Submersible multistage pump with impellers having diverging shrouds

Abstract

A centrifugal pump may include plural pump stages, each comprising an impeller assembly, a stationary disc assembly and a diffuser assembly, all disposed about an impeller shaft that is driven by a motor. The impeller assembly may include upper and lower impeller shrouds having facing surfaces, and a plurality of impeller vanes extending between the surfaces of the shrouds to define a plurality of flow passages for liquid to flow outwardly from a central hub of the impeller assembly. To assist in pressure recovery of the pump, the distance between the surfaces of the impeller shrouds may increase as the radial distance from the central hub increases.

1 . A pump stage for a centrifugal pump having a main impeller shaft with a longitudinal axis driven by a motor, the pump stage comprising:
 a diffuser assembly having a diffuser body with a generally-cylindrical outer wall and a main shaft opening configured to receive the main impeller shaft;   an impeller assembly disposed within the outer wall of the diffuser assembly, the impeller assembly comprising:
 an upper impeller body having a generally-cylindrical central hub with a main shaft bore shaped and sized to receive the main impeller shaft in close fitting relationship so that the impeller assembly rotates with the main impeller shaft, and an upper impeller shroud extending radially from the central hub and having a bottom surface, and 
 a lower impeller shroud having a central fluid inlet opening and a top surface facing the bottom surface of the upper impeller shroud, 
 wherein the top and bottom surfaces are oriented such that the distance between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud increases as the radial distance from the central hub increases; and 
   a disc assembly having a central opening configured to receive the central hub of the upper impeller body and the main impeller shaft, the disc assembly enclosing the impeller assembly within the diffuser assembly.   
   
   
       2 . A pump stage in accordance with  claim 1 , wherein the top surface of the lower impeller shroud is generally planar and approximately perpendicular to the longitudinal axes of the main impeller shaft and the central hub, and the bottom surface of the upper impeller shroud is conical so that the distance between the bottom and top surfaces increases as the radial distance from the central hub increases. 
   
   
       3 . A pump stage in accordance with  claim 1 , wherein the top surface of the lower impeller shroud and the bottom surface of the upper impeller shroud are conical so that the distance between the bottom and top surfaces and the disc assembly increases as the radial distance from the central hub increases, and so that the distance between the bottom and top surfaces increases as the radial distance from the central hub increases. 
   
   
       4 . A pump stage in accordance with  claim 1 , wherein an angle of divergence θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is approximately 5°. 
   
   
       5 . A pump stage in accordance with  claim 1 , wherein a shroud divergence angle θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is greater than 0° and no more than 5°. 
   
   
       6 . A pump stage in accordance with  claim 1 , wherein a shroud divergence angle θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is in the range of 2° to 5°. 
   
   
       7 . A pump stage in accordance with  claim 1 , wherein the diffuser assembly comprises a plurality of circumferentially spaced spiral impeller vanes extending between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud. 
   
   
       8 . A pump stage in accordance with  claim 1 , wherein the distance between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud increases linearly as the radial distance from the central hub increases. 
   
   
       9 . A centrifugal pump comprising:
 a motor;   a main impeller shaft having a longitudinal axis and being coupled to and driven by the motor; and   at least one pump stage comprising:
 a diffuser assembly having a diffuser body with a generally-cylindrical outer wall and a main shaft opening configured to receive the main impeller shaft, 
 an impeller assembly disposed within the outer wall of the diffuser assembly, the impeller assembly comprising:
 an upper impeller body having a generally-cylindrical central hub with a main shaft bore shaped and sized to receive the main impeller shaft in close fitting relationship so that the impeller assembly rotates with the main impeller shaft, and an upper impeller shroud extending radially from the central hub and having a bottom surface, and 
 a lower impeller shroud having a central fluid inlet opening and a top surface facing the bottom surface of the upper impeller shroud, 
 wherein the top and bottom surfaces are oriented such that the distance between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud increases as the radial distance from the central hub increases, and 
 
 a disc assembly having a central opening configured to receive the central hub of the upper impeller body and the main impeller shaft, the disc assembly enclosing the impeller assembly within the diffuser assembly. 
   
