Walschaerts Valve Gear Explained

PLEASE NOTE - this model and explanation contain a glaring error. That is, at the neutral position, the valve ports should not open at all. Thanks to Dave Squire for his keen observation. I'll hope to revise the model and make a new video, soon. -BL
For steam locomotive enthusiasts who've always wondered what all the complicated rods and linkages do. As an instructional video, this is admittedly still a work in progress. So, your constructive comments are welcome. Also, the model shown is one I'm trying to develop for sale, as a kit. If that's of interest to you, please send a private message.

[@Bigbuddyandblue]

Clear, simple and to the point, no filler, no music, no grandstanding, no pimping a product, no sales pitch, no pop-up commercials, no history of the steam locomotive, no drama, no begging for likes and subscriptions, just a great animation and concise explanation! Thanks! Subscribed!

[@philgiglio7922]

💯 agreed. I saw something similar on a working steam tractor many years ago. It was huge and it could go both directions. This must have been how it worked...thank you Also subbed

[@yogiperogy]

Wow! You nailed all the elsewhere ubiquitous irritations of YT!! Thank you very much Brad for tackling this complicated “magical” apparatus and enabling appreciation by the less mechanically-inclined viewer (like me!).

[@dominatorut]

Yes, because we should not enable an informative content creator to earn from their many hours of work. People should be willing to make videos for free!! In fact, let's all work for free! 😊

[@timault8209]

I claim this excellent comment for my own! I have copied it and I will post it to worthy videos. I suspect it won't see much use, unfortunately!

[@Bigbuddyandblue]

@@timault8209 cool!

[@richardbedard1245]

I have enjoyed watching the steam locos all my life, but have never heard an explanation for all the rods and linkage. Thank you!

[@bigblue6917]

Same here.

[@sammolloy1]

Ditto. I was aware of “four clicks forward” but now I see how it works.

[@Mike44460]

Agreed, outstanding.

[@NSBarnett]

@@sammolloy1 I don't. We all have our specialisations and blind spots, and mechanics and engineering are the latter, in my case, and not for the lack of wanting to see how things work. Brad, you need to take this quite a bit slower if you want to get through to people like me. "Steam from the boiler comes in here; it pushes this piston like this; which pushes this rod like this; if you don't have a Walschaerts valve, this happens; this is sub-optimal because of this xxxxx; here's how it works WITH a Walschaerts valve . . . " etc. I couldn't build such a model or create an animated drawing, but I suspect animation could be used to explain it better than a model.

[@jefffrayer8238]

@@NSBarnett Brad has done an excellent job of explaining how this all works on a locomotive other than the tiny error of showing movement in the center between reverse/forward motion. In the center there is no movement of the sliding valve so no steam is admitted. If you aren't certain how all this works simply turn off your sound and slow down the replay settings. I'm sure you'll figure it out watching in slow motion. Also he is explaining that this is an Walschaerts movement common to locomotives but there is other valve movements used in other style steam engines. Thanks for your interest.

[@daleeasternbrat816]

When I was a kid I wrapped my brain around the valves and rods and fly ball governers that control steam engines till it gave me a headache! A model like this would have saved me the headache . Joshua Rose would have loved this! I want one!

[@IndustrialParrot2816]

i could never figure out how the timing on the connecting rods working because they should just get stuck

[@IndustrialParrot2816]

same exept i never notice the second set since i mostly looked at older locomotives with valve between the frames and couldn't figure out how they reversed

[@Tatertot_Tommy]

This really makes one appreciate the genius engineering that went into even just the concept of this system. Let alone the time and effort, as well as the superb workmanship it took to actually get it going down the tracks.

[@simonholyfield3319]

You might have made your 'glaring error', but this is by far the clearest video on the operation of Walschearts vale gear that I've seen. Your voice over is excellent - slow and clear. Well done.

[@Rosie6857]

There is no "glaring error" at all. When in mid-gear the valve still moves owing to that contribution from the movement of the piston, so the movement is in phase with the piston. Even under these conditions some small amount of power will be generated because of the delay between the opening of the valve and the application of pressure to the piston. Even hot steam has a little inertia and the faster the engine is going the greater the delay relative to the piston movement so the greater the power developed but it's still pretty small. All valve gears are designed so that the valve opens just before dead centre to allow the steam in. With Walschaerts gear this is a fixed amount but with Stephenson's Link motion it varies, being greater at shorter cutoffs. It's debatable whether this makes much difference.

