ABSTRACT
The two hydraulic prime movers which have been important instruments of change in rural areas of developing nations in the past, are the waterwheel and the small water turbine which superseded it during the +19C. After 1900, in the United States, the advent of large central thermal and hydro-power stations, rural distribution of electricity, the internal combustion engine, and better rural transportation all contributed to the decline of the small turbine powered mill. The overshot waterwheel had an efficiency around 80 percent which was several times higher than that of the undershot waterwheel. Indeed it was often higher than the efficiency of the early small turbines. Further its efficiency remained high despite variations in load imposed upon it; this superior characteristic was not obtained with the undershot wheel or with the early turbines. When the available heads were greater than the usual wheel diameters, the overshot wheel was used in series.
