216 HYDRAULIC EQUIPMENT 



turbine should be run for the best efficiency at any gate open- 

 ing. 



To show how the curves are constructed a typical example is 

 given, based on actual tests given in Table XXXIX. The values of 

 the abscissae in the curves represent 0, the coefficient of peripheral 

 velocity, although sometimes values of HPi, are used for this 

 purpose. These two quantities are, however, directly propor- 

 tional, so that the change merely affects the abscissa scale of the 

 curves. 



From the report, the values of head, revolutions per minute, 

 horse-power and efficiency are taken from the corresponding col- 

 umns for the various runs at each gate. From these are com- 

 puted the corresponding values of </>, which is equal to 



^ 



" 



eoxVsfcT 



in which D is the nominal diameter of the runner in feet, in the 

 case taken 25 inches or 2.0833 feet, and h is the head 

 in feet. The corresponding values of HPi or the horse-power 

 reduced to 1 foot head are also computed by dividing the 

 given horse-power by the three-halves power of the head, 

 thus 



H.P. 



The result represents the power which the given runner would 

 develop if operated at the corresponding speed, that is, at the same 

 value of under a head of 1 foot instead of the head used in the 

 test. The 0-efficiency and <j>-HPi curves are now plotted for 

 each gate opening, Figs. 110 and 111. 



In order to construct the curves of equal efficiency, Fig. 112, 

 the <f>-HPi diagram is selected and points having the same 

 efficiency on the curves for different gate openings are joined in a 

 curve. In order to keep the diagrams clear the <j>-HPi curves 

 have been repeated in dotted lines on a separate diagram. 



To illustrate the construction of one of the equal efficiency 

 contours for instance, take the line for 86 per cent efficiency. 

 Referring to the 0-efficiency diagram, a horizontal line repre- 

 senting the efficiency selected will intersect the curve for 2.5 gate 

 at = 0.64, and will again intersect the same gate at = 0.725. 



