US3814306A

US3814306A - Centrifuge with lubrication system therefor

Info

Publication number: US3814306A
Application number: US00249173A
Authority: US
Inventors: M Wutz; H Sinn
Original assignee: Heraeus Christ GmbH
Current assignee: Heraeus Sepatech GmbH
Priority date: 1971-05-06
Filing date: 1972-05-01
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04
Also published as: DE2122464C3; DE2122464A1; DE2122464B2; DE2138141A1; FR2135307B1; FR2135307A1; GB1390956A

Abstract

To provide a well lubricated thrust and running bearing, the housing of a centrifuge is formed with a projecting bearing pin over which a cup-shaped element extends which is rotatable over the pin, the cup-shaped element and the pin having cooperative bearing means at the interior wall of the cup-shaped element, and the elements are formed to provide for introduction of lubricant in the space between the interior wall of the cup-shaped element and the opposite projecting, facing surface of the pin, to provide for lubrication without splashing; in a preferred form, the cup-shaped element itself is the rotor of an electric drive motor, and formed internally with a hemispherical projection which fits into a similar hemispherical depression in the pin, the pin being formed with a duct for oil to be supplied under pressure, the oil being introduced in the space between the bottom surface of the cup-shaped rotor element and the top surface of the pin.

Description

United States Patent Wutz et a].

[ June 4, 1974 CENTRIFUGE WITH LUBRICATION SYSTEM THEREFOR Inventors: Max Wutz, Hanan/Main; Hartmut Sinn, Osterode/Harz, both of Germany [73] Assignee: Heraeus-Christ GmbI-I,

Gipsmuhlenweg Osterode/Harz, Germany [22] Filed: May I, 1972 [2]] Appl. 'No.: 249,173

[30] Foreign Application Priority Data May 6, I971 vGermany 2l22464 July 30, 197] Germany 2l38l4l [52] U.S. CI. 233/24 [51] Int. Cl B04b 9/02 [58] Field of Search 233/] R, l A, 23 R, 24, 233/1 B, l C, 27, 28

[ 56] References Cited UNITED STATES PATENTS 1,831,860 ll/l93l Harrison 233/24 X 3.289925 l2/l966 Zippe et fli 233/24 X 3,327,938 6/1967 Stallman 233/l R FOREIGN PATENTS OR APPLICATIONS 9/l96l Great Britain 233/1 C [57 ABSTRACT To provide a well lubricated thrust and running bearing, the housing of a centrifuge is formed with a projecting bearing pin over which a cup-shaped element extends which is rotatable over the' pin, the cupshaped element and the pin having cooperative bearing means at the interior wall of the cup-shaped element, and the elements are formed to provide for introduction of lubricant in the space between the interior wall of the cup-shaped element and the opposite projecting, facing surface of the pin, to provide for lubrication without splashing; in a preferred form, the cup-shaped element itself is the rotor of an electric drive motor, and formed internally with a hemispherical projection which fits into a similar hemispherical depression in the pin, the pin being formed with a duct for oil to be supplied under pressure, the oil being introduced in the space between the bottom surface of the cup-shaped rotor element and the top surface of the pin.

22 Claims, 5 Drawing Figures PATENTEDJUN 4mm 3.814306 SHEEI Q [If 4 CENTRIFUGE WITH LUBRICATION SYSTEM THEREFOR The present invention relates to a'centrifuge and a lubrication system therefor, and more particularly to an ultra high-speed centrifuge in which the substance to be centrifuged is held on a rotor, which is driven, and

secured in bearings which require lubrication.

. It has previously been proposed to locate the material to be centrifuged on a holder, supported by a shaft, which in turn is located above the drive elements which are held in a radial bearing. The axial forces of the centrifuge holder, which usually rotates over a vertical axis, are absorbed by tapered bearings, or by separate axial thrust bearings. The bearings can be sleeve bearings as well as ball bearings. To drive the centrifuges, motors providing output speed of from 20,000 to 100,000 rpm are customarily used. that is, motors of an intermediate frequency. Prime movers other than electric motors can be used, such as turbines or the like, or motors which are coupled to the centrifuge rotor over a gear transmission.

