COMMON THINGS PUMPS. 



Let D c be a wooden tube of any shape, round or square, 

 which descends to a depth in the well or reservoir equal to the 

 F . height above the surface of the reservoir to which 



the water is required to be raised. Thus if D o be 

 the height to which the water is to be raised above 

 the level of the well, then the depth o c must be at 

 least equal to D o. L M is a heavy beam Or plunger, 

 suspended from a chain, and capable of descending 

 by its own weight in water, and passing water- 

 tight through the collar F E. A valve, v, covers an 

 opening placed at the bottom of the tube. By the 

 hydrostatic pressure the water will enter the valve v, 

 and fill the barrel to the level o G of the water 

 in the cistern. G I is a short tube proceeding from 

 the side of the barrel,v at the surface of the water, 

 and communicating with the vertical tube EN by a 

 valve I, which opens upwards. K is the spout of 

 discharge. The plunger L M hangs loosely in the tube, 

 so that it moves upwards and downwards perfectly free 

 from friction, except that of the collar F E, where it is 

 properly lubricated. "When this plunger is allowed to 

 descend by its weight into the water which fills the 

 lower part of the tube, the valve v is closed, and the 

 water displaced by the plunger is forced through the 

 valve i into the tube E JST. When the plunger is raised 

 the valve I is closed, and the water thus forced into 

 the tube E x cannot return. The water from the 

 cistern then flows through the valve r, and rises in the tube to the 

 level G. The next descent of the piston propels more water into the 

 tube E x, and this is continued so long as the piston is worked. 



The manner in which such an apparatus is worked by the weight 

 of a man, or any animal, is represented in fig. 7, p. 183. Two 

 pumps are used, such as that just described, and when the plunger 

 descends in one it rises in the other. The two pumps communicate 

 with one vertical pipe, which therefore receives a continual, supply 

 of water ; for while the action of one pump is suspended the other 

 is in progress. A man walks from one end of an inclined piano 

 to the other, and by his weight upon one side or the other of the 

 fulcrum causes the plungers alternately to rise and fall. 



9. Valves are of such constant use in all forms of pump, that it 

 will be useful here briefly to explain their principal varieties. 



A valve in general is a contrivance by which water or other 



fluid flowing through a tube or aperture is allowed free passage 



in one direction, but is stopped in the other. Its structure 



is such, that while the pressure of the fluid on one side has a 



182 



