Patent Application
20080080965
The single figure shows a cross-section and elevation of the upstream portion of a pump 10 in accordance with the invention, this pump 10 being intended preferably but not exclusively for the pumping of fluid such as liquefied gas. It may advantageously be used for emptying the tanks of liquefied gas carriers.
In the following description, the adjectives “axial”, “tangential” and “radial” are defined relative to the axis of rotation A of the pump 10, whereas the adjectives “upstream” and “downstream” are defined relative to the direction in which the fluid is drawn in.
Moreover, as the pump 10 is generally intended to be arranged vertically, the adjectives “bottom” and “top” will be defined with reference to the vertical position of the pump.
Viewed in the drawing-in direction, indicated in this case by thickly drawn arrows, the pump 10 successively comprises a suction stage 12, a centrifugal wheel 14 and an annular conduit 16 allowing downstream backstreaming of the drawn-in fluid.
The suction stage 12 comprises a rotational impeller 18 equipped with a hub 20 which is driven in rotation by a rotating shaft 22 of the pump 10, the rotating shaft 22 being driven, for its part, by an electric motor (shown in part) arranged downstream of the centrifugal wheel 14.
Furthermore, the centrifugal wheel 14 is also driven in rotation by the rotating shaft 22, with which it is integral.
As may be seen in the figure, the rotating shaft 22 is mounted so as to rotate on a housing 24 of the pump 10 via a bearing 26, for example of the rolling bearing type, the rotating shaft 22 having a shoulder 30 which enters axially into abutment with an inner cage 28 of the bearing 26.
As the pump 10 is arranged vertically, it will be appreciated with reference to the figure that if there is no axial balancing system, the inner cage 28 of the bearing 26 supports the weight of the rotating shaft 22, the rotor of the motor, the centrifugal wheel 14 and the impeller 18—to which weight there is added the tensile force to which the impeller 18 is subjected when the fluid is drawn in.
The general operating principle of an axial balancing system 32 according to the present invention will now be described in greater detail.
In accordance with the invention, the purpose of the axial balancing system 32 is to take up the above-mentioned stresses exerted on the bearing 26.
This stress take-up results from the generation of an axial take-up force opposing the resultant of the above-mentioned stresses, this axial take-up force being exerted on the centrifugal wheel 14.
As the centrifugal wheel 14 is integral with the rotating shaft 22, it will be appreciated that the axial take-up force is transmitted to the rotating shaft 22, thus allowing the axial stresses directed toward the bottom of the pump 10 to be counteracted and the bearing 26 to be relieved.
The manner in which the axial take-up force is generated will now be described.
The axial balancing system 32 comprises a high-pressure centripetal flow space 34 defined between the housing 24 and an upstream face 36 of the centrifugal wheel 14, a low-pressure centripetal flow space 38 defined between the housing 24 and a downstream face 40 of the centrifugal wheel 14.
It will be noted from the figure that the high-pressure flow space 34 comprises an inlet 42 arranged in proximity to the outlet edge 44 of the centrifugal wheel 14 and an outlet 46 arranged in proximity to the inlet edge 48 of the centrifugal wheel 14.
Moreover, the outlet 46 of the high-pressure flow space 34 is equipped with first flow restriction means preferably consisting of a first annular labyrinth seal 50, this seal being partially permeable.
In a particularly advantageous manner, the axial balancing system 32 according to the present invention further comprises a plurality of vanes 52 formed on the housing 24, the vanes 52 extending radially in a centripetal direction from the inlet 42 of the high-pressure flow space 34 while being angularly set apart about the axis of rotation A of the pump 10.
It will be appreciated that there is an interstice between the upstream face 36 of the centrifugal wheel 14 and the housing 24 in such a way that a first fraction of the fluid issuing from the centrifugal wheel 14 is able to surge into the high-pressure flow space 34 during operation of the pump. This flow is indicated in the figure by thinly drawn arrows.