It has been found that, particularly at high speed, bearings which utilize ball bearing arrangements are sensitive to oscillations. Such bearings are usually lubricated by an oil vapor or oil mist and have been found to have a limited life. Bearings which are constructed in the form of sleeve bearings have problems in connection with supply of lubricant, typically lubricating oil, and removal of oil therefrom, particularly with respect to the bearing above the drive element. Such bearings may cause oil spray or splashes and oil vapor which are detrimental to the elements surrounding the bearings. This is particularly serious if the drive arrangement, be-

sides the rotor, is placed within a chamber or vessel which can be evacuated. Intensive oil lubrication is contrary to the use of direct drives with a vacuum. Additionally, known centrifuges do not effectively dissipate heat due-to bearing friction and from the drive motor.

It has been proposed to provide an oil pressure bearing, particularly for ultra centrifuges, in which the shaft passes through a chamber which carries a disk which is rigidly connected to the shaft. The chamber below the disk is connected to an oil pressure line. An oil outlet is formed in the chamber in the region of the level which the disk should have, when in operation (see German Publication Paper No. 1,285,4l2). Such an arrangement is not completely satisfactory for all applications, particularly if the drive arrangement is to be located within a housing which can be evacuated.

It is an object of the present invention to provide an ultra centrifuge, and more particularly a bearing system for ultra high-speed centrifuges which practically has no wear and tear, has long life, and which dampens oscillations, particularly of the rotor. Further, as a desirable feature of the invention, the bearing and the drive arrangement should be improved by better cooling of the components thereof.

Subject Matter of the Present Invention Briefly, the rotor shaft of the centrifuge, or an element rotatable with the shaft, is formed to be cupshaped, with the concave side directed away from the centrifuge rotor. A fixed pin extends into the hollow, or recess of the cup-shaped element, the bearing shaft (or the cup-shaped element secured thereto) being rotatably journalled on the pin. The space between the bottom of the cup-shaped element and the surface of the pin facing the rotor then has lubricant applied thereto. for example by flooding the space.

The bearing arrangement is practically free of wear and tear, even at extremely high speed, and will have long life. The bearing, additionally, acts as a dampening element with respect to oscillations. Oil splashes do not extend into the space surrounding the bearing, which is particularly important when the system operates in a vacuum. The lubricant can also act as a good conductor of heat, the heat being effectively removed so that the drive, particularly upon starting and acceleration, can be loaded substantially higher than heretofore possible. The axial or thrust bearing utilized in accordance with the present invention acts like a hydrostatic bearing and permits practically floating journalling of the rotatable portion. In a preferred form, the shaft on which the centrifugal rotor is located, is preferably at least partly flexible, and vertically arranged.

In accordance with a preferred feature of the inven tion, the surface of the axial pin directed towards the rotor has, at its terminal end, a depression which is preferably approximately hemispherical; the bottom of the cup-shaped element is formed with a corresponding projection, also preferably essentially hemispherical, and fitting into the depression. This arrangement increases the permissible loading on the bearing and reduces friction losses. Other shapes, such as conical surfaces, pin supports, point supports and the like can be used. a In accordance with a feature of the invention, lubricant is supplied under pressure through a central duct formed in the pin. If required, other ducts can be formed in various parts of the centrifuge, and the bearing elements, to provide reliable supply of oil under pressure.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a general schematic view of an ultra highspeed centrifuge with the bearing arrangement in accordance with the present invention, and supplied by oil under pressure;

FIG. 2 is a fragmentary vertical cross sectional view to a greatly enlarged scale illustrating a hydrostatic bearing;

FIG. 2a is a fragmentary detail view of another embodiment of an axial bearing arrangement;

FIG. 2b is a fragmentary axial cross-sectional view of another embodiment of a hydrostatic bearing arrangement; and

FIG. 3 is a fragmentary longitudinal cross-sectional view of a bearing arrangement, including a hydrodynamic brake.

