Screw Pump

Abstract

a screw pump including a pump housing in which a pump spindle is rotatably mounted with the involvement of a hydrostatic thrust bearing for absorbing the axial thrust which is produced at the spindle during operation, the hydrostatic thrust bearing being formed by a housing-fixed bearing surface, against which an end-face, spindle-fixed bearing surface of the pump spindle is indirectly supported, by virtue of the fact that the housing-fixed bearing surface and the spindle-fixed bearing surface form a bearing gap therebetween, which bearing gap is fed, in its central region, with a pressure fluid which flows out through the bearing gap in the radial direction, preferably into the intake region, and the hydrostatic pressure of which counteracts the axial thrust.

Claims

1. A screw pump comprising a pump housing, in which a pump spindle is rotatably mounted with the involvement of a hydrostatic thrust bearing to absorb the axial thrust created during the operation on the spindle, wherein the hydrostatic thrust bearing is formed by a housing-fixed bearing surface, against which an end-face, spindle-fixed bearing surface of the pump spindle is indirectly supported, in that the housing-fixed and the spindle-fixed bearing surface form a bearing gap therebetween, which, in its central region, is fed with a pressure fluid, which flows out through the bearing gap in the radial directionpreferably into the suction regionand the hydrostatic pressure of which counteracts the axial thrust, wherein the pump spindle includes an actuating element, which, as a function of the current axial position of the spindle, mechanically opens or closes a valve, which controls the inflow of pressure fluid into the bearing gap.

2. The screw pump according to claim 1, wherein the valve is operated as throttle valve, the opening degree of which controls the hydrostatic pressure in the bearing gap.

3. The screw pump according to claim 1, wherein the actuating element is a pin, which opens or further opens said valve as soon as the bearing gap falls below a certain gap height due to an axial displacement of the pump spindle.

4. The screw pump according to claim 3, wherein the valve consists of a valve ball, which is pushed onto a valve seat assigned thereto by means of the pressure fluid and then blocks the inflow opening, which is located in the center of the valve seat and which leads to the bearing gap and which, if necessary, is lifted off its valve seat by means of the pin, which engages through the inflow opening, or is further lifted off its valve seat.

5. The screw pump according to claim 1, wherein the housing-fixed bearing surface is formed on the bottom of a bearing pot, with which an end-side bearing journal of the pump spindle, which forms a spindle-fixed bearing surface on the end face, engages in such a way that the outer circumferential surface of the bearing journal and the inner circumferential surface of the bearing pot form an annular gap seal, via which the pressure fluid flows out of the bearing gap in a throttled mannerpreferably into the suction region.

6. The screw pump according to claim 5, wherein the bearing pot rests axially against a wall of the pump housing, but is not fixed in a positive manner with respect to the pump housing in the radial direction.

7. The screw pump according to claim 5, wherein the bearing pot rests axially against a wall of the pump housing and is fixed in a positive manner with respect to the pump housing in the radial direction, for instance by means of pins or screws.

8. The screw pump according to claim 7, wherein the outer circumferential surface of the bearing journal and the inner circumferential surface of the bearing pot form a hydrodynamic radial bearing.

9. The screw pump according to claim 1, wherein the pressure fluid is the fluid pumped by the screw pump and which is removed from the pressure side of the screw pump.

10. The screw pump according to claim 5, wherein the bearing journal has a decreased diameter with respect to the immediately adjacent pump spindle region.

11. The screw pump according to claim 2, wherein the actuating element is a pin, which opens or further opens said valve as soon as the bearing gap falls below a certain gap height due to an axial displacement of the pump spindle.

12. The screw pump according to claim 2, wherein the housing-fixed bearing surface is formed on the bottom of a bearing pot, with which an end-side bearing journal of the pump spindle, which forms a spindle-fixed bearing surface on the end face, engages in such a way that the outer circumferential surface of the bearing journal and the inner circumferential surface of the bearing pot form an annular gap seal, via which the pressure fluid flows out of the bearing gap in a throttled mannerpreferably into the suction region.

13. The screw pump according to claim 2, wherein the pressure fluid is the fluid pumped by the screw pump and which is removed from the pressure side of the screw pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 shows a generic screw pump in half-section.

[0054] FIG. 2 shows the region of the thrust bearing in the sectional view, wherein an axial force is not yet applied to the spindle.

[0055] FIG. 3 shows the region of the thrust bearing in the sectional view, wherein an axial force is applied to the spindle.

DETAILED DESCRIPTION

[0056] The basic mode of operation of the generic screw pumps has already been explained above on the basis of FIG. 1, to which reference is made.

[0057] The further development according to the invention of the screw pump will be explained in an exemplary manner on the basis of FIGS. 2 and 3, but also with a sideways glance at FIG. 1, which forms the starting point.

[0058] The principle of the thrust bearing 8 according to the invention as well as of the valve 15 shall be explained initially in very general terms.

[0059] A pressure acting on the fluid to be conveyed results on the pressure side of the screw pump 1 during the operation of the screw pump 1. This results in an axial force, which acts on the running spindle 4 and which pushes the latter in the direction of the thrust bearing 8, in FIG. 2 from the right to the left.

[0060] The thrust bearing 8 comprises a housing-fixed bearing surface 9 and a spindle-fixed bearing surface 10.

