304 MARKET DAIRYING 
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 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. 
