232 Introduction to the Study of Science 



The important features are shown in Fig. 68. The water enters 

 the wheel at the center, is caught by the blades and driven with 



great velocity into the space 

 surrounding the wheel and 

 into the delivery pipe. The 

 rotary force of the wheel is so 



great that it delivers the water 



. 68. Centrifugal pump. steadily and in large volumes. 



SUMMARY 



Water pressure in supply pipes is due to gravity or force pumps. 



Water pressure due to gravity varies with the depth, and is 62.5 

 pounds per square foot for each foot of depth. 



Water pressure in pipes is reduced by friction. 



The amount of friction in a pipe increases with the length of pipe, 

 the roughness of its inner surface, the number of bends, and the 

 decrease of the diameter of the pipe. 



The pressure and flow at places distant from the reservoir or 

 pumps may be equalized by the use of a standpipe. 



An increase in pressure on any area of an inclosed body of liquid 

 is accompanied by an equal increase on every like area of the liquid. 

 This is Pascal's principle, and accounts for the action of the hydraulic 

 press. 



The force pump delivers water under pressure. 



The centrifugal pump depends on rotation and is used to lift great 

 quantities a short distance. 



REVIEW QUESTIONS 



1. What is the importance of water pressure in any supply system? 

 2. By what means is pressure secured in different systems? Give 

 instances of each. 3. How is pressure of water in a tank measured? 



4. Explain why water has a constant density at different depths. 



5. What conditions reduce the pressure or retard the flow of water 

 in a system of pipes? 6. Compare wooden conduits with steel pipes 

 in their effect upon water pressure. 7. Explain how length and 

 diameter of pipes modify pressure. 8. Explain how a standpipe 

 works. 9. What is shown by Pascal's experiment? Give mechanical 

 uses of this fact. 10. Describe the force pump and its operation. 

 11. Describe the operation of the rotary pump; and state its relation 

 to air pressure. 



