This shows a simple header tank, Michael : **LINK**

https://www.nms.ac.uk/explore-our-collections/stories/science-and-technology/newcomen-engine/

Sorry, I have no experience of scaled-down model versions.

MichaelG.

Depends I think on the date of the engine. This picture is of a Smeaton improved engine, he eventually tripled the efficiency of Newcomen's original by optimising the relationship between piston diameter and length of stroke, the number of strokes per minute, and the size of the boiler.

In this example the boiler isn't immediately below the cylinder, which I think means Smeaton was able to do better than the original pot boiler.

However, the engine:

• Lifts cold-water into high-level tank O with a chain pump dropped down Pipe N. The pipe goes down a well. The pump chain is driven by a separate beam linked to the main beam (I)
• Cold water flows from tank O along Pipe P. A proportion of it is diverted to the top of the cylinder by pipe f. Pipe f feeds water to the top of the piston, the amount being set by Tap r. When the piston rises, any surplus water on top is drained into the Hot Tank S. The purpose of this top feed is a little controversial: some say the water just improves the piston seal, which was very poor. Others say the vacuum stroke also pulls cold water in at the cylinder top and significantly increases the power of the engine.
• The other end of Pipe P feeds cold water into the bottom of the cylinder, via another tap r, which is turned on and off by lever g, is driven by pegs on rod Q. In the original engine, water just flowed from a single orifice into the bottom of the cylinder. In this drawing, dotted lines show pipes set up to spray water into the cylinder from several places. Several sprays condense the steam quicker than a single pipe for more power, better efficiency.
• After the stroke, hot water is emptied into tank S, and used to top up the boiler.

Modelling these engines is said to be difficult because they're intrinsically very inefficient plus their physics don't scale down well. The very best a vacuum can achieve is only 14psi which can't put much force onto a model sized piston driving quite a lot of mechanism. And on practice the vacuum will be much less than 14psi because the surface area of the small cylinder and piston is large compared with their volume. Thus heat is lost rapidly even before any cold water is sprayed in, and there may not be enough vacuum at the right time to rock the beam. Bigger is definitely better when it comes to atmospheric engines.

Dave

There is a working replica of a Newcomen engine in Whangaparaoa near Auckland NZ. It was built by the Auckland Steam Engine Society. When I say replica, there are no scale working drawings of any of the original engines, or any original engines to take drawings from, so the most we can say is that it is like the originals and works on the same principle. It stands about twenty feet high and the pumped water is used to turn a small waterwheel, maybe 6 feet or so in diameter.

There was a kitset for a model one being sold a few years back, one of the local guys here in NZ bought one and it did work to at least some degree, with some difficulty at times. It was maybe 18 inches or so tall.

John

Both versions of this rather splendid image are freely downloadable, at quite a respectable resolution:

**LINK**

https://collection.sciencemuseumgroup.org.uk/objects/co50905/print-of-henry-beightons-engraving-of-a-newcomen-engine-print

MichaelG.

Edited By Michael Gilligan on 12/09/2022 00:09:52

Getting back to the original question, I think that half barrel being hosted up in one of the pictures contains the water that is used for the condensation. It sits on top of the frame, although on an original engine it would probably have been somewhere in the engine house. It doesn't need a lot of head, since the pressure in the cylinder is never high.

If anyone wants to use any of the images, I have no objection to any non commercial use like club newsletters or personal study.

John

Our school history teacher told us a tale of a lad at a mine employed to turn the water and steam on and off. Being perennially sleepy he rigged up an arrangement of levers and string to do it automatically. Foreman found him asleep on the job and he was promptly sacked.

The boy Potter may be a myth, like Newton understanding gravity after being hit on the head by an apple and Watt being inspired to invent the steam engine by his mum's kettle lid lifting when it boiled.

