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.
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.
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.
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.
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?
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?
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!
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
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