Here is a link to a neat program about valve gears.
http://www.alaska.net/~rmorris/als2.html
daveklepper -
N&W used Baker exclusively after the delivery of the Z-1 2-6-6-2s in 1912. There are railroads that didn’t like Baker because it was patented and they had to buy it from the Pilliod Company. Poor old Egide Walschaerts’ patent ran out in the 1800s, so anybody could design and build examples of his gear for free.
N&W didn’t like Walschaerts because of the link blocks; they had some 4-6-2s and 4-8-0s built in 1907 with an unfortunate design of Walschaerts which aggravated link block wear.
The Southern Railway was the opposite, replacing Baker on everything that had it except 0-8-0s and 2-8-8-2s. They claimed that Baker tried to go into reverse at high speeds. N&W ran as high driving wheel RPM as anybody, and never had that problem.
Old Timer
I am not certain that I understand how it could try to go into reverse at high speeds. Unless the thing was out of adjustment or maintenance had been slack and there was too much loose motion. But wouldn’t that be noticed by the cut-off constantly changing before the big problem arose?
daveklepper -
It seems to have been the custom among engineers all over the South, and probably elsewhere, too, to operate the engines hooked up as high as they could get them. I know folks on the Southern and Norfolk and Western that ran this way, and some that even drifted engines this way. This is begging for hot main rod back ends, and I’ve seen these on N&W engines and Southern excursion engines.
This problem was so prevalent on the Central of Georgia that when they ordered their 4-8-4s, they blanked off several notches either side of center on the quadrants in the cab, so that the reverse lever couldn’t be latched that close to center.
When you run an engine like this, it doesn’t take much slop in the reverse gear mechanism to get a Baker yoke over into reverse position - remember, it doesn’t have to go to the back corner to get bad results, it just has to go a few notches. But rather than get the engineers to change, Southern changed valve gears. Of course, this wasn’t the only strange thing Southern did with steam locomotives.
I’ve heard all kinds of arguments in the Baker vs. Walschaerts battle, but it all comes down to the preference of the railroads. If Walschaerts was so much better, why did NYC and N&W and C&O and NKP and ERIE prefer Baker? If Baker was so much better, why did PRR and SRy and ATSF and SP and UP, etc., stick with Walschaerts?
I’m loath to argue against anything N&W did with steam engines, mainly because their operating results (Gross Ton Miles per Train Hour Per Dollar) using steam were better than just about anybody else in the world.
Mechanically, I prefer Baker.
Aesthetically, I prefer Walschaerts. To me, it was just prettier on an engine.
Old Timer
Do you have a picture of the two?
Some UP Mountains and a small group of 2-10-2’s had Young valve gear. It’s driven by a single link connected to the crosshead and there’s no eccentric crank… There appears to be a bellcrank near the front, but I’m not sure how it works. It was never removed and some of the last 2-10-2’s on the system had it, so UP was apparently satisfied with it, but not enough to use it on anything else. Does anyone know the story on this one? Did any other railroads use it?
Young valve gear was predicated on the premise that since the drivers on one side were 90 degrees from those on the other, why not drive the valves on one side from the motion on the other, and eliminate the eccentric cranks. It was a worthy idea but its translation into reality was complicated, with a lot more wear points than other gears.
There is no bell crank in the valve gear; the motion from one side of the engine (taken from the crossheads) drove, through transverse shafting, the valve on the other side. Connected to the crossheads by long union links, the Walschaerts-style links functioned the same as those on a regular Walschaerts locomotive; the radius rods from the links drove rockers located on the ends of the transverse shaft (there were inner and outer shafts on a rod and sleeve arrangement). Lead motion was taken from the top of the links and transmitted to a combination lever located on top of the rockers. The valve rods were connected to the combination lever.
UP still has a 2-10-2 - the 5511, I think - that’s Young-equipped. It was located in Cheyenne the last time I was there, which was about 30 years ago.
There were CP Pacifics with Young gear and probably some other examples, but none come to mind just now.
Old Timer
Asthetically, the Baker gear on the NYC Hudsons looked fine to me.
And I agree that the N&W was absolutely tops in all steam locomotive design. The Y’s and A’s were the most efficient articulateds and the J the most efficient and best designed Northern. I still rate the J as one of the best streamlined steamers, along with the quite similar Daylight (very different in paint, fo course) and NYNH&H I-5.
The class P2 2001 was in France for about three weeks from December 1934, during which time it was tested on the stationary test plant at Vitry and was given some controlled road trials hauling brake locomotives. Oliver Bullied accompanied the locomotive to France and Gresley joined him for the trials. The exhibit at Paris Nord occurred at this time.
I was wrong about the class of 4-6-4, the three simple locomotives were class 232R, the four standard compounds being class 232S. Are you aware
daveklepper - I disagree about the valve gear on the Hudsons; I think the originals with the Walschaerts looked slicker. Part of it was the motion of the eccentric rod as the wheels rotate.
Similarly, I think the Southern Railway’s Ps-4 Pacifics and Ts-1 Mountains looked a lot better after their original Baker was replaced with Walschaerts. (Only the last five Ps-4s, 1405-1409, were built with Walschaerts.)
