PRWCTPLES OF NAVAL ENGINEERING 



INLET 

 VALVE 



> DISCHARGE 



SZZZ^^ZZ^^ VALVE 



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47.155.1 

 Figure 17-6. — Trunk Piston. 



pressure air compressor may require from 10 

 to 20 gallons per minute. 



As previously noted, cooling of the air is re- 

 quired for most economical compression. 

 Another reason for cooling the air between stages 

 and after the last stage is to condense any mois- 

 ture that may be present. The resulting conden- 

 sate is then drained off. If the moisture is not 

 removed from the air, it will be carried into the 

 accumulator or into the air lines, where it can 

 cause serious trouble. 



The intercoolers used between stages and the 

 aftercooler used after the last stage are of the 

 same general construction except that the after- 

 cooler is designed to withstand a higher working 

 pressure than the intercoolers. Water-cooled 

 coolers may be of the straight shell-and-tube 

 type or of the coil type. In coolers designed for 

 air pressures below 250 psig, the air flows either 

 through the tubes or over and around them; in 

 coolers designed for air pressures above 250 

 psig, the air flows through the tubes. In straight- 



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47.155.2 

 Figure 17-7.— Differential Piston. 



tube coolers, baffles are provided to guide the air 

 and water. In coil type coolers, the air passes 

 through the coil and the water flows around the 

 outside. Air-cooled coolers may beof the radia- 

 tor type or may consist of a bank of finned copper 

 tubes located in the path of a blast of air supplied 

 by the compressor fan. 



Both intercoolers and aftercoolers are fitted 

 with moisture separators on the discharge side 

 to remove moisture (and also any oil that may be 

 present) from the air stream. Various designs 

 of moisture separators are in use; the removal 

 of liquid may be accomplished by centrifugal 

 force, impact, or sudden changes in the velocity 

 of the air stream. 



CONTROL SYSTEM. -The control system of 

 a reciprocating air compressor may include one 

 or more devices such as automatic temperature 

 shutdown devices, start-stop controls, constant- 

 speed controls, and speed-pressure governors. 



444 



