326 BUTTER-MAKING. 



and producing cold. During the cooling and condensing pro- 

 cesses each pound of ammonia parts with about 560 units of 

 heat, which amount can again be absorbed when it expands into 

 gas at the lower pressure. 



3. This liquefied gas, which is still under great pressure, is 

 then admitted through what is termed the expansion-valve. 

 This valve is especially constructed for that purpose, and has 

 only a very minute opening in it for the admission of the liquid 

 ammonia. On the expansion side the pressure is low (20 

 to 30 Ibs.). As the liquid ammonia emerges from the high- 

 pressure side through the expansion-valve into the expansion 

 side, it forms a gas. This expanded gas may then be circulated 

 through coils for cooling purposes. From there it passes back 

 into the suction side of the compressor ready to go through 

 another similar cycle. 



From the above description it will be seen that there are two 

 sides to the system, the expansion side and the compression 

 side. The compression side extends from the compressor to 

 the expansion-valve ; the expansion side from the expansion- 

 valve to the suction side of the compressor, inclusive. 



Transferring the Cold. The methods of transferring the 

 cold to the different places in the building vary. There are 

 two systems, viz.: 



1. Direct Expansion. 



2. Brine System. 



1. By the direct-expansion system the condensing-pipes 

 of the system are extended to the room or place at which the 

 cooling is to be done. An extended set of expansion coils then 

 convey the gas which absorbs the heat. A lower temperature 

 can be produced by this method than with the brine system. 



2. In the brine system a large brine-tank is placed some- 

 where in the creamery at a place most convenient with respect 

 to cooling. This tank contains a strong solution of brine. 

 The chief reason why brine is used in preference to water is that 

 brine has a very low freezing-point. This will vary with 

 different degrees of saturation. 