[@c182SkylaneRG]

@@Rosie6857 Thank you! I was trying to figure out what the "glaring error" was, too, because if he built the linkage to the exact proportions as the real thing (which he appeared to), then how it works is how it worked, no errors. If you want to get an exact "neutral" operation of the feed gear, you just need to raise the position slightly further to where the phase of the Walschaerts gear exactly cancels the movement of the drive wheels (and I'm sure such a position was clearly marked on the controls inside the cab). The rod to which the control piston is directly connected is fixed at two ends: one to the driving rod, and one to the control rod. By putting the control rod in the exact neutral position, ONE END of that connecting rod is fixed, which still leaves any point along that rod moving in-phase with the driving piston, and thus the control piston is also still moving in-phase with the driving piston. You need to move the control rod slightly into reverse so that its end is moving backwards at the same time the driving rod is moving forwards by exactly the right proportion to keep the control piston's anchor point stationary. Linkages was one of the more interesting classes in College. :)

[@g8ymw]

@@user-xy7bt8qg8k What has this got to do with the workings of a steam locomotive?

[@davidgarnett5011]

@@g8ymw Nothing really however there is a Grateful Dead tune called "The Wheel" which has a line in the lyrics " Small whell turns by the Fire and Rod.--- Big wheel turns by the Grace of God" But I wouldn't read too much into that.

[@mikado1555]

The valves SHOULD open in center (there is no neutral). In center, the valve opens a little bit - this is called the lead - as the valve is only controlled by the motion of the piston through the lead and lap lever. When the valve gear is properly set, the loco can run in forwards/reverse as the valve events are the same, just not very powerful. As far as the eccentric crank, the eccentric crank is close to 90 degrees off, but due to the piston centerline being higher than axle centerline (dead centers are not 180 degrees apart) and the height difference between the axle centerline and the basked of the link, the angle can vary from loco to loco and with the crank pin at the 6 o'clock position the eccentric crank pin is higher than the axle centerline making the angle listed in this video greater than 90 degrees.

[@DavidLaFerney]

My small town has a steam locomotive (non operating) in a museum park. I thought I was very clever to figure out how it all worked. I could see that the expansion link worked to reverse the engine. I didn't figure out that it also varied the valve timing. I guess I'm not so clever after all, but the engineers who designed this - without computers, or even calculators - certainly were. Great video - thanks!

[@mottthehoople693]

they had calculators....they are called slide rules (both circular and linear) and once you know how to use them they are very quick and accurate

[@jimkadel3003]

@@mottthehoople693 Although only to about *3* figure accuracy.

[@HerroVincey]

There's something so lifelike in the fluid motion of such a system! It feels like seeing the concept of "motion" truly coming to life!

[@ThePaulv12]

If this were a school project you'd get 11/10. Concise, short, to the point. One thing however, if you're not a gunzel you might not know that steam is admitted to both sides of the piston. It could be worth mentioning at the outset of the vid but it is highly likely that the intended viewers all know this by the time they get here - so I'm being somewhat pedantic. .

[@fredred8371]

Good idea, it took me a while to realize that since I'm used to internal combustion engines.

[@wilburfinnigan2142]

thePaulv Would help too if it was explained better HOW the high pressure steam entered the valve and where the exhausted steam went !!!

[@neildahlgaard-sigsworth3819]

ThePaulv12 he did. Good and re-watch the video at about tbe 1:20 mark.

[@TlalocTemporal]

@@wilburfinnigan2142 -- You can see at 1:20 +. High pressure steam is injected in the center of the smaller spool piston at the top from the pipe. The same spool piston can allow access to the exhaust ports on the outer edges.

[@ginalee813]

The red shows high pressure, blue the exhaust, being admitted to both sides of the piston on each stroke. It’s self evident.

[@Bendigo1]

It looks so complicated, but in reality, it is extremely simple. Excellent explanation and demonstration!.

[@chilitoday]

It may “look” simple because it’s been figured out.

[@brucemcnally3924]

I'd never understood those linkages in over 60 years of fascination with steam. Thank you sir!

