Talk:Gresley conjugated valve gear

Edit by 24.4.4.69 regarding cylinder timing and crank angle spacing
Is it possible to get some further documentation on this point? I note that the article previously stated (through several edits) that Gresley 3 cylinder locomotives must have 120 degree spacing of cranks. So was that information factually incorrect for Gresley valve gear equipped locos in general, or merely not true of the UP9000 locomotive which the same user also made reference to in their edit?

My understanding from reading other sources is that the variation in cylinder timing from equal 120 degree spacing relates to the need for the inside cylinder to be angled to clear the leading axle, and the crank spacing will be determined by the angling of the inner cylinder in relation to the outside cylinders for each locomotive, and also the relative size of the inner vs outer cylinders, etc. Because these factors vary by locomotive, so too would the cylinder timing, and as such not all locomotives would share 120 degree spacing, nor would they all share 90/135/135 spacing.

Any comments? Zzrbiker 06:54, 3 October 2006 (UTC)

The suggestion of 90/135/135 spacing is incorrect. In a perfect arrangements the cylinders would operate at exactly 120/120/120 spacing. Where the centre cylinder is raised to clear the leading axle some adjustment may be necessary.--7severn7 19:16, 3 October 2006 (UTC)


 * The article doesn't say that the cranks must be spaced at 120-120-120-- it says the cylinders will operate at that equal spacing. If the center cylinder is inclined 8 degrees (and the outside cylinders are horizontal) then the center crank will be shifted accordingly-- the three cranks will be 120-112-128. The three pistons will reach front dead center at equal 120-degree intervals of driver rotation. Tim Zukas (talk) 01:17, 6 September 2010 (UTC)

Here's a thought. It is arguable the the Gresley - Holcroft valve gear isn't a valve gear per se since it enables a third cylinder to be driven by motion derived from two other valve gears (almost invariably Walchearts). What I mean is it could be used to derive the 3 x 120 degree motion from another valve gear i.e. Stevensons.--7severn7 18:21, 9 October 2006 (UTC)

Mechanical analogue computer, indeed!
It's a basic mechanical analogue computing mechanism, of the type found in linkage-type computers. These were used in the U.S. Navy Mk. 56 Gun Fire Control System and a Librascope sonar fire control computer dating from around 1955 or so. Similar linkages position the typing-element ball's tilt and rotational positions in the IBM Selectric typewriter. Except for the Corliss valve gear, all valve gears that I'm aware of are mechanical analogue multipliers, although arithmetical accuracy is not critical.

Best regards, Nikevich (talk) 07:52, 2 June 2009 (UTC)


 * Corliss, and Caprotti camboxes. Andy Dingley (talk) 08:25, 2 June 2009 (UTC)

Power inequality
I find the claim that excessive valve travel in the middle engine was due to elasticity in the conjugating gear a bit hard to swallow. It would not have been difficult to calculate the forces involved and design accordingly. My understanding is that any slop in the mechanism would allow the valve to overshoot, and this seems a far more likely explanation. Facts, anyone? Globbet (talk) 15:11, 20 December 2009 (UTC)
 * There seem to be various explanations for the problems of Gresley gear. I'm no mechanical engineer, but I suspect the reality is that there are several things wrong with Gresley valve gear that all combine to lead to inaccuries in its valve events. Source material for the Victorian Railways S class and Victorian Railways H class locomotives suggests that heat expansion of the valve spindle caused valve openings for the inside cylinder to deliver it increasingly disproportionate amounts of steam. Note the article (with source material cited) for Holcroft valve gear: Holcroft's attempt to correct that problem by deriving the inside cylinder valve gear directly from the outside gear, rather than the front end of the valve spindles. Then again, the UP's use of roller bearings on their later 4-12-2 locomotives suggest that the problems with Gresley valve gear go beyond issues with valve stem heat expansion. Zzrbiker (talk) 14:05, 28 December 2009 (UTC)
 * Just reread the Holcroft article, and it notes the issue with Gresley valve gear of "flexing of the conjugation assembly that linked to the middle cylinder when under heavy use." Can anyone get their hands on a copy of the source material cited in that article? Zzrbiker (talk) 14:13, 28 December 2009 (UTC)
 * In any discussion of the rights & wrongs of Gresley gear, it's important to distinguish the LNER & Australian cases. The LNER worked harder and longer before the problem arose (and these are usually attributed to wear in the bearings, also to poor alignment on initial erection). The Australian case was a much heavier force and greater bending stress on the combining lever, coupled with concerns over valve spindle expansion. Neither of these separate causes was (AFAIK) seen as significant for the other group of locos. Andy Dingley (talk) 14:51, 28 December 2009 (UTC)

