Capacity of Wells. 



281 



348. The Use of Sand Strainers. Where water must be 

 procured in loose sand, especially if it is fine, some form of 

 sand strainer should be used unless the well is an open one 

 and even then a suitable point will often greatly increase 

 the capacity. 



The difficulty in getting water rapidly from loose sand 

 grows out of its tendency to move with the water, filling up 

 the well or the suction pipe or cutting out the valves. Since 

 the specific gravity of sand is only about 2.65 just as soon 

 as a pressure greater than 3 feet is developed to force the 

 water out of the sand the sand must move with it unless 

 there is something to prevent it. 



FIG. 109. Showing ordinary sand strainers and method of measuring their 



capacity. 



The best sand strainer we have seen is represented in Fig. 

 108 and is made of heavy brass tubing cut as shown in the 

 illustration, the width of the cuts varying for the different 

 degrees of fineness of sand. Made of heavy stock and of 

 one kind of metal it is not liable to corrode and clog as with 

 the common form represented in Fig. 109. 



349. Capacity of Sand Strainers. The capacity of sand 

 strainers varies essentially in the same way as wells of simi- 

 lar dimensions would, made in the same kind of material. 

 The longer the strainer, the coarser the sand and the greater 

 the pressure the larger will be the capacity. 



