Pump shafts for multistage pumps

Abstract

The invention relates to a pump shaft for a multistage pump, in particular for a centrifugal pump, wherein the pump shaft comprises a circumferential groove region for engaging a relief device for introducing forces acting in the axial direction of the pump shaft into the pump shaft. The pump shaft is characterized in that the groove region in a longitudinal section of the pump shaft has a plurality of grooves spaced apart from one another in the axial direction.

Description

Technical Field

[0001] The invention relates to a pump shaft for a multistage pump and a pump having such a pump shaft. Background Art

[0002] In pumps, in particular centrifugal pumps, the fluid to be pumped is sucked in by means of a rotating shaft and delivered via an impeller which is driven in rotation by means of the shaft.

[0003] Since the impeller in a multistage pump - under certain conditions due to the impeller inlet opening - generates a lower pressure on the suction side and thus a lower force in the axial direction, an axial force in the direction of the suction side of the impeller is always generated. This axial force of the impeller is introduced into the shaft. In order to keep the shaft stationary in the housing, a hydraulically generated reaction force is applied to the pump shaft by means of a relief device.

[0004] In the multi-stage pump, the unloading device is connected to the shaft via a split ring and a fixed annular groove in the pump shaft. Engaging in the groove prevents undesired axial movement of the pump shaft relative to the housing.

[0005] The disadvantage here is that shaft fractures only rarely or occasionally occur at this point. This is evidence of a certain weak link in the shaft caused by the retaining ring groove. Since multistage pumps in the energy production sector have been stopped and restarted more and more frequently in recent years, the retaining ring groove is subject to very high mechanical loads, as a result of which the durable pumps have increasingly serious availability problems under changing operating conditions. As a result, the safety factors usually required to prevent fatigue fractures are no longer feasible. Summary of the invention

[0006] The object of the present invention is to overcome this disadvantage. This is achieved with a pump shaft or with a pump. The present invention significantly improves this weak link and also achieves a significantly improved fatigue strength of the pump shaft. The present invention also relates to further advantageous configurations.

[0007] According to the invention, the pump shaft for a multistage pump, in particular for a centrifugal pump, comprises a circumferential groove region for engaging a relief device for introducing forces acting in the axial direction of the pump shaft into the pump shaft. The pump shaft is characterized in that the groove region has a plurality of axially spaced grooves in a longitudinal section of the pump shaft, wherein the plurality of grooves are formed by grooves that are circumferential and independent of each other, or by a single-start or multi-start closed thread, wherein the respective groove bottoms of the plurality of grooves are designed in an arcuate shape in a longitudinal section.

[0008] The pump comprises a pump shaft as described above and a relief device which engages in a plurality of grooves of the groove region in order to introduce a force acting on the relief device in the axial direction of the pump shaft into the pump shaft.

[0009] Different from the above-mentioned background technology, the fixing ring groove for engaging the unloading device is no longer formed by only a single groove, but includes multiple grooves arranged side by side along the longitudinal section direction of the pump shaft. By arranging multiple grooves arranged side by side along the axial direction of the pump shaft, it is possible to construct a larger cross-sectional area of ​​the pump shaft in the groove area - compared with the case where only one groove is provided, this case may cause the groove to extend deeper into the pump shaft. In this way, the fracture tendency of the pump shaft in the groove area is extremely effectively resisted. Similarly, the average stress in this area is also reduced.

[0010] Unlike the prior art, the larger axial force is not introduced into a larger groove, but into the shaft in multiple and smaller grooves and then redirected in the opposite direction. This force redirection generates higher stresses in the groove radius of the shaft. In the case of multiple grooves, each groove only introduces and redirects a small part of the axial force and guides the remaining axial force through. This significantly reduces the stress in the groove bottom and has the result that the maximum stress in the groove bottom of the shaft is significantly reduced by this reconfiguration of the groove, that is, it can be reduced by about half.

[0011] It is also possible to increase the contact surface between the unloading device engaging in the groove and the shaft by means of a new and smaller groove. This significantly reduces the surface pressure in the contact surface. In a first calculation, this results in a reduction of the surface pressure in the contact surface by approximately half.

[0012] Preferably, the plurality of grooves are formed by circumferential grooves that are respectively independent of one another, or by single-start or multi-start closed threads.

[0013] It can be provided that the plurality of grooves define at least one ridge between their groove bases, the height of which corresponds to the outer edge of the groove region. In other words, each groove of the plurality of grooves causes at least one elevation between the grooves to be arranged at the same height (relative to the groove base) as an adjacent region of the groove region. This means that the ridges arranged between the grooves are not arranged at a deeper level than the outer edge of the groove region.

