Multi-stage horizontal centrifugal pump for conveying a fluid and a method for repairing the same

Abstract

A multi-stage horizontal centrifugal pump for conveying a fluid has a rotor including a rotatably arranged shaft and a plurality of impellers for conveying the fluid and a stator. All the impellers are arranged in a rotatably fixed manner on the shaft. The stator includes a plurality of stage casings, which are arranged consecutively one after another with respect to an axial direction determined by a central axis. The stator encompasses the rotor, and each stage casing is designed and arranged centrically with respect to the central axis. A plurality of wear rings is disposed between the rotor and the stator, each of which is fixed with respect to the stator, and surrounds the rotor with a clearance. At least one of the wear rings is designed eccentrically.

Claims

1. A multiple-stage horizontal centrifugal pump for conveying a fluid, comprising: a rotor comprising a rotatably arranged shaft and a plurality of impellers for conveying the fluid, each impeller of the plurality of impellers being arranged in a rotatably fixed manner on the shaft; a stator comprising a plurality of stage casings arranged consecutively one after another with respect to an axial direction determined by a central axis, the stator encompassing the rotor, and each stage casing of the plurality of stage casings being configured and arranged centrically with respect to the central axis; a plurality of wear rings disposed between the rotor and the stator, each wear ring of the plurality of wear rings being fixed with respect to the stator, and surrounding the rotor with a clearance, at least one wear ring of the plurality of wear rings is designed eccentrically and unitarily; and wherein each stage casing of the plurality of stage casings is separate from each other stage casing of the plurality of stage casings.

2. The multiple-stage horizontal centrifugal pump according to claim 1, wherein at least two wear rings of the plurality of wear rings is designed eccentrically.

3. The multiple-stage horizontal centrifugal pump according to claim 1, wherein the least two wear rings of the plurality of wear rings have an eccentricity which increases towards a center of the pump.

4. The multiple-stage horizontal centrifugal pump according to claim 3, wherein the eccentricity of the least two wear rings is adjusted to a sag line of the shaft.

5. The multiple-stage horizontal centrifugal pump according to claim 3, wherein the eccentricity of the at least two wear rings is such that during a standstill of the shaft none of the wear rings is in contact with the shaft or the impellers.

6. The multiple-stage horizontal centrifugal pump according to claim 3, wherein the eccentricity of the at least two wear rings is such that the sag line of the shaft extends essentially centered with respect to the plurality of wear rings at a nominal speed of the pump.

7. The multiple-stage horizontal centrifugal pump according to claim 1, further comprising a plurality of pump stages arranged consecutively one after another with respect to the axial direction, each pump stage comprising an impeller of the plurality of impellers for pumping the fluid, including a front cover plate, a stage casing of the plurality of stage casings and a partition wall for conducting the fluid to the adjacent pump stage, the partition wall being stationary with respect to the stage casing, the stage casing for each pump stage having a stationary impeller opening to receive the front cover plate of a respective impeller, each stationary impeller opening being radially inwardly confined by a first wear ring of the plurality of wear rings, which surrounds the front cover plate of the impeller with the clearance, and each stationary partition wall being radially inwardly confined by a second wear ring of the plurality of wear rings, which surrounds the shaft with another clearance.

8. The multiple-stage horizontal centrifugal pump according to claim 1, wherein the at least one wear ring of the plurality of wear rings comprises a positioning device configured to position the at least one wear ring at a predefined angular orientation in a stage casing or a partition wall.

9. The multiple-stage horizontal centrifugal pump according to claim 8, wherein the positioning device is disposed on the at least one wear ring at a maximum width of the at least one wear ring in a radial direction.

10. The multiple-stage horizontal centrifugal pump according to claim 1, wherein each stage casing of the plurality of stage casings is arranged in a barrel casing.

11. The multiple-stage horizontal centrifugal pump according to claim 1, further comprising an inlet, an outlet, and an intermediate outlet configured to convey the fluid, the intermediate outlet being designed and arranged such that at least a part of the fluid is capable of being discharged at an intermediate pressure through the intermediate outlet, the intermediate pressure being greater than a pressure of the fluid at the inlet (4) of the pump and less than the pressure of the fluid at the outlet of the pump.

