608 HYDRAULICS AND ITS APPLICATIONS 



as the critical velocity, above which separation will occur on the suction 

 stroke. 



Similarly, substituting in equation (2) we obtain : 



Vff 

 T 



(4) 



2 m a d 

 as the velocity, above which separation occurs on the delivery stroke. 



Here 6 is in every case measured from the beginning of the stroke, so 

 that cos 6 in the latter expression is negative. 



Putting ir a = 34 feet, and writing 6 = in equation (3) : 



;{ 84 -*.}_ 



is the limiting speed at which separation will occur at the commencement 

 of the suction stroke. Since o> = (where N = revolutions per 



minute), this becomes : 



With a finite connecting rod of length I, we have : 



^ = 3 ^\/VTT-1 "FT. W 



The action may be shown graphically as follows : 



In Fig. 290, 0' represents the atmospheric pressure line, and, 

 assuming simple harmonic motion, ordinates drawn to the straight line 

 AHA' represent the head necessary to accelerate the water column in 



27 A 



the suction pipe. Then A = 0' A' = - -* . . Vertical ordimites, 



9 a 



set off from A HA' as base line, to the curve ABA', represent the heads 

 necessary to overcome frictional resistance, zero at the ends, and having 



a maximum value ='^- 5 .*- , at the middle of the stroke. 

 2 g af m 



The vertical ordinates of the shaded area then give the differences of 

 head between the two ends of the suction pipe due to friction and inertia, 

 these being negative or positive, according as ordinates are measured 

 below or above 0'. 



If now C C' be drawn at a distance below O 0', representing the avail 

 able head (34 h a ) feet, the ordinates of the curve ABA', nieasure4 



' 



