Concentric multi-stage centrifugal pump with start stage

Abstract

A multi-stage concentric centrifugal pump includes a start stage. An inner impeller stage is driven by drive shaft while an electric motor drive is selectively switched on for starting, and off for normal operation to drive an outer impeller stage. The electric motor driven outer stage builds required system pressure and flow at engine starting, and then permits the electric motor to be switched off and allow the outer stage to act as a free rotating disk to improve operating efficiency of the pump.

1 . A centrifugal pump assembly comprising:
 a first pump stage;   a second pump stage independently rotatable relative to and disposed in concentric relation with the first pump stage; and   a drive assembly operatively associated with the first and second pump stages that rotates the first and second pump stages to a first rotational speed and then (a) turns off drives the first pump stage of the first rotational speed or (b) independently drives the first and second pump stages above the first rotational speed.   
     
     
         2 . The centrifugal pump assembly of  claim 1  wherein the second pump stage rotates freely independent of the first rotational speed. 
     
     
         3 . The centrifugal pump assembly of  claim 2  wherein the first pump stage is an inner impeller stage and the second pump stage is an outer impeller stage. 
     
     
         4 . The centrifugal pump assembly of  claim 2  wherein the drive assembly includes a main drive shaft connected to and selectively rotating the first pump stage. 
     
     
         5 . The centrifugal pump assembly of  claim 4  wherein the drive assembly includes a separate drive means for rotating the second pump stage. 
     
     
         6 . The centrifugal pump assembly of  claim 5  wherein the separate drive means is an electric motor drive. 
     
     
         7 . The centrifugal pump assembly of  claim 6  wherein the electric motor drive is concentrically located about the main drive shaft. 
     
     
         8 . The centrifugal pump assembly of  claim 7  wherein the electric motor drive rotates the second pump stage at a different speed than the main drive shaft rotates the first pump stage. 
     
     
         9 . The centrifugal pump assembly of  claim 1  wherein the first pump stage is an inner impeller stage and the second pump stage is an outer impeller stage. 
     
     
         10 . The centrifugal pump assembly of  claim 1  wherein the drive assembly includes a separate drive motor for rotating the second pump stage. 
     
     
         11 . The centrifugal pump assembly of  claim 1  wherein the drive assembly includes a separate electric motor for rotating the second pump stage that is concentrically located about a main drive shaft that rotates the first pump stage. 
     
     
         12 . The centrifugal pump assembly of  claim 1  wherein the drive assembly rotates the second pump stage at a different speed than the first pump stage to obtain desired performance characteristics. 
     
     
         13 . The centrifugal pump assembly of  claim 12  wherein the drive assembly includes a separate electric motor drive for rotating the second pump stage at a slower speed than a main drive shaft rotates the first pump stage below the first rotational speed. 
     
     
         14 . A method of operating a centrifugal pump assembly comprising:
 providing a first pump stage;   providing a second pump stage concentrically mounted around the first pump stage;   independently driving the first and second pump stages; and   switching off the drive for the second pump stage above a preselected rotational speed.   
     
     
         15 . The method of  claim 14  further comprising allowing the second pump stage to rotate freely relative to the first pump stage above the preselected rotational speed. 
     
     
         16 . The method of  claim 15  further comprising driving the first and second pump stages at different speeds. 
     
     
         17 . The method of  claim 16  wherein the driving step includes using an electric motor drive for rotating the second pump stage. 
     
     
         18 . The method of  claim 15  wherein the driving step includes using an electric motor drive for rotating the second pump stage. 
     
     
         19 . The method of  claim 14  further comprising driving the first and second pump stages at different speeds. 
     
     
         20 . The method of  claim 14  wherein the driving step includes using an electric motor drive for rotating the second pump stage.