Abstract: The inner annular surface of a load ring includes a concave contour such that when pressure is applied to the center of the outer surface the elastomer material will flatten out and cause oppositely disposed feet to kick up and radially outwardly and in turn apply increased pressure to backup rings engaging the cylinder wall. The inner surface of the load ring includes oppositely disposed ramp surfaces which slope radially outwardly and towards each other such that fluid pressure on the backup rings or pressure from the load ring feet will move the backup rings into tighter engagement with the cylinder wall for improved sealing and scraping action.

Abstract: The back-up rings of the present invention are seated on opposite sides of a sealing ring within an annular groove of a hydraulic piston. The sealing ring is in frictional engagement with the interior surface of the hydraulic cylinder, and the back-up rings are positioned within the cylinder groove and on opposite sides of the sealing ring. At least one of the back-up rings includes a vent hole extending axially therethrough to permit the alleviation of any fluid pressure accumulating between the two spaced apart back-up rings. As an alternative to the axial vent hole, a groove may be provided on the interior perimeter of the back-up ring or the back-up ring may include a complete break therein for permitting the venting of fluid trapped between the two back-up rings. The method of the present invention includes venting any fluid which is trapped between the two back-up rings during reciprocation of the piston within the cylinder.