Similar parts have been given similar reference numerals throughout the specification and, having once been described, will not be described again.

The general arrangement of the ultra high-speed centrifuge in accordance with the present invention is best seen in FIG. 1. A portion of the housing of the centrifuge 1 also includes a drive motor 2. This drive motor, in the illustration, is an electrical motor of intermediate frequency, having a rotor 3 which rotates about a fixed pin 4, secured in housing 1. Lubricating oil is supplied by a pump 5 over pressure line 6 into a central duct 15 (FIG. 2) formed in pin 4. It is supplied to the interior of cup-shaped body 3 at the inner end thereof (FIG. 2)

and returns over a return line 7 to pump 5, over an intermediate de-gassing element 8. Suitable filters can be inserted in the line where necessary. To provide for oil pressure at all times, even if the pump should become inoperative, a compressed gas or compressed air vessel 9 is connected to pressure line 6, with an intermediate check valve and choke connection 10. In ordinary, normal operation of the centrifuge, it is preferred to start the pump before the centrifuge itself is placed in operation, so that the bearing 14 (FIG. 2) will have lubricant under pressure applied thereto. The starting switch for the centrifuge may, therefore, first connectthe pump 5 and then, with a predetermined delay, for example controlled by time, or oil pressure, start the drive motor 'for the centrifuge. The centrifuge rotor 17 is secured to a shaft 24, and totally enclosed within housing 1.

The centrifuge shaft 24 is coaxial, and may be formed as one piece with the rotor 3 of themotor (FIG. 2). It is generally cup-shaped and is formed with an interior concave recess or hollow 11. Two sleeve bearings 12 are located within the cup-shaped body to space the body from pin 4. The motor itself has a stator 2, located 'within housing 1, and is separated from the rotor body 3 by a small gap 31. The sleeve bearings 12 are formed with slits or bores 13, extending in axial direction, in order to provide for return flow of oil from the interior of the cup-shaped body 3. The hollow surface of the cup-shaped body 3 can be so arranged that the sleeve bearings themselves are not necesrary, by forming projecting portions 12' thereon, acting, themselves, as axial spacer elements, as seen in FIG. 2a.

The bottom wall 25 of the hollow 11 has a projection 14 formed thereon, which acts as a projecting bearing element. It is freelyrotatable with respect to the facing surface 26 of pin'4, and can adjust itself axially and ,radially with respect thereto, to act as a thrust bearing. As seen in FIG. 2, projection 14 and facing surface 26 of the pin 4 both are essentially hemispherical, so that the thrust bearing formed of the projection and surface 26 will be free floating. Oil under pressure is supplied through bore 15 of pin 4. Additionally, radially extending ducts I6 supply oil under pressure to the bearing sleeves 12 (FIG. 2) or 12 (FIG. respectively. The outer surface 28 of the pin 4 will likewise have oil running thereover, the radially extending ducts l6 penetrating wall 28. The thrust bearing formed by projection 14 and matchingsurface 26 is formed as a hydrostatic bearing. The lubricant is preferably supplied by a volumetric pump having constant supply volume.

The pressure of the lubricant supplied by the pump depends to some extent on the weight of the rotor 17 secured to the flexible shaft 24, and the quantity of substance to be centrifuged to be placed therein. When the rotor 17 is removed from shaft 24, the pressure drops substantially, since the hydrostatic axial bearing is then loaded only by the rather light rotor 3 and the shaft 24, the weight of which itself is negligible. The pressure line 6 is preferably so arranged that, if the pressure in the line drops greatly, current to the motor is interrupted, if no rotor is secured in the centrifuge. Shaft 24, which under all circumstances is somewhat flexible, is thereby protected from operating at high speed and without a rotor. In operation, the oil applied to the bearing surfaces 12 and 26 is thrown and held against the cylindrical inner wall 27 of the cup-shaped hollow within element 3. The return oil is thereby guided away from the bearings, without further contact with the surface 28 of the central pin 4. At the outlet, the oil is collected practically without splashing in the sump 18 from which it is returned through an outlet 19 in housing '1 to the return circuit of the lubricating supply pump.