[@KnightDaylight]

I have learned more about steam engines watching this video than my entire life. I'm disappointed in myself, yet intrigued that now I'm a little bit smarter now.

[@troyclayton]

I'm so glad youtube tweaked the algorithm to bring so many of us here in such a short time. Thanks for the video, I'm now less ignorant of something I thought I knew how it worked, lol.

[@cggage]

Very well explained. Thank you. I often had wondered how this works. I do not think we give enough credit to the engineers of the past. They solved complex problems with pencil & paper and arrived at very elegant solutions - this being one of them - and all mechanically. It's really brilliant. Thanks, again!

[@andrewpetik2034]

Thank you for sharing the fruits of all your hard work! I have loved Steam Locomotives for as long as I can remember and always marveled at the workings of this system of rods, links and pistons. This video is much appreciated!

[@georgeehmke3283]

Wow.... 60+ years old, I just learned this today. Thank you .

[@juliancarrick727]

After decades of fascination with steam, riding the cabs when a kid and driving traction engines when I was a teenager, thank you for the best explanation I've ever seen on the workings of the radius link. Wonderful, you learn something new every day.

[@andredescheemaecker5865]

It's the first time that I really understand how the Walschaerts valve gear works. Thanks for this clearly explained description. And also proud for my Belgian compatriot's invention😀

[@conorlydon4839]

when you realise these steam engines had variable valve timing and direct injection like modern cars

[@SuperIliad]

Just for pernickitiness, modern cars have variable valve timing and direct injection as did these steam engines.

[@ferdouskhan7169]

Hi

[@checkdescriptionordontrepl2897]

I am doing an experiment : which comment will be more popular? My comment or my reply to popular comment? Please like if You want to help with experiment :D

[@revimfadli4666]

And the valve timing here doubles as sort-of-transmission too

[@Jimmyzb36]

Yes! And all analog/mechanical! Very impressive.

[@H.pylori]

This is the only video that I could find that clearly explains the valve and linkage function. Especially how the change to reverse takes place. Thank you.

[@RickyJr46]

Your working model, demonstration, and explanation are all A+ teaching. Fantastic!

[@cogzoid]

Great demonstration and explanation. Keep 'em coming!

[@lesliedickinson198]

A video that explains in the utmost simplicity the complicated method of valve operation on a steam locomotive. I really enjoyed this

[@pneumatic00]

Thanks for posting this! I've never been able to quite wrap my brain around the operation of the Walshaert part of the power train. I think if I watch this ten or so times I'll get it. Nice model!

[@callumk5]

I’ve known the theory for a while but never seen it laid out like that and explained so clearly. Thanks for sharing.

[@e2number1]

I never truly understood how Walschaerts valve gear worked, but this has really shown a lot! Many thanks for the video, it’s been very informative

[@johnnyz4427]

Thanks Brad. As same as you, I, since age 6, have been fascinated by the mechanism of the driving wheels of locomotive engines. I am also a collector of Marklin model trains (mostly locomotives). Your video is very intuitive and clear. I learned a ton.

[@bigblue6917]

I have, on occasion, scratched my head over this wondering what it all did. Well now, thanks to you, I know.

[@Gribbo9999]

Thank you so much. I have been looking at the transmission gear of steam locos since I was boy in the '50s near the end of the steam era in Britain. I could understand the piston connecting rods' action and knew the upper rods were something to do with valve switching but never understood the actual workings. Thanks for the beautiful model and the very clear explanation. How ingenious the steam limiter and reverse linkage is.

[@Andreschannel_SA]

Brad. Thank you for this well explanatory and informative video, using a polite attitude, gentle voice and excellent animations. The absence of harsh music, firework displays and ear-splittingly loud commentary, to exacerbate a point, is greatly appreciated. At least three thumbs up emojis for this clip.

[@36736fps]

As a mechanical engineer I always wondered how the steam valve linkage worked, especially the slotted link. Now I know!

[@stabilini]

Oh man you can’t imagine how thankful I’m now with you. Finally I’ve understood how this freaking ingenious thing works!!! Many many thanks!!!!

[@garryferrington811]

For the first time in my life, I understand what Walshaerts valve gear does! Thank you for this clear, lucid explanation.

[@MrOleg2805]

This is the best video about the operation of a steam engine and a steam locomotive, in particular! Thank you very much for the explanation!

[@AndreiTupolev]

This is very useful. I've been able to work out from videos how it all goes round, but what it all does and how it all goes together has always seemed very complicated. It also makes the concept of cutoff and how that works clearer too.

[@kjamison5951]

Short, to the point and illustrates exactly what is happening. Perfect video! Thank you!

[@SuperIliad]

Since boyhood (a very long time ago), I've been fascinated by those impossible rods and links. Many thanks for the clear tutorial.

[@petergregory5286]

That showed me what I didn’t know I didn’t know and now want to know more. Hope you have more like this for the future. Regards

[@PokoleizKuleckim]

Astonishingly well explained. Thank you so much for sharing. I do admire your ability to explain it so clearly and crisply.

[@vincenzonovi5528]

The clearest video about steam locomotives I've ever seen. A wonderfull English to hear by my Italian ear. Thank you so much.

[@nickkeeling9554]

This is the perfect video, finally simplifies something that many have wondered for years

[@bergasms]

This is one of those videos you never knew you needed to watch.

[@RWBHere]

Very nicely explained and demonstrated. Thank-you. After more than half a century, I can now see clearly how it works.

[@janotterspoor1721]

It only takes 4 minutes to explain how this mechanism works if you can imagine how the minds of technically interested but not gifted people work. I imagine you do. Great Video. Thank you very much!

[@jimkadel3003]

Perhaps an improvement in explanation could be had by using a visible label when referring to a particular link in the diagram?

[@deepdirtysouth2394]

I would just like to take a minute and personally thank you on behalf of everybody let’s watch this video sir. Absolutely brilliant explanation thank you so much.

[@dj6769]

Excellent “Readers Digest” explanation I now have a very basic understanding of how these masterpieces move forward and reverse. Some post are seemingly debating specific operational designs that’s obviously above human comprehension. Thanks for the video great job.

[@Firedog105]

I wish I was smart . No way in a million years and all the college degrees in the world would I ever think of that design . You have to be born with that type of mind.

[@ThePaulv12]

Kevin, don't underestimate yourself. If there is a need for something, you are curious (the most important part) and there is some $$$$$$$$$$$$$$s in it for you, you might just surprise yourself. Saying you can't is a self fulfilling prophecy - now only if I took a dose of my own medecine ...

[@danstrayer111]

check this out: kzbin.info/www/bejne/gHbMhIewgJJ0aKM

[@ddkoda]

@Herbert Norkus It doesn't seem fair. Don't give up hope. Something more worthwhile may come your way in due course. In the meantime look on the bright side. At least you can pay your bills with your meterman employment.

[@jameshollen9723]

"necessary is the mother of invention" Look around you. Look at something and ask yourself, How can I make that better, faster, more efficient, etc. I barely passed High School but I have 3 patents in my name. I have designed countless ideas in the basement. That's the fun ! (O yes, it's nice to make a buck or two doing it !)

[@paperbackwriter4145]

Just one word: motivation. Thats all.

[@davidhall8874]

Finally! The best demonstration and explanation I have ever seen, and I have seen a lot of these! Thank you so very much!! Well done sir!

[@leobuis9568]

Thank you! I've been curious about the valve that controls the direction of the steam for years now. I figured it had to be pretty complicated, but I had no idea it was this complicated until I watched your video! We may think we're really smart today, but your video shows and engineers in the past word just as smart if not more so.

[@FS2K4Pilot]

Wait until you get to valve gear setups like the Baker and Southern valve gear motions.

[@blockstacker5614]

Franklin type B is simpler and more effective, but much less common

[@koyaanisqatsi316]

If you think this piece of old engineering was impressive, then feast your eyes on this one: kzbin.info/www/bejne/opKtiWOqra-WbK8

[@chrisvesy7245]

Since I was a kid I've always asked how the rods & links worked...I always got a "what they do" answer never "how they do it" answer....thank you so much!!👍

[@hamstirrer6882]

Brilliant explanation and model, thank you for a wonderful video. Have always been fascinated by this mechanism

[@gregmead2967]

That was fascinating. Thanks for showing this. I'm amazed that someone could conceive of this and put it into practice.

[@michaelXXLF]

I am starting to get a grip of the function. Thank you for your explanation!

