Steam Turbines.
For a long time, and well into the nineteenth century, water was lifted by pistons moving in cylindrical pumps. Meantime the turbine grew steadily in favor as a water-motor, arriving at last at high efficiency. This gave designers a hint to reverse the turbine and use it as a water lifter or pump: this machine, duly built, with a continuous instead of an intermittent motion, showed much better results than the old-fashioned pump. The turbine-pump is accordingly adopted for many large waterworks, deep mines and similar installations. This advance from to-and-fro to rotary action extended irresistibly to steam as a motive power. It was clear that if steam could be employed in a turbine somewhat as water is, much of the complexity and loss inherent in reciprocating engines would be brushed aside. A pioneer inventor in this field was Gustave Patrick De Laval, of Stockholm, who constructed his first steam turbine along the familiar lines of the Barker mill. Steam is so light that for its utmost utilization as a jet a velocity of about 2,000 feet a second is required, a rate which no material is strong enough to allow. De Laval by using the most tenacious metals for his turbines is able to give their swiftest parts a speed of as much as 1400 feet a second. His apparatus is cheap, simple and efficient; it is limited to about 300 horse-power. Its chief feature is its divergent nozzle, which permits the outflowing steam to expand fully with all the effect realized in a steam cylinder provided with expansion valve gear. Another device of De Laval which makes his turbine a safe and desirable prime mover is the flexible shaft which has a little, self-righting play under the extreme pace of its rotation.
A, De Laval nozzle and valve in section. B, Turbine buckets. C, Turbine wheel.