Volute shaped pump casing for a centrifugal pump

1. A volute shaped pump casing for a centrifugal pump, including a chamber for housing at least one impeller mounted on a shaft for rotating the impeller around an axis of rotation, a volute shaped chamber which forms a flow channel divided into a first volute and a second volute, and a first channel and a second channel connected to the first and the second volute respectively, with the first channel being called long channel and the second channel being called short channel, characterized in that the first or long channel is axially displaced with respect to the second or short channel and/or with respect to the second volute, wherein the first or longer channel has a wall closer to the axis of rotation called inner wall, and wherein a radial distance between the axis of rotation and the inner wall decreases over at least a part of the length of the long channel.

2. The volute shaped pump casing according to claim 1 , wherein a final part of the long channel is arranged in the axial direction at the side of the short channel or side by side with the short channel.

3. The volute shaped pump casing according to claim 1 , wherein the first and the second volute is connected to a single channel each.

4. The volute shaped pump casing according to claim 1 , wherein the channels have a final part each which form a double discharge.

5. The volute shaped pump casing according to claim 1 , wherein the first or longer channel has a wall closer to the axis of rotation called inner wall, and wherein a radial distance between the axis of rotation and the inner wall of the long channel is smaller than the radius of the impeller over a part of the length of the long channel.

6. The volute shaped pump casing according to claim 1 comprising an inlet duct, wherein the first or longer channel has a wall closer to the axis of rotation called inner wall in the following, and wherein over a part of the length of the long channel, a radial distance between the axis of rotation and the inner wall of the long channel is smaller than half of the diameter of the inlet duct, in particular smaller than half of the smallest diameter of the inlet duct.

7. The volute shaped pump casing according to claim 1 , wherein the long channel and/or the short channel have a constant cross section over the greater part of their respective length or a widening cross section over the greater part of their respective length.

8. A centrifugal pump including at least one impeller mounted on a shaft for rotating the impeller around an axis of rotation and a volute shaped pump casing according to claim 1 .

9. The centrifugal pump according to claim 8 , wherein the centrifugal pump is of the radial type or of the mixed flow type.

10. The centrifugal pump according to claim 8 , wherein the centrifugal pump is a multistage pump.

11. The centrifugal pump according to claim 10 , wherein the centrifugal pump is a multistage pump including a back to back impeller arrangement and a discharge stage, and wherein the long channel of the discharge stage passes in-between a center-bush and a crossover of the multistage pump.

12. A volute shaped pump casing for a centrifugal pump, the pump comprising at least one impeller and a shaft, wherein the impeller is mounted on the shaft, wherein the shaft is configured to rotate the impeller around an axis of rotation, wherein the axis of rotation defines an axial direction, the pump casing comprising:

a chamber configured to house the impeller therein; and

a volute shaped chamber defining a flow channel, wherein the flow channel comprises:

a first volute;

a second volute downstream of the first volute and at substantially the same axial position as the first volute;

a first channel fluidly connected to the first volute downstream of the first volute, in parallel with the second volute, wherein the first channel comprises an inner wall near the axis of rotation, and wherein a radial distance between the axis of rotation and the inner wall decreases over at least a part of a length of the first channel; and

a second channel fluidly connected to the second volute downstream of the second volute;

wherein the first channel is displaced in the axial direction with respect to at least one of:

the second channel; and

the second volute.

13. A centrifugal pump, comprising:

at least one impeller;

a shaft, wherein the impeller is mounted on the shaft, wherein the shaft is configured to rotate the impeller around an axis of rotation, wherein the axis of rotation defines an axial direction; and

a volute shaped pump casing, comprising:

a chamber, wherein the impeller is housed within the chamber; and

a volute shaped chamber defining a flow channel, wherein the flow channel comprises:

a first volute;

a second volute downstream of the first volute and at substantially the same axial position as the first volute;

a first channel fluidly connected to the first volute downstream of the first volute, in parallel with the second volute, wherein the first channel comprises an inner wall near the axis of rotation, and wherein a radial distance between the axis of rotation and the inner wall decreases over at least a part of a length of the first channel; and

a second channel fluidly connected to the second volute downstream of the second volute;

wherein the first channel is displaced in the axial direction with respect to at least one of:

the second channel; and

the second volute.