What is "piston ring"

Piston ring \Pis"ton ring\ (Mach.) A spring packing ring, or any of several such rings, for a piston.

n. A ring or seal that fits around a piston, sealing between the piston and the bore in which it slides.

n. seal consisting of a split metal ring that seals the gap between a piston and the cylinder wall

A piston ring is a split 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 :

1. Sealing the combustion chamber so that there is minimal loss of gases to the crank case.
2. Improving heat transfer from the piston to the cylinder wall.
3. Regulating engine oil consumption by scraping oil from the cylinder walls back to the sump.

The gap in the piston ring compresses to a few thousandths of an inch when inside the cylinder bore. Piston rings are a major factor in identifying if an engine is two stroke or four stroke. Three piston rings suggest that it is a four stroke engine while two piston rings suggest that it is a two stroke engine. Most piston rings are made of a very hard and somewhat brittle cast iron.