Abstract:
A centrifugal separator  110  (FIG.  1 ) for removing contaminants from a pumped liquid such as engine lubricant, having a separation rotor  130  rotatable about axis  124  at high speed by a jet  178  of the liquid impinging upon impulse turbine blades  174.  The rotor includes a separation and containment vessel  132  having impervious side wall  134  spaced from the rotation axis and at least one end wall  138  open at  142  permit liquid to leave the vessel as fast as it can enter, so that a zone  140  is defined adjacent side wall  134  that holds a volume of liquid much less than the whole volume encompassed by the vessel walls and filled in conventional high speed separators. Lower inertia and reduced pressure gradients in the liquid permit it to be spaced further from the axis than is conventional, with improved separation efficiency. Liquid may be supplied to zone  140  in any convenient manner but as shown spent turbine liquid  178 ′ is collected on a rotating surface  158  of a divider wall  152  that spreads and/or directs the liquid to transfer passages  164  from which it is flung centrifugally to the separation zone  140.  The outer side wall  134  of the vessel which collects contaminants may be a replaceable attachment to the divider wall/turbine part. The rotor may alternatively comprise such a vessel surrounding a conventional, filled canister to effect a radial increase in such rotor without comparable increase in the volume of liquid contained.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is a continuation of international patent application no. PCT/GB02/00061, filed Jan. 9, 2002, designating the United States of America and published in English on Jul. 18, 2002 as WO 02/055207, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on United Kingdom patent applications nos. GB 0100989.3 and GB 0100993.5, both filed Jan. 13, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to centrifugal separation apparatus for separating particulate contaminants from liquids, such as engine lubricants, passed therethrough to effect cleaning, and in particular relates to rotor means used within such apparatus to perform the actual separation and retention of such contaminants.  
           [0003]    Centrifugal separation apparatus is well known for use within the lubrication systems of vehicle internal combustion engines as efficient means for removing very small particulate contaminants from the constantly recirculated liquid lubricant over a long period of operation, such particulate contaminants arising from abrasion of the metallic components of the engine, decomposition of the lubricant and products of combustion.  
           [0004]    Such centrifugal separation apparatus is sometimes known as being of the sedimenting, solid-wall type in which separated solids are retained within the rotor means as a sediment against an impervious radially outer side wall thereof, and distinct from the so-called filtering perforate-wall type in which the solids are held by the mesh of a perforate radially outer side wall while liquid passes therethrough.  
           [0005]    Insofar as such separators are responsible for cleaning a liquid which is in any event circulated at elevated pressure, the art has concentrated on employing such lubricant pressure to effect rotation of parts responsible for generating centrifugal forces, and as such it includes rotor means comprising an essentially closed vessel, or canister, being supported for rotation about a rotation axis within a housing, and supplied with the liquid lubricant at elevated pressure at the axis. The canister is filled with the liquid and assumes a significant internal pressure before liquid is forced from the base (or other peripheral wall) of the canister by way of tangentially directed jet reaction nozzles, the reaction to said ejection causing the rotor canister and liquid within it to spin at high speed about the axis and thereby force solid particles to migrate from the liquid passing through the canister and agglomerate into a cohesive mass on the peripheral walls spaced from the rotation axis. The reaction nozzles, being directed substantially tangentially with respect to the rotation axis, at least in a plane orthogonal to the axis, define a reaction turbine.  
           [0006]    It will be appreciated that the efficiency of separation is inter alia dependant upon creating the conditions in which any liquid entrained particle can migrate radially to the nearest deposition surface and is a function of the force acting on such particle and the time for which it can act. The former is a function of rotation rate and distance from the rotation axis. The latter is a function of the time taken for the entraining liquid to pass through the rotor canister (also called the residence time) and the proximity of the deposition surface, and may be considered in terms of an effective residence time, that is, influencing the contribution of the actual residence time by positioning the contaminated liquid relatively to an appropriate deposition surface. However both the rotation speed of the rotor canister and contained liquid, and the rate at which liquid is passed through and ejected therefrom, are dependant upon the pressure drop between the canister contents and housing and upon the dimensions of the nozzles, within the constraints of such nozzle dimensions providing sufficient torque from the turbine to overcome inertial and frictional resistance to commencement of, and continuation of, rotation.  
           [0007]    Within an internal combustion engine where lubricant is circulated under an initial (pumped) pressure in a range of about 2 to 6 bars that varies with operating conditions, a canister of relatively modest diameter, say 10 to 15 cms, and reaction turbine nozzles may achieve a rotation speed in the range of 4000 to 9000 r.p.m. which is sufficient for removing the relatively dense, contaminants of lubricant residue and metallic particles traditionally considered to be of principal detriment to the engine.  
           [0008]    Examples of such reaction turbine centrifugal separation are shown in GB 745377, GB 2328891, U.S. Pat. No. 5,575,912 and U.S. Pat. No. 5,906,733, and it can be seen that as developments have been made to increase efficiency of separation, and range of separability, the degree of structural complexity has also increased, not least in optimizing effective residence time and/or placing the liquid to maximize forces acting upon entrained contaminants for the limited rotation forces available.  
           [0009]    This is particularly true in respect of the dual goals of deriving maximum rotation energy from the liquid passing through the rotor whilst providing therein conditions necessary and suited to centrifugal separation of low density contaminant particles such as soot. Such contaminants are now seen as an important cause of engine wear, particularly in compression ignition engines, and require the lubricant to be provided with greater effective residence time and/or be subjected to greater centrifugal forces than hitherto, notwithstanding that providing such conditions in these arrangements also tend to militate against efficient flow of liquid through the canister.  
           [0010]    Obtaining greater rotation rate from such a reaction turbine necessitates ejecting liquid at a greater rate, by increasing the pressure and/or by shortening the residence time or by increasing the volume of liquid contained, whereas attempting to cause the contaminant entraining liquid to traverse the canister at a greater radial distance from the axis is made difficult by the fact that the rotating liquid content of the canister creates a radial pressure gradient tendering to keep newly introduced liquid away from the radially outer region of maximum centrifugal force (unless internal structures are provided that add to the complexity and/or consume energy from the rotation). Therefore, optimizing such rotor canister is not a matter of simply increasing the radial dimensions of the canister but effecting a compromise that nevertheless includes containing within the canister at high pressure a relatively large volume of the liquid lubricant to enable it to have a significant effective residence time while it follows a tortuous path that involves interchanging potential and kinetic energy until it is ejected with sufficient energy for rotation production.  
           [0011]    U.S. Pat. No. 6,017,300 in particular explains in some detail that for properly separating very lightweight soot particles that can contaminate the liquid lubricant as products of combustion, the particles have to be subjected to higher centrifugal forces than readily available from such traditional, reaction turbine drive centrifugal separation arrangements, along with a longer residence time, and proposes to elaborate upon the complex cone stack arrangement of U.S. Pat. No. 5,575,912 by an external impulse turbine, the latter providing for high rotation operation and, being separate from the liquid for cleaning in the container, permits the contaminated liquid to have a longer residence time.  
           [0012]    Separating low density contaminants from constant streams of high pressure liquid is not the only situation for which traditional centrifugal separator designs are inadequate. For example, as described in U.S. Pat. No. 5,906,733 where the liquid to be cleaned is derived only indirectly from a high pressure circulation, either at low pressure or intermittently, a separate flow of the high pressure liquid is employed to effect rotation of the canister whilst the liquid to be cleaned can flow through at lower pressure and/or at lower rate, the separate flow of liquid effecting rotation by way of direct reaction jet nozzles in the container or as an impulse turbine employing external blades against which liquid is directed from stationary nozzles.  
