EP3187736B1 - Multi-stage horizontal centrifugal pump for pumping a fluid and method for repairing the same - Google Patents

Description

The invention relates to a multistage horizontal centrifugal pump for conveying a fluid, as well as a method for repairing or overhauling a multistage horizontal centrifugal pump according to the preamble of the independent claim of the respective category.

Multistage horizontal centrifugal pumps are used in many different technological areas, for example in the oil and gas processing industry or in industrial energy generation. In the latter, such multi-stage pumps are used, for example, as feed pumps or boiler feed pumps in order to feed the water to a steam generator under the necessary pressure.

Usually a plurality of pump stages arranged horizontally next to one another are provided in these pumps, each pump stage comprising a stage housing in each of which an impeller is provided which conveys the fluid, for example water, from the low-pressure side inlet of this pump stage to its high-pressure side outlet, which then connected to the inlet of the next stage. All impellers are rotatably arranged on a common shaft, which consequently extends through all the stage housing and driven by a drive, for. B. an electric motor is driven. The individual pump stages are typically sealed along the common shaft by wear rings which are arranged or mounted in a stationary manner with respect to the stage housing. It is a common measure that two wear rings are provided for a pump stage, namely a first wear ring on the low-pressure side, which surrounds the front cover plate of the impeller, and on the high-pressure side a second wear ring, which is fixedly attached to a partition that guides the fluid from the outlet of the stage to the inlet of the next stage and typically includes a stator for the next stage.

The wear rings are each designed with a predetermined clearance with respect to the shaft, so that an annular gap is formed between the radially inner, cylinder jacket-shaped boundary surface of the wear ring and the rotating outer jacket surface of the shaft, through which a leakage flow from the high-pressure side to the low-pressure side is made possible. This leakage flow is advantageous on the one hand because it contributes to the hydrodynamic stabilization of the rotor (shaft with impellers), on the other hand it also means a certain loss in terms of the efficiency of the pump. The dimensioning of this clearance therefore plays an important role. The aim is, of course, always to avoid direct physical contact between the stationary wear rings and the rotating shaft during operation of the pump. The wear rings are - as their name suggests - wear parts that have to be replaced during the life of the pump. This is primarily due to the fact that the leakage flow causes erosion on the wear rings. This increases the gap between the respective wear ring and the shaft, which leads to an increase in the leakage flow. Since the increase in leakage flow reduces the efficiency of the pump, the wear rings usually have to be replaced with new ones.

A particular problem with multistage horizontal centrifugal pumps, which occurs in particular with higher numbers of stages, lies in the length of the shaft and the mass of the impellers arranged on it in a rotationally fixed manner. In the following, the entirety of the components rotating during operation is referred to as the rotor. The rotor thus includes the shaft and the impellers. With long shafts or rotors, there is a not insignificant deflection of the shaft due to its own mass. This deflection is usually largest in the middle area of the shaft. The center line of the shaft, which without bending would be a straight line that coincides with the center axis of the pump and the axis of rotation, becomes a curved line through the bending, which is referred to below as the bending line of the shaft or the bending line of the rotor. The deviation of the bending line from the central axis of the pump is greatest approximately in the middle between the radial bearings for the shaft. Due to the force of gravity, the bending line in a horizontal pump is a convex function.

Typically, the deflection of the shaft is greatest when the pump is at a standstill. When the shaft rotates, stretching of the shaft usually results, i.e. in particular its maximum deflection is reduced. This stretching is based in particular on hydrodynamic effects such as the lomakine effect.

The problem, which is caused by the deflection of the rotor, results from the fact that the shaft no longer runs vertically through all pump stages or stage housings, but at least through some stage housings at an angle, i.e. with an angle different from 90 °, of course from depends on the bending line of the shaft. Accordingly, the play between the wear rings and the shaft or the cover disk of the impellers must be large enough so that the rotor does not come into physical contact with the wear rings during the rotation despite bending. On the other hand, as already mentioned, one endeavors not to make this clearance too large in order not to reduce the efficiency of the pump too much. As a result, the play is usually measured in such a way that the rotor does not come into physical contact with the wear rings in all normal operating conditions. However, if the pump is stopped, the deflection of the rotor increases, so that when the rotor comes to a standstill at the latest, it comes into physical contact with at least some wear rings and rests on them.

This resting of the rotor on the wear rings at a standstill has several disadvantages. For example, when the rotor is at a standstill, it is no longer possible to turn it by hand, which is particularly the case with the Installation or maintenance of the pump is a significant disadvantage. In addition, when starting and switching off the pump, there is grinding between at least some wear rings and the rotor, which on the one hand leads to increased or accelerated wear of the wear rings and on the other hand shortens the service life of the shaft or the cover disks of the impellers. Although it is possible to protect the wear rings against excessive wear by means of a suitable coating, this makes the manufacture of the wear rings more complex and costly.

Another possibility for solving this problem would be to considerably increase the play between the rotor and the wear rings so that the rotor can rotate freely even when it is at a standstill. For many applications, especially in industrial energy generation, this solution is undesirable or even unacceptable, because this increased play inevitably leads to a reduction in the efficiency or the efficiency of the pump, which leads to the pursuit of minimizing energy consumption and environmentally conscious handling Resources.

To solve this problem, it has already been proposed to no longer arrange the individual stage housings of the pump in the central region of the pump perpendicular to the central axis, but rather to incline them slightly, i.e. to arrange them at an angle, so as to approximately follow the bending line. The entirety of the stage housing then forms a V-shaped stator structure, at least in the central region of the pump, which approximately follows the bending line of the shaft. One such solution is, for example, in the Chinese utility model CN 201288673 disclosed.

