CHAPTER 6REFRIGERATION AND AIR CONDITIONINGAs an EN1 or ENC you have already learnedthe principles of refrigeration and air condition-ing, and the components and accessories thatmake up the system. You have learned how tostart, operate, and secure refrigeration plants. Inaddition, you have performed routinemaintenance jobs such as trouble shooting, andservicing the system, and used correct procedure’sfor leak detecting, and changing the lubricatingoil in refrigeration compressors. As you advancein rate, you will be expected to have a greaterknowledge of the construction and operatingprinciples of refrigerating equipment. You will berequired to perform more complicatedmaintenance jobs, to make repairs as required,and to determine the causes of inefficient plantoperation and accomplish the necessary correc-tive procedures.This chapter provides information that sup-plements related information in other trainingmanuals applicable to your rating and related tothe qualifications for advancement. Informationis included on the construction and maintenanceof refrigeration and air conditioning equipment,and the detection and correction of operatingdifficulties.You should refer to the manufacturer’stechnical manual for details of the plant on yourship.The main parts of an R-12 refrigeration systemare shown in figure 6-1. The primary componentsof the system are the thermostatic expansionvalve, the evaporator, the compressor, the con-denser, and the receiver. Additional equipmentrequired to complete the plant includes piping,pressure gages, thermometers, various types ofcontrol switches and control valves, strainers,relief valves, sight-flow indicators, dehydrators,and charging connections.In the following discussion, we will deal withthe R-12 system as though it had only oneevaporator, one compressor, and one condenser.However, a refrigeration system may (and usuallydoes) include more than one evaporator, and itmay include additional compressor and condenserunits.COMPRESSORSMany different types and sizes of compressorsare used in refrigeration and air conditioningsystems. They vary from the small hermetic unitsused in drinking fountains and refrigerators, tothe large centrifugal units used for air con-ditioning.One of the most commonly encountered com-pressors on today’s modern ships is a high speed,continuous running unit with a variable capacity.This compressor is of the multicylinder,reciprocating design, with a positive unloadedsystem built into the compressor to control thecompressor’s capacity.SHAFT SEALSWhere the crankshaft extends through thecrankcase, a leakproof seal must be maintainedto prevent the refrigerant and oil from escapingand also to prevent air from entering thecrankcase when the pressure in the crankcase islower than the surrounding atmospheric pressure.This is accomplished by crankshaft sealassemblies. There are several types of sealsincluding the rotary seal, and the diaphragm.6-1
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