12. A method for repairing or overhauling a multi-stage horizontal centrifugal pump for conveying a fluid having a rotor comprising a rotatably arranged shaft and a plurality of impellers for conveying the fluid, each impeller of the plurality of impellers arranged in a rotatably fixed manner on the shaft, and having a stator comprising a plurality of stage casings arranged consecutively one after another with respect to an axial direction determined by a central axis, the stator encompassing the rotor, and each stage casing of the plurality of stage casings designed and arranged centrically with respect to the central axis, and a plurality of wear rings disposed between the rotor and the stator, each wear ring of the plurality of wear rings fixed with respect to the stator, and surrounding the rotor with a clearance, the method comprising; replacing at least one wear ring of the plurality of wear rings with an eccentrically and unitarily designed wear ring; and wherein each stage casing of the plurality of stage casings is separate from each other stage casing of the plurality of stage casings.

13. The method according to claim 12, further comprising adjusting the eccentricity of the at least one wear ring of the plurality of wear rings to a sag line of the shaft.

14. The method according to claim 12, further comprising measuring the eccentricity of the at least one wear ring of the plurality of wear rings so that during standstill of the shaft none of the plurality of wear rings contacts the shaft.

15. The method according to claim 12, further comprising measuring the eccentricity of the at least one wear ring of the plurality of wear rings so that the sag line of the shaft extends essentially centered with respect to each wear ring of the plurality of wear rings at a nominal speed of the pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail hereinafter with reference to the drawings.

(2) FIG. 1 is a schematic lateral view of an embodiment of a pump according to the invention in partial cross section,

(3) FIG. 2 is a perspective sectional view of a pump stage of the embodiment from FIG. 1,

(4) FIG. 3 is an enlarged sectional view illustrating the clearance between a first and a second wear ring,

(5) FIG. 4 is a perspective view of an embodiment of a wear ring,

(6) FIG. 5 is a cross sectional through the wear ring from FIG. 4 in the axial direction,

(7) FIG. 6 is a schematic view of the sag line of the shaft at a nominal speed of the pump, and

(8) FIG. 7 is a schematic view of the sag line of the shaft during standstill of the pump.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) FIG. 1 shows in a schematic lateral view an embodiment of a multi-stage horizontal centrifugal pump according to the invention which is designated as a whole by the reference numeral 1. In FIG. 1 some parts of the pump 1 are illustrated in a in cross section. FIG. 2 shows some parts of the pump 1 in an enlarged sectional view.

(10) Such multi-stage pumps are used for example in industrial energy generation, e.g. as feed pumps or boiler feed pumps in which the fluid to be conveyed is water which is transported from the pump 1 to a steam generator. Such pumps are also used in the oil and gas industry for pumping water, for example as injection pumps, or also for extracting oil or other hydrocarbons.

(11) In the embodiment shown in FIG. 1, the pump 1 comprises an outer barrel casing 2 having an inlet 4, an outlet 5 as well as optionally an intermediate outlet 51 for the fluid to be conveyed. The latter one will be described in more detail below.

(12) The pump 1 comprises a rotatable shaft 6 which extends in the centre through the pump 1 and which can be set in rotation by a power unit such as an electric motor which is not shown here. The pump 1 has a central axis A which extends through the centre of the chamber provided for the shaft 6 within the pump 1 and which constitutes the target rotation axis about which the shaft 6 should rotate. If the shaft 6 installed in the pump 1 had no deflection, the central axis A would be congruent with the longitudinal axis of the shaft. In the following, when reference is made to the axial direction, this always refers to the direction of the central axis A of the pump 1. When reference is made to the radial direction, this refers then to a direction which is perpendicular to the axial direction.

(13) In a manner known per se a plurality of pump stages 3in this case for example eightare disposed in the barrel casing 2, which are arranged consecutively one after another with respect to the axial direction. FIG. 1 shows the pump 1 in its normal position, i.e. in the horizontal arrangement where the central axis A extends horizontally or parallel to the subsurface.