However, this inclined or inclined arrangement of the step housing is structurally very complex. In the case of designs as ring section pumps, in which the entirety of the stage casing forms the outer pump casing, changing the rotor setting is often problematic, for example, because new stage casings are usually required for this. In many cases, it is not possible to rework the individual stage housings. Additional challenges arise when the pump with a shell casing (barrel pump) is designed, so if the individual stage housing are arranged in a common outer pump housing. With this configuration, it is necessary to also place the inlet connector on the pump housing at an angle, which is very costly and labor-intensive. The assembly of the individual step housing in the outer pump housing is difficult and labor-intensive due to the inclined position of the step housing relative to the pump housing. Finally, it is also not possible to provide reliable internal seals within the pump housing between a stepped housing and the pump housing, in order to seal different pressure spaces within the pump housing from one another, for example. Similar multistage horizontal centrifugal pumps are also made CN 203 835 734 U and CN 204 878 079 U known.

Based on this prior art, it is therefore an object of the invention to provide a multistage horizontal pump in which physical contact between the rotor and the wear rings is reliably avoided in all normal operating states, but in particular also when the rotor or the shaft is at a standstill without having to make any concessions to the efficiency of the pump. In particular, it should also be possible to design the pump with a long shaft. Furthermore, it is an object of the invention to propose a method for repairing or overhauling a multistage horizontal centrifugal pump so that physical contact between the rotor and the wear rings is reliably avoided in all normal operating conditions, but especially when the rotor or the shaft is at a standstill without compromising the efficiency of the pump.

The objects of the invention that achieve these objects are characterized by the features of the independent patent claim of the respective category.

According to the invention, a multistage horizontal centrifugal pump for pumping a fluid is proposed, with a rotor that comprises a rotatably arranged shaft and several impellers for pumping the fluid, all of the impellers being non-rotatably arranged on the shaft, and with a stator that has several stage housings ( 31), which one behind the other with respect to an axial direction defined by a central axis are arranged, wherein the stator surrounds the rotor, and wherein all stage housings are designed and arranged centrally with respect to the central axis (A), and multiple wear rings are provided between the rotor and the stator, each of which is fixed with respect to the stator, and the Each rotor surrounds with a clearance, and at least one of the wear rings is designed eccentrically. With a rotatably arranged shaft and with several pump stages which are arranged one behind the other with respect to an axial direction defined by a central axis, each pump stage having an impeller provided with a front cover disk for conveying the fluid, as well as a stage housing with a stationary impeller opening for receiving the front cover plate of one of the impellers, and a partition wall, which is stationary with respect to the stage housing, for guiding the fluid to the adjacent pump stage, the impellers of all pump stages in a rotationally fixed manner on the shaft are ordered, each stationary impeller opening being delimited radially on the inside by a first wear ring which surrounds the front cover plate of the impeller with a clearance, and each stationary partition wall being delimited radially on the inside by a second wear ring which surrounds the shaft with clearance, and wherein at least one of the first or the second wear rings is designed eccentrically.

The term "eccentrically designed" with respect to the wear ring means that the radially outer limiting surface of the wear ring is centered around a first axis and the radially inner limiting surface of the wear ring is centered around a second axis, the first and second axes being parallel but not congruent are.

If an eccentric wear ring is provided in particular where the deflection of the shaft or rotor is greatest, it can be ensured that the shaft or rotor in the operating state, especially in the area of the greatest deflection, is approximately centered in the eccentric wear ring rotates, ie the rotor is approximately centered with respect to the eccentric wear ring. If you now stop the rotor, which increases its maximum deflection, then the eccentric wear ring still has enough play so that physical contact between the rotor and the wear ring is reliably avoided even when the rotor is at a standstill. The shaft or the rotor is thus free, in particular, even at a standstill, that is to say without contact with the wear ring, and can for example be rotated by hand.

A particular advantage of this embodiment according to the invention is that the deflection of the shaft can only be compensated for by a very inexpensive component, namely the wear ring, or several of them. In particular, this also enables an extremely cost-effective and less time-consuming adaptation to changes in the rotor setting, because if necessary only one or more wear rings need to be replaced, but in particular no further structural changes to other, significantly more expensive components of the pump, such as one of the stage housings, are required .

In addition, due to the eccentric design, it is not necessary to provide a larger clearance between the wear ring and the rotor, so that no concessions to the efficiency of the pump are necessary.

All stage housings are preferably arranged concentrically to the central axis of the pump. This is particularly advantageous from a structural point of view because the stage housing can then be designed essentially the same for at least almost all pump stages. Since the deflection of the rotor is already compensated for by the eccentric design of the wear ring, it is in particular not necessary to compensate for the deflection of the shaft by structural measures on the stepped housing itself. For example, an eccentric design of one or more stage housings or other components can be dispensed with.

The number of wear rings for which an eccentric design is preferred naturally depends on the specific application and in particular on the length of the shaft, the number of impellers and the mass of the rotor. For many applications it is preferred if a plurality of the wear rings are designed eccentrically.

In particular, it is preferred if the eccentricity of the wear rings is not constant over the length of the shaft. It is particularly advantageous if the wear rings have an eccentricity which increases in the direction of the center of the pump. This means that seen from one end of the pump, the eccentricity of the wear rings initially increases until it reaches its maximum in the area of the center of the pump, i.e. where the shaft is usually the greatest, and then decreases again.

As a measure of the eccentricity of an individual wear ring, the distance between the first axis, around which the radially outer boundary surface of the wear ring is centered, from the second axis, around which the radially inner boundary surface of the wear ring is centered, is taken.

In a particularly preferred embodiment, the eccentricity of the wear rings is adapted to the bending line of the shaft. This means that the greater the distance between the bending line and the central axis of the pump, the greater the selected eccentricity of the wear ring, so that the eccentricity essentially follows the bending line of the shaft. This measure also has the particular advantage that all stage housings can be arranged parallel and perpendicular to the central axis of the pump. It is thus possible to dispense with an inclined arrangement of the stage housing or other components.

