CHAP. III.] 



PUMPS. 



53 



not present any interest here. Sometimes these modifications depend 

 upon the particular employment of the pumps ; in other cases, they 

 result from the way in which the inventor has re-arranged them to 

 remedy some particular inconvenience, or to obtain some special 

 advantage. In order to avoid the intermittence of the jet, double- 

 action suction and force-pumps are sometimes constructed. These 

 are arranged so that the suction 

 and the forcing of the water is 

 done at the same time, both 

 during the rise and fall of the 

 piston. In these machines, the 

 piston is solid, and the body of 



T 



the pump is pierced with four 

 open ings, furnished with valves, 

 as shown in Figs. 32 and 33. 

 During the ascending move- 

 ment of the piston, the valve A 

 is opened, and a certain quan- 

 tity of water is introduced by 

 suction into the lower part v 

 of the pump-barrel; the valve 

 B is closed by that which the 

 forcing-pipe c' already con- 

 tains ; on the other hand, the 

 valve A' is opened, and gives 

 passage to the water contained 

 in V above the piston ; and this 

 water is forced towards c' ; 

 finally, the pressure of this 

 water shuts the valve B'. 

 During the descending move- 

 ment of the piston, the parts 

 act in an opposite direction : 



the valves A and A' are closed, B and B' are open, so that the water 

 is sucked up at the top and forced up at the bottom. The jet is then 

 nearly continuous ; but it is easy to understand that the working of 

 the lever-beam or handle requires double strength. This kind of 

 pump is specially used for draining purposes, and in that case a 



FIG. 34. Common pump, with handle and lever. 