(14) For a better understanding FIG. 2 shows in an enlarged view a perspective sectional view of one of the pump stages 3 (see also FIG. 3).

(15) Each pump stage 3 comprises in a manner known per se an impeller 32, a stage casing 31, as well as on the high pressure side, a partition wall 33 which separates the pump stage 3 from the next pump stage 3. Each impeller 32 is shaped as a closed impeller 32, i.e. it comprises a front cover plate 34, a rear cover plate 35 as well as a plurality of blades 36 arranged between the cover plates 34, 35 for conveying the fluid. Each stage casing 31 comprises a stationary impeller opening 37 for receiving the front cover plate 34 of one of the impellers 32. The partition wall 33 is also stationary with respect to the stage casing 31 and serves to transport the fluid conveyed by the impeller 32 to the inlet, i.e. to the impeller 32 of the next pump stage 3. For this purpose the partition wall 33 comprises a stationary diffuser which is not illustrated in more detail in the drawings.

(16) The impellers 32 of all pump stages 3 are connected in a rotatably fixed manner to the shaft 6 such that the impellers 32 rotate together with the shaft 6.

(17) Within the scope of this application the term rotor means the totality of the components of the pump 1 that rotate in the operating state of the pump 1. The rotor of the pump 1 thus comprises the shaft 6 and all impellers 32 arranged on it as well as possibly further components of the pump 1 rotating together with the shaft 6 or being connected in a rotatably fixed manner to the shaft 6. Within the scope of this application the term stator of the pump means the totality of the stationary, i.e. non-rotating, components of the pump. Thus the stator comprises in particular all stage casings 31 and all partition walls 32.

(18) As it is especially shown in FIG. 1, all pump stages 3 and all stage casings 31 are arranged parallel to each other in such a manner that the areas enclosed by each of the impeller openings 37 are perpendicular to the central axis A.

(19) When the pump 1 is in operation, the fluid to be conveyed, such as water, which enters through the inlet 4 of the pump 1, is transported from the first impeller 32this is the rightmost impeller 32 illustrated in FIG. 1to the annulus between the partition wall 33 and the stage casing 31 and from there it is conducted radially inwardly between the partition wall 33 and the stage casing 31 before reaching the impeller 32 of the adjacent pump stage 31. This process continues through all pump stages 3 up to the final stagethis is the leftmost one shown in FIG. 1conducting the fluid then from the outlet of the final stage to the outlet 5 of the pump 1.

(20) As is usual, two wear rings are provided in each pump stage 3 to seal the respective pump stage 3 against its adjacent pump stages 3 or against the inlet 4 or the outlet 5. A first wear ring 7 is fitted into the impeller opening 37 of the stage casing 31 in such a manner that the stationary impeller opening is radially inwardly confined by the first wear ring 7 which is connected in a fixed manner to the stage casing 3 and consequently is stationary. Thus the first wear ring 7 surrounds the front cover plate 34 of one of the impellers 32. A second wear ring 8 is provided radially inwardly at the stationary partition wall 33 and encompasses the shaft 6, i.e. the stationary partition wall 33 is radially inwardly confined by the second wear ring 8 which is arranged with respect to the radial direction between the partition wall 33 and the shaft 6. The second wear ring 8 is connected in a fixed manner to the partition wall 33 and consequently is also stationary.

(21) As already mentioned, both wear rings 7, 8 serve to seal the pump stages 3 along the shaft 6. Each of the wear rings 7, 8, however, surrounds the rotor with a clearance in such a manner that an annular gap is formed between the radially outer surface of the rotor and the radially inner surface of the wear ring 7, 8, through which gap the leakage flows in the opposite direction to the general conveying direction of the fluid. On the one hand this leakage flow is desirable, in particular to stabilize the rotor in a hydrodynamic manner, but on the other hand it should not be too big, as the leakage flow decreases the efficiency of the pump. Furthermore, during the normal operating state of the pump 1 any direct physical contact between the rotor (shaft 6 or impeller 32) and one of the wear rings 7, 8 should be avoided.

