Abstract: In a centrifugal pump, a barrier ring in the form of a dynamic seal member is interposed between relatively rotating, generally circular wall portions which undergo relative axial movement to vary the width of a gap between the wall portions, the seal member having an outer jacket of flexible material and an annular spring member of frustoconical configuration inserted into offset grooves in the jacket, and when the seal member is mounted under compression between the confronting surfaces will follow the relative axial movement between the wall portions to maintain liquid-tight sealing engagement with the wall portions. In a modified form of invention, the seal member includes a pair of helical spring members inserted into grooves in an outer flexible jacket and, when the seal is mounted under compression between confronting surfaces of the wall portions as described will maintain liquid-tight sealing engagement notwithstanding variations in the width of the gap between members.