Another advantageous measure is that the eccentricity of all wear rings is dimensioned such that when the shaft is at a standstill, none of the wear rings touches the shaft or an impeller. Since the deflection of the shaft or the rotor is greatest at standstill, this measure can minimize the radial width of the gap between the wear rings on the one hand and the rotor (shaft or impeller). It is also preferred if the eccentricity of all wear rings is dimensioned such that the bending line of the shaft runs essentially centrally between all wear rings at a nominal speed of the pump. The bent shaft then rotates at least approximately centered with respect to the wear rings, so it has the same in all radial directions Game. Among other things, this is particularly advantageous for thermally induced changes in the rotor. For example, when the temperature changes. B. in the medium to be conveyed, significantly steeper temperature changes, so larger temperature gradients are allowed without additional measures, such as preheating of the rotor are necessary. This is particularly advantageous with regard to applications in industrial power generation.

In a preferred embodiment, the pump has several pump stages which are arranged one behind the other with respect to the axial direction, each pump stage comprising an impeller provided with a front cover plate for conveying the fluid, as well as one of the stage housings and a partition wall stationary with respect to the stage housing for guiding of the fluid to the adjacent pump stage, the stage housing being designed with a stationary impeller opening for receiving the front cover plate of one of the impellers, each stationary impeller opening being delimited radially on the inside by a first wear ring which surrounds the front cover plate of the impeller with a clearance, and each stationary partition wall being delimited radially on the inside by a second wear ring which surrounds the shaft with play.

Here, too, it is advantageous if the eccentricity of all wear rings is dimensioned in such a way that, when the shaft is at a standstill, none of the wear rings touches the shaft or an impeller. This makes it possible to further reduce both the play between the shaft and the second wear rings and the play between the front cover disks of the impellers and the first wear rings compared to known multiphase pumps, which increases the efficiency of the pump according to the invention.

Due to their eccentricity, the wear rings must be used in a certain angular orientation with respect to the radial plane perpendicular to the central axis in order to ensure their correct functionality. This is in principle possible because the part of the wear ring with the greatest radial width is placed exactly above the shaft (with respect to the normal, horizontal position of use), or the part with the smallest radial width is placed exactly below the shaft. In order to simplify the assembly of the wear rings, it is preferred if each eccentric wear ring has a positioning means in order to position the respective wear ring in a predetermined angular orientation in the respective step housing or the respective partition. This positioning means can be, for example, a visually recognizable marking on the wear ring or a positioning pin which engages in a corresponding bore in the step housing or in the partition.

The positioning means is particularly preferably provided where the respective wear ring has its maximum width in the radial direction, because this enables particularly simple assembly of the wear ring.

In a preferred embodiment, the pump is designed as a barrel casing pump, in which all stage casings are arranged in a casing. Since all stage housings can be arranged parallel to one another and perpendicular to the central axis of the pump, the inlet connector can be manufactured in a conventional manner, that is, the problematic inclination of the inlet connector described at the beginning can be dispensed with. In addition, it is possible to provide reliable seals between the stepped housings and the outer casing. In this way, different pressure spaces can be provided in the interior of the jacket housing, in which the fluid is present at different pressures. This also makes it possible in particular that the pump according to the invention can be designed with an inlet and an outlet and an intermediate outlet for the fluid to be conveyed, the intermediate outlet being designed and arranged in such a way that at least part of the fluid can be removed through the intermediate outlet under an intermediate pressure is which intermediate pressure is greater than the pressure of the fluid at the inlet of the pump and less than the pressure of the fluid at the outlet of the pump. This possibility of intermediate withdrawal of the fluid with a different pressure than that at the outlet is a great advantage for many applications.

The invention also proposes a method for repairing or overhauling a multistage horizontal centrifugal pump for pumping a fluid with a rotor which comprises a rotatably arranged shaft and several impellers for delivering the fluid, with all impellers being arranged on the shaft in a rotationally fixed manner, and with a stator comprising a plurality of stage housings which are arranged one behind the other with respect to an axial direction defined by a central axis, wherein the stator surrounds the rotor, and wherein all stage housings are designed and arranged centrally with respect to the central axis, and several between the rotor and the stator Wear rings are provided, each of which is fixed with respect to the stator, and each surrounds the rotor with a clearance, in which method one or more of the wear rings are replaced, one or more of the wear rings each being replaced by an eccentrically configured wear ring ssring is replaced.

In particular, the method is also suitable for repairing or overhauling a multistage horizontal centrifugal pump for pumping a fluid with a rotatably arranged shaft and with several pump stages which are arranged one behind the other with respect to an axial direction defined by a central axis, each pump stage having a front cover plate provided impeller for conveying the fluid, as well as a stage housing with a stationary impeller opening for receiving the front cover plate of one of the impellers, and a partition wall, which is stationary with respect to the stage housing, for guiding the fluid to the adjacent pump stage, the impellers of all pump stages being arranged in a rotationally fixed manner on the shaft are, wherein each stationary impeller opening is delimited radially inwardly by a first wear ring which surrounds the front cover plate of the impeller with a clearance, and each stationary partition wall radially inwardly by a two th wear ring is limited, which surrounds the shaft with a game. In this exemplary embodiment of the method according to the invention, one or more of the first and / or second wear rings is replaced, one or more of the first and / or second wear rings each being replaced by an eccentrically configured wear ring.

With this method it is possible to maintain a pump designed according to the invention or to adapt it to a different rotor setting, as well as to overhaul or retrofit a conventional pump without eccentric wear rings so that it is then designed according to the invention. This method is therefore particularly suitable for converting existing pumps in such a way that the deflection of the rotor is compensated for or better compensated for by one or more eccentrically configured wear rings. It is particularly advantageous that this conversion can usually only be implemented by replacing the inexpensive wear rings without modifying other components of the pump.

• wenn die Exzentrizität der Verschleissringe an eine Biegelinie der Welle angepasst wird.
• wenn die Exzentrizität der Verschleissringe jeweils so bemessen wird, dass beim Stillstand der Welle keiner der Verschleissringe die Welle berührt, und
• wenn die Exzentrizität der Verrschleissringe jeweils so bemessen wird, dass die Biegelinie der Welle bei einer Nenndrehzahl der Pumpe im Wesentlichen mittig zwischen allen Verschleissringen verläuft.