(22) As the clearance between the rotor and the wear rings 7, 8 is typically very small, it can be recognized neither in FIG. 1 nor in FIG. 2. Therefore FIG. 3 shows an enlarged sectional view for illustrating the clearance of a first and a second wear ring 7 or 8.

(23) As it can be seen in FIG. 3, there is a clearance S1 between the radially inner surface of the first wear ring 7 and the radially outer surface of the front cover plate 34 of the impeller 32, such clearance leading to the formation of an annular gap between the first wear ring 7 and the front cover plate 34. In the same way there is a clearance S2 between the radially inner surface of the second wear ring 8 and the radially outer surface of the shaft 6, such clearance leading to the formation of an annular gap between the second wear ring 8 and the shaft 6. The clearance S1 canbut does not necessarily have tobe as big as the clearance S2.

(24) As already mentioned, in the case of multi-stage horizontal pumps 1, in particular those where the shaft 6 is very long, the mass of the rotor leads to a significant deflection of the shaft 6 or the rotor. Such deflection is illustrated in a very schematic way in FIG. 6 by a sag line B. The sag line B of the shaft 6 constitutes the centerline of the shaft 6, when the shaft 6 including the impellers 32 connected in a rotatably fixed manner to it and other components, thus the rotor, is installed in the pump 1, i.e. when the shaft 6 is arranged in its bearings and in particular radial bearings which are positioned on the outside in the region of both ends of the shaft 6, but which are not shown in more detail.

(25) If there was no deflection, the sag line B would be positioned exactly on the central axis A of the pump 1. The term deflection D of the shaft 6 means the distance of the sag line B from the central axis A. In the case of a horizontal pump 1, due to the direction of the gravitational force, the sag line B constitutes always a convex curve. The deflection D reaches its maximum approximately in the centre of the pump 1, as it is illustrated in FIG. 6. Depending on the length of the shaft 6 and the mass of the impellers 32, the maximum deflection D can be a few tenths of a millimetre, for example 0.2 to 0.5 mm or more.

(26) In order to compensate the problems resulting from the deflection D of the shaft 6, it is suggested according to the invention that at least one of the first or the second wear rings 7 or 8 is eccentrically designed. FIG. 4 shows an embodiment of such an eccentrically designed wear ring 7 or 8 in a perspective view. FIG. 5 shows a section through the wear ring 7, 8 from FIG. 4, wherein the section is performed in the axial direction, i.e. in the same way as in FIG. 3. FIG. 5 illustrates additionally the term of the eccentric design or eccentricity.

(27) The term eccentric design means that the radially outer surface of the wear ring 7, 8 is centred about a different axis than its radially inner surface. This is illustrated in FIG. 5 for the simple embodiment of the wear ring 7, 8 where the cross-sectional area of the wear ring 7 or 8 is rectangular. In this embodiment each surface of the wear ring 7 or 8, i.e. the radially outer surface as well as the radially inner surface, constitutes a cylindrical barrel surface. The radially outer surface has a radius R1 and the radially inner surface has a radius R2, with R2 being, of course, smaller than R1. The radially outer surface is centred about a first axis A1, i.e. in this case A1 is identical to the cylinder axis of the radially outer surface. The radially inner surface is centred about a second axis A2, i.e. in this case A2 is identical to the cylinder axis of the radially inner surface. The axes A1 and A2 are parallel to each other, but they are not congruent. This design of the axes A1 and A2 being not congruent is referred to as eccentric. The eccentricity E which is given by the distance between the two axes A1 and A2 is determined to be a measure for the intensity of the eccentric design.

(28) 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. Thanks to the modern processing methods usually used today it is no problem to produce such eccentricities E in a wear ring 7 or 8 with sufficient accuracy.

(29) Due to the eccentric design the radial width F of the wear ring 7 or 8 varies along its circumference, i.e. there is a maximum radial width F and a minimum radial width F, with the radial width F being the extension of the wear ring 7 or 8 in the radial direction.

