.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.
Offhand I don’t see an error. Where is it?
Dave,
If you would go back to the link that I provided (on page 1 of this thread) and take the time for it to load, then scroll down, you will learn all that you need to know about Baker valver gear.
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, labo
good explanaition
You’re saying the animation at the link doesn’t show Baker valve gear. Are you saying it doesn’t show the gear on steam locomotives that’s usually called Baker gear? Or are you saying the animation correctly shows the locomotive gear that everyone calls Baker, but strictly speaking that gear isn’t Baker?
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.
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?
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.
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.
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?
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!
There is nothing in the animation that even suggests that the reverse yolk oscillates with the gear connecting rod. Also, there is nothing to suggest that anything other than the gear connecting rod is connected to the bell crank.
Because the same color seems to be used for the GCR & Radius Bar, this is where I think people may be getting confused by the linked web site animation. The gear connecting rod is not "pivoted at its center to the bell crank.The gear connecting rod is connected to the bell crank at its upper end. The gear connecting rod is pivoted near its center with the radius rods only. The gear connecting rod and the interaction of the radius bars is better shown in the full animation when the gear is in full reverse in that each part is well separated for clear viewing.
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.
What follows in others replies is a pretty thorough discussion. Little left to add, but so far no one has mentioned:
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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.
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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.
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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.
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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.
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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 mor
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.
Easy to make that mistake-- the colors don’t help-- but if you look again you’ll see the animated diagram is correct, like BigJim said. What you think is “the top of the gear connecting rod” is actually the top of the radius bars that suspend the gear connecting rod.
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.
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.
For your information, animation of Baker valve gear on N&W J 4-8-4: https://www.youtube.com/watch?v=FX3WJW-nlh4&feature=youtube_gdata_player
Can you pass a place along that works? I found out that only two of my downloads from years ago still work and both of them are Baker. An email to Mr. Dockstader was returned and his downloads won’t download for me.