602 



HYDRAULICS AND ITS APPLICATIONS 



base, the area included between the curve, the base line, and any two 

 ordinates, will measure to some scale the volume displaced by the piston 

 in the corresponding interval of time. The curve so obtained is termed a 

 displacement curve. Thus, if Q and Q P represent the crank and 



A ,c E 



FIG. 288A. Displacement Curve for Single-Cylinder Single-acting Pump. 



connecting rod of a pump for a given piston position, and if P Q be 

 produced to meet the perpendicular C to the line of centres in C, then 

 C represents the corresponding piston velocity to the scale on which 

 Q represents o> r the velocity of the crank pin. If a series of such 

 points as Q are taken at equidistant intervals on the crank circle, and the 

 corresponding values of G found, the displacement curve may then be 

 plotted as in Figs. 288A-D. Here Fig. 288A represents the curve for a 



\ 



A A' C C' 



FIG. 288B. Curve for Pair of Single-acting Cylinders with Cranks at Right Angles. 



single-barrel single-acting pump having a connecting rod four cranks in 

 length, A C representing the time to perform half, and A E to complet 

 revolution. 



The area ABC now represents the displacement of the pump 

 revolution, while C E represents the idle stroke. 