           [0013]    Insofar as these modified designs still adopt the principle of defining a rotor vessel whose radial dimensions are optimized for centrifugal forces on liquid entrained particles and function by filling it with the contaminated liquid and then effecting rotation at appropriate speed, they still exhibit significant rotor vessel inertia and have to provide energy to overcome frictional and other bosses, providing a slow response, particularly in start-stop situations.  
         SUMMARY OF THE INVENTION  
         [0014]    It is an object of the present invention to provide an improved centrifugal separation rotor for centrifugal separation apparatus which mitigates disadvantages of known designs.  
           [0015]    Another object of the invention is to provide a centrifugal separation rotor which is suitable for separating low density particulate contaminants from circulated lubricant of an internal combustion engine.  
           [0016]    It is also an object of the invention to provide centrifugal separation apparatus including such rotor means.  
           [0017]    It is furthermore an object of the present invention to provide a method of centrifugal separation which mitigates disadvantages associated with known methods.  
           [0018]    These and other objects of the invention are achieved by providing a centrifugal separation rotor for a centrifugal separator for separating solid contaminants from a liquid, the separator comprising a housing for mounting the rotor for rotation about a rotation axis by a drive, the rotor comprising a walled separation and containment vessel having an impervious radially outer side wall extending about and along the rotation axis to form radially inwardly from the side wall an annular contaminant separation and containment zone; an outlet passage, disposed radially inwardly with respect to the radially outer side wall and leading externally of the vessel to define, during rotation, the radial boundary of the annular contaminant separation and containment zone, and, associated with the vessel; an inlet for conveying liquid to be cleaned to the contaminant separation and containment zone at a rate less than the liquid can be discharged by the outlet passage, the inlet comprising a liquid collector, defining an inlet region about the rotation axis radially inwardly of the outlet passage, and a transfer passage communicating between the inlet region and the contaminant separation and containment zone of the vessel spaced axially from the outlet passage; wherein the liquid collector comprises a divider wall, extending about and along the rotation axis and defining at least in part at one end thereof the transfer passage, having a liquid collection face, facing towards the rotation axis, arranged to receive liquid introduced into the inlet at a part spaced axially from the transfer passage and operable to support the liquid radially in response to centrifugal force exerted by rotation, permitting it to flow along the wall to the transfer passage, and wherein the divider wall collection face increases in radial distance from the rotation axis along its length from the liquid introduction part to the transfer passage, the increase being arranged to cause, in operation, a component of the centrifugal force to confine axial flow of the contaminated liquid over the collection face in a direction towards the transfer passage.  
           [0019]    In accordance with a further aspect of the invention, the objects are achieved by providing a centrifugal separation rotor for a centrifugal separator for separating solid contaminants from a liquid, the separator comprising a housing for mounting the rotor for rotation about a rotation axis by drive, the rotor comprising a walled separation and containment vessel having an impervious radially outer side wall extending about and along the rotation axis to form radially inwardly from the side wall an annular contaminant separation and containment zone; an outlet passage disposed radially inwardly with respect to the radially outer side wall and leading externally of the vessel to define, during rotation, a radial boundary of the annular contaminant separation and containment zone; an inlet for conveying a liquid to be cleaned to the contaminant separation and containment zone at a rate less than the liquid can be passed through the outlet passage, the inlet comprising a liquid collector defining an inlet region about the rotation axis radially inwardly of the outlet passage, and a transfer passage communicating between the inlet region and the contaminant separation and containment zone of the vessel spaced axially from the outlet passage; and at least one further separation and containment vessel associated with the separation and containment vessel and nested radially inwardly of the contaminant separation and containment zone, the further separation and containment vessel having an impervious radially outer side wall, an annular contaminant separation and containment zone bounded radially inwardly of the side wall by an outlet passage, and an inlet arranged to convey liquid to the annular zone at a rate less than the liquid can be discharged from the annular zone through the outlet passage, each further separation and containment vessel being disposed such that the outlet passage of each surrounded vessel permits liquid to be conveyed radially by centrifugal forces to the next surrounding vessel.  
           [0020]    In yet another aspect, the objects are achieved by providing a centrifugal separation rotor for a centrifugal separator for separating solid contaminants from a liquid, the separator comprising a housing for mounting the rotor for rotation about a rotation axis by drive, the rotor comprising a walled separation and containment vessel having an impervious radially outer side wall extending about and along the rotation axis to form radially inwardly from the side wall an annular contaminant separation and containment zone; an outlet passage disposed radially inwardly with respect to the radially outer side wall and leading externally of the vessel to define, during rotation, a radial boundary of the annular contaminant separation and containment zone; an inlet associated with the vessel for conveying a liquid to be cleaned to the contaminant separation and containment zone at a rate less than the liquid can be discharged through the outlet passage, the inlet comprising a liquid collector defining an inlet region about the rotation axis radially inwardly of the outlet passage, and a transfer passage communicating between the inlet region and the contaminant separation and containment zone of the vessel spaced axially from the outlet passage; and a further walled separation and containment vessel coupled to the walled containment and separation vessel for rotation therewith, the further walled separation and containment vessel defining a canister having an outlet passage and an inlet passage having a greater flow capacity than the outlet passage and capable of admitting liquid to the vessel at a rate greater than it can pass through the outlet passage so that the vessel is maintained filled in operation, and having an impervious radially outer side wall extending around and along the rotation axis and forming an annular contaminant separation and containment zone extending radially inwardly from the side wall.  
           [0021]    In a still further aspect, the objects are achieved by providing a centrifugal separator for separating solid contaminants from a liquid, the separator comprising a housing, an inlet opening into the housing for supplying contaminated liquid to the housing at elevated pressure, an outlet for discharging cleaned liquid from the housing, a rotor mounted within the housing for rotation about a rotation axis extending through the housing, and a drive for rotating the rotor about the rotation axis, wherein the rotor comprises a centrifugal separation rotor as described above.  
           [0022]    The objects of the invention are also achieved at least in part by providing a method of separating solid contaminants from a liquid using centrifugal forces, comprising rotating about an axis a vessel having an impervious radially outer side wall displaced from the axis and an outlet passage communicating with the vessel radially inwardly of the outer side wall; introducing liquid to be cleaned to the rotating vessel at a rate not greater than the outlet passage is capable of discharging liquid from the vessel such that the liquid occupies a separation and containment zone bounded by the radially outer side wall and the outlet passage, wherein the liquid is conveyed to a collector face which faces the rotation axis, the collector face being disposed radially inwardly of the separation and containment zone and communicating with the zone via at least one transfer passage, and rotating the collector face about the axis to generate sufficient centrifugal force to maintain the introduced liquid bearing against the collector face and cause liquid flow along the collector face to the at least one transfer passage; wherein the liquid at the collector face is subjected to a component of the centrifugal force in a direction along the collector face towards the at least one transfer passage by increasing the distance of the collector face from the rotation axis in a direction along the axis towards the transfer passage, thereby causing the liquid to flow along the collector face only towards the transfer passage.  
           [0023]    It should be understood in accordance with the invention that any centrifugal separation apparatus which effectively separates low density contaminants is also able to separate relatively high density contaminants mixed therewith or be combined with apparatus optimized for separation of such relatively high density contaminants.  
           [0024]    According to a first aspect of the present invention centrifugal separation rotor means for centrifugal separation apparatus of the type for separating solid contaminants from a liquid and comprising a housing for mounting the rotor means for rotation about a rotation axis by drive means, wherein the rotor means comprises a walled separation and containment vessel having an impervious radially outer side wall extending about and along the rotation axis to form radially inwardly from the side wall an annular contaminant separation and containment zone, outlet passage means leading externally of the vessel and, associated with the vessel, inlet means operable to convey liquid to be cleaned to the contaminant separation and containment zone, is characterized by said vessel outlet passage means being capable of passing liquid from the vessel at a rate greater than the associated inlet means can convey it to the vessel and disposed radially inwardly with respect to the radially outer side wall to define, during rotation, the radial boundary of the annular contaminant separation and containment zone, to which zone said liquid and contaminants separated therefrom are confined in the vessel.  
