214 CREAMERY BUTTER MAKING 



"In nearly all plants the presence of oil in the system of 

 piping is unavoidable. The oil used for lubricating pur- 

 poses, especially at the piston rod stuffing boxes, works 

 into the cylinders and is carried with the hot gas into the 

 ammonia piping, where it never fails to cause trouble. 

 The method of removing the air from the system has 

 already been referred to, but the removal of oil is accomp- 

 lished by means of an oil separator. This is placed in 

 the main pipe between the compressor and the condenser, 

 and is of about the size of the ammonia receiver. Some- 

 times another oil separator is placed in the return pipe 

 close to the compressor, which serves to eliminate any 

 remaining oil in the warmer gas and to remove pieces of 

 scale and other foreign matter which, if permitted to enter 

 the compressor cylinder, would tend to destroy it in a 

 very short time. 



"The oil, which always gets into the system sooner or 

 later and in greater or less quantity, depending upon the 

 care exercised to avoid it, acts as an insulator and pre- 

 vents the rapid transfer of heat from the ammonia to the 

 pipe that ought to obtain, and also occupies considerable 

 space that is required for the ammonia where the best re- 

 sults are to be obtained/' 