For the same reasons as already explained above for the pump according to the invention, it is also advantageous with regard to the method

• when the eccentricity of the wear rings is adapted to a bending line of the shaft.
• if the eccentricity of the wear rings is dimensioned in such a way that none of the wear rings touches the shaft when the shaft is at a standstill, and
• if the eccentricity of the wear rings is dimensioned in such a way that the bending line of the shaft runs essentially centrally between all wear rings at a nominal speed of the pump.

Further advantageous measures and configurations of the invention emerge from the dependent claims.

Fig. 1:

ein schematische Seitenansicht eines Ausführungsbeispiels einer erfindungsgemässen Pumpe mit Ausbruch,

Fig. 2:

eine perspektivische Schnittansicht einer Pumpenstufe des Ausführungsbeispiels aus Fig. 1,

Fig. 3:

eine vergrösserte Schnittdarstellung zur Veranschaulichung des Spiels eines ersten und eines zweiten Verschleissrings,

Fig. 4:

eine perspektivische Ansicht einer Ausführungsform eines Verschleissrings,

Fig. 5:

einen Schnitt durch den Verschleissring aus Fig. 4 in axialer Richtung,

Fig. 6:

eine schematische Darstellung der Biegelinie der Welle bei einer Nenndrehzahl der Pumpe, und

Fig. 7:

eine schematische Darstellung der Biegelinie der Welle beim Stillstand der Pumpe.

In the following, the invention is explained in more detail both in terms of apparatus and in terms of process technology using exemplary embodiments and using the drawing. In the schematic drawing show, partly in section:

Fig. 1:

a schematic side view of an embodiment of a pump according to the invention with a cutout,

Fig. 2:

a perspective sectional view of a pump stage of the embodiment Fig. 1 ,

Fig. 3:

an enlarged sectional view to illustrate the play of a first and a second wear ring,

Fig. 4:

a perspective view of an embodiment of a wear ring,

Fig. 5:

a section through the wear ring Fig. 4 in the axial direction,

Fig. 6:

a schematic representation of the bending line of the shaft at a nominal speed of the pump, and

Fig. 7:

a schematic representation of the bending line of the shaft when the pump is at a standstill.

Fig. 1 shows in a schematic side view an embodiment of a multistage horizontal centrifugal pump according to the invention, which is designated as a whole with the reference number 1. In Fig. 1 some parts of the pump 1 are shown in breakout. Fig. 2 shows some parts of the pump 1 in an enlarged sectional view.

Such multi-stage pumps are used, for example, in industrial energy generation, e.g. B. as feed or boiler feed pumps, in which the fluid to be pumped is water, which is conveyed by the pump 1 to a steam generator. Such pumps are also used in the oil and gas industry, both for pumping water, for example as injection pumps, or for pumping petroleum or other hydrocarbons.

The in Fig. 1 The illustrated embodiment, the pump 1 is designed with an outer casing 2 (barrel casing), which has an inlet 4, an outlet 5, and optionally an intermediate outlet 51 for the fluid to be conveyed. The latter will be discussed further below.

The pump 1 has a rotatable shaft 6 which extends in the center through the pump 1 and which can be set in rotation by a drive (not shown), for example an electric motor. The pump 1 has a central axis A, which extends through the center of the space provided for the shaft 6 in the interior of the pump 1, and which represents the target axis of rotation about which the shaft 6 is to rotate. If the shaft 6 mounted in the pump 1 were not bent, the central axis A would be congruent with the longitudinal axis of the shaft. In the following, when referring to the axial direction, the direction of the central axis A of the pump 1 is always meant. The radial direction then means a direction perpendicular to the axial direction.

In the jacket housing 2, a plurality of - here for example eight - pump stages 3 are provided in a manner known per se, which are arranged one behind the other with respect to the axial direction. In Fig. 1 the pump 1 is shown in its normal position of use, ie in a horizontal arrangement, in which the central axis A runs horizontally or parallel to the ground.

Shows for a better understanding Fig. 2 in an enlarged illustration, a perspective sectional view of one of the pump stages 3 (see also Fig. 3 ).

Each pump stage 3 comprises, in a manner known per se, an impeller 32, a stage housing 31 and, on the high-pressure side, a partition 33 which delimits the pump stage 3 from the next pump stage 3. Each impeller 32 is designed as a closed impeller 32, that is to say it comprises a front cover disk 34, a rear cover disk 35 and a plurality of blades 36 arranged between the cover disks 34, 35 for conveying the fluid. Each stage housing 31 comprises a stationary impeller opening 37 for receiving the front cover plate 34 of one of the impellers 32. The partition 33 is also stationary with respect to the stage housing 31 and serves to convey the fluid conveyed by the impeller 32 to the inlet, ie to the impeller 32 of the next pump stage 3 lead. For this purpose, the partition 33 comprises a stationary guide wheel, which is not shown in more detail in the drawing figures.

The impellers 32 of all pump stages 3 are non-rotatably connected to the shaft 6, so that the impellers 32 rotate together with the shaft 6.

In the context of this application, the term “rotor” means the entirety of all components of the pump 1 that rotate in the operating state of the pump 1. The rotor of the pump 1 thus comprises both the shaft 6 and all of the impellers 32 arranged thereon, as well as possibly other components of the pump 1, which rotate together with the shaft 6 or are connected to the shaft 6 in a rotationally fixed manner. In the context of this application, the term “stator” of the pump means the entirety of the stationary, that is to say non-rotating, components of the pump. The stator thus includes, in particular, all step housings 31 and all partition walls 32.

Like this in particular Fig. 1 shows, all pump stages 3 and all stage casings 31 are arranged parallel to one another in such a way that the surfaces enclosed by the impeller openings 37 are perpendicular to the central axis A.

