686 



HYDRAULICS AND ITS APPLICATIONS 



Experiments on a ram having a drive pipe 85'3 feet long with a 

 supply head of 8*15 feet, show the following approximate results : 



Efficiency of Ram. 



The efficiency of the ram may be considered from two points of view. 

 If q is the volume delivered by the ram, and Q that escaping through the 

 waste valve, H being the effective supply head, and h d the effective 

 delivery head measured from the level of the waste valve and including 

 the friction in the delivery pipe line, the total input of energy to the ram 

 is (Q + q) H, and the total output is q h d . The ratio 



q h d 



known as D'Aubuisson's efficiency ratio, then gives the efficiency of the ram 

 as a machine. 



The ram may, however, be looked upon as a hydraulically-operated 

 pump, actuated by a volume Q under head H and utilising the energy of 

 this supply to lift a volume q. As this q is initially at a height H, the 

 additional energy given to it in the ram is simply (h d H) foot 

 Ibs. per lb., and from this point of view the ratio 



g (h d - H) 



QH 



gives the efficiency of the plant as a whole. This expression is known as 

 Rankine's formula for efficiency. 



Although it is difficult to justify the idea of entire separation of the 

 water pumped from the operating water, yet, for the sake of comparison 

 with other types of pump, the latter formula, which gives results 

 consistently lower than the former, will be adopted in this connection. 



