What Are Aircraft Piston Rings and Their Types?

Piston rings are of undeniable utilitarian significance in the design of an internal combustion engine of an aircraft. Broadly speaking, a piston ring is a metallic split ring attached to a piston’s outer diameter. Piston rings are designed to combat gas pressure leaks from the combustion chamber of an aircraft while limiting the seepage of oil to a minimum at the same time. Piston rings are made to fit into the piston grooves of an assembly, but spring out to press against the cylinder walls with proper lubrication. In conditions of optimum lubrication, these rings form an effective gas seal. With this information in mind, let us now learn more about the working of piston rings.

How Do Piston Rings Work?

Piston rings are intentionally designed to fill the space between the piston and the cylinder wall. If the gap is too small, the piston’s thermal expansion can cause the piston to arrest the cylinder in its place, causing some severe engine damage. Too large of a gap, on the other hand, would result in an incomplete sealing of the piston rings against the cylinder walls, resulting in extreme blow-by (i.e., a situation wherein combustion gasses would enter the crankcase). This would result in lessened pressure on the cylinder, thereby lowering the overall output from the engine.

It is critical to get the oil quantities correct when operating piston rings. Excessive oil will burn off at the time of combustion, potentially triggering the aircraft engine to produce blue smoke, while too little will suspend the active engine midway.

What Are the Functions of Different Piston Rings?

While all aircraft engines have piston rings attached to their outer diameter, each of these piston rings may be a different type and perform specific functions. Below, we will explore the functionalities of each piston ring in further detail.

1. Compression Ring

The primary function of the top compression ring in the piston ring system is to seal off most of the combustion gasses, enabling the engine to optimize most of its available power. Therefore, any weakening or failure of the piston in this area is indicative of the engine not working as effectively as it should.

Sealing the gap with the compression ring between the cylinder walls and the outer diameter of the piston prevents the fuel-air mixture in the combustion engine from flowing down into the crankcase, resulting in lowered power and compression. This ring ensures that the contents of the crankcase and compression chamber do not mix together.

2. Middle Piston Ring

This ring is ergonomically designed to perform the function of both an oil scraping ring and a compression ring. The second ring may only appear as a backup for the rings above and below, but its function extends beyond this role. For instance, if the topmost ring is not performing adequately, the middle ring takes on its role to seal off the accidental connection between the crankcase and the combustion chamber. Similarly, it adopts the bottom ring’s role (that of the oil scraper) in guiding excess engine oil spillage back into the crankcase.

3. Oil Scraper Ring

The bottommost ring is in charge of most of the oil control, ensuring that an adequate amount of oil is utilized to lubricate a cylinder’s working surfaces. The intermediate ring assists with both functions, finishing off the combustion sealing and the downward oil leakage. The net outcome of the three rings working cooperatively is sufficient lubrication within the cylinder bore, ensuring that no dangerous development occurs.

Wrapping Up

If you need premium-quality piston rings, do not hesitate to reach out to ASAP Buying as soon as possible. Our company is a widely-trusted, industry-leading distributor of piston rings and other top-quality aircraft parts. In addition, our team of experts can assist you in locating the exact piston rings (or any other ring type for that matter) for all your civil and military aviation procurement needs.


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