[0014] According to an advantageous development of the invention, it can be provided that the groove bottom of each of the plurality of grooves is designed to be arcuate in longitudinal section. This results in an advantageous groove in which an element engaging in the groove bottom can transmit higher axial forces.

[0015] In this case, the radii of the arcuate groove base can be provided to be different, wherein preferably such a radius of the groove arranged at the outer edge of the groove region is greater than the radius of the groove arranged in the middle section of the groove region.

[0016] Thus, a groove arranged at the edge of the groove region can have a groove bottom whose arcuate longitudinal section has a larger radius than other groove bottoms arranged in the groove region. It is particularly advantageous here if the groove with the larger arcuate groove bottom is arranged on the side facing the piston of the pump or at the edge of the groove region.

[0017] The different radii in the arcuate groove base result in a relatively uniform introduction of forces into the pump shaft.

[0018] According to another optional improvement of the present invention, it can be provided that the groove depths of the plurality of grooves are set to be different, wherein preferably, the groove depth of the grooves arranged at the outer edge of the groove area is lower than the groove depths of the other grooves arranged in the groove area. It is advantageous here when the groove depth of the grooves arranged on the side of the groove area facing the piston is lower. In addition, it can also be provided that the grooves at the edge of the groove area (seen in the longitudinal section direction) are provided with a groove bottom of a smaller depth than the grooves in the middle area of ​​the groove area.

[0019] According to a development of the invention, it can be provided that a plurality of grooves are separated from one another in the longitudinal direction of the pump shaft by a pump shaft section, the radius of which relative to the rotational axis of the pump shaft corresponds to the radius of the pump shaft adjoining the groove region.

[0020] According to a further preferred embodiment, a plurality of grooves are arranged in a sawtooth-like structure in a longitudinal section of the pump shaft, wherein preferably the respective tooth tips of the sawtooth structure have the same radius to the rotation axis of the pump shaft. Since the forces introduced into the pump shaft are caused by the piston of the pump, the sawtooth structure points with its steep sides towards the piston.

[0021] In particular, grooves similar to buttress threads according to DIN 2781 are suitable, since in this case almost no radial forces are introduced into the relief device engaging in the groove, so that this sawtooth shape is an ideal design for the present loads.

[0022] Furthermore, according to the invention, it can be provided that at least one of the respective groove bases of the sawtooth structure has a larger radius to the rotational axis of the pump shaft than at least one other groove base of the sawtooth structure.

[0023] Similarly, it can be provided that at least one groove bottom with a smaller radius is separated from an outer edge of the groove area as viewed in a longitudinal section by at least one groove bottom with a larger radius, wherein, preferably, at least one groove bottom with a smaller radius is separated from two outer edges of the groove area as viewed in a longitudinal section by at least one, preferably at least two, groove bottoms with larger radii.

[0024] According to a further development of the invention, a relief groove is provided in the pump shaft adjacent to the groove region for engaging the relief device, which relief groove is not used for engaging the relief device, wherein preferably, relief grooves are provided in the pump shaft at two outer edge regions of the groove region.

[0025] This leads to a reduction in the stresses in the grooves of the shaft, thereby achieving a more durable construction of the pump shaft.

[0026] In this case, it can be provided that at least one relief groove has a similar depth as the groove of the groove region.

[0027] In this case, the at least one relief groove can be designed in longitudinal cross section such that it slopes steeply on its groove side spaced apart from the groove region and is less steep on its groove side facing the groove region.

[0028] Furthermore, the invention relates to a pump, in particular a centrifugal pump, comprising a pump shaft according to one of the above-mentioned variants and a relief device, which engages in a plurality of grooves in the groove area for introducing forces acting on the relief device in the axial direction of the pump shaft into the pump shaft.

[0029] The unloading device can be provided as a split ring, which surrounds the pump shaft with its two sub-ring segments in the circumferential direction and is shaped on its inner circumference for engagement with a plurality of grooves in the groove region. Instead of the split ring, the unloading device can also be equipped with a similarly constructed one-piece ring. A similar thread is then also present here.

[0030] According to an optional modification of the invention, it is provided that the unloading device has a threaded element for engaging with a corresponding groove for at least one or all grooves of the groove region, as viewed in the longitudinal section direction.

[0031] It can be provided here that one of the multiple threaded elements is radially shortened, i.e., advances to a smaller depth into the rotation axis of the pump shaft than the other threaded elements, wherein preferably this radially shortened threaded element engages in a groove arranged at an edge of the groove area, in particular in the groove of the groove area that is closest to the piston.

[0032] It can also be provided that two radially shortened thread elements lie adjacent to one another and engage in two grooves at the edge of the groove region, preferably on the side of the groove region facing away from the piston.

[0033] In this case, the piston is formed on that side of the groove region which faces the force introduced into the pump shaft and directs this force into the split ring.

