Load-relieving device

Abstract

An arrangement for compensating the axial thrust of a fluid-flow machine is provided. A load-relieving element is non-rotatably connected to a shaft. A flow-restrict gap is formed by the load-relieving element and a counter-element secured to a housing of the fluid-flow machine. The counter-element is provided with a device for maintaining the distance between the load-relieving element and the counter-element. The device includes at least one force-generating element that generates a force that acts in opposition to the axial thrust in order to avoid component contact.

Claims

1. An arrangement for compensating the axial thrust of a fluid-flow machine, comprising: a rotatable shaft; a casing configured to receive the shaft; a load-relieving element configured for conjoint rotation with the shaft within the casing; a counter-element configured to be non-rotatably fixed to the casing, the counter element and the load-relieving element being arranged to cooperate to form a radial flow-restrictor gap therebetween; and a distance-maintaining element configured to prevent the radial flow restrictor gap between the counter element and the load-relieving element being closed, the distance-maintaining element including at least one force-generating element configured to generate a force opposed to an axial thrust created during rotation of the shaft within the casing.

2. The arrangement as claimed in claim 1, wherein the distance-maintaining element includes an axially movable element movable along a longitudinal axis of the shaft.

3. The arrangement as claimed in claim 2, wherein the at least one force-generating element is arranged between the counter-element and the axially movable element.

4. The arrangement as claimed in claim 3, wherein a sliding bearing element is arranged on the axially movable element.

5. The arrangement as claimed in claim 4, wherein the counter-element includes a guide for the axially movable element.

6. The arrangement as claimed in claim 5, wherein at least one sealing element is arranged between the axially movable element and the counter-element.

7. The arrangement as claimed in claim 6, wherein the counter-element includes an opening between a first space in which the force-generating element is located and to a second space.

8. A method for compensating the axial thrust of a fluid-flow machine having a rotatable shaft, a casing configured to receive the shaft a load-relieving element configured for conjoint rotation with the shaft within the casing, a counter-element configured to be non-rotatably fixed to the casing, the counter element and the load-relieving element being arranged to cooperate to form a radial flow-restrictor gap therebetween, and a distance-maintaining element configured to prevent the radial flow restrictor gap between the counter element and the load-relieving element being closed, the distance-maintaining element including at least one force-generating element configured to generate a force opposed to an axial thrust created during rotation of the shaft within the casing, comprising the acts of: generating a force opposing the axial thrust with the at least one force-generating element.

9. The method as claimed in claim 8, wherein during the act of generating the opposing force, the opposing force moves an axially movable element of the distance-maintaining element along a longitudinal axis of the shaft.

10. The method as claimed in claim 9, wherein the at least one force-generating element is arranged between the counter-element and the axially movable element, a sliding bearing element is arranged on the axially movable element, and the axial movement of the axially movable element causes the sliding bearing element to contact the load-relieving element in a manner that prevents contact between the load-relieving element and the counter-element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an arrangement for compensating the axial thrust installed in a centrifugal pump in accordance with embodiments of the present invention.

(2) FIG. 2 shows a detail of an axial section through a multi-stage centrifugal pump in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) FIG. 1 shows a centrifugal pump having a shaft 1, which carries a plurality of rotors 2. The rotors are surrounded by a stepped casing 3. The pumping medium flows through a discharge casing 4.

(4) An axial flow-restrictor gap 8 is formed between a restrictor sleeve 6, which is connected to the discharge casing 4, and a component 7, also referred to as a piston, which is connected for conjoint rotation to the shaft 1 and on the outer circumference of which a polyetheretherketone layer is preferably provided.

(5) Pumping fluid is diverted from the high-pressure region of the centrifugal pump through the axial flow-restrictor gap 8 and routed as a load-relieving flow.

(6) The spaces 9 and 10 shown in FIG. 2 are filled with fluid. This is preferably the pumping medium of the centrifugal pump. During the operation of the centrifugal pump, the pressure in space 9 is significantly higher than in space 10. A load-relieving element 11 is arranged between the high-pressure space 9 and the low-pressure space 10. In the illustrative embodiment, the load-relieving element 11 is a balancing disk. The load-relieving element 11 is connected for conjoint rotation to the shaft 1.

(7) The pressure difference p=p9p10 acting on the surfaces of the load-relieving element 11 results in a load-relieving force opposing the axial thrust Fax. In the illustrative embodiment, the axial thrust acts from left to right when looking at the drawing. The load-relieving force generated by virtue of the pressure difference p=p9p10 acts from right to left when looking at the drawing.

