GB1573244A

GB1573244A - Internally meshing screw pump

Info

Publication number: GB1573244A
Application number: GB1007077A
Authority: GB
Original assignee: Foerdertechnik Streicher GmbH
Current assignee: Foerdertechnik Streicher GmbH
Priority date: 1977-03-10
Filing date: 1977-03-10
Publication date: 1980-08-20

Description

(54) IMPROVED INTERNALLY-MESHING SCREW PUMP (71) We, FÖRDERTECHNIK STREICHER GMBH of D-7953 Bad Schussenreid, Schlosshof, West Germany; a German Body Corporate and MAX STREICHER of D-7988 Wangen/Allgäu Oderstrasse 28, West Germany; a German National do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns an internally meshing screw pump, hereafter called an eccentric screw pump with a screw shaped helical worm rotor, which rotates in a planetary fashion in a multiple hollow spiral within a stator casing which accommodates the cross-section and pitch of the rotor whereby enclosed cavities are formed between the rotor and the part of the hollow spiral which lies about it, and progress helically from an entrance and to an exit end of the casing of the stator.

Eccentric screw pumps are employed for many different purposes, especially for the conveyance of pulpy and viscous material, and material which contains solid particles.

Such pumps are naturally aspirated and can produce relatively high pressures, which depend on the ratio of stator length to pitch.

The material to be conveyed can thereby be partly crushed or homogenised and solid particles pulverised, or, if the stator consists of a yielding substance like rubber, the material can also alternatively be conveyed unchanged.

Due to the relative rotation between the rotor and the stator there arise relatively large pressure and friction stresses, which often lead to rapid wear of the internal contour of the stator spiral. Also with the radial action on the casing the wear is occasionally so great that the stator casing has to be changed after a very short time. The running costs of these pumps are relatively high because of the necessity for the aforesaid repairs.

This invention has as an object to decrease the wear in eccentric screw pumps and to lower their running costs.

To solve this problem, as an experiment a number of interchangeable ring-shaped wear elements were arranged behind one another in an axial series in the zone of friction between rotor and stator. Whereas heretofore the basic consideration was exclusively that continually moving screw surfaces rubs against one another, here the continuous surface of at least one of these two parts is divided into individual, radially running disc planes and on the contact surface individual interchangeable wear elements are provided as discs. With the exception of special cases one is able to use exactly identical wear elements which can be produced in bulk and therefore cheaply and can be changed without much difficulty.

The invention accordingly provides an internally meshing screw pump or so called eccentric screw pump, with a helical screw rotor which rotates in a planetary fashion in a stator which has internal helical grooves with which the rotor engages and is matched to the cross section and pitch of the rotor whereby between the rotor and the part of the hollow spiral lying about it, enclosed helical cavities are formed and precess axially from an entrance end to an exit end of the stator casing, wherein the pump is divided into a plurality of successive angularly staggered pump stages, the helical spiral surface of the screw rotor being formed by a number of stepped annular surfaces angularly displaced with respect to one another and each supporting on it a relatively rotatable ring, and the multiple hollow spiral of the stator being formed by an equal number of step-shaped staggered internal ring surfaces each forming a bearing path for the respective rotat able ring and having substantially the same width as the respective rotatable ring and the ring surface of the associated pump stage.

Replacement of rotatable rings is especially easy if the wear elements are fixed as rotatable rings against one another and against the rotor, so that they rotate axially thereon. This can be changed without any specialist skill. As the rotable rings can turn relative to the rotor, various rotation phenomena, which are caused by radial misalignment in some parts of the rotor, or by solid particles which have been carried along and similar causes are transformed into individual regular rotation processes and thereby the friction on the stator casing and with this its wear is greatly decreased.

The rotatable rings can be kept particularly braceable against one another by an adjusting device attached to the free end of the rotor between the ring shoulders. One can then also balance out by adjustment the wear on the rotating rings particularly when they show yielding material and from time to time introduce one or more additional wear rings.

Depending on the application it can be advantageous if the rotatable rings at least on their outer surfaces which roll against the hollow spiral, has a layer of particularly resilient. yielding wear material. In this way in some circumstances the whole resilience which is necessary for the conveyance of solid particles can be transferred to the rotating rings, i.e. the stator can basically consist of hard, wear-resistant material. At present a wear-resistant, self lubricating synthetic material particularly polytetrafluoroethylene (PTFE) is preferred as wear material.

