Screw pump

Abstract

A screw pump with a housing; a housing cover; at least one idler screw held in a bore in the housing; and a bushing arranged on the housing cover with a receiving space bounded by a cylindrical flange, into which one end of the idler screw engages; wherein the bushing has an opening in its base, through which a fluid, supplied by a feed channel in the cover, can be supplied from the end opposite the idler screw under pressure to the end surface of the idler screw, wherein the bushing engages with radial play in a receptacle in the cover and comprises a radial flange, by which it is supported axially on the housing; and wherein at a least certain part of the ring-shaped flange of the bushing engages in the bore and is accommodated therein with play.

Claims

1. A screw pump, comprising: a housing; a housing cover; at least one idler screw held in at least one bore in the housing; and at least one bushing arranged on the housing cover; each bushing of the at least one bushing has a receiving space bounded by a cylindrical flange, into which one end of one of the at least one idler screw engages, wherein each bushing of the at least one bushing has a base with an opening, through which a fluid supplied by a feed channel in the housing cover can be supplied from an opposite end of each idler screw of the at least one idler screw, relative to the base, under pressure to an end surface of each idler screw of the at least one idler screw within the receiving space, wherein each bushing of the at least one bushing has a radial flange that engages with radial play in a respective receptacle in the housing cover, the receptacle being open toward the housing, the radial flange being supported axially on the housing; and wherein the cylindrical flange of the bushing engages at least in sections in the bore and is accommodated therein with play so that the bushing floats.

2. The screw pump according to claim 1, wherein the cylindrical flange engages over its entire length in a respective bore of the at least one bore.

3. The screw pump according to claim 1, wherein each bushing of the at least one is configured as an aperture in the area of the opening.

4. The screw pump according to claim 3, wherein the opening has a constant diameter over its entire length, or the opening comprises a first section of constant diameter on an inlet side, followed by a second section facing the end surface.

5. The screw pump according to claim 4, wherein the opening with the constant diameter or the second section merges with a circular distribution section open toward the end surface.

6. The screw pump according to claim 4, wherein a ratio of a length of the opening of constant diameter to the diameter of the opening is <1.

7. The screw pump according to claim 1, wherein, between the housing cover and the at least one bushing, a ring-shaped seal is arranged, the diameter of which is between ±10% than a diameter of the end surface of the at least one idler screw.

8. The screw pump according to claim 7, wherein the seal is seated in an annular receptacle in the base of the at least one bushing or in the housing cover.

9. The screw pump according to claim 1, wherein the receiving space, in which a cylindrical end of the at least one idler screw engages, expands conically in a radial direction toward the at least one idler screw.

10. The screw pump according to claim 9, wherein the receiving space opens with an angle in a range of 5-15° between an axis through a center of the receiving space and an inner surface of the conical expansion in the receiving space.

11. The screw pump according to claim 9, wherein an area of the conical expansion extends over at least half of a length of the cylindrical flange.

12. The screw pump according to claim 9, wherein, in an area of the base of the at least one bushing, a ring-shaped collar reducing a diameter of the cylindrical flange is provided.

13. The screw pump according to claim 1, wherein the at least one bushing is prevented from rotating by a securing element.

14. The screw pump according to claim 13, wherein the securing element is a pin, which engages in a bore in the housing cover or in the housing and also in a receptacle formed in an end surface of the base or laterally in the radial flange.

15. The screw pump according to claim 1, wherein two or more idler screws of the at least one idler screw are provided in associated bores of the at least one bore, to each of which a bushing of the at least one bushing is assigned.

16. The screw pump according to claim 15, wherein each of the bushing of the at least one bushing communicates and is supplied simultaneously with fluid through a common feed line.

17. The screw pump according to claim 4, wherein the second section is conically expanding.

18. The screw pump according to claim 10, wherein the angle is in a range of 8-12°.

19. The screw pump according to claim 18, wherein the angle is 10°.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the drawing:

(2) FIG. 1 shows an exploded view, in perspective, of part of a screw pump according to the invention;

(3) FIG. 2 shows a screw pump according to the invention partially in cross section;

(4) FIG. 3 shows a cross-sectional view corresponding to FIG. 2 with additional cross sections of the bushings and idler screws;

(5) FIG. 4 shows a cross-sectional view in a plane oriented 90° to the plane of FIG. 3;

(6) FIG. 5 shows a perspective view of a bushing of the screw pump;

(7) FIG. 6 shows a cross-sectional view through the bushing of FIG. 5;

(8) FIG. 7 shows a magnified, detailed view of the area labeled VII in FIG. 6;

(9) FIG. 8 shows a cross-sectional view through a bushing of a second embodiment; and

(10) FIG. 9 shows a screw pump according to the invention, partially in cross section, over its entire length.

