A piston ring is an open-ended ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.
The three main functions of piston rings in reciprocating engines are:
- Sealing the combustion/expansion chamber.
- Supporting heat transfer from the piston to the cylinder wall.
- Regulating engine oil consumption.[3][1]
The gap in the piston ring compresses to a few thousandths of an inch when inside the cylinder bore.