           [0025]    According to a second aspect of the present invention a separation and containment module for centrifugal separation rotor means of the type for separating solid contaminants from a liquid passed therethrough when driven about a rotation axis and wherein the rotor means has a walled separation and containment vessel with an impervious radially outer side wall, extending about and along the rotation axis and forming radially inwardly of the side wall an annular contaminant separation and containment zone arranged to be supplied with contaminated liquid from associated inlet means, and outlet passage means communicating with the vessel radially inwardly of the outer side wall, comprises at least said vessel impervious radially outer side wall defined about, and spaced radially from, a longitudinal axis, the outlet passage means and means to releasably attach the module coaxially with respect to the rotation axis and define thereabout the outlet passage means able to pass liquid at a rate greater than it can be conveyed to the vessel and adjacent the outer side wall the annular separation and containment zone to which the substantially all of the liquid in the vessel is confined during rotation.  
           [0026]    The operationally partially filled separation and containment vessel defined in the two preceeding paragraphs means may comprise the vessel only or may have coupled thereto a further walled separation and containment vessel defining a canister having outlet passage means and inlet passage means having greater flow capacity than the outlet passage means to convey liquid to the vessel and maintain it filled in operation, and an impervious radially outer side wall extending around and along the rotation axis and forming an annular contaminant separation and containment zone extending radially inwardly from the side wall.  
           [0027]    According to a third aspect of the present invention a separation and containment module for centrifugal separation rotor means, of the type comprising a canister for separating solid contaminants from a liquid passed therethrough when driven about a rotation axis, and wherein the canister has a substantially impervious radially outer side wall extending around and along the rotation axis and outlet passage means arranged not to pass liquid from the vessel at a greater rate than conveyed thereto and cause the vessel to be filled in operation, and form an annular contaminant separation and containment zone radially inwardly of the outer side wall, comprises a walled separation and containment vessel having a longitudinal axis, an impervious radially outer side wall extending about and along the longitudinal axis to receive liquid conveyed thereto, outlet passage means communicating with the vessel radially inwardly of the outer side wall, able to pass liquid at a rate greater than it can be conveyed to the vessel, and means to releasably attach the module co-axially with respect to the canister to define thereabout the outlet passage means and adjacent the outer side wall an annular separation and containment zone to which the substantially all of the liquid in the vessel is confined during rotation.  
           [0028]    According to a fourth aspect of the present invention centrifugal separation apparatus for separating solid contaminant from a liquid comprises a housing into which extends inlet duct means for supplying contaminated liquid thereto at elevated pressure and outlet duct means for drainage of cleaned liquid therefrom, rotor means, mounted within the housing for rotation about a rotation axis and is characterized by the centrifugal separation rotor means or separation and containment module defined in any of the preceding four paragraphs.  
           [0029]    According to a fifth aspect of the present invention a method of separating solid contaminants from a liquid using centrifugal forces comprises rotating about an axis a vessel having an impervious radially outer side wall displaced from the axis and outlet passage means communicating with the vessel radially inwardly of the outer side wall, conveying liquid to be cleaned to the vessel and passing clean liquid from the vessel by said outlet passage means, the method being characterized by defining an annular contaminant separation and containment zone in the vessel bounded radially by the side wall and the outlet passage means, conveying liquid to the zone at a rate not greater than the outlet passage means is capable of passing and rotating the vessel about the axis at such a rate that liquid within the vessel occupies substantially all of, and is confined to, the separation and containment zone.  
           [0030]    According to a sixth aspect of the present invention a method of improving the separation performance of a centrifugal separator having centrifugal separation rotor means mounted for rotation and supplied with liquid at elevated pressure and passed through a canister thereof at such a rate as to keep it filled, is characterized by disposing coaxially with respect to the canister and coupled for rotation therewith, a separation and containment vessel having an impervious radially outer side wall displaced from the axis and outlet passage means communicating with the vessel radially inwardly of the outer side wall, defining an annular separation and containment zone in the vessel bounded radially by the side wall and outlet passage means, conveying liquid to be cleaned to the separation and containment zone at a rate not greater than the outlet passage means is capable of passing and rotating the canister and vessel about the axis at such a rate that liquid within the vessel occupies substantially all of, and is confined to, the annular separation and containment zone displaced radially outwardly of the canister. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures, in which:  
         [0032]    [0032]FIG. 1 is a sectional elevation through a first embodiment of centrifugal separation apparatus in accordance with the invention, including impulse turbine drive means as the source of contaminated liquid and inlet means in the form of an axially extending, perforated divider wall;  
         [0033]    [0033]FIG. 2 is a sectional elevation through a second embodiment of centrifugal separation apparatus in accordance with the invention, illustrating a divider wall of tapered form;  
         [0034]    [0034]FIG. 3 is a sectional elevation through a third embodiment of centrifugal separation apparatus in accordance with the invention illustrating variants of components;  
         [0035]    [0035]FIG. 4 is a sectional elevation through a part of a fourth embodiment of centrifugal separation apparatus in accordance with the invention illustrating a variant of impulse turbine drive means;  
         [0036]    [0036]FIG. 5 is a sectional elevation through a part of a fifth embodiment of centrifugal separation apparatus in accordance with the invention illustrating a further variant of impulse turbine drive means in which the spent liquid is not the source of the contaminated liquid to be cleaned;  
         [0037]    [0037]FIG. 6 is a sectional elevation through a sixth embodiment of centrifugal separation apparatus in accordance with the invention illustrating a further variant of inlet means;  
         [0038]    [0038]FIG. 7 is a sectional elevation through a seventh embodiment of centrifugal separation apparatus in accordance with the invention including reaction turbine drive means;  
         [0039]    [0039]FIG. 8 is a sectional elevation through an eighth embodiment of centrifugal separation apparatus in accordance with the invention illustrating a further variant of reaction turbine drive means, the spent liquid of which is the source of contaminated liquid to be cleaned;  
         [0040]    [0040]FIG. 9 is a sectional elevation through a ninth embodiment of centrifugal separation apparatus in accordance with the invention illustrating a further variant of reaction turbine drive means in which the spent liquid is not the source of the contaminated liquid to be cleaned;  
         [0041]    [0041]FIG. 10 is a sectional elevation through a tenth embodiment of centrifugal separation apparatus in accordance with the invention, illustrating further variants to the rotor means;  
         [0042]    [0042]FIG. 11 is a schematic representation in sectional elevation of part of an eleventh embodiment of centrifugal separator in accordance with the invention, illustrating the inclusion of further vessels within the walled contaminant separation and containment vessel;  
         [0043]    [0043]FIG. 12 is a schematic representation in sectional elevation of part of a twelfth embodiment of centrifugal separator showing modification of the multi-vessel arrangement of FIG. 11, and  
         [0044]    [0044]FIG. 13 is a sectional elevation through a thirteenth embodiment of centrifugal separator in accordance with the present invention in which, within the walled contaminant separation and containment vessel, a further contaminant separation and containment vessel is provided in the form of a conventional, liquid filled canister that also provides the drive means. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0045]    Referring to FIG. 1, a first embodiment of centrifugal separator  110  comprises a housing  112  defined by a base  114 , adapted to be affixed to the engine block of an internal combustion engine (not shown), and a removable cover  116 . The base includes inlet duct means  118 , by which contaminated liquid is supplied at elevated pressure, and outlet duct means  120  for drainage of liquid from the housing to the engine sump.  