In operation of the pump 1, the fluid to be pumped, so z. B. Water entering through inlet 4 of pump 1 from first impeller 32 - this is in FIG Fig. 1 the right impeller 32 according to the illustration - conveyed into the annular space between the partition 33 and the stage housing 31 and from there guided radially inward between the partition 33 and the stage housing 31 and thus arrives at the impeller 32 of the adjacent pump stage 31. This process continues through all pump levels 3 to the last - this is in Fig. 1 the one on the extreme left according to the illustration - from the outlet of which the fluid is then led to the outlet 5 of the pump 1.

As is customary per se, two wear rings are provided in each pump stage 3 in order to seal the respective pump stage 3 from its adjacent pump stages 3 or from the inlet 4 or the outlet 5. A first wear ring 7 is fitted into the impeller opening 37 of the stage housing 31 so that the stationary impeller opening is delimited radially on the inside by the first wear ring 7, which is firmly connected to the stage housing 3 and is therefore stationary. The first wear ring 7 thus surrounds the front cover disk 34 of one of the running wheels 32. A The second wear ring 8 is provided radially on the inside on the stationary partition 33 and surrounds the shaft 6, i.e. the stationary partition 33 is delimited on the radially inside by the second wear ring 8, which is arranged between the partition 33 and the shaft 6 with respect to the radial direction. The second wear ring 8 is firmly connected to the partition 33 and is therefore also stationary.

As already mentioned, the two wear rings 7, 8 serve to seal the pump stages 3 along the shaft 6. However, each of the wear rings 7, 8 surrounds the rotor with play, so that there is a gap between the radially outer boundary surface of the rotor and the radially inner boundary surface of the wear ring 7, 8 forms an annular gap through which a leakage flow flows counter to the general conveying direction of the fluid. This leakage flow is desirable on the one hand, in particular in order to stabilize the rotor hydrodynamically, but on the other hand it should not be too large because the leakage flow reduces the efficiency of the pump. Furthermore, during the normal operating states of the pump 1, direct physical contact between the rotor (shaft 6 or impeller 32) and one of the wear rings 7, 8 should be avoided.

Since the play between the rotor and the wear rings 7, 8 is typically very small, it can in the representations of the Fig. 1 and Fig. 2 cannot be recognized. Hence shows Fig. 3 an enlarged sectional view to illustrate the play of a first and a second wear ring 7 and 8, respectively.

Like this in Fig. 3 As can be seen, there is a play S1 between the radially inner boundary surface of the first wear ring 7 and the radially outer boundary surface of the front cover disk 34 of the impeller 32, through which an annular gap is formed between the first wear ring 7 and the front cover disk 34. In an analogous manner, there is a play S2 between the radially inner limiting surface of the second wear ring 8 and the radially outer limiting surface of the shaft 6, through which an annular gap between the second wear ring 8 and the shaft 6 is formed. Game S1 can, but does not have to be, the same size as game S2.

As already mentioned, in multi-stage, horizontal pumps 1, particularly when the shaft 6 is long, there is a noticeable deflection of the shaft 6 or of the rotor due to the mass of the rotor. Such a deflection is in Fig. 6 shown very schematically on the basis of a bending line B. The bending line B of the shaft 6 means the center line of the shaft 6 when the shaft 6, including the impellers 32 and other components connected to it in a rotationally fixed manner, i.e. the rotor, is mounted in the pump 1, i.e. when the shaft 6 is in its bearings and in particular the radial bearings are arranged, which are here on the outside in the region of the two ends of the shaft 6, but are not shown in more detail.

If the deflection did not exist, the bending line B would lie exactly on the central axis A of the pump 1. The deflection D of the shaft 6 is understood to mean the distance between the bending line B and the central axis A. Due to the direction of the gravitational force, the bending line B in a horizontal pump 1 is always a convex curve. The maximum of the deflection D is approximately in the middle of the pump 1, as shown in FIG Fig. 6 is shown. Depending on the length of the shaft 6 and the mass of the running wheels 32, the maximum deflection D can be a few tenths of a millimeter, for example 0.2-0.5 mm or more.

In order to compensate for the problems resulting from the deflection D of the shaft 6, it is now proposed according to the invention that at least one of the first or the second wear rings 7 or 8 be designed eccentrically. In Fig. 4 an embodiment of such an eccentrically designed wear ring 7 or 8 is shown in a perspective view. Fig. 5 shows a section through the wear ring 7, 8 from Fig. 4 , the cut being made in the axial direction, i.e. in the same way as in Fig. 3 . Additionally illustrated Fig. 5 the concept of eccentric design or eccentricity.

The eccentric configuration means that the radially outer limiting surface of the wear ring 7, 8 is surrounded by a different one Axis is centered than its radially inner boundary surface. This is in Fig. 5 for the simple embodiment of the wear ring 7 or 8, in which the cross-sectional area of the wear ring 7 or 8 is rectangular. In this embodiment, both the radially outer and the radially inner limiting surface of the wear ring 7 and 8 are each a cylinder jacket surface. The radially outer boundary surface has a radius R1 and the radially inner boundary surface has a radius R2, whereby of course R2 is smaller than R1. The radially outer limiting surface is centered around a first axis A1, ie A1 is here identical to the cylinder axis of the radially outer limiting surface. The radially inner limiting surface is centered around a second axis A2, ie A2 is here identical to the cylinder axis of the radially inner limiting surface. The axes A1 and A2 run parallel to one another but are not congruent. This configuration of the non-congruent axes A1 and A2 is referred to as eccentric. The eccentricity E, which is given by the distance between the two axes A1 and A2, is established as a measure of the strength of the eccentric configuration.

Depending on the maximum deflection D of the shaft 6, the eccentricity E can be in the range of up to a few tenths of a millimeter. With modern machining methods customary today, it is not a problem to produce such eccentricities E with sufficient accuracy in a wear ring 7 or 8.

Due to the eccentric configuration, the radial width F of the wear ring 7 or 8 varies along its circumference, that is, there is a maximum radial width F and a minimum radial width F, the radial width F being the radial extent of the wear ring 7 or 8 Direction is.

