Prime movers of another or third general class derive their energy more directly from the sun and operate by means of the winds, waves and tides. This class includes solar engines that concentrate and utilize the sun's heat directly. It also includes wind mills. Water wheels of all kinds belong to this general class. The source of their power is the sun's heat. operat ing through the hydrologic cycle of precipita tion, evaporation and run off. Vapor evaporat ing from the seas and lands is condensed in the upper air, and falls again on the uplands as rain, running in streams and riven down the hillsides and valleys to the lakes and seas. and again evaporated, is kept in • perpetual cycle of change by the opposing forces of the energy of the son's heat and the earth's gravity. It is the um winch supplies the power to overcome gravi tation and lift the water to a height from which m falling it drives the water wheel.
runner. The hydraulic turbine is usually encased or submerged in a flume, and is often gout of siOt, and out of mind,' to the extent that it lubricates itself, and frequently does not receive or require direct attention for years of operation.
The usual efficiencies of different types of fuel engines are shown graphically by Fig. 1. The ascrage efficiency of fuel engines in use at the present time, of all kinds, including gasoline and steam engines, steam turbines and locomo Uses, is probably about 10 per cent.
A water-power development consists essen tially of a turbine or water wheel with ade quate means of supplying the water and regulat ing the supply. Types and methods of water power development are so closely related to types of water wheels that it is necessary to give Fig. 2 shows the 'average efficiency (solid black) and the best efficiency (shaded) ordi narily obtained from various types of hydraulic motors. This diagram shows, for purposes of comparison, the efficiency of various early and obsolete types of water wheels, such as current, flutter and central discharge wheels. Even these were more efficient than the best fuel engines. At the present time practically all water wheels in use are of one or the other of the last three types shown on Fig. 2. These have efficiencies ranging from 70 to 93 per cent. The great effi ciency of hydraulic turbines as compared with other prime movers is strikingly illustrated by the fact that if it were possible to replace all fuel engines now in use by some improved type, has ing an efficiency equal to that of the hydraulic turbine the effect would be the same as if the existing supply of coal in the world was in creased at least seven times. Not only is a
developed water power the most efficient means of converting natural energy into mechanical work. but the hydraulic turbine is the simplest of all prime movers. Such a water wheel usually contains only one continuously moving part —.the here some description of the A water wheel is a hydraulic motor that operates con tinuously by rotation in the same direction. A canal lock lifting a boat is a water motor but is not a water wheel. A water wheel usually con sists of various parts, of which the most im portant is the runner, or moving part. A run ner is usually divided into various compartments into, or through which. the water flows. These compartments are properly called buckets. The word bucket is often used incorrectly to describe the vanes or partition walls which form part of the boundary of the bucket It is better to de scribe the partition walk between adjacent buck ets as vanes. It is often convenient to speak of the passage through or into which the water flows, and these passages are sometimes them selves called buckets, but may be more properly referred to as bucket passages. As stated above. the buckets are separated by vanes, which form the boundary walls on two sides of each bucket. The bontiflary walls on the remaining two sides are usualls formed by the crowns. The com partments through which the water flows into the buckets are properly termed chutes or guide chutes. The passage through a chute may be conveniently called a guide passage, and the partition walls between adjacent chutes are properly termed guide vanes. Usually a water wheel of the turbine type is enclosed in a case. of which the guide chutes form a part, and within which the runner is placed. As a rule, the case also contains gates for regulating the water supply. These may be classified as cylinder gates, register gates and wicket or pivot gates. Turbines are set in compartments called penstocks to which the water is led by means of a flume. The words penstock and flume are often used with the meanings here given trans posted. A penstock of sheet iron or steel is often spoken of as a case, but inasmuch as the wheel proper has a case which is placed inside the penstock, it is better to make the distinction of meaning given above.