According to a further suggestion a preferably continuous layer of wear resistant material is applied to the inner and outer surfaces of at least one lateral face of each rotatable ring. This is of particular importance when using self lubricating wear materials, as then the friction af these rings against one another, against the rotor and against the stator are eased.

In the simplest version the rotatable rings consist entirely of such a wear material.

They can be curved diagonally internally and externally to fit the curved surfaces of the stator and rotor, for which O-rings with a circular cross-section for example would be suitable. In so far as the rotating rings consist of a slightly deformable material or of a material which slides easily over metal, they can also be alternated with metal intermediate rings.

According to a further version rotating rings may be provided each comprising at least two joined ring elements, of which at least one consists of metal and one, on at least one border area, consists of wear material. For example a metal core ring can be covered all round with wear material.

For this it is preferable to have a core ring with a square cross-section which is surrounded by a ring casing with a barrelshaped external section. The core rings can then be produced by separation from a cylindrical tube, and in the middle of the ring there arises a relatively thick cushion of wear material, while the frontal areas are kept even and thereby by means of the large surface construction improved relative setting and insulation can be attained.

The production of the casing can be simplified if a casing ring of wear material has a side ring opening bordered by holding lips for subsequent insertion of the core ring whereby preferably one lateral face of the core ring juts out at least into the other lateral face of the rotating ring, there wear material and metal slide on one another.

The core ring can for example have a T-shaped cross-section, whereby the flange ends are surrounded by the holding lips and the stem and juts out into the proper lateral face of the rotating ring. The core ring and the casing ring can also have a barrel-shaped cross-section, whereby the core ring is displaced to the side against the casing ring. The axial holding power is then reduced in one direction, so that here subsequent connection by prevulcanization, adhesives or similar must be considered.

According to a further model a rotating ring has at least two coaxial ring elements fitted inside one another and rotatable against one another. By this means the turning control is placed in the rotating ring, so the inner ring element can be fastened to the rotor.

A core ring can accordingly be designed to be between two casing rings, which surround it from outside, or where applicable, from within, in a U-shape. The core ring can turn relative to at least one of these casing rings, but can be fastened if required to the other and it is completely sealed off from outside.

Furthermore a rotating ring can have two metal ring bearings aligned against one another on one side by a ring shoulder. In this purely metal friction bearing one ring can be made of steel and the other of a suitable bearing material.

Sliding friction during the rotation process can be replaced by rolling friction, if the rotating ring has a roller bearing installation with distributed rolling bodies like balls, rollers or barrels about its circumference. This is relatively simple if a rotating ring is formed as a wear material cage for the rolling bodies. In the rotating ring only the recesses required for the rolling bodies have to be provided, which roll bodies directly on rotor and stator.

However the bearings can also be installed on ring surfaces of the rotor, by steps offset sideways from each other. If the rotor itself is designed to be in one piece, then between the inner ring and the seating area a diagonally divided or resilient, deformable seating ring must be added to render possible the passage of the inner ring over the steps.

The rotor, however, can also be formed by individual, cylindrical rotor discs, whose thickness corresponds to the width of the bearing, whereby each disc is mounted, twisted against the neighbouring disc by an rector angle of displacement that remains uniform. The discs need then only be centred on the rotor axis and after the adjustment for fitted such that they can be turned on one another. For example the rotor discs with respective eccentric bores can sit on a cylindrical shaft set in the rotor axis and at times be fixed to this such that they do not run, in particular they engage in a screw-shaped key groove in the shaft with an inner projecting key. In the case of thick discs it is possible to set the projecting keys obliquely in accordance with the inclination of the screw.It is always possible to produce the discs economically by a single or at the most twofold punching prcoess or broaching process and then join them together as required on whatever length of rotor is wished.

In place of or in addition to the rotatable rings there can be fitted also on the inner surface of the stator casing, behind one another, individual oval wearing rings fitted onto the spiral cross-section of the casing, for example in inward opening grooves in the stator casing. If the stator casing in the above manner consists of individual, ring-shaped stator discs, radially, angularly displaced with respect to one another by rector angle of displacement, then it is recommended alternately to provide the first stator discs with a smaller and the second stator discs with a larger oval perforation and to retain the wearing rings thereby.

