The present invention also relates to a pump comprising a suction stage according to the present invention.
The present invention further relates to an impeller for a suction stage of a pump with centrifugal wheel, the suction stage comprising a diffuser arranged upstream of the centrifugal wheel, the diffuser comprising blades having free ends, the impeller being arranged upstream of the diffuser and comprising a hub having a downstream surface which the free ends of the blades of the diffuser are capable of making flush, said downstream surface extending axially so as to converge toward the centrifugal wheel.
Further characteristics and advantages of the invention will become clearer on reading the following description of an embodiment of the invention given by way of non-limiting example.
The description will refer to the appended figure showing the upstream portion of a pump with centrifugal wheel comprising a suction stage according to the present invention.
The single figure shows a pump with centrifugal wheel 10 intended preferably but not exclusively for the pumping of fluid such as liquefied gas. This pump 10 may, for example, be used for emptying the tanks of liquefied gas carriers.
In the following detailed description, the adjectives “axial” and “radial” are defined in relation to the axis of rotation A of the pump 10, whereas the adjectives “upstream” and “downstream” are defined in relation to the direction in which the fluid is drawn in.
Viewed in the drawing-in direction indicated in the present case by arrows, the pump 10 successively comprises a suction stage 12, a centrifugal wheel 14 and an annular conduit 16 allowing backstreaming of the drawn-in fluid.
The suction stage 12 according to the invention 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 24 arranged downstream of the centrifugal wheel 14.
As may be seen in the figure, the electric motor 24 is bordered by the backstreaming conduit 16.
It will also be noted that the rotating shaft 22 also drives the centrifugal wheel 14 in rotation.
It will be understood with reference to the figure that the fluid is drawn in via the suction stage, accelerated via the centrifugal wheel 14 then guided toward the downstream portion via the backstreaming conduit 16.
The hub 20 of the impeller 18 has an outer surface comprising an upstream surface 20a extending toward the upstream portion of the pump 10 so as to converge and also a downstream surface 20b advantageously extending so as to converge toward the centrifugal wheel 14 in such a way that the hub 20 has a greater diameter in its median portion than at its ends.
The term “converging surface” refers to the fact that the generatrix of this surface tends to draw closer to the axis A of the pump.
As shown in the figure, the upstream surface 20a of the hub carries paddles 28 extending radially toward an outer shell 30 surrounding the hub 20, whereas the downstream surface 20b of the hub is substantially smooth.
It will be appreciated that during rotation of the impeller 18, the fluid drawn in by the impeller flows, in the annular duct V defined by the space located between the outer surface of the hub 20 and the outer shell 30, toward the downstream surface 20b of the hub 20.
In accordance with the invention, the suction stage 12 further comprises a diffuser 34 which is arranged between the impeller 18 and the centrifugal wheel 14.
This purpose of the diffuser 34 is to reduce the rotational component of the fluid originating from the impeller 18 before it enters the centrifugal wheel 14, said wheel having an inlet 32 located at the outlet of the diffuser 34.
In order to do this, the diffuser 34 comprises a plurality of diffusion blades 36 protruding from an annular portion 30a of the outer shell 30 toward the downstream surface 20b of the hub 20, these blades 36 having free ends located on the side opposing the outer shell 30.
It may be seen in the figure that the diffuser 34 surrounds the downstream surface of the hub of the impeller, i.e. the hub 20 of the impeller 18 is integrated into a cavity delimited by the free ends of the blades 36.
In a particularly advantageous manner, each of the blades 36 is shaped in such a way that its free end makes the downstream surface 20b of the hub 20 flush, preferably over the entire length of said free end, i.e. such that there nevertheless remains a slight clearance between the free end of each of the blades 36 and the downstream surface 20b.
As may be seen in the figure, the annular portion 30a of the outer shell 30 has an axial length substantially equal to the axial length of the downstream surface 20b, on the one hand, and extends axially so as to converge toward the centrifugal wheel 14, on the other hand.
The space delimited between the downstream surface 20b and the annular portion 30a therefore defines a converging annular duct for the flow of the fluid, said fluid accordingly being directed toward the centrifugal wheel 14 while drawing closer to the axis A of the pump owing to the convergence of the annular duct.
A benefit of making the fluid enter the centrifugal wheel 14 as close as possible to the axis of rotation of this wheel consists in the fact that the diameter of the centrifugal wheel can advantageously be reduced and the compactness of the pump 10 can therefore be further improved.
It will be appreciated that the present invention advantageously allows the outer shell 30 to be moulded in one piece with the blades 36 of the diffuser 34, and this simplifies production of the pump and improves the reliability thereof.
It will therefore be understood that the suction stage 12 according to the present invention can advantageously consist of two moulded parts, i.e. the outer shell equipped with the blades 36 of the diffuser, on the one hand, and the impeller 18, on the other hand.
Number | Date | Country | Kind |
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0653985 | Sep 2006 | FR | national |