the plug tree device (the first form of [[valve gear]]) was very likely established practice before 1715, and is clearly depicted in the earliest known images of Newcomen engines by [[Henry Beighton]] (1717)<ref>
{{cite web
|url=http://www.scienceandsociety.co.uk/results.asp?image=10280720&wwwflag=2&imagepos=4
|title=Science and Society Picture Library – Search
|publisher=www.scienceandsociety.co.uk
|access-date=6 July 2009}}</ref> (believed by Hulse to depict the 1714 Griff colliery engine) and by Thomas Barney (1719) (depicting the 1712 Dudley Castle engine). Because of the very heavy steam demands, the engine had to be periodically stopped and restarted, but even this process was automated by means of a buoy rising and falling in a vertical stand pipe fixed to the boiler. The buoy was attached to the ''scoggen'', a weighted lever that worked a stop blocking the water injection valve shut until more steam had been raised.

===Pumps===
Most images show only the engine side, giving no information on the pumps. Current opinion is that at least on the early engines, dead-weight force [[pumps]] were used, the work of the engine being solely to lift the pump side ready for the next downwards pump stroke. This is the arrangement used for the Dudley Castle replica which effectively works at the original stated rate of 12 strokes per minute/{{convert|10|impgal|l|abbr=off}} lifted per stroke. The later [[Watt engine]]s used lift pumps powered by the engine stroke and it may be that later versions of the Newcomen engine did so too.