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In high pressure centrifugal pumps the magnitude of the critical speed is strongly affected by the presence of liquid in the close clearance spaces of sealing rings and throttle bushings. The stiffening and damping effect resulting from the non-axisymmetric pressure drop across such gaps is often large compared with the elastic stiffness of the shaft. In many cases it raises the critical speed far above the “dry” value, and in some cases it eliminates the critical speed altogether. As a consequence, design specifications based on shaft critical speeds, calculated disregarding the effects of the fluid, become quite meaningless. In this paper simplified equations are derived for the calculation of the effect of the fluid gap. The results have been verified by measurements on a test pump. Sample calculations for a typical multistage boiler feed pump are included as illustration.