EP2376789B1 - Pump having an axial balancing device - Google Patents

Description

The present invention relates to the axial balancing of a pump, in particular a turbopump, in particular a space engine.

It is known that the rotors of these machines support often considerable axial thrusts due to the pressure differences that are established on either side of the wheels, to the variations in the amount of movement of the fluids conveyed and, in some cases, to the weight or at a fraction of the weight of the rotor itself.

As a result, there are usually devices in the pumps for compensating the axial thrust exerted by the fluid on the rotor.

These devices are capable of using all the surfaces on the front face (on the blade side) and vice versa on the rear face or on the back of the centrifugal wheels as surfaces on which fluid is just circulated, so as to compensate for the axial resultant. forces exerted on the rotor parts. In known manner, it is used more particularly to achieve this balance the back of the last centrifugal wheel, which is called for this reason the 'balancing piston'.

The Figures 1 and 2 represent such a known axial thrust balancing device, arranged between a wheel 11 and a stator 12.

The turbopump of the figure 1 comprises essentially a rotating assembly constituted around a central shaft 26, of reduced length, and comprising a single-stage centrifugal pump impeller 11 mounted on the shaft 26, in the middle part thereof, and two wheels turbine 22, mounted on the shaft 26 in the rear portion thereof.

The turbine wheels 22, mounted cantilevered at the rear of the shaft 26, drive the latter in rotation under the action of a hot gas flow applied to the periphery of the turbine wheels 22, from a torus 24 for supplying gases.

On the figure 1 for the single-stage pump is shown an open-type impeller 11 with vanes 6 receiving the working fluid through a suction channel 2 and discharging the pressurized working fluid through a delivery channel 3.

The working fluid is introduced axially through the inlet section 28 and passes directly into the suction channel 2 of the pump.

The different components of the pump are known and their description will not be detailed further, with the exception of the axial balancing system of the pump, part of which is visible on the pump. figure 2 .

This device for axial balancing or axial thrust balancing of the rotating assembly is integrated with the impeller 11 and comprises a single rear balancing chamber 18 interposed between the rear part of the wheel 11 and a portion of the stator 12, and a passage 20 connecting the rear balancing chamber to the fluid stream.

A balancing chamber is a chamber in which there is a fluid pressure, the action of this pressure on a movable member (here, the rotor) for regulating and controlling the position of said movable member.

Via the passage 20, a portion of the fluid passing through the fluid stream is removed to feed the rear balancing chamber 18 located on the rear face 16 of the wheel 11.

The front face of this wheel 11 receives the pressure of the fluid stream 14 which tends to move the rotor 10 rearwardly. On the other hand, the fluid pressure in the rear balancing chamber 18 instead tends to move the rotor 10 forward. Equilibrium is achieved when these forces compensate axially, the force exerted by the fluid on the rotor 10 at the rear chamber 18 then compensating for the axial resultant forces exerted by the fluid on the other parts of the rotor, during the various phases of operation of the pump.

To achieve and maintain this equilibrium, the axial balancing device modulates the supply pressure of the rear chamber 18, via the axial displacement of the rotor, as follows:
The fluid transfer passage 20 has a radial nozzle 40 extending between the rotating wall connected to the rotor 10, that is to say to the centrifugal wheel 11, and a wall facing the stator. 12, that is to say a fixed wall of the pump. The section for the fluid passage of this radial nozzle depends on the relative axial position of the rotor and the stator: It increases as the rotor moves backwards (increase in thickness A of fluid film passing through the passage 20, on the figure 2 , when the wheel 11 moves to the right), which causes an increase in the flow entering the rear chamber, a rise in the pressure in the rear chamber, and therefore an increase in the restoring force exerted by the fluid on the rotor tending to push it forward. Conversely, if the rotor 10 tends to move forward (at the expense of the fluid film thickness A), by a reverse mechanism the return force decreases which causes the rotor to return further back.

