274 



THE FORCING PUMP. 



"F 



A 



each stroke, and if A = the area of the piston, the tension 

 on the piston-rod = gpA BK, until the water is lifted to 

 the valve D, since the air is expelled before the machine is 

 in full action. After this, the power applied to the piston- 

 rod must be increased until the pressure of the water opens 

 the valve D, i. e., until the pressure = gp (li + DF), where 

 F is the surface of the water in the tube. The water will 

 then be forced up the tube, the tension of the rod increas- 

 ing as the surface F ascends. 



147. The Forcing Pump. This pump is a further 

 modification of the simple suction pump ; it has no valve in 

 its piston, which is perfectly solid, 

 and works water-tight in the barrel, 

 ranging over the space AE. At the 

 top of the suction pipe BC is a valve, 

 and at the entrance to the pipe DF is 

 a second valve D. 



When this pump is first set in ac- 

 tion, water is raised from the well as 

 in the common pump, by means of 

 the valve B and piston M, the air at 

 each descent of the piston being 

 driven through the valve D into the 

 pipe DF. When the water has risen 

 through B, the piston, descending, 



forces it through D ; and when the piston ascends, the valve 

 D closes, and more water enters through B. The next de- 

 scent of the piston forces more water through D, and so on 

 until the pipe is filled, as in the lifting pump. 



The stream which flows from the top of the pipe will be 

 intermittent, as it is only on the descent of the piston that 

 water is forced into the pipe ; but a continuous stream can 

 be obtained by means of a strong air vessel N" (Fig. 76), 

 which consists of a strong brass or copper vessel, at the bot- 

 tom of which is a valve V. Through the top of the air 



Fig. 75 



