Talk:Valve gear

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Aiga railtransportation 25.svg To-do list for Valve gear: edit·history·watch·refresh· Updated 2006-06-24

  • Make the list of valve gears more complete
  • Nice to have an image of the Stephenson gear
  • Info about what gears are used on stationary steam engines, steam cars, etc.
  • Timeline of history
  • Review for organization


I've put the various valve gears in their own category. Please add future pages (e.g. for Young etc.) in category:Locomotive valve gear and do not add them to category:Locomotive parts. Mangoe 03:35, 23 June 2006 (UTC)

Improving valve gear articles[edit]

I could use a little help:

  1. I only know about American (and a smidgin of British) usage. Someone with continental/other knowledge needs to take a stab at expanding/filling in those.
  2. I also don't know much about the poppet systems. I've looked at Caprotti valve gear, and it could use some help. Someone especially needs to tackle Franklin because it is important to the PRR T1.
  3. I'm not sure I'm naming the parts correctly. I especially need someone who can name the parts of Baker valve gear.
  4. I know the idea behind Young valve gear but am not up to actually writing the article.
  5. Southern valve gear needs a history review.
  6. Surviving engines with some of the odder varieties would be nice. (I have examples for Baker and Southern.)
  7. Steam locomotive nomenclature doesn't show much of the valve gear. We may want to help this out more than I've attempted to do, but I'm not sure how.

Mangoe 03:20, 24 June 2006 (UTC)

I have added preserved examples with Allan, Joy and Bagnall-Price valve gears. 10:01, 14 March 2007 (UTC)

Sleeve Valves[edit]

Hi Mangoe Thanks for amending the bit I added about sleeve valves and the Leader. I knew it didn't read well when I wrote it.--7severn7 19:01, 3 October 2006 (UTC)

Bias towards railway locomotives[edit]

As so often with steam articles, the bias (of knowledge, not POV) is towards railway locomotives. It would be good if an editor with stationary and marine steam knowledge had a look in here.--John of Paris (talk) 12:42, 17 February 2008 (UTC)

I've added a short paragraph on Corliss valve gear with a link to Corliss steam engine#Corliss valve gear. --Roly (talk) 15:20, 22 March 2013 (UTC)

Trofimoff valve[edit]

I wasn't sure where to add the above link, so I've put it pro tem under the "see also" section. Please feel free to move it to a more appropriate place in the article. --Bermicourt (talk) 20:03, 29 January 2012 (UTC)

crankshaft/crank/big end[edit]

Redrose64 - railway locos may not have a traditional crankshaft but other engines do. This article should not apply only to railway locos. Even on a railway loco, the crankshaft can be considered to be the driving axle. However, what I'm really getting at is that the motion of the valve gear is not normally derived from the main crank or big end. The motion is normally derived from an eccentric or return crank, attached to somewhere on the crankshaft or driving axle at around 90 degrees to the crank pin. There may also be a secondary connection to some point at 0 degrees but this is usually the crosshead (as in Waltschearts) rarely the main crank or big end. Is there some wording that we can agree on? How about something like "...from the motion of the main crankshaft or driving axle."? Roly (talk) 18:05, 4 October 2012 (UTC)

There are several places that the valve motion can be derived from. Some are the crankshaft (eccentrics for Stephenson etc.), some the connecting rod (radial valvegears like Joy or Marshall) or the beam engine valvegears. The only one I can think of offhand that uses a return crank is Walschaerts, although that's obviously very important. On the whole I'd go with a deliberately vague term like "motion", rather than being specific to the crankshaft.
As to crankshaft vs crank axle, then I see crankshaft as a perfectly good synonym for crank axle or return crank. Especially so as it works equally well for stationary or locomotive engines, which crank axle wouldn't do. Andy Dingley (talk) 18:24, 4 October 2012 (UTC)
I think Andy has a good point here. I'd go along with "motion". Roly (talk) 18:38, 4 October 2012 (UTC)
OK; but I think the entire paragraph is a bit confused. The implication is that in most valve gears, the primary movement of the valve is obtained from the same crank as is driven by the connecting rod. The problem with this implication is that except for the Joy gear (a pin part-way along the connecting rod) and certain unusual types like the Hawthorn-Kitson valve gear, this movement is around 90° out of phase with the desired movement. So, in the commoner types of locomotive valve gear, such as the Stephenson and Walschaerts', the primary motion comes from an eccentric. But the 90° difference is not ideal, and to obtain the desired lead, either the eccentric is positioned away from the 90° angle (Stephenson) or an additional movement is derived from the crosshead (Walschaerts'). I don't know of any valve gears that derive the lead from the crank. --Redrose64 (talk) 20:48, 4 October 2012 (UTC)
I agree it is not good. While we are at it, I think "In the internal combustion engine ... commonly used with steam engines, partly because achieving variable engine timing using cams is complicated." is speculative OR. That they just happened to evolve that way, eg. from gab gear, is at least as likely. Globbet (talk) 22:25, 4 October 2012 (UTC)