The hydrodynamic bearing for the centrifuge is generally hemispherical; as seen in FIG. 2b, the receiving surface, that is surface 26 of pin 4 is formed with spiral grooves, projection 14 fitting within this grooved, receiving recess. This arrangement further decreases friction losses, and provides a bearing for centrifuges which can be highly loaded and which is particularly suitable for extremely high rotational speeds of centrifuging apparatus. The bearing surface of the pin-4 not only is hemispherical, but formed as a hemispherical cup 32. This cup 32 need not be hemispherical, but may have other shapes, so long as the surfaces thereof correspond to the surface configuration of the projection 14 of the rotor element 3. The spiral groove in cup 32 may, for example, be in the form of an Archimedian spiral, when looked at in plan view. The side or radial bearings 12 may be sleeve bearings, or may be formed as ball bearings, roller bearings, needle bearings or the like, set in the space betweenthe pin 4 and the interior surface 27 of the cup-shaped element (FIG. 2), extending from the cup-shaped element (FIG. 2a) or being secured to the pin 4 (FIG. 2b).

High-speed centrifuges, particularly when supported by low-friction bearings will coast for an appreciable period of time even after the motor is disconnected. Braking effects can be obtained electrically. Independently'therefrom, or in addition thereto, a hydrodynamic brake may be provided, as seen in connection with FIG. 3. Housing 1 has a pair of

outlet openings

20, 21. During operation of the centrifuge, that is, when thecentrifuge is being driven, oil is removed from the housing 1 over bore 20, where it flows through a valve 22, preferably electrically operable, to the de-gasser, a filter if desired, and the suction inlet of pump 5. To effect hydrodynamic braking, valve 22 is closed so that oil now must flow through a braking duct 23, and then can escape from housing 1 only over bore 21 into a bypass line 30. The braking duct 23 is preferably so formed that, when valve 22 is closed, oil is directed counter the normal supply derived from pump 5. This, additionally, provides for some lubrication if the pump should fail and, under such emergency condition, provides for unloading of the thrust bearing. The rotating element 3- is formed with a duct 13, located between wall 29 and the inner surface thereof. Wall 29 can be a ring unitary with the housing 1, or separately secured therein.

The duct 23 is so arranged that at the inner surface thereof, grooves in the form of a spiral or thread are cut which are so directed that they rise in the direction of rotation of shaft 24, in order to choke or throttle the passage of oil therethrough and, in an extreme case, completely block oil passage, in order toprovide for counter pressure upon passage of oil through duct 23, when operating in braking mode.

Pin 4, and the matching interior surface of the concave element 3 need not be cylindrical, but other shapes, and particularly differences in diameter of pin 4 are equally suitable. As seen in FIG. 3, the pin is offset axially and decreases in diameter towards the interior of the rotor; the radial bearings 12 are located at points of different diameter. The pin 4 may also be formed in frustro-conical shape.

The outer housing 1 completely encloses the stator 2 of the motor, and is sealed around the lower part thereof, as best seen in FIG. 2. The centrifuge itself, together with the motor, can be supported by springs on a surface to reduce vibrations. The from the outer wall of housing 1 to the wall of the housing surrounding the rotor may be by means of a flexible interconnection, as

schematically shown in FIG. 1, from which vacuum generating means to evacuate the space in the region of the centrifuge rotor 17 have been omitted.

