PUMP SHAFT FOR A MULTI-STAGE PUMP

Description

[0001] The present invention relates to a pump shaft for a multi-stage pump and a pump with such a pump shaft.

[0002] In pumps, especially centrifugal pumps, a fluid to be pumped is sucked in with the help of a rotating shaft and pumped away by an impeller that is driven by rotation by the shaft.

[0003] Since in multi-stage pumps, the impellers' suction side develops lower pressure and thus lower axial force due to the impeller inlet opening, an axial force always develops toward the suction side of the impeller. This axial force from the impellers is transferred to the shaft. To keep the shaft stationary in the housing, a hydraulically generated counterforce is applied to the pump shaft by means of a balancing device.

[0004] In multi-stage pumps, the balancing device is connected to the pump shaft by a split ring and a retaining ring groove in the pump shaft. Engaging in this groove prevents unwanted axial displacement from the pump shaft to the casing.

[0005] The disadvantage of this is that shaft fractures rarely or occasionally occur at this point. This indicates a certain weakness in the shaft due to the retaining ring groove. Since multistage pumps in the power generation sector have been stopped and restarted more frequently in recent years, the retaining ring groove is subjected to considerable mechanical stress, which is seen as a growing and serious availability problem for fatigue-resistant pumps under changing operating conditions. As a result, the required safety factor against fatigue fracture is often no longer achieved.

[0006] CH 376 774 A, for example, describes a relief device by means of which the axial thrust absorbed by a relief disc is transferred to the shaft by means of thrust rings located in annular grooves in the shaft, wherein the relief disc, which is fixed in its position relative to the shaft and supported against a thrust ring, has an auxiliary member which is axially movable in relation to it arranged upstream or downstream thereof, which auxiliary member transfers part of the axial thrust to a further thrust ring, and the auxiliary member which is axially movable: (6) is guided on the relief disc (5) and is sealed off from it in such a way that a space is formed between these two parts, in which space the pressure prevails behind or in front of the relief disc through corresponding bores.

[0007] US 1,499,056 A shows a pump with a housing consisting of two longitudinally separable halves. The pump comprises a suction chamber on the suction side of the pump and a high-pressure chamber on the pressure side of the pump. The pump also has a pressure equalization chamber at the outlet end of the pump, which is connected to the high-pressure outlet chamber. A thrust equalization disc is rigidly arranged on the shaft in a balancing pressure chamber. A counter-balancing pressure chamber is provided on the side of the disc opposite the balancing pressure chamber, the disc controlling the connection between the two chambers. The pump further comprises a reversible thrust ring and a receiver for the disc, the thrust ring being provided with a groove on its outer edge and the pump housing being provided with a split rib extending around the inner sides of its two halves and adapted to be received in the groove of the thrust ring.

[0008] Further examples are known from documents CN 109 469 624 A and US 2017 / 248001 A1.

[0009] The aim of the present invention is to overcome this disadvantage. This is achieved with a pump shaft having all the features of claim 1 or with a pump according to claim 9. The invention significantly improves this weak point and, among other things, achieves significantly improved fatigue strength of the pump shaft. Further advantageous embodiments of the invention are formulated in the dependent claims.

[0010] According to the invention, the pump shaft for a multi-stage pump, in particular a centrifugal pump, comprises a circumferential grooved region for engaging a relief device to introduce a force acting in the axial direction of the pump shaft into the pump shaft. The pump shaft is characterized in that, in a longitudinal sectional view of the pump shaft, the grooved region has a plurality of grooves spaced apart from one another in the axial direction.

[0011] In contrast to the previously known prior art, the retaining ring groove for engaging a relief device is no longer formed by just a single groove, but comprises, when viewed along a longitudinal section of the pump shaft, a plurality of grooves arranged next to one another. By providing several grooves arranged next to one another in the axial direction of the pump shaft, it is possible to make the cross-sectional area of the pump shaft larger in the groove area than would have been possible with just one groove, which consequently also extends deeper into the pump shaft. This effectively counteracts any tendency of the pump shaft to fracture in the groove area. The mean stress in this area also decreases analogously.

[0012] Unlike the state of the art, the large axial force is not introduced into the shaft in one large groove, but rather in several smaller grooves, and is immediately redirected in the opposite direction. This force redirection creates high stresses in the groove radius of the shaft. With the multiple groove, only a small portion of the axial force is introduced and redirected per groove, while the remaining axial force is passed through. This significantly reduces the stress in the groove base and means that, thanks to this redesign of the groove, the maximum stress in the groove base (also known as the groove bottom) of the shaft is significantly lower – approximately halved.