DETAILED DESCRIPTION OF THE INVENTION

(11) FIG. 1 shows a partial, exploded view of a screw pump 1 according to the invention. What is shown is a housing 2, in which a first bore 3 for holding a drive screw is formed in the middle, and in which, laterally offset from that, two additional bores 4, 5 are formed, each of which accommodates an idler screw, which meshes with the drive screw. The screws are not shown. The bores 4, 5 holding the idler screws extend up to a point directly level with the end surface 6 of the housing 2.

(12) As shown is a housing cover 7, which is tightly screwed by suitable fastening screws to the housing 2 and thus closes it off.

(13) Also shown are two bushings 8, 9, which are part of a hydraulic thrust compensation system, by which the two idler screws are axially supported. The design and function of the bushings 8, 9 will be discussed further below. Two pins 10, 11 serve to hold the bushings nonrotatably in position; at one end, the pins are inserted into corresponding, blind holes 12, 13 in the housing, and at the other end they fit into appropriate lateral recesses 14, 15 in the bushings 8, 9. This prevents the bushings 8, 9 from being rotated by the idler screws, which are inserted into them.

(14) FIG. 2 shows the screw pump 1 of FIG. 1, partially in cross section, wherein it is the housing 2 which is shown in cross section. What can be seen first is the drive screw 16 and the two idler screws 17, 18, wherein the corresponding profiles of the screws mesh with each other. The housing cover 7 is set onto the housing 2 and screwed to it. The two bushings 8, 9 have been pushed onto the idler screws 17, 18; that is, the ends of the screws have been inserted into the bushings 8, 9. It can be seen that each of the bushings 8, 9 has a cylindrical flange 19, 20, by which the bushings are accommodated with slight play in the bores 4, 5 in which the idler screws 17, 18 are held; by this means, the bushings 8, 9 are centered. At their other ends, they are held in corresponding receptacles 21, 22, which are formed in the cover. The base 23, 24 of each bushing is provided with a radial flange 25, 26, which, as will be explained further below, is supported against the end surface 6 of the housing 2.

(15) Also shown is a feed channel 34, which is formed in the housing cover 7, and from which two branch channels 35, 36 proceed, which run to the bushings 8, 9 and which therefore lead to the corresponding receptacles 21, 22. These channels make it possible to supply a pressure-compensating fluid, by means of which the axial thrust compensation is realized.

(16) FIG. 3 shows a cross section through the screw pump 1 according to FIG. 2, wherein the drive screw 16 and the two idler screws 17, 18 are also shown, and wherein the bushings 8, 9 are shown in cross section.

(17) It can be seen that the bushings 8, 9 are held in the corresponding receptacles 21, 22. Their radial flanges 25, 26 rest against the end surface 6 of the housing 2, which is possible because the bores 4, 5 extend all the way to the end surface 6, wherein the housing cover 7 rests directly on the end surface 6.

(18) The cylindrical ends 28, 29 of the two idler screws 17, 18 can be seen. It can also be seen that the ends 28, 29 of the screws fit into the bushings 8, 9. They are held in the bushings 8, 9 with minimum play, wherein there is in each case a receiving space 32, 33 formed between the base 23, 24 of the bushing and the associated end surface 30, 31 of the idler screw 17, 18; into this space, the fluid, i.e., the fluid to be conveyed by the pup, is introduced via the feed channel 34 and the two branch channels 35, 36. For this purpose, each bushing comprises an aperture opening 37, 38 in the base 23, 24; through this opening, the fluid supplied via the feed channel 34 and the branch channels 35, 36 can enter the receiving space 32, 33. The fluid flow is represented by the corresponding arrows in FIG. 3.

(19) The bushings 8, 9 are configured as apertures insofar as the associated openings 37, 38 are concerned, as will be explained further below. This means that, by means of these apertures or aperture openings, a defined, viscosity-independent pressure drop from the feed side with the feed channel 34 to the outlet side leading to the associated idler screw 17, 18 can be realized.