It is therefore understood that the displacement of the rotor makes it possible to modulate the pressure in the rear balancing chamber 18, and thus to keep the rotor in a substantially constant axial position, and this advantageously with a minimum of friction. The system is self-regulating, and tends to keep the rotor in its equilibrium position.

However, in such a load balancing system, the fluid passage section is inherently variable, the only degree of freedom available to the designer to vary the effect of the device and therefore the pressure drop between upstream and downstream. the downstream of this passage, is the radial distance B traversed by the fluid in the nozzle of the passage, which in this case corresponds to the distance between the inner and outer radii of the crown that forms this nozzle.

However, it is not necessarily desirable to increase this distance B too much, and with it the size of the corresponding walls of the rotor and / or the stator, because the pump is then more sensitive to the deformations of these parts, because of the risk of harmful contacts between the rotor and the stator.

In addition, the increase in this distance B may not be sufficient to obtain the pressure drop required to achieve axial thrust balancing, particularly in the case of a single-stage centrifugal pump open: In this case indeed , the only surface on which we can come to circulate fluid is the balancing piston located at the back of the wheel. In multi-stage pumps, each wheel can contribute to the axial balancing of the pump.

As a known alternative solution, if the increase in the width of the radial nozzle is not sufficient to compensate for the axial forces, it is possible to resort to an offset axial balancing plate. This causes an increase in the complexity of the pump and its implementation, and a loss of efficiency of the pump. Moreover, in particular because of the elongation of the shaft which results, the axial and / or radial size of the pump is increased.

Other solutions for the axial balancing of pumps are proposed by the documents From 19631824 , DE 922,807 , DE 1528717 and CH330272 .

The object of the invention is to overcome the aforementioned disadvantages by defining a pump comprising a stator, a rotor comprising at least one impeller, and an axial balancing device arranged on at least one impeller of the rotor in which ( or in particular, but not exclusively, having a wall, in particular a front wall, against which passes a stream of fluid, said device comprising for each wheel involved in this device, a balancing chamber extending between a wall of said involved wheel and the stator, and a passage arranged between said wheel involved and the stator, allowing a discharge of fluid from said vein of fluid to said balancing chamber, said rotor having a slight axial clearance allowing limited axial displacement, the fluid pressure in the balancing chamber (s) can thus compensate for the pressures exerted by the fluid on the other parts of the rotor to achieve r axial balancing of the rotor; pump whose axial thrust balancing device is achievable with the conventional machining means, and has an optimized radial and axial dimensions so as to obtain a compact pump with good hydraulic efficiency.

This objective is achieved thanks to the fact that said passage comprising an upstream nozzle and a downstream nozzle, both axially variable, extending between two crown walls facing each other with a positive, zero or negative overlap, respectively of the wheel involved and of the stator, and an intermediate annular chamber arranged between walls of the involved wheel and the stator, opening downstream of the upstream nozzle and upstream of the downstream nozzle of said passage.Through the arrangement of the passage with a chamber annular disposed between two nozzles, the jet of fluid is passed through and circulate in the intermediate chamber, wherein it dissipates its kinetic energy by swirling, resulting in increased pressure loss on both sides of the passage. The term "chamber" here implies that the annular chamber is distinguished from the upstream and downstream nozzles by a large passage section relative to that of the nozzles, which can be in particular greater than triple their passage section. In the preceding formulation, said upstream and downstream nozzles are annular parts of the passage presenting sections that are particularly small relative to the remainder of the passage, or at least smaller than the average section thereof. These nozzles are said to be axially variable, since their passage sections vary as a function of the axial displacements of the rotor relative to the stator. An example of an axially variable nozzle is a passage extending radially between two parallel plane circular rings, perpendicular to the axis of rotation of the pump. The approximation or the axial spacing of these rings causes a reduction or a proportional increase in the cross section between the crowns.

