478 



WATER SUPPLY AND SEWAGE DISPOSAL 



Any pump so constructed that it may be used to force water 

 to a height above the pump is called a FORCE-PUMP. 



As far as the lower portion of a force-pump is concerned, it 

 may be either a suction-pump or a lift-pump. Figure 292 

 shows the construction of an iron force-pump. It differs from 

 the ordinary iron suction-pump only in having a portion of the 

 head somewhat enlarged so as to enclose a 

 considerable quantity of air, forming an 

 AIR CUSHION, and In having the opening at 

 the top through which the plunger rod 

 A passes packed air-tight. Explain the use 

 \\ of the three valves, A, B, and C. 

 \^ The air cushion is necessary on all force- 

 \\ pumps if we are to secure a fairly steady 

 stream from the pump. With each upward 

 stroke of the plunger, the air in the air 

 cushion is compressed. While the plunger 

 is descending, this compressed air, pressing 

 downward upon the water in the pump, 

 keeps forcing a steady stream of water 

 through the delivery pipe into the tank. 



562. The Pneumatic Tank System. 

 The convenience and comfort derived from 

 having an ample supply of water under 

 pressure in a dwelling can be appreciated 

 only by those who have lived with, and 

 again without, such conveniences. Not only can all of the con- 

 veniences of modern plumbing be obtained, but a reasonable 

 protection against fire is thus secured. Figure 293 shows how 

 such a system may be installed and the conveniences which it 

 makes possible. In such a system the tank is placed in the 

 basement of the house, safe from frost and easy of access. 



The water is raised from the well or cistern and forced into 

 the tank by means of a force-pump. The lower portion of the 

 tank contains water and the upper portion compressed air. 

 This compressed air constantly presses downward upon the 



- B 



FIG. 292. The force 

 pump. 



