BigJim Overmod,This the best I can do...
Overmod,This the best I can do...
Now, this drawing shows the arrangement EXACTLY (although I suspect the gear connecting rod as drawn has been moved to the right a bit relative to the reverse yoke in order to show the arrangement of the parts better). THANK YOU, JIM!
Note when I said (pivoted at the center) I meant as a fulcrum. Otherwise the motion of the eccentric at the bottom of the gear connecting rod would not create the proper motion at the top pin joint to the bell crank.
Many a happy hour I have spent tweaking parameters in the DOS version, and then the Windows port, of Charlie's software. Thankfully, it is now available for download in several 'permanent' places.
I asked this question over on RyPN, and I am delighted to note that someone there has scanned the entire Baker catalogue #3 from 1946, and provided it here (PDF download). I encourage anyone who appreciates his doing this to go to RyPN and thank him.
OvermodIn the animated diagram on steamlocomotive.com, as near as I can make out, the swing link depends from the arm of the bell crank, and the top of the gear connecting rod (which ought to attach to the bell crank) is on a fixed pivot in the reverse yoke.
Look closer at the colors-- the gear connecting rod is magenta, top and bottom, and the radius bars are brownish. On the diagram they form a sort of Y, and you've misidentified the legs of the Y.
Overmod,This the best I can do. I think this screen shot shows things a little clearer. Also note that in the program you can change all sorts of parameters, such as speed, amount of cut-off, visual steam, sound and a lot of variable geometry.
.
What follows in others replies is a pretty thorough discussion. Little left to add, but so far no one has mentioned:
1. Unlike diesels, steam locomotives usually were designed for the specific on-site task at hand. What gear was best for one was not necessarily best for others. All had to address the basic problem, which was to set the valves in the cylinder to regulate the cutoff of the steam.
2. No one so far has mentioned the effect that superheating had on the problem. I've always been told that Stephenson only could be used with slide valves, which could not be used once superheating became the standard practice. This explains why Walschaerts took over at the turn of the last century even though it was invented half a century earlier.
3. Why a road preferred one to another depended on several factors. Union Pacific, with its long runs typical of transcontinental bridge routes, liked Walschaerts because it was easy to maintain and easy to teach. And, as UP accumulated more engines, there also was the benefit for having to store fewer kinds of replacement parts. Remember: It was maintenance, not performance which killed the steam locomotive. There were no diesels at the time which could outperform an NKP S-3 or a Fetters 4-8-4.
4. U.P. did experiment with the clever Young gear, which used the motion of the opposite side of the locomotive to set the timing and valve travel. This was sold by the companies as a maintenance improvement; but, in the end, U.P. changed its Young engines (by then mostly 4-8-2s and 2-10-2s) to Walschaerts, again because of the parts-inventory problem and to effect standardization.
5. Of course, U.P. also is famous for use of the Gresley gear, which is needed for three-cylinder engines like the 4-12-2s. UP experimented with substituting a double-Walschaerts on the engineman's side (the "bald-faced" Nines) in an effort to obtain more standardization, but apparently this was not completely successful since not all of the Nines were converted.
6. The Baker is a perfectly good gear, very heavy, so one sees it a lot on big engines in the East. It was more complex and came along much later, so again roads very familiar with Walschaerts and not wanting to accumulate a lot of parts from different systems tended to be averse to using it. Avoiding royalties also may have been a factor, but remember that royalties are only part of the bottom line, which was the critical factor when it came to purchasing new engines. I am told that Baker gear, for being so massive, tends to hold its setting better, but that's just what I'm told.
7. I confess to not being that familiar with Southern gear. It was a latecomer, which apparently hindered its adoption; however, it was billed as an efficiency improvement over the Walschaerts.
In addition to the sources cited by others, infra, valve gears are discussed in Model Railroader's MR Cyclopedia, vol. 1 (Steam Locomotives) and a neat little book all steamers should have: Steam Locomotive Maintenance. (I don't have it at hand at this time and don't recall the author.)
