THE LIFTING PUMP. 



273 



Fig. 74 



146. The Lifting Pump. AVhen water has to be 

 raised to a height exceeding about 30 feet, the suction pump 

 will not work (Art. 143, Sch. 1), and 

 the lifting pump is commonly used. 

 By means of this instrument, water 

 can be lifted to any height. It con- 

 sists of two cylinders, in the upper 

 of which a piston M is movable, the 

 piston-rod working through an air- 

 tight collar. A pipe DF is carried 

 from the barrel to any required 

 height; at D there is a valve which 

 opens into the pipe. The suction 

 pipe BC is closed by a valve V, as 

 in the suction pump, and the piston 

 M usually * has a valve V. 



The action of this pump is precisely the same as that of 

 the suction pump in raising water from the well into the 

 barrel. Suppose the piston at its highest point, and the 

 surface of the water in the barrel at K ; then, as the piston 

 is depressed, its valve V will open, {aid the water will flow 

 through it till the piston reaches its lowest point. When 

 the piston ascends, lifting the water, the valve D opens, and 

 water ascends in the pipe DF. On the descent of the piston, 

 the valve D closes, and every successive stroke increases the 

 quantity of water in the pipe, until at last it is filled, after 

 which every elevation of the piston will deliver a volume of 

 water equal to that of a cylinder whose base is the area of 

 the piston and whose height is equal to its stroke. The 

 only limit to the height to which water can be lifted is that 

 which depends on the strength of the instrument and the 

 power by which the piston is raised. 



Coit. If CK = h, the piston lifts the volume BK at 



* Sometimes the piston has no valve in it, but is replaced by a solid cylinder, 

 called a plunger, which is operated by a handle as before. 