(30) Due to the variation in the radial width F the wear ring 7 or 8 has to be fastened at the stage casing 31 and the partition wall 33, respectively, in the correct angular orientation. As the deflection D of the shaft 6 occurs always downwards with respect to the normal position, the wear ring 7 or 8 is inserted in such orientation positioning the wear ring with its maximum radial width F perpendicularly above the central axis A or with its minimum radial width F perpendicularly below the central axis A.

(31) In order to realize the correct angular orientation of the wear ring 7 or 8 in a simpler way, it is advantageous, if each eccentric wear ring 7 or 8 comprises a positioning means 9. This positioning means 9 (see FIG. 4) can, for example, be a pin 9 protruding in the axial direction from the ring and engaging during the installation into a corresponding hole (not shown here) provided in the respective stage casing 31 or the respective partition wall 33. Of course, it is also possible to use other positioning means 9, such as a projection or recess at the wear ring 7 or 8, which interacts in an interlocking manner with a projection or recess provided in the stage casing 31 or in the partition wall 33, or visually recognizable markings such as notches, lines or arrows.

(32) For reasons of assembly the positioning means 9as shown in FIG. 4is preferably provided where the respective wear ring 7 or 8 has its maximum radial width F.

(33) It is self-explanatory that the rectangular cross-sectional area of the wear ring 7 or 8 illustrated in FIG. 5 is only to be taken as example. Of course, the wear rings 7 or 8 can have other and more complex cross-sectional areas, in particular those used in the prior art for wear rings in centrifugal pumps. The cross-sectional area of the wear ring 7 or 8 can, for example, have an L-shaped or trapezoidal form, it can comprise borderlines extending at an oblique angle or acute angle to each other. Furthermore, rounding offs or cants may be provided. The man skilled in the art knows many possibilities for forming these cross-sectional areas.

(34) Furthermore, it is evident that the first wear ring 7 usually has a different geometrical configuration than the second wear ring 8, even if, in principle, the geometrical configurations can be identical.

(35) The radially inner surface of each wear ring 7 or 8 is usually a cylindrical barrel surface having a radius R2 (see FIG. 5). Typically, the radius R2 of the first wear rings 7 is different from the radius R2 of the second wear rings 8. The radius R2 of the second wear rings 8 is usually smaller than those of the first wear rings 7.

(36) As regards the material used for the production of the wear rings 7, 8, the man skilled in the art knows many possibilities. One example of this are martensitic premium steels or stainless steels.

(37) The at least one wear ring 7 or 8 having an eccentric design according to the invention is provided where the deflection D of the shaft 6 reaches its maximum. The eccentricity E of this wear ring is preferably measured such that the rotating shaft 6 or the rotating cover plate 34 of the impeller 32 is at least approximately centred with respect to the radially inner surface of the eccentric wear ring 7 or 8; i.e. the eccentricity E is selected such that it is at least approximately adjusted to the deflection D of the rotating shaft 6 at the place of this wear ring 7 or 8. As a result, the rotating shaft 6 or the rotating cover plate 34 in that eccentrically designed wear ring 7 or 8 is at least approximately centred with respect to the second axis A2 (see FIG. 5).

(38) This eccentrically designed wear ring 7 or 8 is then fastened at the stage casing 31 and the partition wall 33, respectively, preferably by using the positioning means 9, such that its region having the maximum radial width F is arranged perpendicularly above the central axis A. If the rotor rotates then, it is essentially centred in that wear ring 7 or 8, i.e. the rotor isas described aboveat least approximately centred with respect to the axis A2. This means that the clearance S1 or S2 (see FIG. 3) is at least approximately constant within this wear ring 7 or 8 in the circumferential direction of the rotor. As a consequence, the rotor can rotate without contacting the wear ring 7 or 8.

(39) If the pump 1 is then turned off in such a manner that the rotor stops, the deflection D usually increases, in particular also in this region where the deflection D reaches its maximum. Due to the clearance 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 permitting the rotor to avoid direct physical contact with the wear ring 7 or 8 despite the increased deflection D of the rotor. This means that the rotor or shaft 6, even during standstill, is free in the sense that the rotor or shaft 6 does not rest upon the wear ring 7 or 8. This has particularly the advantage that it is possible to manually rotate the rotor during standstill of the pump 1, which constitutes an enormous advantage in particular for maintenance and assembly work.