[0013] The new, smaller grooves also make it possible to increase the contact area between the load-relief device engaging in the grooves and the shaft. This significantly reduces the surface pressure in the contact surfaces. Initial calculations indicate a reduction in the surface pressure in the contact surfaces by approximately half.

[0014] According to the invention, the plurality of grooves are formed by separate circumferential grooves or by a single or multi-start closed thread.

[0015] It can be provided that the multiple grooves define at least one ridge between their groove bottoms, the height of which corresponds to the outer edges of the groove area. In other words, each of the multiple grooves results in the at least one elevation located between the grooves (relative to the groove bottoms) being arranged at the same height level as the adjacent areas of the groove area. The ridges arranged between the grooves are therefore not arranged at a lower level than the outer edges of the groove area.

[0016] According to the invention, each groove base of the plurality of grooves is designed in the shape of a circular segment in a longitudinal section. This results in an advantageous recess in which an element engaging in the groove base can transmit a high axial force.

[0017] It can be provided that the radii of the circular segment-shaped groove bottoms are different, wherein preferably such a radius of a groove arranged at the outer edge of the groove region is larger than a radius of a groove arranged in a central section of the groove region.

[0018] For example, a groove located at the edge of the groove area can have a groove base whose circular segment-shaped longitudinal section has a larger radius than another groove base located in the groove area. It is particularly advantageous if the groove with the larger circular segment-shaped groove base is located on the side or edge of the groove area facing the pump piston.

[0019] The different radii in the circular segment-shaped groove bottoms allow a relatively uniform force introduction into the pump shaft.

[0020] According to a further optional development of the invention, it can be provided that the groove depths of the plurality of grooves are different, wherein preferably a groove depth of a groove arranged at the outer edge of the groove region is less than a groove depth of another groove arranged in the groove region. It is advantageous if the groove depth of the groove arranged on the side of the groove region facing the piston is less. Furthermore, it can also be provided that the grooves at the edge (seen in the longitudinal section direction) of the groove region are provided with a less deep groove base than those in a central region of the groove region.

[0021] According to a modification of the invention, it can be provided that the plurality of grooves are separated from one another in the longitudinal direction of the pump shaft by a pump shaft section which, in its radius from the rotational axis of the pump shaft, corresponds to a radius of the pump shaft adjacent to the groove region.

[0022] According to a further preferred embodiment, the plurality of grooves represent a sawtooth-like structure in a longitudinal sectional view of the pump shaft, wherein the respective tooth tips of the sawtooth-like structure preferably all have the same radius relative to the rotational axis of the pump shaft. The sawtooth-like structure is directed with its steep flanks toward the piston of the pump, since the force to be introduced into the pump shaft originates from the piston.

[0023] Grooves analogous to the buttress thread according to DIN 2781 are particularly suitable because almost no radial force is introduced into a relief device engaging in the grooves, so that such a sawtooth shape is ideally designed for the existing load.

[0024] In addition, according to the invention, it can be provided that at least one of the respective tooth bases of the sawtooth-like structure has a larger radius to the rotation axis of the pump shaft than at least one other tooth base of the sawtooth-like structure.

[0025] It can also be provided that the at least one tooth base with a smaller radius is separated from an outer edge of the groove region, seen in longitudinal section, by at least one tooth base with a larger radius, wherein preferably the at least one tooth base with a smaller radius is separated from both outer edges of the groove region, seen in longitudinal section, by at least one, preferably at least two, tooth bases with a larger radius.

[0026] According to a further development of the invention, it can be provided that a relief groove is provided in the pump shaft adjacent to the groove area for engaging a relief device, which relief groove does not serve for engaging a relief device, wherein a relief groove is preferably provided in the pump shaft at both outer edge areas of the groove area.

[0027] This results in stresses in the grooves of the shaft being reduced, resulting in an even more robust design of the pump shaft.

[0028] It can be provided that at least the relief groove has a similar depth to the grooves of the groove area.

[0029] The at least one relief groove can be designed along the longitudinal cross-section in such a way that it slopes steeply on its groove side spaced from the groove area and is designed less steeply on its groove side facing the groove area.

[0030] The invention also relates to a pump, in particular a centrifugal pump, comprising a pump shaft according to one of the preceding variants, and a relief device which engages in the 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.

[0031] According to the invention, the relief device is a ring that circumferentially surrounds the pump shaft and is shaped on its inner circumference to engage the multiple grooves of the groove area. The relief device can be a split ring, with its two partial ring pieces engaging the groove area. Instead of the split ring, however, the relief device can also be equipped with a similarly designed, one-piece ring. In this case, a similar thread is also present.

[0032] According to an optional modification of the invention, it is provided that the relief device, viewed in the longitudinal section direction, has a gear element for engaging in a corresponding groove for at least one or all grooves of the groove area.

