Multistage centrifugal pump with shaft hydraulic force compensation

A multistage centrifugal pump (1) has impellers (9) arranged on a common shaft (8), which is rotatably arranged within a pump casing (2-4). One end of the shaft (8) is led out of the casing (2-4) for connection to a drive motor and another shaft end (15) is rotatably mounted in the pump casing (2-4). The shaft end (15) which is mounted within the pump casing (2-4) is subjected to a counter-force which is produced by way of pressure subjection via a conduit connection to a delivery side of the pump. An axial seal (11) is provided on the shaft end (15) arranged within the pump casing (2-4). The rotating part of the axial seal is led on the shaft end and the non-rotating part is led, axially movably, within the pump casing (2-4). A sealing arrangement is provided between the pump casing and the axially movably mounted part.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 of European Application 15 195 416.1 filed Nov. 19, 2015, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a multi-stage centrifugal pump with which the impellers of the pump stages are arranged on a shaft which is rotatably arranged within a pump casing and which at one end is led out of the casing for connection to a drive motor and at the other end is arranged within the pump casing.

BACKGROUND OF THE INVENTION

With multi-stage centrifugal pumps, with which the impellers of the pump stages are arranged on a common shaft and are rotatably arranged within a pump casing, the drive is often effected via an external motor which is drivingly connected to the pump shaft by a coupling and is received and fastened on a motor stool, which is to say a casing part which is designed for receiving the motor. For this, the one shaft end is sealingly led through the pump casing and out of this, and the other shaft end is mounted within the pump casing. Thereby, it is counted as belonging to the state of the art to accommodate the forces acting upon the pump shaft by way of the motor bearings and to merely provide a radial guiding, for example by way of shaft sleeves which are arranged in the region of the pump stages, within the pump casing. In contrast, the pump-side shaft end is mounted radially and/or axially within the pump casing, in order to relieve the motor bearings, in the case of larger multi-stage pumps. Common to all designs however is an increased loading and thus an increased wear of the motor bearings.

Thereby, it is counted as belonging to the state of the art, to compensate these axial forces upon the shaft which result due to the hydraulic forces, be it by way of subjecting the shaft end mounted in the casing to the pressure of the delivery side or by way of the provision of recesses in the shrouds of the impellers. The latter results in a significant loss in the efficiency, on account of the backflows which are caused by way of this. With hydraulic force compensation, there exists the problem that a highly-loaded seal is to be provided between the rotating shaft end and the stationary casing, which, if it has a good sealing effect, creates a high friction and thus also a high wear and leads to overflow losses given the degradation of the sealing effect.

SUMMARY OF THE INVENTION

Against this state of the art, it is an object of the present invention, to design a multi-stage centrifugal pump of the known type, such that on the one hand the hydraulically caused forces upon the shaft can be reduced, but on the other hand a good, low-friction and low-wear sealing, which is therefore stable over the long term, is effected.

With the multi-stage centrifugal pump according to the invention, the impellers of the pump stages are arranged on a shaft in a direct manner or via a carrier body, said shaft being rotatably arranged within a pump casing. This shaft, at one end, is led out of the casing in a sealed manner for connection to a drive motor and at the other end this shaft is arranged within the pump casing. The shaft end arranged within the pump casing is subjected to a counter-force which is produced by way of pressure subjection via a conduit connection to a delivery side of the pump, typically, but not necessarily to the pressure of the last pump stage, thus the delivery side of the pump. According to the invention, an axial seal is provided on the shaft end which is mounted within the pump casing, a rotating part of said axial seal being led on the shaft end and a non-rotating part of the axial seal being led within the pump casing in an axially movable manner. Thereby, according to the invention, a sealing means (a sealing device) is provided between the non-rotating, axially movably mounted part and the pump casing, in order there to prevent a flow of fluid from the delivery side over to the suction side. A pump casing in the context of the present invention is also to be understood as an intermediate component which is integrated into the pump casing and on which the sealing means engage.

