Tài liệu Diezel 1410 P8

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Purpose of cooling systems. The high-speed high-output diesel engines of today are strictly limited as to the maximum temperature at which they can safely operate.

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Nội dung Text: Tài liệu Diezel 1410 P8

8 COOLING SYSTEMS A. GENERAL 8A1. Purpose of cooling systems. The result in a variation of clearances high-speed high-output diesel engines between the moving parts. Under normal of today are strictly limited as to the operating conditions these clearances are maximum temperature at which they very small and any variation in can safely operate. To maintain the dimension of the moving parts may cause temperature below the maximum insufficient clearances and subsequent allowable limit, various types of inadequate lubrication, increased friction, cooling systems are used. The thermal and possible seizure. efficiency of an engine would be greatly improved if it were not 3. To retain the strength of the metals necessary to provide a cooling system. used. High temperatures change the The cooling system losses, together strength and physical properties of the with the loss of heat during the various ferrous metals used in an engine. combustion, working, and exhaust For example, if a cylinder head is periods, cut down the thermal subjected to high temperatures without efficiency of the engine to a relatively being cooled, the tensile strength of the small percentage. Shown below are the metal is reduced, resulting in possible percentages of useful work and various fracture. This high temperature also losses obtained from the combustion of causes excessive expansion of the metal a fuel oil in a diesel cylinder: which may result in shearing of the cylinder bolts. To useful work (brake 30-35 thermal efficiency) percent Cylinder heads, cylinder jackets, cylinder To exhaust gases 30-35 liners, exhaust headers, valves, and percent exhaust elbows usually are cooled by To cooling water and 30-35 water. Pistons may be cooled either by friction percentwater or oil. In present fleet type Radiation, lube oil, and so 0- 5 submarine installations, the pistons are forth percentcooled by lubricating oil which is in turn cooled by engine cooling water. It is There are three practical reasons for important to keep all parts of the engine cooling an engine: at as nearly the same temperature as possible. This can be accomplished to 1. To maintain a lubricating oil film on some extent by engine design. For pistons, cylinder walls, and other instance, the water jacket should cover moving parts as explained in Chapter 7. the entire length of the piston stroke to This oil film must be maintained to avoid possible unequal expansion of insure adequate lubrication. The various sections of the cylinder and formation of an oil film depends in cylinder liner. large degree on the viscosity of the oil. If the engine cooling system did not It requires time to conduct heat through keep the engine temperature at a value any substance, therefore the thicker the that would insure the formation of an metal, the slower the conduction. This is oil film, insufficient lubrication and one of the reasons the size of cylinders in consequent excessive engine wear diesel engines is limited, because the would result. If the engine is kept too larger the cylinder, the thicker the cool, condensation takes places in the material necessary for liners and cylinder lube oil and forms acids and sludge. heads in order to withstand the pressures of combustion. Thicker metals cause the 2. To avoid too great a variation in the inside surfaces to run hotter, because the
dimensions of the engine parts. Great heat is not conducted so rapidly to the differences between operating cooling water. temperatures at varying loads cause excessive changes in the dimensions of 8A2. Operation of a cooling system. the moving parts. These excessive One of the principal factors affecting the changes also occur when there are large proper differences between the cold and operating temperatures of the parts. These changes in dimensions 159 cooling of an engine is the rate of flow 8A3. Types of cooling systems. Two of water through the system. The more types of cooling systems are in common rapid the rate of flow, the less danger use, the open system and the closed there is of scale deposits, and the system. In the open system the engine is formation of hot spots, since the high cooled directly by salt water. In the water velocity has a scouring effect closed system the engine is cooled by upon the metal surfaces of the jackets, fresh water and the fresh water is then and the heat is carried away more cooled by salt water. The closed type of quickly. When the velocity of the cooling system is in common use today circulating water is slower, the in all modern medium- and high-speed discharge temperature is higher and diesel engines. more heat per gallon of water circulated is carried away. When the circulation is The open type of cooling system has speeded up, each gallon of water carries many disadvantages, the most important away less heat and the discharge being the exposure of the engine to scale temperature of the water drops, formation, marine growth and dirt resulting in a relatively cool running deposits in the piping, and fluctuating sea engine. water temperature. Scale or deposits not only restrict water flow in the engine The temperature of the engine can be water passages but also act as a blanket controlled by the discharge temperature and hinder heat transfer to