OvermodBut let's be honest: those aren't steam engines, they're atmospheric engines.
Yes, Bob. Thomas Savery's engine is powered by atmospheric pressure, not steam. And Thomas Newcomen's engine was also powered by the atmosphere. But when James Watt put a cap on the top of the cylinder of a Newcomen engine and began putting steam on both sides of the piston did he invent something new or was that an evolutionary step in the development of the steam engine?
The real honest truth is that I understand and agree with your distinction between an atmospheric engine and a steam engine. But Savery's engine would not have worked without steam even though he condensed the steam to create a vacuum. So in my own head I wonder if Savery really did have a steam engine but a different kind of steam engine.
John
From what I remember reading a long time ago, both Saverys and Newcomens engines were a bit of a flop, inefficient and with a bad habit of stalling. It was James Watt who made the steam engine truly practical.
And Overmod me old son, if the N&W Mighty 611 is awakened from her 18 year sleep, then we'll KNOW God is a railfan!
Firelock76 From what I remember reading a long time ago, both Saverys and Newcomens engines were a bit of a flop, inefficient and with a bad habit of stalling. It was James Watt who made the steam engine truly practical
From what I remember reading a long time ago, both Saverys and Newcomens engines were a bit of a flop, inefficient and with a bad habit of stalling. It was James Watt who made the steam engine truly practical
Wayne,
They certainly were inefficient. However, an experienced operator could get them working smoothly. Savery's was a vacuum pump which limited it severely. Newcome's however, was not. Newcomen engines were used for a great many years despite their inefficiency and there are some that still are operated on special occasions.
James Watt certainly made a big contribution to the development of the steam engine. However, Watt was afraid of high pressure steam. His stationary engines did power factories and even steam boats they they never ever would have powered a locomotive; they just did not have high enough pressure to do so.
Mostly, I see Savery, Newcomen and Watt as developing engines that had to be developed before we could get to steam locomotives.
John WR ... when James Watt put a cap on the top of the cylinder of a Newcomen engine and began putting steam on both sides of the piston did he invent something new or was that an evolutionary step in the development of the steam engine?
... when James Watt put a cap on the top of the cylinder of a Newcomen engine and began putting steam on both sides of the piston did he invent something new or was that an evolutionary step in the development of the steam engine?
Yes, he did, and yes, it was. The earlier point about Watt's 'retarding' the progress of high-pressure steam is quite valid, but we also need to remember that Watt, after inventing the condenser to improve operation of atmospheric engines, also developed the true steam engine using pressure to push the pistons. Most of what I (pedantically) was trying to establish was that pressure on a piston to produce engine was not a 'new' thing with Watt et al., and that steam as a means of producing that pressure had been considered (and rejected) before Pepin's time.
Yes, but under that definition the Space Shuttle also uses a different kind of steam engine. With more in common with Isaac Newton's application (over a hundred years before Watt). Speaking strictly for myself (and specifically NOT claiming that my definition has to be accepted) I reserve the 'steam engine' label to engines that actually use steam for power, not non-motive (or, indeed, anti-motive) displacement of air.
In fact, in a sense, the Savery/Newcomen principle is still with us as a primary 'evil' in steam-locomotive design; nucleate condensation is a primary drag on the efficiency of any long-stroke long-expansion engine -- and I also argue that reducing this, not overcoming 'wall losses' per se, is the most important advantage of superheat on modern locomotives.
(BTW, comments I make on here are not intended as criticism or one-upsmanship of your ideas, or as "I know more than you, nyah nyah nyah' show-offery. If they come across that way, I apologize in advance, repeatedly as necessary)
Firelock76From what I remember reading a long time ago, both Saverys and Newcomens engines were a bit of a flop, inefficient and with a bad habit of stalling. It was James Watt who made the steam engine truly practical.
Your comment about the Newcomen engine set off questions in my mind. Why would it stall?
I do know one thing James Watt did was to fit the size of the boiler to the size of the cylinder. If the boiler was too small then it might not generate enough steam or be slow to generate the steam the piston needed. That could slow or even stall the engine for a while. Do you know if that is the reason?
Another question occurs to me. How did they start a Newcomen engine? When the engine was stopped the pump was at the bottom of its stroke and the steam cylinder was at the top of its stroke so the stean cyliner would be filled with air. I have never seen any reference to exhausting this air to start the engine. If the steam piston was a little loose the air might escape around it but if it fit well air could not escape. Then when the steam was admited only a little steam would enter the cylinder and when it was condensed the cylinder would still be full of air. I've never seen any refernce to this issue so I don't know how it was dealt with. I can think of ways to deal with it but I wonder what they did back when the engines were used.
