PRINCIPLES OF NAVAL ENGINEERING 



VALVE CAGE 



DISCHARGE 



VALVE 



DISK 



SUCTION 



VALVE 



DISK 



47.94 



Figure 19-6.— Reciprocating compressor for R-12 refrigeration plant. 



regulating valve is installed at the outlet of 

 each evaporator except the evaporator in the 

 space in which the lowest temperature is to be 

 maintained. The evaporator pressure regulating 

 valve is set to keep the pressure in the coil 

 from falling below the pressure corresponding 

 to the lowest temperature desired in that space. 

 The low pressure cutout switch is the con- 

 trol that causes the compressor to go on or 

 off as required for the normal operation of the 

 refrigeration plant. This switch is located on 

 the suction side of the compressor and is 

 actuated by pressure changes in the suction 



line. When the solenoid valves in the lines to 

 the various evaporators are closed, so that 

 the flow of refrigerant to the evaporators is 

 stopped, the pressure of the vapor in the com- 

 pressor suction line drops quickly. When the 

 suction pressure has dropped to the desired 

 pressure, the low pressure cutout switch causes 

 the compressor motor to stop. When the tem- 

 perature in the refrigerated space has risen 

 enough to operate one or more of the solenoid 

 valves, refrigerant is again admitted to the 

 cooling coils and the compressor suction pres- 

 sure builds up again. At the desired pressure. 



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