SEPARATION IN A PUMP 



613 



1 - = COS to 



r 



A/: 



2 x /,. A 



9 *a h, h t ) a-/ 

 an equation from which x may be obtained by trial. For purposes of 

 calculation h t may be taken as zero. An attempt to include the effects of 

 friction and of a finite connecting rod greatly complicates the result unless 

 hf be taken to be constant and to have 

 a value corresponding to the mean 

 velocity during the period of separation. 

 By this means a close agreement with 

 experimental results is obtained. 



The above formula has been applied 

 to the case of a pump described by 

 Professor John Goodman 1 and having 

 the following dimensions : 



- = 1*83 ; I, = 63 feet ; r = '25 feet. 



&s 



In this particular experiment the 

 pressure in the suction valve chamber 

 was measured, the loss of head due to 

 height of suction, to friction, and to air tension, being approximately 

 8'0 feet, making 



( 77a _/ ?s _ h f h t ) = 26-0. 



The revolutions per minute were 70, making = - - ,. /% - = 7*33. 



FIG. 292. 



The equation then becomes : 



A/126 X 1-83 



60 



* 32X26 

 or cos 3*86 V x = 1 4 x 



giving a value of x = *47 feet ; 



47 

 i.e., knock takes place at ^r = *94 of the stroke. 



The indicator diagram, of which Fig. 293 is a copy, shows this to occur 

 at about *95 of the stroke. 



The velocity of the water column immediately before impact may be 

 deduced from the equation 



i ., . I 2 X acceleration X space covered under this ,. 



acceleration 



1 " Proc. last. Mech. Engineers," 1903, part 1 (p. 143). 