A basic concept of the solution according to the invention, on the one hand is to provide a hydraulic force compensation which reduces the axial forces of the pump shaft acting upon the bearings, but on the other hand to provide an axial seal which only has a low friction and thus a low wearing, but which is simple in construction and reliable with regard to its effect, on the shaft end mounted within the casing. This is achieved by way of the rotating part of the axial seal being provided on the shaft end, and the non-rotating part within the pump casing. However, the non-rotating part of the axial seal is advantageously mounted and guided within the pump casing in an axially movable manner, in order be able to compensate possible wear or axial play of the shaft, wherein sealing means are provided between the axially movably mounted part of the axial seal and the pump casing. The complete sealing is thus divided into a purely axial seal as well as a further seal, preferably a radial seal, wherein the predominant movement is accommodated in the region of the axial seal, whereas the other, in particular radial seal only has to carry out small axial movements and thus, inherent of the design, is only subjected to low wear. This further, in particular radial seal can therefore be formed inexpensively, for example by way of an elastic sealing ring, whereas the axial seal can be designed exclusively for sealing with respect to the rotation movement, by way of suitably designed sealing surfaces. Thereby, given a suitable design of the axial seal, this can also accommodate axial forces and thus assume the function of a thrust bearing.

According to the invention, one envisages subjecting the shaft end which is mounted within the pump casing to the pressure of the delivery side, in order in particular to largely compensate the axial forces resulting due to the hydraulic forces. However, the design according to the invention in a particularly advantageous manner envisages the sealing not being effected by a seal between a stationary and a rotating component, but between the pump casing and the axially movably mounted and non-rotating part of the axial seal. This solution has the advantage that the seal merely needs to accommodate the typically slight axial movement of the non-rotating part of the axial seal, but not the friction-intensive and wear-creating movement to the rotating part and which is accommodated by the axial seal. Inasmuch as this is concerned, the sealing is effected by the sealing gap itself, which, given suitably dimensioned axial seal, is sufficiently small so as to be able to neglect overflow losses. The sealing means can therefore be designed in an inexpensive manner and in a manner which is stable over the longer term, without this having a noticeable influence on the efficiency of the pump.

The solution according to the invention also has the advantage that axial forces of the shaft can be accommodated by the axial seal in the pump casing, at least to a limited measure. The significant part of the axial forces however is produced by the hydraulic compensation, which means the leading of the pressure level produced by the pump, back onto the free shaft end within the pump casing, so that the drive of the pump can be ensured by a standardized motor, irrespectively of the stage number. The dynamic force compensation of the hydraulically caused axial forces acting upon the shaft limits the forces to be accommodated by the thrust bearing to a minimum. The hydraulic force compensation also has the advantage that a force compensation is also not effected in the case of a dry running, when these restoring forces do not occur, so that even then the wearing is kept to within acceptable limits.

The design according to the invention moreover has the advantage that with a suitable design implementation, the axial seal as well as the remaining sealing means, in particularly the radial seal, can be exchanged without having to remove the shaft out of the pump casing. Pump stages, which is to say the impellers with the associated diffusers can therefore also remain in their designated position.

It is particularly advantageous if the non-rotating part of the axial seal is subjected to the pressure of the delivery side of the pump, at the axial side of this non-rotating part which is away from the sealing surface, thus rear side. The necessary support force for the axial seal or for the thrust bearing function is mustered by way of this, and specifically in a dynamic manner, which is to say in dependence on the exit pressure of the pump.

This can advantageously be developed further by way of the non-rotating part of the axial seal comprising a ring, whose one axial face side forms a sealing surface of the axial seal and whose other axial side which is away from this, thus the rear-side axial side is configured in a closed manner and comprises at least one recess, whose pressure-effective cross-sectional area is smaller than the pressure-effective cross-sectional area of the conduit connection to the delivery side. Thereby, a recess in the context of the present invention can be an edge gap, an opening, one or more through-holes or a combination thereof. What is essential is the fact that the pressure-effective cross-sectional area of the one or more recesses is always smaller than the pressure-effective cross-sectional area of the one or the several conduit connections to the delivery side, in order to ensure that a pressure firstly forms in front of this closed surface of the ring on starting operation of the pump, and this pressure leads to the ring moving axially in the direction of the counter-sealing surface at the shaft end, and this additional axial force creating the movement of the ring only decreasing when the interior delimited by the ring is completely filled with fluid after a certain time.

An O-ring which is held in a radially peripheral groove is advantageously provided for sealing the axially movable part of the axial seal and the pump casing or the component which is provided within the pump casing for receiving the axially movable part. This radially peripheral groove can either be provided on the casing side or ring side, thus bearing side. Such an O-ring is inexpensive, simple to assemble and exchange as the case may be, and forms a reliable seal over the longer term.