It will be noted that the crown walls facing each other of the upstream and / or downstream nozzles may have a positive, zero or negative overlap. These walls may or may not have a radial overlap. There is radial overlap when the two facing surfaces which constitute the nozzle, have an effective overlap in the radial direction, that is to say are at least partly opposite to the axis of the pump (this means that a displacement along the axis of the rotor pump with respect to the stator could bring these surfaces into contact). Conversely, the absence of recovery corresponds to the situation in which these two surfaces have no vis-à-vis along the axis of the pump; that, although they face each other, that is to say, although their normals are of the same direction but of opposite directions. In all cases (with or without radial overlap), the surfaces of a nozzle are arranged in such a way that their relative axial displacement induces a variation of the passage section of the nozzle, that is to say of the passage section between them.

In one embodiment, the section of the annular chamber in a meridian plane is slightly elongated, i.e., has a larger dimension less than twice its smaller dimension. This arrangement promotes the dissipation of energy by vortex.

The invention is particularly advantageous in the case of pumps arranged for pumping liquid hydrogen. In such pumps indeed, the wheel or wheels may reach a peripheral speed greater than 400 m / s or 500 m / s.

It is understood that under these conditions, any unwanted contact occurring at the periphery of the wheels between a blade wheel and the stator can have considerable consequences. The shape of the fluid evacuation passage is therefore essential, since it concerns precisely this part of the pump. Advantageously, the invention allows the passage creates a significant pressure drop, while having a very small axial and radial dimensions, and without causing additional manufacturing cost unacceptable.

In one embodiment, the fluid discharge passage is substantially sealed, except for the fluid inlet via the upstream nozzle, and fluid discharge via the downstream nozzle. Thus, no evacuation or fluid intake occurs from upstream to downstream of the passage. In particular, the intermediate annular chamber is substantially sealed except for the passage of fluid through the upstream and downstream nozzles, and no fluid exchange path other than the upstream and downstream nozzles is provided.

Finally, in one embodiment the upstream nozzle and the downstream nozzle are radially staggered. In other words, the upstream nozzle and the downstream nozzle are located at different distances from one another relative to the axis of rotation of the pump. With this arrangement, it is possible to achieve an axially compact axial balancing device, that is to say of short length along the axis of the pump. The annular chamber may in particular be arranged radially between a radius of the upstream nozzle and a radius of the downstream nozzle (a radius of a nozzle here designating the radius of a lesser passage section of the nozzle).

In general, various forms of revolution around the axis of the pump may be adopted for the nozzles, the nozzles necessarily necessarily extending radially, but may for example have a conical or other shape, and the respective facing surfaces wheel and stator to be geometrically matched. It will be noted that the expression "facing each other" indicates here that for each of the nozzles, the walls of the wheel and of the stator are substantially opposite one another, the two nozzles being moreover offset one by the other. relative to the other axially and / or radially.

Due to the presence in the passage, instead of a single radial nozzle, of two nozzles separated by an intermediate chamber, for a given axial clearance the pressure drop generated by the passage is increased, without the radial extension of the Nozzle has increased.

Conversely, the pressure drop that allows the balancing of the rotor being given, the choice of this conformation advantageously leads to increase the axial clearance between the rotor and the stator, which leads to increased operational safety for these two parts.

The axial and / or radial compactness of the pump is improved, in particular by avoiding the addition of an offset axial balancing plate.

In one embodiment, at least one of the upstream nozzle and the downstream nozzle extends in a plane perpendicular to the axis of the pump.

Furthermore, advantageously, the axial thrust balancing device can be arranged only in a single impeller. It can therefore be used when the rotor has only one impeller.

However, the thrust balancer may be used in a rotor having a plurality of impellers.

In this case, it can be provided that the only wheel involved is the last wheel behind the pump, that is to say the one located furthest downstream in the direction of advance of the fluid in the pump.

As an alternative solution, it can also be provided that the axial thrust balancing device involves at least two wheels, and in particular all the wheels. Thus, the forces are distributed more homogeneously within the rotor.

