Talk:Piston

Re-cast this article?

A piston is only a part of an assembly correctly called a cylinder, in mechanical engineering. There should be (note below) an article describing such a device, and this article could (and probably should) be merged into it. A cylinder consists (typically) of

• The cylinder itself, nearly always having a cylindrical bore (in the geometrical sense)
• Sometimes a piston rod (e.g. steam engine, hydraulic cylinder)
• Some sort of seal[s], usually on the piston itself (piston rings) and piston-rod seal (if there is a piston rod)
• Ports, often but not necessarily at one or both ends
• Supports for mounting, of some sort.

Note: At this writing, my priority queue before I go to sleep is already about eight entries deep, so I'm not checking... Nikevich (talk) 01:59, 11 November 2010 (UTC)

Poorly worded introduction?

Am I the only one who noticed that the introduction is worded funny?

"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."

If it is, is there a way to reword this? SniperWolf1564 10:57, 16 May 2007 (UTC)

I realize that this introduction was deliberately worded this way, however, I think it's informative while also humourous and should be left the way it is. -Sparky 00:32, 18 May 2007 (UTC)

I agree that the introduction was awful and I have re-written it. Biscuittin (talk) 11:09, 30 March 2008 (UTC)

Rewording is fine but redefining? This could have legal implications by patents for instance. In this version outside of "reciprocating engines, pumps and gas compressors" there are no pistons. What do you call an object that is driven through a long tube for instance by an expanding gas and possibly connected at its ends through a valve box to itself?

AdrianAbel (talk) 11:49, 29 April 2008 (UTC)

I noticed that restricted list of practical applications; added text to generalize it. Pistons are among the most-basic elements of mechanical design; somehow, the author didn't seem to realize that. One unusual example is the Airpot™, which has a precision graphite piston quite closely-fitted in precision-bore glass tubing. The fit is nearly gas-tight, yet the piston has notably-low friction. It's used in scientific and measuring instruments and other equipment of basically related construction. Another is the differential piston, part of the high-pressure "air-spring" recoil mechanism in the U.S. Navy 5-inch/38 caliber guns. Nikevich (talk) 01:59, 11 November 2010 (UTC)

Angular Moving Piston

Hello. Does anybody heard about a new kind of piston, connected to a shaft? Such piston have angular motion (rather than linear motion) and produces less friction to the chamber walls.

A while ago I saw a documentary (in Discovery Channel or BBC, doesn't fully remember) that shows a Japanese engine that uses such piston. I think it would enrich this article.

If anybody know piston specifications mail to me at : karthirevi@rediffmail.com (I did: Nikevich (talk) 01:59, 11 November 2010 (UTC))

The old windshield-wiper pneumatic motors used for windshield (windscreen, UK) wipers on earlier 20-Century cars had such pistons. These motors were powered by manifold vacuum, and stopped when the throttle was opened wide. Nikevich (talk) 01:59, 11 November 2010 (UTC)

Piston seizure

Is there no article on piston seizures in the English language WP (cause and effect)? In the German language WP, there is de:Kolbenfresser. --Abe Lincoln 15:07, 11 October 2006 (UTC)

timing

hello, could anyone tell me the length of time that a piston is still for between directions (from down back up ) and also is there a name for this. Thanks

Whilst the crank is turning the piston only stops instantaneously at the top and bottom of it's stroke. These are known as 'top dead centre' and 'bottom dead center' respectively.

The exact amount of time spent at top and bottom dead centre depends on the speed of rotation of the connecting crankshaft and the amount of play at the big and small ends. As long as the crankshaft is running at a continuous speed and any play in the big and small end is negligible why should the piston connected to it spend any more time at angle zero as at any other angel of its rotation?

AdrianAbel (talk) 12:05, 29 April 2008 (UTC)

More specifically, if the crankshaft is turning at 360 RPM which is slower than most internal combustion engines run at idle speed (usually between 400 and 800 RPM) it needs one second to traverse one degree.

AdrianAbel (talk) 10:50, 2 May 2008 (UTC)

I'd say that "dwell" is a term that could apply. Nikevich (talk) 01:59, 11 November 2010 (UTC)

Governing equations

I am attempting to model the flow in and out of a single piston cylinder arrangement. On the down stroke the pressure in the cylinder decreases and a one way valve opens to admit fluid into the cylinder, on the up stroke the other one way valve opens (and the first closes) as the piston “pushes” fluid out of the cylinder. I will firstly begin modeling assuming the fluid in the cylinder is incompressible but later as the model becomes more complex I will model using compressible theory gas theory. If any one has any information or knows where I can get any information on the basic formulations of the energy, continuity and momentum equations could you please email me at: 14107864@sun.ac.za Thank you Paul

Suggest physics and mechanical-engineering texts, handbooks, and/or courses. Sorry not to be of more help. Nikevich (talk) 01:59, 11 November 2010 (UTC)

Piston and plunger

I am an engineer and I can not believe what is happening here. I can not find a word about materials for piston, and than I tried plunger, and I discovered an engineering article there. Wow--Billy the lid (talk) 08:55, 27 December 2007 (UTC)

Hey Billy,

A new article for called "Piston pump" still needs to be made; at present it simply links to this article; so the redirect needs removing and text has to be added. I made an additional image for the types of piston pumps which can be added to that article: File:Piston pump types.png KVDP (talk) 09:25, 27 May 2010 (UTC)

What about a piston for a Pneumatic cylinder?

The introduction assumes that all pistons are reciprocating, hence implying that all are continuously moving. This is clearly wrong (see the first query on this talk page). What about the piston used in a Pneumatic cylinder? That article links here, but there is no suggestion here that a piston could be part of a linear actuator of some kind. -- EdJogg (talk) 13:15, 18 August 2010 (UTC)

Not so sure that reciprocating implies continuous motion. It does, however, imply that the reciprocating element moves in a straight line, has limited travel, and of necessity, reverses direction (not necessarily immediately) when it reaches the limit of its travel. Nikevich (talk) 01:59, 11 November 2010 (UTC)

Magnetic pistons?

I just deleted a discussion line about magnetically moving pistons, it seemed not serious, but then I started searching about the subject on the net and found lots of things. I'm wondering if it should not be mentioned in the article. —Preceding unsigned comment added by 70.187.173.135 (talk) 16:12, 30 October 2010 (UTC)

Pistons for rodless cylinders

Double-acting cylinders (usually, if not always pneumatic) do not necessarily have piston rods. It is likely to amaze people who know something of technology, but, there are several companies who make these, and they are a commercial success. I'm not sure about high-flux magnets installed into the piston that "couple" with external magnets (or just solid ferromagnetic pieces), but there are definitely rodless cylinders with a relatively-wide slot in the cylinder wall. A sealing strip prevents leakage, and the piston is relatively long -- maybe 3 or4 times its diameter. Piston rings (O-rings or other) are at both ends, and the center portion, as it moves, "peels" off the sealing strip, permitting the actuator to move through the slot. At the other end, an identical structure "re-applies" the sealing strip. There probably are wipers for the slot edges and the strip.

This topic should be part of an article (again, not checking) about rodless cylinders, better yet, part of an article about cylinders in mech. engineering in general. Nikevich (talk) 01:59, 11 November 2010 (UTC)

Piston skirt?

This should be an article about a piston - not a piston engine. There should be explained the parts of a piston, for instance what is a "Piston skirt" etc. Is it called wall, skirt, mantle, mantel? no help from wikipedia.--173.170.92.3 (talk) 17:02, 20 January 2011 (UTC)