The radial bearings l2, l2 reduce oscillations and vibration and, in combination with the thrust bearing as disclosed, can operate at high speed with low wear and tear. The bearings 12 are preferably located in the region of the upper and lower ends of the central pin, to provide for reliable guiding and thus stabilization of the rotor and the suspension thereof on the thrust bearing. Forming the bearings unitary with either the central pin or the rotating element 3 is particularly advantageous when the radial bearings are formed as sleeve or sliding bearings, rather than as ball, pin, or needle bearings. Locating the radial bearings at points of different diameter has been found to be of particular advantage when the centrifuge is combined with a hydrodynamic braking arrangement (FIG. 3) so that braking forces will act on the rotatable elements of the centrifuge. The hydrodynamic brake is simple and does not contribute to heating of the rotor, as is the case with electrical braking. The braking forces due to hydrodynamic braking, additionally, are substantially higher than those arising with electrical braking, and no expensive switch-over circuits are necessary.

The arrangement whereinthe cup-shaped element simultaneously acts as a shield for the hydrostatic bearing, as well as a rotor for the electric motor is particularly advantageous, since the rotor is effectively cooled from the inside by the lubricant, whichadheres to the inner surface thereof by centrifugal force, and provides for particularly good heat transfer to the cooling oil. Thus, the motor can be located within the housing subject to evacuation, and can be highly loaded. The air gap can be additionally provided with a sealing arrangement, so as to be a sealed and to provide for highintensity oil lubrication without danger that the oil being removed from the bearing will be introduced into the space to be centrifuged by splashes. Use of a medium or center frequency motor has the advantage that it operates at high speed with low vibrations or oscillations. and utilizes a massive rotor which can be easily balanced. lts asynchronous starting permits high loading upon starting when the bearing and lubricating system in accordance with the present specification is used.

lf pump 5 supplying lubricant under pressure is, as is preferred, a constant volume supply pump, then pressure regulator 40 is preferably interposed in the pressure line of the fluid supply circuit, the pressure regulator 40 being responsive to weight of the rotor 17, to provide the proper amount of oil pressure between the spherical surfaces at the inner end of pin 4 and at projection l5 and thus to provide for hydrostatic support of the bearing surfaces.

Various changes and modifications may be made within the inventive concept.

We claim:

l. Centrifuge with lubricating system therefor comprising a housing (1); V

a rotor (17) having a shaft (24) holding the rotor at one end of the shaft and extending in generally vertical direction;

bearing means rotatably securing the rotor in the housing, the bearing means including afixed pin (4) secured to the housing (1);

a cup-shaped element (3) rotatable with the shaft (24) and secured thereto at the opposite end of the shaft surrounding the pin, the cupshaped element being formed with an internal hollow region (11);

hearing means located between the pin and the interior'surface 0f the hollow region (11);

and means introducing lubricant in the space between the bottom surface (25) of the hollow region (11) in the cupshaped element (3) and the surface (26) on the pin (4) facing said bottom surface (25) of the hollow region.

2. Centrifuge according to claim 1, wherein the surface (26) of the pin (4) facing the bottom surface (25) of the hollow region (11) of the cup-shaped body (3) is formed with a depression;

and the bottom surface (25) of the cup-shaped body (3) is formed with a projection l4) fitting into said depression.

3. Centrifuge according to claim 2, wherein the depression is hemispherical and the projection (14) is ballshaped. v

4. Centrifuge according to claim 1, further comprising at least one radial bearing located between the inner side wall (27) of the hollow region and the outer wall (28) of the pin (4).

5. Centrifuge according to claim 4, wherein at least two radial bearing means are provided, one each 10- catedadjacent the inner, and outer ends of the pin.

6. Centrifuge according to claim 4, wherein the radial bearing is unitary with the rotatable cup-shaped element.

7. Centrifuge according to claim 4, wherein the radial dimension of the inner surface of the cup-shaped element adjacent the inner end of the pin is less than the radial dimension adjacent the outer end of the pin;

and a radial bearing each is located adjacent said inner and outer ends, and having different radial dimensions.