[0033] It can be provided that one of the plurality of gear elements is radially shortened, i.e. penetrates less deeply to the rotational axis of the pump shaft than another gear element, wherein preferably such a radially shortened gear element engages in a groove arranged at the edge of the groove region, in particular in the groove of the groove region closest to the piston.

[0034] It can also be provided that there are two radially shortened gear elements which are adjacent to one another and engage in the two grooves located at the edge of the groove area, which are preferably located on the side of the groove area facing away from the piston.

[0035] The piston is arranged on the side of the groove area that faces the force to be introduced into the pump shaft and introduces this force into the split ring.

[0036] Preferably, the thread elements that engage in grooves at both edges of the groove area are radially shortened thread elements. It is therefore also possible for both edge sections of the relief device to be provided with at least one radially shortened thread element, while the unshortened thread elements are arranged only in a central section of the relief device.

[0037] It can also be provided that the gear elements are designed in the shape of a circular segment, wherein in particular some or all of the radially shortened gear elements are larger in diameter than the radially normal gear elements.

[0038] Preferably, the diameters of those gear elements that engage in grooves located at the outer edge of the groove area are enlarged. It is also possible for such a gear element to be enlarged in diameter and engage in the groove located at the edge of the groove area, which faces the piston.

[0039] Further details, advantages, and features of the invention will become apparent from the following description of the figures. These show: Fig. 1: a longitudinal sectional view of a conventional pump, Fig. 2: an enlarged section of Fig. 1 in area A, Fig. 3: an enlarged section around the area of a retaining ring groove of a pump according to the invention, and Fig. 4: an enlarged section of Fig. 3 in area Z

[0040] Fig. 1 shows a longitudinal section along the pump shaft 1 of a pump 10. The rotation of the pump shaft 1 causes the impellers 102 to rotate, which carry away a fluid to be pumped. There is an inlet 101 and several pump stages arranged in series, each of which is provided with impellers 102 rotating around the pump shaft 1.

[0041] After the downstream impellers 102, the pumped fluid leaves the pump 10 via an outlet 103.

[0042] When the fluid is pumped, a force F is generated parallel to the pump shaft, which is introduced into the pump shaft 1 via a piston 104. This prevents unwanted relative movement of the pump shaft and other components of the pump 10.

[0043] The force F is introduced by a reduction in the cross-section of the pump shaft 1, into which a relief device 3 engages. This device is therefore immovable in the axial direction of the pump shaft. However, rotation of the pump shaft 1 is not affected.

[0044] The groove in the pump shaft 1 of the pump 10 is subjected to high loads due to the absorption of the axial thrust F and is therefore also a possible location for a shaft breakage.

[0045] Fig. 2 shows an enlarged view of area A from Fig. 1 in which the area around the groove 4 is shown enlarged. It can be seen that the axial thrust F typically passed on from the piston 104 to the relief device 3, i.e. the force F to be introduced into the pump shaft 1, is introduced into the pump shaft 1 via the groove area 2.

[0046] Fig. 3 shows an inventive embodiment of the groove region 2, in which a plurality of grooves 4 are now provided for absorbing the force F. The relief device 3 is provided with a corresponding design, so that a gear element of the relief device 3 engages in the respective grooves 4. This engagement results in the force F to be diverted being introduced into the pump shaft 1 without penetrating particularly deeply into the cross-section of the pump shaft 1. This is advantageous because, in contrast to the implementation with only one groove, a more stable pump shaft 1 is now present at this point, the stability of which is significantly increased.

[0047] It should be noted that the relief device does not necessarily have to be 100 percent complementary to the groove area.

[0048] How to Fig. 4As can be seen, it can be advantageous for a uniform introduction of the force F into the pump shaft 1 if the flight elements 11, 12 of the relief device 3 have flight elements 12 that are shortened in the radial direction towards their outer edges, as seen in the longitudinal section, for engaging in the associated grooves 5. This is illustrated here using a sawtooth-like configuration 7 (in the longitudinal section direction of the pump shaft).

[0049] The grooves 5 at the outer edges of the groove area 2 can be as deep as all the other grooves. However, it is also possible for the grooves at the edge of the groove area 2, particularly at the edge facing the piston 104, to be shallower than other grooves 4.

[0050] In particular, the grooves 5, which are arranged on the edge facing the piston 104, are provided with a larger radius in their circular segment-shaped bottom than the other grooves 4 arranged in the central region.

[0051] For example, the two right-hand gear elements 12 can be radially shortened, so that the two corresponding grooves 5 in the shaft 1 need to be made less deep and, at the same time, larger radii can be provided in their groove bottoms 5. This reduces the stresses in the grooves 4 of the shaft 1.

