Talk:Dashpot

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Caption

How do you make the caption stay on one line?

Added a diagram and removed reqdiagram. I don't know how to make caption stay on one line, try looking through Picture_tutorial. Egmason (talk) 09:15, 7 February 2012 (UTC)[reply]

When was the dashpot invented and how was it used in the early years?

A combination of Dashpot and Spring is used in Control Theory to represent a more complex system, so the mathematical stuff needs to be shown here, I wasn't that good at it but it's something like $Cdx/dt$ Where C is the dashpot constant, and $Kx$ Where k is the spring constant. (x is distance, t is time).
You then use them to predict the reaction to a given input using Laplace Transforms --Stripy42 09:07, 31 August 2007 (UTC)[reply]

This article needs a section on the use of dashpots in mechanical and biomedical engineering to simulate the behavior of muscles. --azide13 19:02, 7 December 2008 (UTC)[reply]

Eddy current damper

That doesn't seem to be a reliable source.

The thing is, I'm pretty sure they've linearised the equation.

The equation for eddy current power has a square law on the frequencies and the frequencies generated by the magnet are proportional to the relative speed. Since energy is force times distance, power is force times speed, and hence the force should be a square law. However, there's a second effect due to skin depth which comes into play at high frequencies that is inversely proportional to the square root of speed that reduces the power dissipated.

The source is therefore pretty dubious.- Wolfkeeper 00:06, 30 May 2010 (UTC)[reply]

Additional, reliable-looking sources confirm. Perhaps you can find some that disagree. -AndrewDressel (talk) 02:36, 30 May 2010 (UTC)[reply]

Discussion for merging shock absorber to here

The two topics are the same, a shock absorber is simply a dashpot that is used in vehicles, but they're not differently constructed, or working along different principles, or anything like that, it's simply a different name when a dashpot is used in one application. I therefore propose that they be merged here (since this is the primary topic). Otherwise there's far too much overlap.Planetscared (talk) 21:52, 30 January 2012 (UTC)[reply]

Please !vote below:Planetscared (talk) 21:53, 30 January 2012 (UTC)[reply]

The topics are quite different, even though they share operating principles.

Shock absorbers are a concrete device. They are also familiar to many readers from their automotive applications.

Dashpots are a more conceptual and idealised mechanism. Although they are sometimes encountered as a physical device, even under that name, the dashpot coverage is more appropriately focussed on their theoretical aspect, as a topic within dynamics and mechanics.

There is also the issue that a dashpot is (IMHE) always based on a viscous mechanism, at least if they're referred to under that name. Shock absorbers are broader than that. Andy Dingley (talk) 21:58, 30 January 2012 (UTC)[reply]

The point is that they're all significantly the same topic. Shock absorber isn't the correct term for a damper on a door even though they work the same way, and merely replacing a viscous damper with an eddy current damper doesn't significantly change its behavior. I also looked around, and a dashpot can be considered to be a perfect damper, of which one implementation is a viscous damper. Keeping different implementations of the same idea in one article is in no way a bad thing, and shock absorber is a bad place to discuss eddy current dampers or air dampers for example, because vehicle shock absorbers don't usually work like that.Planetscared (talk) 22:32, 30 January 2012 (UTC)[reply]

"Shock absorber isn't the correct term for a damper on a door"

Then don't merge the two articles in which they're described.

I'm not seeing either of these articles as referring to "dampers", other than in the US sense for automotive shock absorbers. If we want coverage of dampers (door closers and many others), then they should be described under that as an article title. Eddy current dampers certainly aren't dashpots. Nor are Friction disk shock absorbers. Andy Dingley (talk) 00:03, 31 January 2012 (UTC)[reply]

That's not especially relevant; encyclopedias are not primarily about how things are referred to, it's about what they are. The shock absorbers that are used in the vast majority of automotive cases are dashpots, as are very many door dampers. The scope of THIS article includes ALL such "shock absorbers" dashpots. The idea that you can have or move 'shock absorber' dashpots out of this article into a separate article and expect this article to still make much sense is not correct. The term 'shock absorber' nearly always simply refers to a dashpot. The situation we have at the moment is that most of the coverage of dashpots is in the shock absorber article, and that's clearly not correct, nor is it sustainable.Planetscared (talk) 04:44, 31 January 2012 (UTC)[reply]

~~Merge~~ - There is a ton of overlap between the two articles and I think a merger at this point, probably into dash-pot and with a section on shock-absorbers, would be a useful exercise. The fact that these things go by several different names, depending on field and use, and can be implemented in many ways, actually argues for merger to me. If at some point in the future, the section on shock-absorber became unwieldy, it could be split out again. The downside to not merging is that a reader will find one and not the other, or find both and wonder what the difference is. I don't see a downside to merging unless it is done poorly and information is lost. -AndrewDressel (talk) 06:40, 31 January 2012 (UTC)[reply]

Making shock absorber a redirect to dashpot is going to give a very bad service to the vast majority of readers looking for car suspension.

