Talk:Stephenson valve gear

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[edit] Picture Goof?

According to Vol. 1, of Audel's Engineer's and Mechanics Guide, The Stephenson gear has a curved link, the straight link-variant of the Stephanson gear as is shown in the picture is more correctly called the Gooch gear. This is an important difference, as the curved link tends to give better equalization at varied cutoffs.-WK-139.78.96.115 02:02, 8 March 2007 (UTC)

I've just removed a caption by an IP poster from Czech Republic which labelled the motion as "Allan-Trick" valve gear. It was not summarised or sourced, but there is such a system, from that part of the world, and it does look a bit like this. --Old Moonraker 15:11, 9 March 2007 (UTC)
Just found this on Commons.--Old Moonraker 15:55, 9 March 2007 (UTC)
OK, I looked when I got home and what is shown is the Allan gear, or, at least, a variant on it. The Allan gear has a straight link as is shown, pivoted at its end and on a pendulumn rod, but from a fixed point. A radius rod is moved up and down on the link to give different cut-off and reverse. The Allan-Trick variant shown here seems to be different in that the link too moves up and down but in the opposite direction as the link and at a different rate, and that it is pivotes at the middle

The gooch link has a curved link. There are endless variants. This site here has downloadable animations of many different steam engine valve gears. [Valve Gear]

The Czech IP poster, above, has just drawn our attention to this link. It's in German, unfortunately, and the pictures don't exactly match the photograph accompanying the article. The closest is, as suggested above, the Allan variant. Old Moonraker 15:21, 13 March 2007 (UTC)
More from Czech IP poster (who is PetrS. on the Czech wikipedia): referring again to the above image he identifies the difference from the normal Stephenson gear as "the valve stem hangs on the same arm as the link". Now, as the picture here is of the same mech, it does look as though the caption is wrong. Should we label is as a variation of the Stephenson link, included because it is fitted externally and therefore easy to see, or try to find another? --Old Moonraker 09:41, 14 March 2007 (UTC)
I think that Allan-Trick (Allan was english, Trick german and they invented this gear in the same time independently) valve gear is an evolution of the Stephensons gear. I am not expert in the branch of steam valve gears but i suppose that the reasons were two - faster operation an better distribution of steam. PetrS.
Someone's changed the caption. Old Moonraker 17:08, 15 March 2007 (UTC)

[edit] Animation

The animated gif is broken. Instead of the crankshaft rotating around the its center, and the eccentrics doing their thing, the crankshaft is rotating around the crankpin. That results in the drawing losing all meaning. I'd try to fix it, but I don't have the tools to that were used to create the original image.

I left a note on the creator's talk page. He promised to fix it, but he's a busy chap... Old Moonraker 11:58, 18 September 2006 (UTC)

I agree the gif had me perplexed for a few moments. I could see something amiss but it took a moment or two for the penny to drop. The article also needs a note about the subtle difference between Launch and Loco links.--7severn7 19:11, 3 October 2006 (UTC)

[edit] New edits

Hope these are alright. I have been wondering if there should not be a new article on gab motion; the trouble is that references are rather hard to come by. There were lots of operating systems, often combined with expansion valves worked by fiendishly complicated mechanisms, not really worth the study as they were a blind alley.--John of Paris 12:42, 12 June 2007 (UTC)

[edit] Title

This article covers Gooch and Allan valve gears, as well as Stephenson, so I am thinking of moving it to Link valve gears. Please discuss. Biscuittin 21:47, 25 September 2007 (UTC)

Sounds like a sensible idea. I've been worried about that too.--John of Paris 15:39, 26 September 2007 (UTC)