DISPLACEMENT CURVES 



603 



If F G be drawn parallel to A E, so that A F represents the mean 

 velocity of the piston, the area A F G E = area ABC. 



Similarly, Fig. 288e represents the displacement curve A B D B f C' E, 

 for a pair of single-acting pumps having cranks at right angles and 



ACS 



FIG. 288C. Curve for Pair of Double- Acting Pumps with Cranks at Right Angles. 



drawing from and delivering into a common main. Here A B C and 

 A' B' C' are the respective curves for each piston, and these are com- 

 pounded by adding ordinates so as to give the displacement curve. The 

 area A F G E is now equal to the sum of the areas ABC and A' B' C', 

 or to the whole area A B D B' C'. 



Again, Fig. 288c, obtained in a similar manner, shows the curve for a 

 pair of double-acting pumps having cranks at right angles, F G again 



A C 



FIG. 288o. Displacement Curve for Three-Throw Single-Acting Pump 



with Cranks at 120. 



representing the mean velocity line. Here H K represents what would 

 be the mean velocity line for a single double-acting pump. 



Similarly, Fig. 288o represents the curve for a three-throw pump 

 having cranks at intervals of 120. 



It will be noted that as the frequency with which the pumps discharge 

 per revolution increases, the range of velocities in the discharge and 



