APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 37 
as an explosion is likely to occur, due to the vaporization of oil 
which may have lodged in the coils. The temperature of the air ; 
when pumped into the system at a high pressure, is liable to exceed 
the flash point of the oil, resulting in an explosion. 
For the same reason it is also dangerous, especially in the case of 
small, fast-running machines, to allow too much air to enter when 
pumping out the compressor in case it becomes necessary to pack 
the s tuning box; for should the attendant neglect to purge the 
condenser after the operation, the air in the system will be car- 
ried along with the ammonia gas, necessitating a higher pressure 
and a consequent higher temperature than would otherwise be 
attained; and should the temperature in the system get too great, 
there is danger of the oil which may be deposited in the coils Teaching 
a point where flash- 
ing will take place, , -£ 
which will result in ^ — — k 
an explosion. C? "^ 
In small installa 
tions usually found in 
£ 
■suctioh y^-Lva 
YOT CAS FROM CONOENSEFe. 
•f>«<\AfJ/0/V VALVS 
milk plants, cream- Cl Z— ,*, JT 
eries, and dairies the 
, „ Fig. 15. — Conventional diagram. 
condensers are or 
small dimensions; consequently, they can not hold large quantities 
of excess air. Hence great care should be taken to thoroughly purge 
the system of air when starting up after pumping out the compressor 
by blowing the air from the system. Manufacturers provide cocks 
for this purpose. 
In cleansing old plants or those that have been shut down for 
some time from deposits of oil, it is a good plan to pump hot ammonia 
gas into the system. The gas should be taken from the line just 
before it enters the condenser. If taken from the top of the con- 
denser, the gas will probably contain air and other impurities which 
would be liable to cause an explosion. 
Referring to the conventional diagram, figure 15, the method of 
operation should be as follows: Connect a temporary pipe line with 
valve from the lowest part of the condenser or to the pipe line just 
before entering the condenser. Close the expansion valve and 
pump hot ammonia gas into the coils. Have the suction valve 
opened slightly and occasionally open it wide quickly to allow the 
oil to be carried out and deposited in the oil trap, from which it can 
be drawn off. 
Before starting up the plant care should be taken to see that all 
oil cups are filled and the oil ways open, in order that all wearing 
surfaces may be well lubricated before the machine is started. 