the cooling of the cooling water. This can be done water. This prevents adequate cooling of in two ways, depending upon the engine parts which may result in serious arrangement of the piping and the type difficulties. of pump used. A common and simple method is to control the amount of 8A4. Open type cooling systems. The water pumped, by means of a throttling term open system is used because salt valve in the pump discharge to the water is drawn directly from sea, passed engine cooling system. The water can through the system, and then discharged then be made to pass more slowly overboard. through the engine and be discharged at a higher temperature, or to pass more In a typical system the salt water is rap idly at a lower temperature. If the drawn through sea valves and a strainer pump is driven separately by an electric by a centrifugal pump and then motor, the same effect can be obtained discharged through the lubricating oil by slowing down or speeding up the heat exchanger or cooler where it cools pump. The other method to control the the lubricating oil. The water then passes temperature is to bypass some of the to the cylinder liner jackets, exhaust warm discharged water around the manifold jackets, exhaust uptake jackets, cooler and directly to the suction side the inboard exhaust valve, overboard sea of the pump. This method gives a more valves, and to the outboard exhaust valve uniform temperature throughout the jackets and sprays. Part of the water may cooling system and keeps the passage be piped to the fuel compensating water
system. The remaining water passes of water at a higher velocity. through the muffler jackets and then In all modern engines, the latter method overboard. is used and accomplished automatically by means of a temperature regulator. The open type of cooling system is used These regulators may be set to give any only on engines in the older types of desired temperature at the engine submarines, particularly the O, R, and S outlet. They are used not only to classes. All of the later fleet type regulate the fresh water but also to submarine engines are designed with regulate indirectly the temperature of cooling systems of the closed type. the lubricating oil leaving the lubricating oil cooler. This is possible 8A5. Closed type cooling systems. because the fresh water that is passed Closed type, or fresh water cooling through the regulator and fresh water systems consist basically of two entirely cooler is used as the cooling agent in separate systems-the fresh water cooling the lubricating oil cooler. This permits system and the salt water cooling system. the maximum amount of controllability In the fresh water cooling system the of fresh water and lubricating oil same fresh water is reused continuously temperatures with the use of the for cooling the engine. The water is minimum amount of equipment. circulated throughout the engine cooling spaces 160 by an attached circulating fresh water the salt water circulating water overboard pump. The water is then led to a fresh discharge. water cooler, where it is cooled by the salt water of the salt water cooling On generator type engines the attached system. After it leaves the cooler, the salt water pump furnishes salt water to fresh water may or may not, depending the generator air coolers and returns the on the installation, go through the water to the overboard discharge. lubricating oil cooler to act as cooling Throttling valves frequently are placed in agent for the lubricating oil. The water lines to the fresh water cooler and then returns to the fresh water pump, generator air coolers to control the flow completing the circuit. of water through these heat exchangers. Fresh water temperature is usually Thermometers and pressure indicators regulated by means of an automatic are placed in the system at various regulating valve which maintains the places. Salt water temperatures should fresh water temperature at any desired not exceed 122 degrees F. Fresh water value by bypassing the necessary temperatures should be between 140 amount of water around the fresh water degrees F and 180 degrees F, with a cooler. minimum of 140 degrees F at the engine inlet. Outlet fresh water temperatures An expansion tank is provided which should be between 160 degrees F and aids in keeping the fresh water system 180 degrees F. Cooling water filled at all times by keeping available a temperatures should not be allowed to ready supply of water. A vent usually is drop below 140 degrees F, otherwise provided in the high point of the line to excessive engine wear and corrosion may keep the system free of air, thereby result if the temperature drops, below the preventing the water pump from dewpoint. becoming air bound. The expansion tank also is equipped with a gage glass 8A6. Detached fresh water circulating by which the level of water in the tank pumps. Earlier General Motors and may be constantly observed. If the level Fairbanks-Morse models (the GM 16-248
