30 
BULLETIN 
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 diagrammatic ally the essential members of a 
compression-refrigerating system, in which A represents the direct 
expansion j Ls, 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 
►v peicssvrte me*H PKESzunc 
fterff/aeftATox. 
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 
