Piston Ring is a metal ring used to insert into the groove of the piston. There are two types of piston rings: compression rings and oil rings. The compression ring is used to seal the combustible mixture in the combustion chamber; the oil ring is used to scrape excess oil from the cylinder. The piston ring is a metal elastic ring with large outward expansion deformation, which is assembled into the annular groove corresponding to the cross section. Reciprocating and rotating piston rings rely on the pressure difference of gas or liquid to form a seal between the outer circular surface of the ring and the cylinder and one side of the ring and the ring groove.