Centrifugal pump stage, centrifugal pump and use of a pump stage

Abstract

The pump stage for a centrifugal pump comprises an impeller unit ( 10 ) having an axial hub and a diffuser unit ( 20 ) extended at a first face of said impeller unit ( 10 ). The impeller unit ( 10 ) is supported floating inside the diffuser unit ( 20 ). A shim ring ( 40 ) is associated with the impeller unit ( 10 ) and is sustained in sliding support on a washer ( 27 ) housed in a fixed position in a correspondent seat ( 26 ) of the diffuser unit ( 20 ) of an adjacent pump stage.

1 . A pump stage for a centrifugal pump, comprising:
 an impeller unit comprising an axial hub suitable to be mounted on a pump shaft of the centrifugal pump coaxial with the pump shaft;   a diffuser unit extending at a first face of said impeller unit;   an aspiration lid associated with said diffuser unit and extended at a second face of said impeller unit, said impeller unit floating inside said diffuser unit, said impeller unit being associated with a shim ring mounted fixed on said axial hub and sustained in sliding support on a washer housed in a fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage, said impeller unit being in sliding contact with said aspiration lid, along an annular portion extended at said second face.   
     
     
         2 . A pump stage according to  claim 1 , wherein, in a starting or breaking in step, between said annular portion of said impeller unit and said aspiration lid a little play is shaped, such as to minimize hydraulic losses by leak without there being a contact. 
     
     
         3 . A pump stage according to  claim 1 , herein a portion of said shim ring protrudes from said axial hub of the impeller unit and axially crosses said aspiration lid of the impeller unit for engaging in sliding support said washer of the diffuser unit of the adjacent pump stage. 
     
     
         4 . A pump stage according to  claim 2 , wherein, at an end of said starting or breaking in step, said impeller unit is in support with said shim ring on said washer of the diffuser unit of the adjacent pump stage and with said annular portion on said aspiration lid. 
     
     
         5 . A pump stage according to  claim 1 , wherein said shim ring is made of low friction coefficient and high resistance to wear and tear material and is sustained in sliding support on said washer of metallic material. 
     
     
         6 . A pump stage according to  claim 1 , wherein said washer is housed in said seat made at a circular opening axially made up by said diffuser unit. 
     
     
         7 . A pump stage according to  claim 1 , wherein said aspiration lid comprises a disc of metallic or partially metallic material centrally having a circular opening with a raised rim on which said annular portion of said impeller unit is in sliding contact. 
     
     
         8 . A centrifugal pump comprising:
 a pump comprising a plurality of pump stages, one or more of said pump stages comprising an impeller unit comprising an axial hub suitable to be mounted on a pump shaft of the centrifugal pump coaxial with the pump shaft, a diffuser unit extending at a first face of said impeller unit and an aspiration lid associated with said diffuser unit and extended at a second face of said impeller unit, said impeller unit floating inside said diffuser unit, said impeller unit being associated with a shim ring mounted fixed on said axial hub and sustained in sliding support on a washer housed in a fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage, said impeller unit being in sliding contact with said aspiration lid, along an annular portion extended at said second face.   
     
     
         9 . A method, comprising:
 using a centrifugal pump stage, said centrifugal pump stage comprising an impeller unit comprising an axial hub suitable to be mounted on a pump shaft of the centrifugal pump coaxial with the pump shaft, a diffuser unit extending at a first face of said impeller unit and an aspiration lid associated with said diffuser unit and extended at a second face of said impeller unit, said impeller unit floating inside said diffuser unit, said impeller unit being associated with a shim ring mounted fixed on said axial hub and sustained in sliding support on a washer housed in a fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage, said impeller unit being in sliding contact with said aspiration lid, along an annular portion extended at said second face;   providing a starting or breaking in stage in which said impeller unit is arranged in support with said shim rig on said washer of the diffuser unit of the adjacent pump stage and a clearance is shaped between said annular portion of said impeller unit and said aspiration lid, a width of said clearance undergoing to a progressive reduction by wear out effect of said shim ring, until annulling in a condition of normal functioning or speed, in which said annular portion of said impeller unit is in support on said aspiration lid.   
     
     
         10 . A method according to  claim 9 , wherein said wear and tear effect, in said starting or breaking in step, said shim ring is polished and consequently acquires a high endurance. 
     
     
         11 . A pump stage according to  claim 2 , wherein a portion of said shim ring protrudes from said axial hub of the impeller unit and axially crosses said aspiration lid of the impeller unit for engaging in sliding support said washer of the diffuser unit of the adjacent pump stage. 
     
     
         12 . A pump stage according to  claim 3 , wherein, at an end of a starting or breaking in step, said impeller unit being in support with said shim ring on said washer of the diffuser unit of the adjacent pump stage and with said annular portion on said aspiration lid.