An apparatus includes a bearing housing, a shaft assembly that extends through the bearing housing along a shaft axis, an annular groove formed on the shaft assembly, and a piston ring assembly that is engaged with the bearing housing and extends into the groove of the shaft assembly. The piston ring assembly includes a first ring portion and a second ring portion. The first ring portion has a first contact face that is oriented at a non-perpendicular with respect to the shaft axis, and the second ring portion has a second contact face that is oriented at a non-perpendicular angle with respect to the shaft axis and is engageable with the first contact face.