(40) Furthermore, the fact that there is no contact is also advantageous for starting and turning off the pump 1, as the rotor does not grind against the wear ring 7 or 8. Consequently, on the one hand it is not necessary to provide the wear ring 7 or 8 with a coating, and on the other hand the useful life of the rotor increases, as its components do not mechanically grind against the wear ring 7 or 8.

(41) For most applications it is advantageous, if a plurality of the first as well as of the second wear rings 7 or 8 is eccentrically designed. In this respect the eccentricity E of an individual wear ring 7 or 8 is adjusted to the deflection D of the shaft 6 at its individual position.

(42) Therefore, as regards the sag line B illustrated by way of example in FIG. 6, the eccentricity E of the wear rings 7 or 8 preferably increases from both ends of the shaft 6 towards the centre of the pump 1.

(43) It is particularly preferred that the eccentricity E of the first and second wear rings is adjusted over the whole length of the part of the rotor enclosed by the wear rings 7, 8 to the sag line B of the shaft 6, as it will be explained in the following on the basis of FIGS. 6 and 7.

(44) The sag line B of the shaft arranged in a pump 1 can for example be determined on the basis of empirical or historical data. It is, of course, also possible to determine the sag line B by measurement or calculations such as simulations.

(45) If the sag line B is at least approximately known for a certain pump 1, it is also possible to determine the regions of the rotor where the deflection D of the shaft 6 is such that eccentrically designed wear rings 7 or 8 are advantageous there.

(46) Then it is determined which eccentricity E each individual wear ring 7 or 8 should advantageously comprise. For this purpose there are two particularly preferred criteria. Firstly, the eccentricity E of the wear ring 7 or 8 is measured such that during standstill of the shaft 6 none of the wear rings 7 or 8 contacts the shaft 6 such that the shaft 6 during standstill does not rest upon any of the wear rings 7 or 8 and therefore is freely rotatable, in particular by hand. The second criteria is to measure the eccentricity for each individual wear ring 7 or 8 such that the sag line B of the shaft 6 extends at a typical rotational speed of the pump 1, when operating, such as the nominal speed, essentially or at least approximately centered with respect to all wear rings 7 or 8. That means, as already described above in the case of an individual wear ring 7 or 8, one intends to centre at least approximately for each individual wear ring 7 or 8 the shaft 6 with respect to the axis A2 of the radially inner surface of that wear ring 7 or 8.

(47) FIGS. 6 and 7 show in a schematic view this adjustment of the eccentricity E to the sag line B of the shaft 6. For a better understanding the rotor is represented in each of the FIGS. 6 and 7 only by the sag line B of the shaft 6; i.e. FIG. 6 and FIG. 7 do not take into account the finite extent of the rotor in the radial direction. Thus, the radial extension of the rotor is not shown, but the sag line B represents symbolically the rotor or the shaft 6 with the impellers 32.

(48) With reference to the embodiment shown in FIG. 1, FIG. 6 shows the situation of the shaft 6 rotating at a typical rotational speed, such as the nominal speed of the pump 1. It can be recognized that the eccentricity E of the first as well as of the second wear rings 7 or 8 increases first from the left end of the illustration to approximately the centre of the pump 1, then decreasing towards the right end of the pump. It can also be recognized that the sag line B is at least approximately centred with respect to the radially inner surface of all wear rings 7 or 8. As a consequence, also the clearance S1 or S2 (see FIG. 5) is at least approximately constant for each of the wear rings 7 or 8 in the circumferential direction.

(49) With reference to the embodiment shown in FIG. 1, FIG. 7 shows the situation when the shaft 6 is not in motion. It can be recognized 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 6represented by the sag line Bis not in direct physical contact with the wear rings 7 or 8, i.e. it is freely rotatable with respect to the wear rings.

