The Supply and Uses of Water 



231 



FIG. 67. Diagram of force pump. 

 Explain action of valves C and D as the 

 piston moves up and down. 



depends upon the amount of force applied to the piston and the 

 strength of the pump. 



A simple form of the force pump is illustrated in the diagram of 

 Fig. 67. It is seen to be somewhat different from the suction 

 or lift pump. The piston in 

 this form is solid and valve- 

 less and made to fit the cyl- 

 inder very closely. The dis- 

 charge pipe is provided with 

 a valve (D) and with an air 

 chamber. The upward stroke 

 of the piston admits water 

 into the pipe and cylinder; 

 and the downward stroke 

 forces the water to close the 

 intake valve (C) and to open 

 valve (D). It also drives the water from the cylinder into 

 the discharge pipe. Part of the water is forced into the air 

 chamber, compressing the air, which, as soon as the pressure 

 from the piston ceases, expands like a coil spring and causes the 

 water to flow more uniformly. 



There are many forms of the force pump, examples of which 

 may be found in rural homes. They may be operated by hand, 

 by a windmill, by a steam or gasoline engine. More complex, 

 double action pumps are employed in the large pumping plants 

 of cities where great pressure must be supplied. Such, too, 

 are the pumps on fire engines. By these pumps a stream of 

 water may be delivered with tremendous velocity and steadi- 

 ness. The ammonia compressor shown in Fig. 42 is of the 

 double acting type. 



96. The centrifugal pump. The centrifugal pump may be 

 used where it is necessary to lift great quantities of water a short 

 distance. The centrifugal pump may be likened to a fan such 

 as is used to drive air through a building or to force the draft of 

 a furnace. The wheel is inclosed in a water-tight metal casing. 



