APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 33 
The suction and discharge valves should be wide open while the 
machine is being charged. When one tank is emptied the charging 
valve should be closed and another tank placed in position, this being 
repeated until the system is sufficiently charged for work, when the 
charging valve should be closed and the main expansion valve 
adjusted. The ammonia drums should be weighed before and after 
being emptied or partially emptied, and a record kept of the amount 
necessary for charging. The glass gage on the liquid receiver will 
show the amount of liquid contained, and the pressure gages, as well 
as the gradual cooling of the brine in the refrigerator and the frost 
collecting on the expansion pipe, will indicate when a sufficient 
amount of the refrigerant has been inserted to start working. 
OPERATING. 
After the machine has been started and the expansion valve ad- 
justed, the temperature of the delivery pipe should be carefully 
noted, and should a tendency to heat be observed, the expansion 
valve should be opened wider, while, on the other hand, if it should 
become cold, the valve should be slightly closed, the adjustment 
being continued until the temperature of the pipe is the same as that 
of the cooling water leaving the condenser. If there is an insufficient 
charge of the refrigerant, the delivery pipe will become heated, even 
though the expansion valve is wide open. 
Some of the signs which indicate the proper working of the plant, 
other than the fact that it is satisfactorily performing its refrigerating 
functions, are: The vibrations of the pointers on the high and low 
pressure gages; the frost on the exterior surface of the refrigerating 
pipes; the liquid refrigerant can be plainly heard passing through the 
expansion valve; and the difference in temperature between the 
liquid leaving the condenser and the final temperature of the cooling 
water, and between the refrigerator and the brine. 
Should it become necessary to disconnect any part of the ammonia 
system for any reason, the ammonia must be pumped out of that part 
and stored in another part of the system. After making repairs, 
all the air must be exhausted from that part of the system before the 
ammonia is again allowed to enter. 
To pump ammonia out of the condenser. — Close valves in the liquid 
pipe, the main suction, and discharge valves, and open the by-pass 
valves after draining the water from the condenser to prevent freezing 
and bursting of the pipes. Start the machine and pump out the ammo- 
nia until a partial vacuum is indicated by the high-pressure gage; 
then stop the machine and allow it to -stand for two or three hours 
in order that any liquid ammonia lying in the pipes may have time to 
evaporate. Start up the machine again and pump down to a 25-inch 
40083°— Bull. 98—14 3 
