Development of pumps and steam engines:- Part 2
James Watt repaired the Newcomen model, but upon its being set to work, it was discovered that it would only go a few strokes at a time, though the boiler was big enough to keep it well supplied with steam. The large amount of water that it was necessary to inject to condense the steam, put Watt on the track of the theory of latent heat.
Upon thinking the matter over, Watt saw that there was a great wastage of steam and power through the alternate heating and cooling of the cylinder, and, upon reflecting further, he perceived " that in order to make the best use of steam, it was necessary first, that the cylinder should be maintained always as hot as the steam which entered it; and, secondly, that when the steam was condensed, the water of which it was composed, and the injection itself, should be cooled down to a 100 degrees, or lower where it was possible"
The means of accomplishing these points did not immediately present themselves; but early in 1765 it occurred to me that if a communication were opened between a cylinder containing steam and another vessel, which was exhausted of air and other fluids, the steam, as an elastic fluid, would immediately rush into the empty vessel, and continue to do so until it had established an equilibrium; and if that vessel were kept very cool by an injection, or otherwise, more steam would continue to enter until the whole was condensed. But both the vessels being exhausted, or nearly so, how were the injection water, the air which would enter with it, and the condensed steam, to be got out ? " This was eventually solved " by employing a pump or pumps to extract both the air and the water, which would be applicable in all places, and essential in those cases where there was no well or pit."
This is Watt's great discovery the theory of separate condensation, it made the steam-engine a useful and economical source of power, and was so successful, that for a hundred years after his invention no drastic alterations were made in the type of steam-engines in common use.
Following naturally from the main discovery were these corollaries. The piston in Newcomen's engine was kept air-tight by a supply of cold water on it upper surface- this was no longer possible, and Watt was forced to use " oils, wax, resinous bodies, fat of animals, quicksilver, and other metals in their fluid state."
Again, the cylinder being open, the air which entered to press down the piston in the old atmospheric engine would cool the cylinder. Therefore, he proposed to close the head of the cylinder, and to allow the piston rod to slide through a stuffing box, while the piston was to be forced down, not by the air, but by steam introduced above it.
The cylinder in the Newcomen engine was cooled, too, by the open air on its side; this Watt remedied by enclosing the cylinder in a second case covered with wood, and filling the space between with steam. Thus, all Watt's improvements were economical of heat. Economy in heat meant economy in steam, and economy in steam meant economy in working costs, and, above all, in coal. The atmospheric force to force the piston down in the Newcomen engine or force the water into the chamber of the Savery engine, was replaced by steam in Watt's engine. This was hence the first true steam engine rather than atmospheric engine.
Boulton and Watt steam engine
Watt now spent all his spare time in reducing the theory of his improvement to practice; he carefully thought out all the details, and calculated the amount of steam required. But, before long, he felt the need of an experiment on a large scale.
The invention was a long way from being a commercial proposition, and much money had to be spent, and much capital laid out before Watt was in a position to supply " power to order." His first patent was produced in 1769. He continued to add improvements and was the first to make a steam engine produce rotary action rather than just reciprocating motion to pump water.
Recognising that there was a considerable energy loss by constantly heating up and cooling the main cylinder, he insulated the main cylinder and provided a separate condenser.
He made the cylinder double-acting by closing the top end and providing a gland which would seal the rod.
As you have a double acting cylinder, and chains can't push, provided a rod to the beam. But the beam describes and arc, so also invented parallel motion to transfer the power from the cylinder to the beam.
He designed sun and planet gear so that reciprocating motion could also be made rotary - for winding, etc. We now have the steam whim. (note here - in general a beam engine without a flywheel is used for pumping, one with a flywheel is a whim, a winding engine or one supplying power to stamps).
Using a feedback governor to regulate engine speed.
Designing a pump to draw air and water from the condenser.
Designed for the expansive working of steam, where the steam is admitted for only part of the stroke of the piston, and the expansion of the steam does the rest of the work.
Using steam at higher pressure necessary for working expansively and with better boiler designs this became possible.