It is particularly advantageous if the O-ring lies in a peripheral groove which is provided on the inner side of a holding ring and which is fixed in the pump casing. Such a design, with which the O-ring is not led directly in the pump casing, but in an intermediate component, has the advantage that here only the holding ring needs to be machined in a material-removing manner, and the holding ring for example is integrated by way of pressing into the pump casing, and no chucking of the pump casing on manufacture of the groove is necessary inasmuch as this is concerned.

The non-rotating part of the axial seal can be formed from a solid material, for example as a turned part, in order to form the closed axial side of this part. However, it is particularly advantageous if this part is formed as a ring from a tube section, and the closed axial side can be created by a sheet-metal section which can be inexpensively manufactured by way of punching. This sheet-metal section which covers the ring at the rear side and thus forms the initially pressure-effective closed axial side with the at least one recess, can moreover be advantageously utilized, in order to form the rotation lock of the non-rotating part of the axial seal, in particular of the ring and to fix this in a rotationally fixed manner either on the holding ring and/or on the pump casing. Since only small forces are to be accommodated inasmuch as this is concerned, this function can also be realized by way of an inexpensive punched part which as the case may be is likewise machined in a shaping manner.

According to the invention, one envisages connecting a holding ring in a sealed and fixed manner to the shaft end, at the shaft side, wherein this holding ring is either itself configured as a sealing ring and forms an axial sealing surface or advantageously receives a rotating ring forming the axial sealing surface. Such a rotating ring for example can consist of a highly wear-resistant silicon carbide, wherein the holding ring can consist of a less expensive, preferably metallic material. Thereby, the rotating ring forming the axial sealing surface can advantageously be fixed on the holding ring or with this holding ring by way of a threaded sleeve which is screwed into the holding ring, or by a sleeve. This permits the exchange of the rotating ring forming the axial sealing surface, likewise without a disassembly of the shaft, since the free end of the shaft is accessible from outside the pump casing and can be blocked from rotating by way of a tool.

The centrifugal pump according to the invention is advantageously configured as an inline pump, thus comprises a pump casing with which the suction connection and delivery connection are arranged on the same axis. A channel between the delivery connection and a space which receives the non-rotating part of the axial seal and is typically arranged in the foot of the pump casing can be realized in a simple manner with such an arrangement. Several channels can also be provided as the case may be, in order to realize the required conduit cross sections.

One of the sealing surfaces of the axial seal is advantageously configured as a three-point contact, thus comprises three macroscopic prominences which are distributed over the periphery, and which one the one hand ensure a defined contact to the plane counter-sealing surface and on the other hand are particularly advantageous with regard to the build-up of a lubricant film, wherein this lubricant film should be built up as rapidly as possible on starting up the pump, so that the advantageous and low-wear sliding friction arises. The design of this three-point contact is effected advantageously on the rotating ring, since this as a separate component can be machined less expensively with a lower tolerance than the remaining components.

The design according to the invention permits the axial mounting of the shaft to be provided exclusively at the motor side, wherein the axial forces which thereby occur are so small inherently of the design, that they can be accommodated by the motor bearings, without noticeably increasing their wear. The axial mounting of the shaft is therefore advantageously effected by way of one or more bearings which are arranged on the motor side, preferably a motor-side bearing close to the pump-side end of the motor shaft.

According to an advantageous further development of the invention, the ring of the non-rotating part of the axial seal can alternatively or additionally be constructed in a multi-part manner and comprise a highly wear-resistant part having the sealing surface, as well as a carrier receiving the highly wear-resistant part, as has already been specified above for the rotating part of the axial seal.

The rotating ring and/or the highly wear-resistant part of the ring can advantageously be formed of silicon carbide or a comparably highly wear-resistant material, which permits particularly long service lives.