As the flow is restricted at the outlet of the high-pressure flow space 34, it will be understood that the hydrostatic pressure of the first fluid fraction is greater than the hydrostatic pressure of the fluid at the inlet of the centrifugal wheel 14.
When it issues from the centrifugal wheel 14, this first fluid fraction has a tangential speed substantially equal to the speed of the outlet edge 44 of the centrifugal wheel 14.
In accordance with the invention, the radial vanes 36 obstruct the tangential flow of the first fluid fraction in such a way that the first fluid fraction is slowed down by the vanes and flows only in a centripetal radial direction into the high-pressure flow space 34.
This leads to a reduction in the overall speed of the first fluid fraction, said fraction being equal to the square root of the sum of the squares of the tangential, radial and axial components of the fluid speed.
As the dynamic pressure is proportional to the square of the overall speed of the fluid, it will be appreciated that the reduction in the overall speed of the first fluid fraction brings about a reduction in the dynamic pressure of the fluid, as a result of which the hydrostatic pressure of the first fluid fraction increases in a particularly advantageous manner owing to the fact that the overall pressure of the first fluid fraction is a constant.
The hydrostatic pressure of the first fluid fraction therefore remains substantially constant and equal to that of the fluid issuing from the centrifugal wheel 14.
It will also be noted that the low-pressure flow space 38 comprises an inlet 54 arranged in proximity to the outlet edge 44 of the centrifugal wheel 14, said inlet 54 being equipped with second flow restriction means preferably consisting of a second annular labyrinth seal 56, this seal being partially permeable.
It will be understood that there is an interstice between the downstream face 40 of the centrifugal wheel 14 and the housing 24 in such a way that a second fraction of the fluid issuing from the centrifugal wheel 14 is able to surge into the low-pressure flow space 38 during operation of the pump 10. This flow is indicated in the figure by thinly drawn arrows.
With reference to the figure, it will be noted that the low-pressure flow space 38 further comprises an outlet 58 having an annular passage 60 forming an axially variable flow restriction and opening radially onto an annular discharge space 62 defined around said rotating shaft 22 radially internally relative to the annular passage 60.
Furthermore, the annular passage 60 is defined between a first annular rib 60a formed on the downstream face 40 of the centrifugal wheel 14 and a second annular rib 60b which is integral with the housing 24.
As the axial balancing system 32 allows slight axial displacement of the centrifugal wheel 14 relative to the housing 24, it will be appreciated that the axial width of the annular passage 60 may vary.
The annular space 62 also communicates with a region in which the pressure is lower than that in the low-pressure flow space 38, this region preferably being arranged upstream of the centrifugal wheel 14.
Preferably, at least one reinjection channel 64 provided axially in the centrifugal wheel 14 provides fluid communication between the annular discharge space 62 and the region located upstream of the centrifugal wheel 14.
As the flow is restricted at the inlet of the low-pressure flow space 38, it will be appreciated that the pressure of the second fluid fraction is lower than the pressure of the fluid at the outlet of the centrifugal wheel 14.
It will therefore be appreciated that the hydrostatic pressure differential between the high and low-pressure flow spaces generates an axial take-up force applied to the centrifugal wheel 14 while being oriented toward the top of the pump 10.
This take-up force therefore counteracts the gravitational and tensile forces to which the rotational elements of the pump are subjected and which are applied to the inner cage 28 of the bearing 26.
The axial balancing system according to the present invention thus allows greater relief of the bearing 26.
The annular passage 60 allows the axial balancing to be regulated in the following manner: if the axial take-up force is too great, the annular passage 60 tends to close, thus restricting the flow at the outlet of the low-pressure flow space 38 to a greater extent, as a result of which the hydrostatic pressure in this flow space increases; this leads to a reduction in the axial take-up force.
The reinjection channel 64 allows the second fluid fraction to be reinjected at the inlet of the centrifugal wheel 14, as indicated in the figure by the thinly drawn arrows.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0653984 | Sep 2006 | FR | national |
