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Circular metallic elements that ride in the grooves of a piston and provide compression sealing during combustion.
Piston Rings are made of alloying cast iron with chromium, molybdenum, vanadium, titanium, nickel and copper. They are harder than the cylinder liner in which they run to give them a maximum life. Piston rings seal the gas space by expanding outwards due to the gas pressure acting behind them. They also spread the lubricating oil up and down the cylinder liner and transfer heat to the liner walls.
When overhauling the piston, it is important to check the ring grooves for wear and the piston ring condition. The axial and butt clearances should be measured and recorded.
The function of the piston ring is to give a gas-tight sealing of the clearance between the piston and cylinder liner. This seal is brought about by the gas pressure above and behind the piston ring, which forces it downwards, against the bottom of the ring groove, and outwards against the cylinder wall. In-order to ensure optimum sealing, it is therefore important that the piston rings, the grooves, and the cylinder walls, are of proper shape, and that the rings can move freely in the grooves (since the piston will also make small horizontal movements during the stroke). The lubrication of the piston rings influences the sealing as well as the wear and deposits.
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Related Terms

ALKALINE BOIL-OUT

Employed to remove oil and grease deposits from heating surfaces.

BULK CARGO

Cargo such as oil, coal, ore, woodchips, etc. not shipped in bags or containers

OILING SPLASH SYSTEM

Method of lubricating moving parts by agitating or splashing oil in the crankcase.

CROWN

The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.

CROWN

The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.

CAM

Eccentric shaft used in most internal combustion engines to open and close valves.

EMULSIFIER

Additive that promotes the formation of a stable mixture, or emulsion, of oil and water. Common emulsifiers are: metallic soaps, certain animal and vegetable oils, and various polar compounds.

CLOUD POINT

The temperature at which waxy crystals in an oil or fuel form a cloudy appearance.

CORROSION INHIBITOR

Additive for protecting lubricated metal surfaces against chemical attack by water or other contaminants. There are several types of corrosion inhibitors. Polar compounds wet the metal surface preferentially, protecting it with a film of oil. Other compounds may absorb water by incorporating it in a water-in-oil emulsion so that only the oil touches the metal surface. Another type of corrosion inhibitor combines chemically with the metal to present a non- reactive surface.

CARBON RESIDUE

Coked material remaining after an oil has been exposed to high temperatures under controlled conditions.
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