How do Piston Rings work?

The piston rings must possess both spring-like tension and the properties to become a true circle when closed simultaneously. Piston rings keep a close contact with the cylinder walls through their own spring tension, carrying out three main functions below in reciprocating engines as:
 

1. Seal the combustion chamber so that there is minimal loss of gases from the combustion chamber to the crank.
2. Improve heat transfer from the piston to the cylinder wall by thermal conduction.
3. Regulate engine oil consumption as controlling the thickness of the lubricating oil film on the cylinder wall.

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