Abstract
A single-stage or multi-stage centrifugal pump has a balancing disc for balancing the axial forces of the pump. The balancing disc includes at least one annular groove in at least one of the non-axial counter surfaces and of the balancing disc and the counter member.
Claims
1. A centrifugal pump, comprising: a pump casing with an inlet and an outlet; a shaft sealed and mounted with slide bearings to the pump casing, the shaft being movable in axial direction; at least one impeller fastened on the shaft for rotation therewith and a balancing device configured to balance axial forces, the balancing device comprising a balancing disc fastened on the shaft for rotation therewith and having an outer circumference; and a stationary counter member arranged in connection with the pump casing, the balancing disc and the counter member forming therebetween a balancing cavity, the balancing disc having a first non-axial surface delimited to the outer circumference and the counter member having a second non-axial surface, the first and the second non-axial surfaces facing one another and forming a thin gap therebetween, at least one of the first and the second non-axial surfaces including at least one annular groove, a throttling being arranged downstream of the balancing disc and the counter member includes a counter ring having the second non-axial surface or the balancing disc includes an annular ring having the first non-axial surface.
2. (canceled)
3. (canceled)
4. The centrifugal pump in accordance with claim 1, wherein the at least one annular groove is a plurality of annular grooves, and at least one of the first and the second non-axial surfaces includes circular rings forming the plurality of annular grooves therebetween.
5. The centrifugal pump in accordance with claim 1, wherein the annular groove has a depth of at least 10-fold to that of the thin gap.
6. The centrifugal pump in accordance with claim 1, wherein the annular groove has a dimension of 1 to tens of millimeters in a direction at right angles to the first and the second non-axial surfaces.
7. The centrifugal pump in accordance with claim 1, wherein the annular groove has a dimension of 1 to tens of millimeters in a direction parallel with the first and the second non-axial surfaces.
8. The centrifugal pump in accordance with claim 1, wherein the counter member is a rear wall of the centrifugal pump.
9. The centrifugal pump in accordance with claim 1, wherein the at least one annular groove is in the balancing disc, and the at least one annular groove faces is facing a groove in the counter member.
10. The centrifugal pump in accordance with claim 1, wherein the throttling is arranged downstream of a cavity downstream of the balancing disc.
11. The centrifugal pump in accordance with claim 1, wherein the throttling downstream of the balancing device is one of a slide bearing, a valve and a pipeline having a suitable cross sectional flow area.
12. A method of balancing an axial thrust of a centrifugal pump in accordance with claim 1, the method comprising: arranging the throttling downstream of the balancing disc for controlling the amount of liquid leaking via the balancing device, providing the counter member with the counter ring having the second non-axial surface, and providing the balancing disc with the annular ring having the first non-axial surface.
13. (canceled)
Description
DESCRIPTION OF THE DRAWINGS
[0027] The invention will be explained in more detail hereinafter with reference to the drawings.
[0028] FIG. 1 illustrates schematically, and in an axial cross section, a multi-stage centrifugal pump including a disc-type balancing device in accordance with a first preferred embodiment of the present invention;
[0029] FIG. 2 illustrates schematically an axial, more detailed cross section of the balancing device in accordance with a first preferred embodiment of the present invention;
[0030] FIG. 3 illustrates a detailed axial cross section of the balancing device in accordance with a first variation of a first preferred embodiment of the present invention;
[0031] FIG. 4 illustrates a detailed axial cross section of the balancing device in accordance with a second variation of the first preferred embodiment of the present invention;
[0032] FIG. 5 illustrates a detailed axial cross section of the balancing device in accordance with a third variation of the first preferred embodiment of the present invention;
[0033] FIG. 6 illustrates a detailed axial cross section of the balancing device in accordance with a second preferred embodiment of the present invention;
[0034] FIG. 7 illustrates a detailed axial cross section of the balancing device in accordance with a third preferred embodiment of the present invention;
[0035] FIG. 8 illustrates a detailed axial cross section of the balancing device in accordance with a fourth preferred embodiment of the present invention;
[0036] FIG. 9 illustrates a detailed axial cross section of the balancing device in accordance with a fifth preferred embodiment of the present invention;
[0037] FIG. 10 illustrates a detailed axial cross section of the balancing device in accordance with a sixth preferred embodiment of the present invention;
[0038] FIG. 11 illustrates a detailed axial cross section of the balancing device in accordance with a seventh preferred embodiment of the present invention; and
[0039] FIG. 12 illustrates a detailed axial cross section of the balancing device in accordance with an eighth preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0040] FIG. 1 illustrates an axial cross section of a multi-stage centrifugal pump having a casing 10 with an inlet 12 and an outlet 14, the casing 10 housing a plurality of, here four, impellers 16 attached on a shaft 18 for rotation therewith and a balancing device (means) 20.