[0052] In addition, relief grooves 8 are also provided, in particular in the immediate vicinity of the outer edges of the groove area 2. However, such a relief groove 8 can also be provided in the relief device 3 itself.

[0053] This is then a recess that enlarges towards the piston 104, which means that each of the gear elements 11, 12 introduces the same amount of force into the respective corresponding groove 4.

Claims

1. Pump shaft (1) for a multi-stage pump (10), in particular a centrifugal pump, comprising: a circumferential groove region (2) for engagement of a load-relieving device (3) which comprises a ring, in order to impart a force (F) acting in the axial direction of the pump shaft (1) to the pump shaft (1), wherein the groove region (2) has, in a view of the pump shaft (1) in longitudinal section, a plurality of grooves (4) spaced apart from one another in the axial direction, characterized in that the plurality of grooves (4) are formed by respective circumferential grooves (4) separated from one another or by a single-start or multi-start closed screwthread, wherein a respective groove base (5) of the plurality of grooves (4) is configured in the shape of a segment of a circle, viewed in a longitudinal section.

2. Pump shaft (1) according to Claim 1, wherein the radii of the groove bases (5) in the shape of segments of a circle are different, wherein such a radius of a groove (4) arranged at the outer edge of the groove region (2) is preferably larger than a radius of a groove (4) arranged in a central section of the groove region (2).

3. Pump shaft (1) according to one of the preceding claims, wherein the groove bases (5) of the plurality of grooves (4) have different depths, wherein preferably a groove base depth of a groove (4) arranged at the outer edge of the groove region (2) is preferably less than a groove base depth of a groove (4) arranged in a central section of the groove region (2).

4. Pump shaft (1) according to one of the preceding claims, 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) with a radius from the axis of rotation (R) of the pump shaft (1) which coincides with a radius of the pump shaft (1) which adjoins the groove region (2).

5. Pump shaft (1) according to one of the preceding claims, wherein the plurality of grooves (4) represent, in a view of the pump shaft (1) in longitudinal section, a sawtooth structure (7), wherein the respective tooth tips of the sawtooth structure (7) preferably all have the same radius with respect to the axis of rotation of the pump shaft (1).

6. Pump shaft (1) according to Claim 5, wherein at least one of the respective tooth bases (5) of the sawtooth structure (7) has a larger radius with respect to the axis of rotation (R) of the pump shaft (1) than at least one other tooth base (5) of the sawtooth structure (7).

7. Pump shaft (1) according to Claim 6, wherein the at least one tooth base (5) with a smaller radius is separated from an outer, viewed in a longitudinal section, edge of the groove region (2) by at least one tooth base (5) with a larger radius, wherein the at least one tooth base (5) with a smaller radius is preferably separated from both outer, viewed in a longitudinal section, edges of the groove region (2) by in each case at least one tooth base (5), preferably at least two tooth bases (5), with a larger radius.

8. Pump shaft (1) according to one of the preceding claims, wherein a load-relieving groove (8), which does not serve for engagement of a load-relieving device (3), is provided in the pump shaft (1), adjoining the groove region (2) for engagement of a load-relieving device (3), wherein a load-relieving groove (8) is preferably provided in the pump shaft (1) at both outer edge regions of the groove region (2).

9. Pump, in particular a centrifugal pump, comprising: a pump shaft (1) according to one of the preceding claims, a load-relieving device (3) which engages in the plurality of grooves (4) of the groove region (2) in order to impart a force (F), acting on the load-relieving device (3) in the axial direction of the pump shaft (1), to the pump shaft (1), wherein the load-relieving device (3) is a ring which surrounds the pump shaft (1) in the circumferential direction and is formed on its inner circumference in order to engage in the plurality of grooves (4) of the groove region (2).

10. Pump according to Claim 9, characterized In that the ring is a split ring which engages with its two partial ring pieces in the groove region (2).

11. Pump (10) according to one of the preceding Claims 9 or 10, wherein the load-relieving device (3) has, viewed in a longitudinal section, a thread element (11, 12) for engagement in a corresponding groove (4) for at least one or all the grooves (4) of the groove region (2).

12. Pump (10) according to Claim 11, wherein at least one of the plurality of thread elements (12) is radially shortened, i.e. penetrates less deeply with respect to the axis of rotation of the pump shaft (1) than other thread elements (11), wherein such a radially shortened thread element (12) preferably engages in a groove (4) arranged at the edge of the groove region (2).

13. Pump (10) according to Claim 11 or 12, wherein the thread elements (11, 12) are the radially shortened thread elements (12) engage in grooves (4) at the two edges of the groove region (2).