(50) The adjustment of the eccentricity E of the wear rings 7 or 8 to the sag line B which has been described above is advantageous in particular with regard to temperature changes, especially rapid or temporary temperature changes. As the rotor or the shaft 6, when operating, is always in an optimal position with respect to the stage casing 31 or the partition walls 32, or, more generally, with respect to the stator of the pump 1, larger temperature changes, i.e. larger temporal temperature gradients are possible without any risk to the rotor to come into direct physical contact with the wear rings 7 or 8 and without the need to provide other measures such as preheating the pump 1.

(51) A further advantage resulting from the adjustment of the eccentricity E of the wear rings 7 or 8 to the sag line B of the shaft 6 is the possibility to reduce the clearance S1 or S2 (see FIG. 3) in many applications due to the optimized positioning of the rotor with respect to the stator, leading to an increase in efficiency or effectiveness of the pump 1.

(52) A particular advantage of the configuration according to the invention is the possibility to realize the adjustment of the stator of the pump 1, i.e. in particular of the stage casings 31, the partition walls 32 and the wear rings 7, 8, to the sag line B of the shaft 6 only by the wear rings 7 and 8 which can be manufactured as wear parts in an especially cost-effective manner. No further modifications or constructional measures are necessary for this adjustment. Neither one nor more stage casings 31 have to be arranged in a tilted position, nor other components such as the stage casing 31 nor the partitions walls 32 have to be eccentrically designed. All components except for the wear rings 7, 8, i.e. in particular also the stage casings 31, can be designed and arranged centrically or concentrically to the central axis of the pump 1. This constitutes an enormous advantage for the construction and the production.

(53) As regards the configuration as pump 1 with barrel casing 2, there is the further constructional advantage that it is not necessary to tilt the inlet 4 of the pump 1 with respect to the central axis A, butas usualit can be designed and arranged such that the axis C of the inlet 4 (see FIG. 1) is perpendicular to the central axis A.

(54) A further advantage is that due to the parallel alignment of all pump stages 3, in particular of all stage casings 31 in pumps 1 with barrel casing 2, as it is the case in this embodiment, reliable seals can be provided between the outer surfaces of the stage casings 31 and the barrel casing 2. As a consequence, it is possible to provide different pressure chambers in the barrel casing 2, which are sealed against each other and in which the fluid to be conveyed such as water is available at different pressures.

(55) This has the advantage that the intermediate outlet 51 can be provided at the barrel casing 2, such intermediate outlet permitting to discharge the fluid at an intermediate pressure from the pump, wherein the intermediate pressure is smaller than the pumping pressure of the fluid at the outlet 5 of the pump 1 and greater than the suction pressure at the inlet 4 of the pump 1. In industrial energy generation, for example, it is often desirable that the water as medium to be conveyed is available at different pressures.

(56) As the adjustment of the pump 1 to the sag line B of the shaft 6 can be realized only by means of the wear rings 7, 8 and without having to take other constructional measures, the invention is also particularly suitable for maintaining, repairing and overhauling pumps which are already in operation and in particular for such pumps which have not yet been adjusted or not sufficiently been adjusted to the sag line B of the shaft 6.

(57) In the method according to the invention, in the same sense and way as previously described, at least one of the first and/or of the second wear rings is replaced in each case by an eccentrically designed wear ring 7 or 8.

(58) Also with regard to the method it is preferred, if the eccentricity E of the wear rings 7 and 8 is adjusted to the sag line B of the shaft.

(59) It is obvious that the invention is not limited to the pump type described in the embodiment according to FIG. 1, but is suitable for all multi-stage horizontal centrifugal pumps. The pump 1 can, for example, also be shaped as ring section pump, in which the totality of stage casings 31 form the outer pump casing, i.e. no additional barrel casing 2 is provided. The invention is particularly suitable also for those pumps in which the impellers 32 are arranged in a so-called back-to-back arrangement. In the case of this arrangement the multi-stage pump comprises two groups of impellers, namely a first group of impellers which are oriented with their inlet (their suction side) towards the one end of the pump, and a second group of impellers which are oriented with their inlet (their suction side) towards the other end of the pump. Thus, these two groups are arranged back to back to each other. It is obvious that in the case of a two-stage pump each of the two groups comprises only one impeller. These two impellers are then arranged such that their suction sides are turned away from each other.