[0041] FIG. 2 illustrates schematically an axial, more detailed cross section of the balancing device 20 and the end part of the centrifugal pump in accordance with a first preferred embodiment of the present invention. Here in this embodiment the balancing device 20 is formed of a balancing disc 22 attached on the shaft 18 for rotation therewith. In connection with the balancing disc 22 there may be a separate sleeve or the balancing disc may include an integrated axial extension, i.e. a cylindrical sleeve 24, either one of the sleeves extending from the disc up to the hub of the impeller 16. The balancing device 20 further comprises a counter member 28 extending from the pump casing 10 radially inwardly between the balancing disc 22 and the impeller 16. The counter member 28 is, in this embodiment, either the rear wall of the centrifugal pump or a specific part attached thereto. In more general terms, the counter member is a part of the casing of the centrifugal pump or a specific part attached thereto. The counter member 28, preferably but not necessarily, includes a counter ring 26 attached to the counter member 28 such that it faces the area of the balancing disc 22 immediately radially inside the outer circumference of the balancing disc 22. The Figure shows by the black thick flow line how the pumped liquid is able to flow from the rear side cavity 30 of the impeller 16 to a radial clearance 32 between the sleeve 24 and the inner circumference 34 of the counter member 28 to an outwardly extending balancing cavity 36 between the balancing disc 22 and the counter member 28. At the radially outer end of the balancing cavity 36 the liquid flows via a thin gap 36 between the balancing disc 22 and the counter member 28 (here in this embodiment the counter ring 26 is the part of the counter member 28 facing the balancing disc 22) to a space radially outside the balancing disc 22. The space outside the balancing disc 22 is in flow communication with the cavity 38 axially behind the balancing disc 22 when viewed from the direction of the pump inlet 12. The liquid leaked through the balancing device 20 continues towards the slide bearings 40 of the pump shaft 18 such that the liquid is used to lubricate the slide bearings 40 while passing the bearings 40. When having passed the bearings 40 the liquid enters the end cavity 42 of the pump from where it is either introduced via pipeline 44 to the suction of the pump or to the bearings at the opposite end of the pumps shaft 18. The bearings 40 form a fixed throttling in the flow passage of the leaked liquid keeping the amount of leaked liquid the desired one.
[0042] FIG. 3 illustrates a detailed axial cross section of the balancing device 20 in accordance with a first variation of a first preferred embodiment of the present invention. The balancing disc 22 has a counter surface 50 facing the counter ring 26. The counter surface 50 and the surface 52 of the counter ring 26 facing thereto are, coated with or otherwise manufactured of a material suitable for working as counter surfaces. The counter ring 26 is fastened on the counter member 28 or in an annular groove in the counter member 28 by screws, adhesives, welding, riveting, just to name a few examples without any intention of limiting the options to the listed ones. The counter ring 26 has in its surface 52 facing the surface 50 of the balancing disc 22 a, preferably but not necessarily, circular groove 54. The groove 54 is, preferably but not necessarily, rectangular of its cross section and has a depth of 1 to tens of millimeters depending on the liquid to be pumped, i.e. the more foreign abrasive material the liquid carries the deeper the grooves should be to allow the depth of the grooves to wear down without losing their ability to work in the desired manner. The basic property of the groove is that it increases the cross sectional flow area in the gap 36 between the balancing disc 22 and the counter ring 26 by subjecting the leakage flow from the gap 36 to sudden expansion and contraction type flow resistances. In other words, when entering the groove the liquid loses its flow velocity almost entirely, and when entering the thin gap again the liquid has to be accelerated to the flow velocity corresponding to the thin gap. The thickness dimension of the flow area is increased, when entering the groove, from a micron range to a millimeter range, i.e. to a value from 1 mm to tens of millimeters. In other words, the cross sectional flow area, or in fact the radial depth thereof (as the width, i.e. the circumference remains substantially the same), is increased to at least 10-fold, preferably to more than 50-fold or more 100-fold depending again on the type of liquid to be pumped. And after the groove, the same is decreased back to micron range again.
[0043] As to the orientation of the balancing disc 22 and its counter member 28 it is preferably radial, as in such a case, the axial dimension the balancing device requires is the smallest. However, the advantages of the present invention are available as soon as the direction of the counter surfaces 50 and 52 of the thin gap 36 clearly differs from axial direction. In other words, as soon as the movement of the counter surfaces 50 and 52 relative to one another cause a change in the dimension of the gap 36 the advantages of the invention are available. Thus, the basic requirement for the direction of the counter surfaces 50 and 52 is that the direction thereof is non-axial. However, it could be assumed that the orientation of the counter surfaces 50 and 52 should be between 30 and 90 degrees from the direction of the axis A (see FIG. 2) of the pump.
