104 FIRST YEAR COURSE IN GENERAL SCIENCE 



By means of a handle attached to the piston rod, the piston 

 is raised and lowered. As the piston goes down, the air in 

 the cylinder pushes up through the yalve in the piston, 

 while the valve in the pipe below remains closed by its 

 own weight. Conditions in the cylinder are now just as at 

 first, except that the piston is as far down as the length of 

 its rod allows. There is air above and below the piston. 



FIG. 51. THE LIFT PUMP 



FIG. 52. THE FORCE PUMP 



FIG. 51. This diagram shows the essential parts of a common lift pump. 



1. What relation must there always be between the area of the piston and 

 the cylinder? 2. In what direction does the piston valve open? 3. What 

 opens it on the first downward motion of the piston? 4. Why is 30 ft. the 

 greatest practicable distance between the surface of the well and the valve 

 in the pipe? 



FIG. 52. 1. Why is there no valve in the piston of a force pump? 



2. Why, if there were no air chamber, would water be delivered in spurts 

 from the side of the cylinder? 3. For what use is a constant stream neces- 

 sary? 4. In Fig. 52, what shows that the air in the chamber is compressed? 



The water in the lower end of the pipe is at the same level 

 as the water in the well. 



When the piston is raised, its valve remains closed by its 

 own weight and pressure of the air above. As the piston 

 rises, the air space beneath becomes larger and therefore 

 the pressure of the air within this space is decreased. The 

 air in the pipe below, at the same pressure as that outside, 