Finally, it should be noted that the principle of intermediate chamber interposition, separated by radial nozzles, can be multiplied or reiterated. Thus according to the invention, it is possible to provide that the passage further comprises at least one other intermediate nozzle extending between two opposite crown walls, respectively of the rotor and the stator, and at least one other chamber. annular intermediate arranged between the rotor and the stator, opening downstream of the intermediate nozzle, the intermediate nozzle (s) and intermediate annular chamber (s) being interposed alternately on the path of fluid downstream of the first intermediate annular chamber and upstream of the downstream nozzle.

In the configuration thus obtained, there is therefore a succession of intermediate chambers following, separated by radial nozzles. At the same fluid flow rate, the pressure jump generated by the passage can thus be even greater than with a single intermediate chamber.

Finally, the invention applies more particularly to the realization of turbopumps for space engine, associating a pump as described previously coupled to a turbine.

• la figure 1 déjà décrite est une vue en coupe axiale d'une pompe centrifuge équipée d'un dispositif d'équilibrage de poussée axiale,
• la figure 2 déjà décrite est une vue en coupe axiale d'un passage de transfert de fluide de ce dispositif, dans une conformation connue,
• la figure 3 est une vue en coupe axiale d'un passage de transfert de fluide d'un dispositif d'équilibrage axial de pompe, dans un premier mode de réalisation de l'invention,
• la figure 4 est une vue en coupe axiale d'un passage de transfert de fluide d'un dispositif d'équilibrage axial de pompe, dans un deuxième mode de réalisation de l'invention, et
• la figure 5 est une vue en coupe axiale d'un passage de transfert de fluide d'un dispositif d'équilibrage axial de pompe, dans un troisième mode de réalisation de l'invention.
• Lorsqu'un élément apparaît sur plusieurs figures, soit à l'identique, soit sous une forme analogue, il est décrit en relation avec la première figure sur laquelle il apparaît ; sur les suivantes, il porte une référence numérique qui est sa référence numérique initiale, augmentée de 100, 200, etc. ; de plus, la description de l'élément n'est faite qu'une fois ; dans les figures suivantes, elle est omise ou simplifiée.
• Les figures 3 à 5 présentent des dispositifs d'équilibrage axial, susceptibles d'être mis en oeuvre dans une pompe telle que celle présentée en relation avec la figure 1.

The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings, in which:

• the figure 1 already described is an axial sectional view of a centrifugal pump equipped with an axial thrust balancing device,
• the figure 2 already described is an axial sectional view of a fluid transfer passage of this device, in a known conformation,
• the figure 3 is an axial sectional view of a fluid transfer passage of an axial pump balancing device, in a first embodiment of the invention,
• the figure 4 is an axial sectional view of a fluid transfer passage of an axial pump balancing device, in a second embodiment of the invention, and
• the figure 5 is an axial sectional view of a fluid transfer passage of a pump axial balancing device, in a third embodiment of the invention.
• When an element appears in several figures, either identically or in a similar form, it is described in relation to the first figure on which it appears; on the following ones, it carries a numerical reference which is its initial numerical reference, increased by 100, 200, etc. ; moreover, the description of the element is made only once; in the following figures, it is omitted or simplified.
• The Figures 3 to 5 have axial balancing devices which can be used in a pump such as that presented in connection with the figure 1 .

The operation of an axial pump balancing device, in a first embodiment of the invention, will now be described with reference to the figure 3 .

The figure 3 is a partial section of a pump roughly similar to that presented on the figure 1 that is, a single-stage pump having an open-type wheel 111. However, the device balancing the pump of the figure 3 is different from that of the pump of the figure 1 .

The pump shown on the figure 3 comprises a rotor 114 and a stator 112, and a thrust balancing device comprising in particular a fluid passage 120 formed between the rotor 114 and the stator 112.

On the pump of the figure 3 , the thrust device is arranged on the rear wall of the impeller. It will of course be understood that, in general, the thrust device may be arranged both on a rear wall of the wheel 111 and on a front wall thereof.

