22 



BULLETIN^ 57, U. S. DEPARTMENT OF AGRICULTURE. 



lifted more than 100 feet, or where the working pressure on the pump 

 does not exceed 65 pounds. 



Figure 18 illustrates the appUcation of this system to a farm home. 



The water level in shal- 

 low wells is usually near 

 enough to the surface to 

 be within the limits of 

 suction. The limiting 

 practical suction lift for 

 a pump is about 20 feet, 

 although it will vary with 

 the elevation above sea 

 level. This means that 

 the pump cylinder which 

 raises the water by suction 

 in lift pumps and which 

 raises by suction and also 

 forces the water in force 

 pumps should not be more 

 than 20 feet above the 

 water level in the weU. 

 To practically eliminate 

 suction Hft the cyhnder 

 may be submerged as 

 shown in figure 19, thus 

 making the cyhnder and 

 pump frame separate and 

 connected only by a sec- 

 tion of pipe. This pre- 

 vents the valves from dry- 

 ing out and makes the 

 pump self-priming. Force 

 pumps often have two 

 cyhnders, and in deep 

 wells it is necessary that 

 the lower or suction cyl- 

 inder be either submerged 

 or within at least 15 feet 

 of the water level. In 



Fig. 19. — Force pump with cylinder suljmerged in shallow well. 



the figure shown the forcing cyhnder is within the suction cyhnder. 

 The suction of any type of pump must be au'-tight. 