         [0046]    A spindle  122 , having longitudinal axis  124 , is supported at one end thereof  122 , by the base and extends through the housing and engages at its other end  122   2  with the cover  116 .  
         [0047]    Mounted on the spindle for rotation about the axis  124  within the housing is rotor means  130 , comprising a walled containment separation and containment vessel  132  (hereafter referred as “the vessel”) which has an impervious, radially outer side wall  134  extending about, and lengthways of, rotation axis  124  between end walls  136  and  138 . Radially inwardly from the side wall  134  is an annular contaminant separation and containment zone  140  (hereafter referred to as “the zone”), the radially inner boundary of the zone, as denoted by the broken line  141 , being defined by outlet passage means  142  in the end wall  138  which leads externally of the vessel within the housing. The outlet passage means  142  may comprise one or more apertures, in the form of circumferentially extending slots, in the end wall or may comprise an annular gap representing a radial space between the end wall  138  and inlet means, indicated generally at  150  and described hereinafter, which is arranged to convey contaminated liquid from radially inwardly thereof to the zone  140 .  
         [0048]    The rotor means is mounted with respect to the spindle  122  by way of a tubular axle  144  which surrounds the spindle and is mounted by axially spaced needle roller bearings  146   1 ,  146   2 , or equivalent low friction bearings, and held captive by a nut  148 .  
         [0049]    The inlet means  150  comprises collection means  151  having a divider wall  152 , also extending about and lengthways of the rotation axis  124 , disposed radially between the tubular axle  144  and the zone  140 , preferably adjacent the latter and possibly defining one boundary of the outlet passage means  142 . The divider wall  152  is mounted in fixed relationship to the tubular axle, at one of its axial extremities by radially extending wall  154  and at the other, optionally, by bracing spars  156 , but nevertheless apertured for drainage and possibly absent altogether. The wall  152  has an inlet or collection face  158  facing towards the rotation axis and defining between the face and the tube axle  146  an inlet region  160 .  
         [0050]    Transfer passage means, indicated generally at  162 , communicates between the collection face  158  and the zone  140 , taking the form of a plurality of through-apertures  164  in the divider wall. Preferably the apertures are concentrated in density towards the end of the divider wall axially remote from the outlet passage means but at any axial position are uniformly distributed circumferentially.  
         [0051]    With the tubular axle  144 , the divider wall  152  and the end wall  154 , form the main structural element of the rotor means by which it is carried on the spindle and with respect to the housing.  
         [0052]    The radially outer wall  134  and end walls  136  and  138 , which define the contaminant separation and containment zone  140  and outlet passage means  142 , are formed as a discrete separation and containment module  132   1  arranged to be removably mounted with respect to the inlet means  150  by means, indicated at  135  comprising a radially overhanging lip  154   1  of the end wall  154  engageable with the radially inner edge  136   1  of the end wall  136 . The module  132 , is conveniently molded of synthetic resin material (i.e., plastic) and may include any conventional strengthening features, such as circumferential ribs to enable it to withstand the stresses of high speed rotation and the forces exerted by the liquid and deposited contaminants in the zone  140 .  
         [0053]    The inlet means  150  also collects contaminated liquid to be cleaned on the collection face, which it does by way of rotor drive means, indicated generally at  170 . The drive means comprises a fluid motor in the form of an impulse turbine  172 . The impulse turbine  172  comprises a plurality of turbine blades  174 , each of which may have a concave, bucket-like form also known as a Pelton wheel, arrayed surrounding the rotation axis  124  and fixed with respect to the rotor means. The blades may individually, or as an array sub-assembly, be secured to an end region of the tube axle  144  or formed integrally therewith as shown.  
         [0054]    The turbine  172  also comprises a plurality of liquid jet nozzles  176 , each of which extends from the base  114  and is coupled to the high pressure supply duct  118  to direct a jet  178  of the contaminated liquid at a particular bucket position, substantially tangentially with respect to the rotation axis but also inclined longitudinally with respect thereto such that liquid deflected by, or otherwise splashed after, impact with a blade is caused to enter inlet region  160  and impinge upon the collection face  158  of the inlet means, as illustrated by broken boundary lines  178 ′.  
         [0055]    Thus, in operation contaminated liquid supplied to the arrangement initially uses its energy to effect high speed rotation of the rotor means including the collection face  158 , so that spent turbine liquid which impinges upon the collection face is spread into a covering film by the centrifugal forces of rotation. Liquid of the film passes through the apertures  162  of the passage means and is thrown towards the radially outer wall  134 .  
         [0056]    The turbine means is arranged in conjunction with the outlet passage means to ensure that contaminated liquid is supplied to the collection face  158  at a rate less than that at which it can drain through the outlet passage means  142  , so that a layer of liquid and contaminants is held against the outer wall  134  to a thickness no greater than the contaminant separation and containment zone  140  defined by the radial position of the outlet passage means and the vessel is otherwise substantially empty. Insofar as such zone is at maximum distance from the rotation axis, centrifugal forces are at maximum and any heavier contaminants are separated from the liquid to agglomerate into a layer against the wall with the liquid overlying it. Separation can thus continue until the contaminant deposits fill the zone and further contaminants are washed directly through the outlet passage means.  
         [0057]    Thereafter, separation and contaminant module  132 , can readily be separated from the inlet means and cleaned or discarded, being replaced with a cleaned or new module. As indicated above the module may be manufactured from molded synthetic resin material which enables it to be manufactured cheaply as a “consumable” which can readily be destroyed with the contaminants collected therein and which reduces the inertia of the rotor means in operation.  
         [0058]    In keeping with reducing the inertia of the rotor means, it is an important feature of the invention that in operation the vessel of the rotor means is not filled with the liquid, unlike the normal operating conditions of such cleaning arrangements, and rapidly brought up to operating speed by direct turbine drive and without awaiting for the rotor to fill with liquid. Also, because in this embodiment the tubular axle is not filled with liquid at elevated pressure, the bearings  146   1  and  146   2  may be chosen for low energy loss without regard to liquid containment.  
         [0059]    Many of the individual components may take alternative form, and in general may be varied independently of each other.  
         [0060]    Referring now to FIG. 2, this shows in similar sectional elevation a second embodiment of centrifugal separator  210  which illustrates one such variant. Identical components retain the same reference numbers and corresponding, but different components have reference numbers with a leading “2”.  
         [0061]    The separator  210  comprises the aforementioned housing  112  defined by base  114  cover  116  and spindle  122 . Housed rotor means  230  is substantially the same as rotor means  130  except in respect of inlet means  250  which includes collection means  251  having a divider wall  252  of slightly conical form, increasing in radius with distance from the end  252   1  at which liquid is introduced towards end  252   2  adjacent wall  254  and defining a similarly shaped inlet region  260 . Also, instead of aperture means in the form of an array of through-apertures scattered radially and axially thereof, aperture means  262  comprises circumferentially extending slots  264  disposed only towards the end of maximum radius.  
         [0062]    Impulse turbine drive means  172  is as described above, and contaminated liquid is directed by nozzles  176  towards impulse turbine blades  174  to effect rotation of the rotor means and spent liquid is directed on to collection face  258  of the divider wall. As described above, the centrifugal forces of rotation spread the liquid as a film over the collection face and here the variation in radius encourages the liquid to migrate to the upper end  252   2 , whereupon it passes through slots  264  and is flung toward the outer wall  134  of the module  1321 . Insofar as the liquid enters the contaminant separation and containment zone  140  at the end remote from the outlet passage means  142 , it is caused to dwell in the zone for the maximum possible separation time.  