of water in the tank becomes too low, and the F-M 38D 8 and the 9-cylinder the system may be replenished from the 38D 8 1/8) were equipped only with ship's fresh water service system attached fresh water pumps. This design through a make-up line into the suction made it impossible for fresh water to be side of the attached fresh water pump. circulated in the engine for cooling Any large rapid fluctuation in the levelpurposes after the engine had been of water in the expansion tank signifiesstopped. During normal operations in some type of leak into or out of the peacetime this is not too great a fresh water system. It usually indicatesdisadvantage because before stopping, the engine can be idled until it is properly a cracked cylinder liner. cooled. During the war, however, emergency dives were a common The salt water section of the closed occurrence and lack of a detached pump type cooling system consists of an resulted in very high engine and engine attached salt water pump, usually similar to the fresh water pump which room temperatures immediately after draws salt water from sea through a sea diving. This was not particularly good for the engine and imposed a hardship on chest, a stop and check valve, and a engine room crews, especially in tropical strainer, and discharges it through the fresh water cooler and then overboard. climates. This condition resulted in the installation in all new submarines of The overboard discharge performs varying functions, depending upon the detached fresh water pumps for circulation of the water after the engine individual installation. Normally it is has been stopped. An authorized used to cool the outboard exhaust alteration provides for the same valve, outboard exhaust piping, and muffler. The ship's compensating water installation in older fleet type submarines. and header box discharge lines also receive their water from 161
Figure 8-1. Typical fresh and salt water cooling systems. 162
Figure 8-2. Salt water cooling system in superstructure. 163 8A7. Fresh water coolers. The engine cooled enters the cooler at a higher water is cooled in a Harrison type heat pressure than the cooling agent. Thus, in exchanger or cooler, similar to the a fresh water cooler the pressure of fresh cooler used in the lubricating oil water should, if possible, be greater than system. Although coolers used on the pressure of salt water, so that in case various installations may differ in of leaks, the fresh water will leak into the appearance and possibly to some extent salt water, a more desirable condition in interior design, their operating than leakage of the salt water into the principle is identical. fresh water system. This is also true in a lubricating oil cooler wherein the pressure of the lubricating oil is found to The cooler consists of a tube nest be greater than that of the fresh water. containing a number of oblong tubes fastened to a header plate at each end to This prevents water from getting into the form a core assembly. This assembly is engine lubricating oil if cooler leaks develop. attached to the cooler casing. The oblong tubes are baffled to form a winding passage for the liquid to be 8A8. Temperature regulator. The fresh cooled. The liquid is cooled as it passes water in the engine is maintained at a through the tubes, by the cold salt water uniform temperature by the temperature (fresh water in lubricating oil coolers) regulator which controls the amount of which enters the casing, flows between fresh water flowing through the fresh the tubes and is discharged through the water cooler and by bypassing the salt water outlet. The cooler is equipped remainder of the water around the cooler. with zinc plates in the sea water inlet and outlet passages and at the bottom of When the fresh water temperature is the cooler. These zincs centralize the higher than the temperature for which the electrolysis present in all submarine salt regulator is adjusted, the regulator valve water systems. Their presence causes is actuated to increase the flow of fresh electrolytic action to eat away and water through the fresh water cooler and disintegrate the zincs rather than the decrease the flow through the bypass. material of which the cooler tubes are When the engine water temperature is
made. This reduces to a minimum the lower than the temperature for which the number of cooler leaks to be expected in submarine installations. Zincs should be examined every 30 days or oftener where experience indicates the necessity. At each inspection they must be scraped clean. If this is not done, the efficiency of the zincs may become negligible and the electrolytic action will work on the tubes. When more than 50 percent of the zinc has been eaten away, the zinc should be renewed. Figure 8-3. Salt water corrosion of zincs. Coolers should be cleaned as frequently as found necessary to provide an unrestricted flow of water. In certain types of climate and service, deposits form more rapidly than in others. Heavy deposits cause an objectionable increase in pressure drop through the cooler and a consequent decrease in the cooling effect. Chemical cleanings at regular intervals in accordance with approved instructions will insure maximum operating efficiency at all times. Wires or prods which would damage the internal structure of the tubes must not be used in the cleaning operation. It is a universal rule that where the installation permits, the liquid to be 164 regulator is adjusted, the valve The temperature control element consists decreases the flow of fresh water of a bellows connected by a flexible through the fresh water cooler and armored tube to a bulb mounted in the increases the flow through the bypass. engine cooling water discharge line. The temperature control element is essentially two sealed chambers. One is formed by The temperature regulator consists of a the bellows and cap which are sealed valve and a thermostatic control unit together at the bottom. The other which is mounted on the valve. The chamber is in the bulb. The entire system thermostatic control, unit consists of (except for a small space at the top of the two parts, the temperature control bulb) is element and the control assembly.