Do we really need two very similar photos of the Walschaerts valve gear at the top of the article? One of these could be replaced by a decent photo of Stephenson's gear. I know Stephenson's is typically inside the frames of a loco but there is at least one exception (a Black 5? named after RS himself) and there were (still are?) some stationaries with accessible Stephenson's gear. Some more photos of less common gears would not be out of place either. Unfortunately, I don't have any suitable photos myself. --Roly (talk) 12:44, 4 April 2013 (UTC)

That was partly my fault. The previous photo claimed to be "a close up on the left-hand Walschaerts valve gear", but omitted the return crank and the return crank rod, both being important components; and it also seemed to give undue prominence to items which are nothing to do with the valve gear - buffers, front axle, chimney and ejector. I wanted to replace that with a photo which showed a complete set of the gear on a British loco. --Redrose64 (talk) 18:33, 4 April 2013 (UTC)
From fairly extensive past searches, there are no useful Commons photos of British locos with Stephenson gear. The Black 5 with the external gear doesn't have a great photo and although I did take some fairly decent ones when I found a saddle tank with a skinny boiler, those of internal gear can't show a decent side view of the overall gear, both link and eccentric. However for German and Austrian locos, where external Stephenson gear was much more common, there are plenty of them. Andy Dingley (talk) 19:23, 4 April 2013 (UTC)
Well, the article is not solely about railway locomotive valve gears, so a photo of the valve gear of a marine or traction engine would be appropriate, and would help to present the wider application of valve gears, most commonly Stephenson's. Globbet (talk) 22:28, 5 April 2013 (UTC)
I have deleted one of the two almost identical photos. I thought it was pointless having both. I still think we should have a good photo of a Stephensons gear if someone can find one. --Roly (talk) 18:47, 16 May 2014 (UTC)

Inside vs outside admission.[edit]

Could we perhaps get a section explaining the difference between inside and outside admission? I googled around fruitlessly for an illustration, and found nothing but descriptions. The only Wikipedia reference to the two that I came up with is on the Walshaerts valve gear article, but there is no explanation, and I find nothing else even referring to the two types (I think maybe the article on slide valves mentioned that they "are always outside admission", but with no further detail). I finally figured it out by looking at the illustrations of the Walshaerts gear and comparing it to the illustrations on the slide valve, and applying the things I had read in OTHER places to the illustrations, but it would be nice if one could find all of that information and illustrations right here on Wikipedia. As it is, I don't even find a simple (or even complex) explanation here. It would be nice if I could look right at that image of the locomotive piston and have a caption explaining that if the steam is admitted through the central portion of the piston gear, it is inside admission. If it's the opposite, it's outside admission. That seems very obvious in retrospect, but it wasn't so obvious when I was reading various things about how "the steam exhausts through the center of the piston"; I had an image in my mind of the steam exhausting down through the core of the piston and out the end, even though that didn't seem to match what I had seen of piston valves before. Also maybe a brief caution not to confuse "inside and outside valve gear" with "inside and outside admission"? .45Colt 13:46, 5 February 2014 (UTC) — Preceding unsigned comment added by .45Colt (talkcontribs)

Indicator diagram steam admission.svg
Refer to the upper part of the diagram at right. The valve consists of a spindle (the valve stem) upon which are mounted two solid cylindrical valve heads. The valve is concentric with a cylindrical tube (the valve chest). The valve heads are a close fit in the valve chest, like the piston in a cylinder, hence the term piston valve. The fit is normally improved by the use of rings made of a springy material, much like the piston rings of a car engine; steam therefore cannot pass from one side of a valve head to the other. Adjacent to each valve head, in the lower wall of the valve chest, is a port leading to one end of the cylinder. The valve stem is free to move along its axis, and depending upon its position, each port may be covered up, preventing the passage of steam; or it may be uncovered, allowing steam to pass from the valve chest to the cylinder, or vice versa. Since the valve can move in either direction, steam can pass either between the cylinder and the end of the valve chest (the outside), or between the cylinder and the part of the valve chest that is between the two valve heads (the inside). There are three more ports, shown in the upper wall of the valve chest, and these are so positioned that they are never covered by the valve head.
First assume that the steam supply from the boiler is connected to the central port in the upper side of the valve chest; the outer two ports in the upper side of the valve chest are connected to exhaust via the blastpipe. This is known as inside admission, since the steam is admitted inside (between) the valve heads. In the position shown, with the valve towards the right (the rear of the locomotive), the left-hand (front) port is uncovered to exhaust, and the right-hand (rear) port is uncovered to admission. This is the normal arrangement for a piston-valve locomotive in Great Britain.
Now assume that the steam supply from the boiler is connected to the outer two ports in the upper side of the valve chest; the central port in the upper side of the valve chest is connected to exhaust via the blastpipe. This is known as outside admission, since the steam is admitted outside the valve heads. In the position shown, with the valve towards the right (the rear of the locomotive), the left-hand (front) port is uncovered to admission, and the right-hand (rear) port is uncovered to exhaust. This is an unusual arrangement for a piston-valve locomotive; examples of its use in Great Britain are LNER Class D9, LNER Class D10, SR Merchant Navy class and the SR West Country and Battle of Britain classes. --Redrose64 (talk) 18:39, 5 February 2014 (UTC)

