Of the many varieties of locomotive valve gears, two principal type played important role. The Stephenson gear located between the wheels, this gear was successful up to the time when modern developments in locomotive practice crowded the space between wheels. When this condition become serious the Stephenson gear was abandoned in favor of the Walschaert type shown in this animation, which, in various modifications, has been adopted later on practically all modern locomotives.

The principal advantage of the Walschaert gear lieas in accessibility of its parts, which are placed entirely outside the driving wheels. This facilitates inspection, oiling, and cleaning.

The various parts of the Walschaert gear are pin-connected and are easily lubricated; hence troubles due to overheating are reduced to the minimum. The Walschaert gear also transmits the moving force of the valve in practically a straight line; consequently there are less springing and yielding of the parts than in the Stephenson gear. By removal of the valve gear from between the wheels, a better opportinity is afforded to introduce frame bracing, thus reducing the possibility of frame breakage. The Welschaert type of valve gear also possesses advantages of steam distribution and operation.

The general adoption of the Walschaert valve gear has been accompanied by a number of variations which, do not eliminate its esential elements. The Baker, the Young, and the Southern valve gears, other well-known locomotive valve gears, are simply variations of the Walschaert gear.

Please Let Me Know How Much You Like This (1 is very Bad - 10 is Excellent)
29 Oct 2012

good show to you guys and i like to thank is mekanizmalar

02 Nov 2012

Thank you very much for this display; wonderful. I'm building a 4-4-0 Virginia as per LBSC's book. I am not a machinist and have rather modest equipment: vintage lathe, stand mounted mill-drill, several files and all materials are gleaned from junk. I was hung up on just how I could most easily mount the valve crank. Your working drawing and some photos I took of some modern locomotives have made me confident that I can satisfactorily accomplish the task. I'm hopeful that I will be ready to start building the boiler shortly after the first of the year, 2013. My locomotive is in 7 1/2" gage. Thanks again Dan Manley.

14 Dec 2012

I want to download this but i can not.help me please...

06 Jan 2013

not true of British Great Western design which had external cylinders but internal valve gear on the larger locos (Castles, Hall, Kings etc)

02 Feb 2013

Nice animation. Only that the reverse motion is incorrect.

06 Feb 2013

Any chance you could add the components that cause the link block (British: die block) to slide up and down in the link (british: expansion link)? These would be 1) engineman's reverse lever, 2) reach rod, 3) reversing shaft (end view), 4)reverse arms and 5 hanger. I could attach a diagram to an email to label those parts for you. It would be wonderful, because then it would show not only how the engineman reverses the locomotive, but also how he can shorten the back and forth travel of the valve o cause steam supply to the cylinder to be cut off earlier in the piston stroke to save steam and use the expansive properties of the steam (= to extracting more of the thermal energy in the steam before it is exhausted) I suppose that I'm asking a lot! I could attach diagrams showing how shortening of valve travel influences the timing of the four primary valve events: admission, cutoff, release and compression. In any case, congratulations for a great animation!

06 Feb 2013

PS--I just LOVE it that your animations can be SLOWED DOWN. Far too many animations on the Web go too fast for a viewer to get a good understanding of how it works,

13 Apr 2013

you cant download it.....but u can use snagit screen recorder to record the animation and save it..

Barakat Latif
22 May 2013

حقاً إنها لعمل رئع يسهل الشرح و يوضح كافة المعلومات عن البخار، وسير الحكة به و كيفية تحويل طاقة البخار لعمل ميكانيكي مفيد ... جزيل الشكر لكم
أنا سائق قطار قضيت معظم عمري مع القاطرات البخارية في الخط الحديدي الحجازي قاطرات من نوع (Hartman _Jung - witertour.

Barakat Latif
22 May 2013

It is wonderful work the steam engine animated, and eases description.
How we can changing the steam to do make machines useful.
I am steam engine driver in Hedjaz railway.

15 Jun 2013

This is neat

04 Jul 2013

This is very inspired me.. I love steam engine so much. Thank you for this neat and clear animation

04 Jul 2013

Fabulous animation. I agree with Marek (2/2/13) and with Steven (2/6/13). Having the "interactive" aspect of this animation include positioning the valve gear into mid-gear and reverse gear (and all the intermediate notches) would be great if it were possible. This would also involve controlling the steam flow. And to take the animation to a "steroid" level, have meters to show cut-off, etc. Otherwise, it's a fabulous animation.

04 Jan 2014

Congratulations on producing an animation that demonstrates with clarity the elegance of Walschaerts valve gear.

13 Nov 2014


Steven Smith
09 Jun 2015

Congratulations on creating such an animation! The slowdown feature is very good for slow-witted persons such as this writer. One criticism: You depict the locomotive with outside admission valves. The New York Central Hudsons all three series of them--J-1, J-2 and J-3--had INSIDE admission valves. In fact, very few locomotives in the United States were built with the combination of piston valves and outside admission. Outside admission was seldom used once the piston valve mostly replaced the slide valve (also called the D-valve or hat valve because of its appearance in a cross sectional view).

On the New York Central Hudson type locomotives, in forward motion the eccentric crank lagged the main crank. Thus your animation is correct. But a lagging eccentric crank combined with use of the outside admission valve, requires the link block (American term for British term die block) to be carried ABOVE the pivot point of the link (British: expansion link). This creates a hazard: Should the hanger break, the link block falls to the bottom end of the link and puts that side of the engine in reverse. For that reason, most railroads arranged the Walschaert valve gear so that in forward running the link block is in the lower part of the link. (Generally the locomotives spent more time traveling forward than they did traveling backward.)

The New York Central Hudsons built earlier had Walschaerts valve gear, but the later ones had Baker valve gear, and eventually the Walschaerts valve gear on the earlier Hudsons was replaced with Baker. Baker gear has only pin joints, and the Baker gear on the Hudsons had needle bearings for those joints. Hence the Baker gear required little maintenance. The link on the Walschaert valve gear suffers rather rapid wear because in operation the link block oscillates slightly with respect to the link (a phenomena referred to as "slip," which was also a problem with the Stephenson valve gear). In my teenage years I had the great thrill--three times--of long rides in the cabs of New York Central Hudsons--pleasures I will remember as long as my brain continues functioning!

08 Oct 2015

I want a playable steam locomotive working animation! Please make that!

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