[0034] Preferably, the threaded element engaging in the grooves of the two edges of the groove area is radially shortened. It is also possible that at two edge sections (viewed in the longitudinal section) the two edge areas of the unloading device are provided with at least one radially shortened threaded element, and that the non-shortened threaded element is arranged only in the middle section of the unloading device.

[0035] It can also be provided that the threaded element is designed in an arcuate manner, wherein in particular part or all of the radially shortened threaded elements are larger in diameter than the radially standard threaded elements.

[0036] Preferably, the diameter of the threaded element engaged in the groove arranged at the outer edge of the groove area is configured to be larger. It is also possible that such a threaded element is enlarged in its diameter and is engaged in the groove arranged at the edge of the groove area towards the piston. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other details, advantages and features of the present invention will be clarified according to the following description of the accompanying drawings. Figure 1 Shown: a longitudinal sectional view of a conventional pump,

[0038] Attached Figure 2 Shown: From the attached Figure 1 A partial enlarged view of area A in the middle.

[0039] Attached Figure 3 Shown is a partial enlarged view of the fixed ring groove area of ​​the pump according to the present invention, and

[0040] Attached Figure 4 Shown: From the attached Figure 3 A partial enlarged view of the middle area Z. DETAILED DESCRIPTION

[0041] Attached Figure 1 The longitudinal section along the pump shaft 1 of the pump 10 is shown. The rotation of the pump shaft 1 causes the impeller 102 to rotate, which conveys the fluid to be conveyed. There is an inlet 101 and a plurality of pump stages arranged in series, each of which is provided with an impeller 102 that rotates about the pump shaft 1.

[0042] After the most downstream impeller 102 , the pumped fluid leaves the pump 10 through an outlet 103 .

[0043] When the fluid is pumped, a force F is generated parallel to the pump shaft, which is introduced into the pump shaft 10 via the piston 104 . This prevents undesired relative movements between the pump shaft and other components of the pump 10 .

[0044] Here, the introduction of the force F is achieved via a cross-sectional constriction of the pump shaft 1, into which the relief device 3 engages. The relief device 3 is therefore immovable in the axial direction of the pump shaft. However, the rotation of the pump shaft 1 is not impeded thereby.

[0045] The groove in the pump shaft 1 of the pump 10 is under certain conditions highly loaded due to the axial thrust F and is therefore also a possible location for shaft fracture.

[0046] Attached Figure 2 Shown from the attached Figure 1 4 , in which the area around the groove 4 is shown enlarged. It can be seen that the axial thrust F, which is typically transmitted by the piston 104 to the unloading device 3 , i.e. the force F introduced into the pump shaft 1 , is introduced into the pump shaft 1 through the groove area 2 .

[0047] Attached Figure 3 The embodiment according to the invention of the groove region 2 is shown, in which a plurality of grooves 4 for absorbing the force F are now provided. The relief device 3 is designed accordingly, so that the threaded elements of the relief device 3 engage in the corresponding grooves 4. This engagement results in the introduction of the guided force F into the pump shaft 1 without penetrating too deeply into the cross section of the pump shaft 1. This is advantageous because, in this respect, a more stable pump shaft 1 is present compared to an embodiment with only one groove, the stability of which is significantly increased. The plurality of grooves 4 are separated from one another in the longitudinal direction of the pump shaft 1 by pump shaft sections 6, the radius of which to the rotation axis R of the pump shaft 1 corresponds to the radius of the pump shaft 1 adjacent to the groove region 2.

[0048] It should be noted that the unloading device does not necessarily have to be designed to be 100% complementary to the groove area.

[0049] From the attached Figure 4 It can be seen from the drawing that it can be advantageous for a uniform introduction of the force F into the pump shaft 1 if the threaded elements 11, 12 of the unloading device 3 have threaded elements 12 which are radially shortened towards their outer edges as viewed in the longitudinal section direction and which are used to engage in the associated groove bottom 5. This is illustrated in the present case by means of a sawtooth structure 7 (in the longitudinal section direction of the pump shaft).

[0050] Here, the groove bottom 5 at the outer edge of the groove area 2 can be designed to be as deep as the other grooves. However, it is also possible that the groove at the edge of the groove area 2, in particular the edge facing the piston 104, has a smaller depth than the other grooves 4.

[0051] In particular, the groove bottom 5 arranged at the edge facing the piston 104 is provided with a larger radius at the bottom of its arcuate shape than the other grooves 4 arranged in the central region.

[0052] It can be provided that the two right-hand thread elements 12 are radially shortened, whereby the two corresponding groove bases 5 in the shaft 1 must be constructed with a smaller depth and a larger radius can be provided in their groove bases at the same time. This reduces the stress in the groove 4 of the shaft 1.

