PRINCIPLES OF NAVAL ENGINEERING 



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Figure 22-29.— Sump-type lubricating oil filtering system. 



change both the speed and the direction of shaft 

 rotation in the driven mechanism. There are 

 various methods by which required changes of 

 speed and directions may be made during the 

 transmission of power from the driving unit 

 to the driven unit. In most installations the job 

 is accomplished by a drive mechanism consist- 

 ing principally of gears and shafts. 



The process of transmitting engine power to 

 a point where it can be used in performing 

 useful work involves a number of factors. Two 

 of these factors are torque and speed. 



The force which tends to cause a rotational 

 movement of an object is called torque or 

 "twist". The crankshaft of an engine supplies 

 a twisting force to the gears and shafts which 

 transmit power to the driven unit. Gears are 



used to increase or decrease torque. If the right 

 combination of gears is installed between the 

 engine and the driven unit, the torque or "twist" 

 will be sufficient to operate the drivenunit. 



If maximum efficiency is to be obtained, an 

 engine must operate at a certain speed. In order 

 to obtain efficient engine operation, it might be 

 necessary in some installations for the engine 

 to operate at a higher speed than that required 

 for efficient operation of the driven unit. In 

 other cases the speed of the engine may have 

 to be lower than the speed of the driven unit. 

 Through a combination of gears, the speed of 

 the driven unit can be increased or decreased 

 so that the proper speed ratio exists between 

 the units. 



578 



