ELASTICITY OF SUCTION COLUMN 



615 



by the sum of the water hammer and the retardation pressures, and is 

 219 Ibs. per square inch. 



By exterpolation from the curves showing the results of the experiments 

 under consideration, the actual pressure at this speed would apparently 

 vary from about 115 Ibs. per square inch with a delivery pressure of 

 20 Ibs. per square inch, to about 195 Ibs. per square inch with a delivery 

 pressure of 60 Ibs. per square 

 inch. This is a result which 

 might have been inferred, since 

 directly the delivery pressure 

 is exceeded, the delivery valve 

 opens, and the maximum pres- 

 sure is reduced by an amount 

 which cannot be deduced quan- 

 titatively. 



It is, however, to be ex- 

 pected and this is verified in 

 practice that this reduction 

 will be greater as the delivery 



Delivery. ^ 



Atmoi. 



Zero 



.Pressure 



Line 



*_ Pressure 



FIG. 293. 



valve area is increased, and 

 as the delivery pressure is reduced, since the latter reduces the pressure 

 necessary to produce flow through the valves, while the former ensures a 

 more easy delivery. 



ART. 165. EFFECT OF THE ELASTICITY OF THE SUCTION COLUMN. 



"While the formulae already obtained enable the pressure on the piston 

 to be calculated with fair accuracy for the greater part of the stroke, it is 

 found that the pressures actually obtained towards the end of the suction 

 stroke, even when separation does not take place, are usually much greater 

 than those calculated in this manner. So far, it will be noted, any effect 

 which the elasticity of the water column may have in modifying this 

 pressure has been neglected. Because of this elasticity, however, the 

 change of velocity and of pressure at the open end of the pipe will lag 

 behind that at the piston by the time necessary for a pressure wave to 



traverse the pipe, i.e., by a time -7-^7; seconds, and if the acceleration 



4, i UU 



at the plunger end at a given instant be a, the difference in velocity at 



I 



the two ends will be a x 



4,700 



f.s. 



Thus, assuming S.H. motion, when the piston comes to rest the 



