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 main three functions of piston rings,
truck parts, in
reciprocating engines are:
*) Sealing the combustion/expansion chamber.
*) Supporting heat transfer from the piston to the cylinder wall.
*) Regulating engine oil consumption.
The gap in the piston ring compresses to a few thousandths of an inch
when inside the cylinder bore.