According to an advantageous further development of the invention, a closable opening can be provided in the pump casing, preferably aligned to the axial seal, through which opening the axial seal can be exchanged, in order to be able to exchange the axial seal and the sealing means between the non-rotating part of the axial seal and the pump casing, without having to disassemble the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With the centrifugal pump which is represented by way ofFIGS. 1-10it is the case of a multi-stage centrifugal pump1of the inline construction type which is operated in a standing manner. The pump casing comprises a foot part2, a head part3and a cylindrical jacket4which is arranged therebetween and which surrounds the pump stages and is clamped between the head part3and the foot part2. The foot part2comprises a suction connection5as well as, aligned to this, a delivery connection6. The head part3is designed as a motor stool and surrounds a coupling7which connects a shaft51of an electric motor50schematically represented inFIG. 1and attached on the head part3, to a shaft8of the pump1in a rotationally fixed manner. The shaft8of the pump1carries the impellers9of the pump stages and is rotatably arranged within the pump casing. A radial seal10is provided in the head part3, and an axial seal11is provided in the foot part2. The construction of this axial seal11is evident in detail from theFIGS. 3 to 8and is described in a detailed manner further below. Fluid is brought into the pump casing on operation via the suction connection5, when the shaft8rotates, and this fluid enters into the suction port12of the first pump stage and is delivered through the pump stages which are formed in each case by an impeller9and a surrounding diffuser13, until it exits from the last pump stage in the head part3and is led back via an annular channel14to the delivery connection6, through which the fluid leaves the pump again.

The casing-side shaft end15of the pump in the region of the suction port12lies below the first pump stage. It comprises a pocket-hole bore16which is provided with a thread and in which a cap screw17is seated, with which cap screw a holding ring18is sealingly and fixedly fastened on the shaft end15. The holding ring18comprises a wall19which is directed to the suction port12and is closed with the exception of a central recess for leading through the screw17, thus is configured in a pot-like manner and is fixedly connected to the shaft end15in a sealed manner.

The holding ring18is configured as a turned part, is stepped to the side which is away from the shaft end15and is formed with a peripheral groove which is open to the bottom and which is provided for receiving a rotating ring20. The rotating ring20consist of silicon carbide and is rotationally secured in the holding ring18by way of pins21and is otherwise fastened together with the holding ring18on the shaft end15, by way of a sleeve22which radially encompasses the rotating ring20on the inner side and by way of the screw7. The rotating ring20comprises a downwardly directed axial surface23thus which is directed away from the shaft end15and this surface forms the rotating axial surface of the axial seal11. This axial surface23is not completely planar, but comprises three macroscopic prominences which are uniformly distributed over the periphery and which on the one hand form a defined contact on the counter-surface24, which is to say on the axial surface24of the non-rotating axial seal part25, and on the other hand serve for the rapid build-up of the lubricative film. The axial surface24is configured in a planar manner and is part of the non-rotating part, here of the ring25which is arranged in an axially movable manner within a holding ring26integrated in a corresponding receiver in the lower side of the foot part2of the pump casing.

The holding ring26comprises a peripheral groove27on its inner side, in which groove an O-ring28is integrated, said O-ring radially sealing the ring25with respect to the holding ring26and thus with respect to the pump casing. The holding ring26is moreover yet sealed with respect to the receiver in the pump casing by way of an outer-peripheral seal58, as is evident from the sectioned representations4and7.

The non-rotating ring25at the rear side which is away from the axial sealing surface24is covered by a sheet metal section20which almost completely covers this rear side of the sealing ring25. The sheet-metal section20comprises bent-over tongues30, with which the sheet metal section is integrated within corresponding recesses52on the rear side of the ring25with a positive fit. These tongues30project radially beyond the ring25and engage into these recesses52in the ring25and form part of a rotation lock of the non-rotating ring25. Moreover, the sheet-metal section29comprises two diametrically opposite tongues31which are offset by 90° to the tongues30and which are bent away upwards out of the plane of the main material by 90° and connect the sheet-metal section29in an axially distanced manner to the ring25, in which the ends53engage into a shoulder54on the inner side of the ring25in a locking manner.