Marshall valve gear[edit]

I think the section on Marshall valve gear may be inaccurate. There are at least two different Marshall valve gears, invented by two different Marshalls. I am doing some research on this. Biscuittin (talk) 16:52, 11 February 2015 (UTC)

Yes, and there is a third. LNWR Whale Experiment Class no. 1361 Prospero was fitted with what some sources describe as "Marshall valve gear", others as "Dendy Marshall valve gear". This is Chapman Frederick Dendy Marshall (1873-1945), the same man that wrote History of the Southern Railway in 1937. Note that "Dendy" isn't a forename, it's the first word of an unhyphenated double-barrel surname, like "Bonham" in Helena Bonham Carter. --Redrose64 (talk) 17:12, 11 February 2015 (UTC)
Here are some patents:
  • James Marshall of Gainsborough, GB189700518, [1] Very hard to follow but I think it allows the cut-off to be varied by the governor
  • James Thompson Marshall of Leeds, GB190103761, [2] This appears to be a modified Walschaerts gear in which the drive from the crosshead is replaced by drive from a second eccentric
  • Dendy Marshall, GB191118805, [3] Piston valve arrangement (inside/outside admission) for engine with cranks at 180 degrees

Biscuittin (talk) 19:37, 11 February 2015 (UTC)

The valve gear on Badger [4] does not seem to resemble any of these so there seems to be a fourth Marshall gear. Biscuittin (talk) 19:43, 11 February 2015 (UTC)
And I can't understand how Badger's valve gear is linked up. There must be some arrangement of levers to replace the Hackworth slide but I can't see them. Biscuittin (talk) 19:48, 11 February 2015 (UTC)
18,805 of 1911 is the right number for Dendy Marshall - it matches steamindex (above). I notice that they incorrectly give his name as "Marshall, C. F. D" - it should be "Dendy Marshall, C. F." --Redrose64 (talk) 20:30, 11 February 2015 (UTC)
I'm finding quite a lot of old patent numbers in books but they are not on Espacenet. Perhaps the original documents have been lost or perhaps they have not yet been digitised. Biscuittin (talk) 23:14, 11 February 2015 (UTC)
Perhaps Espacenet concentrates on patents that are still in force, possibly also those which were themselves improved upon by current patents? The Patents Act 1977, section 25, says that a patent lasts for 20 years. Although this period may have been different in the past, presumably it won't have been much different (perhaps 10 or 30 years) - but even if the duration of patents was 50 years at some point, these valve gear patents will have expired several decades ago. It's unlikely that any current patents use these older ones as a basis - the development of steam technology in modern times has been pretty much all to do with turbines, not reciprocating engines. --Redrose64 (talk) 00:20, 12 February 2015 (UTC)
As for that of J.T. Marshall, see
  • Bradley, D.L. (April 1980) [1961]. The Locomotive History of the South Eastern & Chatham Railway (2nd ed.). London: RCTS. p. 93. ISBN 0-901115-49-5. OCLC 60250456.
this says that he was from Harrogate. --Redrose64 (talk) 11:29, 12 February 2015 (UTC)
Thanks. I've discovered there is a Wikipedia article on James Thompson Marshall. Biscuittin (talk) 13:51, 13 February 2015 (UTC)
I've worked out the valve gear on Badger. [5] The horizontal link at the top is pinned to another horizontal link (painted black) behind it and the gear is linked up by raising or lowering the black link. Biscuittin (talk) 13:58, 13 February 2015 (UTC)

Dalby, p246, "In 1879 specification No 2138 Marshall patented an arrangement of Hackworth gear" which uses a rocking lever instead of a slide. This is the arrangement used on "Badger" which links up as you say. Some of the comments on the Badger page are a bit odd. Firstly, in this application the susceptibility of the Marshall gear to vertical motion of the axle is no different from that of Hackworth gear, and secondly, the 'pendulum link' supporting the valve rod, and introduced to reduce wear, would seem to be a source of wear of its own. Steam boat guru Roger Mallinson regards silence as a measure of engineering quality, and to that end he uses this Marshall gear in his engines because there are no slides and die-blocks to wear and slap.

