THE EVAPORATION OF THE JUICE TO SYRUP. 



of any size. In Fig. 182 is shown in plan a convenient method of arranging 

 the evaporators and pans for use with a central condenser ; the triple is shown 

 at a, the pans at b, both leading to the vapour main c connected to the central 

 condenser d. 



Vacuum Pumps, The pumps used in sugar factories to create 

 and to maintain the vacuum fall into two main classes dry and 

 wet vacuum pumps. In the former type the incondensible gases and the 

 water used in condensation are removed separately, and in the latter class 

 together. 



In Fig. 183 is given a sectional view of a vertical pump. At a is the 

 piston or bucket, at b the foot or suction valves, and at c the discharge valves. 

 These pumps are usually worked in pairs off a beam engine, and are not to be 

 found in recent factories ; in older factories as many as six or eight pumps may 



be worked off one beam, a method which, 

 while economizing steam and labour, runs 

 the risk of stopping the whole factory in case 

 of a small mishap. 



In Fig. 18J/. is shown a horizontal torpedo 

 plunger pump, of which many have been and 

 are being used in recent factories. The 

 plunger e moving from right to left, the 

 valve a ' opens and water enters and fills the 

 space behind the plunger ; at the same time 

 ijp i i n m i gaa| the water in front of the plunger is discharged 



i- -J^ix-- ->JL \ through the valve b ; the valves a and b being 



closed, the water is discharged through d 

 into the main factory sewer. The valves 

 shown at b and b' are india rubber disc valves 

 resting on a perforated iron or brass grill ; 

 those shown at a and a' are clack valves 

 working on a hinge ; in modern works it is 

 the former type of valves that is employed. 

 Pumps of this type cannot be worked 



efficiently at a greater speed than 40 revolutions per minute, as it is important 

 that the air drawn in be expelled as completely as possible ; this only occurs 

 when the air is allowed to pass through the water, then expelled, followed 

 by the water. If the pump works at a high speed, the water is agitated, air 

 cannot pass through, and more air is left in the barrel than would be the case 

 at a lower speed. 



The above-described pump is the type usually provided by European 

 engineering firms ; where factories have been erected under the influence of 

 United States engineers, wet vacuum pumps of or derived from the 



FIG. 183. 



327 



