Abstract: A gasket assembly is located between two cylindrical components capable of being displaced telescopically into one another. The gasket assembly includes an annular flange held stationary with respect to one of the components and associated therewith first and second annular sealing rings spaced radially apart by an annular piston capable of relative axial movement between the sealing rings to compensate for pressure and for wear on the sealing ring adjacent the movable cylindrical component relative to said flange. The adjacent surfaces of the annular piston and the latter sealing ring are designed for the assembly to function in this manner. A venting hole in the annular flange and the sealing characteristics of the other sealing ring further aid in accomplishing the sealing function of the assembly.