OvermodNo part of the reverse yoke oscillates with the gear connecting rod. As you move the yoke over from forward to reverse position, the radius bars swing independently, with pin F, the fulcrum of the gear connecting rod, moving in an arc at the bottom of the 'swing link' arrangement. Anything that purports to show these links connected to the bell crank, or oscillating fully and directly with the movement of the eccentric, is simply wrong, no matter whether it is interactive or not.
The portion of the valve motion that is of interest is that proceeding from the eccentric rod through the gear connecting rod (pivoted at its center) to the bell crank.
Going back to the linked web site animation, the Gear Connecting Rod is shown in the shape of a backward S "Zig-Zag" with three pivot points. The bottom point connects to the eccentric crank. The top point connects to the bell crank. The middle point connects to the bottom of the radius bars. From this mid-point in the GCR, the radius bar extends up to be connected to the reverse yolk.
Dave,Go back to my first post. The "baloney" part stems from Paul's misconception that the Baker valve gear was a "Minority" valve gear, when in fact it was used by many locomotives. Please read at the bottom of page 9: http://www.railarchive.net/bakervalve/parts_09.htm and the top of page 10: http://www.railarchive.net/bakervalve/parts_10.htm No small number, eh?By the end of steam, Baker and Walschaerts were the majority of valve gears used on mainline locomotives. Also his statement that "no one seems to understand how it works geometrically let alone how to make adjustments to its proportions to get different valve gear "events" is shown to be completely false by the book, that I linked to. That book was written by steam people (who knew and understood exactly what they were writing about) for the education of steam people, firemen and engineers (to name two) wanting to better understand the machines in their charge. It is but one volume of the vast number of volumes published by the International Correspondence School for the education of railroad employees of the day. These books are, in my opinion, the best books available for anyone who is a student of the steam locomotive. The books themselves are hard to come by. However, ICS has scanned many of them for which we should be grateful. They are available online at their web site, which is where my link came from.
I will also say that I never questioned "Prof. Milenkovic's understanding of machine geometry".
Big Jim: Whether you or Paul are correct is beside one point: Paul has remained thoroughly polite in this discussion. The Forum would benefit if everyone did so. Please don't use words like baloney and troll in the future. We all have respect for your vast hands-on railroad experience, and you do not need to belittle anyone who disagrees with you for us to retain that respect. Please keep the conversation polite. Thanks!
BigJimThat is a very good picture and it only supports the fact that the computer animation is correct.
Not to me, it doesn't. Look at fig. 16 in the ICS reference, particularly with respect to pins E and the location of pin F. (Fig. 21A shows the relationship between the gear connecting rod and the 'radius bars' a bit more clearly.) Now look at the section regarding the movement of parts at the reverse yoke (sec. 31) and particularly the arcs drawn in Fig. 33.
No part of the reverse yoke oscillates with the gear connecting rod. As you move the yoke over from forward to reverse position, the radius bars swing independently, with pin F, the fulcrum of the gear connecting rod, moving in an arc at the bottom of the 'swing link' arrangement. Anything that purports to show these links connected to the bell crank, or oscillating fully and directly with the movement of the eccentric, is simply wrong, no matter whether it is interactive or not.
The portion of the valve motion that is of interest is that proceeding from the eccentric rod through the gear connecting rod (pivoted at its center) to the bell crank. What would be nice to have at this point would be one of those 'apprentice models' with all the parts of the gear modeled to scale, and a crank to turn the arrangement and show positions of the components and arcs at the joints for different points on a driver rotation for different degrees of reverse-yoke angle. This would certainly show something different from what is on the steamlocomotive.com site.
I doubt that Charlie Dockstader got this wrong in the original, but without access to a Windows computer I can't pull up the program to see. Can somebody prepare an animated view from his program and provide it here?
Overmod,That is a very good picture and it only supports the fact that the computer animation is correct. As I said, you need to look at the interactive animation where you can change the gear from forward to reverse. I believe Mr. Paul and others are looking at the animation wrong and that is crux of this discussion.
timz Paul MilenkovicThat link another person contributed http://www.steamlocomotive.com/appliances/valvegear.php showing the major types of valve gear has the Baker gear . . . wrong! Offhand I don't see an error. Where is it?