         [0063]    Other components and structural relationships may be employed without departing from the spirit of the invention and FIG. 3 shows in sectional elevation a third embodiment of centrifugal separator  310  which illustrates possible variants. Components identical to those of the first and second embodiments have the same reference numbers whilst differing components have reference numbers with a leading “3”.  
         [0064]    The separator  310  comprises the aforementioned housing  112  defined by base  114  cover means  116  and spindle  122 , the latter defining rotation axis  124 . Housed rotor means  330  is mounted on the spindle  122  by tubular axle  344 .  
         [0065]    The rotor means comprises a walled vessel  332  bounded externally by impervious outer side wall  334  extending about, and lengthways of, the rotation axis between end walls  336  and  338 . The end wall  336  is clamped with respect to the end of the axle means by nut  148  which also locks the tubular axle onto the spindle.  
         [0066]    The end wall  338  contains therein outlet passage means  342  displaced radially inwardly of the side wall  334  to define between the passage means as said side wall a contaminant separation and containment zone  340  as indicated by broken lines  341 . Displaced radially inwardly of the outlet passage means and extending substantially parallel to the outer wall  334  is an optional inner wall  335  which defines a physically bounded separation and collection chamber  340   1  of separated contaminants little greater than the  340 .  
         [0067]    Inlet means  350  includes collection means  351  having a divider wall  352  which surrounds and extends axially of, the rotation axis  124 , and the tubular axle  344 , being disposed with respect to the tubular axle by spars  353 . The divider wall is tapered, increasing in radius as a function of distance from the end  352   1  adjacent base  114 , and otherwise open at its upper end  352   2  which is spaced axially from the end wall  336  so as to provide a substantially unobstructed annular transfer passage means  362  between collection face  358  of the divider wall and the contaminant separation and containment zone  340  at the outer wall  334 .  
         [0068]    As a matter of structural convenience and to impart operational strength thereto, the upper end of the inner chamber wall  335  is shaped to locate over the upper end  352   2  of the divider wall  352 .  
         [0069]    Furthermore, and illustrative of a further variant, drive means  370  takes the form of an impulse turbine  372  having stationary liquid jet nozzles  376  and generally flat blades  374  fixed with respect to the tubular axle between its ends so that substantially all of the spent turbine drive liquid impinges upon collection face  358  of the divider wall.  
         [0070]    Operation is substantially as described above, with contaminated liquid supplied at elevated pressure to supply duct  118  from where it is directed by nozzles  376  towards turbine blades  374  to effect rotation; spent liquid, deflected by the turbine blades to impinge upon the conical collection face  358 , is held there by centrifugal forces of rotation and migrates towards the upper end  352   2  of the divider wall before being flung by these centrifugal forces through the annular gap  362  towards outer wall  334 , whereupon it further spreads and flows generally towards outlet passage  342 , heavier contaminants being separated from the liquid and caused to agglomerate against, and bond to, the wall or any previously separated contaminants.  
         [0071]    When the zone  340  is filled by the separated contaminants, the separation and containment module  332   1  is readily removed from the rotor means by releasing nut  148  and replaced with an empty one. The optional inner wall  335  effectively prevents any inadvertent dislodging of the deposited contaminants from the outer side wall  334 , and as described above, the separation and containment module  332   1  may be formed as a discardable molded synthetic resin article.  
         [0072]    In all of the above described embodiments the drive means for the rotor means is an impulse turbine having blades fixed to a tubular axle surrounding a stationary spindle and supplied with liquid by stationary feed nozzles.  
         [0073]    Considering further structural variants, such impulse turbine blades (whether flat or bucket-like) may be mounted elsewhere, provided the spent liquid impinges directly or indirectly upon the collection face of the divider wall. Referring to FIG. 4, in which is illustrated in sectional elevation a part of a fourth embodiment of separation apparatus  410 , this is the same as the third embodiment except for drive means  470  in the form of an array of bucket-like turbine blades  474  mounted directly on collection face  458  of the divider wall.  
         [0074]    Referring now to FIG. 5, this shows in sectional elevation part of a fifth embodiment of centrifugal separation arrangement  510  that is generally similar to the separation arrangement  210  in respect of the inlet means and impulse turbine, but wherein the liquid to be cleaned is directed totally or in part directly upon the collection face  258  of divider wall  252  by way of feed nozzle means  576   1  and the turbine operated in isolation therefrom or in conjunction therewith, being fed by nozzle means  576   2 , to effect rotation of the rotor means at an appropriate high rate. It also illustrates the possibility of supplying contaminated liquid to feed nozzle  576   1  completely independently from the supply to nozzle means  567   2 , although of course they may have a common supply as described above. It may be advantageous to have such discrete supplies when for instance, the liquid to be cleaned is heavily contaminated and unsuitable for passing through a relatively small nozzle jet for driving the turbine and/or is available at a low or variable pressure or intermittently, such as in the circumstances discussed in the aforementioned U.S. Pat. No. 5,906,733.  
         [0075]    Referring to FIG. 6, a sixth embodiment of centrifugal separator  610  is shown in sectional elevation and once more, previously described parts have the same reference numbers whilst parts unique to the embodiment have reference numbers with a leading “6”. The housing  112 , with base  114  and cover  116 , is as described above. Spindle  622  corresponds to the above-described spindle  122  except that it has the supply duct  118  extending axially therealong as inlet passage  618  to cross drillings  619 .  
         [0076]    Rotor means  630  mounted on the spindle comprises a separation and containment vessel  632  having a side wall  634 , extending about and along the rotation axis  124 , and radially directed end walls  636  and  638 . The side wall defines one radial limit of contaminant separation and containment zone  640 , the other radial limit being defined by outlet passage means  642  in the end wall  638 . Bearings  646   1  and  646   2  carried by said end walls mount the vessel rotatably on the spindle without the need for a separate, tubular axle.  
         [0077]    Inlet means, by which contaminated liquid is fed to the zone  640 , is indicated generally at  650 , comprising the spindle passage  618  and cross drilling  619  which deliver the liquid directly into the vessel and directed towards the zone  640  and without the intermediary of a divider wall, although for comparison with the above described embodiments, the spindle surrounding the passage  618  may be considered to form the divider wall and the cross drilling  619  to form the transfer passage means.  
         [0078]    Drive means, indicated generally at  670 , comprises impulse turbine  672  of blades  674  and tangentially directed feed nozzle  676 .  
         [0079]    As with the fifth embodiment, the liquid to be cleaned within the vessel is separate from that of the drive means, although from the same supply duct  118 , and permits the flow of each to be optimized. The supplies could, of course, be separate as illustrated by the sixth embodiment.  
         [0080]    It will be appreciated that insofar as the rotor means is operated with relatively little liquid therein, it may be spun at high speed using the contaminated liquid pressure by drive means other than an impulse turbine, such as the more traditional reaction turbine. Referring to FIG. 7, a seventh embodiment of centrifugal separator  710  is shown in sectional elevation and once more, previously described parts have the same reference numbers whilst parts unique to the embodiment have reference numbers with a leading “7”. The housing  112 , with base  114  and cover  116 , as described above. Spindle  722  corresponds to the above-described spindle  122  except that it has the supply duct  118  extending therealong axially as inlet passage  718  to cross drillings  719 .  
         [0081]    Rotor means  730  is mounted on the spindle by way of bearing bushes  746   1  and  746   2  disposed at opposite ends of tubular axle  744 . The tubular axle is surrounded by a walled separation and containment vessel  732  defined by an outer side wall  734  spaced therefrom by end walls  736  and  738 , the wall  738  including outlet passage means  742  positioned radially to define contaminant separation and containment zone  740 . The tubular axle  744  provides both inlet means, indicated generally at  750 , and drive means, indicated generally at  770 .  