I say this even with the feeling that mechanically, the Baker was the better gear.
Old Timer
[quote]
QUOTE: Originally posted by trainjunky29
Just to nitpick, the 85% cutoff figure makes sense, but cutoff can go down to 0% when the reverser is in the center.
Not sure what steam theory you’re working with, but based on my experience in the backshops at Steamtown, the mechanical practicality of the real world of steam locomotives, once the reversing quadrant reaches a certain point near the center, the valve no longer moves far enough to allow steam into the cylinder, hence the 15% figure.
Also, while it is true that back pressure slows down an engine, in any cutoff position, the force of the forcing steam will be much greater than that of the exhaust steam. Given an infinte amount of steam, maximum speed would be found with the reverser all the way forward or back. The only reason to bring the reverser back is to conserve on steam, since at high speed you would otherwise quickly lower your steam pressure.
Again, not sure of what theory you’re quoting, but that “infinite amount of steam” needs to be contained and controlled through valve(s) and piston(s) to be converted into mechanical energy. The steam passages through the valve for steam admission or exhaust are about the same size, since the pistons are double ended, so the volume of the steam does become a factor. In the real world, the reverser being at either limit will severely limit your maximum speed, not allow maximum speed.
About the slide valves and superheating, there is no real problem (as far as I know) with slide valves on a superheated engine. It seems to me that this is the case simply because piston valves were widely adopted before superheating was.
The main problem was lubrication, as stated above. A slide valve was basically a plate with passages cast or machined into it, maiking it more difficult to lubricate than a piston valve
[quote]
QUOTE: Originally posted by marknewton
The main difficulty was in properly lub
Looking at the shortening of the cutoff question, trainjunky said that, given an infinite steam supply, maximum speed will be attained with the reverser in the corner.
This is not true. The steam is expanded during the power stroke; with full valve travel, the expansion is less than it would be with the travel reduced. Shortening the cutoff of the valve allows less steam to be admitted, but the steam utilizes its power and loses heat by expanding more. A smaller weight of steam does more work. If this is not true, why use steam? Compressed air would, under that thinking, do the same work.
Not only would full valve travel not produce higher speed because of the steam question, you’d have a much larger quantity of steam to exhaust during the time the port is open on the other end, causing more back pressure. If you are using less steam on the power stroke but allowing it to expand, you have less steam to get out of the cylinder before the next power stroke, during the port opening for exhaust. Your back pressure is going to be much less.
There were two reasons why slide valves went out of fashion. First was the difficulty of lubricating them and the fact that steam pressure had a mechanical effect on them, pressing them into their seats. The second was that port area was limited, because of clearances and the limited width available for the seats. The piston valve ports were all around the circumference of the valve. And steam had no mechanical effect on the operation of the valve.
Old Timer
“cutoff can go down to 0% when the reverser is in the center.”
Remember that Walschaerts (and Baker?) is a constant-lead gear-- so the valve is always open at the end of the piston stroke, and cutoff is never zero.
The term “cutoff” in this example means that the steam flows for a certain percentage of the stroke, then the valve cuts it off. A zero cutoff would be a mechanical impossibility.
I have been told that Baker Gear, and Southern valve gear which was in some respects similar to Baker, required less maintenance effort than Walschearts gear.
Southern gear looked more clumsy, and wasn’t used as much as Baker. I was told that the long hanging arms of the Southern gear could at times get an alarming swaying motion, although I don’t know if this resulted in the gear impacting the connecting or coupling rods. That story related to the first test run of Queensland Railways experimental 2-6-2 locomotive, the only one on the system with Southern valve gear.
New South Wales had 120 2-8-0s fitted with Southern gear, the remaining large 2-8-0s having inside “Allan straight link” valve gear, a variation of Stephenson gear with a straight expansion link (which was much easier to machine).
A problem related by a senior engineer was that the Southern gear gave so little trouble that nobody ever looked at it, and the first sign of trouble was one of the major shafts failing and the valve gear falling off. This may be an exaggeration but the locomotives fitted with Southern gear kept it for their entire lives, even after Walschearts became common on later types.
The 2-8-0s with Southern gear could certainly run faster than those with inside gear, although this wasn’t actually permitted. I’m sure that the outside gear got better attention than that inside, given the relative ease of access, even if it didn’t need much.
Peter
The radius hangers and transmission yokes of Southern valve gear were designed with a wide enough base at the top (especially the transmission yoke - the forward of the two vertical members) that getting out of line laterally far enough to contact the main rod was not going to be a problem. The bell crank had two horizontal members, far enough apart(one inside and one outside of the valve gear hanger) to give the necessary stability to the transmission yoke.
The Southern gear required a long eccentric throw because the leverage inherent in the gear reduced the eccentric motion so much that even a 6-inch valve travel required a lot of movement to work with. That long throw gave the impression at speed that the stuff was going to fly off the engine. But it seldom, if ever, did . . .
In Southern steam excursion’s early days, I worked on both the little Consolidations - the 630 and 722 - that were equipped with Southern gear. They ran just fine. The valves were square and stayed that way.
Old Timer