688 



HYDEAULICS AND ITS APPLICATIONS 



(4) The loss of energy due to resilience, being proportional to the square 

 of the pressure of the water at the instant of closing the delivery valve, will 

 vary as the square of the delivery head, and also with the mass of water 

 affected, and will therefore increase with the length of the supply pipe 

 and with the ratio I -f- H. 



Evidently, then, the most economical working is to be expected with a 

 ram in which the delivery head is low and in which the ratio I -f- H is 

 small. While the latter factor is not essential for fairly efficient working, 





FIG. 332. Efficiency Curves for Hydraulic Ram working under a constant head of 4-5 feet. 



it is. advisable where possible that this ratio should not exceed 2*5. How- 

 ever, where necessary this may be largely exceeded, and a supply pipe 

 length of 1,000 feet with a ratio I -r- H = 25 is well within the limits of 

 everyday practice. 



The delivery head may be anything up to about 250 feet and the supply 

 head anything above 18 inches,but the ram becomes very inefficient as the 

 ratio of delivery to supply head becomes great. 



The ram will work with this ra,tio as great as 30 to 1, but under such 

 circumstances has an efficiency not exceeding about 20 per cent. With 

 lower delivery heads, up to about four times that of the supply, the ram 



