EVAPORATION 



365 



valve b remains closed, and the suction and delivery ports open. At the 

 end of the stroke the valve a is again nearly central, and the same process 

 is repeated. 



A second means of obtaining equalization of pressure by the use of a rotary 

 valve is indicated in Fig. 223. This type is constructed by the Alberger 



FIG. 222 



Condenser Co. There are numerous other devices putting this principle 

 into operation. 



Lift Valve Reciprocating Dry Air Pumps. In place of adopting equaliza- 

 tion of pressure some recent designs obtain high efficiency by superior 

 workmanship and small clearances in the cylinder. The Blancke air pump, 



FIG. 223 



Fig. 224, is of this type. Consider the motion of the piston as from left 

 to right, so that gases are being aspirated in on the left-hand side and dis- 

 charged on the right-hand side. The suction valve is composed of a series 

 of sleeves, with rectangular 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 com- 



