70 SMALL WATER SUPPLIES. 



The length of drive pipe required in feet 



. . . ( 27 ) 



The capacity of the air vessels should be equal to 



005 5 d' 2 H . . . (28) 



The diameter D and d being in inches. Of course 

 it must not be supposed that a hydraulic ram can 

 be used under all circumstances and any place 

 instead of another kind of pump ; but it is surprising 

 how many different circumstances it is adaptable to. 

 In the first place, a stream of flowing water, no matter 

 how small, is essential. A small spring or brook will 

 usually suffice. Other important considerations are 

 the total height the water must be lifted and the 

 length of piping through which it has to be forced. 

 Finally, the most important consideration, and 

 usually that upon which the practicability of the 

 scheme will depend, is the fall available for working 

 the ram. In such cases as old mills, etc., there will 

 usually be ample fall, while a swift mountain stream 

 which never runs very low or dry in the summer 

 will in most cases provide it ; but when flat country 

 and slow-moving rivers have to be considered the 

 question is a little more complex, and accurate levels 

 must be taken by an experienced surveyor. In most 

 cases it will suffice to find the difference in level 

 between the surface of the flowing water at points 

 500 yards apart, one of the two points being that at 

 which the ram will be placed, or in the case of a 

 surface spring, if there is a suitable place to discharge 

 the exhaust from the ram within, say, 300 yards. 

 Having ascertained these items the engineer may 

 rest assured that a high-class firm can supply a ram 



