Piston Ring: Function, Types, and Working

What is Piston Ring?

piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine.

It maintains gas compression between the piston and the cylinder wall. Piston rings seal the cylinder so that combustion gas generated at the time of ignition does not leak into the opening between the piston and the cylinder.

Improving heat transfer from the piston to the cylinder wall. And maintaining the proper quantity of the oil between the piston and the cylinder wall. Also, regulating engine oil consumption by scraping oil from the cylinder walls back to the sump.

Pistons equip with some metal rings which perform many functions. These rings are identified as piston rings.

Material Use for Piston Ring

Piston rings are commonly made from cast iron. Cast iron retains the integrity of its original shape under heat, load, and other dynamic forces.

Also cast iron contains graphite in the lamellar form which itself acts as a lubricant assisting the sliding motion between the rings and the liner. Alloys and coatings are done on the piston rings, and it will vary as per the type of the ring as the functionality of these rings are different from each other. 

The most common forms of alloy cast iron are chromium, molybdenum, vanadium, titanium, nickel, and copper. The piston ring material is kept harder than the cylinder liner to provide maximum life.

Function of Piston Ring

Gas Seal Function

Piston rings maintain gas compression between the piston and the cylinder wall. Piston rings seal the cylinder so that combustion gas generated at the time of ignition does not leak into the opening between the piston and the cylinder.

This means that the combustion chamber should be as gas-tight as possible. So, that the pressure generated by the burning combustion gases quickly transfers the piston to the cylinder. Causing the crankshaft to turn, thereby providing power.

Gas Seal Function

Not only important for the combustion/expansion stroke, but gas-tightness is also very important for the intake, compression, and exhaust strokes as well. This general function can only called “gas sealing”.

Heat Transfer Function

Piston rings transfer heat from the piston crown to the cylinder. When gas ignition takes place, the temperature inside a piston reaches approximately 300 C. If heat accumulates inside the piston, the engine may be damaged. For that reason, it is necessary to release the heat build-up. Piston rings help release this heat.

Heat transfer Function

This heat transfer function is very important to maintain acceptable temperature and stability in pistons and piston rings so that the sealing capacity is not impair.

Oil Control Function

Piston rings usually make necessary minimum lubricating oil film for preventing scuffing. Since gas ignition is repeated many times, the piston goes up and down inside the engine at a rate of several thousand times per minute. A small amount of oil is poured over the pistons so they move smoothly, with little friction between metal and metal. Piston rings adjust the amount of oil.

In this way, oil consumption is at acceptable levels and harmful emissions reduce. older than the cylinder liner to provide maximum life.

oil Ring Function

Types of Piston Ring

Piston rings commonly used on small engines include the three types of piston ring as mention bellow:

  • Compression piston ring,
  • Wiper piston ring
  • Oil piston ring

Compression Ring

The compression ring is the top or nearest ring for the combustion of gases. It exposes to the highest amount of chemical corrosion and the highest operating temperature. However, this may vary according to the design of the engine.

The compression ring assigns 70% of the combustion chamber heat from the piston to the cylinder wall. Most engines use either taper-face or barrel-face-compression rings.

Taper faced compression ring

A Taper faced compression Ring which is a piston ring with a taper angle of about 1 ° on the moving surface. This cone provides light wipes to prevent any excess oil from reaching the combustion chamber.

Piston

Barrel faced Compression Ring

A barrel faced compression ring is a piston ring with a curved surface rotating to provide continuous lubrication of the piston ring and cylinder wall. It also provides a spike effect to optimize oil distribution during the entire stroke of the piston. In addition, the curved moving surface reduced the possibility of an oil film breaking due to excess pressure or excessive piston tilt at the ring edge during operation.

Wiper Ring

The wiper ring, sometimes called the scraper ring, Napier ring, or back-up compression ring is the next ring apart from the cylinder head on the piston. The wiper ring provides a consistent thickness of the oil film to lubricate the running surface of the compression ring.

Most wiper rings have a taper angle face that positions downward to provide a wipe action as the piston moves toward the crankshaft.

The taper angle provides contact that routes excess oil to the oil ring on the cylinder wall to return to the oil reservoir. A wiper ring is closest to the incorrectly tapped angle to the compression ring, resulting in excessive oil consumption. This cause by the wiper ring wiping off excess oil towards the combustion chamber.

Oil Ring

An oil ring consists of two thin rails or a running surface. The cut holes or slots in the radial center of the ring allow excess oil to flow back into the reservoir. Incorporating all these features, oil rings are usually one piece.

Some oil rings use a spring expander to apply additional radial pressure to the piston ring. This increases the pressure applied to the unit (the amount of force and the size of the movable surface) on the cylinder wall.

The oil ring has the highest inherent pressure out of the three rings on the piston. Tree-piece oil ring consisting of two rails and an extender. The oil rings are positions on each side of the expander. The expander usually has multiple slots or windows to return oil to the piston ring groove.

oil Ring

The oil ring uses built-in piston ring pressure, external pressure, and high unit pressure. And that provided by the small running surface of the thin rail.

How Do Piston Rings work?

Piston rings maintain gas compression between the piston and the cylinder wall. Piston rings seal the cylinder so that combustion gas generated at the time of ignition does not leak into the opening between the piston and the cylinder.

The topmost groove of the piston consists of a compression ring whose main function is to seal any kind of leakage inside the combustion chamber during the combustion process. When the air-fuel mixture is ignited. Pressure from the combustion gases is applied to the piston head, forcing the piston towards the crankshaft.

Pressurized gases pass through the gap between the cylinder wall and the piston and into the groove of the piston ring. During the combustion process, the force of high-pressure gases presses the piston ring against the cylinder liner wall which helps it to form an effective sealing. This pressure pushing the piston ring is proportional to the combustion gas pressure.

The next set of rings in the piston which are placed below the compression ring and above the oil rings are called wiper rings.

They have a tapered face construction and it is used to further seal the combustion chamber. As the name suggests, they assist in wiping the liner wall clean of any excess oil and impurities. If any of the combustion gases were able to pass by the compression ring. These gases will be blocked by the wiper ring in good condition.

The last set of rings are oil rings which are located at the bottom grooves of the piston closest to the crankcase. The main function of the oil ring is to scrape any excess oil from the walls of the cylinder liner when the piston is in motion. The majority of the wiped oil is directed into the crankcase back to the oil sump. These oil rings come with spring fitted at the back in a 4-stroke engine to provide an additional push for wiping the liner.

Top Ask Questions

What is Piston Ring?

piston ring is a metallic split ring that is attached to the outer diameter of a piston in an internal combustion engine or steam engine.

The main functions of piston rings in engines are:

  • Sealing the combustion chamber so that there is minimal loss of gases to the crankcase.
  • Improving heat transfer from the piston to the cylinder wall.
  • Maintaining the proper quantity of the oil between the piston and the cylinder wall
  • Regulating engine oil consumption by scraping oil from the cylinder walls back to the sump.

What is function of piston rings?

Piston rings maintain gas compression between the piston and the cylinder wall. Piston rings seal the cylinder so that combustion gas generated at the time of ignition does not leak into the opening between the piston and the cylinder.

What are the types of piston ring?

Piston rings commonly used on small engines include compression rings, wiper rings, and oil rings. A compression ring is the piston ring located in the ring groove closest to the piston head. The compression ring seals the combustion chamber from any leakage during the combustion process.

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