[0044] FIG. 4 illustrates a detailed axial cross section of the balancing device in accordance with a second variation of the first preferred embodiment of the present invention. Here, in the second variation the counter ring 26 is not radial but somewhat inclined as was discussed already above. Naturally, also the counter surface in the balancing disc 22 is inclined in a corresponding manner. In the variation having inclined non-axial counter surfaces the same advantage as in the radial variation is gained, i.e. the gap between the surfaces adjusts automatically such that the gap remains the same for the entire inclined length thereof. A further advantage gained with the inclined counter surfaces is the fact that for a certain radial dimension a higher number of grooves may be fitted in an inclined counter surface than in a radial counter surface.
[0045] FIG. 5 illustrates a detailed axial cross section of the balancing device in accordance with a third variation of the first preferred embodiment of the present invention. Here, in the third variation the counter ring 26 is not radial but somewhat inclined as was discussed already above. Naturally, also the counter surface in the balancing disc 22 is inclined in a corresponding manner. Furthermore, the entire balancing disc 22 is also inclined. [0039] The inclination of the machine elements discussed above may be needed for some constructional reasons. For instance, with the structure of FIG. 5 the shaft bearing may be brought somewhat closer to the impeller.
[0046] FIG. 6 illustrates a detailed axial cross section of the balancing device in accordance with a second preferred embodiment of the present invention. Here, in the second embodiment, the groove 64, similar to that in the first embodiment is arranged in the balancing disc 22.
[0047] FIG. 7 illustrates a detailed axial cross section of the balancing device in accordance with a third preferred embodiment of the present invention. Here, in the third embodiment, there are several grooves 74, similar to that in the first embodiment arranged in either the counter ring 26 (as shown) or in the balancing disc 22 (not shown).
[0048] FIG. 8 illustrates a detailed axial cross section of the balancing device in accordance with a fourth preferred embodiment of the present invention. Here, in the fourth embodiment, there are grooves 84 and 84 in both the balancing disc 22 and in the counter ring 26, the grooves being similar to that in the first embodiment.
[0049] FIG. 9 illustrates a detailed axial cross section of the balancing device in accordance with a fifth preferred embodiment of the present invention. Here, in the fifth embodiment, there are grooves 84 and 84 in both the balancing disc 22 and in the counter ring 26, the grooves being similar to that in the first embodiment. Additionally, the balancing disc 22 here includes an annular ring 86 having a radial surface 50. The annular ring 86 is, preferably but not necessarily, made of the same material as the stationary counter ring 26. Naturally, the annular ring 86 may be used in connection with any one of the earlier or following embodiments, i.e. the surface 50 thereof includes grooves or not. The annular ring 86 may be fastened on the balancing disc 22 or in a groove arranged in the balancing disc. The annular ring 86 may be fastened to the balancing disc 22 by screws, adhesives, welding, riveting, just to name a few examples without any intention of limiting the options to the listed ones.
[0050] FIG. 10 illustrates a detailed axial cross section of the balancing device in accordance with a sixth preferred embodiment of the present invention. Here, in the sixth embodiment, the balancing disc 22 is disposed near its outer circumference with a number of circular rings 94 extending axially outwardly from the surface 50 of the balancing disc 22 and leaving annular grooves 94 therebetween. Such circular rings may be disposed in at least one of the balancing disc 22, the counter member 28, the counter ring 26 and the annular ring 86 in the balancing disc 22. The grooves left between the circular rings are similar to that in the first embodiment. The circular rings 94 are, preferably but not necessarily, made of the same material as the stationary counter ring 26 and fastened to the balancing disc and the annular ring by screws, adhesives, welding, riveting, just to name a few examples without any intention of limiting the options to the listed ones.
[0051] FIG. 11 illustrates a detailed axial cross section of the balancing device in accordance with a seventh preferred embodiment of the present invention. Here, in this embodiment, the balancing disc includes circular rings and the counter ring with annular depressions into which the circular rings are extended. The circular rings and the walls of the depressions define therebetween the grooves of the present invention.
[0052] FIG. 12 illustrates a detailed axial cross section of the balancing device in accordance with an eighth preferred embodiment of the present invention. Here, in this embodiment, the balancing disc includes an annular ring and the counter member with the counter ring. Both the annular ring and the counter ring have annular grooves. What makes a difference in this embodiment is that at least one groove in the annular ring is facing at least one groove in the counter ring, whereby the cavity to which the liquid flows from the thin gap expands in both axial directions, and not only in one axial direction as shown in the other embodiments.
[0053] The operation principle of the above described balancing device will be explained in the following by referring mainly to FIGS. 2 and 3.
