30 



BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. 



pressor or pump, the liquefied refrigerant again expands into a vapor 

 after passing into the coils, taking up from whatever substance sur- 

 rounds it an amount of heat exactly equal to that which was given 

 up during condensation. The vapor is again drawn back into the 

 compressor, compressed, condensed, and expanded, the cycle of op- 

 eration being repeated indefinitely with the same refrigerant. 



Figure 13 presents diagrammatically the essential members of a 

 compression-refrigerating system, in which A represents the direct 

 expansion coils, in which the refrigerant is expanded after leaving the 

 expansion valve E; B, the compressor or pump, which takes the warm 

 gas or vapor from the expansion coils A and compresses them into the 

 condenser 0; 0, the condenser for cooling and liquefying the gasi- 

 fied refrigerant; R, the receiver, into which the liquefied refrigerant 

 flows from the condenser; E, the expansion or throttling valve, which 

 controls the flow of the liquid refrigerant from the receiver R to the 



nerff/amATon. 



Fig. 13. — Elementary diagram of direct expansion system. 



expansion coils A, where a materially lower pressure is maintained 

 by the compressor, which causes the liquid to boil at a temperature 

 sufficiently low to absorb heat from and therefore refrigerate the 

 surrounding air. 



In practice, however, the system is more elaborate, as will be 

 noted by referring to figure 14, which shows a complete compression- 

 refrigerating plant with all the accessories necessary for its opera- 

 tion. 



DIRECTIONS FOR INSTALLING, CHARGING, AND OPERATING INCLOSED TYPE OF 

 AMMONIA COMPRESSION MACHINES. 



INSTALLING. 



The compressor, condensor, and receiver should be located in a 

 dry and. well-lighted place where they will be accessible at all times 

 for inspection and repairs. The liquid receiver and connections 



