BARKER'S MILL 



473 



and on differentiating and equating the result to zero we get, for 

 maximum efficiency 



In genera] the maximum hydraulic efficiency of the wheel does not 



e 



70 



E/v 



in .P/ SCfiq/yqE.. 



WO/IK 







IOO 00 



FIG. 216. Curves showing Distribution of Energy in a Barker's Mill. 



exceed 66*0 per cent., while the mechanical friction losses bring this down 

 to about 60 per cent. 



If the wheel is loaded by means of a brake, the magnitude of the various 

 transformations of energy may be determined as follows : 



Let L = nett brake moment in foot pounds. 



N = number of revolutions of wheel per second. 



Then useful work per second = 2 ir L N ft. Ibs. = U, 