Figure 8-4. Fulton-Sylphon temperature regulator. 165 filled with a mixture of ether and adjusting wheel located under the spring alcohol which vaporizes at a low seat. A pointer attached to the spring seat temperature. When the bulb is heated, indicates the temperature setting on a the liquid vaporizes and increases the scale attached to the regulator frame. The scale is graduated from 0 to 9, pressure within the bulb. This forces representing the total operating range of the liquid out of the bulb and through the regulator. the tube to move the bellows down and operate the valve. The temperature regulator can be controlled manually by turning the The control assembly consists of a manual crankpin projecting from the side spring-loaded mechanical linkage of the frame. This operates the regulating which connects the temperature control valve spring through a pair of beveled element to the valve stem. The coil gears and a threaded sleeve. A pointer, spring in the control assembly provides attached to the threaded sleeve, indicates the force necessary to balance the force the valve position. When the pointer is in of the vapor pressure in the temperature the BYPASS CLOSED position, the control element. valve is set to allow all of the fresh water to be pumped directly through the water Thus, the downward force of the temperature control element is balanced cooler. When the pointer is in the at any point by the upward force of the THERMOSTATIC position, it indicates spring. This permits setting the valve to that the unit is controlled completely by the automatic system as described. When hold the temperature of. the engine cooling water within the allowed limits. the pointer is in the COOLER CLOSED position, it indicates that all of the fresh
The regulator operates only within the water is being bypassed around the water temperature range marked on the name cooler. For automatic operation the plate, and may be adjusted for any pointer must be set at the temperature within this range. The THERMOSTATIC position. setting is controlled by the range Figure 8-5. Thermostatic control unit. Figure 8-6. Temperature control element. 166 Figure 8-7 METHOD OF ADJUSTING AUTOMATIC TEMPERATURE REGULATORS. dissolved in warm water, then added to the circulating pump suction. To determine whether the water contains a sufficient amount of treating compound, a sample of water is drawn from the system. After cooling the sample to 85 degrees F or lower, about 10 milliliters of the cooled sample is transferred to a test tube and one drop of indicator solution, known as corrosion control indicator, is added. The addition of the one drop of indicator solution will change the color of the sample water. If the resulting color is yellow, insufficient treatment is indicated. If the color is red, Figure 8-8. Temperature regulator satisfactory treatment is indicated, and if bulb. the resulting color is purple, it denotes that an excessive amount of treating 8A9. Fresh water treatment. A compound has been added. treating compound may be added to fresh water in a closed cooling system It should be noted that the addition of the for the prevention of scale formation treating compound is a preventive and corrosion. This compound, when treatment only. It will not remove scale added, must be correctly measured in deposits already in the cooling system. If relation to the amount of water in the the system is clean and filled with fresh system. Too little will have no effect on water only, a test of the water as outlined the prevention of scale formation, above should result in a yellow color.
whereas too much will increase the This indicates that the fresh water is corrosion tendencies of the cooling suitable for use and that it will require the water. The compound consists of a addition of at least one standard dose of mixture of six parts (by weight) of treating compound, consisting of an trisodium phosphate and one part of ounce of treatment per 100 gallons of cornstarch. The mixture must be water, to bring it into the satisfactory completely (red) range of the test. If the color of the same test remains yellow after the addition of one standard dose, another dose should be added and this process repeated until a red color is obtained. Should the test sample result in a purple color, about one-fourth of the cooling water should be drained from the system and replaced with fresh water. If on retest the purple color Figure 8-9. Cutaway of thermal bulb. 167 persists, additional water must be glycol (Prestone). During freezing drained and replaced with fresh water. weather, all water jackets, cooling The color of the test sample must be chambers, etc., not filled with anti-freeze red. It should never be permitted to solution must be thoroughly drained and enter the purple range. blown out one at a time, using low- pressure air. Proper blowing out of the water can be accomplished only by Anti-freeze solutions. Approved anti- freeze solutions may be used to obviate closing off all cooling spaces and emptying them separately. the necessity of draining fresh water systems during freezing temperatures. The liquid usually used is ethylene B. FAIRBANKS-MORSE COOLING SYSTEM 8B1. System piping. The F-M engine pressure gages. After performing its is cooled by circulating fresh water engine cooling functions, the water through its water passages. This water leaves the engine and is piped to the fresh circulates in a closed system. water cooler. There the fresh water is cooled by being passed through a large The external part of the system consists number of tubes around which cool sea water flows. After leaving this cooler, the of the expansion tank, electrical fresh water is used as the coolant for the resistance thermometer, high- temperature alarm contact maker, fixed lubricating oil coolers. It is then piped back to the suction inlet, to repeat its orifice, temperature regulator, fresh passage through the engine. water and lubricating oil coolers, and connecting piping with mercury bulb thermometers and A cooler bypass pipe connects the outlet