Due to the variation in the radial width F, the wear ring 7 or 8 must be fastened to the stepped housing 31 or to the partition 33 in the correct angular orientation. Since the deflection D of the shaft 6 always takes place downwards with respect to the normal position of use, the wear ring 7 or 8 is used in such an orientation that the The area of its maximum radial width F is perpendicular above the central axis A, or the area of its minimum radial width F is perpendicular below the central axis A.

In order to implement the correct angular orientation of the wear ring 7 or 8 more easily, it is advantageous if each eccentric wear ring 7 or 8 has a positioning means 9. This positioning means 9 (see Fig. 4 ) can be, for example, a pin 9 which protrudes in the axial direction from the ring and engages in a corresponding bore (not shown) in the respective step housing 31 or in the respective partition 33 during assembly. Of course, other positioning means 9 are also possible, e.g. B. a projection or a recess on the wear ring 7 or 8, which interacts positively with a recess or a projection in the step housing 31 or in the partition 33, or optically recognizable markings such as notches, lines or arrows.

For reasons of assembly technology, it is preferred if the positioning means 9 - as in FIG Fig. 4 is provided where the respective wear ring 7 or 8 has its maximum radial width F.

It goes without saying that the in Fig. 5 The illustrated rectangular cross-sectional area of the wear ring 7 or 8 is only to be understood as an example. Of course, the wear rings 7 and 8 can also have other and more complex cross-sectional areas, in particular those known from the prior art for wear rings in centrifugal pumps. The cross-sectional area of the wear ring 7 or 8 can, for example, also be L-shaped or trapezoidal; it can have boundary lines running at an oblique or acute angle to one another. Furthermore, roundings or bevels can be provided. A sufficient number of possibilities for the design of this cross-sectional area are known to those skilled in the art.

Furthermore, it goes without saying that the first wear ring 7 generally has a different geometrical configuration than the second wear ring 8, even if the geometrical configurations can in principle be the same.

The radially inner boundary surface of each wear ring 7 or 8 is usually a cylinder jacket surface with a radius R2 (see Fig. 5 ). This radius R2 is typically different for the first wear rings 7 and the second wear rings 8. Usually, the radius R2 for the second wear rings 8 is smaller than for the first wear rings 7.

Many possibilities are also known to the person skilled in the art with regard to the material from which the wear rings 7, 8 are made. Martensitic stainless steels or stainless steels are mentioned here as an example.

The at least one wear ring 7 or 8, which is designed eccentrically according to the invention, is provided where the deflection D of the shaft 6 is greatest. The eccentricity E of this wear ring is preferably dimensioned in such a way that the rotating shaft 6 or the rotating cover disk 34 of the impeller 32 is at least approximately centered with respect to the radially inner boundary surface of the eccentric wear ring 7 or 8, i.e. the eccentricity E is selected in this way that it is at least approximately the deflection D of the rotating shaft 6 at the location of this wear ring 7 or 8. This then results in the rotating shaft 6 or the rotating cover disk 34 in this eccentrically configured wear ring 7 or 8 with respect to the second axis A2 (see FIG Fig. 5 ) is at least approximately centered.

This eccentrically designed wear ring 7 or 8 is now attached to the stepped housing 31 or to the partition 33, preferably using the positioning means 9, in such a way that its area in which the radial width F is at a maximum is arranged vertically above the central axis A. When the rotor now rotates, it is essentially centered in this wear ring 7 or 8, that is to say the rotor is - as described above - at least approximately centered with respect to the axis A2. This means that the game S1 or S2 (see Fig. 3 ) is at least approximately constant within this wear ring 7 or 8, viewed in the circumferential direction of the rotor, so the rotor can rotate without contact with respect to the wear ring 7 or 8.

If the pump 1 is now switched off so that the rotor comes to a standstill, this generally leads to an increase in the deflection D, in particular also at the point where the deflection D is at a maximum. Due to the play S1 or S2 between the rotor and the eccentrically designed wear ring 7 or 8, there is still enough space below the rotor in the wear ring 7 or 8, so that the increase in the deflection D of the rotor does not lead to the rotor in direct physical contact with the wear ring 7 or 8 comes. This means that the rotor or the shaft 6 is free even at a standstill in the sense that the rotor or the shaft 6 does not rest on the wear ring 7 or 8. This results in the particular advantage that the rotor can be rotated by hand when the pump 1 is at a standstill, which is an enormous advantage in particular for maintenance or assembly work.

In addition, this freedom from contact is also advantageous for starting and stopping the pump 1 because there is no dragging between the rotor and the wear ring 7 or 8. As a result, on the one hand, a coating of the wear ring 7 or 8 can be dispensed with and, on the other hand, the service life of the rotor is increased because its components are not subjected to any mechanical grinding on the wear ring 7 or 8.

For most applications it is advantageous if a plurality of both the first and the second wear rings 7 and 8 are designed to be eccentric. The eccentricity E of an individual wear ring 7 or 8 is adapted to the deflection D of the shaft 6 at its individual location.

In the case of a bending line B, as it is for example in Fig. 6 is shown, therefore the eccentricity E of the wear rings 7 and 8, preferably seen from both ends of the shaft 6 in the direction of the center of the pump 1 increases.

The eccentricity E of the first and second wear rings over the entire length of the wear rings 7, 8 is particularly preferred The enclosed part of the rotor is adapted to the bending line B of the shaft 6, as follows with reference to FIG Fig. 6 and 7th is explained.

The bending line B of the shaft arranged in a pump 1 can be determined, for example, on the basis of empirical or historical data. It is of course also possible to determine the bending line B by measurement or to determine it by means of calculations, for example simulations.

If the bending line B for a specific pump 1 is known at least approximately, it can also be decided in which areas of the rotor the deflection D of the shaft 6 is so great that there eccentrically configured wear rings 7 and 8 are advantageous.

