Page:Collier's New Encyclopedia v. 09.djvu/92

LEFT STEAM TURBINE 66 STEAM WHISTLE nozzles, the front blades are not sub- jected to the action of superheated steam and so do not require to be con- structed of special metal for resisting high temperatures. Regulation of speed is obtained by closing one or more noz- zles. Other types of turbine are the Riedler- Stumpf, the Rateau, the Melins and Pfenniger, the Schulz, and the Zolly. While each one has its special features, they all follow the general principles outlined above. As an indication of the speed at which the shafts run in differ- ent engines, the following figures may be taken as representative. The velo- city of the tips of the rotating blades in the Parsons turbine is 100-150 feet per second at the front end, and at the back end, where the diameter of the shaft in- creases, 3G0-350 feet per second. In the Rateau, the speed is 350-400 feet per second, and in the Curtis a little higher. On the other hand, the buckets in the De Laval and the Riedler-Stumpf tur- bines reach a velocity of 1,000 feet per second. STEAM TURBINES, MARINE. The first vessel to be fitted with turbines was the "Turbinia." In 1897 she was equipped with turbines of the Parsons type, three engines being used, high pressure, intermediate and low. Each shaft was fitted with three propellers. She attained the remarkable speed of 34y2 knots per hour, and the results ob- tained in her trials were considered so successful that the adoption of turbines in other vessels very quickly followed. In 1900 the British destroyer "Viper," turbine driven, made 3QV2 knots per hour. Passenger vessels, being built for convenience rather than speed, naturally did not make such a remarkable show- ing, but nevertheless, greater speeds were attained than had been found pos- sible with the ordinary reciprocating engine. The first turbine driven pas- senger vessel was the "King Edward," which reached 20y2 knots in 1901. The first transatlantic liners fitted with tur- bines were the "Victorian" and "Vir- ginian," whose maximum speed reached only 17 knots per hour. In 1907, how- ever, the Cunard line built the "Lusi- tania" and the "Mauretania." These were quadruple screw turbines of 67,- 000 indicated horse power, equipped with two high pressure, two low pres- sure, and two reversing turbines. These vessels were capable of maintaining an average speed of 26 knots per hour. In 1906, the British battleship "Dread- nought" was built and fitted with tur- bines, this being the first battleship to be so equipped. During her trials a speed of 21.25 knots was attained. Of recent years the number of vessels which have been equipped with turbines of im- proved pattern has been very great, the advantage of the turbine for marine work being now generally recognized. The superiority of turbines over recip- rocating engines is not solely due to the extra speed which can be attained. A turbine is lighter, of simpler construc- tion, and more compact than a recipro- cating engine. There is also much less vibration. At high speed there is a marked economy of fuel, but at low or moderate speed, the turbine consumes more coal than the reciprocating engine. For general purposes, the turbine is proving more satisfactory than the re- ciprocating engine in nearly all cases where high speed is required. It is, however, of little use for low speeds, or in those cases where a heavy resistance has to be overcome when starting from rest. It is peculiarly adapted for driv- ing dynamos. Its simpler construction is a strong point in its favor, its moving parts being much fewer than in the re- ciprocating engine. Moreover, the fact that the steam acts directly on the mov- ing shaft without the intervention of pistons, connecting rods, etc., leads to greater efficiency. The comparatively late date at which it was developed for practical purposes is explained by the need for special steels and other alloys possessing the unusual strength and other properties required in engines of this type. In this connection, Kempe's "Engineer's Year Book" states, "A very important fact in the evolution of the steam turbine has been the introduction of the high grade steels now available, which alone have made the highest peri- pheral speeds now to be met with pos- sible, and further developments may be expected to follow any reduction in the cost of finest steels." STEAM WHISTLE, a sounding device connected with the boiler of a steam engine, either stationary, locomotive, or marine, for the purpose of announcing the hours of work, signaling, etc. In the ordinary locomotive steam whistle the foot is bolted onto the fire box, has an opening for the admission of steam, and is provided with a cock, by turning which steam is permitted to rush into the hollow piece, which is provided with holes around its lower and narrower portion, through which the steam rushes into the cavity of the cup, and, passing out through the narrow annular opening, impinges against the rim of the bell, causing a shrill, piercing sound. The calliope is a series of such whistles tuned to a scale and operated by keys.