         [0082]    In respect of the inlet means, the tubular axle comprises an effective divider wall  752  of collection means  751  and defines with the spindle an annular inlet region  760  fed by way of the passage  718 . The tubular axle/divider wall is also provided with transfer aperture means  762  in the form of a plurality of apertures  766 . In respect of the drive means  770 , the apertures  766  comprise tangentially directed jet reaction nozzles, which eject contaminated liquid from the inlet chamber and by reaction thereto cause the rotor means to spin about the spindle.  
         [0083]    Thus, the reaction nozzles spray ejected liquid, spent of most but not all of its energy, in a direction away from the rotation axis of the rotor means, which liquid impinges upon the vessel outer wall  734  and spreads thereon as a film overlying the wall, and subsequently overlying contaminants separated from the liquid, within the zone  740  as described above. Insofar as the divider wall is spaced from the boundary of the zone  740  and the outlet passage means defining the zone, and there exists a risk of deposited contaminants falling from a filled vessel when it is not rotating, it may be desirable to define a floor to the vessel radially inwardly of the outlet passage means, as shown by broken lines  780  or define the outlet passage means at an upwardly facing end, that is, in end wall  736  rather than end wall  738 .  
         [0084]    It will be appreciated from the Figure that the high pressure liquid in inlet region  760  also provides lubrication for the bearing bushes  746 , and  746   2  and some of the liquid escapes through the bushes directly into the housing without passing through transfer passage nozzles  766 . It is possible to treat such liquid in respect of separation as also supplied to vessel  732  by extending the side wall  734  to beyond one bush bearing as shown for end wall  736 , or both bearings.  
         [0085]    It also will be appreciated that although the inlet region  760  within the axle tube is filled with liquid and the effect thereof, in terms of the need to effect substantial sealing of the axle chamber on the spindle by the bearing bushes (or otherwise) and the lower efficiency of reaction jet turbine, is an improvement over existing reaction driven separation arrangements because the liquid is confined to smaller radially inner and outer proportions of the rotor means.  
         [0086]    Referring now to FIG. 8 this shows a sectional elevation an eighth embodiment of centrifugal separation arrangement in accordance with the present invention, and a variant of the seventh embodiment, at  810 . Within housing  112 , fixed spindle  822  has a supply duct  818  for incoming contaminated liquid at elevated pressure and has mounted rotatably thereon a walled separation and containment vessel  832  defined by radially outer wall  834  and end walls  836  and  838 , in the latter of which is formed outlet passage means  842  that defines a contaminant separation and containment zone  840  adjacent the wall  834 . The radially inner boundary of the vessel is the spindle, that is, there is no separate tubular axle, although there could be if desired. As in the previous embodiment, the arrangement combines inlet means, which is here indicated generally at  850 , and drive means, indicated generally at  870 . The vessel  832  is divided internally at least in part by a radially extending divider wall  852  which forms annular inlet chamber  860  surrounding the spindle and fed by way of the duct  818  and cross drilling  819 . In respect of inlet means, the divider wall  852  is also provided with transfer aperture means  862  in the form of a plurality of apertures  866  by way of which contaminated liquid is directed to the zone  840 . In respect of the drive means  870 , the apertures  866  comprise tangentially directed jet reaction nozzles, which eject contaminated liquid from the inlet chamber towards the zone  840 , and by reaction thereto cause the rotor means to spin about the spindle, enabling separation of contaminants to be effected in the zone  840  at the radially outermost part of the vessel.  
         [0087]    The inlet chamber  860  thus comprises a drive chamber and may be of small volume sufficient to function as a reaction turbine to rotate the other vessel  832  at high speed and preferably is shaped to encourage contaminated liquid passing therethrough to do so without separation of contaminants. The major part of the vessel  832  which receives the ejected and spent liquid directed towards its outer wall, is not filled with the liquid but in operation contains only a relatively small amount as dictated by the contaminant separation and containment zone.  
         [0088]    Referring now to FIG. 9, this shows in sectional elevation a ninth embodiment of centrifugal separator  910 .The arrangement is somewhat similar to the eighth embodiment in having rotor means  930  in the form of a pair of axially disposed, rotationally coupled vessels defined about spindle  922 , one of which,  932 , defines contaminant separation and containment zone  940  and the other of which comprises drive means  970 .  
         [0089]    Inlet means to the vessel  932  comprises spindle duct  918  and cross drilling  919 , which preferably contains some form of diffusing means (not shown) to spay the liquid towards the outer wall  934 , where it forms a layer only to the thickness of the contaminant separation and containment zone  940  defined by outlet passage means  942 .  
         [0090]    Drive means  970  comprises a reaction jet turbine  972  formed by vessel  973 , closed except in respect of liquid inlet from the spindle by way of cross drilling  919   2  and liquid outlet by way of reaction jet nozzles  966  in the vessel wall. The vessel  973  has small volume, sufficient to function as a reaction turbine to rotate the other vessel  932  at high speed and preferably is shaped to encourage contaminated liquid passing therethrough to do so without separation of contaminants.  
         [0091]    Insofar as the contaminated liquid supplied to the contaminant separation and containment zone is separate from that employed to rotate the rotor means, the relative flow rates may be chosen having regard to maximising the rotation rate whilst providing a relatively long residence time in the contaminant separation and containment zone.  
         [0092]    In accordance with the spirit of the present invention the above described reaction turbine drive chamber  860  and vessel  973  each has a small, but nevertheless significant volume. It will be appreciated that if desired, such a reaction drive may be defined without filtering such a chamber per se, that is, with minimal volume, by means of discretely feeding the reaction jet nozzles by individual ducts in the manner set out in U.S. Pat. No.  5 , 906 , 733 .  
         [0093]    It will be appreciated that although all of the above described embodiments have shown the outlet passage means defined at the lower wall of the rotor vessel in relation to a vertical rotation axis, this is not a functional necessity. The outlet passage means may be defined in the upper end wall or radially outer wall or any combination thereof, provided that the contaminant separation and containment zone is properly defined and liquid exiting the vessel by way of the outlet passage means does not interfere with the rotation. In this context the impervious nature of the radially outer wall should be taken to be exclusive of such outlet passage means. Likewise, depending upon the drive means, it may be possible to operate with the rotation axis at any non-vertical orientation.  
         [0094]    Furthermore, although all of the above embodiments have been described with a stationary spindle, such may be rotatably mounted with respect to the housing for rotation about the axis  124 , a discrete tubular axle  124  being then unnecessary. Furthermore, spindle means may comprise a pair of axially spaced stub axles at opposite ends of the housing and carried by, or extending into, the rotor means.  
         [0095]    Referring now to FIG. 10, this shows in sectional elevation a tenth embodiment of centrifugal separation arrangement  1010  in accordance with the present invention. Housing  1012  is defined by base  1014  and removable cover  1016 . The base includes inlet duct means  1018  and recess  1019  for supporting one end  1022   1  of spindle  1022  for rotation with respect thereto by way of bearing means  1046   1 . The supply duct opens into the recess  1019  and the spindle contains a duct  1018   1  extending therealong from the end and in communication with the supply duct by way of the recess. A further spindle  1022   2  is mounted by way of bearing means  1046   2  to the cover  1016  for rotation relative to the common longitudinal axis  1024 . The spindles form part of rotor means indicated generally at  1030 . The spindle duct  1018   1  connects to a pair of axially spaced cross drillings  1019   1  and  1019   2 . Mounted on the spindle  1022   1  in alignment with the cross drilling  1019   2  is a vessel  1032  having an impervious outer wall  1034  extending about and along the axis  1024  and displaced therefrom by end wall  1036  which is fixed permanently, or releasably threaded, to the spindle  1022   1 . At the other end of the outer wall  1034 , end wall  1038  is connected to the spindle  1022   2  but apertured at a predetermined distance from the rotation axis to define outlet passage means  1042 , and thereby contaminant separation and containment zone  1040 . The rotor means also comprises drive means  1070  in the form of reaction turbine means  1072 , comprising a plurality of stand pipes  1073  each aligned with the cross drilling  1019   1  and terminating adjacent the cover  1016  in a jet reaction nozzle  1076 .  