(20) As discussed, each of the bushings 8, 9 comprises a cylindrical flange 19, 20. It is with this flange that, as explained, the bushing engages with slight play in the associated bore 4, 5. In addition to its base 23, 24, each flange 19, 20 is provided on its interior surface with a cylindrical inside circumferential area 39, 40 (see FIG. 6 among others), which is followed in each case by a conically expanding area 41, 42 (see again FIG. 6). This configuration makes it possible to regulate the pressure. Depending on how deeply the end 28, 29 of the screw in question extends into the associated bushing 8, 9, an annular gap of greater or lesser size is formed, through which the supplied fluid can flow onward to the suction side of the pump. If the end 28, 29 of the screw is inserted deeply, then the associated end surface 30, 31 is located in the area of the cylindrical inside circumference, i.e., in the circumferential area 39, 40. When the idler screw 17, 18 is pushed back out somewhat by the pressure formed or generated in the receiving space 32, 33, the associated end surface 30, 31 moves into the conical expansion area 41, 42, so that an annular gap is produced, which becomes larger as the idler screw 17, 18 is pushed farther out. The fluid in the receiving space 32, 33 can escape through this annular gap to the suction side, as a result of which the pressure falls again, and the associated idler screw 17, 18 moves back into the bushing 8, 9 to some degree. Overall, this results very quickly in a static equilibrium state, in which the associated idler screw 17, 18 is hydraulically thrust-compensated.

(21) FIGS. 3 and 4 show the fluid supply of the thrust compensation system comprising the bushings 8, 9 configured and supported in the manner according to the invention. A fluid channel 43 running from the pressure side to the suction side, i.e., to the housing cover 7, is formed in the housing 2; this channel leads via a branch channel 44 to a fluid channel 45 in the cover, which for its own part leads to the feed channel 34. Insofar as necessary, the corresponding channels are closed by sealing plugs 46, 47. The fluid by which the hydraulic thrust compensation is achieved is therefore supplied from the pressure side at the corresponding pump pressure. This pressure acts on the bottom surface 48, 49 of each of the bushings 8, 9. This bottom surface 48, 49 is sealed off against the receptacle 21, 22 by a sealing element 50, 51. For this purpose, corresponding annular grooves 52 are formed in the bases 23, 24 of the bushings (see FIG. 6, where a cross-sectional view through the bushing 8 is shown by way of example), wherein the bushing 8 and the bushing 9 are of identical configuration.

(22) The bushings 8, 9 are held in the corresponding receptacles 21, 22 with slight radial play; they are therefore supported in a “floating” manner with lateral mobility. They are also held by their associated flanges 19, 20 in the bores 4, 5 with slight play, so that a floating support is obtained overall.

(23) This floating support is also retained even under load, i.e., when fluid is being conveyed. In this case, a defined pressure drop occurs across the openings 37, 38, configured as aperture openings, in the bushings 8, 9. This pressure drop is selected so that the force which pushes the bushings 8, 9 against the housing cover 7 (a force which results from the overcompensation attributable to the size of the associated end surfaces 30, 31 of the idler screws 17, 18) is reduced or minimized and compensated to such an extent that, in the loaded state, even though the bushings are pressed tightly against the housing cover 7 under compression of the associated sealing elements 50, 51, they are still able to move laterally, precisely because this resultant force has been largely compensated. This makes it possible for any lateral migration of the associated idler screw 17, 18 to be compensated; that is, the end 28, 29 of the screw in question pushes and carries along the associated bushing 8, 9 laterally, wherein this lateral offset, of course, occurs over a range only a few hundredths of a millimeter. In any case, however, the bushings 8, 9 can move to the side even under load, so that they follow the idler screws 17, 18 and the cylindrical flanges 19, 20 do not attack them abrasively.

(24) FIGS. 5-7 show a first embodiment of a bushing used in accordance with the invention, wherein the bushing 8 is shown by way of example. Bushing 9, of course, is designed in the identical way. It comprises a cylindrical flange 19, and also a radial flange 25, which laterally extends the base 23 of the bushing.

(25) The cross-sectional view of FIG. 6 and the magnified detailed view of FIG. 7 show in detail additional design features of the bushing 8. As can be seen, the conically expanding area 41 of the inside circumference extends over about half or somewhat more than half of the axial length of the flange 19; this is followed by a cylindrical inside circumferential area 39 with a constant diameter.

