38 



BULLETIN 98, U. S. DEPARTMENT OP AGRICULTURE. 



To start. — (1) Turn the water on the condenser and water jacket, 

 and open the discharge valve on the compressor; (2) start the 

 machine slowly at first and after the machine is in motion and the 

 pressures are at proper point open the suction valve on the com- 

 pressor gradually; (3) open the expansion valve sufficiently to give 

 the required back pressure and the machine is in full operation. 



To stop. — (1) Close the king valve which is between the receiver 

 and the expansion valve and pump the low pressure to zero. This 

 is considered better practice than closing the expansion valve each 

 time the machine is stopped, thereby necessitating readjustment of 

 the expansion valve upon starting up again; (2) open all drips and 



CCOLtNa •ivATEfi 



COOt/'Vft *r/)Y£B 



Fig. 16.— Elementary diagram of absorption system. 



drains and shut down the machine; (3) close the suction and dis- 

 charge valves, and all oil cups and water valves; (4) clean the ma- 

 chine thoroughly and examine all bolts and nuts to see that they 

 are tight and see that the bearings arc properly adjusted. 



VAPOR ABSORPTION SYSTEM. 



The absorption and expulsion of ammonia gas by water forms the 

 basic principle of the absorption process of refrigeration. 



By referring to the elementary diagram, figure 16, the principles 

 of this system of refrigeration will be understood. The generator G 

 is an inclosed vessel which is partly filled with a solution of ammonia 

 gas in water, under high pressure. Heat is applied to the generator, 