The first stator discs can then have wear material at least on the inside, as long as they do not consist entirely of such material.

Preferably, however, the wearing rings should be fixed in the plane of the second stator discs between the first stator discs.

If such wearing rings consist of plastics material, they can be removed if the tension between the stator discs is decreased sufficiently.

The material of such wearing rings or the material of the rotatable rings can according to the particular specifications can be chosen as required. If the most important thing is smooth running and the conveyance of solid particles without any great fragmentation, then a resilient plastics material should be used. Where solid particles are to be ground or crushed, hard, abrasive material like sintered metal or similar should be employed. One can use wearing ringsand/or rotating rings of differing composition in the same pump and re-equip the unchanged pump- simply by replacing such rings for conversion from one application to another.

At present an embodiment is preferred in which rotor and stator are composed of discs of equal width, whereby rotatable bearing rings fitted on the rotor discs have cylindrical inner and outer surfaces. By this means the rotor discs can be held through a polygonal array of ribs and grooves evenly distributed about the circumference so that it cannot turn on a notional shaft central to the rotor axis. Such an axial shaft and if necessary the a rod required to brace the rotor should then extend along particular pump length. The pump can be constructed as required in a very short time from cheaply available discs and rotating rings, from which results sealing between neighbouring stepped, confined, spiral-shaped cavities on partly cylindrical surfaces.

The polygonal array can for example run in helical screw shape and have the same pitch as the rotor spiral. All rotor discs are then fixed on the shaft in the same starting position and screwed on to this; Indeed the array can also run parallel to the rotor axis, if the division of its ribs and grooved is equal to the ratio of disc width to pitch.

The figures give different versions of the invention as examples. In the drawings: Fig. 1 is a longitudinal section corresponding to Fig. 1 through an eccentric screw pump according to the invention constructed of rotor stator discs of equal width; Fig. 2 shows a section through this pump along the line in fig. 1.

Fig. 3 is a longitudinal section through a double pump corresponding with Fig. 2; Fig. 4 shows an embodiment of rotatable bearing ring in two parts; Fig. 5 is a section through a rotatable ring with a covered, circular core ring; Fig. 6 is a section through a rotatable ring with a barrel-shaped core ring section; Fig. 7 is a similar section of a square cored rotatable cross-section.

Fig. 8 is a section through a rotatable ring with a T-shaped core ring cross-section with the side surface of the stem cut away; Fig. 9 is a section through a rotatable ring corresponding to Fig. 6 with the side surface of the core ring cut away; Figs. 10-12 are cross-sections through friction bearing-rotating rings.

Figs. 13-15 are cross-sections through firotating rings formed as roller bearing cages: Fig. 16 shows a rotating ring with roller bearing covered inside and outside; Fig. 17 shows a part-longitudinal section through a second embodiment screw rotor with stepped cylinder surfaces provided and with roller bearings set over intermediate rings.

Fig. 18 shows a part-longitudinal section through further embodiment screw rotor of individual joined rotor discs with ball bearings set on them: and, Fig. 19 shows a section along the line IX/IX in Fig. 18.

In the first embodiment shown in Figs. 1 and 2 the rotor and stator are both divided into individual equally wide ring-shaped rotor discs 451 and stator discs 538 with a continuous cylindrical shaft 461 and cylinder ring shaped relatively rotatable rings 163. The rotor discs 451 are braced against each other and against a shoulder of the shaft by nuts 60 which are screwed at the thread end 61 of the shaft 461 The external surface of the shaft is provided with a grooved edge 62 in the manner of a screw gear wheel along the whole circumference which is preferably formed by triangular teeth. The same grooved profile is fitted on the inner surface of disc 451 and can be achieved by a screw-shaped pressing or broaching process. The screw pitch corresponds to the sine curve 63 of the pitch of the centre screw spiral of the rotor.All discs 451 can therefore be screwed on this in the same direction of alignment which can be determined by markings on the discs and the shaft. Thereby consecutive, individual pump planes can be joined from rotor discs 451, rings 164 and stator disc 538. In any case the bearing rings 163 should be drawn on at the same time as the rotor discs 451. The stator discs 538 can also be assembled later with their oval perforations 54. They are subsequently braced by a tie rod 64 between entry tube support 2 and exit tube support 3 or between, separately mounted end flanges, after the stator discs have aligned themselves over the rotating rings in peripheral direction. For radial centring a cylindrical casing can also be drawn over the stator discs.

