PURPOSE: To provide a piston ring composed of a dead ring without having an intrinsic radial tension to be capable of correctly making action.

CONSTITUTION: An annular piston 104 reciprocates along a vertical axial line within an inner diameter of a cylinder 102. The piston 104 is generally provided with two grooves 106, 108 forming inclined walls of a generally keystone wedge 110. A single metal strip is formed into a one-piece split annular top land type piston ring 120 with little or no intrinsic load. The piston ring 120 is received into the piston grooves 106, 108 to provide sealing contact between the piston 104 and an inner cylinder wall 103. The shape of the piston ring 120 and the wedge 110 of the piston 104 provide a smooth sliding movement between mating components as a dynamic force component is generated in a radial direction in response to piston reciprocation along the vertical axial line of the cylinder 102.