I seen and heard of many different types of valve gear for steam locomotives, like Walschaerts, Baker, Southern, Etc. I know this is a silly question, but why are there so many types? Was some types of valve gear better for different jobs (Walschaerts for speed, Baker for switching, Etc)? Or was simply one type improving on the other?
Lone Geep
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From what I've read that's basically it, one type improving on the others. Also, some 'roads had their own ideas and preferences for various reasons. All the later types you mentioned were pretty good.
lone geep I seen and heard of many different types of valve gear for steam locomotives, like Walschaerts, Baker, Southern, Etc. I know this is a silly question, but why are there so many types? Was some types of valve gear better for different jobs (Walschaerts for speed, Baker for switching, Etc)? Or was simply one type improving on the other?
Every inventor and developer think they have THE BEST idea at the time they present it to the world. That is they way the world progresses it's technologies.
Never too old to have a happy childhood!
By and large, there are two valve gear types you will see on almost any locomotive.
Stephenson gear was invented first, and it is perhaps the first full-function valve gear offering not only forward and reverse but also a range of steam cutoffs during the piston stroke. A long (near 100%) cutoff gives maximum tractive effort for starting or climbing a ruling grade, but it is not energy efficient. A short cutoff (say, near 25%) is much more economical of steam and in turn water and coal use.
Walschaerts gear was invented not that long afterward, but its widespread adoption didn't happen until nearly a half century later.
Both valve gear types use a curved "expansion" link in which tracks a "die block" that is hidden from view. The "reversing link" raises or lower that die block within the expansion link, placing it at different points that move in different directions and by different amounts, effecting the forward/reverse function by changing the direction the die block rocks back and forth inside the expansion link, changing the cutoff of steam to the cylinder by changing the amount it rocks.
The expansion link, in turn, is rocked back and forth by a connection to one of the engine drivers. The Stephenson gear uses a pair of cranks to do the necessary rocking. Traditionally, Stephenson gear is used between the wheels and inside the frames, and those cranks take the form of a pair of eccentrics to drive the gear for each cylinder. Those eccentrics are disks surrounding the axle where the axle runs through each disk off center, and the motion is taken from a band running around each disk.
The Walschaerts gear rocks the expansion link back and forth by a single crank, where the expansion link pivots about a bearing connection to the locomotive frame. To get the correct valve timing with a single crank, the Walschaerts gear has a "combination lever" up by the valve that combines some of the motion of the die block in the expansion link with a small amount of the main piston motion from the crosshead.
The Walschaerts gear became popular when the locomotive designers and railroad maintenance people wanted to move the gear from inside the frames to the outside, where not only can railfans admire the valve gear in motion, but where it is easier to maintain and repair on later locomotive models where the space inside the frames becomes hard to get at.
You could put the Stephenson gear outside, but a double crank is needed (or a double eccentric or a crank and an eccentric -- remember that with steam locomotives there is a prototype, somewhere, someplace, and at some historical time for everything). That takes up width and there may not be that much width available. Also, by using a single outside crank, called a "return crank" in valve gear terminology, in place of a pair of eccentrics, there is less friction and power loss, especially as locomotives got bigger.
Whether every inventor thinks they have the best idea at the time is a kind of call made by each inventor. The Gooch gear is a rearrangement of the Stephenson gear because Daniel Gooch was a rival British railroad pioneer in England and it appears he didn't want to pay patent royalties to the Stephenson father and son. So there are many minority valve gear types, some of them aiming to solve what the inventor sees as a problem with an existing arrangement, some of them devised to circumvent patents.
I have studied the Walschaerts and Stephenson arrangements but I am not that familiar with Southern gear, although I am told that the great 20th century steam locomotive innovator Livio Dante Porta thought the Southern gear was a good choice. L. D. Porta didn't invent the Southern gear, but as a locomotive designer, he thought it was a good choice.
The one "minority gear" that I am particularly interested in is Abner Baker's gear marketed by the Pilliod Company. Baker gear was found on late-model steam locomotives of notably the New York Central (the Niagara had it) as well as the Norfolk and Western (the J-class had it).
The Baker gear does away with the sliding die block inside the expansion link in the Walschaerts and substitutes what could be characterized as an ingenious arrangements of links and simple pin joints (what engineers call "revolute joints").
The Baker gear does away with the wear of the die block along with the manufacturing challenge of grinding the exact curve on both the die block and a track inside the expansion link for the die block to slide. 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 patent royalties may have also impeded its adoption "back in the day" when the patent was in force.
There was a scholarly paper published this Fall in the ASME Journal on Mechanisms and Robotics describing an all-revolute drive for a variable displacement pump, for use in a tractor hydro transmission or other important uses. The drive effects a similar variable cutoff effect as a valve gear, but this pump uses yet something else than the Baker gear. So the subject of variable stroke mechanisms is one of ongoing concern, long after the end of widespread use of steam locomotives.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
BALTACD said, "That is the way the world progresses its tech..."
What made the machines (steam engines) work was the valve's gear's (levers) and other stuff, integrally parts of the mechanical structure.
A different arrangement might make:
more precise control of pulling air thru the firebox to the stack?
another way to control the amount of steam for each cylinder stroke? Valve Pilot?
a way to reduce valve gear maintenance? Yes.
If you can find a copy of John H. White's book about early american steam locomotives he has a lot of info on the development of valve gears before 1900.
If you would like to view many of the various valve gears that have been invented, get a copy of Charles J. Dockstader's Valve Gear program. It contains animations of over 60 different valve gear's with the ability to change some of the parameters so you can adapt or alter a particular gear type to any steam engine. You can speed up or slow down or single step the animations to your heart's content.
This is one place it is available: http://www.billp.org/Dockstader/ValveGear.html
Here is another: http://www.jf2.com/bcwrr/Dockstader-Valve-Gear.html
I am not sure where the latest and greatest version is, but any of them will get you something to "watch" and aid in understanding how they work.
As for the OP's question as to why there were so many types, I think it was a combination of wanting to circumvent patent royalties and "better idea" factors. The physics of moving steam under pressure from one place to another and obtaining work from it is fraught with little problems that get magnified to various degrees in some people's minds and compel those people to try to cure the ills thereof... not unlike people that design automotive engines!
Also, I have some copies of Chas Shane's "The Locomotive Up-To_Date" and the 1890's edition has barely a paragraph about the Walshaerts valve gear, saying it is primarily only in use on the Belgian State Railways, but the 1909 edition has nearly a whole chapter devoted to it, because it is the most prevalent form of valve gear in the world!
Semper Vaporo
Pkgs.
There was a "rotary" valve gear developed around the turn of the 20th Century. One of the issues of "Classic Trains", one I should have kept by the way, had a broadside photo of a Chicago area locomotive taken around the time of the First World War. No, I don't remember the name of the 'road or the valve gear. hence my saying I should have kept the issue. I'm assuming the rotary valve gear didn't live up to expectations. Anyone know anything about it?
If this helps, the photo showed a cylinder on top of the piston housing turned 90 degrees from where you'd normally expect to see a valve casing.
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.)
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!
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.
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!
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
.
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.
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.
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
A Southern engineer named WILLIAM SHERMAN Brown? He may have worked for the Southern, but you can bet he wasn't from the South!
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.
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 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!
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.
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.
.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.
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!
daveklepper .Paul, now we need someone to post a correct diagram for Baker valve 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, 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.
good explanaition
Paul MilenkovicThe linked Web page has it wrong by having the eccentric rod connected to the crank (part number 2, the initial moving part).
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.
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?
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?
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.
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