MECHANICAL REFRIGERATION 195 



on the suction stroke, compressed and discharged on the 

 return stroke. The pressure generated varies between 

 1 20 and 175 pounds per square inch. During the com- 

 pression, heat is developed in proportion to pressure ex- 

 erted. The greater the pressure, the higher the tempera- 

 ture of the gas. Part of the heat of compression is carried 

 off by means of a continuous stream of water running 

 through a jacket around the cylinder. 



2. From the compressor the gas is forced through the 

 pipes into the condensing coils, in which the warm com- 

 pressed gas is cooled still more. When sufficient heat 

 has been removed from this gas, it assumes a liquid con- 

 dition and is ready to expand into a gaseous form for the 

 purpose of absorbing heat and producing cold. During 

 the cooling and condensing processes each pound of ammo- 

 nia parts with about five hundred and sixty units of heat, 

 which amount can again be absorbed when it expands 

 into gas at the lower pressure. 



3. This liquefied gas, which is still under great pressure, 

 is then admitted through what is termed the expansion 

 valve. This valve is especially constructed for that pur- 

 pose, and has only a very minute opening in it for the 

 admission of the liquid ammonia. On the expansion side 

 the pressure is low (20 to 30 pounds) . As the liquid ammo- 

 nia emerges from the high-pressure side through the ex- 

 pansion valve into the expansion side it forms a gas. 

 This expanded gas may then be circulated through coils 

 for cooling purposes. From there it passes back into the 

 suction side of the compressor ready to go through another 

 similar cycle. 



From the above description it will be seen that there 

 are two sides to the system, the expansion side and the 

 compression side. The compression side extends from 