Paul MilenkovicThat link another person contributed http://www.steamlocomotive.com/appliances/valvegear.php showing the major types of valve gear has the Baker gear . . . wrong!
http://www.steamlocomotive.com/appliances/valvegear.php
showing the major types of valve gear has the Baker gear . . . wrong!
He's actually right. Have a look here:
http://www.railarchive.net/bakervalve/parts_60.htm
which is an official Pilliod Co. catalogue picture. It shows the mechanism from the rear, with the swing arms slightly articulated. You can see rather clearly how the motion from the eccentric rod is carried through the bellcrank, and how the swing arms pivot. The top of the 'gear connecting rod' is what attaches to and moves the bell crank; the swing arms depend from the reverse yoke and only 'walk' fore and aft with the motion.
In the animated diagram on steamlocomotive.com, as near as I can make out, the swing link depends from the arm of the bell crank, and the top of the gear connecting rod (which ought to attach to the bell crank) is on a fixed pivot in the reverse yoke.
I would very, very strongly recommend that Prof. Milenkovic's understanding of machine geometry be given some respect, and that at least a modicum of actual fact-checking be undertaken before accusing him of 'trolling' for raising what to me is a valid issue. If the steamlocomotive.com diagram is Baker, it is certainly not the Pilliod Company's Baker.
No doubt we all agree how the locomotive valve gear usually called "Baker" connects:
The eccentric crank is fixed to the locomotive's main crankpin, on the main driver. It connects to
The eccentric rod, which connects to
The bottom of the gear connecting-rod, the top of which connects to
The bellcrank, which connects to
The valve rod, which connects to
The top of the combination lever, which connects to the valve stem.
Is anyone saying the animation in the link above shows something different? If so, at which point?
Paul Milenkovic The linked Web page has it wrong by having the eccentric rod connected to the crank (part number 2, the initial moving part).
Paul,You are doubly full of baloney as you don't know what you are looking at. While you can't do it on the linked web site, if you have the full interactive Baker valve gear computer program, by moving the gear forward and reverse, you can see that it is plainly connected to the proper part and works in the proper manner. Go troll somewhere else.
Paul MilenkovicThe linked Web page has it wrong by having the eccentric rod connected to the crank (part number 2, the initial moving part).
good explanaition
The Baker "gear" is actually the system of links connecting the "eccentric rod" (the link connection to the offset crank on the engine driver) and the "radius rod" (the link connection to the valve). These links that are at the core of Abner Baker's patent replace the die block that can slide inside the curved "expansion link" in the Walschaerts. The Baker valve gear is just like the Walschaerts, only a sliding element is replaced with multiple links containing only "pin" joints.
The heart of the Baker gear is what engineers call a "four-bar linkage", and as the name suggests, it has four parts. Part number 1 is the locomotive frame, part number 2 is the "crank", part number 3 is the "coupler", and part number 4 is the "follower."
When you rotate the crank (part 2), the follower (part 4) also rotates because those two parts are connected by the coupler (part 3).
The motion of the crank and the follower are pretty simple -- each of them just rotates about its pin connection to ground (part 1, the frame or bracket connection to the locomotive). The follower can rotate by a different amount depending on how the coupler connection (part 3) is arranged.
The interesting thing about the four-bar linkage is the "coupler curve." By turning the crank, not only can you get the follower to turn, you can get the connecting coupler link (part 3) to move in interesting and complicated ways. The four-bar linkage is the go-to way of generating "interesting" and complicated mechanical motions in repetitive motion devices. It is the most simple kind of "factory automation" gadget, but there is nothing simple about the possible coupler curves along with the design process to get a desired coupler curve.
Our library has an oversized book, written by a student at MIT, which is an enormous catalog of possible coupler curves, laboriously generated by the graphical methods shown in the article.
What is special about the Baker gear is that the "eccentric rod" (from the driver) is connected not to the crank (part number 2) but to the coupler (the middle moving part, part number 3). The linked Web page has it wrong by having the eccentric rod connected to the crank (part number 2, the initial moving part).
Looking at BigJim's linked article, you cannot initially tell the difference between these two cases. The animation in the Dockstader article shows it clearly.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
daveklepper .Paul, now we need someone to post a correct diagram for Baker valve gear.
.Paul, now we need someone to post a correct diagram for Baker valve gear.
