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There are three practical reasons for cooling an engine:

1. To maintain a lubricating oil film on pistons, cylinder walls, and other moving parts as explained in Chapter 7. This oil film must be maintained to insure adequate lubrication. The formation of an oil film depends in large degree on the viscosity of the oil. If the engine cooling system did not keep the engine temperature at a value that would insure the formation of an oil film, insufficient lubrication and consequent excessive engine wear would result. If the engine is kept too cool, condensation takes places in the lube oil and forms acids and sludge.

2. To avoid too great a variation in the dimensions of the engine parts. Great differences between operating temperatures at varying loads cause excessive changes in the dimensions of the moving parts. These excessive changes also occur when there are large differences between the cold and operating temperatures of the parts. These changes in dimensions

3. To retain the strength of the metals used. High temperatures change the strength and physical properties of the various ferrous metals used in an engine. For example, if a cylinder head is subjected to high temperatures without being cooled, the tensile strength of the metal is reduced, resulting in possible fracture. This high temperature also causes excessive expansion of the metal which may result in shearing of the cylinder bolts.

Cylinder heads, cylinder jackets, cylinder liners, exhaust headers, valves, and exhaust elbows usually are cooled by water. Pistons may be cooled either by water or oil. In present fleet type submarine installations, the pistons are cooled by lubricating oil which is in turn cooled by engine cooling water. It is important to keep all parts of the engine at as nearly the same temperature as possible. This can be accomplished to some extent by engine design. For instance, the water jacket should cover the entire length of the piston stroke to avoid possible unequal expansion of various sections of the cylinder and cylinder liner.

It requires time to conduct heat through any substance, therefore the thicker the metal, the slower the conduction. This is one of the reasons the size of cylinders in diesel engines is limited, because the larger the cylinder, the thicker the material necessary for liners and cylinder heads in order to withstand the pressures of combustion. Thicker metals cause the inside surfaces to run hotter, because the heat is not conducted so rapidly to the cooling water.

8A2. Operation of a cooling system. One of the principal factors affecting the proper

The temperature of the engine can be controlled by the discharge temperature of the cooling water. This can be done in two ways, depending upon the arrangement of the piping and the type of pump used. A common and simple method is to control the amount of water pumped, by means of a throttling valve in the pump discharge to the engine cooling system. The water can then be made to pass more slowly through the engine and be discharged at a higher temperature, or to pass more rap idly at a lower temperature. If the pump is driven separately by an electric motor, the same effect can be obtained by slowing down or speeding up the pump. The other method to control the temperature is to bypass some of the warm discharged water around the cooler and directly to the suction side of the pump. This method gives a more uniform temperature throughout the cooling system and keeps the passage of water at a higher velocity.

In all modern engines, the latter method is used and accomplished automatically by means of a temperature regulator. These regulators may be set to give any desired temperature at the engine outlet. They are used not only to regulate the fresh water but also to regulate indirectly the temperature of the lubricating oil leaving the lubricating oil cooler. This is possible because the fresh water that is passed through the regulator and fresh water cooler is used as the cooling agent in the lubricating oil cooler. This permits the maximum amount of controllability of fresh water and lubricating oil temperatures with the use of the minimum amount of equipment.

The open type of cooling system has many disadvantages, the most important being the exposure of the engine to scale formation, marine growth and dirt deposits in the piping, and fluctuating sea water temperature. Scale or deposits not only restrict water flow in the engine water passages but also act as a blanket and hinder heat transfer to the cooling water. This prevents adequate cooling of engine parts which may result in serious difficulties.

8A4. Open type cooling systems. The term open system is used because salt water is drawn directly from sea, passed through the system, and then discharged overboard.

In a typical system the salt water is drawn through sea valves and a strainer by a centrifugal pump and then discharged through the lubricating oil heat exchanger or cooler where it cools the lubricating oil. The water then passes to the cylinder liner jackets, exhaust manifold jackets, exhaust uptake jackets, the inboard exhaust valve, overboard sea valves, and to the outboard exhaust valve jackets and sprays. Part of the water may be piped to the fuel compensating water system. The remaining water passes through the muffler jackets and then overboard.

The open type of cooling system is used only on engines in the older types of submarines, particularly the O, R, and S classes. All of the later fleet type submarine engines are designed with cooling systems of the closed type.

8A5. Closed type cooling systems. Closed type, or fresh water cooling systems consist basically of two entirely separate systems-the fresh water cooling system and the salt water cooling system. In the fresh water cooling system the same fresh water is reused continuously for cooling the engine. The water is circulated throughout the engine cooling spaces

Fresh water temperature is usually regulated by means of an automatic regulating valve which maintains the fresh water temperature at any desired value by bypassing the necessary amount of water around the fresh water cooler.