         [0096]    Operation is essentially as described above in relation to the seventh, eighth and ninth embodiments driven by reaction turbines but with minimal liquid contained in the rotor means for minimum inertia. Also, this embodiment illustrates the outlet passage means at the upper end of the housing. The spindle ends  1022   1  and  1022   2  may of course, comprise end regions of a single spindle  1022  as shown by the broken joining lines  1022   3 .  
         [0097]    It will be appreciated that outlet passage means may be disposed at such “upper end” of the separation and containment vessel in any of the above described embodiments, or indeed at both ends.  
         [0098]    All of the embodiments described above have employed drive means in the form of impulse or reaction turbines which are powered by the contaminated liquid either separately from or as a precursor to it undergoing contaminant separation, this being one of the most convenient power sources available to such arrangement within a functioning internal combustion engine. It will be appreciated that there are numerous other forms or turbines or non-turbine motors driven by liquid or gaseous fluids that could be adapted for an arrangement in accordance with the present invention. Also, insofar as the arrangement is capable of being designed to effect centrifugal cleaning of contaminated liquid separately from driving the rotor means, the drive means does not need to be powered by the contaminated liquid, nor indeed liquid or any other fluid at all. For example, the rotor means could be driven by electric motor means or mechanical linkage to an engine whose lubricant is being cleaned and achieve high rotation speeds by way of gearing.  
         [0099]    Other structural variations are possible. For instance, the inlet means may be displaced axially from the separation and containment vessel, particularly where the inlet means directs incoming liquid axially to a transfer passage and the transfer passage shares the same axial position at at least one end of the vessel.  
         [0100]    Although for optimum conditions of minimal inertia and separation radius, the separation and containment vessel comprises little more than a radially impervious wall at maximum distance, it will be appreciated that if it anticipated that only a minor proportion of the particulate contaminants are of such low density as to require these conditions, then it may be feasible to include coaxially within the vessel, radially between the outer wall and the rotation axis, one or more nested further vessels having substantially the same structure, in terms of outlet passage means defining a contaminant separation and containment zone adjacent an impervious radially outer wall, but each providing by such outlet passage means the liquid for the next outer vessel.  
         [0101]    Referring, now to FIG. 11, this shows a schematic representation in sectional elevation of part of a an eleventh embodiment of centrifugal separation apparatus  1110  in accordance with the invention, and based upon the embodiment  210  to which reference is made for the parts not shown. The Figure does show a portion of (static) cover  116  enclosing rotor means  1130 .  
         [0102]    The rotor means comprises inlet means  1150 , in the form of tapered divider wall  1152  having radially inwardly facing collector face  1158 , and, adjacent the end thereof, transfer passage means  1162 , as well as separation and containment vessel  1132  mounted thereto by radially extending spacer spars (not shown) for rotation therewith. The vessel  1132  comprises axially extending, impervious wall  1134  and at each end thereof vestigial end walls  1136  and  1138  which are directed both axially and radially to collect liquid approaching in a radial direction and to define the radial limit of a contaminant separation and containment zone  1140 , that is, the radial limit of outlet passage means  1142 .  
         [0103]    Also mounted on, and coaxially with, the inlet means are a plurality, here two, of further separation and containment vessels  1132   A  and  1132   B  radially inwardly of the vessel  1132 . The further vessels are substantially identical to the vessel  1132  in having vestigial end walls  1136   A ,  1138   A ,  1136   B  and  1138   B  that define outlet passage means  1142   A ,  1142   B  and thereby contaminant separation and containment zones  1140   A  and  1140   B  respectively, but also are progressively shorter in axial length towards the inlet means so that liquid exiting the outlet passage means of each is flung radially outwardly towards, and collected by, the next vessel. As can be seen, the transfer passage  1162  of the inlet means is aligned substantially with the mid points of the surrounding vessels.  
         [0104]    Operation will be seen to correspond to that described above with each vessel or further vessel containing a relatively thin, annular skin of liquid and contaminants separated therefrom having densities appropriate to the distance from the axis, progressively cleaner liquid with lower density contaminants eventually arriving at the outermost vessel  1132 . Insofar as each of the further vessels may be made of low density, synthetic resin materials (i.e., plastics), the weight, and thus inertia of the multi-vessel rotor means, can still be significantly less than a single vessel completely filled with liquid.  
         [0105]    There are may structural variations possible in terms of the size and dispositions of such further vessels and FIG. 12 illustrates some of these in a composite construction of such a schematic part view of separation apparatus  1210 . Referring to the Figure, the outer cover  116  and inlet means  1250  is substantially as described above. Rotor means comprises an outermost separation and containment vessel  1232  and coaxially therein, a plurality of spaced apart further vessels  1232   i , where i is here A to E.  
         [0106]    Considering the further vessels  1232   E  and  1232   D  that make up section I, these (and possibly all vessels) are of uniform length, but the outlet passage means  1242   E  and  1242   D  is defined at one end only of each, which end alternates for successive vessels so that the liquid follows a meandering path along the full length of each.  
         [0107]    Considering the further vessels  1232   D ,  1232   C  and  1232   B  that make up section II, these (and possibly all vessels) are progressively shorter with distance from the rotation axis as well as being disposed axially to effect a meandering path for the liquid. Such arrangement has the functional effect of minimising the inertia of the rotor means and permitting a more tapered, streamlined shape for the cover.  
         [0108]    Consider the further vessel  1232   A  and vessel  1232  that make up section III, these (and possibly all vessels) have at the end where liquid is received from the outlet passage means  1242   A  of the preceding further vessel an end wall  1236  which is shaped as a splitter to divert only a proportion of the liquid into the vessel.  
         [0109]    It will be appreciated that where one or more further vessels are employed nested within the outer vessel, the outer side walls need not extend parallel to that of the outer vessel. Likewise, although each outlet passage means and further outlet passage means has been shown in an end wall of each vessel or further vessel, it may be provided in an appropriately shaped side wall.  
         [0110]    It is a fundamental feature of all of the embodiments described above that the separation and containment vessel defined by, and radially inwardly of, the impervious radially outer side wall, is not filled with liquid and has a relatively thin contaminant separation and containment zone adjacent the wall and as such provides a structure wherein the radial position of the outer wall is not a determining factor in the bulk of the liquid contained and rotated and is free of centrifugal pressure gradient flow behaviors of such liquid.  
         [0111]    These operating principles thus enable completely novel constructions of rotor means for this type of engine lubricant cleaning arrangement which is readily substituted within the “real estate” made available on such an engine for cleaning by the traditional arrangements.  
         [0112]    However it will be appreciated that there are circumstances in which a walled separation and contaminant vessel as defined by a liquid filled canister is, notwithstanding the above outlined conflicts regarding diameter and separation force, nevertheless optimized dimensionally for removing all but the lowest density contaminants, such as soot, and providing an adaptation which builds upon such optimization to increase the range of particulate separation whilst avoiding the conflict is desirable and within the purview of the present invention.  