The final version of the new Watt engine worked in 1778, and it consumed 1/3 of the steam that the Newcomen engine used. This engine worked a crossbeam for pumping.
Watt himself had no money to spend on experiments, and no capital with which to start manufacturing steam-engines, should his experiments prove successful. Therefore, he had to look elsewhere for his capital, and the two men who provided it, and made possible the successful development, were Roebuck and Boulton.
Roebuck was a mining man who saw the use of Watts pump to dewater his mines. He agreed to pay Watt up to £1000 in expenses in return for 2/3 of the profits from the steam engines Watt developed. The first steam engine was set up in Roebuck's house in Edinburgh in 1769. However the manufacturing capabilities of the time were not adequate for the small tolerance required of the Watt Steam engine. At around this time Roebuck got into financial difficulties with his mines and was made bankrupt in 1773 when his support of Watts work had to be stopped.
In 1774 Mathew Boulton another great industrialist of the time offered to take over Roebuck's part of the Watt partnership in exchange for some debt that Roebuck owed him. Mathew Boulton had been interested in Watt's Steam engines to replace the Newcomen engines which he used in his many manufacturing works. It was Boultons skilled men who were able to produce the fine tolerance work necessary to make Watt's engine work by around 1774.
In 1775 the first Watt engine was put to work pumping water from Bloomfield colliery near Birmingham.. Here it was said that the Watt engine could pump as much water as the Newcomen engine for 1/3 of the fuel costs. In 1778 one was fitted at Chacewater copper and tin mine in Cornwall. Over the next few years Watt's engine with some refinements came to replace all earlier engines.
In 1819 Michael Faraday visited the Parys mines and described the pumping operation he found there :-
...We had now reached the well of the mine situated at its lowest point nearby. Here all the waters that run from the earth into the excavation are collected together to be pumped up. There was a large quantity in a sort of tank boarded over and containing much copper in solution. The waters it appears had risen a little and they were very particular about them just now because close at hand they were deepening the mine and working at a level below that of the well...
... After a little further progress we came to the pump shaft, an aperture cut down from the surface to this spot. It was 360 ft. deep and we could see no daylight up it. Below it was a small well connected with the large one before mentioned and into this were inserted pumps. The first was a lifting pump and raised the water a few feet. Then a forcing pump took it and made it ascend up pipes far away out of sight. The pumps were worked by the steam engine we had seen above being connected with it by beams of wood descending in the shaft and continually rattling up and down in it. In the small part of the shaft left vacant by the pistons pipes and beams were fixed ladders which ascending from stage to stage conducting to the top and up. There we had to go bathed in the shower of water which was shaken off from all parts of the pump works. After long climbing we came to a part of the shaft where the first forcing pump delivered its water into a little cistern and then another pump of the same construction threw it up to the surface. Still proceeding we at last got a glimpse of daylight above and were soon able to see the pump rods by it. Now the danger of the ascent appeared far greater than before for the more extensive light showing in the well above and something of the depth below made us conscious of our real situation whereas before we only thought of the small spot illuminated by our candles. The agitation of the pump rods was more visible too and appeared greater from being seen over a larger space and their rattling and thumping was quite in accordance with appearances. But in spite of all things we gained the surface in high glee and came up into the world above at the engine after a residence of about two hours in the queer place below...
The result of all of Watts and Boulton's work was that the efficiency improvements not only saved money for the industry, but also gave Boulton and Watt a considerable income, not only from the sale of their engines, but from the licence of a the equivalent of third of the fuel saving made over the Newcomen type. As an example of the saving, a 30 inch (cylinder diameter) engine was doing better work than a 72 inch Newcomen type, with a considerable saving in coal.
The licence system was to cause problems and friction between the Boulton and Watt company and the mine owners and effectively stifle improvements in the technology until 1800, when the patents ran out. The subject of this is a very interesting, contested and long account, ably described by other writers.
Suffice to say that the Watt technical innovations on steam technology saved many mines. Their costs for so doing were also high and although improving the profitability initially, then depressed the profitability of the mines hampered by the continual charges made. The protectionist nature of the patent also meant that improvements could not easily be made.
