MECHANICAL REFRIGERATION 2OI 



be higher and the effect of the apparatus as a whole will 

 be changed, and, of course, not so good. These changes 

 will be quickly noticed by a person accustomed to the con- 

 ditions obtaining when everything is in order and working 

 properly. 



" The presence of oil or water in the system is generally 

 detected by shocks occurring in the compressor cylinder. 



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

 of piping is unavoidable. The oil used for lubricating 

 purposes, 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 al- 

 ready been referred to, but the removal of oil is accomplished 

 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. Sometimes 

 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 com- 

 pressor 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, .and also occupies considerable space that is re- 

 quired for the ammonia where the be&t results are to be 

 obtained." 



Insulation. Where mechanical refrigeration is used the 

 insulation of cooling rooms, brine tank and pipes is of great 

 importance from an economic point of view. 



The insulating material must be a non-absorbent of 

 moisture, a poor conductor of heat, and of sufficient strength 

 and durability to remain for many years without crumbling 

 or decomposing. 



