Piston

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Dictionary Meaning and Definition on 'Piston'

Piston Meaning and Definition from WordNet (r) 2.0
    Piston n
  1. United States neoclassical composer (1894-1976) [syn: Walter Piston}]
  2. mechanical device that has a plunging or thrusting motion [syn: plunger]
Piston Meaning and Definition from Webster's Revised Unabridged Dictionary (1913)
    Piston \Pis"ton\, n. [F. piston; cf. It. pistone piston, also pestone a large pestle; all fr. L. pinsere, pistum, to pound, to stamp. See Pestle, Pistil.] (Mach.) A sliding piece which either is moved by, or moves against, fluid pressure. It usually consists of a short cylinder fitting within a cylindrical vessel along which it moves, back and forth. It is used in steam engines to receive motion from the steam, and in pumps to transmit motion to a fluid; also for other purposes. Piston head (Steam Eng.), that part of a piston which is made fast to the piston rod. Piston rod, a rod by which a piston is moved, or by which it communicates motion. Piston valve (Steam Eng.), a slide valve, consisting of a piston, or connected pistons, working in a cylindrical case which is provided with ports that are traversed by the valve.

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Wikipedia Meaning and Definition on 'Piston'


In general, a piston is a lubricated sliding shaft that fits tightly inside the opening of a cylinder. Its purpose is to change the volume enclosed by the cylinder, to exert a force on a fluid inside the cylinder, to cover and uncover ports, or some combination of these. A rubber seal is sometimes used to keep the lubricate within the shaft. Due to the constant motion of the machine this seal wears quickly and should be replaced with every servicing. If the seal should break during usage there can be disastrous long lasting consequences for the machine.

There are two ways that a piston engine can transform combustion into motive power. These are two-stroke and four-stroke.

A single cylinder two-stroke engine produces power every crankshaft revolution, while a single cylinder four-stroke engine produces power once every two revolutions. Older designs of small two-stroke engines produced more pollution than four stroke engines. However, modern two-stroke designs, like the Vespa ET2 Injection utilise fuel-injection and are as clean as four-strokes. Large diesel two-stroke engines, as used in ships and locomotives, have always used fuel injection and produce low emissions. One of the biggest internal combustion engines in the world, the Wärtsilä-Sulzer RTA96-C is a two-stroke; it is bigger than most two-story houses, has pistons nearly 1 metre in diameter and is one of the most efficient mobile engines in existence. In theory, a four stroke engine has to be larger than a two stroke engine to produce an equivalent amount of power. Two stroke engines are becoming less common in developed countries these days, mainly due to manufacturer reluctance to invest in reducing two-stroke emissions. Traditionally, two stroke engines were reputed to need more maintenance. Even though the simplest two stroke engines have fewer moving parts, they could wear out faster than four stroke engines. However fuel-injected two-strokes achieve better engine lubrication, and cooling and reliability should improve considerably.

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