[@PanzerBuyer]

Great presentation. The designers were truly brilliant!!

[@Lincoln1242]

I have been a model train enthusiast for 30 years, but I never thought so much about the mechanisms of a steam locomotive, because I assumed it would be to complicated for me to understand. This video has just proved me wrong😅

[@GJBricks]

That’s brilliant! This was on my list to look into, thank you! Fascinating and such a work of art. I just love steam engines.

[@markdombek2551]

Beautiful work and concise narrative. Thank you for this.

[@StonyRC]

That, Sir is a wonderful explanation of a complex mechanism. The model you built is excellent. Many Thanks.

[@gedungisphoopnuchle9121]

The steam engine is one of mankind's best innovations, right next to the SaturnV rocket! Great job!

[@terrymarkowski8762]

a great explanation with the best demo i have ever seen the books tell you how but unless you see it etc. thank you!

[@thematthewexpress5999]

It's very satisfying to watch the Walschaerts valve gear go round on steam locomotives, also very interesting. Good model and video.

[@B-and-O-Operator-Fairmont]

Thanks for this tutorial. I knew steam locomotive engineers could adjust power by "hooking up" the reverser to just about center, but I never knew why that worked. It should also be pointed out that the drive rods are "quartered" to ensure that at no time will the locomotive be unable to start if one of the cylinders happens to be stopped on "dead center". There were lots of different valve gear arrangements, but Walschaerts was not only easy to understand but pleasing to the eye.

[@carelpienaar8486]

Thank you for this explanation - it took a lot of work to construct it! Well done!

[@ChrisG3253032]

Excellent explanation. Much appreciated. I'd often wondered how the system works, now I know. 👍

[@jeffreyc3314]

Brad, Thank you for your hard work on this. I never could quite figure out how the 'reverser' worked. Now I know. Great info, great video.

[@newq]

The KZbin algorithm tried to get me interested in trains for years and I resisted until it started showing me steam stuff. Now I'm wild about steam locomotives! The modern stuff just bores me to death.

[@rogerletsom2127]

This is a very fascinating working model. There are three points of difference I've seen in other diagrams and models, however: connecting rod(main or driving rod), tie rod(side rod or connecting rod) and combination link(combination lever). I'd like to see more steam locomotive related models. Thanks!

[@jirizlamal69]

This is what I've been looking for for years! Great video, everything is clear now! Thanks!

[@santeebandit3246]

Great great explanation of the valve timing adjustment, and how it effects operation. 👍🏻👍🏻

[@acescionti711]

This is exactly the explanation I needed I plane on designing and building my own class of steam locomotive full scale and have already started the design process so I’m watching a lot of these videos

[@schrauberhugo2594]

Videos like this make KZbin that valuable. Thank you, Brad !

[@major_nobody311]

My own projects of steam engineering will greatly benefit from this video, thank you imensly.

[@horrorman9]

Thank you for explaining this process. I'm playing a steam engine simulator game, and didn't understand this process, but now I do and will help me greatly.

[@Stussmeister]

Very interesting and informative. I had a basic understanding of how the rods allow all wheels to move uniformly and convert the back-and-forth motion of the pistons to the rotary motion necessary to turn the wheels, but this explains their functions and connections very well.

[@currentbatches6205]

I had no idea that the linkage disassociated the timing from the piston stroke! I'll have to give it more study earlier in the day soon to really get a handle on it, but thank you for pointing out a complexity which was not even visible to me.

[@cfa61]

Thank you! A very clear, concise, explanation! Nice work, and generously shared.

[@Ronnymikkonen2686]

I Love it it's just so clever. The fine tuning system of power regulation. One important and major detail is that on the opposite side of the machine you have the same system 90 degree of align with the other side. And that's wery important because otherwise the whole setup would bottom up and close. That's why the choo choo sound came from the train. The little pause between the choo choos indicate that arrangement. Thanks for an fantastic explanation.

[@robertwestreicher1924]

You are a LEGEND!!! thank you so much for unraveling this black magic. I have loved steam engines my whole life and never understood this until today.

[@NCXDesigns]

I've always wondered what the crank part did. My dad introduced me to steam locomotives and ever since they have been my favorite type of locomotive. The fascinating parts that move the way they do and cause the reactions they do is just genius engineering. It looks impressive to see in person, not to mention hearing, smelling and feeling it all in person. Thanks for this great explanation on how these rods work and what purpose they served. This will also help me do my steam locomotive that I am making for a computer game as animations have to be done by hand.

