Definition
Sealing rings made of cast iron or steel that fit into grooves cut around the outside of a piston. They press outward against the cylinder wall to seal the combustion chamber, control the flow of oil on the cylinder wall, and transfer heat from the piston to the cylinder. A typical aircraft piston has compression rings near the top of the piston and oil control rings below them.
Plain English
Springy metal rings that wrap around a piston and press against the cylinder wall. They seal in the burning gases above the piston, wipe excess oil off the cylinder wall, and help carry heat away from the piston.
Context Anchor
You will see this term in piston-engine aircraft maintenance discussions, especially when talking about oil use, cylinder condition, engine wear, or loss of power.
Why Pilots Care
Worn or broken rings allow loss of compression, increased oil consumption, and power reduction, directly affecting engine reliability and safety.
Analogy
They work somewhat like the sealing ring on a hand pump: the moving part can slide, but the ring helps keep pressure from leaking around it.
Intuition Check
Piston rings are not just spacers that hold the piston in place. Their main jobs are sealing pressure, controlling oil, and helping move heat away from the piston.
Example Sentence 1
The mechanic suspected worn piston rings after the compression check showed excessive air leaking past the pistons into the crankcase.
Example Sentence 2
Excessive oil consumption often points to worn piston rings that no longer control oil on the cylinder walls.