Figure 8-10. Fresh wafer system, F-M. 168 line from the engine and the suction A small pipe leads from the engine water line to the pump. An orifice in this pipe header to the expansion tank. Another permits passing a predetermined small pipe leads from the pump suction portion of the fresh water directly back line to the expansion tank. This to the pump, rather than through the arrangement enables the closed system to coolers. This permits cooling of that accommodate variations in water volume which result from the expansion and portion of water going through the contraction of heating and cooling. Water complete part of the system sufficiently is added to the system through the fresh so that it, in turn, can cool the water filling line from the ship's fresh lubricating oil adequately. From the oil water system. Excess water is discharged cooler the water mixes with the through the expansion tank vent. The uncooled fresh water, and enters the bulb of a continuous reading electrical engine at the desired temperature. resistance thermometer is in the line from the engine to the cooler. The indicator for A bypass pipe is installed across the fresh water cooler inlet and outlet. Flow the thermometer is mounted on the engine gage board. Between the fresh of water through this cooler bypass is controlled by the automatic temperature water pump and the engine inlet a small tube leads to the fresh water pressure regulator. By adjustment of this regulator, the temperature of the water gage on the engine gage board. A can be controlled at the desired point in mercury bulb thermometer is installed near the inlet to the lubricating oil cooler, the engine under varying operating and another on the line from the coolers conditions. Also, when starting the to the fresh water pump. engine, cold water is quickly brought up to good operating temperature The other pump mounted opposite the range. If the fresh water temperature fresh water pump on the engine circulates exceeds a certain set limit, a high- the salt water. This pump draws salt temperature alarm contact maker, mounted in the line between the engine water from the ship's sea chest and forces it through the outlet and the cooler, closes the alarm circuit to ring a warning gong.
Figure 8-11. Salt water system, F-M. 169 Figure 8-12. Fresh water passage through F-M cylinder. fresh water cooler and the generator air side of each cylinder. These elbows carry cooler. Leaving the coolers, the salt the water to the spaces between the water flows through the exhaust piping cylinder liner and its jacket. Cast-in ribs jackets and overboard. A mercury bulb on the cylinder liner direct the water thermometer indicates the temperature upward, to cool the liner thoroughly from of the salt water, flowing from the fresh the bottom. Water passages also lead to water cooler. From the pump discharge the water jackets on the injection nozzle, pipe, a small tube leads to the salt water cylinder relief valve, and air start check pressure gage on the engine gage board. valve adapters, to cool these units. Upon reaching the top of the cylinder liner jacket, the water passes out of the 8B2. F-M engine cooling passages. Entering the engine through an inlet in cylinder water space through an outlet pipe which leads to the water header. each exhaust nozzle, the fresh water This header, rectangular in cross section, moves through passages which extends along the opposite side of the surround the exhaust nozzles, and on cylinder block from the control quadrant, into the exhaust manifold water just below the air receiver. Its outlet passages extending the full length of the engine. The exhaust passages from flange is at the control end of the engine
the cylinder liners and the lower part of where it joins the external part of the the liner are also cooled by the fresh system piping. water circulation around the exhaust belts. The water enters from the exhaust 8B3. Fairbanks-Morse water pumps. manifolds at openings at the lower side The fresh water and salt water circulating of the belts and returns to the manifolds pumps in the F-M installations are at openings at the top. The water then identical centrifugal pumps. The pumps, rises from the exhaust manifolds to mounted on opposite sides at the control pass through an inlet elbow on either end of the engine, are driven by 170 the lower crankshaft through the end and a thrust bearing at the drive end. flexible drive which also drives the fuel Lubricating oil reaches the bearings from and lubricating oil pump and the the control end compartment of the governor. engine through openings in the pump frame. The oil is distributed by the bearing spacer on the pump shaft. The internal construction of the pump Leakage of oil to the outside of the at the impeller end is similar to that of engine is prevented by an oil seal ring the GM pump. The pump shaft, and retainer. however, is supported on two bearings, a guide bearing near the impeller Figure 8-13. Cross section of F-M circulating water pump. 171 C. GENERAL MOTORS COOLING SYSTEM
