Watt steam engine
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Improving on the design of the 1711 Newcomen engine, the Watt steam engine, developed in 1765, was the next great step in the development of the steam engines. Offering a dramatic increase in fuel efficiency for what was a minor design change, the new design was soon retrofitted to almost all existing Newcomen engines, and then went on to be used in place of most natural power sources such as wind and water. James Watt's design became synonymous with steam engines, due in no small part to his partner, Matthew Boulton.
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[edit] Introduction
In 1698, the English mechanical designer Thomas Savery wrote out the designs for the world's first operational steam engine. The Newcomen engine was modeled on Savery's designs.
Thomas Newcomen's design was both powerful and useful; the first example from 1711 was able to replace a team of 500 horses that had powered a wheel to pump out a mine. In over fifty years few detail changes had been made to the basic design, seventy-five of which could now be found at mines all over England.
However effective the system was, it was also expensive to run. It worked by creating a vacuum in a cylinder by condensing steam inside it. This process was normally so slow that the engine was not very effective, so to improve the condensation a small spray of water was introduced when the cylinder was filled with steam. Unfortunately the water also cooled the cylinder walls, so when the next charge of steam was introduced it spent some time simply warming the cylinder back up to boiling temperatures, condensing while this occurred.
[edit] Separate condenser
A Scottish instrument maker, James Watt, was given the job in 1763 of repairing a model Newcomen engine for the University of Glasgow, and noted how inefficient it was. In 1765, while wandering across Glasgow Green he conceived the idea of a separate condensing chamber for the steam engine. Watt's idea was to separate the condensation system from the cylinder, injecting the cooling water spray in a second cylinder, C, attached to the main one through a valve V'. When the piston had reached the top of the cylinder, the valve V was closed and V' was opened. External atmospheric pressure would then push the steam and piston towards the condenser. Thus the condenser could be kept cold and under less than atmospheric pressure, while the cylinder remained hot.
[edit] Matthew Boulton
Watt met Matthew Boulton and became a member of the Lunar Society. He told Boulton about his ideas on improving the engine, and Boulton, an avid entrepreneur, agreed to fund development of a test engine at Soho, near Birmingham. This proved frustrating and Watt repeatedly almost gave up on the project, only to be convinced to continue by the ever-cheery Boulton.
The improvement due to this change was dramatic: Watt's design used about 75% less fuel than a similar Newcomen engine. Since the changes were fairly limited, Boulton and Watt licensed the idea to existing Newcomen engine owners, taking a share of the cost of fuel they saved.
Watt was unwilling to rest on his laurels, and continued to improve his designs throughout his life. He realised that the new means of evacuating steam from the cylinder might quicken the operating engine cycle. Suppose low pressure steam could be substituted for atmospheric pressure? If the top of the cylinder was closed off, the steam could act upon the piston in the power stroke. (The steam pressure would not be able to move it in normal circumstances, but it could if acting upon a vacuum.)
This raised the possibility of reciprocal action. An arrangement of valves could admit steam at either end, or connect either end with the condenser. Consequently, the direction of the power stroke might be reversed. The resulting two strokes gave a very even movement of the beam.
[edit] Later improvements
He turned his attention to providing rotary power from his engines, introducing the sun and planet gear system invented by his employee William Murdoch, and later adopting the more familiar crankshaft seen on most engines today. This allowed the steam engine to be used to replace water wheels, thereby freeing British industry from geographical constraints and becoming one of the main drivers in the industrial revolution.
In order to improve reliability, he introduced further improvements. The operation of the condensor was assisted by an air pump, driven by an eccentric rod attached to the beam. As the pace of the operation of the machine increased, it needed to operate at a constant speed. He employed a centrifugal governor earlier used in windmills to automatically control the pressure between the millstones, automatically controlling steam flow to the engine and keeping it at a steady speed. He also introduced the manometer to measure steam pressure within the engines, which, when connected to a linkage to the position of the piston and a pencil that recorded both, could enable a record to be produced of the action of the machine throughout the cycle--the indicator diagram.
The oldest working engine in the world is the Smethwick Engine, brought into service in May 1779 and now at Thinktank in Birmingham (formerly the Birmingham Museum of Science & Industry). The oldest still in its original engine house and still capable of doing the job for which it was installed is the 1812 Boulton and Watt engine at the Crofton Pumping Station. This was designed to pump water for the Kennet and Avon Canal; on certain weekends throughout the year the modern pumps are switched off and the two steam engines at Crofton still perform this function. The oldest rotative steam engine (the third rotative engine ever built) is located in the Powerhouse Museum in Sydney, Australia.
[edit] See also
[edit] External links
- Watt atmospheric engine - Michigan State University, Chemical Engineering
