MECHANICAL REFRIGERATION 305 
“Tn 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.” 
