2<X> FARM MACHINERY 



2. Pumps having valves in the piston or bucket pumps. 



Plunger pumps will not be considered in this discus- 

 sion, for, at the present time, their use is confined almost 

 entirely to steam and large power pumps. Pumps used 

 for agricultural purposes are almost universally of the 

 latter type. 



Pumps may further be divided into two distinct 

 classes : 



1. Suction or lift pumps. 



2. Force pumps. 



Suction pumps do not elevate the water above the 

 pump standard. The pump standard is the part which 

 is above the well platform when speaking of pumps for 

 hand or windmill power. A pump will then necessarily 

 include the standard, cylinder, and pipes. 



370. Pump principles. Before continuing the discus- 

 sion it will be well to take some of the principles con- 

 nected with the action of pumps. The action of a plain 

 suction pump when set in operation is to create a vacuum, 

 and atmospheric pressure when the lower end of the suc- 

 tion pipe is immersed in water causes the vacuum to be 

 filled. Atmospheric pressure amounts to about 14.7 

 pounds per square inch. Water gives a pressure of .434 

 pound per square inch for each foot of depth, or each foot 

 of head, as it is usually spoken of. Thus atmospheric 

 pressure will sustain a water column only about 33.9 feet, 

 above which a vacuum will be formed. Pumps will not 

 draw water satisfactorily by suction more than 25 feet, 

 and it is much preferred to have the distance less than 

 20 feet. It is often an advantage to have the cylinder 

 submerged. 



371. Hydraulic information. The following informa- 

 tion will be useful in making calculations involving 

 pumping machinery: 



