Impeller adjuster for centrifugal pump

A centrifugal pump comprising a bladed impeller in a stationary pump housing, the leading edges of said blades being adjacent a first radially extending wall of said housing, a rotatable shaft on which said impeller is mounted, a shaft support for rotatably holding the end of said shaft which is opposite said impeller, and adjustable fastening means for connecting said shaft support to a stationary member, said impeller, shaft and shaft support together being adapted for axial adjustment upon axial adjustment of said fastening means, said fastening means comprising at least two threaded bolts projecting from said stationary member in a direction parallel to the axis of said shaft, and reference nuts for fixing the position of said shaft support on said bolts, said reference nuts having marks at regular angular intervals, and at least one reference mark on said shaft support adjacent each reference nut cooperating with said marks on said reference nuts for indicating the axial position of said impeller with respect to said pump housing.