COMMON THINGS PUMPS. 



Fig. 14. 



II 



piston within it, having a valve opening upwards. The other 

 parts of the apparatus are marked with letters corresponding with 

 those of fig. 12. 



15. Another form of pump, called the forcing-pump, is attended 

 with many advantages, and is extensively used. This instrument 



is represented in fig. 14. The suction- 

 pipe c E is similar to the suction-pump. 

 The piston c d is a solid plug without 

 a valve. 



The forcing-pipe G n has at its base 

 e f a valve v' which opens upwards. 

 When the piston c d is raised, the valve 

 v is opened, and the water rises from 

 the suction-pipe into the pump-barrel. 

 When the piston c d is pressed down- 

 wards, the valve v is closed, and the 

 water is forced by the pressure of the 

 piston through the valve v' into the force- 

 pipe, and thus while the operation is 

 continued, at each upward motion of the 

 piston, water is drawn from the suction- 

 pipe into the pump-barrel, and at each 

 downward motion it is forced from the pump-barrel into the force- 

 pipe. 



16. In order to produce a continued flow of water in the force- 

 pipe, an air-vessel is often attached to force-pumps. Such an ap- 

 pendage is represented in fig. 15. 



When the piston descends, the water 

 is driven through the valve V into the 

 vessel which is closed and contains air. 

 The force-pipe G H descends into this vessel, 

 and terminates near the bottom. The 

 water which is forced in rises in it to a 

 certain level, w w' } the air above it being 

 compressed. The return of the water 

 through the valve v' being stopped, it is 

 subject to the elastic pressure of the air 

 confined in the air-vessel M ]S T . This pres- 

 sure forces the water through the tube n G 

 from the top of which it issues in a con- 

 stant stream. 



The forcing-pump with its air-vessel, as constructed for demon- 

 stration at popular lectures, is shown in fig. 16, p. 189, where all 

 the parts are indicated by the same letters as in figs. 14 and 15. 

 The water which flows in a continual stream from the force- 

 188 