Upstream of the side of the fluid stream, the passage 120 comprises an upstream axial portion 130 extending between two substantially cylindrical walls 131,132 of circular section facing each other, respectively of the wheel 111 (wheel involved) and the stator 112, located upstream of the upstream nozzle 140. This upstream axial portion constitutes a cavity which advantageously allows a first dissipation of kinetic energy of the fluid passing through the passage 120.

Immediately downstream of the upstream axial portion extends the upstream nozzle 140. This is a passage extending radially over a distance B between the walls 141 and 142 respectively of the wheel and the stator. There is therefore, on the distance B, an effective radial overlap between the surfaces 141 and 142

Downstream of the upstream nozzle 140, extends the intermediate chamber 150. This is of annular shape and extends between the walls 151 and 152 of the wheel 111 and the stator 112. The chamber can indifferently be arranged in the volume of the wheel and / or the stator. With the exception of the upstream and downstream nozzles, the chamber 150 is sealed.

The annular chamber 150 is of short length in the radial direction, since it extends radially on less than one tenth, and more precisely less than one twentieth of the radius of the wheel 111 at the level of the upstream nozzle.

In addition, it is also of short length in the axial direction, since it extends axially on less than one tenth, and more precisely less than one twentieth of the radius of the wheel 111 at the level of the upstream nozzle.

Downstream of this intermediate chamber 150 extends the downstream nozzle 160, between the walls 161 and 162 respectively of the wheel and the stator. It is also positive recovery.

The upstream and downstream radial nozzles respectively define axial clearances A101 and A102, equal or otherwise, between the wheel 111 and the stator 112.

In addition, the upstream and downstream nozzles are radially staggered. Thus, the upstream nozzle 140 is at a smaller radial distance from the axis of rotation of the pump than the downstream nozzle 160. These two nozzles are separated by the distance radially separating the walls 151 and 152 respectively of the rotor and stator, which corresponds to the radial extension of the annular chamber 150.

Finally, downstream of the downstream nozzle 160, the passage 120 comprises a downstream axial portion 170 extending between two substantially cylindrical walls 171,172 of circular section facing each other, respectively of the wheel 111 (wheel involved) and the stator 112, located downstream of the downstream nozzle 160.

Like the upstream axial part, this downstream axial part also constitutes a cavity allowing the dissipation of kinetic energy of the fluid passing through the passage 120.

Even if a cylindrical shape of circular section (the axis being that of the pump) is preferable, these axial portions upstream and downstream of the passage 120 may adopt other forms of revolution around the axis of the pump, for example present a convergent (upstream) or a divergent (downstream) between frustoconical surfaces facing respectively the wheel 111 and the stator 112.

Referring to the figure 4 , a device in a centrifugal pump in a second embodiment of the invention, will now be described.

In this embodiment, at least one wheel involved in the axial balancing device, and in this case the impeller 211 is a closed wheel, or flanged, that is to say closed by a lid 290 (or flange) on the front side of the blades. To allow axial balancing in both directions along the axis of the pump, the axial balancing device is doubled, comprising first axial balancing means (including a first passage 220) very similar to those presented in FIG. relationship with the figure 3 , and second axial balancing means acting in the opposite direction, arranged on the side of the lid.

In this embodiment, the various elements of the first axial balancing means, and in particular the passage 220, are substantially the same as in the previous embodiment and will therefore not be described again in detail.

Regarding these first axial balancing means, arranged on the rear side of the wheel 211, the differences are as follows.

Firstly, the upstream and downstream radial nozzles extend substantially in the same plane perpendicular to the axis of rotation of the rotor, whereas on the contrary in the embodiment presented in FIG. figure 3 the upstream and downstream radial nozzles 160 140 are slightly offset along the axis of rotation of the pump. So in the embodiment of the figure 4 , in which the upstream and downstream radial nozzles are in the same plane, the machining of the surfaces 241, 261 of the wheel and 242, 262, of the stator is simplified. In addition, the axial size of the axial balancing device is thus not increased, compared with the axial balancing device presented in FIG. figure 1 .