Richard Trevithick who was born at Illogan on 13th April 1771 to a mining family made the next step forward. His first contribution to steam development came when he used higher pressure steam, and got around the Watt patent by dispensing with the separate condenser.
Trevithick's engine, which worked a pump by way of a crossbeam, was very successful and was in use for a long time. The steam (at 3-4 kg/cm²), was admitted in the cylinder only for 1/10 or 1/5 of the active stroke. When the inlet valve is closed, the piston continues its active stroke by steam expansion. When the piston reaches the bottom of the stroke an equilibrium valve opens to allow the steam to pass from above to below it. The pressure above and below the piston is now equalized.
The upstroke is assisted by the crossbeam and the descent (by gravity) of the very heavy pump piston and rod. When the piston has almost completed the upstroke, the equilibrium valve closes to make a steam cushion which reduces impact vibration. The exhaust valve opens before the inlet valve opens. The beam moves slightly under vacuum pressure alone and then accelerates greatly when the inlet valve opens. In the cylinder below the piston, through a connection to the condenser, a partial vacuum is created. This assists the steam pressure above to drive the piston down, increasing the engine's efficiency.
After 1800 Tevithick concentrated on road locomotives, but in 1812, partially as a result of this work, came up with the Cornish boiler.
The Workings of a Cornish
At rest, the piston is at the top of the stroke and consequently the pump rods are down.
To start, the driver opens the exhaust valve linking the space below the piston and the condenser. The steam valve to the annulus, the upper part of the cylinder, is opened, and 40-50psi steam forces the piston down and consequently the pump rods up.
Because of the expansive nature of steam the valve is closed at about one third stroke and the rest of the stroke carried out by the steam expanding. This is the indoor stroke, the beam coming down over the cylinder.
At the bottom of this stroke the equilibrium valve is opened
and the steam above the piston, now at about atmospheric pressure to escape to the underside of the piston. The weight of the pump rods is allowed to carry the piston to the top of the stroke again.
However, just before the top is reached the equilibrium valves closes and cushions the ascent of the cylinder as the remaining steam is compressed (this is the outdoor stroke). Just before the steam valve is opened again the condenser valve is opened to allow the exhausted steam to escape and created a vacuum below the cylinder, generating a considerable force by itself. The cycle then restarts.
As soon as the enginemen had felt that all the air had been expelled (had become solid) then the driver would engage the automatic valve systems and the engine would work by itself.
Mostly whim engines are double acting, with steam being admitted to both the full bore and annulus sides of the piston. There was no counterweight to draw the beam down for the outdoor stroke, merely a flywheel and for winding you need a constant power. In this type of engine ( at one time known as a Trevithick puffer) the technology is akin to a steam locomotive. Here power is applied on both strokes to keep the load coming up the shaft.
The tall chimneys were used to draw the fire - the convection of the flue drawing more air through the fire. This is unlike the later railway locomotives where there was a blower - a pipe from the boiler led to the flue and steam was bled off and provided a venturi type effect to draw more air through the fire and therefore encourage the more rapid burning of the coals - this was a purely convective effect. Unfortunately if you tried too tall a chimney then your fire got sucked up the flue as well!
Every part of an engine house was built to protect the engine rather than the workers. The methods of construction were to build the stonework, the bob and side walls, install the beam - they put that through the door and then by a combination of balance, labour and luck mounted the beam in the trunnions, then put the roof on. This was because the beam was elevated at substantial angle while being mounted. Then the cylinder came in, the mechanics were connected up then the steam connections came from the boiler house, which was usually built alongside. First steaming were usually accompanied by some sort of party.
In parts where the weather was more than usually wild, Botallack Crowns for example, the flue was built into the corner of the engine house. This kept it warm for better convection and provided some comfort for the driver of the engine.
(Proceeding section after John & Sandy Colby)
This was a technological advance because the hot flue gasses could also be used to heat the water, so improving efficiency. In addition the fire was inside boiler and so was more efficient. Trevithick's combined improvements made the new design of Cornish engine do double or treble the duty of the Watt type, and so they supplanted them as the Watt type had supplanted the Newcomen styles.
