piston

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Images

piston and cylinder

Close-up of chrome-plated hydraulic piston shafts and yellow cylinders on heavy machinery, with black hoses attached to the pistons.

internal-combustion engine: four-stroke cycle

compressed air and decompressed air

Diagram of a gasoline engine showing a cross-section of a piston and cylinder. Key parts such as the spark plug, valves, camshaft, piston, connecting rod, and crankshaft are labeled.

piston

engineering

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July 2, 2026

Quick Summary

piston and cylinder — piston and cylinder An automobile engine block showing pistons within cylinders.

In mechanical engineering, a piston is a sliding component with a closed head that moves back and forth within a cylindrical chamber. This reciprocal motion is driven by or against the pressure of a fluid, such as in an engine or pump.1

Pistons are typically made of steel or aluminum alloy and are grooved to fit piston rings. These rings create a seal between the piston and the cylinder wall, preventing gas leakage and controlling lubricant.2

The piston and cylinder system is a fundamental part of mechanisms like reciprocating piston engines and pumps, converting straight-line motion to rotary motion or vice versa. This design is central to engines like those found in automobiles and other machinery.1342

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history of flight
Pistons in the air
During World War I several farsighted European entrepreneurs, emboldened by wartime progress in aviation, envisioned the possibilities of postwar airline travel. For many months after the war, normal rail travel in Europe remained problematic and irregular because of the shortage of…
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During World War I several farsighted European entrepreneurs, emboldened by wartime progress in aviation, envisioned the possibilities of postwar airline travel. For many months after the war, normal rail travel in Europe remained problematic and irregular because of the shortage of…
Read More

diesel engine
…combustion and expansion actuate a piston. It converts the chemical energy stored in the fuel into mechanical energy, which can be used to power freight trucks, large tractors, locomotives, and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets.
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…combustion and expansion actuate a piston. It converts the chemical energy stored in the fuel into mechanical energy, which can be used to power freight trucks, large tractors, locomotives, and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets.
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Pascal’s principle
…a pressure exerted on a piston produces an equal increase in pressure on another piston in the system. If the second piston has an area 10 times that of the first, the force on the second piston is 10 times greater, though the pressure is the same as that on…
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…a pressure exerted on a piston produces an equal increase in pressure on another piston in the system. If the second piston has an area 10 times that of the first, the force on the second piston is 10 times greater, though the pressure is the same as that on…
Read More

gasoline engine
Pistons
The pistons are cup-shaped cylindrical castings of steel or aluminum alloy. The upper, closed end, called the crown, forms the lower surface of the combustion chamber and receives the force applied by the combustion gases. The outer surface is machined to fit the cylinder…
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The pistons are cup-shaped cylindrical castings of steel or aluminum alloy. The upper, closed end, called the crown, forms the lower surface of the combustion chamber and receives the force applied by the combustion gases. The outer surface is machined to fit the cylinder…
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piston and cylinder
… with a closed head (the piston) that is moved reciprocally in a slightly larger cylindrical chamber (the cylinder) by or against pressure of a fluid, as in an engine or pump. The cylinder of a steam engine (q.v.) is closed by plates at both ends, with provision for the piston…
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… with a closed head (the piston) that is moved reciprocally in a slightly larger cylindrical chamber (the cylinder) by or against pressure of a fluid, as in an engine or pump. The cylinder of a steam engine (q.v.) is closed by plates at both ends, with provision for the piston…
Read More