It is now established for each individual wear ring 7 or 8 which eccentricity E it should advantageously have. Two criteria are particularly preferred for this. Firstly, the eccentricity E of the wear ring 7 or 8 is dimensioned such that when the shaft 6 is at a standstill, none of the wear rings 7 or 8 touches the shaft 6, so that the shaft 6 does not lie on any of the wear rings 7 or 8 at a standstill is thus freely rotatable, especially by hand. The second criterion is to dimension the eccentricity for each individual wear ring 7 or 8 so that the bending line B of the shaft 6 at a typical speed at which the pump 1 is operated, for example the nominal speed, is essentially or at least approximately in the middle runs between all wear rings 7 and 8, respectively. This means, as already described above for an individual wear ring 7 or 8, the aim is that for each individual wear ring 7 or 8, the shaft 6 is at least approximately centered with respect to the axis A2 of the radially inner boundary surface of this wear ring 7 or 8 .

The Fig. 6 and 7th show in a schematic representation this adaptation of the eccentricity E to the bending line B of the shaft 6. Because it is better for understanding, the rotor is in the Fig. 6 and 7th each represented only by the bending line B of the shaft 6, ie in Fig. 6 and Fig. 7 does not take into account that the rotor has a finite extent in the radial direction. The radial expansion of the rotor is not shown, but the Bending line B is to be understood as symbolic for a representation of the rotor or the shaft 6 with the impellers 32.

Fig. 6 shows for the exemplary embodiment Fig. 1 the situation for the state when the shaft 6 rotates at a typical speed, for example the nominal speed of the pump 1. It can be seen that the eccentricity E of both the first and the second wear rings 7 and 8 increases from the left end according to the illustration to approximately the middle of the pump 1 and then decreases again in the direction of the right end of the pump according to the illustration. It can also be seen that the bending line B is at least approximately centered with respect to the radially inner boundary surface of all wear rings 7 and 8, respectively. Thus, the play S1 or S2 (see Fig. 5 ) for each of the wear rings 7 and 8, viewed in the circumferential direction, at least approximately constant.

Fig. 7 shows for the exemplary embodiment Fig. 1 the situation for the state when the shaft 6 is stationary. It can be seen that the deflection D of the shaft 6 and in particular the maximum of the deflection D has increased, but that the rotor or the shaft 6 - represented by the bending line B - at no point is in direct physical contact with the wear rings 7 or 8 comes, so is freely rotatable with respect to the wear rings.

The above-described adaptation of the eccentricity E of the wear rings 7 and 8 to the bending line B is particularly advantageous with regard to temperature changes, especially rapid or temporary temperature changes. Since the rotor or the shaft 6 is always in an optimal position with respect to the stage housing 31 or the partition walls 32, or more generally expressed with respect to the stator of the pump 1, steeper temperature changes, ie larger temperature gradients, are possible without the There is a risk that the rotor will come into direct physical contact with the wear rings 7 or 8, and without it being necessary to take other measures, such as preheating the pump 1, for example.

Another advantage that results from the adjustment of the eccentricity E of the wear rings 7 or 8 to the bending line B of the shaft 6 is that the clearance S1 or S2 ( please refer Fig. 3 ) can be reduced, so that the efficiency of the pump 1 or its efficiency can be increased.

A particular advantage of the design according to the invention is the possibility of adapting the stator of the pump 1, i.e. in particular the step housing 31, the partition walls 32 and the wear rings 7, 8, to the bending line B of the shaft 6 only with the help of the wear rings 7 and 8 realize that can be manufactured particularly inexpensively as wear parts. No further modifications or structural measures are required for this adaptation. There is no need for one or more of the step housing 31 to be inclined, nor is there a need for an eccentric configuration of other components such as the step housing 31 or the partition walls 32.All components with the exception of the wear rings 7, 8, i.e. especially the step housing 31, can be centered or concentric to the central axis A of the pump 1 are designed and arranged. This is a very significant advantage for structural and manufacturing reasons.

Specifically in the configuration as a pump 1 with casing 2, there is the further structural advantage that the inlet 4 of the pump 1 does not have to be inclined with respect to the central axis A, but can be configured and arranged, as is generally customary, so that the axis C of the Inlet 4 (see Fig. 1 ) is perpendicular to the central axis A.

In addition, there is the advantage that due to the parallel alignment of all pump stages 3, in particular all stage housings 31 in pumps 1 with jacket housing 2, as in the exemplary embodiment described here, reliable seals can be provided between the outer sides of step housing 31 and jacket housing 2. There is thus the possibility of providing different pressure spaces in the jacket housing 2, which are sealed off from one another and in which the fluid to be conveyed, for example water, is present at different pressures.

This has the advantage that the intermediate outlet 51 can be provided on the casing 2, through which the fluid can be withdrawn from the pump at an intermediate pressure which is lower than the delivery pressure at the outlet 5 of the pump 1 and higher than the suction pressure at the inlet 4 of the pump 1. For example in industrial power generation it is often desirable that the water can be made available as the medium to be conveyed at different pressures.

Since the adjustment of the pump 1 to the bending line B of the shaft 6 is only possible with the aid of the wear rings 7, 8 and without other structural measures, the invention is particularly suitable as a method for maintaining, repairing and overhauling pumps that have already been commissioned especially for those pumps in which no or insufficient adjustment to the bending line B of the shaft 6 has been made.

In the method according to the invention, in the same way as described above, at least one of the first and / or the second wear rings is replaced by an eccentrically configured wear ring 7 or 8, respectively.

With regard to the method, too, it is preferred if the eccentricity E of the wear rings 7 and 8 is adapted to the bending line B of the shaft.

It goes without saying that the invention is not based on the embodiment according to Fig. 1 The type of pump described is limited, but is particularly suitable for all multistage horizontal centrifugal pumps. For example, the pump 1 can also be configured as a section pump (ring section pumps), in which the entirety of the stage housing 31 forms the outer pump housing, where no additional casing housing 2 is provided. The invention is also particularly suitable for pumps in which the impellers 32 are arranged in a so-called back-to-back arrangement. In this arrangement, the multistage pump has two groups of impellers, namely a first group of impellers, which are aligned with their inlet (their suction side) in the direction of one end of the pump, and a second group of impellers, which are aligned with their inlet (their suction side) are each aligned in the direction of the other end of the pump. These two groups are therefore arranged back to back to one another. It goes without saying that in the case of a two-stage pump each of the two groups comprises only one impeller. These two impellers are then arranged in such a way that their suction sides face away from each other.

