Centrifugal pump with auxiliary impeller operatively associated with a primary impeller to balance the forces on the opposite sides thereof

A centrifugal pump which comprises

• a pump casing which includes a first annular portion that defines a generally cylindrical intake duct and an axis through said pump casing;
• a second annular portion which extends outwardly from said first annular portion;
• a third annular portion which is located at an outer end of said second annular portion;
• and a fourth annular portion which extends from said third annular portion in parallel with said first annular portion, said fourth annular portion providing an annular inner surface and an annular end surface remote from said third annular portion, said fourth annular portion forming with said third annular portion an annular pressure chamber having an annular inlet mouth, said fourth annular portion also providing a plurality of circumferentially spaced control slots which communicate with said annular inlet mouth and a plurality of circumferentially spaced bores which extend from said annular pressure chamber to outlet openings in said inner surface of said fourth annular portion,
• a motor casing which defines an annular end surface at one end thereof which is in abutment with said annular end surface of said fourth annular portion of said pump casing and an end wall at its opposite end, said motor casing and said pump casing together forming a housing,
• a generally cap-shaped isolation shell having a head portion and a side portion mounted in said motor casing, said side portion being in contact with the end wall of said motor casing and said head portion facing said intake duct of said pump casing,
• an inner magnet rotor rotatably mounted within said isolation shell,
• a bearing means located along said axis within said pump casing, said bearing means defining two end stops,
• a primary impeller rotatably mounted on said bearing means and axially movable therealong between said two end stops, said primary impeller, when rotated, causing fluid passing into said pump casing through said intake duct to be pressurized and delivered to said annular pressure chamber via said annular inlet mouth, and
• an auxiliary impeller rotatably mounted within said pump casing between said primary impeller and the head portion of said isolation shell and operatively connected with said primary impeller such that rotation of said auxiliary impeller will cause rotation of said primary impeller, said auxiliary impeller including an annular flange which extends outwardly of said side portion of said isolation shell and includes an outer magnet rotor, said auxiliary impeller being axially movable with said primary impeller, said auxiliary impeller and said primary impeller providing at least one radial relief channel therebetween which extends from an annular hub chamber between said primary impeller and the head portion of said isolation shell to a peripheral mouth located near said annular inner surface of said fourth annular portion and between said annular inlet mouth and said outlet openings of said bores;
• the flow of pressurized fluid from said annular pressure chamber through said bores and the flow of fluid from said hub chamber through said at least one radial relief channel to said annular pressure chamber via said control slots when said primary and auxiliary impellers are rotated creating a balancing of forces on opposite sides of the primary impeller such that it will remain positioned between said end stops of said bearing means.