An expansion tank is provided which aids in keeping the fresh water system filled at all times by keeping available a ready supply of water. A vent usually is provided in the high point of the line to keep the system free of air, thereby preventing the water pump from becoming air bound. The expansion tank also is equipped with a gage glass by which the level of water in the tank may be constantly observed. If the level of water in the tank becomes too low, the system may be replenished from the ship's fresh water service system through a make-up line into the suction side of the attached fresh water pump. Any large rapid fluctuation in the level of water in the expansion tank signifies some type of leak into or out of the fresh water system. It usually indicates a cracked cylinder liner.

The salt water section of the closed type cooling system consists of an attached salt water pump, usually similar to the fresh water pump which draws salt water from sea through a sea chest, a stop and check valve, and a strainer, and discharges it through the fresh water cooler and then overboard. The overboard discharge performs varying functions, depending upon the individual installation. Normally it is used to cool the outboard exhaust valve, outboard exhaust piping, and muffler. The ship's compensating water and header box discharge lines also receive their water from

On generator type engines the attached salt water pump furnishes salt water to the generator air coolers and returns the water to the overboard discharge. Throttling valves frequently are placed in lines to the fresh water cooler and generator air coolers to control the flow of water through these heat exchangers.

Thermometers and pressure indicators are placed in the system at various places. Salt water temperatures should not exceed 122 degrees F. Fresh water temperatures should be between 140 degrees F and 180 degrees F, with a minimum of 140 degrees F at the engine inlet. Outlet fresh water temperatures should be between 160 degrees F and 180 degrees F. Cooling water temperatures should not be allowed to drop below 140 degrees F, otherwise excessive engine wear and corrosion may result if the temperature drops, below the dewpoint.

8A6. Detached fresh water circulating pumps. Earlier General Motors and Fairbanks-Morse models (the GM 16-248 and the F-M 38D 8 and the 9-cylinder 38D 8 1/8) were equipped only with attached fresh water pumps. This design made it impossible for fresh water to be circulated in the engine for cooling purposes after the engine had been stopped. During normal operations in peacetime this is not too great a disadvantage because before stopping, the engine can be idled until it is properly cooled. During the war, however, emergency dives were a common occurrence and lack of a detached pump resulted in very high engine and engine room temperatures immediately after diving. This was not particularly good for the engine and imposed a hardship on engine room crews, especially in tropical climates. This condition resulted in the installation in all new submarines of detached fresh water pumps for circulation of the water after the engine has been stopped. An authorized alteration provides for the same installation in older fleet type submarines.

The cooler consists of a tube nest containing a number of oblong tubes fastened to a header plate at each end to form a core assembly. This assembly is attached to the cooler casing. The oblong tubes are baffled to form a winding passage for the liquid to be cooled. The liquid is cooled as it passes through the tubes, by the cold salt water (fresh water in lubricating oil coolers) which enters the casing, flows between the tubes and is discharged through the salt water outlet. The cooler is equipped with zinc plates in the sea water inlet and outlet passages and at the bottom of the cooler. These zincs centralize the electrolysis present in all submarine salt water systems. Their presence causes electrolytic action to eat away and disintegrate the zincs rather than the material of which the cooler tubes are made. This reduces to a minimum 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.

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

8A8. Temperature regulator. The fresh water in the engine is maintained at a uniform temperature by the temperature regulator which controls the amount of fresh water flowing through the fresh water cooler and by bypassing the remainder of the water around the cooler.

When the fresh water temperature is higher than the temperature for which the regulator is adjusted, the regulator valve is actuated to increase the flow of fresh water through the fresh water cooler and decrease the flow through the bypass. When the engine water temperature is lower than the temperature for which the

Figure 8-3. Salt water corrosion of zincs.

The temperature regulator consists of a valve and a thermostatic control unit which is mounted on the valve. The thermostatic control, unit consists of two parts, the temperature control element and the control assembly.

The control assembly consists of a spring-loaded mechanical linkage which connects the temperature control element to the valve stem. The coil spring in the control assembly provides the force necessary to balance the force of the vapor pressure in the temperature control element.

Thus, the downward force of the temperature control element is balanced at any point by the upward force of the spring. This permits setting the valve to hold the temperature of. the engine cooling water within the allowed limits.

The regulator operates only within the temperature range marked on the name plate, and may be adjusted for any temperature within this range. The setting is controlled by the range

Figure 8-5. Thermostatic control unit.

The temperature regulator can be controlled manually by turning the manual crankpin projecting from the side of the frame. This operates the regulating valve spring through a pair of beveled gears and a threaded sleeve. A pointer, attached to the threaded sleeve, indicates the valve position. When the pointer is in the BYPASS CLOSED position, the valve is set to allow all of the fresh water to be pumped directly through the water cooler. When the pointer is in the THERMOSTATIC position, it indicates that the unit is controlled completely by the automatic system as described. When the pointer is in the COOLER CLOSED position, it indicates that all of the fresh water is being bypassed around the water cooler. For automatic operation the pointer must be set at the THERMOSTATIC position.

