Principles of naval engineering - Historic Naval Ships Association

Chapter 6-THEORY OF LUBRICATIONPURIFIED OtLREGULATING TUBETUBULAR SHAFTDISTRIBUTINGPLUG75.233Figure 6-3.— Path of contaminated oil throughdisk-type purifier bowl (DeLAVAL).are in solution. However, water can be separatedfrom lubricating oil because water and oil do notform a solution when mixed. For separation totake place by centrifugal force, there must be adifference in the specific gravity of oil and thespecific gravity of water.When a mixture of oil, water, and sedimentis allowed to stand undisturbed, gravity tends tocause the formation of an upper layer of oil, anintermediate layer of water, and a lower layerof sediment. The layers form because of differencesin the specific gravities of the various substances.If the oil, water, and sediment mixtureis placed in a rapidly revolving centrifugal purifier,the effect of gravity is negligible in comparisonwith the effect of centrifugal force. Centrifugalforce, acting at right angles to the axisof rotation of the container, forces the sedimentinto an outer layer, the water into an intermediatelayer, and the oil into an innermost layer. Centrifugalpurifiers are so designed that the separatedwater is discharged as waste and the oil isdischarged for use. The solids remain in the rotatingunit and are cleaned out after each purificationoperation.Two types of centrifugal purifiers are usedaboard ship. The main difference between thetwo types is in the design of the rotating units.In the disk-type purifier, the rotating elementis a bowl-like container which encases a stackof disks. In the tubular-type purifier, the rotatingelement is a hollow tubular rotor.A disk-type centrifugal purifier is shown infigure 6-2. The bowl is mounted on the upperend of the vertical bowl spindle, which is drivenby a worm wheel and friction clutch assembly.A radial thrust bearing is provided at the lowerend of the bowl spindle tocarry the weight of thebowl spindle and to absorb any thrust createdby the driving action.Contaminated oil enters thetopof the revolvingbowl through the regulating tube. The oil thenpasses down the inside of the tubular shaft andout at the bottom of the stack of disks. As thedirty oil flows up through the distribution holes inthe disks, the high centrifugal force exerted bythe revolving bowl causes the dirt, sludge, andwater to move outward and the purified oil tomove inward toward the tubular shaft. The disksdivide the space within the bowl into many separatenarrow passages. The liquid confined withineach passage is restricted so that it can only flowalong that passage. This arrangement preventsexcessive agitation of the liquid as it passesthrough the bowl and creates shallow settlingdistances between the disks. The path of contaminatedoil passing through a disk-type purifieris shown in figure 6-3.Most of the dirt and sludge remains in thebowl and collects in a more or less uniform layeron the inside vertical surface of the bowl shell.Any water that may be present, together withsome dirt and sludge, is discharged through thedischarge ring at the top of the bowl. The purifiedoil flows inward and upward through thedisks, discharging from the neck of the top disk.A tubular-type centrifugal purifier is shownin figure 6-4. This type of purifier consists essentiallyof a hollow rotor or bowl which rotatesat high speeds. The rotor has an opening in thebottom through which the dirty lubricating oilenters; two sets of openings at the top allow theoil and water (or the oil alone) to discharge. (Seeinsert, fig. 6-4.) The bowl or hollow rotor of thepurifier is connected by a coupling unit toa spindle which is suspended from a ball bearingassembly. The bowl is belt-driven by an electricmotor mounted on the frame of the purifier.The lower end of the bowl extends into a flexiblymounted guide bushing. The assembly, ofwhich the bushing is a part, restrains movementof the bottom of the bowl but allows enough movementso that the bowl can center itself about itsaxis of rotation when the purifier is in operation.Inside the bowl is a device which consists of threeflat plates equally spaced radially. This deviceis commonly referred to as the three-wing device117