(8) A radial flow-restrictor gap 13 is formed between the load-relieving element 11 and a counter-element 12. The counter-element 12 is firmly connected to the casing.

(9) If the axial thrust changes during operation and the load-relieving force falls, the rotor moves in the direction of the intake side of the pump and the radial flow-restrictor gap 13 becomes narrower. Owing to the greater restriction across the flow-restrictor gap 13, the pressure p9 increases, as does therefore the load-relieving force. If the load-relieving force is greater than the axial thrust, the excess force moves the rotor toward the rear side of the pump, and the flow-restrictor gap 13 becomes larger. This has the effect that the pressure p9 acting on the load-relieving element and also the load-relieving force fall again. Force equilibria, at which a flow-restrictor gap of about 0.05 to 0.1 mm is formed, are established at the rotor. The load-relieving element 11 acts as a self-regulating hydrodynamic thrust be in the arrangement according to the invention.

(10) To ensure that the system remains stable and the control movements do not take place too quickly, the axial flow-restrictor gap 8 must be designed in such a way that a radial flow-restrictor gap 13 of more than 0.01 mm and less than 0.12 min is established.

(11) The relatively small load-relieving flow is advantageous when using a balancing disk as a load-relieving element 11 ensuring that high volumetric efficiencies are achieved. In the case of conventional balancing disks, the increased susceptibility to gear was previously a disadvantage.

(12) In the device according to the invention, wear is prevented by a device for maintaining the distance between the load-relieving element 11 and the counter-element 12 when starting up and/or shutting down. According to the invention, the device is arranged on the counter-element 12. The device comprises a force-generating element 14. The force-generating element 14 generates a force opposed to the axial thrust when starting up and/or shutting down, said force ensuring that a distance is maintained between the load-relieving element 11 and the counter-element 12.

(13) The device for maintaining the distance has an axially movable element 15. The force-generating element 14 is arranged between the axially movable element 15 and the counter-element 12 fixed in relation to the casing.

(14) The device furthermore comprises a sliding bearing element 16, which is supported by the axially movable element 15. For this purpose, the axially movable element 15 has a recess 17, in which the sliding bearing element 16, which is designed as a ring, is arranged. The recess 17 is designed as a circular groove.

(15) The end of the sliding bearing element 16 faces the load-relieving element 11. The sliding bearing element 16 is composed of polyetheretherketone (PEEK).

(16) The sliding bearing element 16 preferably has a structured end facing the load-relieving element 11 and having channels (not shown). A sliding bearing lubricated by the medium is thereby made possible.

(17) During startup and shutdown, the pressure difference p=p9p10 is so small that the load-relieving element 11 would rest against the counter-element 12 if an axial thrust were to occur. This rubbing of the load-relieving element 11 against the counter-element 12 would lead to considerable wear phenomena.

(18) In the arrangement according to the invention, the force-generating element 14 moves the axially movable element 15 from right to left when looking at the drawing. During this process, the sliding bearing element 16 rests on the load-relieving element 11, which has an armored region 18 on the side facing the sliding be g element 16. During startup or shutdown, a sliding bearing lubricated by the medium is thus created between the load-relieving element 11 and the sliding bearing element 16. Rubbing of the load-relieving element 11 against the counter-element 12 is prevented in this case.

(19) As soon as a sufficient pressure difference p=p9p10 has built up between the two spaces 9 and 10, a flow-restrictor gap is established between the load-relieving element 11 and the counter-element 12. An increased pressure p9 also acts on the end of the sliding bearing element 16. Owing to this pressure p9, the axially movable element 15 is moved from left to right when looking at the drawing. The device is now in its retracted operating position.

(20) The arrangement according to the invention thus provides a device which disengages during startup or shutdown and thus moves from right to left, and moves back into its operating position during the operating state and is thus moved from left to right when looking at the drawing.

(21) The axially movable element 15 has a first groove 19, in which a sealing element 20 designed as an O-ring is arranged. Moreover, the axially movable element 15 has a second groove 21, in which a sealing element 22 designed as an O-ring is arranged. Sealing elements 20 and 72 separate the high-pressure space 9 from the low-pressure space 10.

(22) The counter-element 12 has an opening 23, which connects a space in which the force-generating element 14 is arranged to the load-relieving space 10. The opening 23 is embodied as a pressure equalizing bore.

(23) When the delivery pressure falls during shutdown, the axially movable element 15 moves back into its advance position and prevents the e restrictor surfaces from running up against one another.

(24) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.