Patent ID: 7954823

Claim:
A sealing ring for a reciprocating motion, the sealing ring being held to one member in two relatively moving members and slidably brought into close contact with the other member, and a sliding portion with said other member being formed in a circular arc cross sectional shape, the sealing ring comprising a shape having a concave surface in both side surfaces facing in an axial direction, said concave surface in said both side surfaces being symmetrical with each other, and a back surface at an opposite side to said sliding portion, said back surface including a central concave portion in the axial direction of said back surface, said central concave portion defining a pair of lips, each of the lips being located on an opposite side of said central concave portion, the sliding portion including a central concave portion in the axial direction for holding a lubricating oil, said central concave portion of the sliding portion being shallower than the central concave portion of the back surface, the shape of the sealing ring satisfying the expression A/ 2 <R< 13 A 2 where R denotes a radius of curvature of said sliding portion and A denotes a width in an axial direction of said sealing ring, and a thickness C of the shape in the axial direction between deepest portions of the concave surfaces of both of the side surfaces in the axial direction is set to 0.5A<C<A.