Walschaerts Valve Gear Explained

[@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.

[@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]

@@عبدللهبنعبدلله-ن8و 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.

[@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

[@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.

[@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.

[@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.

[@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!

[@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!

[@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!

[@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.

[@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.

[@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.

[@garryferrington811]

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

[@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!

[@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.

[@georgeehmke3283]

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

[@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.

[@tobyLikesTrains06]

I would love to see this as a kit

[@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.

[@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?

[@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.

[@vincenzonovi5528]

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

[@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.

[@bergasms]

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

[@36736fps]

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

[@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😀

[@bigblue6917]

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

[@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

[@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.

[@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

[@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.

[@gedungisphoopnuchle9121]

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

[@cogzoid]

Great demonstration and explanation. Keep 'em coming!

[@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.

[@RickyJr46]

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

[@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.

[@RWBHere]

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

[@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😅

[@lesliedickinson198]

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

[@timault8209]

Thanks for posting this exceptional video. I shall now endeavor to build a full scale model for my living room wall!

[@BLitwin]

Go for it! Send pix

[@callumk5]

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

[@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.

[@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!

[@gervaissawyer4779]

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

[@BLitwin]

Glad it helped!

[@TempoDrift1480]

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

[@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.

[@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!

[@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.

[@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!!👍

[@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!

[@MrChrisKnowlton]

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

[@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.

[@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!

[@rand49er]

Not to cause you more work, but now I'd love to hear a history of the design of the Walschaerts mechanism ... how various improvements were made and how it evolved over time. What components were problematic and what was done to remedy them. I find this fascinating. Thanks for your explanation.

[@BLitwin]

Those kinds of stories are probably lost to the ages, alas.

[@mikado1555]

The curved link was already around and used in Stephenson valve gear. The radius of the link is the length of the radius rod (valve does not move when the valve gear is moved from full forward to full reverse with the piston on front/rear dead center). The movement of the link is derived from the eccentric crank (which returns the link to the same location on front and rear dead center). The eccentric rod connects the motion of the eccentric crank to the link. The backset of the link is to create an equal swing about the vertical plane. The lead and lap lever moves the valve twice the quantity of lap + lead. The union link connects the piston movement to the lead and lap lever. When the valve gear is in center and piston is centered, the lead and lap lever should be vertical and the valve should be centered.

[@kjamison5951]

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

[@Crazystuffyousee]

This video will nowhere ever receive the respect it deserves for being very informative while also being precise and to the point.

[@thematthewexpress5999]

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

[@theeastman9136]

Best explanation I've seen yet and I'm an old man. Thank you.

[@HalfKaztBoy]

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

[@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

[@c182SkylaneRG]

You should update your description: there are no "glaring errors". Your video was spot-on. The neutral position of the Walschaerts gear is not the neutral position of the control piston. You have to move the Walschaerts gear slightly into reverse to neutralize the control piston (and I'm sure that position was clearly marked on the cab controls). Play with your model, and you'll see what I mean. For my part, I really appreciate the color overlay, because at first I thought the control piston was solid and I wasn't sure where the steam was being injected from. :)

[@c182SkylaneRG]

The vertical linkage directly behind the pistons is the key: that rod has one pivot point that does not move, but that pivot point changes location (including beyond the end of the rod) depending on the gearing position selected from the cab. When the Walschaerts gear is placed in exactly neutral, that pivot point is placed at the upper connecting bolt. The control piston is connected at its own bolt a few inches down, and is not stationary in that position. If you put the Walschaerts gear slightly into reverse, you move that fixed position down the rod. At exactly the right amount of "reverse", that pivot point is placed in-line with the control piston's connecting bolt, and the control piston stops moving. Linkages was probably one of the most interesting classes in College. :)

[@PokoleizKuleckim]

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

[@xqqqme]

Very deserving of all the praise you have already received. One suggestion: from the comments, I can tell that most if not all of your audience is already familiar with the hardware. However, I was not...and had no idea what rod was what as you mentioned them. A couple of labels would be helpful for the truly unwashed.

[@michaelXXLF]

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

[@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.

[@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.

[@StonyRC]

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

[@PanzerBuyer]

Great presentation. The designers were truly brilliant!!

[@carbidegrd1]

brilliant! The mind that could assemble such a complex idea is a rare one indeed.

[@SuperIliad]

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

[@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.

[@organbuilder272]

How nicely done, But it should operate in neutral because the pins or pivot points int he conbination arm are offset and still moving. But this is so nicely done. Beautiful model. I think it is one of the best on YT. You explanation is so simple I think almost anyone can somprehend what this strange and fascinating collection of steel bars is all about. I think you are correct when you suggest it was of interest yo you. I think this little subset of pistons and rods is what make the steam locomotive so interesting.

[@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.

[@cfa61]

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

[@VK-xw4yz]

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

[@BLitwin]

You are most welcome

[@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.

[@mellissadalby1402]

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

[@luigicorte]

Finally, a well made explanation!

[@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!

[@schrauberhugo2594]

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

[@grahambird1570]

I did my Apprenticeship on Rhodesia Rails in the 70's on these Motion Gear stats. You're pretty close - Well done !!!

