Atmospheric and early beam engines
The 'prehistory' of the steam engine is not wholly clear, in AD100 Hero decribes the Aeolipile - a 'philosophical toy' which consisted of a steam raising vessel or boiler surmounted by a rotating hollow sphere with two tangential jets, which, once steam was issuing from the jets, caused the shere to rotate - the first reaction turbine. There is also a description of a steam or atmosherically operated device for opening or closing temple doors.
In the early 1600's, the effects of using steam to displace the atmosphere and then harnessing the atmospheric pressure (14 - 15 pounds on each square inch of surface) available when the steam was condensed and a vacuum formed were being explored by numerous people throughout Europe, including Solomon de Caus, Roger North, Robert Hooke, Robert Boyle, Denis Papin (the inventor of the pressure cooker) and the Marquis of Worcester in England, Gallileo and Torricelli in Itally and Otto von Guericke in Germany.
It was not until 1698 that the first steam engine to perform useful work was built by Thomas Savery and a Patent granted 'for raising water by the impellent force of fire'.
The 'Miners Friend' used the vacuum produced by condensing steam in metal bulbs to suck water up from a lower level and the pressure of steam to force the water up to a higher level. With the steam acting directly on the water, they were very inefficient. Due to the poor materials available at the time, unreliable and dangerous but they fulfilled the need to drain mine workings - particularly where coal was abundant. None are known to have survived
The wet mines promoted the next stage of steam engine development when in 1712, Savery and Thomas Newcomen built the first atmospheric beam pumping engine near Dudely Castle. It utilised a piston working within an open topped cylinder. The piston was connected by chains to a rocking beam or lever, the other end of which connected to the pumps situated down the mine and actuated by long timber rods. On the outboard stroke, the cylinder was filled with steam from the boiler (which operated barely above atmospheric pressure) a jet or spray of water was introduced into the cylinder to condense the steam and the difference in air pressure above and below the piston caused it to move down, pulling the beam and the pump rod with it, raising water as a result. The operation of the various control valves was quite complicated and initially were driven manually at each stroke, however they were soon automated to operate on their own. Over the years many atmospheric beam engines were built and a few still survive, including one in Newcomen's home town of Dartmouth.
Many variants of the atmospheric engine were developed, initially only capable of pumping they were often used to return water to streams above waterwheels in an effort to increase the power available from the waterwheels or the length of time that they could be used where water supply was poor. The goal of direct rotary drive to machinery was satisfied and the three blocks above show a single acting rotative beam engine of 1780, a double cylinder rack and pinion drive engine of 1794 and a double acting rotative engine of 1793. The repeated heating and cooling of the cylinder made them very inefficient and the next major leap forward in efficiency came in 1765 when James Watt developed the seperate condenser, a vessel seperate from the cylinder which allowed the steam to be condensed without the need to cool the cylinder, Watt also started using steam at low pressure to push the piston, a function in the atmospheric engine which had been performed by gravity, the outboard end of the beam being heavier than the inboard.
James Watt, in partnership with Matthew Boulton developed the beam engine to a level of economy not previously possible, they were astute enough to Patent their developments and for a period had a virtual monopoly on the more efficient engines, they charged their customers a third of the claculated savings in coal compared to using an atmospheric engine of the same power, the fees were considerable.
Watt's proudest achievement was to devise the parallel motion that connected and guided the end of the piston rod which moved in a straight line, to the end of the beam which moved in an arc. As can be seen he had several ideas before settling on the method on the right, which was subsequently used on the great majority of centre pivoted beam engines.
His other contributions were to make the engine double acting, (that is the steam / atmospheric pressure was operating alternately on either side of the piston in turn) Making the engine rotate a shaft - initially by use of the 'sun and planet' gears pictured in the block above - often attributed to the crank having been patented by another engineer but in my opinion primarily due to the fact that for every stroke of the engine the shaft would rotate twice and finally controlling the speed of the engine by a rotating governor which reduced the steam available if the engine increased in speed and increased the steam supply if it slowed down. Watt also developed the indicator, a device by which the pressure inside the cylinder in relation to the position of the piston could be measured - the steam engineers primary tool for ensuring that the engine was working to it's best effect.
Whilst the impact of their engines made should not be underestimated, Watts Patent was restrictive to the further development of steam power for many years and the costs of licensing one of their engines (they were all fitted with locked counters so B & W would know the number of strokes or 'duty' the engine had made and from which the could be calculated - a bit like today's electricity, gas or water metering) high - although Watt countered this by pointing out they were only charging a part of the savings of using an atmospheric engine !
This situation caused a number of others to either challenge, attempt to circumvent or just ignore the Watt patents. As a result a number of other designs came about - especially in Cornwall, where the deep wet tin mines and high coal costs made cheap powerful pumping essential, Engineers such as Arthur Woolf started using steam at higher pressures - something Watt resisted in his own machinery - as a result of this, what has become known as the Cornish pumping engine was developed,.
The two blocks above illustrate the type, many of which were also built for public waterworks service. A single acting engine using both high pressure steam above the piston and a vacuum created below the piston by transferring and then condensing the exhaust steam of the previous stroke to drive the piston down and lift the pump rods, the weight of the pump and pump rods dragging the engine back to the staring position.With their numerous rods and valve handles operated by movement of the beam, and the stroke timing controlled by the 'cateract' a form of water clock, these engines are fascinating to watch in action.
Cornish engines were made in substantial numbers and some very large sizes - the largest being three built to drain the Haarlemeer in Holland with pistons 144" or (12 feet if you prefer) across, one of these is preserved at Cruckquis. The largest surviving in the UK are at Kew Bridge pumping station, (close to the junction of the north circular road and M4 in West London) where a 100" bore engine is under renovation and a 90" works under steam most weekends. Several have also survivied in Cornwall and other parts of the country.
Another development of the Cornish engine was the rotative version, used for mine shaft haulage or driving stamps which crushed the ore or other machinery.
The tremendous weight of the rocking beam increased as the power of the engine increased - some of the largest were around 100 tons ! As a result of this attempts were made to produce a direct acting pumping engine working on the Cornish principle, it is not certain who produced the engine above but it shows the principle, with the cylinder inverted and with the pump rod suspended directly below it, there were disadvantages, particularly if you dropped a nut, bolt or spanner down the shaft while working on the engine.
Edward Bull produced the most successful engines of this pattern, so they are now known as Bull engines - this one survives at Kew Bridge and is to be made workable again.