[0061] The housing-fixed bearing surface 9 is formed here by the bottom of a bearing pot 12. For the most part, the spindle-fixed bearing surface 10 is formed by the end face of a bearing journal 13. A bearing gap 11 is always located here between the two bearing surfaces 9 and 10. Even if the spindle 4 were to rest with its shoulder 25 on the thrust bearing 8, which is usually not the case during the error-free operation of the screw pump 1, the two bearing surfaces 9 and 10 generally do not rest on one another.

[0062] A pressure fluid, which, in the case of this exemplary embodiment, is a portion of the fluid to be conveyed, which is located on the pressure side of the screw pump 1, flows into the bearing gap 11 via the return duct 23 as well as the chamber 24 and the inflow opening 18 of the valve 15.

[0063] At the same time, the pressure fluid located in the bearing gap 11 initially flows radially to the outside. It subsequently flows out of the bearing gap 11 via the gap between the bearing pot 12 and the bearing journal 13.

[0064] As long as the volume flow flowing into the bearing gap 11 and the volume flow flowing out of the bearing gap 11 are of equal size, an at least approximately hydrostatic stress state results in the pressure fluid at least in the central region of the bearing gap 11when the running spindle 4 experiences axial thrust as a result of the pressure prevailing on the pressure side of the screw pump 1 and is thus pushed in the direction of the thrust bearing 8. The spindle-fixed bearing surface 10 can then be indirectly supported on the housing-fixed bearing surface 9 via the pressure fluid.

[0065] Without the actuating element in the form of the pin 14, the valve ball 16 would be moved in the direction of the valve seat 17 by means of the pressure fluid flowing through the chamber 24 and would close the inflow opening 18 of the valve 15. As soon as the volume flow flowing into the bearing gap 11 is reduced due to the valve ball 16, which approaches the valve seat 17, more pressure fluid flows out of the bearing gap 11 than flows into it.

[0066] In combination with the axial force acting on the spindle 4, this results in a movement of the spindle 4 in the direction of the thrust bearing 8 and therefore in a reduction of the distance between the bearing surfaces 9 and 10. However, the actuating element in the form of the pin 14, which is located on the spindle-fixed bearing surface 10, together with the spindle 4 is thereby also moved in the direction of the valve ball 16. In the course of this, the pin 14 comes into contact with the valve ball at some point and prevents a complete closure of the inflow openings 18 through the valve ball 16 or pushes the valve ball 16 further into the chamber 24, respectively.

[0067] The movement of the spindle 4 and of the pin 14 as a result of the pressure on the pressure side of the screw pump 1 in the direction of the thrust bearing 8 continues until the valve ball 16 has been pushed into the chamber 24 to the extent that the volume flow flowing to the bearing gap 11 and the volume flow flowing out of the bearing gap 11 are in balance. A hydrostatic state then approximately results again in the pressure fluid located in the bearing gap 11, and the spindle-fixed bearing surface 10 is indirectly supported on the hosing-fixed bearing surface 9 via the pressure fluid. The movement of the spindle 4 in the direction of the thrust bearing is thus stopped.

[0068] The volume flow flowing into the bearing gap 11 thus always results independently as a function of the pressure prevailing on the pressure side of the screw pump 1 as well as of the position of the spindle 4, so that a state of balance is created.

[0069] A state of the screw pump 1 is illustrated in FIG. 2, in which pressure is not yet applied on the pressure side to the fluid, which is pumped through the screw pump 1. An axial force pushing the running spindle 4 in the direction of the thrust bearing 8 thus also does not yet act on the running spindle 4. The fluid located in the return duct 23 is additionally not under pressure yet. As long as an axial force does not yet act on the running spindle 4, the distance between the bearing pot 12 of the thrust bearing 8 and the shaft shoulder 25 at the transition between the bearing journal 13 and the remaining running spindle 4 is still relatively large. The actuating element embodied as pin 14 is additionally not yet in contact with the valve ball 16 of the valve 15. Due to the fact that no flow prevails in the return duct 23 and the chamber 24, the valve ball 16 rests on the bottom of the chamber 24 and not on the valve seat 17 of the valve due to the force of gravity.

[0070] The state of the spindle pump 1 is shown in FIG. 3, in which the spindle 4 has already been moved in the direction of the thrust bearing 8 as a result of a pressure prevailing on the pressure side of the spindle pump 1. Only a minimal gap, which cannot be seen in FIG. 3, is thereby still located between the shaft shoulder 25 and the bearing pot 12. The pin 14 is already in contact with the valve ball 16 and lifts the latter off the valve seat 17.

[0071] The valve seat 17 of the valve 15 as well as the inflow opening 18 are introduced into a wall element 19, which is located between the remaining pump housing 2 and the bearing pot 12. The bearing pot 12 is secured against a shifting or twisting along the wall element 19 via a pin 20. An axial securing of the bearing pot 12 with respect to the wall element 19 is not required because the forces resulting on the thrust bearing 8 always push the bearing pot 12 in the direction of the wall element 19. An O-ring seal 22 is located between the wall element 19 and the remaining pump housing.

[0072] In cooperation with the pressure fluid, which flows out of the bearing gap 11 through the gap between the bearing pot 12 and the bearing journal 13, the bearing pot 12 and the bearing journal 13 form a hydrodynamic radial bearing 21 for the spindle 4.