AIE VESSELS FOE PUMPS 

 ART. 168. 



628 



If it be assumed that the velocity of flow along the suction and delivery 

 pipes is sensibly uniform, and equal to the mean velocity of the pump 

 plunger, multiplied by the ratio of areas of plunger and pipe, the volume 

 of water entering the air chamber per stroke may be determined with fair 

 accuracy. Thus, if the ordinates of the displacement curves ABODE 

 (Fig. 296) represent piston velocities, and if A F represent the mean 



C 

 FIG. 296. 



piston velocity, on multiplying the vertical scale by 



the curve would 



give the velocities of flow along the delivery pipe if no air vessel were 

 fitted. A F measuring the mean velocity. 



Thus the ratio of each of the sectional areas to the whole area A F G E 



A 



XI' r 



FIG. 297. 



C 



gives the ratio of the volume entering the air vessel per cycle to the total 

 discharge per revolution. This applies to a double-acting pump. In a 

 single-acting pump the volume discharged will be given by the area 

 A H K E, where A II ^ AF, while the volume entering the air vessel 

 will be given by the area L B M. In the case of a double-acting duplex 

 pump, having cranks at right angles, Fig. 297 represents the state of affairs. 



