144 MARKET DAIRYING 



frost on the pipes entering and leaving the refrigerator 

 will be about the same. By placing the ear close to the 

 expansion valve the ammonia can be heard passing 

 through it, the sound being uniform and continuous when 

 everything is working properly. 



"When air is present the flow of ammonia will be more 

 or less intermittent, which irregularity is generally notice- 

 able through a change in the usual sound heard at the ex- 

 pansion valve. The pressure in toe condenser will also 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 

 conditions obtaining when everything is in order and 

 working properly. 



"The removal of air is accomplished in practically the 

 same manner as when charging the system,- permitting 

 it to escape through the purging valve a little at a time 

 so as not to lose any more gas than is absolutely necessary. 



"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 imavoidable. 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 accom- 

 plished 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 