The sheet-metal section29forms a closed surface of the lower side of the ring25and comprises a central rectangular recess32, into which a pin55which is rectangular in cross section engages, said pin forming part of the holding ring26, on which the ring25comprising the axial sealing surface24is guided in a rotationally fixed, but axially movable manner. The pin55and the recess32with regard to cross section are dimensioned such that this recess32with the pin55located therein, together with any gap tolerances of the sheet-metal section29form a through-gap with a cross-sectional area which is significantly smaller than the cross-sectional area of channels33which are provided in the foot part2of the pump casing or in the holding ring26and which ensure that the interior34of the ring25with the sheet-metal section29and the holding ring26is subjected to the pressure of the delivery side of the pump, thus to the pressure at the delivery connection6. These channels33, on starting up the pump after an effected pressure build-up ensure that the sheet-metal section29with the ring25bearing thereon is firstly subjected to force and is pushed, in the direction of the free shaft end, thus towards the motor, since firstly fluid must flow via the smaller cross section of the gap between the recess32and the pin55, into the space enclosed by the ring, before a corresponding counter-pressure is built up. The ring25is moved axial upwards inFIG. 1, which is to say is moved axially within the holding ring26by way of this, until the axial surface24bears on the counter-surface23, by which means a separation between the suction-side space in the region of the shaft end15and the installation space34of the stationary part of the axial seal11is then also formed. The pressure of the delivery side also prevails within the ring25and this at the face side of the shaft8, as soon as the space which is enclosed by the ring25and the sheet-metal section29has filled via the gap of the recess32, by which means the certain force compensation with regard to the hydraulically caused axial force of the shaft8and which is desired on operation is effected.

As can particularly be deduced fromFIG. 9, the holding ring26is part of a circular disc56which is provided for integration in a base-side maintenance opening60of the pump casing, here of the foot part2. The disc56, in a manner closing this base-side opening60, lies in a shoulder64on the lower side of the foot part2and is releasably connected to the foot part2via four screws57which are led through recesses61in the edge62of the disc56. An O-ring58which is integrated in a peripheral radial groove of the ring26and serves for sealing this component with respect to a recess63in the foot part2, is arranged in the upper region of the ring26, thus at a small distance to the disc25, for sealing with respect to the foot part2. A second O-ring59is integrated at an axial distance to this, in a peripheral, radial groove in the lower part of the ring26and serves for sealing with respect to the maintenance opening60in the foot part2. A connection to the delivery side of the centrifugal pump1which is connected in a fluid-leading manner to the interior of the ring26via channels33in the ring26, connects within the foot part2, between the O-rings58and59, so that the pressure of the delivery side via this connection is present at the surface of the non-rotating part25of the axial seal, said surface being formed by the sheet-metal section29and at the beginning being pressure-effective. The ring26via the O-ring28lying in a groove on the inner side of the holding ring26is sealed with respect to the ring25which forms the non-rotating part of the axial seal with the axial surface24of the seal. This O-ring28thus forms a radial seal which however only has to accommodate the comparatively small movements in the axial direction and therefore is only subjected to a low wear.

The axial seal can be overhauled and exchanged as the case may be, by way of removing the disc56with the holding ring26which is located thereon, after the screws57have been released, due to the fact that the pump casing at the lower side, thus in the base of the foot part2, comprises a maintenance opening60which is closed by the disc56. The shaft38of the pump does not have to be removed for this. All components of the axial seal which are represented in the exploded representation according toFIG. 9can be exchanged through the opening61in the base of the foot part2. An exchange of the components comprising the axial surfaces23and24as well as of the O-ring28is effected in the simplest case. The shaft8in the region of the motor stool has a cross-sectional profile which permits a locking of the shaft by way of laterally engaging a tool, in order to be able to release the threaded connections which are connected to the shaft8. Thus, the cap screw17can be released after the shaft8is held in a rotationally fixed manner by way of a spanner introduced in the region of the motor stool, and this screw can then be tightly screwed again after exchange of the rotating ring20and, as the case may be, further seals of the holding ring18.

The axially stationary part of the seal, thus the non-rotating ring25with its seals and the holding ring26which with the disc56forms the cover for closure of the casing opening of the maintenance opening60, together with the cover56are pulled out downwards and thereby the upper part of the holding ring26with the peripheral O-ring58is pulled out of the recess63, and the lower part of the holding ring26with the O-ring59is pulled out of the maintenance opening60. These seals as well as the O-ring28and the non-rotating part of the axial seal25can then be exchanged and together are inserted from below into the maintenance opening60or the recess63of the foot part2, until the upper part of the holding ring26with the O-ring58sealingly bears in the recess63and the lower part with the O-ring59sealingly bears in the maintenance opening60.

APPENDIX

List of Reference Numerals