Claims (15)

1. Multi-stage horizontal centrifugal pump for conveying a fluid having a rotor (6, 32) comprising a rotatably arranged shaft (6) and a plurality of impellers (32) for conveying the fluid, wherein all impellers (32) are arranged in a rotatably fixed manner on the shaft (6), and having a stator (31, 33) comprising a plurality of stage casings (31), which are arranged consecutively one after another with respect to an axial direction determined by a central axis (A), wherein the stator (31, 33) encompasses the rotor (6, 32), and wherein all stage casings (31) are designed and arranged centrically with respect to the central axis (A), and wherein a plurality of wear rings (7, 8) is provided between the rotor (6, 32) and the stator (31, 33), each of which is fixed with respect to the stator (31, 33), and respectively surrounds the rotor (6, 32) with a clearance (S1, S2), characterized in that at least one of the wear rings (7, 8) is designed eccentrically, wherein the eccentric design of the wear ring means that the radially outer boundary surface of the wear ring is centred about a first axis and the radially inner boundary surface of the wear ring is centred about a second axis, wherein the first and second axes are parallel but not congruent.
2. Pump according to claim 1, wherein a plurality of wear rings (7, 8) is designed eccentrically.
3. Pump according to one of the preceding claims, wherein the wear rings (7, 8) have an eccentricity (E) which increases towards the centre of the pump.
4. Pump according to claim 3, wherein the eccentricity (E) of the wear rings (7, 8) is adjusted to the sag line (B) of the shaft (6).
5. Pump according to claim 3 or 4, in which the eccentricity (E) of all wear rings (7, 8) is measured such that during standstill of the shaft (6) none of the wear rings (7, 8) is in contact with the shaft (6) or an impeller (32).
6. Pump according to one of the claims 3 to 5, in which the eccentricity (E) of all wear rings (7, 8) is measured such that the sag line (B) of the shaft (6) extends essentially centered with respect to all wear rings (7, 8) at a nominal speed of the pump.
7. Pump according to one of the preceding claims with a plurality of pump stages (3), which are arranged consecutively one after another with respect to the axial direction, wherein each pump stage (3) comprises an impeller (32) for pumping the fluid, wherein the impeller is provided with a front cover plate (34), as well as one of the stage casings (31) and a partition wall (33) for conducting the fluid to the adjacent pump stage (3), wherein the partition wall is stationary with respect to the stage casing (31)), wherein the stage casing (31) is designed with a stationary impeller opening (37) to receive the front cover plate (34) of one of the impellers (32), wherein each stationary impeller opening (37) is radially inwardly confined by a first wear ring (7), which surrounds the front cover plate (34) of the impeller (32) with a clearance (S1), and wherein each stationary partition wall (33) is radially inwardly confined by a second wear ring (8), which surrounds the shaft (6) with a clearance (S2).
8. Pump according to one of the preceding claims, wherein each eccentric wear ring (7, 8) comprises a positioning means (9) to position the respective wear ring (7, 8) at a predefined angular orientation in the respective stage casing (31) or the respective partition wall (33).
9. Pump according to claim 8, wherein the positioning means (9) is provided where the respective wear ring (7, 8) has its maximum width (F) in the radial direction.
10. Pump according to one of the preceding claims, wherein all stage casings (31) are arranged in a barrel casing (2).
11. Pump according to one of the preceding claims having an inlet (4) and an outlet (5) as well as an intermediate outlet (51) for the fluid to be conveyed, with the intermediate outlet (51) being designed and arranged in such a manner that at least a part of the fluid can be discharged at an intermediate pressure through the intermediate outlet (51), which intermediate pressure is greater than the pressure of the fluid at the inlet (4) of the pump and smaller than the pressure of the fluid at the outlet (5) of the pump.
12. Method for repairing or overhauling a multi-stage horizontal centrifugal pump (1) for conveying a fluid having a rotor (6, 32) comprising a rotatably arranged shaft (6) and a plurality of impellers (32) for conveying the fluid, wherein all impellers (32) are arranged in a rotatably fixed manner on the shaft (6), and having a stator (31, 33) comprising a plurality of stage casings (31), which are arranged consecutively one after another with respect to an axial direction determined by a central axis (A), wherein the stator (31, 33) encompasses the rotor (6, 32), and wherein all stage casings (31) are designed and arranged centrically with respect to the central axis (A), and wherein a plurality of wear rings (7, 8) is provided between the rotor (6, 32) and the stator (31, 33), each of which is fixed with respect to the stator (31, 33), and respectively surrounds the rotor (6, 32) with a clearance (S1, S2), in which method one or a plurality of the wear rings (7, 8) is replaced, characterized in that one or a plurality of the wear rings (7, 8) is replaced in each case by an eccentrically designed wear ring (7, 8), wherein the eccentric design of the wear ring means that the radially outer boundary surface of the wear ring is centred about a first axis and the radially inner boundary surface of the wear ring is centred about a second axis, wherein the first and second axes are parallel but not congruent.
13. Method according to claim 12, in which the eccentricity (E) of the wear rings (7, 8) is adjusted to a sag line (B) of the shaft (6).
14. Method according to claim 12 or 13, in which the eccentricity (E) of each wear ring (7, 8) is measured such that during standstill of the shaft (6) none of the wear rings (7, 8) contacts the shaft (6).
15. Method according to one of the claims 12 to 14, in which the eccentricity (E) of each wear ring (7, 8) is measured such that the sag line (B) of the shaft (6) extends essentially centered with respect to all wear rings (7, 8) at a nominal speed of the pump (1).

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