It is further noted that the intermediate chamber was arranged only in the stator. As this chamber can be subjected to rapid wear and / or vibration, these are advantageously concentrated in the stator and not in the rotating assembly of the pump.

On the other hand, an annular chamber 273 is arranged in the upstream portion of the downstream axial portion 270, in the vicinity of the outlet section of the downstream nozzle 260 of the passage 220. Forcing the fluid to flow also in this annular chamber 273, the pressure drop is further increased when passing through the passage 220. A similar cavity may symmetrically be provided in the downstream portion of the upstream axial portion 230, in the vicinity of the inlet section of the upstream nozzle. 240.

Finally, the axial balancing device comprises second axial balancing means for the wheel 211, to prevent movement of the latter forward.

The axial balancing device thus comprises another balancing chamber 288, called the front balancing chamber, extending between a front wall of the cover 290 and the stator 212, a second passage 292 arranged between the cover and the stator, allowing a discharge of fluid from the fluid stream 214 to the front balancing chamber 288, the second passage 292 comprising an upstream nozzle 294 and a nozzle 296, these nozzles extending between two crown walls facing each other, respectively the lid 290 on the front side and the stator 212 on the back side, and an intermediate annular chamber 298 arranged between walls respectively of the lid 290 and the stator 212, the intermediate annular chamber 298 s opening downstream of the upstream nozzle 294 and upstream of the downstream nozzle 296 of the second passage 292.

The structure of the second balancing means is functionally equivalent to that of the first means, but the second means are arranged in a direction opposite to the axis of the pump. Due to this conformation of the axial balancing device with counterbalancing means in opposite directions disposed on both sides of the wheel, the axial displacements of the rotor are compensated in both directions. Note finally that according to the invention, the balancing device can be disposed on one or more flasks, each provided with balancing means in both directions.

Referring to the figure 5 , a device in a centrifugal pump in a third embodiment of the invention, will now be described.

In this embodiment, the various elements of the axial balancing means, and in particular the passage 320, are substantially the same as in the first embodiment and will therefore not be described again in detail.

The particularity of this third embodiment, with respect to the first embodiment, lies in the absence of radial overlap between the surfaces of the upstream and downstream nozzles 360 and 360.

In this embodiment, the nozzles 340 and 360 do indeed have no radial overlap. Indeed, for each of these nozzles, the surfaces of the nozzles 341, 361; 342,362 respectively of the rotor and the stator, do not comprise any portion vis-à-vis along the axis of the pump. More specifically, concerning the upstream nozzle 340, the surfaces 341 and 342 constituting this nozzle are separated by a radial gap C; concerning the downstream nozzle 360, a radial gap D separates the surfaces 361 and 362 constituting this nozzle. The interest of this conformation is that, the surfaces of the nozzles having no radially common portion, or in other words, being radially offset, the relative axial movements of the rotor relative to the stator can not lead to a contact between the rotor and the stator. This property can be absolutely essential, in case such contact would cause a heating for the machine that could lead to the destruction of it.

Claims (14)

