610 



HYDBAULICS AND ITS APPLICATIONS 



The coefficient of discharge now becomes greater than unity. Its 

 value may be deduced since the area A' E" E' represents the work done 

 in pumping a volume of water v cubic feet against a head h d (= O E) 

 feet. 



The area A E" E' thus represents 62'4 v h d foot Ibs. 



v = 



area . 



62-4 h d 

 The scale to which this area is to be measured is given by the product of 



. 290A. Pump Diagram showing delivery during Suction Stroke. 



the scales to which ordinates of the diagram represent heads in feet and 

 abscissae represent pounds of water. 



ay 



The Coefficient of discharge C d = 1 + -rr where F is the piston dis- 



placement per stroke. 



Assuming simple harmonic motion, the area A' E" E' may be calculated 

 analytically. In more complicated cases, it is preferable to measure it by 

 planimeter. 



Where an actual diagram is to be estimated (Fig. 290A), the suction 

 head curve A B E" may be produced by hand with fai accuracy to A f , 

 and the area then measured. 



Since, at the speed at which separation occurs, water hammer raises the 

 pressure towards the end of the suction stroke by an abnormal amount, it 

 is to be inferred that about this speed a sudden increase in the discharge 

 coefficient will take place. This inference is justified by the results of 



