High efficiency low specific speed centrifugal pump

Abstract

A centrifugal pump comprising: a casing; a rotary shaft arranged for rotation in the casing; a plurality of pump stages, each pump stage comprising an impeller secured on said rotary shaft and arranged for rotation in a respective impeller chamber formed in the casing. The pump further comprises a plurality of sealing members for reducing leakage between a rotary component and a respective stationary component. At least one of the sealing members comprises an arrangement of compliant plate members attached in facing relation at root ends to the respective stationary component and forming a sealing ring between the stationary component and the respective rotary component. Moreover, at least some pump stages have a specific speed of 25 or less.

What is claimed is: 
     
         1 . A centrifugal pump comprising:
 a casing;   a rotary shaft arranged for rotation in the casing;   at least one pump stage comprising an impeller secured on the rotary shaft and arranged for rotation in a respective impeller chamber formed in the casing; and   a plurality of sealing members, each arranged for reducing leakage between a rotary component and a respective stationary component in the centrifugal pump.   wherein at least one of said the sealing members comprises an arrangement of compliant plate members attached in facing relation at root ends to the respective stationary component and forming a sealing ring between the stationary component and the respective rotary component, and   wherein the at least one pump stage has a specific speed defined as:
     Ns =(ωq 1/2 )( h   3/4 )
 
 equal to or less than 25, where:
 ω is a pump shaft rotational speed expressed in rpm, 
 q is a flow rate across the stage, expressed in m 3 /s at Best Efficiency Point (BEP), and 
 h is a head rise across the stage expressed in m. 
 
   
     
     
         2 . The centrifugal pump of  claim 1 , comprising a plurality of pump stages, each comprising an impeller secured on the rotary shaft and arranged for rotation in a respective impeller chamber. 
     
     
         3 . The centrifugal pump of  claim 2 , comprising N stages, wherein (N−m) stages have a specific speed Ns equal to or less than 25. 
     
     
         4 . The centrifugal pump of  claim 3 , wherein m=1. 
     
     
         5 . The centrifugal pump of  claim 1 , wherein all stages have a specific speed equal to or less than 25. 
     
     
         6 . The centrifugal pump of  claim 1 , wherein each pump stage comprises an inlet-side sealing member, and wherein at least one of the inlet-side sealing members comprises an arrangement of compliant plate members. 
     
     
         7 . The centrifugal pump of  claim 6 , wherein each inlet-side sealing member of the plurality of pump stages comprises an arrangement of compliant plate members. 
     
     
         8 . The centrifugal pump of  claim 6 , wherein each inlet-side sealing member comprising an arrangement of compliant plate members is arranged and configured for co-action with an impeller eye of the respective impeller. 
     
     
         9 . The centrifugal pump of  claim 2 , wherein at least one pump stage comprises an outlet-side sealing member arranged and configured for co-action with an impeller hub and comprising an arrangement of compliant plate members. 
     
     
         10 . The centrifugal pump of  claim 2 , wherein each pump stage comprises an outlet-side sealing member comprising an arrangement of compliant plate members. 
     
     
         11 . The centrifugal pump of  claim 1 , comprising at least one shaft-sealing member between a stationary component and the shaft or a bushing mounted on the shaft, wherein the at least one shaft-sealing member is comprised of an arrangement of compliant plate members attached in facing relation at root ends to the stationary component and forming a sealing ring between the stationary component and the rotary shaft or the bushing mounted on the rotary shaft. 
     
     
         12 . The centrifugal pump of  claim 1 , wherein each the compliant plate member of at least one of the sealing members comprises at least one slit extending radially into the compliant plate member from a radially outermost root end of the compliant plate member to a radially intermediate location, between the root end and a radially innermost tip end of the compliant plate member, the slits of the compliant plate members being aligned to form an annular slot; and wherein at least one stationary ring attached to the stationary component extends radially into the annular slot formed by the compliant plate members. 
     
     
         13 . The centrifugal pump of  claim 1 , wherein each the compliant plate member of at least one of the sealing members comprises a plurality of slits extending radially into the compliant plate member from a radially outermost root end of the compliant plate member to a radially intermediate location, between the root end and a radially innermost tip end of the compliant plate member, the slits of the compliant plate members being aligned to form an annular slot; and wherein a plurality of stationary rings attached to the stationary component extend radially into the annular slots formed by the compliant plate members.