[This is my first contribution to a talk page.] I assume the word 'cooled' should be inserted before the word 'before' in "and the gear would need to be before it was possible to remove valves for maintenance" but I'm not absolutely certain. Should I go ahead?Hayttom (talk) 17:05, 30 May 2016 (UTC)


 * No, it's just "removed". It's a run-on sentence, with two totally different drawbacks in it. One is the potential problem of heat expansion affecting timing (the gear isn't hot, but the valve spindles lengthen relative to the gear's unchanging pivot position). Secondly the gear is ahead of the cylinders, so simply in the way for pulling valves out forwards. That's not a big problem, as it's rare to take valves out except during the scale of overhaul when the linkage would probably need attention anyway.
 * These few sentences could certainly use some copy-editing, if you fancy an edit. Andy Dingley (talk) 18:15, 30 May 2016 (UTC)
 * I've done my best. Is "lined up" (of the diameter-reduced inner cylinder) good terminology? It sounds as if an inner lining (a tube) was inserted; whether or not that is correct, "lined up" does not sound quite right to me.Hayttom (talk) 19:19, 30 May 2016 (UTC)
 * I'd have thought "lined down" or "sleeved down" more usual than "up". Andy Dingley (talk) 20:55, 30 May 2016 (UTC)
 * 'sleeved down' it now is. Hayttom (talk) 03:13, 31 May 2016 (UTC)

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This article was written by engineers for engineers which is the very contrary of Wikipedia’s purpose
Hi. I came here knowing that a Gresley conjugated valve gear was a component used on some steam locomotives, and I left knowing very little more.

The terminology used is highly technical, lacking in links and the drafting is predicated on a high level of engineering knowledge.

None of the three photographs has any on-photo legending, and the NSW and USA photos may significantly underexpose the point being described, making it dark and difficult to discern. I say “may” since I don’t know precisely the point my eye is supposed to be being led to because there is no on-photo legending on the photos. QED.

The section entitled “Operations” seems to have been written to demonstrate the knowledge of its author, rather than any desire to explain to a non-insider. The related article on “Walschaerts valve gear” which I have also read is better than this article for neophytes, although the more opaque elements of it are stylistically very similar to “Operation” here, making me wonder if there is commonality of authorship. The “Walschaerts valve gear” article includes both best practice (animation and a detailed numbered, legended diagram) and poor practice: the first photograph is captioned “A set of Walschaerts valve gear on 60163 Tornado. Note that the radius bar is set to reverse.” The first sentence of the caption could be clearer since I by now believe that the “valve gear” is in fact the apparatus mounted above and between the smaller wheels to the right, rather than the totality of what I see in the photo. The second sentence is totally obscure to a non-railway engineer or enthusiast and is not even clearly relevant to the article (other than, again, the recurring theme of showing off the author’s knowledge).

Since I came here not understanding what Gresley conjugated valve gear is, I am not competent to amend the article. Would someone who is both (a) competent and (b) desirous of explaining to non-engineers, please take a stab at rewriting it?

Sorry if this all sounds a bit harsh, but Wikipedia is so full of technical articles written with an animus of explanation and education that when I come across a rare article such as this one (and parts of its related articles), it really does stick out like a sore thumb.

Thank you

31.52.101.10 (talk) 13:09, 28 February 2021 (UTC)

Source?
Is the paragraph 'Operation' WP:OR or is a cite available?

86.142.118.46 (talk) 16:11, 11 September 2021 (UTC)