Piston

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For other uses see Piston (disambiguation).

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A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.

1 Piston engines
- 1.1 Internal combustion engines
- 1.2 Steam engines
2 Air cannons
3 See also
4 References
5 External links

[edit] Piston engines

Main article: Reciprocating engine

[edit] Internal combustion engines

Components of a typical, four stroke cycle, DOHC piston engine. (E) Exhaust camshaft, (I) Intake camshaft, (S) Spark plug, (V) Valves, (P) Piston, (R) Connecting rod, (C) Crankshaft, (W) Water jacket for coolant flow.

There are two ways that an internal combustion piston engine can transform combustion into motive power. These are the two-stroke cycle and the four-stroke cycle. 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 (despite exceptions like the Ricardo Dolphin engine, and the Twingle engines of the Trojan car and the Puch 250 motorcycle). 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.

Gallery

A piston and its connecting rod.

CAD drawing of crankshaft and pistons.

Large pistons (over 0.5 m incl. connecting rod).

Simplified piston animation.

[edit] Steam engines

Steam engines are usually double-acting (i.e. steam pressure acts alternately on each side of the piston) and the admission and release of steam is controlled by slide valves, piston valves or poppet valves.

[edit] Air cannons

There are two special type of pistons used in air cannons: close tolerance piston and double piston. While in close tolerance piston, O-rings are used as valve but in double piston, O-rings are not used.

There are some features of close tolerance piston mentioned below:

Piston can swell and stick.
Fits tightly in the cylinder.
Tight Tolerance fit.
Properties alter due to atmospheric change.
Backlash may such,some of the bin material into the valve which also can cause the piston to stick.

Common features of double piston: