Professor Curtis of New York has designed large steam-turbines which follow Parsons' very closely in theory, but are differently worked out mechanically. Few revolving discs of com paratively large diameter are arranged, and the fixed steam nozzles only play upon part of their periphery, in some cases only two nozzles being employed on the first disc. Provision is made for altering the nozzle areas according to load by opening or closing their tapered walls, thus leaves the chambers at almost the same pressure at which it enters, the wheel vanes merely ceiving the impulse due to the velocity of the particles; there is, therefore, in this case no tendency to leakage and no necessity for ance.
The Dow Turbine.— The turbine invented by Dow is an inward-flow wheel with concentric sets of guides and vanes in series, and is said to have attained 35,000 revolutions per minute, working regularly at 25,000, consuming 45 pounds of steam per horse power per hour. The Dow turbine, as built for work in connec don with the Howell torpedo, gives an average of about II horse power in coming up to speed in regular working, at 60 pounds sure, and weighs from 100 to 150 pounds, or not far from 13 pounds per horse power. Its fir wheel rim attains a speed of nearly seven miles a minute at 10,000 revolutions per minute. The designer estimates its power at 150 pounds steam-pressure and the same speed at 40 horse power, or one horse power to three and seventy five hundredths pounds weight, and states that this may be still further reduced to the extraor dinary minimum of two and one-half pounds weight per horse power, a figure within the estimated allowable maximum for use in aero nautic work. These engines have been suc
cessfully employed in driving electric machin ery and in the of the Howell torpedo. For alternating currents, this system possesses the peculiar advantage of permitting a to be employed having but two poles. In the United States the substitution of the Dow turbine for the system previously in use for spinning torpedoes has brought down the weight and volume of machinery from the earlier minimum of 360 pounds and three cubic feet per machine to 55 pounds and one cubic foot.
The Tesla About 1910 Nicola Tesla exhibited a remarkable 100 horse-power engine, so light that an ordinary man could hold it at arm's length. It was a steam turbine utilizing a new principle. He made a wheel of parallel circular plates about three-sixteenths inches apart and boxed it in, with apartments at the centre and the periphery. Admitting steam at the periphery in a tangential position, the steam rotated the plates by side friction, and i continuing around in reducing spirals continued to give out its propelling face as its speed re duced. Thus it was doing the work of a mul tiple expansion engine with uniquely simple apparatus. The spent steam escaped at the cen tre. Though most wonderful in theory, this machine has not become commercially useful. See STEAM; STEAM-ENGINE.