Here individual, sickle-like spaces 65, bordered by radial planes sometimes joined together rotationally displaced relative to one another by an angular step and thereby form step-shaped arranged cavities 121, which in longitudinal direction are divided from one another sometimes by at least one partly cylindrical sealing point 111. While rotor and stator discs are suitably stamped from steel one uses for the rotatable rings 163 corresponding to their particular application, for example a suitable wear resistant artificial material. Also these rings can basically consist of metal for example a bearing metal like bronze or in the manner previously described from several different materials.

Instead of the screw-shaped grooved profile 62 one can use the kind of profile which runs parallel to the shaft axis, if the division of the individual teeth corresponds to the division necessary through the width of the discs. One need then only remove the rotor discs 451 sometimes relatively displaced by an angular step. Equally the engagement in a single screw-shaped key slot can be used.

The advantage of the above described embodiment lies above all in the fact that merely the relatively simply formed shaft 461 and the tie rod 64 must be suited to the pumped length. Rotor and stator discs can equally like the rotating rings be stored in large numbers and then as necessary be constructed on the required pump length.

Through the width of the partly cylindrical sealing surfaces there is a remarkable security of wear and with this a considerable increase in the running live span is achieved with only one set of rotating rings.

The pump shown in Fig. 3 differs from Fig.

1 and 2 merely by the fact that each disc packet is divided into two single packets, between which a ring sleeve 66 is held by pipe supports 67. Thereby under little changed pressure ratios fluid from two outer pipe supports 2 to the pipe supports 67 or vice versa according to the direction of rotation here serving as outlets 4 or inlets, versa from this to the outer pipe supports 2 twice as much material can be conveyed.

To avoid friction losses between rotor and stator discs it can be expedient for example to renew the rotor discs from their seat on the shaft 46 from outside a little.

Originating from a short hub part, the outer side surfaces can be set back by about 2 or 3 mm while the slip rings 561 have the same width as the stator discs 538. As experiments prove no pressure losses arise from this especially as considerably greater running pressures can be achieved than with conventional eccentric screw pumps.

Figs. 4 to 16 illustrate different possible embodiments of rotatable rings for use in place of ring 163 or 561. According to Fig. 4 rotating rings 151 are divided into inner rings 22 and outer rings 23. These rings can be attached firmly to one another but also turn against one another in the joint face 24. The joint face is designed here as a tongue-groove-engagement for axial security. For example the inner ring 22 can consist of metal and sit on the rotor, firmly pressed thereon and sealing, while the outer ring 23 of PTFE or other yielding artificial material or rubber can be drawn on under stress, yielding and therefore sealing as it lies on the inner contour 13 and will glide on the joint face 24.The inner surface 25 and outer surface 26 of these rotating rings are so strongly curved diagonally that they fit all curves of the contour 13 and the outer surface of the rotor shaft.

In the rotatable ring 152 in Fig. 5 there is a core ring 27, circular in cross-section, surrounded by a sheath ring 28 of suitable wear material. In the rotatable ring 153 in Fig. 6 the core ring 271 has a barrel-shaped cross-section and is covered in a coat 281 of wear material. This coat can for example have a greater thickness on the outside than on the other three sides.

Similarly the rotatable ring 154 in Fig. 7 has a core ring 272 with a square crosssection, which makes possible particularly easy production through the division of a cylindrical tube. The coat 282 is then strengthened like a cushion by the curving outside and inside, whereby the outer layer can be thicker than the inner one.

In the rotatable rings of Figs. 5 and 7 the ring and coat can be joined together by the coating in one piece. According to Figs.

8 and 9 these parts can be produced separately then inserted into one another, which does not exclude one from joining them firmly together bv, say, vulcanisation. The core ring 273 in Fig. 8 has T-shaped crosssection, the jacket 283 of this rotating ring 154 has a U-shajed cross-section, clasps the flange ends with the inward reaching projections of its holding lips 29 and encloses the stem so that its end surface 30 juts out at least into the joint slide surface. In this ring area the material of the core ring can also glide on the material of the jacket of the neighbouring ring.

