534 



U. S. BUREAU OF FISHERIES 



REFRIGERATION MACHINERY 



Ammonia machinery is almost universally used in the United States 

 for freezing fish. In some of the plants machines of the absorption 

 type are used. While these are less efficient than compression 

 machines for theoretical reasons, they are found in some excellent 

 freezers. The loss of efficiency at low temperatures is relatively less 

 than it is in compression machines, and the temptation to allow the 

 temperature to rise is not so great. Therefore, though they are less 

 efficient at all temperatures than compression machines, the very low 

 temperatures necessary for the best freezing of fish are almost always 

 maintained by them. 



Fig. 11. — Refrigeration machinery, ammonia compression, electric drive. The elec- 

 tric drive is becoming more and more used. Where steam power is employed 

 the compound Corliss engine gives a highly efficient service. Courtesy, Bay City 

 Freezer 



The two-stage compression machine that has come into use within 

 the past few years is much more efficient than the single type at low 

 temperatures. A large cylinder draws in the gas from the expansion 

 element, gives it a preliminary compression, and passes it on to the 

 final-stage cylinder of smaller diameter, where it is compressed to 

 the condenser pressure. These machines approach the absorption 

 machine in their maintained efficiency at low temperatures and are 

 well suited to fish freezers. 



For compression machines electric power is preferred ; for absorp- 

 tion machines steam, of course, is necessary. 



Many plants employ brine circulation, which gives more stable 

 temperatures and permits easier regulation. 24 When brine is circu- 



M For a compact and practical handbook of operating refrigerating plants see " Instruc- 

 tions for the care and operation of refrigeration plants." Department of the Navy, 

 Bureau of Engineering, N. Eng. 144, revised edition, 1921. Washington. 



