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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.

In general, a piston is a rigid, 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 lubricant 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.

Main article: two-stroke cycle

Main article: 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.

Pistons used in 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:

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

Common features of Double piston:

1. Cannot swell and stick.
2. Fits loosely in the cylinder.
3. No tight tolerance fit.
4. Properties are not altered due to atmospheric change.
5. Even if foreign material enters the valve,the double piston does not stick.

A piston and its connecting rod.

CAD drawing of crankshaft and pistons.

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

Simplified piston animation.

Look up Piston in
Wiktionary, the free dictionary.

• Knurling
• Wankel engine (an internal combustion engine with a rotary 'piston')

• Piston highlight: Hypervideo of construction and operation of four cylinder internal combustion engine courtesy of Ford Motor Company