Case construction for multi-stage pump

Claim 1

A pump apparatus comprising: an outer case assembly having an inlet port leading to a suction chamber at a forward end of the pump and an outlet port leading to a discharge chamber at a rearward end of the pump; a shaft sealably extending through walls of the outer case assembly; an inner case assembly disposed within the outer case assembly and having a plurality of pump stages which are axially spaced along the shaft to povide fluid communication between the suction chamber and the discharge chamber, the pump stages including a first stage and one or more booster stages, each pump stage being characterized by an impeller secured for rotation with the shaft, the inner case assembly having an interior network of hydraulic passages for fluid communication between successive pump stages, the inner case assembly being characterized by a forward case section of a unitary annular construction housing the first pump stage and two rearward case sections housing the booster pump stages, an axial joint being defined between adjacent surfaces of the rearward case sections, a radial joint being defined between a surface of the forward case section and adjacent surfaces of the assembled rearward case sections, the forward case section being surrounded at least in part by the suction chamber, the rearward case sections being surrounded at least in part by the discharge chamber; and locating means provided on an interior wall of the outer case assembly for preventing the forward movement of the forward case section beyond a predetermined position within the outer case; whereby the fluid pressure within the discharge chamber during operation of the pump applies a radially acting force to the rearward case sections to form a fluid-tight seal at the axial joint and applies an axial force acting in the forward direction against the rearward case sections to form a fluid-tight seal at the radial joint.