I see that you're a cyclist. Suspension forks use shock absorbers, but how many of those are dashpots, rather than elastomer blocks? Andy Dingley (talk) 11:43, 31 January 2012 (UTC)[reply]

Oppose - Upon review, I now see that dash-pots are strictly defined to contain a fluid. There is some overlap in their definitions, "preventing vibration" vs "damp vibration", but even those phrase are not identical, and the OED keeps the definitions distinct. Part of a shock-absorber may by implemented as a dash-pot. I learn something knew every day, when I'm lucky. -AndrewDressel (talk) 13:23, 31 January 2012 (UTC)[reply]

dash-pot, n. a contrivance for producing gradual descent in a piece of mechanism or for preventing vibration or sudden motion, consisting of a cylinder or chamber containing liquid in which a piston moves; a hydraulic buffer.
shock-absorber, n. a device, esp. on a motor vehicle, aircraft undercarriage, etc., which serves to absorb mechanical shock and to damp vibration.

Note that fluid is broader than liquid, Many low-energy dashpots use atmospheric air as their working fluid, for convenience. The dampers on video player doors and kitchen drawers are of this type. Andy Dingley (talk) 15:13, 31 January 2012 (UTC)[reply]

Note that the one source cited so far to define dash-pot specifies liquid, not fluid, so a device that uses atmospheric air may be a shock-absorber, but is not a dash-pot under this definition. In fact, the incompressability of an ideal liquid appears to be required to meet the mathematical definition of a dashpot, "where the resistance force is proportional to the velocity."^[1] To model a device containing compressible atmospheric air, a spring must be added in series to a pure dash-pot. -AndrewDressel (talk) 11:17, 7 February 2012 (UTC)[reply]

^ Mark H. Holmes (2009). Introduction to the Foundations of Applied Mathematics. Springer. p. 329.

For low enough forces, the compressibility of air is negligible. Hence air dashpots can be used easily for low forces. These are common in all sorts of small instruments, from door anti-slam devices to weighing scales and equipment anti-vibration mounts. Even where air's compressibility is noticeable, the device is still a dashpot, it's just not as simple to model it according to simple physical assumptions. Your ref here doesn't say that air dampers aren't dashpots, but rather that their behaviour differs from that of the simple idealised dashpot (and can still be modelled by the addition of a series spring element to the model). Viscous-damped air shock absorbers are used - better suspension mountain bikes use them. They're even used on motorcycles (although I'm not sure of their details). For car masses though, the viscosity is too low to make a practical damper. Andy Dingley (talk) 11:56, 7 February 2012 (UTC)[reply]

Cool. All we need is a reliable source that says that air dampers are dash-pots. -AndrewDressel (talk) 09:40, 8 February 2012 (UTC)[reply]

Oppose a dashpot is a component of a shock absorber, a shock absorber is one of many applications in which a dashpot is used, but a dashpot is not a shock absorber and a shock absorber is not a dashpot. --Biker Biker (talk) 12:16, 31 January 2012 (UTC)[reply]

Oppose merge; the automotive world calls them shock absorbers and they are at best a very specialized derivation of the "dashpot" concept. --Wtshymanski (talk) 14:31, 31 January 2012 (UTC)[reply]

Comment - does a vehicle gas shock absorber also utilise a dashpot? Reading through what I can find about this common type of shock absorber I don't think it does. If so then there is more weight to my argument that the dashpot is a component of a shock absorber and therefore the two articles should remain distinct. --Biker Biker (talk) 14:42, 31 January 2012 (UTC)[reply]

Yes. "gas shock absorbers" aren't purely gas, they're gas/liquid. Air suspension (which can use a gas alone) isn't (usually) a dashpot. Andy Dingley (talk) 15:04, 31 January 2012 (UTC)[reply]

No. As you note above a gas shock absorber is still a dashpot. Dashpots work by fluid viscosity, not necessarily liquid.Planetscared (talk) 17:18, 31 January 2012 (UTC)[reply]

You can't make an air dashpot for something the mass and amplitude of a bouncing car, in the size of a car shock absorber. Air is much less viscous than oil, so it won't give you adequate damping. Andy Dingley (talk) 20:46, 31 January 2012 (UTC)[reply]

I have installed and used air shocks on vehicles as early as a 1968 Pontiac Catalina. Air shocks use pre-compressed air in series with a small fluid chamber and are regularly adjusted by varying the internal pressure of the gas. They can break the shock mounts if overloaded. — Preceding unsigned comment added by 205.153.180.229 (talk) 18:18, 1 March 2012 (UTC)[reply]

Comment With all due respect, everyone is missing the point. Encyclopedias don't work by endlessly breaking subjects down into individual definitions of words or phrases, that's what dictionaries do. You end up with lots of disconnected definitions that are very hard to get an understanding of. Encyclopedias join similar things together into topics. In this case I'm claiming that the topics are probably 'mechanical damping' which covers everything and maybe 'dashpot' could have its own subarticle. It's really bad everything is currently scattered like it is. For example, where's the equation of the force of a hydraulic damper? It's kinda in damping, except hydraulic dampers are not linear, because flow through an orifice isn't. Where's the equation for the flow through an orifice? It's in orifice or something, and it's not linked here or anywhere. Like a lot of mechanics in Wikipedia it's just a total fucking mess right now, and keeping these separate articles, which are 95% the same subject is not helping in the slightest bit.Planetscared (talk) 17:18, 31 January 2012 (UTC)[reply]