[0053] Furthermore, a relief groove 8 is provided, in particular in the immediate vicinity of the outer edge of the groove region 2. Moreover, such a relief groove 8 can be provided in the relief device 3 itself. There, the relief groove is a groove that increases toward the piston 104, which causes each of the threaded elements 11, 12 to introduce the same amount of force into the respectively assigned groove 4.

Claims

1. A pump shaft (1) for a multi-stage pump (10), comprising: A circumferential groove region (2) for engaging a relief device (3) for introducing a force (F) acting axially on a pump shaft (1) into the pump shaft (1), characterized in that the groove region (2) has a plurality of grooves (4) spaced apart from one another in the axial direction in a longitudinal section through the pump shaft (1), The plurality of grooves (4) are composed of circumferential grooves (4) that are independent of each other, or are composed of single-start or multi-start closed threads. The groove bottoms (5) of the plurality of grooves (4) are each configured to be arcuate in a longitudinal section.

2. The pump shaft (1) according to claim 1, wherein: The radii of the arcuate groove bottoms (5) are different.

3. The pump shaft (1) according to claim 1 or 2, wherein: Such a radius of the groove (4) arranged at the outer edge of the groove region (2) is greater than the radius of the groove (4) arranged in the middle section of the groove region (2).

4. The pump shaft (1) according to claim 1 or 2, wherein: The depths of the groove bottoms (5) of the plurality of grooves (4) are different.

5. The pump shaft (1) according to claim 4, wherein: The groove bottom depth of the groove (4) arranged at the outer edge of the groove area (2) is lower than the groove bottom depth of the groove (4) arranged in the middle section of the groove area (2).

6. The pump shaft (1) according to claim 1 or 2, wherein: The plurality of grooves (4) are separated from one another in the longitudinal direction of the pump shaft (1) by a pump shaft section (6), the radius of which to the rotation axis (R) of the pump shaft (1) coincides with the radius of the pump shaft (1) adjacent to the groove region (2).

7. The pump shaft (1) according to claim 1 or 2, wherein: The plurality of grooves (4) present a sawtooth structure (7) in a longitudinal cross-sectional view of the pump shaft (1).

8. The pump shaft (1) according to claim 7, wherein: The respective tooth tips of the sawtooth structure (7) have the same radius to the rotation axis of the pump shaft (1).

9. The pump shaft (1) according to claim 7, wherein: At least one of the respective groove bottoms (5) of the sawtooth structure (7) has a larger radius to the rotation axis (R) of the pump shaft (1) than at least one other groove bottom (5) of the sawtooth structure (7).

10. The pump shaft (1) according to claim 9, wherein: At least one groove base (5) with a smaller radius is separated from the outer edge of the groove region (2) as seen in longitudinal section by at least one groove base (5) with a larger radius.

11. The pump shaft (1) according to claim 10, wherein: At least one groove base (5) with a smaller radius is separated from two outer edges of the groove region (2) as seen in longitudinal section by at least one groove base (5) with a larger radius.

12. The pump shaft (1) according to claim 1 or 2, wherein: A relief groove (8) is arranged in the pump shaft (1) adjacent to the groove region (2) for engaging the relief device (3), said relief groove (8) not being used for engaging the relief device (3).

13. The pump shaft (1) according to claim 12, wherein: Relief grooves (8) are provided in the pump shaft (1) at two outer edge regions of the groove region (2).

14. Pump, including: The pump shaft (1) according to any one of claims 1 to 13, A relief device (3) engages in a plurality of grooves (4) of the groove region (2) in order to introduce a force (F) acting on the relief device (3) in the axial direction of the pump shaft (1) into the pump shaft (1).

15. The pump (10) according to claim 14, wherein: The unloading device (3) is a ring which surrounds the pump shaft (1) in the circumferential direction and is shaped on its inner circumference so as to engage in a plurality of grooves (4) of the groove region (2).

16. The pump (10) according to claim 15, wherein: The ring is a split ring which engages with its two partial ring segments in the groove area (2).

17. The pump (10) according to claim 14 or 15, wherein: For at least one groove (4) of the groove region (2), the unloading device (3) has, viewed in the longitudinal section direction, a threaded element (11, 12) for engaging in the corresponding groove (4).

18. The pump (10) according to claim 17, wherein: At least one of the plurality of thread elements (12) is radially shortened, ie has a smaller depth to the rotation axis of the pump shaft (1) than the other thread elements (11).

19. The pump (10) according to claim 18, wherein: The radially shortened thread element (12) engages in a groove (4) arranged at the edge of the groove region (2).

20. The pump (10) of claim 17, wherein: The thread elements (11, 12) engaging in the groove (4) at both edges of the groove region (2) are radially shortened thread elements (12).

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