54 Condensed Milk and Milk Powder 



tents of the trap are drawn from the bottom and are condensed with 

 the next batch ; or the bottom of the trap may be connected with the 

 pan so that the milk thus carried over flows back into the pan auto- 

 matically. In this case a small trap only is necessary. 



It should be understood that the milk trap is only a remedy and 

 not a preventive. Where the capacity of the pan is in proportion 

 to the amount of milk to> be condensed, as it should be, and where 

 the pan is operated properly, the trap is unnecessary. The trap is 

 an additional piece of apparatus to be kept clean. Unless it is so 

 constructed that access can be had to all parts of its interior and un- 

 less it really is kept clean at all times, it may become a serious source 

 of contamination. 



The Vacuum Pump. — The vacuum pump is, strictly speaking, 

 not a part of the vacuum pan, but its intimate connection with the 

 — -jMfc, P an ma kes it necessary to briefly 



consider it at this point. The 

 suction end of the vacuum 

 pump is connected with the end 

 of the condenser farthest from 

 the pan. The vacuum pump 

 exhausts the pan, forming a 

 partial vacuum. There are prin- 



Fig. 18. Vacuum pump .. . 



Courtesy of Arthur Harris & Co. Cipally tWO types of vaCUUm 



pumps used in the milk con- 

 densery, 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 advantage 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. 