[@gregorymalchuk272]

What valve gear were they using in Rhodesia?

[@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!!!!

[@malcolmabram2957]

Thank you for this. It is somewhat surprising that this running gear is so ubiquitous on so many locomotives, but even on KZbin its explanation is short in supply. One 'addition' as I see it, is at full power the two cylinders are in effect a compound, the top high pressure running cyinder feeding into the lower larger low pressure cylinder before final exhaust. This double expansion gets more work out of the steam, but a the cost of steam. At low power, steam is just run straight into the lower cylinder, as the higher cylinder effectively stops running, giving less work, but also conserving steam. A brilliant design, and difficult to illustrate.

[@simonholyfield3319]

actually, you don't get a double expansion effect. the piston valve (above) is just a valve - it does no work because the steam pressure is balanced - the steam exerts the same pressure on both ends of the valve, in opposite directions, so they cancel each other out.

[@malcolmabram2957]

@@simonholyfield3319 Thank you for clarifying this with me.

[@BillSikes.]

Nice one, i always wondered what all those rods do on steam trains

[@robertramsay5963]

Thanks Brad. I'd never quite figured this out, especially how the reverse would work. Thanks for the clear illustration.

[@BLitwin]

Glad to help

[@BertGrink]

That is such an ingenious solution; it must have taken the inventor a lot of mental effort to figure this out. Mindboggling, i'd say.

[@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!

[@CAMacKenzie]

Mr. Litwin, Thank You for your video! It has sparked a glimmer of an idea, which I will try to pursue. Stay well, you and yours!

[@BLitwin]

Best of luck!

[@weylinwest9505]

Thank you random KZbin recommendations. And you for making this video. And YOU for reading this comment.

[@jirizlamal69]

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

[@jordenconrad8827]

Brilliant demonstration and explanation. Fascinating

[@davesquire4943]

There seems to be some confusion about how the parts all work. The combination lever moves the valve back and forth a fixed part of the piston's stroke; it never opens the valve. This motion is needed because the portion of the valve that covers the steam ports is wider than the ports. If the combination lever opened the valve any amount on its own, there would be no way to put the engine in 'neutral'. The angle of the eccentric does not determine inside/outside admission. If the valve rod connects to the combination lever below the radius rod (as in the model), the engine is inside admission. The confusion is caused because the valve gear may be direct motion or indirect motion. With direct motion valve gear, the eccentric rod moves in the same general direction as the valve. If you change the eccentric from leading to trailing, you change the relative angle 180 degrees. You can get the same 180 degree change by moving the radius rod between the top and bottom of the expansion link. So either leading or trailing eccentric is correct for inside or outside admission; you just have to 'reverse' the direction of the radius rod. In fact, many Garratts are built with one engine with direct motion and the other with indirect motion.

[@BLitwin]

Wow! That's good info, Dave. I should've realized the center position shouldn't open the ports, at all. I'll have to modify my model, now, and add a note to the explanation, above.

[@simonwass6315]

@@BLitwin You can have port opening with the gear in mid position, it provides what is called lead (not the metal!). You need lap and lead movement which is provided by the combination lever, any extra valve movement comes from the expansion link. Stephensons gear has a habit of causing negative lead at small cut offs.

[@stephenwiseman1816]

Some good information here! Can I also add, regarding lap and lead steam, as has been said for lap it is necessary to have valve heads that are wider than the valve ports. I know that on the miniature loco's that both my dad and my brother have built, the valve heads are twice the size of the valve ports themselves. Furthermore, it was always my understanding that when the valves are sitting central over the valve ports, the outside edge of the valve heads (the exhaust side on inside admission) are just about closing the valve ports on both ends, i.e. the outside edge of the valve head is inline with the outside edge of the valve port.

[@hackenbush23]

The combination lever moves the valve lap + lead, hence the name combination lever. For one complete stroke of the piston, the combination lever moves the valve (lap + lead)x2. This movement occurs no matter where the die block is in the link and opens the valve the lead amount even in mid gear. This crosshead derived motion is referred to as the 'The short' travel. The 'long travel' is derived from the return crank, which is 90 degrees out of phase to the combination lever, and is what opens the ports beyond any lead. This also applies to Baker valve gear.

[@hackenbush23]

@@stephenwiseman1816 What you refer to is exhaust clearance if there is a gap between valve and port on the exhaust side, if there is no gap and the valve is directly in line with the port this is 'line on line". If the valve extends over the port on the exhaust side this is exhaust lap, very rare on locomotives though.

[@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.

[@ratheonhudson3311]

I agree, it's an amazing work or engineering and steam engines give a feeling of being alive, more than any diesel or electric does. Also, thank you for this detailed explanation. I didn't know how these worked

[@peterallam6494]

20/5 23, An original form of Variable Valve Timing with equal importantance as the invention of steam power. Many locos were later modified to include this device & improve efficiency. Your demo' illustrates how a simple design addition can increase performance using less fuel. Appreciate your explanatory technique !

[@gregmead2967]

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

[@marksherrill9337]

Both simple and brilliant and beautiful to watch.

[@major_nobody311]

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