Yes, so we should cover the relevant concepts, at the level where they're most useful to our readers. That means shock absorbers (the well-known car component) in one, dashpots (the obscure idealised device in mechanical theory) in another. Andy Dingley (talk) 20:46, 31 January 2012 (UTC)[reply]

What is the reader's perspective? If she types in "shock absorber", is she expecting a treatise on fluid mechanics? Link to the fluid mechanics concepts where appropriate, but tehre's a substantial literature on this specialized application. --Wtshymanski (talk) 20:49, 31 January 2012 (UTC)[reply]

Oppose - several good reasons mentioned above why this merger is not appropriate. Warren (talk) 17:59, 31 January 2012 (UTC)[reply]

Oppose - but both articles need some severe clean up. My understanding is that a shock absorber is meant to damp the oscillations of a spring (coil, leaf, torsion, etc). One way to do this is via a dashpot. As I understand it, a dashpot relies on forcing fluid through a restriction to damp out a force. Fluid dynamics classifies gas as a very low density fluid, so the common form of the car shock absorber and also the pneumatic forms found on some motorbikes are dashpots. However, I'm not convinced that magnetic eddy currents count as a fluid, so I would not include eddy current shock absorber devices as dashpots. Friction dampers used on early cars are definitely not dashpots. Rubber dampers are also not dashpots. The shock absorber article should be more of an overview article that then passes the reader to other articles such as dashpot and Friction disk shock absorber to give the fine detail of particular mechanisms. Fine details such as the equations of fluid dynamics would belong either in dashpot or more likely be passed off again to fluid dynamics but definitely not in the generic overview article shock absorber. As a last side comment, in 'gas' shock absorbers, the high pressure gas only stops the working fluid from boiling and/or frothing. But the gas doesn't go through the restriction - only the oil goes through the restrictions. Stepho talk 23:29, 31 January 2012 (UTC)[reply]

Oppose: Dashpot is a generic object, a shock absorber is a specific version of it. It's relevant enough to have a separate article, and there's enough text for it. --NaBUru38 (talk) 21:14, 20 March 2012 (UTC)[reply]

Wow: Thank God all of that didn't happen. The article on shock absorbers remains a pastiche of barely coherent concepts (almost two years after the above discussion) but merging into dashpots... Man, just for the record, that would have been nuts and someone would probably have undone the merge within 48 hours. The article on shock absorbers gets more than 300 hits per day, which is enough to show some enduring public interest in the term. I am all for umbrella concepts and the merging of similar topics into a broader category of ideas, but shock absorbers and dashpots are not subjects that work like that. The article on dashpots gets about a third as much traffic as the one on shock absorbers. The world seems okay this way. KDS4444^Talk 05:55, 31 December 2013 (UTC)[reply]

high energy motor starter contactors

I deleted this once for being unintelligible, but it was restored, so I'm putting it here until someone can clean it up. It should not be in the article in this state. -AndrewDressel (talk) 23:36, 23 May 2013 (UTC)[reply]

Some high energy motor starter contactors have used the dashpot. The Allen West type, for example, uses a hydraulic piston. The rod of the piston is part of the built in 'over current' function. The current sensing coil and rod act as a solenoid. The rod is the plunger in the over current coil. During over current the plunger moves up and releases the dropout lever cutting power to the motor. During motor start, current in-rush time is short in comparison with dashpot action and so start current cannot pull the plunger as quick. The damping of the current coil plunger prevents the motor start current from unlatching the dropout lever. On three phase units there is one dashpot for each of the three contactors so excess current in either phase will drop all three contactors as the dropout lever encompasses all contactors.

I think it belongs in (just) as an example application, but to pass WP:UNDUE it shouldn't be more than half this length. It should also focus more on why and less on how.

"Electrical switchgear may uses dashpots in their overcurrent sensing mechanism; so as to reduce reaction speed to brief events, thus making them less sensitive to false-triggering during transients whilst still remaining sensitive to sustained overloads." Andy Dingley (talk) 08:09, 24 May 2013 (UTC)[reply]

Perfect. -AndrewDressel (talk) 13:50, 24 May 2013 (UTC)[reply]

Erroneous redirect and eddy current dampers

I notice that for some reason, typing "Shock absorber" into the search bar brings you to Shock absorber, but typing "Shock Absorber]] brings you to "Dashpot". I don't see how the presence of a single capital "A" should change the meaning at all. I would fix it, but I don't know how. Also, I notice that in the comments below, someone plainly states that eddy current dampers are NOT dashpots, but it says they are in the article. Which is it? .45Colt 20:37, 26 September 2015 (UTC)[reply]

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[1] Mark H. Holmes (2009). Introduction to the Foundations of Applied Mathematics. Springer. p. 329.

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