SOME COMMON MECHANICAL MOTORS 557 



employ. In this section we shall study briefly the principles 

 of some of the more common mechanical motors; in the 

 following section we shall see where the losses of energy occur 

 in using them and note the approximate relative cost of 

 operating them. 



Nearly all power used today to run the machinery in 

 factories and mills and about mines, to pump the water for 

 city water systems, and to light city streets and homes by 

 electricity, to propel ships at sea, and railroad and interurban 

 trains on land, to run street cars and automobiles in 

 fact, to operate machinery for any purpose is derived 

 from a few different kinds of mechanical motors. These 

 motors are (1) water motors, (2) steam motors, (3) gas motors, 

 including gasoline or crude oil motors, and (4) electric motors. 



WATER MOTORS 



663. Kinds of Waterwheels. Running and falling water 

 has been used since the beginning of civilization to produce 



FIG. 341. The overshot water wheel. FIG. 342. The breast wheel. 



power and do work for man. Waterwheels of different kinds 

 have been used. OVERSHOT, BREAST, AND UNDERSHOT WHEELS 

 are the older types, while the IMPULSE AND TURBINE WHEELS 

 are of recent origin. 



664. Overshot Wheels. OVERSHOT WHEELS have generally 

 been used when a small stream having a considerable fall is 

 available (Fig. 341). Why? Such wheels are sometimes 

 50 or 60 ft. in diameter and may develop an efficiency of 80 

 or 90 per cent. How is the power produced by such a wheel? 



