MECHANICAL REFRIGERATION 299 
ammonia, under pressure, is again liquified by running 
cold water over the coils. From the condenser coils it 
enters the liquid receiver, thence again on its journey 
through the refrigerating coils. 
The intensity of refrigeration is regulated by an ex- 
pansion valve, which is placed between the liquid receiver 
and the refrigerating coils. This valve may be adjusted 
so as to admit the desired quantity of liquid ammonia to 
the coils. 
Systems of Refrigeration. There are two ways in 
which the cooling may be accomplished by mechanical 
refrigeration: (1) by evaporating the liquid ammonia 
in a series of pipes placed in the room to be refrigerated ; 
and (2) by evaporating the liquid ammonia in a series of 
coils laid in a tank of brine and forcing the cold brine 
into coils laid in the room to be refrigerated. The former 
is known as the direct expansion system, the latter as the 
indirect expansion or brine system. 
Brine System. In creameries where the machinery is 
run only five or six hours a day the brine system is the 
more satisfactory as it permits the storing of a large 
amount of cold in the brine, which may be drawn upon 
when the machinery is not running. 
The brine tank is preferably located near the ceiling in 
the refrigerator where it will serve practically the same 
purpose as an overhead ice box. In addition to this, the 
refrigerator should contain a coil of direct expansion 
pipes which may be used when extra cold is desired. 
Brine from the above tank may be used for cooling 
cream by conducting it through coils which are movable 
in the cream vat; it may also be conducted through sta- 
tionary pipes placed in the make room for the purpose 
