100 



SCIENCE OF COMMON THINGS. 



Forcing-pump. 



Construction of chain-pump. 



Fig. 24. 



641 When it is desired to raise ivater above thirty -four feet, as in fire- 

 engines, etc., how is it accomplished ? 



By means of tliQ forcing-pump. 



643 In what manner is the forcing-pump con- 

 structed ? 



In the forcing-pump atmospheric 

 pressure plays but a small part. There 

 is no valve in the piston c (fig. 24), 

 but the water raised through the suc- 

 tion-pipe #, and the valve <?, is forced 

 by each depression of the piston -up 

 through the pipe e e, which is furnished 

 with a valve to prevent the return of 

 the fluid. 



643 What is a chain-pump f 



The chain-pump consists 

 of a tube or cylinder, the 

 lower part of which is im- 

 mersed in a well or reser- 

 voir, and the upper part 

 enters the bottom of a cistern 

 into which the water is to 

 be raised. A chain is carried 

 round a wheel at the top, 

 and is furnished at equal 

 distances with movable 

 bottoms, which fit water- 

 tight in the tube. As the 

 wheel revolves, they succes- 

 sively enter the tube, and 

 carry the water up before 

 | them, which is discharged 

 into the cistern at the top 

 of the tube. 



Fig. 25 represents the construction 

 and arrangement of the chain-pump. 



644 Under what Circumstances is 

 the chain-pump generally employed 1 



When the height through which the water is to be 



