What are Piston Rings and Their Common Types?

A piston engine is a powerful apparatus, capable of harnessing the pressure of combusted fuel-and-air mixtures to generate a rotational movement. In order for proper combustion and operations, piston engines require minimal loss, efficient heat transfer, and much more. With a metallic split ring known as a piston ring, the gaps between the piston and the cylinder wall may be sealed for the protection of the engine assembly and its performance. There are also multiple types of piston rings, each of which may be implemented in varying areas of the assembly to provide different functions.

Piston rings are typically constructed from cast iron or steel, and they are connected to the outer diameter of a piston. Serving both internal combustion engines and steam engines, piston rings seal off the piston and cylinder wall gap in order to ensure minimal loss of gases, improve heat transfer to the cylinder wall, maintain oil, and regulate oil consumption. It is crucial that the wall gaps of the cylinder wall are properly sealed with piston rings as too small of a gap could lead to serious damage from thermal expansion while too big of a gap would result in poor engine performance.

In order for a piston engine to be properly sealed, such apparatuses will often have two or more rings per cylinder. The compression ring is a common piston engine component, placed within a groove that is situated near the piston head. Such rings are used to seal off the combustion chamber, preventing any leakage. During the standard combustion process, fuel-and-air mixture ignition results in a large force being applied to the piston head. As the piston is driven towards the crankshaft, pressurized gases push their way into the ring groove where a seal will be applied with the implementation of a compression ring.

The wiper ring is the next common type, coming in the form of a tapered face ring that is placed in a groove located under the compression ring. With the wiper ring, the combustion chamber may be further sealed while also providing a way for the cylinder wall to be cleaned of any excess oils. If combustion gases are capable of passing the compression ring, the wiper ring will ensure that they are stopped.

The final common type of piston ring is the oil ring, that of which is placed below the wiper ring. Within the groove that is closest to the crankcase, the oil ring serves to remove excess oil from the cylinder wall during operations. When the excess oil is removed, it flows through ring openings so that it may reach the engine block oil reservoir. For engines that operate through the two-stroke process, oil rings are not a required component as oil reservoirs are not present.

For a piston ring to efficiently serve an engine, it must have a positive radial fit between the cylinder wall and ring surface so that an optimal seal is achieved. While inherent pressure is paramount for a radial fit, applied pressure ensures expansion when combustion gases force up against the ring. As contact pressure is also an important consideration for such assemblies, piston rings with certain degrees of elasticity are useful.

When searching for the right piston rings for a particular engine, one should never settle for anything less than the best. At NSN Sourcing, we operate as a leading online distributor of aircraft parts, providing customers unmatched pricing on over 2 billion new, used, and obsolete items. Pursue our expansive catalogs where you can find highly sought-after piston ring components that come from leading manufacturers that we trust. Get started today and see why customers steadily depend upon NSN Sourcing for all their operational needs.


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September 3, 2021

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