60 



BULLETIN 718, U. S. DEPARTMENT OF AGEICULTURE. 



per minute multiplied by the height of fall in feet, multiplied by the 

 weight of a cubic foot of water, and divided by 33,000, gives the horse 

 power per minute. 



Amount of iratcr required to dcrrlop a given Itorsepoirer with a given available 



effective head.^ 



EfCectivehead. 



Flow of water per minute. 



10 H. P. 



20 H. P. 



30 H. P. 



40 11. P. 



50 feet 



Cubicfeet. 

 125 

 104 

 8S 

 77 

 70 

 63 



Cubicfeet. 

 250 

 208 

 177 

 155 

 140 

 125 



Cubicfeet. 

 375 

 312 

 266 

 232 

 210 

 186 



Cubicfeet. 

 500 



60 feet 



416 



70 feet 



355 



SOfest 



311 



90 test 



280 



100 feet 



248 







1 Horsepower based In 85 per cent efficiency of the wheel. 



Water wheels are built either overshot, breast, undershot, or tur- 

 bines. 



Overshot icheel. — The effective power is 60 to 75 per cent of possible 

 power. The proper velocity of the circumference is 5 feet per second 

 and is equal to approximately one-half the velocity of the water. 

 The water velocity must be greater than the rim of the wheel. In 

 falls pi from 20 to 40 feet in height the overshot wheel is mora 

 effective than a turbine. The buckets should have a capacity three 

 times as large as the volume of water actually carried, should have 

 holes in the bottom in order to allow the escape of air, and have a 

 depth of from 12 to 14 inches and be 12 inches apart at least from 

 centers. The speed necessary to run a sawmill with this power is 

 obtained by countersliaft or gears. 



Breast wheel. — ^The water acts by weight and impact, dropping 

 vertically into the buckets. The efficiency varies from 45 to 65 per 

 cent of possible power and works best in falls from 8 to 16 feet hav- 

 ing a discharge from 20 to 80 cubic feet per second. The speed of 

 the wheel should be such as to fill the buckets one-half their capacity 

 each revolution. Other forms of breast wheel are called " high 

 breast," " low breast," and " flutter " wheels. The old form of water 

 wheel had radial buckets, but the modern idea is in favor of curved 

 buckets which give a higher efficiency. 



UTidershot wheel. — The undershot or current wheels have a low 

 efficiency and are usually anchored in rapid streams in such a position 

 as to be safe during floods or high water. The size of the wheel 

 varies. It usually has 12 blades, each one of which is submerged 

 as it passes directly under the axle. All of those wheels have become 

 practically obsohite in this country. 



The Pelton turbine is a type of axial flow impulse turbine in which 

 a small jet issues from a nozzle and strikes on a series of cups of 