Hi John!
Oh boy, it's going to take a bit of remembering on Mr. Newcomen, it's been years since I've read about it. Without resort to "Da Wikepedia" I think it went something like this"
Newcomen's engine was a stationary engine primarily used to pump water from mines, coal or otherwise. The piston was attached to, in effect, a "walking beam" which operated the pump mechanism. It had a habit of stalling in mid-stroke, so the engineer would have to give the beam a good shove up or down to get it running again. A good shove on the beam is what got it started to begin with. It got the job done but there was definately room for improvement.
If I'm wrong, wrong, wrong on this don't anyone of you hesitate to correct me.
Wayne
Firelock76Newcomen's engine was a stationary engine primarily used to pump water from mines, coal or otherwise. The piston was attached to, in effect, a "walking beam" which operated the pump mechanism. It had a habit of stalling in mid-stroke, so the engineer would have to give the beam a good shove up or down to get it running again. A good shove on the beam is what got it started to begin with.
Especially during the early years Newcomen's boilers were too small for his engine. Steam would enter they cylinder, the piston would rise and a spritz of water would condense the steam and cause the cylinder to fall back. Since the walking beam was heavier on the pump side it began to draw the piston up again actually drawing steam into the cylinder. However, if the too small boiler had not recovered the piston would rise to the top of the cylinder which was not full of steam. The steam valve was shut off and water spritzed in again. But with the cylinder only partly full of steam the piston would stall in mid stroke. Of course the operator could grab the beam and pull it the rest of the way down to help the engine. When the piston got to the bottom hopefully the boiler would recover.
Newcomen designed a special valve activated by a "bouy" in a tube which floated on top of the water. As steam pressure built in the boiler it pushed the bouy up which then opened a valve to the steam injector when the boiler was ready. This solved the problem but slowed down the boiler.
Ultimately larger boilers were installed. That was the real solution.
Of course there was room for improvement. If there were not we would still be using Newcomen eingines today. Yet Thomas Newcomen figured out how to combine steam and the force of gravity on the atmosphere to raise water to a much greater height than had ever been possible. I think that is pretty impressive.
What Watt initially did was do the condensation of the steam to water+vacuum in a SEPARATE vessel (condenser) rather than sprinkling water directly into the cylinder to accomplish the condensation as Savery and Newcomen had done. Since the whole cylinder and piston didn't have to be thermally cycled, the engine required much less mass flow of steam to 'break the vacuum (and incidentally displace any atmosphere that has leaked in) on each stroke, therefore less fuel had to be burned.
(One little point: on an atmospheric engine, the condensate helps seal the piston. Which is why the normal location of the cylinder is 'on top' and the stroke is up, not down...)
John WRYour comment about the Newcomen engine set off questions in my mind. Why would it stall?
Any time the generated 'vacuum' was insufficient to give enough pressure differential to move the load completely up to 'spill'. This might happen if the steam were not hot or dense enough to displace the atmosphere completely before a given stroke. It might happen if there were too poor a seal between piston and cylinder, resulting in the atmospheric equivalent of blow-by. It might happen if there were too much water, or a hydraulic lock of some kind, on one of the cascaded pump cylinders down in the mine, or too much cumulative load in the pump stages -- the flow of water might be variable, in a way the operator up at the head of the shaft could not see or predict.
Remember that, as with British vacuum brakes, the absolute highest pressure that could be exerted on the piston is around 14 and a half psi, and practically it would be some fraction of that. Not difficult to lose a significant amount of that pressure for little causes... and when the force of the atmosphere up no longer exceeds the gravitational attraction of water, pump rods, and the rest of the stuff... you will get a stall.
That would certainly be a good reason. On the other hand, inadequate steam generation would (in my opinion) reduce the cyclic rate of the engine, rather than predisposing to stall, unless whoever or whatever was working the valves was cutting off too soon -- leaving an incomplete vacuum inside the cylinder, or not purging enough to overcome leaks and losses.
Another question occurs to me. How did they start a Newcomen engine? When the engine was stopped the pump was at the bottom of its stroke and the steam cylinder was at the top of its stroke so the stean cyliner would be filled with air.
I must be missing something, because this is exactly the situation that has to prevail to start a Newcomen engine.
You turn the steam into the air-filled steam cylinder. This heats the air (which is a gas) so that it displaces quickly and is replaced with a (smaller, actually) mass of hot steam in vapor phase. At this point there is pressure equalization between whatever mix of steam and air -- increasingly steam, as the admission continues -- and the air under the piston, until you close the admission valve.
