STEAM TURBINE. A form of prime motor in which the kinetic energy of expanding steam acts upon a wheel provided with vanes so as to cause rotation. The ordinary method of using steam to obtain power is to admit it into a closed cylinder, where it acts upon a movable piston. ( See STEAM and STEAM ENGINE.) In this ease work is performed by the static ex pansive force of the steam pressing against the vented by Branca in 1629 and consisted simply of a jet of steam impinging upon the vanes of a paddle wheel and blowing it around. Branca's device was the first impulse steam turbine. Prac tically no attention was given to the steam tur bine from this time until the last quarter of the nineteenth century, when several inventors began experimenting, among whom C. A. Par sons of England and Dr. de Laval of Sweden deserve particularly to be noted. "Mr. Parsons built his first turbine in 1884. and Dr. de Laval recorded his first patent in 18S9. The first Par sons turbine developed 10 horse power at 1S,000 revolutions per minute, and proved entirely prac tical. The Parsons turbine consists of several successive turbine wheels, or rows of blades, on one drum or shaft within a concentric case bay ing interior blades; the moving vanes or blades on the shaft are in circumferential rows project ing outwardly from the shaft and nearly touch ing the ease, and the fixed blades on the casing are in similar rows, projecting inwardly from the case and nearly touching the spindle or shaft. This construction constitutes what practically amounts to a series of turbine wheels on one shaft, each one complete in itself,like a parallel flow or Jonval water turbine, through which the steam is forced to pass. Each successive turbine is also slightly larger in passageway than its predecessor. to allow for the increasing bulk of the elastic steam as it exerts its force on each turbine successively and expands with a conse quent reduction of pressure. The steam in pass
ing through the successive turbines transmits to each a rotative impulse partly by reaction and partly by impulse, and thus the Parsons turbine involves the germinal principles of both the Branca turbine and llero's engine. The notable feature of the Parsons turbine is the 'compound ing' of the steam, or its expansion in successive Two other turbines which have gained some prominence are the Seger turbine, a Swedish in vention, which is similar in principle to the De Laval, hut which employs two revolving vane wheels, instead of one, upon which the steam acts successively, and the turbine invented by J. H. Dow of Cleveland, 0., which is notable as hav stages, losing a few pounds in pressure at each stage. This quality of the machine permits a slow enough speed of rotation without serious loss of efficiency to allow the turbine to be coupled direct to a dynamo or even a screw propeller without the necessity of reduction gearing. It has been successfully employed in both these capacities.
The De Laval turbine is simply a highly im proved form of Branca's impulse turbine. It con sists of a divergent nozzle which directs the jet of steam upon suitably formed buckets which are attached to the periphery of a revolving wheel. The outer edge of the buckets is shrouded by a steel ring which prevents the centrifugal escape of the steam. These turbines. especially in the larger sizes, are equipped with several nozzles. They are essentially of very high speed. the smaller sizes running at 30,000 revolutions per minute and the larger sizes at 10.000 revo lutions per minute. A train of gearing reduces the speed to reasonable working velocities.
ing the same principle of 'compounding' the steam as does the Parsons turbine, but which differs materially in construction from the Par sons machine.