8. Centrifuge according to claim 1, wherein the pin (4) is formed with a duct, said duct being connected to a lubricant supply under pressure and terminating adjacent the inner surface (26) of the pin to supply lubricant under pressure between said surface and the bottom surface (25 of the hollow region (11) of the cupshaped element (3).

9. Centrifuge according to claim 8, wherein the duct (15) is centrally located with respect to pin (4).

l0. Centrifuge according to claim 8, further comprising at least one radial bearing located between the inner side wall (27) of the hollow region and the outer wall (28) of the pin (4);

and lubricating supply ducts extending from said duct (15) in the pin to said radial bearings to include the space between the interior surface (27) of the rotatable element, and the outer surface (28) of the pin in the lubricant circuit.

' bricant fluid supply means is a volumetric pump 13. Centrifuge according to claim 11, including a pressure fluid supply (9) connected (10) to the lubricant fluid supply (6) to automatically place the lubricant under pressure.

14. Centrifuge according to-claim 11, including a drain opening (19; 20, 2]) formed in said housing (1) to remove lubricant fluid from the space between the interior surface of the rotatable element and the pin; and means (22) closing off drainage from said open- 15. Centrifuge according to claim 14, wherein a pair of drain openings (20, 21) are provided, located radially spaced from each other, and the housing is formed with an interior separating wall (29) located between the radially spaced openings, the radial interior opening being closable; and a bypass duct (30) interconnecting the radially outer opening with the return line of the lubricating fluid circuit.

16. Centrifuge according to claim 15, wherein the separating wall (29) is spaced from the rotatable element (3) by a small gap (23) forming a narrow duct.

l7. Centrifuge according to claim 16, wherein the separating wall is ring-shaped at least partly surrounding said rotatable element; and the separating wall, in the surface facing the narrow duct (23) is formed with a spiral thread extending towards the rotatable element, the thread rising in direction of the direction of rotation of the centrifuge in order to effect movementof the lubricating fluid counter the direction of fluid flow as deterimed by said fluid pressure supply means l8. Centrifuge according to claim 1 1, including control means (40) responsive to the weight of the rotor and controlling the pressure within the pressure supply 6) of lubricating fluid pressure supplied to the bearing means.

l9. Centrifuge according to claim 1, including electric drive means, said drive means being an electric motor located within the housing, the cup-shaped rotatable element forming the rotor for the-motor.

20. Centrifuge according to claim 19, wherein the motor is a center frequency motor, and the stator (2) of the motor is separated from the cup-shaped element (3) forming the rotor by a sealed gap (31).

21. Centrifuge according to claim 1, wherein the bearing between the surface (26) on the pin (4) facing the bottom surface (25) of the hollow region (11) of the cup-shaped rotatableelement (3) is formed as a hydrodynamic bearing (32).

22. Centrifuge according to claim 21, wherein the surface (26) of the pin (4) facing the bottom surface (25 of the hollow region (11) of the cup-shaped element (3) is formed with a depression having spiral grooves (32) formed therein to provide a grooved bearing cup;

and the bottom surface (25) of the cup-shaped body (3) is formed with a projection (l4),extending within said bearing cup and fitting therein, lubricant being introduced into said bearing cup and into said spiral grooves.

Claims

1. Centrifuge with lubricating system therefor comprising a housing (1); a rotor (17) having a shaft (24) holding the rotor at one end of the shaft and extending in generally vertical direction; bearing means rotatably securing the rotor in the housing, the bearing means including a fixed pin (4) secured to the housing (1); a cup-shaped element (3) rotatable with the shaft (24) and secured thereto at the opposite end of the shaft surrounding the pin, the cup-shaped element being formed with an internal hollow region (11); bearing means located between the pin and the interior surface of the hollow region (11); and means introducing lubricant in the space between the bottom surface (25) of the hollow region (11) in the cupshaped element (3) and the surface (26) on the pin (4) facing said bottom surface (25) of the hollow region.

