75.170Figure 3-5.—Pyrometers used in diesel exhaust systems.terminals (see figure 3-6). A pyrometer (millivoltmeter) measures the voltage produced and showsthe results on a scale which has been calibratedto read in degrees of temperature. In fixed installa-tion pyrometers, if the connecting wires are of thesame type as those of the thermocouples, the ther-mocouple element becomes, in effect, extendedto the pyrometer terminals and the temperatureat the meter (now the cold junction) becomes thereference temperature. Then the selector switchcan be rotated to any cylinder and contact canbe made between the pyrometer and the hot junc-tion. A reading can then be obtained for that par-ticular point.The hand-held pyrometer consists of anindicator and a pair of pointed prods attached toa sub-base and supported by a handle. To obtaina reading, the prod points are pressed against theexposed thermocouple terminals. The reading istaken from the scale. A point to remember is thatthe zero adjuster must be set to indicate roomtemperature rather than 0° temperature.GRAPHIC RECORDSAs you read in chapter 2, graphic records playan important part in keeping an engine in properoperating condition. When used properly they can75.171Figure 3-6.—Sectional view of a thermocouple.tell you how your engine is performing and whatis happening inside the engine. Graphic recordsindicate the overall condition of an engine andwarn you when certain parts are beginning to wearout so that you may take prompt corrective ac-tions and prevent major casualties.ADJUSTMENT AND MAINTENANCEAn internal combustion engine is a com-plicated machine, built with a high degree of preci-sion throughout and capable of long dependableservice if it is kept in good operating condition.To keep an engine in good operating condi-tion you must perform all the adjustments andmaintenance prescribed in your installed PMS andthe manufacturers’ technical manuals. In this sec-tion you will read about the adjustment andmaintenance of various components of an inter-nal combustion engine.AUTOMATIC REGULATING VALVEIn many engines, freshwater temperature isregulated by an automatic regulating valve whichmaintains the freshwater temperature at anydesired value by bypassing a portion of the wateraround the freshwater cooler. An automatictemperature regulator of the type commonlyused in the cooling systems of marine engines isshown in figure 3-7. Even though these regulatorsare automatic (self-operated), provisions are in-cluded in most installations for manual operationin the event that the automatic feature fails.ENGINEMAN 1 & C3-6
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