1. A pump (8) comprising
   a stator (112),
   a rotor (10) comprising at least one impeller, and
   an axial balancing device arranged on at least one impeller (111) of the rotor in which a fluid duct (114) passes,
   said device comprising for each involved wheel in this device a balancing chamber (118) extending between a wall (116) of said involved wheel (111) and the stator (112), and
   a passage (120) arranged between said involved wheel (111) and the stator, allowing evacuation of fluid from said fluid duct (114) to said balancing chamber (118);
   said rotor having slight axial clearance allowing limited axial shift;
   said passage (120) comprising an upstream nozzle (140) and a downstream nozzle (160), both axially variable;
   said axial balancing device being characterised in that the upstream nozzle (140) and the downstream nozzle (160) extend between two walls (141,142;161,162) in crown opposite to one another with a positive, zero or negative overlap, respectively of the involved wheel (111) and of the stator (112), and
   said passage (120) further comprises an intermediate annular chamber (150) arranged between walls (151,152) of the involved wheel (111) and of the stator (112), opening downstream of the upstream nozzle (140) and upstream of the downstream nozzle (160) of said passage.
2. The pump as claimed in Claim 1, characterised in that the intermediate annular chamber (150) is substantially airtight with the exception of the fluid passage via the upstream and downstream nozzles.
3. The pump as claimed in Claim 1 or 2, characterised in that one at least of the upstream nozzle (140) and the downstream nozzle (160) extends in a plane perpendicular to the axis of the pump.
4. The pump as claimed in any one of Claims 1 to 3, characterised in that said passage (120) also comprises an upstream axial part (130) extending between two substantially cylindrical walls (131,132) of circular section facing each other, respectively of the involved wheel (111) and of the stator (112), and situated upstream of the upstream nozzle (140) .
5. The pump as claimed in any one of Claims 1 to 4, characterised in that said passage (120) also comprises a downstream axial part (170) extending between two walls (171,172) substantially cylindrical of circular section facing each other, respectively of the involved wheel (111) and of the stator (112), and situated downstream of the downstream nozzle (160).
6. The pump as claimed in Claim 5, characterised in that an annular chamber (273) is arranged in the upstream part of the downstream axial part (270), in the vicinity of the outlet section of the downstream nozzle (260) of the passage (220).
7. The pump as claimed in any one of Claims 1 to 6, characterised in that said passage (120) also comprises at least one other nozzle known as intermediate, extending between two crown walls facing each other, respectively of the rotor and of the stator, and
   at least one other intermediate annular chamber arranged between the rotor and the stator, opening downstream of this intermediate nozzle,
   said at least one intermediate nozzle and at least one intermediate annular chamber being interposed alternated on the trajectory of fluid downstream of said intermediate annular chamber and upstream of said downstream nozzle.
8. The pump as claimed in any one of Claims 1 to 7, characterised in that the upstream (240) and downstream (260) nozzles extend substantially in the same plane perpendicular to the axis of rotation of the rotor.
9. The pump as claimed in any one of Claims 1 to 8, characterised in that the rotor (10) comprises only one impeller (111).
10. The pump as claimed in any one of Claims 1 to 8, characterised in that the rotor (10) comprises a plurality of impellers (111), the only involved wheel being that situated the farthest downstream in the direction of advance of the fluid in the pump.
11. The pump as claimed in any one of Claims 1 to 9, characterised in that at least one involved wheel in the axial balancing device is a flanged wheel closed by a cover (290) on the front side of the vanes;
    said balancing chamber and said passage are arranged on a rear side of said flanged wheel, between a rear wall of the flanged wheel and the stator;
    said device also comprises for said flanged wheel another balancing chamber (288) known as front balancing chamber, extending between a front wall of said cover and the stator,
    a second passage (292) arranged between the cover and the stator, allowing evacuation of fluid from said fluid duct (214) to said front balancing chamber (288),
    said second passage (292) comprising an upstream nozzle (294) and a downstream nozzle (296), these nozzles extending between two crown walls facing each other, respectively of the cover (290) on the front side and of the stator (212) on the rear side, and an intermediate annular chamber (298) arranged between walls respectively of the cover (290) and of the stator (212), said intermediate annular chamber (298) opening downstream of the upstream nozzle (294) and upstream of the downstream nozzle (296) of said second passage (292).
12. The pump as claimed in any one of Claims 1 to 11, whereof said involved wheel is provided to reach a periphery speed greater than 400 m/s.
13. The pump as claimed in any one of Claims 1 to 12, arranged for pumping liquid hydrogen.
14. The pump as claimed in any one of Claims 1 to 13, characterized by being a spatial motor turbopump.

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