8C1. System piping. With the The salt water overboard discharge is exception of minor differences in the split into several parts. Some of the water piping arrangement, the cooling system goes to the outboard exhaust lines where for GM engines is similar to that used it circulates through the exhaust line in F-M engines. The external part of the jacket. This water then goes through the closed system is composed of the outboard exhaust valve for cooling expansion tank located at the highest purposes and into the exhaust muffler. point in the system, the fresh water and Part of this water is sprayed into the lubricating oil coolers, the automatic muffler to act as a spark arrester, and the temperature regulator, electrical rest is piped over the side. resistance and mercury bulb thermometers, a pressure gage at the Another line from the salt water system fresh water pump discharge, and the connects into the fuel compensating necessary piping. After circulating water line and to the header box. Most of through the engine, the fresh water the water going into this line is passes through a temperature regulator discharged over the side through the before reaching the fresh water cooler. header box, but any water needed to keep Water passing through the fresh water the fuel oil and compensating water cooler is cooled by salt water. Part of systems filled flows by gravity to the the water is bypassed around the cooler desired tank through the fuel and part of it flows through it, compensating water line. depending on the setting of the temperature regulator. The water then 8C2. General Motors engine cooling goes through the lubricating oil cooler passages. The attached fresh water pump where it acts as the cooling agent. From forces fresh water to a manifold located the lubricating oil cooler, the fresh in the scavenging air chamber in each water returns to the suction side of the cylinder bank. From the manifolds, the fresh water pump for recirculation water passes into the cooling spaces of through the engine. Variations in water the cylinder liners by way of a water volume resulting from expansion and contraction caused by heating and cooling are controlled by two pipe lines, one extending from the expansion tank to the suction side of the pump, the other extending from the expansion tank to the engine fresh water manifold. A vent line at the expansion tank keeps the system free of air, thereby preventing the fresh water pump from becoming air bound, a condition that would result in excessive water temperature. The salt water pump draws salt water from the sea chest through a strainer Figure 8-14. Cross section of GM and forces it through the fresh water cylinder liner showing cooling passages. cooler and out through the overboard discharge. A branch line leaving the main line ahead of the fresh water cooler supplies salt water to the generator air cooler. The discharge from the generator cooler joins the outlet pipe extending from the fresh water cooler for overboard discharge. The pressure of the salt water before
entering the fresh water cooler is indicated by a pressure gage and is controlled by a throttling valve located between the salt water pump discharge and the fresh water cooler. A similar valve is used to control the flow of water to the generator cooler. 172 Figure 8-15. FRESH WATER SYSTEM, GM 16-278A. Figure 8-16. SALT WATER SYSTEM, GM 16-278A. Figure 8-17. Cross section of circulating wafer pump, GM. connection at the lower deckplate in the through the pump outlet. The impeller engine cylinder block. The water is rotates in the housing on two pairs of then forced upward into the cylinder replaceable wear rings. A valve sleeve heads through ferrules in the top of the that prevents shaft wear is keyed to the liner, into the water jacket around the pump shaft and butts against the exhaust elbows, and finally into the impeller. A small packing ring fitted in a water jacket surrounding the exhaust recess in the end of the valve sleeve manifold. From the exhaust manifold, provides a watertight seal. The packing is the water enters the external piping compressed between the sleeve and the leading to the temperature regulator. shaft by a locking sleeve held in place by a setscrew. When tightening the packing it is first necessary to remove the packing 8C3. General Motors water pumps. gland which provides access to the The salt water and fresh water pumps used in GM. cooling systems are of the setscrew. After loosening the setscrew, the locking sleeve can be rotated with a centrifugal type. The pumps are spanner wrench. mounted on opposite sides of the blower housing of the engine and are driven by the crankshaft through the The stuffing box packing that surrounds accessory drive gear train. The the shaft sleeve is made up of five rings principal differences between the two composed of a plastic binder pumps are in size and capacity. The salt impregnated with lead and graphite. Each water pump has a capacity of 560 ring is about 5 1/16 inch thick. gallons per minute, the fresh water pump, 350 gallons per minute. The The pump drive shaft rotates in a ball following description applies to both bearing that is pressed on the shaft and is
supported in a bearing housing inside the pumps. supporting head of the pump. The The principal parts of the pump are the bearing is splash lubricated from the accessory drive gear train. A felt seal housing, impeller, drive shaft, and pump supporting head. The impeller is prevents oil from leaking out of the keyed to the tapered end of the driving housing. Water that may work its way shaft and consists of a number of vanes along the shaft is prevented from reaching the bearing by a finger locked to which throw the water entering at the the shaft with a setscrew. center of the impeller, outward 173