The rotatable ring 155 in Fig. 9 has, like its core ring 274, a barrel-shaped crosssection, whereby again an end surface 301 of the core ring at the side is exposed.

The axial holding power of the holding lips 291 is relatively small there so that a later to be produced firm connection of the core ring 274 with the jacket 284 is recommended.

The rotating ring 156 in Fig. 10 has also a barrel-shaped cross-section, whereby the inner ring 221 corresponds to the inner ring, say 22 in Fig. 4. Also the joint face 241 here has the same shape, but is formed against a T-shaped core ring 275 with a Ushaped jacket 285. This jacket can be fixed firmly or loosely, or where applicable so that it can turn. In any case it can be turned against the inner ring 221 in order to execute a small rolling movement on the rotor.

According to Fig. 11 for the rotating ring 157 a metal core ring 272 is completely enclosed by two ring caps 32, 33 which are U-shaped in cross-section. The core ring can be fitted so that it will turn against one or both ring caps.

In the rotating ring 158 of Fig. 12 the core ring 272 with ring bearing 34 angular in cross-section forms a metal friction bearing. Both rings are likewise surrounded by U-shaped ring caps 321 and 311 of wear material. The core ring 272 can consist for example of steel, the ring bearing 34 of a suitable bearing metal like bronze. The axial pressure which arises through runningin one direction is transferred metallically through the side shoulder 35.

The rotatable ring 159 of Fig. 13 is of an resilient wear material and has recesses 36 in even circular pitch for hardened steel balls 37. The recesses 36 can be designed as continuous cylindrical bores, which have -a smaller diameter than the steel balls 37, so that these are held fast in the wear material under a light spring pressure, but otherwise roll directly between rotor and stator. The steel balls can thus take over the crushing while the sealing is effected by the wear material.

The rotating ring 160 of Fig. 14 is formed similarly except that barrel-shaped rotating bodies 371 are inserted instead of balls.

In the rotating ring 161 of Fig. 15 the steel balls 37 are driven in a metal cage 38 whereby the space between the outer surfaces of the metal cage and the steel balls is filled with wear material. This should not happen in such a way that the steel balls do not bind with the wear material. Before they are coated they should therefore be covered with a suitable separative material.

The rotating ring 162 of Fig. 16 shows a normal ball bearing 39 with steel balls 37 passed between the inner ring 40 and the outer ring 50 and side seals 42. Again ring caps 322 and 332 serve to fit it on the smooth surfaced contours of the rotor and stator and afford an additional side seal.

According to the second embodiment of Fig. 17 the rotor is divided corresponding to its screw run into stepped, cylindrical seats 43, joined on to one another, to take up the ball bearing rotating rings 391, whereby the outer ring 41 presents a diagonally curved outer surface. So that the inner ring 14 can be pushed on to is seat, here a separated seat ring 44 must be actuated. Such a seat ring can for example be formed by a metal ring divided diagonally into two half rings or consisting of a resilient material like rubber, which can be pushed up over the shoulder surfaces on to the particular seat. The outer ring 41 can above all when the stator consists of rubber like material roll directly on its inner contour, or here again a ring cap can be fitted as the cap covering off Fig. 16 is inserted in the model of Fig. 17.

The construction of the seat makes it further possible as in Fig. 18 and 19, to divide the rotor into individual cylindrical rotor discs 45 which need only be swung round their eccentric shaft core against one another in corresponding order of the seats 431. These discs can be bound individually by screws provided at the circumference or a similar location. However it is better to set them with an eccentric bore on a shaft 46 central to the rotor axis 8 and have them engage with a projecting key 47 in a screwshaped key groove 48 in the shaft. Instead of a single key groove, of course several grooves or smaller grooves divided equally along whole circumference and instead of the key projection 47 several smaller inner projections are provided. The discs 45 can be cheaply mass-produced as stamped parts.The ball bearings 39 are inserted here unchanged and can be drawn on without intermediate seat rings. If the rings run directly on the inner contours of the stator spiral, the outer rings 41 could be surrounded by a curved layer 49 of wear material.

