MECHANICAL REFRIGERATION 213 



the delivery pipe, and if there is a tendency to heat open 

 it wider, and vice versa. This valve should be carefully 

 regulated until the temperature of the delivery pipe is 

 practically the same as the water discharged from the 

 ammonia condenser. With too light a charge of am- 

 monia the delivery pipe will become heated even when 

 the regulating valve is wide open. As a general thing 

 when the plant is working properly the temperature of 

 the refrigerator is about 15° lower than the brine being 

 used, the temperature of the water discharged from the 

 ammonia condenser will be about 15° lower than that of 

 the condenser, the pointers on the gauges will vibrate the 

 same distance at each stroke of the compressor and the 

 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 the condenser will also be 

 higher and the efifect 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. 



