CANE SUGAR. 



channel d and equalizes the pressure on both sides of the piston ; the valve I 

 now closes and a opens, and as the piston moves from right to left air is drawn 

 into the vacuum ; the equalizing valve I remains closed and the suctiun and 

 delivery ports open ; at the end of the stroke the valve a is again nearly central 

 and the process described above repeats itself. 



The Blancke air pump is of recent introduction and uses flap valves ; it is 

 shown in Fig. 188. The motion of the cylinder is from left to right, so that 

 gases are being aspirated in on the left hand side and discharged on the right 



FIG. 186. 



hand side. The suction valve is composed of a series of sleeves, with rectan- 

 gular openings, A and B, and a ring and flap valve C telescoping together and 

 forming the annular spaces C and D. E is a spring, helping to close the valve 

 under a slight difference of pressure. On the compression side of the pump 

 all of the sleeves of the valve are forced together, and the annular spaces C ; 

 and D 7 and the openings A y and B' are all closed ; the compressed air escapes 

 by el, f and g' ; on the aspirating side these openings are closed by the spring 

 H. The discharge valves are arranged on the lower side of the pump so as to 

 facilitate the removal of water. 



330 