WHAT WE CLAIM IS: 1. An internally meshing screw pump or so called eccentric screw pump, with a helical screw rotor which rotates in a planetary fashion in a stator which has internal helical grooves with which the rotor engages and is matched to the cross section and pitch of the rotor whereby between the rotor and the part of the hollow spiral lying about it, enclosed helical cavities are formed and precess axially from an entrance end to an exit end of the stator casing, wherein the pump is divided into a plurality of successive angular staggered pump stages, the helical spiral surface of the screw rotor being formed by a number of stepped annular surfaces angularly displaced with respect to one another and each supporting on it a relatively rotatable ring, and the multiple hollow spiral of the stator being formed by an equal number of step-shaped staggered internal ring surfaces each forming a bearing path for the respective rotatable ring and having substantially the same width as the respective rotatable ring and the ring surface of the associated pump stage.

2. An eccentric screw pump according to claim 1 characterised by the bearing elements which are as rotatable rings against one another and against the rotor such that they can be turned axially thereon.

3. An eccentric screw pump according to claim 2, characterised by the fact that the rotatable rings are held particularly braced against one another by an adjusting device mounted on the free rotor and between ring shoulders.

4. An eccentric screw pump according to claims 2 or 3 characterised by the fact that the rotatable rings at least on their outer surface which rolls in the hollow spiral have a layer of particularly elastic, resilient wear material.

5. An eccentric screw pump according to claim 4 characterised by the fact that the wear material is formed of a wear resistant, low friction artificial material, particularly polytetrafluoroethylene.

6. An eccentric screw pump according to claims 4 or 5 characterised by the fact that a preferably cohesive layer of wear resistant material is fitted on the inner and outer surface and at least one side surface of the rotating rings.

7. An eccentric screw pump according to claim 6 characterised by the fact that the rotatable rings consist entirely of wear resistant material.

8. An eccentric screw pump according to any of Claims 2 to 7, characterised by the fact that the rotatable rings are diagonally curved inside and outside.

9. An eccentric screw pump according to claim 8 characterised by the fact that the rotatable rings are formed as O-rings with a circular cross-section.

10. An eccentric screw pump according to any one of Claims 6 to 9 characterised by the fact that rotatable rings and metal intermediate rings are alternatively axially joined to one another.

11. An eccentric screw pump according to any one of the Claims 4 to 6 or 7 to 10, characterised by the fact that rotatable rings are provided formed of at least two ring elements held together, of which at least one consists of metal and one on at least one side consists of wear material.

12. An eccentric screw pump according to Claim 11, characterised by the fact that a metal core ring is surrounded by wear resistant material on all sides.

13. An eccentric screw pump according to claim 12, characterised by the fact that a core ring with a square cross-section is surrounded by a ring casing with a barrel shaped outer cross-section.

14. An eccentric screw pump according to claim 12, characterised by the fact that a covering ring of wear material exhibits a side ring opening bordered by hilding lips for the later insertion of the core ring.

15. An eccentric screw pump according to claim 14 characterised by the fact that a side surface of the core ring protrudes at least into the outer side surface of the rotating ring.

16. An eccentric screw pump according to claim 15 characterised by the fact that

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. like material roll directly on its inner contour, or here again a ring cap can be fitted as the cap covering off Fig. 16 is inserted in the model of Fig. 17. The construction of the seat makes it further possible as in Fig. 18 and 19, to divide the rotor into individual cylindrical rotor discs 45 which need only be swung round their eccentric shaft core against one another in corresponding order of the seats 431. These discs can be bound individually by screws provided at the circumference or a similar location. However it is better to set them with an eccentric bore on a shaft 46 central to the rotor axis 8 and have them engage with a projecting key 47 in a screwshaped key groove 48 in the shaft. Instead of a single key groove, of course several grooves or smaller grooves divided equally along whole circumference and instead of the key projection 47 several smaller inner projections are provided. The discs 45 can be cheaply mass-produced as stamped parts.The ball bearings 39 are inserted here unchanged and can be drawn on without intermediate seat rings. If the rings run directly on the inner contours of the stator spiral, the outer rings 41 could be surrounded by a curved layer 49 of wear material. WHAT WE CLAIM IS:

