76 MANAGEMENT OF DAIRY PLANTS 



pressor walls cool and thus removes a portion of the heat in 

 the ammonia. 



2. Double-Acting Compressor. — Fig. 17 represents the com- 

 pressor cylinder of a double-acting compressor. This cyUnder has 

 both a suction and a discharge valve in each end of the cylinder, 

 and while the gas is being discharged from one end of the 

 cylinder the other end is being filled with gas at suction 

 pressure. 



3. Advantages of Each Type of Compressor. — The principal 

 advantages and disadvantages of each type of compressor have 

 been considered by F. Newkirk,' as follows: 



" The single-acting maclhine has a simpler stuffing box for the 

 reason that it is not subjected to high pressure as in case of the 

 double-acting machine. The double-acting machine has a deep 

 stuffing box which must be kept very tight in order to prevent 

 loss of ammonia. This causes much friction on the piston rod 

 and requires more oil. This, if not properly separated from the 

 ammonia before same enters the ammonia condenser, will be 

 carried along to the condenser and reduce the efficiency of 

 same. In case of the vertical machine, the piston does not wear 

 on one side due to its own weight; the valves are more readily 

 adjusted, so the clearance is reduced to the minimum. It is 

 evident that the machine of the least clearance is of the greatest 

 efficiency. 



"The double-acting machine, if properly adjusted, does 

 nearly as much work in one cylinder as the single-acting does in 

 two cylinders. The machine is low down and therefore more 

 convenient to look after, and it has only about half as many 

 moving parts as has the vertical machine." 



Ammonia Condenser. — This consists of a series of coils 

 kept constantly cooled by water applied as a bath or as a trick- 

 ling stream. Into these cooled coils the compressed ammonia 

 vapor is forced from the compressor, passing through an inter- 

 vening oil separator. As the ammonia vapor passes through 

 these coils, the cold water absorbs the excess heat from the 

 ammonia and the latter collapses and passes out of the con- 



^ Creamery Journal, July i, 191 1. 