[0054] When any single suction centrifugal pump having one or more impellers is pumping liquid, the suction created by the impeller/s draws the impeller/s towards the pump inlet, i.e. creates thrust. The thus created thrust requires the use of thrust bearings that prevent the impeller(s) from making mechanical contact with the volute of the pump. Another way to prevent the mechanical contact is to arrange balancing device on the shaft of the impeller(s). The balancing device discussed in the present invention are mainly formed of a balancing disc fastened on the shaft for rotation therewith. The balancing device operate such that the pumped liquid is guided to the balancing cavity between the balancing disc and its stationary counter member, whereby the liquid pressure acting on the balancing disc tends to move the shaft away from the inlet of the pump, i.e. in a direction contrary to the thrust created by the impeller(s). The force the balancing disc is capable of creating is proportional to the radius of the balancing disc. In other words, the stronger force is needed the bigger the radius of the balancing disc should be. However, the power consumption of the balancing disc is also proportional to the radius of the balancing disc.
[0055] If the power consumption of the disc is to be reduced, the only way, in practice, is to decrease the diameter of the balancing disc. But, when the diameter of the balancing disc 22 (naturally together with the counter ring 26) is reduced without any other measures the pressure difference radially across the thin gap 36, i.e. from the inner diameter of the counter ring 26 to the outer diameter thereof, is very high in relation to the cross sectional flow area in the gap 36 between the counter ring 26 and the balancing disc 22. The high pressure difference across the thin gap results in the very high flow velocity at the entrance to the thin gap, whereby occasional local low pressure zones are formed in the gap so that the liquid is able to evaporate into vapor. While the liquid in the gap is evaporated, the disc loses its load carrying capability at least partially at the area of the counter ring 26 as the vapor escapes from the gap 36 very quickly. The loss of load carrying capability allows the shaft 18 to move towards the pump inlet, whereby the non-axial counter surfaces 50 and 52 may end up into contact in substantially dry conditions. When the non-axial counter surfaces contact the power consumption increases rapidly, the friction heats the non-axial counter surfaces, and may at its worst damage the surfaces.
[0056] In other words, the reason for the loss of load carrying capability of the balancing disc is the combination of too high a pressure difference radially across the thin gap 36 and too little resistance to flow in the gap area. When the behavior of the liquid in the thin gap 36 between the counter ring 26 and the balancing disc 22 was considered in more detail, it was learned that the problem could be solved by adding resistance to flow in the gap 36 at the counter ring area by dividing the total pressure difference into two or more partial pressure differences by arranging one or more annular grooves either in the balancing disc or in the annular ring, or in the counter member or in the counter ring, or in both between the inner and outer circumferences of the counter ring area. By arranging one or more annular grooves in the surfaces 50 and/or 52 the resistance to flow between the inner and outer circumference of the counter ring 26 is increased such that the liquid entering the thin gap 36 between the counter ring 26 and the balancing disc 22 sees only the pressure difference between the entrance to the thin gap 36 and the first groove 54, whereby the velocity of the liquid induced by that particular pressure difference is smaller than in such a case that the total pressure difference would act in the liquid. Thereby the local pressure in the thin gap 36 is high enough for not allowing the liquid to evaporate. Furthermore, the flow velocity of the liquid in each groove is reduced close to nil, as the height or thickness of the flow cross section is suddenly changed from that of the thin gap 36, i.e. from a micron range, to that in the groove, i.e. to a millimeter range. For the above reason the liquid pressure everywhere in the thin gap 36 is able to carry some load, and as the pressure in the groove area is able to carry a substantial load, abrupt mechanical impacts of the balancing disc 22 to the counter ring 26 or counter member are prevented.
[0057] On the one hand, the fluctuation in the power consumption is a clear indication of occasional evaporation, whereas, on the other hand, the lack of fluctuations indicates the lack of evaporation.
[0058] In view of the above discussed various embodiments it should be understood that the details, i.e. grooves, circular rings, counter rings etc. thereof are interchangeable with those of any other embodiment whenever applicable. The same applies to the variations discussed in FIGS. 4 and 5. In other words, in the variations having inclined counter surfaces in both the radial or non-radial balancing disc and the counter member, the counter surfaces may have any imaginable combination of grooves or circular rings discussed in FIGS. 3, 6-12.
[0059] A feature that is in most cases, but not always, necessary for the working of the present invention is a throttling downstream of the balancing me device ans, i.e. a device that controls the liquid flow from the cavity downstream of the balancing disc further. Such a device may be a manual or otherwise controlled valve or a pipeline having a suitable cross sectional flow area for the throttling purpose. However, a preferable throttling device is the slide bearing shown in FIG. 2, for instance. In other words, as slide bearings, which now may be used, as the thrust of the impeller is balanced and there is thus no need for axial bearings, need liquid for lubrication purposes, it is quite practical to lead the liquid leaked via the balancing device to one or both shaft bearings of the centrifugal pump.
[0060] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.
