An intershaft seal assembly (2) for maintaining separation between a piston ring (3) and a pair of mating rings (4, 5) is presented. The assembly includes a piston ring (3) interposed between forward and aft mating rings (4, 5) and a plurality of hydrodynamic grooves (18) disposed along a sealing face (11, 12) of each mating ring (4, 5). Each hydrodynamic groove (18) further includes at least two adjoining steps (23) wherein each step (23) is defined by a base wall (24) arranged to decrease depthwise in the direction opposite to rotation of an inner shaft (8). Two adjoining base walls (24) define a base shoulder (25) which locally redirects potion of a longitudinal flow (32) within the groove to form an outward flow (30) in the direction of the piston ring (3). Base walls (24) are bounded by and intersect a pair of side walls (26) with at least one side shoulder (27) thereon which narrows the groove (18) widthwise and locally redirects portion of the longitudinal flow (32) to form a lateral flow (31) from one side wall (26) toward another side wall (26). Outward and lateral flows (30, 31) cooperate, with or without the longitudinal flow (32), to increase fluid pressure and maintain separation between the piston ring (3) and the mating rings (4, 5)·