         [0113]    An essentially non-filled, walled separation and containment vessel in accordance with the present invention may be defined radially outwardly of, and conveniently surrounding a part of, such a closed separation canister for rotation therewith, providing a means of centrifugal separation forces at maximum radius and maximum effective residence time because of the shallow contaminant separation and containment zone whilst not significantly increasing the volume of liquid contained in, and thus the inertia of, the main, reaction driven separation vessel.  
         [0114]    Expressed in accordance with the positional relationships described hereinbefore, the further separation and containment vessel, the canister, may be said to be disposed having outlet passage means and inlet passage means operable to attempt to convey liquid to the vessel at a rate greater than it can pass through having greater flow capacity than the outlet passage means to convey liquid to the vessel and maintain it filled in operation, and an impervious radially outer side wall extending around and along the rotation axis and forming an annular contaminant separation and containment zone extending radially inwardly from the side wall.  
         [0115]    The canister may simply sit between the contaminant separation and containment zone and the rotation axis, analogous to those described in the eleventh and twelfth embodiments in providing fluid rotor means for, and physically coupling the outer vessel rotation but with said radially outer side wall arranged to extend along the axis and upon which contaminants are deposited, operating on different (denser) parts of the contaminated liquid supplied to the separation apparatus.  
         [0116]    Referring now to FIG. 13, a thirteenth embodiment  1310  of centrifugal separation apparatus in accordance with the present invention is shown in sectional elevation, comprising the common features of housing  112  defined by base  114 , cover  116  and rotation axis  124 , in addition to inlet duct  118  extending through the base. It also has spindle  1322  fixed to, and extending from, the base along rotation axis  124  and along which spindle the housing inlet duct  118  extends as passage  1318  to cross drilling  1319 . Rotor means  1330  includes at least part of bearing means  1346  arranged to mount the rotor means on the spindle by way of a tubular axle  1344  and more particularly bearing bushes  1346   1  and  1346   2  disposed at opposite ends of the tubular axle arrangement to interface with the spindle  1322  and be lubricated by liquid at elevated pressure.  
         [0117]    As described briefly in respect of the seventh embodiment, the region  1360  between the spindle and tubular axle is supplied with liquid at high pressure and some of this is forced to pass through the interface  1364  between the bushes and spindle to lubricate them, thereafter being flung radially outwardly by the rotation.  
         [0118]    The rotor means  1330  comprises a walled separation and containment vessel  1332  defined by outer side wall  1334  and end walls  1336  and  1338 , the former being positioned axially to collect liquid flung outwardly by the bearing bush  1346   2  and the latter defining outlet passage means  1342 . The outlet passage means in turn defines within wall  1344  contaminant separation and containment zone  1340 .  
         [0119]    In keeping with the terminology employed hereinbefore, the tubular axle comprises inlet means, indicated generally at  1350 , and the region  1360  the inlet region. Also the interface gap  1363  between the bush  1346   2  and spindle through which liquid passes to the vessel wall  1334  may be considered as transfer passage means  1362 .  
         [0120]    Within the vessel  1332 , and supporting it with respect to the bearing bushes, is a further separation and containment vessel  1332   A  comprising an impervious outer side wall  1334   A  extending substantially parallel to the wall  1334  but spaced from both the zone  1340  and the tubular axle and joined to the latter by end walls  1336   A  and  1338   A , which walls define an essentially closed annular volume  1340   A  for containing liquid at elevated pressure.  
         [0121]    The further vessel  1332   A  is essentially a rotor canister as employed in prior separation apparatus and has associated therewith further transfer passage means, indicated generally at  1362   A , comprising one or more through apertures  1364   A  which couple the canister volume, and the pressure therein, to the inlet region  1360 , and further outlet passage means  1342   A , in the form of one or more tangentially directed reaction nozzles  1366   A  in the canister end wall  1338   A , which couple the canister volume to the housing. The further vessel  1332   A  differs from the vessel  132  also in that the further outlet passage means, as defined by the reaction nozzles  1366   A  has such flow capacity that it is not capable of passing liquid from the vessel at a greater rate than it is conveyed thereto, on this case from the pressurized source so that in operation the canister rapidly fills with, and is maintained filled with, the liquid. Thus in known manner the high pressure of liquid entering the canister is exchanged as it leaves through the nozzles for a reaction force that rotates the canister and tubular axle about the axis  124 , and, in doing so, subjects the liquid within the canister volume to centrifugal forces which cause solid contaminants to migrate towards the outer wall and be deposited thereon as a cohesive layer. That is, the canister volume  1340   A  defines a further contaminant separation and containment space  1340   A  adjacent to, and extending radially inwardly from, the radially outer wall  1334   A .  
         [0122]    As a consequence of the further vessel canister being filled with the liquid at elevated pressure derived from the supply to effect rotation, and as outlined in the introduction to this specification, the liquid passing therethrough also has a rotation related radial pressure gradient that limits the density of contaminant particles that can efficiently migrate to the outer wall and the effective radius thereof practicable for any particular through-flow rate and rotation speed available thereby. However, known design criteria can provide such canisters that efficiently remove significant, particularly dense, contaminants at modest and readily attainable angular speeds and radii, and the further vessel  1332   A  functions to provide for such separation.  
         [0123]    Notwithstanding the limitations of the further vessel in terms of particle density it can efficiently separate, insofar as it includes reaction turbine drive means and the vessel  1332  is supported coaxially thereabout, the further vessel  1332   A  thus comprises, indicated generally at  1370 , drive means for the vessel  1332  and such vessel provides simply and efficiently increased radius and longer effective residence time for a proportion of the liquid that enables separation of low density particles without significantly increasing the overall inertia of the rotor means by containing more liquid in an enlarged canister.  
         [0124]    The means by which the vessel  1332  and further vessel  1332   A  are juxtaposed and mounted with respect to the spindle is open to variation, but as illustrated, the vessel  1332  has, optionally, the skeletal, removable separation and containment module form  1332   1  similar to that  132 , of FIG. 1, which permits it to be releasably attached to, and removed from, the further vessel  1332   A  by way of ‘spider’ limbs and, enables such a vessel to be formed that is capable of being retro-fitted to existing centrifugal separation canisters, particularly where, as shown in FIG. 13, the liquid inlet comprises an existing outflow from bearing means that requires no modification of the spindle or canister of the existing apparatus.  
         [0125]    However, modification may be employed to optimize operation ranging form relatively simple measures, such as surface features in the bearing bush surfaces to facilitate delivery of liquid to the vessel  1332  at a rate that is more consistent with, but still less than, the rate at which it can leave by the outlet passage means  1342 ; or from a specific passage  1318   1  in the spindle, including the possibility of being from a different supply source and/or at different pressure from that required to make the further vessel  1332   A  rotate; or by way of one or more through-apertures in a wall of the further vessel canister, either specific to, and dimensioned for, this purpose or the reaction jet nozzles  1366  analogously to the seventh and eighth embodiments.  
         [0126]    It will also be appreciated that insofar as the further vessel  1332   A  operates filled with liquid at the same pressure as inlet region  1360 , the tubular axle  1344  is not essential to the functionality, although offering structural strength to the further vessel. Therefore, in appropriate circumstances the further vessel may be formed absent such tubular axle, in the manner of the eighth embodiment.  
         [0127]    It will be understood that whilst a convenient and compact arrangement may be formed by disposing the liquid filled further separation and containment vessel within the partially filled vessel, this may be disposed coaxially and coupled but separated axially. In particular the partially filled vessel need not have separation and containment zone at a greater radial distance than that of the fully filed canister if the desire to increase the capacity for separating particles of the same density without significantly increasing the weight of liquid rotated.  
         [0128]    The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the sprit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.