US Patent 11346332 Piston ring and compressor

A piston ring includes a first ring portion which is fitted onto an outer circumferential portion of a piston and which is capable of sliding relative to an inner wall surface of a cylinder, and a second ring portion which is fitted onto the outer circumferential portion of the piston, arranged side-by-side with the first ring portion in the axial direction, and which is capable of sliding relative to the inner wall surface of the cylinder. The second ring portion is fitted onto the outer circumferential portion of the piston in such a way as to be positioned on a side opposite to a compression chamber inside the cylinder, relative to the first ring portion, and has a greater hardness than the first ring portion has.