84 SWEETENED CONDENSED MILK CONDENSING 



necessary to briefly consider it at this point. The suction end 

 of the vacuum pump is connected with the condenser. The 

 vacuum pump exhausts the pan, forming a partial vacuum. 

 There are principally two types of vacuum pumps used in 

 the milk condensery, the dry-vacuum pump and the wet- 

 vacuum pump. The dry-vacuum pump is used in the factories 

 with the dry-vacuum system, i. e., where the cooling water 

 and the condensation water escape to the sewer direct 

 and without passing through the vacuum pump, as is the case 

 with the surface condenser and the barometric condenser. The 

 wet-vacuum pumps are used with the wet-vacuum system, where 

 the cooling water and the condensation water pass through the 

 cylinder of the pump. The dry-vacuum pumps have the advan- 

 tage of permitting the operation of the machine at a* higher 

 piston speed than the wet-vacuum pumps in which the water 

 must be displaced at the end of each stroke. The cylinders of 

 the dry-vacuum pump are cooled by water jackets. The initial 

 cost of the dry-vacuum pumps, however, is greater than that 

 of the wet-vacuum pumps. 



The efficiency of the vacuum apparatus depends very largely 

 on the vacuum pump. Rapid evaporation at a relatively low 

 temperature necessitates the maintenance of a high vacuum. The 

 type, material, construction, workmanship, installation and oper- 

 ation of the vacuum pump should be such as to insure the maxi- 

 mum efficiency. 



The pump should be placed on a good foundation and as 

 near the vacuum pan as practicable in order that the full benefit 

 of the vacuum may be realized. The suction pipe and all con- 

 nections must be tight. The suction pipe must be of the size 

 directed by the manufacturer, as short as possible and with few 

 and easy bends. The grade of the suction pipe should be uni- 

 form in order to avoid air pockets. 



The water should be turned into the condenser before the 

 vacuum pump is started. The pump should not run at a higher 

 speed than is necessary to secure the required vacuum. Exces- 

 sive speed means high ste#m consumption and heavy wear and 

 tear on the pump. The amount of water supplied to the con- 

 denser should be regulated to suit the requirements. Ordinarily, 

 and with a vacuum of twentv-five to twentv-six inches, the 