It is in the Dockstader software, which can be downloaded online.
I hadn't looked too deeply into the Southern gear as I have have a research-engineering interest in all-revolute drives, and this gear has a slider-in-a-track.
The difference is that the slider-in-a-track is for the base of the reverser link so it doesn't get nearly as much wear as the die block in a Walschaerts. Apart from that feature, the Southern gear is all-revolute and appears to be contructed from a pair of four-bar linkages.
To the extent that L. D. Porta favored it, it may be simpler to adjust its proportions to get desired valve events.
BigJim What a bunch of BALONY! You obviously haven't read very much about the Baker gear have you? Baker adorned many famous classes of locos that performed extremely well. I'm not going to sit here an list them for you. Go do your own homework!
What a bunch of BALONY!
You obviously haven't read very much about the Baker gear have you? Baker adorned many famous classes of locos that performed extremely well. I'm not going to sit here an list them for you. Go do your own homework!
Thank you for all your help and explanations. I was looking on the internet to see what some of them looked like and came up with this. http://www.steamlocomotive.com/appliances/valvegear.php.
BigJim:
Do you want your baloney on white bread, rye, or a hard roll?
That link another person contributed showing the major types of valve gear has the Baker gear . . . wrong! The correct way is shown in the Charles Dockstader valve gear software program.
The Baker gear contains a four-bar linkage as one of its parts. A four-bar has, four bars or links. One "bar" is the ground connection (locomotive frame). Bar number two is the crank, three is the coupler, and four is the follower. The four-bar linkage also famously appears in Watt's "parallel motion" for his pioneering double-acting steam engine.
The wrong-way Baker drives the four-bar crank from the return crank. I will have to study it again, but a recent article in the ASME Journal of Mechanisms and Robotics on a drive for a variable-displacement pump (as in a tractor hydro transmission) is a "wrong-way Baker."
The right-way Baker drives the coupler from the return crank, and the reverser moves the ground connection of the coupler. A recent peer-reviewed article in a scholarly journal doesn't even consider the "right-way" Baker as a variable-stroke drive. As I said, it is completely ingenious and not-very-well understood.
Lone Geep
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Just to add to the additional locomotoives with Baker gear, I believe all NYC (and B&A) Hudsons, the K3 Pacifics and possibly earlier ones, the Mowhawks, B&A and P&LE Berkshires, and possibly the later Mikes as well.
A Southern engineer named WILLIAM SHERMAN Brown? He may have worked for the Southern, but you can bet he wasn't from the South!
According to the edition of The Locomotive Up To Date that was copyrighted in 1920, the Southern valve gear was invented by a Southern engineer, William Sherman Brown (p. 319).
The Stephenson, Walschaerts, and Young valve gears are also discussed, as well as the Southern gear--complete with instructions for setting each type of gear.
Apparently, rotary valve gear had an extremely limited application at the time this edition was published, since it is not even mentioned.
I do not know just when my father obtained this book, but it probably was of use to him, as he worked in the ACL shops in Tampa. I understand that his last responsibility was operating an overhead locomotive crane.
Johnny
Thank you Overmod. Now that I think about it I believe the photo I saw was of a C&NW locomotive. And I kind of suspected rotary valves didn't pan out too well in locomotive service.
Like I said, I should have kept the issue. I DID keep the big interurban issue. I'm not particularly interested in interurbans but that issue of "Classic Trains" was utterly fascinating.
What the hey, a good scolding to round things out regarding making too broad a claim after an insufficient literature search is par for the course for me at work too . . .
The article indeed discusses graphical techniques for making design changes to the gear, such as to effect changes to valve timing and stroke for different reverser settings. Mathematical/analytical/numerical techniques for making such design changes exist, but as of the early 21st century, they are still an active area of research disclosed in scholarly journals.
Back in the day, the adoption of the Baker gear could have been limited by railroads not wanting to pay patent royalties to the Pilliod Company. But if the operation of the gear, along with how to make design adjustments were well understood, why did the 5AT project, served by some of the top minds in 21st century steam locomotive design, decide to "pass" on it and go with a Walchaerts?
