70 MANAGEMENT OF DAIRY PLANTS 



coils; third, the liquefying stage, during which the vapor or gas 

 is again reduced to its liquid form in two successive steps 

 compression and heat extraction or condensation. Being thus 

 returned to its original liquid form, the ammonia may be used 

 over and over again in successive cycles of refrigerating activity. 



The machinery through which this cycle operates is com- 

 posed of four principal parts: First, the expansion coil; second, 

 the ammonia compressor; third, the condenser, and fourth, the 

 expansion or regulating valve. 



Expansion Coil. This is that part of the system where 

 refrigeration takes place. Through reduction in pressure, the 

 liquid ammonia is there changed into a gas, thus absorbing heat 

 from its surroundings and thereby effecting refrigeration. 



This expansion coil may be located directly in the refriger- 

 ator and serve as the refrigerating coil, in which case it is called 

 the " Direct Expansion" method of cooling. On the other 

 hand, the expansion coils may be placed in a tank of brine 

 from which the brine in turn is circulated through refrigerating 

 coils located in the refrigerating room. This indirect method of 

 cooling is known as the " Brine Method." 



1. Direct Expansion. The system of direct expansion is 

 adapted especially for rooms that are to be cooled to an ex- 

 tremely low degree of heat and in places where the machine is 

 operated constantly. It cannot, therefore, be considered the 

 most ideal method for the smaller creamery or dairy. 



2. Brine Method. This is the system which is most suitable 

 for the average creamery. The brine tank should be located 

 in the refrigerator in a position and with insulation similar to 

 that of the ice bunker described under the natural system of 

 refrigeration (Chapter V). The larger body of brine retains a 

 more constant temperature, and in a smaller dairy the com- 

 pressor may be operated only for a short time daily in order to 

 reduce the temperature of the brine and so maintain the neces- 

 sary refrigeration. 



The brine, when thus cooled, may be circulated by the aid of 

 a pump through a system of coils extending through various 

 refrigerator rooms. This brine carries back to the brine tank 



