42 



AIR AND FIRE 



If we put the open end of a pipe under the water of a 

 well or cistern, and remove the air of the pipe, the atmos- 

 pheric pressure will raise the water into the pipe about 34 

 feet (cf. 40). In other words, the pipe 

 and the well become a water barometer. 



The simple lift pump (Fig. 33) not only 

 removes the air from the pipe, but lifts the 

 water to the spout. It consists of a cylin- 

 der in which a tightly fitting piston can be 

 moved up and down by means of a handle. 

 The cylinder is attached to a pipe, which 

 extends into the water. 



The Lift Pump. I n the bottom of the cylinder there is a cylinder 



valve, which opens upwards so as to admit water 

 from the pipe. There is also a valve in the piston. This, too, opens 

 upwards, admitting water above the piston. When the piston is 

 forced downwards, the water in the cylinder opens the piston valve 

 and closes the cylinder valve. Some of 

 the water of the cylinder then collects 

 above the piston. When, now, the piston 

 is raised, as in Fig. 33, the water above it 

 closes the piston valve, and the water 

 above the piston is discharged through 

 the spout. At the same time the cylin- 

 der valve is opened by the water below it, 

 and more water is forced into the cylin- 

 der. Thus the up and down strokes of 

 the piston cause a more or less regular 

 discharge of water from the spout. 



Force Pumps and Rotary Pumps. In 

 the force pump (Fig. 34) the piston has 



no valve. When the piston is raised, water rises into the pipe and 

 into the cylinder. When the piston descends, the water below it 

 closes the cylinder valve, and water is forced out through the discharge 



FIG. 34. 



A Force Pump with Its Air 

 Chamber. 