It's possible the "boy" in question is a misunderstanding. Another explanation is that early automatic atmospheric engines featured a Buoy Valve, which someone assumed meant a child was involved. Buoy valves aren't unlikely in pumping engines – Cornish Engines all had Cataract valves. (In British English buoy is pronounced boy, rather than Boo-ee in English as she is spoke in the USA! )

It's true the valves on Newcomen's first engines were operated manually and so it's possible the job was done by a real boy with strong practical skills and engineering insight. But if I'd built an expensive state of the art pumping engine to keep a costly coal mine dry enough to work in, I'm not sure I'd trust an unsupervised boy to drive it! More likely various clever experienced men tried a number of different methods, and settled on what seemed the best. At that point the small-c conservatives who infest British engineering seem to have taken over: a century later the beam and valve-gear on Watt's early engines is very Newcomen.

We will never know whether or not the boy really existed unless something turns up in a musty archive.

Dave

You need to get hold of a copy of 'The Steam Engine of Thomas Newcomen', by Rolt and Allen. Get the Landmark edition of 1997 if possible, it has a better bibliography. This book does mention a wide range of information about this engine.

Gravity was used to give a pressure to the injection water. It was simple and effective. When John Smeaton started to look at the design of the engine around 1770, he said that the injection water system should be as high as possible in the engine house. He also specified that the injection water nozzle should be square. This broke the jet up to provide a better spray. To see how this works, look at the internet site ' physicsgirl smoke rings ', and see the effect of blowing a square smoke ring. Water, being denser than air would be slightly different, it would tend to fly outwards.

Getting water up into the injection tank was an interesting problem. The Thomas Barney 1719 engraving of the Dudley Castle engine shows a small pump connected to the beam by a heavy connecting rod to pressurise the water sufficiently for it to rise to a level where it could flow into the injection cistern. The jack head pump came a little later ; it was connected on the main pump end of the beam by a light chain. As the main pump was lifted, the jack head piston was also lifted, forcing water up a pipe to the cistern. The John Smeaton engine drawing shows a more complicated arrangement using an auxiliary beam to operate a lift pump by a chain connection.

Model Newcomen engines have different problems, you would probably need a small motor driven pump to supply injection water at three or four psig. The main pump on such an engine works best using a jack head pump with an adjustable valve to control the flow of water from the pump. A friend of mine had a model engine, built by a toolmaker from his scrap box. I first saw it about 1998 or 99 at a Heritage weekend at Elsecar. I walked into a room with this model working away in a corner, started talking to the operator, and over twenty years later we are still talking. His engine was driven by steam from a pressure cooker, ran very effectively, and provided information about these engines that can be found nowhere else. This engine has now worn out, he has another that he built based on the Dartmouth engine. The single lever valve gear has caused problems, so is probably unsuitable for a model. He thinks that model Newcomen engines can work very well, but do need care, starting with the fit of the piston in the cylinder.

The model Newcomen engine that James Watt worked on still exists. It is in the Hunter Museum in Glasgow, an example of a clock maker's or instrument maker's skill. There is a similar model in Kings college at the University of London.

Jim Andrews wrote a paper about the differences between the Newcomen and Watt engines, and gave talks about it. The paper does not appear to have been published.

Over the last three hundred years a huge amount has been written about the Newcomen engine. The Newcomen Society has published nearly ninety papers about it. Over thirty years ago I began to read about it, and when I was deemed too expensive to employ in 1992, I began work on a patented version dating from 1790, the Heslop engine. Twenty years later I had just about worked out who did what and when and read a paper to the Midlands branch of the Newcomen Society when a row broke out about the site of the 1712 Newcomen engine. So, along with some other people I started to look at the evidence. I did come to a conclusion about it that fitted with some of the contemporary writings ( Well, about thirty years after. ) I have continued to collect information about this engine and others. We still have large gaps in our knowledge and understanding of these machines. People talk about the lack of efficiency of these machines, but at the time there was nothing else that could get water out of mines, apart from water wheels and windmills. The problems that they had are still with us in renewable generation of power.

I think that is all for now. The history of this engine sprawls everywhere, and fresh items keep coming to light. In 2020 I found nine separate items from auction sales to paintings, drawings and one article about a well known engine that I did not know existed. Two items allowed me to estimate the size of engines that we know existed, but knew nothing about. If you think that we do not know a lot about English engines, then the Scottish engines hardly exist at all, and European engines are very difficult to find anything about apart from the fact that they existed in some cases.

If anyone has any further questions I would be happy to discuss them.

Regards. Mike Potts.