The reliability and performance of modern diesel engines are directly dependent on the effectiveness of their lubricating systems. To be effective, an engine lubricating system must successfully perform the functions of minimizing friction between the bearing surfaces of moving parts, dissipating heat, and keeping the engine parts clean by removing carbon and other foreign matter. In almost all modern internal-combustion engines, the system that provides the oil for these functions is the forced-lubrication type of design. Although there are many variations in lubricating systems for internal-combustion engines, the components and method of opera-tion are basically the same for all designs. The following discussion of the basic components can be applied to almost any variation or design of lubricating system.
COMPONENTS OF A LUBRICATING OIL SYSTEM
The lubricating system of an internal-combus-tion engine consists of two main divisions: (1) one that is inside the engine, and (2) one that is outside the engine. The internal system consists mainly of passages and piping. The external system includes several components which aid in supplying the oil in the proper quantity, at the proper temperature, and free of impurities. In the majority of lubricating oil systems for internal-combustion engines, the external system includes such parts as tanks and sumps, pumps, coolers, strainers, and filters.
TANKS AND SUMPS
The lubricating systems of propulsion installa-tions use tanks to collect, store, and recirculate oil after it has been used for lubrication and cool-ing. Some installations have a sump or drain tank under the engine to collect the oil as it drains from the engine crankcase. Separate storage and sump tanks are not common in auxiliary engines; these engines generally contain the oil supply directly within the engine oil pan.
Positive-displacement, rotary-gear pumps de-liver oil under pressure to the various parts of the engine. Since the pumps are gear driven by the engine camshaft or, in some engines, directly by the crankshaft, the oil is supplied at flow rates adjusted to the needs of the engine. Changes in engine speed will cause corresponding changes in pump output.
The operating pressure is normally controlled by one or more pressure-regulating valves, which open or close as necessary to maintain the specified flow rate to various load-bearing parts of the engine. These spring-actuated devices divert excess oil directly to the engine sump or back to the inlet of the lubricating oil pump.
Detached lubricating pumps on large diesel engines fill the sump tanks from the storage tanks and flush and prime the lubricating oil system. You should be thoroughly familiar with these components before attempting to transfer oil or to flush and prime the engine. When priming or flushing the engine, you should know that prolonged flushing or priming of the lubricating oil system on any engine may cause oil to accumulate in the air intake passages and cause overspeeding upon starting. To prevent this, you must observe the following precautions:
1. Prime the engine lubricating oil system before the engine is turned over by hand or by motor-driven jacking gear. This ensures that a film of oil is deposited to prevent friction when parts start to move.
2. Continue to prime the engine ONLY until the engine lubricating oil pressure gauge registers a slight pressure or until you see oil at each main bearing.
3. Before starting the engine after a pro-longed shutdown, inspect the air receiver and blower discharge passages and remove any accumulation of lubricating oil.
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