1. An internally meshing screw pump or so called eccentric screw pump, with a helical screw rotor which rotates in a planetary fashion in a stator which has internal helical grooves with which the rotor engages and is matched to the cross section and pitch of the rotor whereby between the rotor and the part of the hollow spiral lying about it, enclosed helical cavities are formed and precess axially from an entrance end to an exit end of the stator casing, wherein the pump is divided into a plurality of successive angular staggered pump stages, the helical spiral surface of the screw rotor being formed by a number of stepped annular surfaces angularly displaced with respect to one another and each supporting on it a relatively rotatable ring, and the multiple hollow spiral of the stator being formed by an equal number of step-shaped staggered internal ring surfaces each forming a bearing path for the respective rotatable ring and having substantially the same width as the respective rotatable ring and the ring surface of the associated pump stage.

the core ring has a T-shaped cross-section whereby the flange ends are surrounded by the holding lips and the stem end protrudes into the respective side surface of the rotating ring (154) (Fig. 8).

17. An eccentric screw pump according to claim 15, characterised by the fact that core ring and covering ring have a barrelshaped cross section and the core ring is displaced to the side against the covering ring.

18. An eccentric screw pump according to claim 11, characterised by the fact that a rotating ring shows at least two co-axial ring elements arranged within one another and rotatable against one another.

19. An eccentric screw pump according to claim 18 characterised by the fact that a core ring is fitted between two U-shaped covering rings, surrounding it from the outside or inside.

20. An eccentric screw pump according to claim 18 or 19 characterised by the fact that a rotating ring exhibtis two metal bear ing rings directed against one another by guide plates.

21. An eccentric screw pump according to claim 20 characterised by the fact that the bearing rings are supported directly against one another on one side by a ring shoulder.

22. An eccentric screw pump according to any one of the claims 2 to 21 characterised by the fact that the rotating ring shows a roller bearing arrangement with rotating bodies distributed around its circumference like balls, rollers or barrels.

23. An eccentric screw pump according to claim 22 characterised by the fact that a rotating ring is formed as a cage of wear material for the rotating bodies.

24. An eccentric screw pump according to claim 23 characterised by the fact that a metal cage is embedded in the wear material of the rotating ring.

25. An eccentric screw pump according to claim 22 characterised by the fact that complete roller bearings with metal inner and outer rings sealed against one another at the side are provided.

26. An eccentric screw pump according to any one of the claims 18 to 21 or 25 characterised by the fact that the bearings are mounted on stepped ring surfaces twisted sideways to one another of the rotor.

27. An eccentric screw pump according to claim 26 characterised by the fact that between the inner ring and the seat there is a diagonally divided or elastic, resilient seating ring fitted.

28. An eccentric screw pump according to claim 26 characterised by the fact that the rotor is formed of individual cylindrical rotor discs whose width is suited to the width of the bearing, whereby each disc is fitted angular displaced relative to the neighbouring disc by a constant angular step.

29. An eccentric screw pump according to claim 28 characterised by the fact that the rotor discs with an eccentric bore sit on a cylindrical shaft arranged in the rotor axis and are fastened to this so that they cannot turn.

30. An eccentric screw pump according to claim 29 characterised by the fact that the rotor discs engage in a screw-shaped key groove in the shaft with an inner key projection.

31. An eccentric screw pump according to one of the claims 28 to 35 characterised by the fact that rotor and stator are composed of discs of equal width.

32. An eccentric screw pump according to claim 36 characterised by the fact that rotating rings fitted on the rotor discs have a cylindrical inner and outer surface.

33. An eccentric screw pump according to claim 36 characterised by the fact that the rotor discs are held by a many-sided profile of evenly distributed ribs and slots on the circumference such that they will not turn on the shaft central to the rotor axis.

34. An eccentric screw pump according to claim 38 characterised by the fact that the many-sided profile runs in a screw shape and has the same pitch as the rotor spiral.

35. An eccentric screw pump according to claim 38, characterised by the fact that the many-sided profile runs parallel to the rotor axis and the division of its ribs and slots is the same as the ratio of the disc width to pitch.

36. An internally meshing screw pump or so called eccentric screw pump substantially as hereinbefore described with reference to Fig. 1 to 3, or figs. 1 to 3 as modified in any one of Figs. 4 to 16; or in Figs. 17 and 18 or Fig. 19.