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 stuffing 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 reaching 

 a point where flash- 

 ing will take place, . _____ H £_ 



which will result in ^ ^ 



an explosion. £ 



.SUCTION VP*LV3 

 TO Mac«m f 



HOT HAS FROM CONOgNSEft 



-exPS\N5IOt1 i/ALve 



In small installa- * -P 



tions usually found in ^ |_, 



milk plants, cream- v I X \ 



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. 