(26) The opening 37, which is configured as an aperture, is also shown. This area is shown magnified in FIG. 7.

(27) The opening 37 comprises, first, a first section 53, which has a constant diameter. The axial length of this section 53 is preferably equal to the diameter of this cylindrical opening, so that a ratio of 1 is obtained between the length of the opening and its diameter. Alternatively, the ratio can be less than 1; this would mean that the diameter is larger than the length of the opening.

(28) In the example shown, a conically expanding second section 54 follows this first section 53. In this area, the pressure is already beginning to drop, and the process continues in a following distribution section 55.

(29) As previously described, FIG. 6 shows the annular groove 52, in which the corresponding ring seal 50 is seated. The annular groove 52 and thus, after assembly, the ring seal 50 have a diameter which is approximately equal to the diameter of the inside circumferential area 39 and therefore to the diameter of the end surface 30 or 31 as well. This means that the surface at the bottom of the bushing against which the flow impinges is approximately equal to the end surface 30, 31, i.e., to the opposing pressure surface. The “flow impingement” surface is to be seen as the entire surface defined by the associated ring seal 50, 51, because, during operation, although the associated bushing 8, 9 is pressed against the housing cover 7, the bushing 8, 9 can be a certain minimal distance away from the housing cover 7 as a result of the defined pressure drop which has been produced and thus as a result of the equalization of forces, and therefore the fluid can distribute itself over the entire surface bounded by the associated seal 50, 51.

(30) During operation, as described above, the fluid is guided by the associated channel geometry to the associated aperture bushing 8, 9 and enters the associated receiving space 32, 33. The flow thus impinges on the associated end surface 30, 31, i.e., the opposing pressure surface. Because of the defined pressure drop attributable to the configuration of the associated aperture, the forces are largely equalized, so that only a relatively small resultant force occurs, by which the associated bushing 8, 9 is pressed against the housing cover 7, so that, now as before, a floating support is present even under load or pressure conditions.

(31) As a result of the geometry of the inside circumference of the associated bushing 8, 9 according to the invention, a static equilibrium state develops quickly and easily with respect to the axial position of the screw. For the pressure acting on the end surface 30, 31 in question moves the associated idler screw 17, 18 axially relative to the bushing 8, 9, resulting in a corresponding change in the cross section of the associated gap across which the fluid can flow away as leakage flow from the associated receiving space 32, 33, as a result of which a corresponding static state is reached.

(32) The assembly of this thrust compensation system is as easy as could be desired. After the housing 2 has been equipped with the drive screw 16 and the two idler screws 17, 18, the only additional step necessary is to push the two bushings 8, 9 onto the ends 28, 29 of the screws and to introduce the corresponding flanges 19, 20 into the associated bores 4, 5. This results in an automatic centering. At the same time, the bushings are prevented from rotating when the pins 10 engage in the corresponding lateral recesses 14, 15. The only remaining steps are to set the housing cover 7 in place and to position it circumferentially so that the bases 23, 24 of the bushings 8, 9 engage in the corresponding receptacles 25, 26, after which the housing cover 7 can be screwed down.

(33) FIG. 8, finally, shows an embodiment of a bushing 8 according to the invention (the same being true for the bushing 9), in which a ring-shaped collar 56 is formed additionally on the inside circumference in the area 39 with the effect of reducing the diameter at that point. The associated end surface 30, 31 can move against this ring-shaped collar 56 when the idler screw, for whatever reason, enters axially far enough. When the associated end surface 30, 31 runs up against the associated ring-shaped collar 56, the opposing pressure surface, against which the fluid acts, is decreased. Because no more fluid can flow away through the axially closed gap, a correspondingly high pressure builds up which pushes the idler screw back again in the axial direction. That is, the pressure in the associated receiving space 32, 33 increases, which has the effect of pushing the associated idler screw 17, 18 immediately back again out of contact with the associated ring-shaped collar 56, whereupon the static equilibrium state is immediately restored.

(34) FIG. 9, finally, shows a cross-sectional view through a screw pump 1 according to the invention, wherein the housing 2 consists here of several separate housing elements 57, which are assembled axially and connected to each other. It is possible to see the housing cover 7 and the axial thrust compensation system realized by the bushings 8, 9, by means of which the two idler screws 17, 18 are hydraulically thrust-compensated.

(35) While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.