A cylindrical seal apparatus according to one embodiment includes a split spring ring and a split seal ring supported in a groove for example defined in a piston. The split spring ring in a tensioning condition presses against a tapered annular inner surface of the split seal ring to create a radial pre-load and an axial pre-load to the slit seal ring to establish a primary sealing contact between the seal ring and a cylinder, and a second sealing condition between the seal ring and a lower-pressure side of the groove, before the working fluid pressure is built up.