Chapter 6-THEORY OF LUBRICATION 



REGULATING TUBE 



TUBULAR SHAFT 



PURIFIED OtL 



DISTRIBUTING 

 PLUG 



75.233 

 Figure 6-3.— Path of contaminated oil through 

 disk-type purifier bowl (DeLAVAL). 



are in solution. However, water can be separated 

 from lubricating oil because water and oil do not 

 form a solution when mixed. For separation to 

 take place by centrifugal force, there must be a 

 difference in the specific gravity of oil and the 

 specific gravity of water. 



When a mixture of oil, water, and sediment 

 is allowed to stand undisturbed, gravity tends to 

 cause the formation of an upper layer of oil, an 

 intermediate layer of water, and a lower layer 

 of sediment. The layers form because of differ- 

 ences in the specific gravities of the various sub- 

 stances. If the oil, water, and sediment mixture 

 is placed in a rapidly revolving centrifugal pu- 

 rifier, the effect of gravity is negligible in com- 

 parison with the effect of centrifugal force. Cen- 

 trifugal force, acting at right angles to the axis 

 of rotation of the container, forces the sediment 

 into an outer layer, the water into an intermediate 

 layer, and the oil into an innermost layer. Cen- 

 trifugal purifiers are so designed that the sepa- 

 rated water is discharged as waste and the oil is 

 discharged for use. The solids remain in the ro- 

 tating unit and are cleaned out after each purifi- 

 cation operation. 



Two types of centrifugal purifiers are used 

 aboard ship. The main difference between the 

 two types is in the design of the rotating units. 

 In the disk-type purifier, the rotating element 

 is a bowl-like container which encases a stack 

 of disks. In the tubular-type purifier, the rotat- 

 ing element is a hollow tubular rotor. 



A disk-type centrifugal purifier is shown in 

 figure 6-2. The bowl is mounted on the upper 

 end of the vertical bowl spindle, which is driven 

 by a worm wheel and friction clutch assembly. 

 A radial thrust bearing is provided at the lower 

 end of the bowl spindle tocarry the weight of the 

 bowl spindle and to absorb any thrust created 

 by the driving action. 



Contaminated oil enters thetopof the revolv- 

 ing bowl through the regulating tube. The oil then 

 passes down the inside of the tubular shaft and 

 out at the bottom of the stack of disks. As the 

 dirty oil flows up through the distribution holes in 

 the disks, the high centrifugal force exerted by 

 the revolving bowl causes the dirt, sludge, and 

 water to move outward and the purified oil to 

 move inward toward the tubular shaft. The disks 

 divide the space within the bowl into many sepa- 

 rate narrow passages. The liquid confined within 

 each passage is restricted so that it can only flow 

 along that passage. This arrangement prevents 

 excessive agitation of the liquid as it passes 

 through the bowl and creates shallow settling 

 distances between the disks. The path of contam- 

 inated oil passing through a disk-type purifier 

 is shown in figure 6-3. 



Most of the dirt and sludge remains in the 

 bowl and collects in a more or less uniform layer 

 on the inside vertical surface of the bowl shell. 

 Any water that may be present, together with 

 some dirt and sludge, is discharged through the 

 discharge ring at the top of the bowl. The puri- 

 fied oil flows inward and upward through the 

 disks, discharging from the neck of the top disk. 



A tubular-type centrifugal purifier is shown 

 in figure 6-4. This type of purifier consists es- 

 sentially of a hollow rotor or bowl which rotates 

 at high speeds. The rotor has an opening in the 

 bottom through which the dirty lubricating oil 

 enters; two sets of openings at the top allow the 

 oil and water (or the oil alone) to discharge. (See 

 insert, fig. 6-4.) The bowl or hollow rotor of the 

 purifier is connected by a coupling unit to 

 a spindle which is suspended from a ball bearing 

 assembly. The bowl is belt-driven by an electric 

 motor mounted on the frame of the purifier. 



The lower end of the bowl extends into a flex- 

 ibly mounted guide bushing. The assembly, of 

 which the bushing is a part, restrains movement 

 of the bottom of the bowl but allows enough move- 

 ment so that the bowl can center itself about its 

 axis of rotation when the purifier is in operation. 

 Inside the bowl is a device which consists of three 

 flat plates equally spaced radially. This device 

 is commonly referred to as the three-wing device 



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