The Baker gear is by far easier to manufacture and maintain than something having a curved die block sliding on a track inside a curved expansion link. The Baker gear, on the other hand, is a far more challenging design problem, the article you have been kind enough to share notwithstanding. You can pretty much decide on how much stroke you get at what reverser setting on a Stephenson or Walschaerts gear by tracing the desired curve in the expansion link. I defy you to come up with an equally simple explanation of how to do that on a Baker gear, even following the article.
The most basic planar curve-generating linkage is the four-bar linkage with one input motion. That linkage may go back to antiquity, but the first modern application was in James Watt's "parallel motion" linkage on his double-acting steam engine invention. Design methodolgies to use the full capabilities of that geometry to control the "coupler curve" have occupied nearly 2 centuries of scholarly writings. The Baker gear is a planar linkage with two mechanical inputs -- the eccentric crank and the reverser -- a yet more complicated problem.
Thank you once again for the link to the article. It looks to be quite useful in my current work.
Paul Milenkovic The one "minority gear"... ...On the other hand, the Baker gear may be too clever -- no one seems to understand how it works geometrically let alone how to make adjustments to its proportions to get different valve gear "events.
The one "minority gear"... ...On the other hand, the Baker gear may be too clever -- no one seems to understand how it works geometrically let alone how to make adjustments to its proportions to get different valve gear "events.
And since you are "particularly interested", take the time to read the following:
http://www.icsarchive.org/icsarchive-org/bb/ics_bb_504d_section_5370_baker_locomotive_valve_gear.pdf
Trains had an excellent article on valve gear in the early '70s. I think it was written by Robert LeMassena (hope that's close) and even a weak minded hoghead could derive valuable knowledge from it. (not much stuck)
In the Apex of the Atlantics, there is a chapter where Pennsy's transition from Stephenson's to Walshaerst's valve motion is discussed. As has been mentioned, locomotives had reached a size beyond the practical limit of a Stephenson arrangement. They first applied Walshaersts on H6b 2-8-0s and were quite impressed with the results. Application on Atlantic class E3d and E2d brought complaints from some of the engineers. They said that these engines were somewhat sluggish compared to E3a and E2a locomotives, which were identical, aside from having slide valves and Stephenson valve gear. This was attributed to Walshaerts valve gear having constant lead, whereas Stephensons has variable lead. I take this to mean that Stephensons not only shortens the valve stroke when "hooking up", but also advances the valve events. Walshaerts can not do that, so a "happy medium" lead is established. This was also one of the modifications L D Porta made to those neat little 2-10-2s way down Argentina land. To improve performance and economy in line of road running, he altered the lead in the valve events, at the expense of performance when running in reverse. This was a good trade, as the locomotives rarely ran backwards, except during switching.
I'm not really sure my concept of lead is correct. Perhaps one of the smart fellers can help here. Thanks in advance!
There were many rotary valve (not rotary 'valve gear') systems tried, the most successful setup probably being the Corliss arrangement (which used spring acceleration to snap the valves between positions).
There is a good side picture of a rotary arrangement applied to a 4-4-2 in Staufer's original Pennsy Power. This used long cylindrical rotary valves (two of them, not one) arranged laterally with one at each end of the cylinder, to give very large port width with quick action, and minimal dead space. (The arrangement also allowed separation of inlet timing and duration from exhaust, to an extent). Problem IIRC was that the seals couldn't be made to live, and lubrication was difficult leading to wear problems comparatively quickly. Drive and cutoff management were done from a more-or-less conventional radial (Walschaerts in the PRR example) valve gear, which drove a wristplate and lever arms.
A substantial part of an early-20th-Century class of C&NW 4-4-2s were delivered with rotary valves straight from the factory. They didn't keep them particularly long. I suspect a C&NW fan knows the full story here.
Implementing proper rotary-valve cutoff was more of a problem on a locomotive than on a stationary engine, which spends much of its time at fairly constant speed and load (for example, driving a mainshaft arrangement in a factory). There was also probably the issue of patent rights, the consequences of a broken accelerating spring, etc., as well as the general difficulty of beefing up the working parts to accommodate larger and larger port areas needed as locomotive size increased in the early 20th Century (the same thing that killed the riding cutoff, Stephenson with normal eccentrics, etc.)
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