432 



HYDKAULICS AND ITS APPLICATIONS 



As in the case of the overshot wheel, the maximum efficiency is obtained 

 when the bucket angles are arranged so as to give entry without shock 

 and when the peripheral speed of the wheel is one half v cos a. Here a 

 is the angle which the direction of the inflowing stream makes with the 

 tangent to the wheel at the point of entry. 



For maximum efficiency the level in the tail-race should be the same as 

 that in the buckets at discharge. In this type of wheel, on account of the 



FIG. 189. Breast Whee). 



manner of filling the buckets, special provision must be made for letting 

 air out as the water rushes in. To this end air vents are usually formed 

 in the inner circumference of the buckets. The wheel is capable of more 

 accurate speed regulation under varying heads than is the overshot, and 

 its efficiency under favourable circumstances may be as high as 65 per 

 cent. 



ART. 122. THE SIDE WHEEL. 



Where the fall is between 3 feet and 6 feet, the breast wheel becomes 

 unsuitable because of the smallness of its diameter, and in such a case the 