[@september1683]

I came here by accident. And I left with a smile on my lips, because of your beautiful explanation. Best wishes from Bavaria. Have a nice day!

[@chuckthebull]

Great demonstration and art work on that model..it really helped me understand the system THANKS!

[@TMCNJ]

I never knew this is how they worked. Thank you for explaining it so clearly 😌

[@mellissadalby1402]

That's a great demonstration. I never knew that.

[@Qdogsman]

I don't think you made a glaring error at all. It is true that in the center position, the radius rod is stopped. But since the union link is still moving and the valve is connected to a point on the combination link near, but not at the top, the valve still moves although a lot less. I think you got it right. BTW I am one of those who also wondered about that linkage all my life ever since I used to meet those locomotives to pick up the newspapers for my paper route in around 1950. I really appreciate your explanation. Great job.

[@davidzachmeyer1957]

Correct, the combination rod is included for the specific purpose of allowing valve travel at the neutral position. The model is correct and operates exactly as it should!

[@johnm2012]

@@davidzachmeyer1957 I'm not saying that you are both wrong because I don't know enough about the subject but if one extreme is full power in the forward direction and the opposite extreme is reverse there _has_ to be a neutral position somewhere in between. Whether that position is the centre position or not determines whether he made an error in the model. The thing is, two 90-degrees out of phase rotating motions can never cancel to zero, whatever their relative amplitudes - this is the mathematical approach, which I understand better than the mechanical approach.

[@davidzachmeyer1957]

@@johnm2012 read up on the Walschaerts mechanism to understand the function of the combination lever. As I stated, the OP's model properly represents the correct motion of the valve when the reverser is at the center position.

[@u1zha]

@@johnm2012 If one extreme is full power in the forward direction and the opposite extreme is reverse there has to be a neutral position somewhere in between, yes, and that position is not necessarily engine at complete rest, nor coasting for that matter; I think in this case "neutral" amounts to powering forward half a cycle and powering backward half a cycle. But I'm not a steam engine expert either.

[@69Applekrate]

How cool! thanks for taking the time to explain and show. I learned from you today

[@jordenconrad8827]

Brilliant demonstration and explanation. Fascinating

[@FrakMunkie]

PLEASE GO INTO VIDEO NARRATION. Your voice is perfect, not too slow, not slurred and not too fast, it doesn't bore me as you add some emotion every so often. Love it.

[@TempoDrift1480]

Wild to think someone came up with that concept out of thin air.

[@theunderrated86]

Thanks for the explanation. Short, concise, and to the point.

[@WillN2Go1]

Brilliant demonstration, model, explanation. (Even with the error) Thank you.

[@paulsullivan3291]

Great video! Thanks for taking the time and follow up to your informative video!

[@alancordwell9759]

Thank you for that very clear explanation!

[@MrChrisKnowlton]

Very well done! I always wondered how the secondary linkages worked.

[@TheDIYScienceGuy]

Best explanation of this system ever! Thank you so much!

[@VK-xw4yz]

Best explanation of the mechanism available on the KZbin ! Thank you so much sir for uploading !!!

[@BLitwin]

You are most welcome

[@SammoKarm]

Absolutely brilliantly explained, well done.

[@gervaissawyer4779]

Excellent. Really clear explanation. Just makes you appreciate what a clever guy Walschaerts was.

[@BLitwin]

Glad it helped!

[@Rayo_Rob_No.17]

Nice model, I appreciate this, I will share it with my friends who "don't get" steam engines. Like your self, I grew up loving steam locomotives for the simple fact, I love watching the drive wheels and rods. They truly were a genius design and, I try and see them run, when excursions happen. I don't live too far from Santa Fe 3751, she's a special treat to see out on the high iron.

[@HalfKaztBoy]

After all the steam engine videos I watched, it was yours that made the most sense

[@Gator_Bait_Motorsports]

Very interesting. I always wondered what all the linkages did, now I know. Thanks for the very clear explanation :-)

[@jackspink2676]

Thank you!! I have wondered just how steam engines reversed direction for a long time and now I finally know!!! Great vid!