the lowest tubes at the front of the condenser,reversing direction at the water boxes three times,and leaving at the top of the tubes in the con-denser. Each condenser has a pet cock forventing entrained air and noncondensable gases.The evaporator stages become larger in thedirection of reduced pressure. The feedwater loopseals which extend from the bottom of evaporatorstage one through four are visible as cylinders.An evaporator drain is located in the center ofthe dished bottom of each loop seal. The flangedbrine outlet from the evaporator is at the bottomof the fifth stage.The distillate loop seal between the distillatecollection trough of one stage, and the condensersof the following stages, also protrude below thebottom of the evaporator.If the salinity of the distillate reaches 0.065epm per gallon, a warning device indicates thehigh salinity. The salinity cell shutoff valves per-mit withdrawal and descaling of the salinity cellswithout securing the unit.Although each stage condenser produces anequal amount of distillate, the amount flowingfrom each stage is larger than the preceding. Con-sequently, the loop seal piping grows progressivelylarger.The total distillate production of the fivestages is withdrawn from the bottom of stage fiveand pumped into the shell of the distillate cooler,and on to the storage tanks.The DISTILLATE COOLER is a heatexchanger of the shell-and-tube type, in which theheat of the hot distillate flowing around the tubesis transferred by conduction to the cooler feed-water flowing through the tubes.Distillate flows into the shell space sur-rounding the tubes through an inlet near the feed-water outlet. The distillate is retained in the coolerlong enough to efficiently transfer its heat throughthe tubes by vertically placed baffles, as it flowsfrom top to bottom of the cooler.Thermometers are mounted on the inlet andoutlet piping of the cooler and on the feedwaterinlet piping.As the distillate leaves the cooler, it is pumpedto storage tanks, provided the salinity does notexceed 0.065 epm per gallon. (If the salinityexceeds 0.065 epm per gallon, a solenoid trip valveoperated by a salinity indicating cell, dumps theChapter 7—AUXILIARY MACHINERYdistillate to the bilges or waste tank until the salin-ity is again back to or below 0.065 epm pergallon .)Pet cocks are located on each end of the coolerto bleed off any accumulation of air or non-condensable gases.The FEEDWATER PREHEATER is a gas orliquid heat exchanger of the shell-and-tube type,similar in design to the distillate cooler. Thepreheater is located in the feedwater line betweenthe condenser of the first evaporator stage andthe saltwater heater.High pressure ship’s steam, first used by theair ejectors to evacuate the stage evaporators, ispiped into the preheater shell. A series of five baf-fles, spaced closely together in the top steamoutlet, reduce the velocity of the steam and letthe steam condense on the outside of the heattransfer tubes.Feedwater that has already been partiallyheated in the tubes of the distillate cooler and thefive-stage condensers flows through the tubes ofthe preheater via the front water box in a singlepass and acquires the heat of condensation of theair ejector steam before leaving the preheater atthe rear water box outlet.A salinity cell is set to energize at 0.10 epm.It operates as a shutoff valve in the piping belowthe condensate outlet to dump high salinity waterto the bilge or the drain tank. A 6-inch loop sealin the condensate line ensures that the salinity cellis submerged at all times.A thermometer is located on the front of thepreheater, and a pet cock for venting is locatedon the water box.The SALT WATER HEATER is a gas orliquid heat exchanger designed to raise the feed-water temperature prior to its entrance into theflash chamber of the first evaporator stage. Thesaltwater heater is mounted on the operating endof the evaporator and extends the full width ofthe unit. Feedwater enters and leaves the heaterfrom the front water box after making four passesthrough the heater.Four thermometers are installed on the heater:two to measure the feedwater inlet and outlettemperatures; a third, mounted on the heatershell, to measure the steam temperature sur-rounding the tubes; and a fourth, mounted on topof the heater shell, to measure the temperature7-29
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