Now you have a cylinderful of glorified water, that wants very badly to be water again (and shrink that 1200x in volume when it does), and under it you have... well, atmosphere, which would be leaking in even if you didn't give it really good access to the bottom of the piston. Spray in the water, and the steam condenses (to about 1/1200th of the displaced volume... leaving some small amount of vapor corresponding to equilbrium for the effective degree of vacuum in the remaining space.
I think I can ASSURE you that the movement would be self-starting with little manipulation under those conditions. If you happen to have too much water in the pump down the shaft... spill out a little water. At some point it will certainly self-start.
To get the beam back down, you have to admit fresh steam to the cylinder, and any residual atmosphere that has sneaked past the seal into the cylinder will rapidly be heated and displaced. Again, self-starting, with a little more 'oomph' since the purge doesn't need to absorb heat from the steam this time.
I have never seen any reference to exhausting this air to start the engine.
What did you think made the vacuum to start the engine? Some sort of Bernoulli ejector? The steam dilutes and purges the air during initial admission, and the seal keeps atmosphere from rushing in through the piston-cylinder gap after that first stroke... if all goes as designed.
If the steam piston was a little loose the air might escape around it...
Exercise for the reader: What would MAKE the air 'escape around it'. Gravity is all pulling down on the piston. Steam used for compression would be pushing down on the piston. But ONLY when the piston moves UP will you get 'air to escape around it' ...
... when the steam was admitted only a little steam would enter the cylinder and when it was condensed the cylinder would still be full of air.
Gas laws are different. The steam is hot, but when it gives up its heat to make the air hot, that percentage of it condenses and its volume gets very small with the phase change. Gas kinetics (if you don't trust me on this, look the subject up) very rapidly get the hot gas to purge, relative to the continued admission of steam -- it is not long before things have 'equalized' with mainly steam instead of air in the cylinder. And a little water down at the bottom helping to seal the piston, etc.
I've never seen any reference to this issue so I don't know how it was dealt with.
I can't remember having seen an engineering reference to atmospheric engines that did NOT describe how it was dealt with. Once you understand that steam admission is used to purge the atmospheric mass, the rest should be easy to see.
Overmod I think I can ASSURE you that the movement would be self-starting with little manipulation under those conditions. If you happen to have too much water in the pump down the shaft... spill out a little water. At some point it will certainly self-start.
Your explanation hangs together, Bob, but I have to say it sounds counter intuitive to me.
Back in my school days I learned that air is a fluid. If you are going to have a container of air and you want to replace the air with another fluid such as steam you must give the air a way to get out. If the piston has a tight seal and is at the top of the cylinder and the steam injector is turned on it seems to me that a little steam would be admitted but not much. So when water is sprtized in there won't be much steam to condense and there won't be much of a vacuum.
It also occurred to me that maybe the seal was not real tight. As the steam is admitted the air can escape around the edge of the piston. As the steam reaches the top the seal is both heated and moistened and that might lead it to swell and give the tight seal the machine need to operate.
What I do know is that Newcomen engines were used for a great many years and they worked well enough to do their job.
If I am not mistaken (I don't have a detailed diagram at hand) there is a starting or purge valve in the head of the cylinder. This is opened to blow out the air before the engine starts working steam.
Oddly enough, there is some modern steam machinery that does not work right when trapped air is present -- some flavors of condenser and feedwater heater, and the Holcroft-Anderson recompression setup, come to mind -- and these have to have purge valves or 'air pumps' of some sort, too.
The steam and air mix, and not really 'segregate', as you indicate. But it only takes a few moments for kinetics to mix air and steam, and eject an increasing net amount of the air from the system. I think you are correct in thinking it would take a MUCH longer time to start the engine if the relief valve were not present...
OvermodIf I am not mistaken (I don't have a detailed diagram at hand) there is a starting or purge valve in the head of the cylinder. This is opened to blow out the air before the engine starts working steam.
I was wondering about a purge valve. But I have never read of one in any description of a Newcomen engine and I've never seen one in a diagram.
OvermodSpeaking strictly for myself (and specifically NOT claiming that my definition has to be accepted) I reserve the 'steam engine' label to engines that actually use steam for power, not non-motive (or, indeed, anti-motive) displacement of air.
My own experience is that whenever the history of steam engines is discussed Savery and Newcomen engines are part of it. However, there is usually mention that those engines are really atmospheric engines rather than true steam engines.
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