a diffuser assembly has pairs of split rings rotationally locked to each other in an alternating array with other pairs of split rings where adjacent pairs are responsive to pressure differential to be biased toward a sliding sleeve or the surrounding housing in an alternating pattern . the split rings are made to have an interference initial fit to the sleeve or housing and the splits on adjacent rings are offset while a relation of a projection to a depression between adjacent rings prevents relative rotation to keep the desired circumferential offset in the splits between adjacent rings . end tapers can bias adjacent pairs in opposed directions responsive to applied differential pressure . the rings are preferably metallic and can have a coating to facilitate relative sliding and enhance durability .