CANE SUGAR. 



enters at J, overflows over a series of rings and discs in a fine shower, meeting 

 the vapour which moves in the opposite direction forming what is known as a 

 counter- current condenser ; as shown this form is applied to what is termed 

 the dry vacuum. The method of this form will be readily understood on 

 referring to Fig. 181 ; a is a pipe more than 33 ft. high with its lower end 

 immersed in a tank of water ; the atmospheric pressure will support a column 

 of water 33ft. high, and above this will be a vacuum. Into the condenser 

 water is pumped through the pipe b ; this water overflowing at e meets the 

 vapour from the effect conducted through the pipe d. The steam is condensed, 

 and, together with the injection water, discharges itself on to the surface of 

 the column a, and is eventually discharged into the tank/. The incondensible 

 gases are drawn off by an air pump through c. 



A large number of patterns of condensers are made, the distribution of the 

 cooling water being very frequently obtained by devices similar to that shown in 

 Fig. 181, the arrangement of the rings and discs being capable of great variety. 



FIG. 182. 



Each of these systems has its advantages ; a more complete vacuum can 

 be obtained with the dry air pump, but in general two pumps are required ; 

 in certain cases where a natural head of water exists the lifting pump may be 

 dispensed with. In the wet system with large plants the size of the pump 

 becomes very inconvenient. 



It is impossible to calculate from first principles what should be the size 

 of condensers; Jelinek recommends that they should be not less than 1-5, and 

 Horsin-Deon from 2-5 to 3 times the volume of the pump. 



Central Condensation. Instead of each unit having its own 

 condenser and pump, it is now often the practice to instal one central con- 

 denser and pump. A very great economy in steam, piping, oil, repairs, and 

 attendance is thus obtained. In such a case a dry vacuum pump should be 

 used, as a wet pump would have to be of exaggerated dimensions in a factory 



326 



