Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGCHARGINGCONNECTIONDRAIN -TOFROMEXPANSIONVALVECONDENSERFigure 19-8.— Receiver for R-12refrigeration system.47.96improper setting of the high pressure cutoutswitch. If the relief valve opens, it dischargeshigh pressure vapor to the suction side of thecompressor.A water regulating valve, as shown in figure19-11, is usually installed to control the quantityof circulating water flowing to the refrigerantcondenser. The valve is located either at theinlet to the condenser or at the outlet from thecondenser. The valve is actuated by the refrigerantpressure in the compressor discharge line;this pressure acts upon a diaphragm or a bellowsarrangement which transmits motion to thevalve stem. As the temperature of the circulatingwater increases, the temperature of therefrigerant vapor increases; this causes thepressure of the refrigerant to increase, andthereby raises the condensation point . When thisoccurs, the increased pressure of the refrigerantcauses the water regulating valve to openwider, thus automatically permitting more circulatingwater to flow through the condenser.When the condenser is cooler than necessary,the water regulating valve allows less water toflow through the condenser. Thus the flow ofcooling water through the condenser is automaticallymaintained at the rate actually requiredto condense the refrigerant under varyingconditions of load and temperature.A water failure switch is provided to stopthe compressor in the event of failure of thecirculating water supply. This is a pressureactuatedswitch, generally similar to the lowpressure cutout switch and the high pressurecutout switch previously described. If the waterfailure switch should fail to function, the refrigerantpressure in the condenser wouldquickly build up to the point where the highpressure cutout switch would function.Because of the solvent action of R-12, anyparticles of grit, scale, dirt, and metal thatthe system may contain are very readily circulatedthrough the refrigerant lines. To avoiddamage to the compressor from such foreignmatter, a strainer is installed in the compressorsuction connection. In addition, a liquid straineris installed in the liquid line leading to eachevaporator; these strainers serve to protectthe solenoid valves and the thermostatic expansionvalves.A number of pressure gages and thermometersare used In refrigeration systems. Acompound refrigerant gage is shown in figure9-12. The temperature markings on this gageshow the boiling point (or condensing point) ofthe refrigerant at each pressure; the gage cannotmeasure temperature directly. The darkpointer (which is actually red in color) is astationary pointer that can be set manually toindicate the maximum working pressure. Otherpressure gages and thermometers include awater pressure gage, installed in the circulatingwater line to the condenser, and standard thermometersof appropriate range, installed in therefrigerant lines.Refrigerant piping is normally made ofcopper. Copper is particularly good for thispurpose because it does not become corrodedby the refrigerant, the internal surface is smoothenough to minimize friction, and the tubing iseasily shaped to meet installation requirements.AIR CONDITIONINGAir conditioning is a field that deals withthe design, construction, and operation of equipmentused in establishing and maintaining desirableindoor air conditions. It is the scienceof maintaining the atmosphere of an enclosureat any required temperature, humidity, and purity.As such, air conditioning involves thecooling, heating, dehumidifying, ventilating, andpurifying of air.Aboard ship, air conditioning serves to keepthe ship's crew comfortable, alert, and physicallyfit. The temperature, humidity, cleanliness,quantity, and distribution of the conditionedair supply is a matter of vital concern.482