2. Centrifuge according to claim 1, wherein the surface (26) of the pin (4) facing the bottom surface (25) of the hollow region (11) of tHe cup-shaped body (3) is formed with a depression; and the bottom surface (25) of the cup-shaped body (3) is formed with a projection (14) fitting into said depression.

3. Centrifuge according to claim 2, wherein the depression is hemispherical and the projection (14) is ballshaped.

5. Centrifuge according to claim 4, wherein at least two radial bearing means are provided, one each located adjacent the inner, and outer ends of the pin.

7. Centrifuge according to claim 4, wherein the radial dimension of the inner surface of the cup-shaped element adjacent the inner end of the pin is less than the radial dimension adjacent the outer end of the pin; and a radial bearing each is located adjacent said inner and outer ends, and having different radial dimensions.

8. Centrifuge according to claim 1, wherein the pin (4) is formed with a duct, said duct being connected to a lubricant supply under pressure and terminating adjacent the inner surface (26) of the pin to supply lubricant under pressure between said surface and the bottom surface (25) of the hollow region (11) of the cup-shaped element (3).

10. Centrifuge according to claim 8, further comprising at least one radial bearing located between the inner side wall (27) of the hollow region and the outer wall (28) of the pin (4); and lubricating supply ducts extending from said duct (15) in the pin to said radial bearings to include the space between the interior surface (27) of the rotatable element, and the outer surface (28) of the pin in the lubricant circuit.

11. Centrifuge according to claim 10, including lubricating fluid pressure supply means (5) to maintain lubricant supplied to the duct (15) under constant pressure during operation of the centrifuge.

12. Centrifuge according to claim 11, wherein the lubricant fluid supply means is a volumetric pump (5).

13. Centrifuge according to claim 11, including a pressure fluid supply (9) connected (10) to the lubricant fluid supply (6) to automatically place the lubricant under pressure.

14. Centrifuge according to claim 11, including a drain opening (19; 20, 21) formed in said housing (1) to remove lubricant fluid from the space between the interior surface of the rotatable element and the pin; and means (22) closing off drainage from said opening.

15. Centrifuge according to claim 14, wherein a pair of drain openings (20, 21) are provided, located radially spaced from each other, and the housing is formed with an interior separating wall (29) located between the radially spaced openings, the radial interior opening being closable; and a bypass duct (30) interconnecting the radially outer opening with the return line of the lubricating fluid circuit.

17. Centrifuge according to claim 16, wherein the separating wall is ring-shaped at least partly surrounding said rotatable element; and the separating wall, in the surface facing the narrow duct (23) is formed with a spiral thread extending towards the rotatable element, the thread rising in direction of the direction of rotation of the centrifuge in order to effect movement of the lubricating fluid counter the direction of fluid flow as deterimed by said fluid pressure supply means (5).

18. Centrifuge according to claim 11, including control means (40) responsive to the weight of the rotor and controlling the pressure within the pressure supply (6) of lubricating fluid pressure supplied to the bearing means.

19. CEntrifuge according to claim 1, including electric drive means, said drive means being an electric motor located within the housing, the cup-shaped rotatable element forming the rotor for the motor.

21. Centrifuge according to claim 1, wherein the bearing between the surface (26) on the pin (4) facing the bottom surface (25) of the hollow region (11) of the cup-shaped rotatable element (3) is formed as a hydrodynamic bearing (32).

22. Centrifuge according to claim 21, wherein the surface (26) of the pin (4) facing the bottom surface (25) of the hollow region (11) of the cup-shaped element (3) is formed with a depression having spiral grooves (32) formed therein to provide a grooved bearing cup; and the bottom surface (25) of the cup-shaped body (3) is formed with a projection (14) extending within said bearing cup and fitting therein, lubricant being introduced into said bearing cup and into said spiral grooves.