An experimental investigation has been conducted to determine the magnitudes and directions of the unbalanced radial forces on centrifugal pump impellers. The work covers single volutes for a wide specific speed range, double volutes, concentric casings, and modifications of the concentric casing. The results are presented in graphical form and are discussed. A method, making use of strain gages, was devised for determining the magnitudes and directions of the resultant radial forces and is described.