Figure 8-6. Temperature control element.

Figure 8-8. Temperature regulator bulb.

8A9. Fresh water treatment. A treating compound may be added to fresh water in a closed cooling system for the prevention of scale formation and corrosion. This compound, when added, must be correctly measured in relation to the amount of water in the system. Too little will have no effect on the prevention of scale formation, whereas too much will increase the corrosion tendencies of the cooling water. The compound consists of a mixture of six parts (by weight) of trisodium phosphate and one part of cornstarch. The mixture must be completely

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, satisfactory treatment is indicated, and if the resulting color is purple, it denotes that an excessive amount of treating compound has been added.

It should be noted that the addition of the treating compound is a preventive treatment only. It will not remove scale deposits already in the cooling system. If the system is clean and filled with fresh water only, a test of the water as outlined above should result in a yellow color. This indicates that the fresh water is suitable for use and that it will require the addition of at least one standard dose of treating compound, consisting of an ounce of treatment per 100 gallons of water, to bring it into the satisfactory (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

Anti-freeze solutions. Approved anti-freeze solutions may be used to obviate the necessity of draining fresh water systems during freezing temperatures. The liquid usually used is ethylene

The external part of the system consists of the expansion tank, electrical resistance thermometer, high-temperature alarm contact maker, fixed orifice, temperature regulator, fresh water and lubricating oil coolers, and connecting piping with mercury bulb thermometers and

A cooler bypass pipe connects the outlet

A bypass pipe is installed across the fresh water cooler inlet and outlet. Flow of water through this cooler bypass is controlled by the automatic temperature regulator. By adjustment of this regulator, the temperature of the water can be controlled at the desired point in the engine under varying operating conditions. Also, when starting the engine, cold water is quickly brought up to good operating temperature range. If the fresh water temperature exceeds a certain set limit, a high-temperature alarm contact maker, mounted in the line between the engine outlet and the cooler, closes the alarm circuit to ring a warning gong.

The other pump mounted opposite the fresh water pump on the engine circulates the salt water. This pump draws salt water from the ship's sea chest and forces it through the

8B2. F-M engine cooling passages. Entering the engine through an inlet in each exhaust nozzle, the fresh water moves through passages which surround the exhaust nozzles, and on into the exhaust manifold water passages extending the full length of the engine. The exhaust passages from the cylinder liners and the lower part of the liner are also cooled by the fresh water circulation around the exhaust belts. The water enters from the exhaust manifolds at openings at the lower side of the belts and returns to the manifolds at openings at the top. The water then rises from the exhaust manifolds to pass through an inlet elbow on either

8B3. Fairbanks-Morse water pumps. The fresh water and salt water circulating pumps in the F-M installations are identical centrifugal pumps. The pumps, mounted on opposite sides at the control end of the engine, are driven by

The internal construction of the pump at the impeller end is similar to that of the GM pump. The pump shaft, however, is supported on two bearings, a guide bearing near the impeller

The salt water pump draws salt water from the sea chest through a strainer and forces it through the fresh water 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.

Another line from the salt water system connects into the fuel compensating water line and to the header box. Most of the water going into this line is discharged over the side through the header box, but any water needed to keep the fuel oil and compensating water systems filled flows by gravity to the desired tank through the fuel compensating water line.

8C2. General Motors engine cooling passages. The attached fresh water pump forces fresh water to a manifold located in the scavenging air chamber in each cylinder bank. From the manifolds, the water passes into the cooling spaces of the cylinder liners by way of a water

Figure 8-14. Cross section of GM cylinder liner showing cooling passages.

8C3. General Motors water pumps. The salt water and fresh water pumps used in GM. cooling systems are of the centrifugal type. The pumps are mounted on opposite sides of the blower housing of the engine and are driven by the crankshaft through the accessory drive gear train. The principal differences between the two pumps are in size and capacity. The salt water pump has a capacity of 560 gallons per minute, the fresh water pump, 350 gallons per minute. The following description applies to both pumps.

The principal parts of the pump are the housing, impeller, drive shaft, and pump supporting head. The impeller is keyed to the tapered end of the driving shaft and consists of a number of vanes which throw the water entering at the center of the impeller, outward

The stuffing box packing that surrounds the shaft sleeve is made up of five rings composed of a plastic binder impregnated with lead and graphite. Each ring is about 5 1/16 inch thick.

The pump drive shaft rotates in a ball bearing that is pressed on the shaft and is supported in a bearing housing inside the supporting head of the pump. The bearing is splash lubricated from the accessory drive gear train. A felt seal prevents oil from leaking out of the housing. Water that may work its way along the shaft is prevented from reaching the bearing by a finger locked to the shaft with a setscrew.