MECHANICAL REFRIGERATION 



75 



and there condensed back to its liquid form. The compressor 

 takes care of the first factor in this liquefaction; namely, the 

 subjection of the ammonia gas to the pressure necessary for 

 liquefaction. The condenser takes care of the second factor; 

 namely, the removal of 

 heat and the resultant 

 condensation to liquid 

 form. 



We distinguish be- 

 tween two forms of com- 

 pressors — the " Single- 

 Acting" and the 

 "Double-Acting." The 

 single-acting compressor 

 is always of vertical con- 

 struction; the double- 

 acting is most commonly 

 horizontal, although a 

 few of them are of the 

 vertical type. 



I. Single-Acting Com- 

 pressor. — Fig. 1 6 rep- 

 resents the compressor 

 cylinder of a single-act- 

 ing compressor. The 

 gas enters at the bottom 

 of the cylinder, passes 

 up through the suction 

 valve in the piston, and 

 by the up stroke of the 

 piston is compressed and 

 driven out through the 

 discharge valve in the 

 center of the safety head. The piston and the bottom of the 

 safety head, each being faced off square and coming in contact, 

 allow a complete discharge of the gas. The compressor of this 

 type is incased in a water jacket. The water keeps the com- 



FiG. 17. — Vilter double-acting ammonia 

 compressor. 



