COMMON THINGS PUMPS. 



its ascent it is employed in drawing the water from the suction- 

 pipe into the pump-barrel, and in its descent it is employed in 

 forcing that water from the pump- barrel 

 into the force-pipe. Now the piston being 1 

 solid, and not furnished with any valve, 

 there is no reason why its upper surface 

 should not be employed in raising or pro- 

 pelling water as well as the lower. While 

 the lower surface is employed in drawing 

 water from the suction-pipe, the upper 

 surface might be employed in propelling 

 water into the force-pipe ; and, on the 

 other hand, in the descent of the piston, 

 when the lower surface is employed in. 

 propelling water into the force-pipe, the 

 upper surface might be engaged in draw- 

 ing water from the suction-pipe. To 

 accomplish this, it is only necessary that 

 the top of the cylinder should be closed, 

 and that the piston-rod should play 

 through an air-tight collar, the top of 



the cylinder communicating with the force-pipe and the suction- 

 pipe, as well as the bottom. 



Such an arrangement is represented in fig. 18. "When the 

 piston ascends, the suction-valve F is opened, and water is drawn 

 into the pump-barrel below the piston; 

 and when the piston descends, the suction- 

 valve F is closed, and the pressure of the 

 piston on the water below it opens the 

 valve c, and propels the water into the 

 force-pipe c G. Also, while the piston is 

 descending, water rises through the suc- 

 tion-valve E into the barrel above the 

 piston ; and when the piston ascends, the 

 water being pressed upwards keeps the 

 valve E closed, and opens the valve D, and 

 is thus propelled into the force-pipe. By 

 this arrangement the force-pipe receives a 

 continual supply of water from the pump- 

 barrel without any intermission; and in 

 like manner the pump-barrel receives an 

 unremitting flow from the suction-pipe. 

 This will be distinctly seen, if it is con- 

 sidered that either of the two valves E 

 or r must always be open. If the piston go down E is open and F 

 190 



Fig. IS. 