The Gainsborough Marshall is probably Marshall, Sons & Co., who's excellent late 'S' series traction engines and rollers used their own configuration of Hackworth gear, rotated through almost 90° to fit neatly above the boiler and driving the valve rod via a bell-crank. This has a straight slide, as in Hackworth, not a link. There is an illustration in Hughes, p149. They may well have another patent for governor control, but that would not be what is usually meant by (their version of) Marshall gear.

Harris, p149, uses a similar configuration for a twin launch engine design, with the only difference that it uses a curved slide instead of a straight one. He attributes it to Dendy Marshall, but I think he is (unusually) wrong.

Ahrons, p365, describes the Dendy Marshall gear applied to a 4-cylinder LNWR loco, in which one valve stem has four valve bobbins serving two cylinders. A footnote points to pieces in The Engineer of 1915-09-24 and The Locomotive 1915-10-15. Harris also mentions this arrangement.

As far as I can tell, the first above was quite widely used, the second also a well designed and successful gear, but only used by one manufacturer, and J T Marshall & Dendy Marshall only ever being experimental odd-balls. The J T Marshall gear in the photo of SR 1850 on his page looks over-complicated and fragile.

Dalby, W. E. (1906). Valves and Valve Gear Mechanisms. London: Edward Arnold

Hughes, W. J. (1970) [1959]. A Century of Traction Engines. Newton Abbot: David & Charles. ISBN 7153 4230 4

Ahrons, Ernest Leopold (1969) [1927]. The British Steam Railway Locomotive 1825-1925. Shepperton, Surrey: Ian Allan. ISBN 711001243

Harris, K. N. (1964) [1958]. Model Stationary and Marine Steam Engines (2nd ed.). London: Percival Marshall & Co. Globbet (talk) 00:45, 14 February 2015 (UTC)

I have Ahrons. Page numbers are 354 (J.T. Marshall's valve gear, as applied to a GNR goods engine and a 4-4-0 passenger engine: Ahrons gives a ref to The Engineer 3 November 1905) and 365 (C.F. Dendy Marshall's system as applied to LNWR 4-6-0 (no. 1361 Prospero as I mentioned earlier) ref. The Engineer 24 September 1915 and The Locomotive 15 October 1915). --Redrose64 (talk) 16:03, 14 February 2015 (UTC)
I have now seen the patents for one of the Marshall gears (using links instead of a slide). The patentee is Francis Carr Marshall of Newcastle-on-Tyne, not the Gainsborough Marshalls, although I suppose they might have been related. They are British patents 2138 of 1879 and 4185 of 1880. This is original research so I suppose I can't put it in the article. Biscuittin (talk) 12:46, 20 February 2015 (UTC)
I have had a quick look at the James Marshall of Gainsborough patent, GB189700518, [6] and it is clearly a type of trip gear. Globbet (talk) 16:46, 25 February 2015 (UTC)

F.C.Marshall was the boss of Hawthorn Leslie ship builders of Newcastle. The gear is usually used on marine engines. — Preceding unsigned comment added by Jmaltbyengineer (talkcontribs) 16:32, 23 October 2018 (UTC)

What is the point of valve gear?[edit]

There is a glaring hole in the article. It does not explain what valve gear actually does. For sure it talks about inlet and exhaust opening and cut off points. It also explains how the clever linkages switch between forward and reverse mode. But at no time does it relate the valve events to the steam engine cycle.

Everybody who even thinks about contributing to this article (and everyone who reads the Talk page) knows that piston and sleeve valves have to be 90° out of phase with the main driving pistons and that the engine will run forwards or backwards depending on whether the valves are leading or lagging the drive. (Okay the valve gear always lags because if it leads the engine reverses direction.) But this is never explained. Consequently the purpose of the clever linkages remains a mystery to anyone who doesn't already know what they are for.

As an example it is explained that the Stephenson Motion has two eccentrics and you can see how the Stephenson link allows the Radial arm to select which eccentric to use. But it does not specify the phase angle between the eccentrics and the power crank nor does it show what actually happens inside the steam chest.OrewaTel (talk) 12:30, 13 June 2020 (UTC)

Non-Rotative valve gear[edit]

I've recently created a page on Cornish engine valve gear. I was planning to link to it from this page, however there seems to be a strong concentration on rotating engines and I'm not sure where best to slot it in. Any suggestions ? Kewnut (talk) 15:03, 1 July 2020 (UTC)