A blowing engine is a large stationary steam engine directly coupled to air pumping cylinders. They deliver a very large quantity of air at a pressure lower than an air compressor, but greater than a centrifugal fan.
Smelters are most economically located near the source of their ore, which may not have suitable water power available nearby. There is also the risk of drought interrupting the water supply, or of expanding demand for the furnace outstripping the available water capacity.
These restrictions led to the very earliest form of steam engine used for power generation rather than pumping, the water-returning engine. With this engine, a steam pump was used to raise water that in turn drove a waterwheel and thus the machinery. Water from the wheel was then returned by the pump. These early steam engines were only suitable for pumping water, and could not be connected directly to the machinery.
Beam blowing engines
Early steam prime movers were beam engines, firstly of the non-rotative (i.e. solely reciprocating) and later the rotative type (i.e. driving a flywheel). Both of these were used as blowing engines, usually by coupling an air cylinder to the far end of the beam from the steam cylinder. Joshua Field describes an 1821 trip to Foster, Rastrick & Co. of Stourbridge, where he observed eight large beam engines, one of 30 hp working a blowing cylinder of 5 feet diameter and 6 feet stroke.
Where the later beam engines drove flywheels, this was useful for providing a more even action to the engine. The air cylinder was still driven by the beam alone and the flywheel was used solely as a flywheel, not driving an output shaft. A well-known surviving example of this type are the paired beam engines "David & Sampson", now preserved at Blists Hill open-air museum, Ironbridge Gorge. These are a pair of single-cylinder condensing beam engines, each driving an air cylinder by their own beam, but sharing a single flywheel between them. They are notable for their decorative Doric arches. The engines had a long working life: 50 years of primary service from 1851 providing the blast for the Priors Lee furnaces of the Lilleshall Company, then a further 50 years until the plant's closure as reserve engines, still being worked occasionally.
Semi-rotative blowing engines
The large vertical blowing engine illustrated at the top was built in the 1890s by E. P. Allis Co. of Milwaukee (later to form part of Allis-Chalmers). The steam cylinder (lower) is 42 inches (1.1 m) diameter, the air cylinder (upper) 84 inches (2.1 m) and both with a stroke of 60 inches (1.5 m).
The steam cylinder has Reynolds-Corliss valve gear, driven via a bevel-driven auxiliary shaft beneath, at right-angles to the crankshaft. This also means that the Corliss' wrist plate is at right-angles to the flywheel, rather than parallel as is usual. Edwin Reynolds was the designer of the Allis company and in 1876 had developed an improved version of the Corliss valvegear, with improved trip gear capable of working at higher speeds. The air valves are also driven by eccentrics from this same shaft.
Like the beam engines, the main force of the piston is transmitted to the air cylinder by a purely reciprocating action and the flywheels are there merely to smooth the action of the engine. To permit adjustment though, the steam piston rod only goes as far as the crosshead and above this there are twinned rods to the air piston. The flywheel shaft is mounted below the steam piston, the paired connecting rods driving downwards and backwards to make this a return connecting rod engine.
Replacement by rotary blowers
As blast furnaces re-equipped after World War II, the favoured power source was increasingly either the diesel engine, or the electric motor. These both had a rotary output, which worked well with contemporary developments in centrifugal fans capable of handling the huge volumes of air. Although the reciprocating steam blowing engine continued where it was already in use, they were rarely installed after the war. These older plants began to close in the 1950s and numbers were drastically reduced throughout the West during the 1970s. Blowing engines of this form are now rare.
Surviving examples today
Examples of both a beam blowing engine and a vertical engine may be seen at the Blists Hill open-air museum, Ironbridge Gorge. The beam engines "David & Sampson" are scheduled Ancient Monuments.
An 1817 beam blowing engine by Boulton & Watt, formerly used at the Netherton ironworks of M W Grazebrook, now decorates Dartmouth Circus, a traffic island at the start of the A38(M) motorway in Birmingham (see picture above, location: ).
|Wikimedia Commons has media related to
- Hills, Richard L. (1989). Power from Steam. Cambridge University Press. p. 37. ISBN 0-521-45834-X.
- Rolt, L T C; Allen. Steam Engine. p. 122.
- Joshua Field (24 Aug 1821). "Foster, Rastrick & Co. of Stourbridge". Author's tour through the Midlands.
The third engine is very handsome a 6 column engine [a beam engine with a horizontal frame raised on columns] of 30 H Power working a blowing cylinder of 5 feet, 6 feet stroke"
- "David and Sampson - a vintage beam engine and a scheduled Ancient Monument at the Blists Hill Site." (image).
- Jameson, John H. (2004). David & Samson at Blists Hill. The reconstructed past. p. 182. ISBN 0-7591-0376-3.
- Mike Ashton. "David & Sampson: Doric arch" (photograph).
- "Lilleshall Collection at Blists Hil".
- "The Lilleshall Company".
- "Blists Hill, Ironbridge Gorge Museum, Madeley, Shropshire". Viewfinder. English Heritage.
- Hawkins, Nehemiah (1897). New Catechism of the Steam Engine. New York: Theo Audel. pp. 335–337.
- Hawkins, New Catechism of the Steam Engine, p.225, p.172