   
   
       10 . A centrifugal pump in accordance with  claim 9 , wherein the top surface of the lower impeller shroud is generally planar and approximately perpendicular to the longitudinal axes of the main impeller shaft and the central hub, and the bottom surface of the upper impeller shroud is conical so that the distance between the bottom and top surfaces increases as the radial distance from the central hub increases. 
   
   
       11 . A centrifugal pump in accordance with  claim 9 , wherein the top surface of the lower impeller shroud and the bottom surface of the upper impeller shroud are conical so that the distance between the bottom and top surfaces and the disc assembly increases as the radial distance from the central hub increases, and so that the distance between the bottom and top surfaces increases as the radial distance from the central hub increases. 
   
   
       12 . A centrifugal pump in accordance with  claim 9 , wherein an angle of divergence θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is approximately 5°. 
   
   
       13 . A centrifugal pump in accordance with  claim 9 , wherein a shroud divergence angle θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is greater than 0° and no more than 5°. 
   
   
       14 . A centrifugal pump in accordance with  claim 9 , wherein a shroud divergence angle θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is in the range of 2° to 5°. 
   
   
       15 . A centrifugal pump in accordance with  claim 9 , wherein the diffuser assembly comprises a plurality of circumferentially spaced spiral impeller vanes extending between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud. 
   
   
       16 . A centrifugal pump in accordance with  claim 9 , wherein the distance between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud increases linearly as the radial distance from the central hub increases. 
   
   
       17 . An impeller assembly for a pump stage of a centrifugal pump having a main impeller shaft with a longitudinal axis driven by a motor, the pump stage including a diffuser assembly having a diffuser body with a generally-cylindrical outer wall and a disc assembly, the diffuser assembly and the disc assembly being configured to receive the main impeller shaft, the impeller assembly comprising:
 an upper impeller body having a generally-cylindrical central hub with a main shaft bore shaped and sized to receive the main impeller shaft in close fitting relationship so that the impeller assembly rotates with the main impeller shaft, and an upper impeller shroud extending radially from the central hub and having a bottom surface, and   a lower impeller shroud having a central fluid inlet opening and a top surface facing the bottom surface of the upper impeller shroud,   wherein the impeller assembly is disposed within the outer wall of the diffuser assembly and enclosed therein by the disc assembly, and wherein the top and bottom surfaces are oriented such that the distance between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud increases as the radial distance from the central hub increases.   
   
   
       18 . An impeller assembly in accordance with  claim 17 , wherein the top surface of the lower impeller shroud is generally planar and approximately perpendicular to the longitudinal axes of the main impeller shaft and the central hub, and the bottom surface of the upper impeller shroud is conical so that the distance between the bottom and top surfaces increases as the radial distance from the central hub increases. 
   
   
       19 . An impeller assembly in accordance with  claim 17 , wherein the top surface of the lower impeller shroud and the bottom surface of the upper impeller shroud are conical so that the distance between the bottom and top surfaces and the disc assembly increases as the radial distance from the central hub increases, and so that the distance between the bottom and top surfaces increases as the radial distance from the central hub increases. 
   
   
       20 . An impeller assembly in accordance with  claim 17 , wherein an angle of divergence θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is approximately 5°. 
   
   
       21 . An impeller assembly in accordance with  claim 17 , wherein a shroud divergence angle θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is greater than 0° and no more than 5°. 
   
   
       22 . An impeller assembly in accordance with  claim 17 , wherein a shroud divergence angle θ between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud is in the range of 2° to 5°. 
   
   
       23 . An impeller assembly in accordance with  claim 17 , wherein the diffuser assembly comprises a plurality of circumferentially spaced spiral impeller vanes extending between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud. 
   
   
       24 . An impeller assembly in accordance with  claim 17 , wherein the distance between the bottom surface of the upper impeller shroud and the top surface of the lower impeller shroud increases linearly as the radial distance from the central hub increases.