Condensed Miek and Milk Powder 55 



The efficiency of the vacuum apparatus depends very largely 

 on the vacuum pump. Rapid evaporation at a relatively low tem- 

 perature necessitates the maintenance of a high vacuum. The type, 

 material, construction, workmanship, installation and operation of 

 the vacuum pump should be such as to insure the maximum 

 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 connections must 

 be tight. The suction pipe must be of the size directed by the man- 

 ufacturer, as short as possible and with few and easy bends. The 

 grade of the suction pipe should be uniform 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. Excessive 

 speed means high steam consumption and heavy wear and tear on 

 the pump. The amount of water supplied to the condenser should 

 be regulated to suit the requirements. Ordinarily, and with a 

 vacuum of twenty-five to twenty-six inches, the temperature of the 

 condenser discharge should be about no degrees F. A lower tem- 

 perature would cause excessive and uneconomic use of water. The 

 basin on the vacuum cylinder should be kept filled with water to 

 prevent admission of air to the cylinder through the stuffing box, and 

 the spray pipe or jet in the condenser should be inspected often to 

 make sure that the perforations are not clogged. The stuffing box 

 of the cylinder should be well packed with a good quality of packing 

 and the steam cylinder well oiled. Start the pump slowly. Belt 

 driven pumps, especially those equipped with a fly-wheel, insure 

 greater uniformity of speed than direct-acting, steam-driven pumps. 

 Steam-driven pumps should be furnished with a high grade gov- 

 ernor. The vacuum pump should have a capacity, proportionate to 

 the size of the vacuum pan, amount of heating surface, steam pres- 

 sure for boiling and temperature of condensing water. 



Science and Practice of Evaporating in Vacuo. — Purpose oe 

 Condensing in Vacuo. — The important advantages gained by evap- 

 orating milk under reduced pressure, or in vacuo, are : economy of 

 evaporation, rapidity of evaporation, low temperature and large ca- 



