Steam locomotive valve gear

[Anonymous]

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

[M636C]

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

[TomDiehl]

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.

[timz]

"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.

[Anonymous]

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

[TomDiehl]

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: Originally posted by marknewton


The main difficulty was in properly lubricating the valves. The temperature of superheated steam was well above the flashpoint of the mineral oils in use at the time.

Um...oil can't burn when surrounded by steam, only in the presence of oxygen molecules, so the steam temperature doesn't really matter as far as the oil burning. Consider these two locomotives: Grizzly Flats Railroad (ex-Nevada Central) no. 2 and Ventura County Railway no. 2. GF no. 2 was built in 1881, Baldwin 5575, has slide valves and is not superheated. Ventura County Railway no. 2 was built in 1922, Baldwin 55415, and has piston vavles and is superheated. They both use Nathan hydrostatic lubricators, both using steam oil, also known as valve oil (as opposed to journal oil).

Sincerely and respectfully,
Daniel Parks

Two last points, the oil wouldn't necessarily burn in the common sense, it would vaporize. And vaporized oil would lose most of its lubricating properties. The other question to ask, is the Ventura County engine using the original type oil it was designed to use, ot is it using a newer type? As stated above this is a GENERAL rule.

[Anonymous]

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

[M636C]

QUOTE: Originally posted by marknewton

QUOTE: Originally posted by M636C

The two Pacifics were 3.1249 and 3.1250 which were built as experimental four cylinder compounds with poppet gear, one with Caprotti and one with Dabeg gear (if my memory is correct). The rebuild used the standard cylinders and valve gear from the 2-8-2s, thus making them two cylinder simples. While there were high hopes for these locomotives, they were not regarded as highly as the standard 3.1200 and no more were converted. I think one of these two was displayed at Paris Nord with Gresley's 2001 "**** o' the North" (another locomotive with experimental vave gear) during its period in France.

Well, there you go! I wasn't aware that "**** o' the North" had been in France, either. That would have been something worth seeing. How long was it there?

QUOTE: I think De Caso used the Cossart gear in conjunction with poppet valves on the three cylinder simple 232S class Baltics (or Hudsons, I can't remember which name they had), but this may have been changed later.

Yes, they were the engines I had in mind when replying previously. As far as I 'm aware, they were referred to as "Baltics" - the preserved 232U1 at Mulhouse is labelled as such. Now there's another magnificent loco - I'd happily trade my granny for a day on the footplate of that engine!

All the best,

Mark.

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 of the Ian Allan book "French Steam" with photographs by Yves Broncard and Felix Fenino (1970)? The final photograph is of 232U1, 232R001 and 232S001 coupled together running light on their withdrawal on 9 October 1964. 232R001 still has the Cossart valve gear.

Peter

[daveklepper]

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.

[Anonymous]

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

[Anonymous]

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?

[Tim Burton]

Do you have a picture of the two?

[Anonymous]

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

[daveklepper]

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?

[Anonymous]

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

[BigJim]

Here is a link to a neat program about valve gears.
http://www.alaska.net/~rmorris/als2.html

[daveklepper]

Which railroads used the Baker valve gear other than the NYCentral and its subsidiaries? The standard USRA WWI locomotives used Walschearts and locomotives were built to these patterns right up through WWII, Baker must have been in the minority. But I know others used it. Who?

[marknewton]

QUOTE: Originally posted by trainjunky29

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.

There is a very real problem. High temperature steam is a very effective cutting tool. With superheated steam the large flat surfaces of the slide valve quickly cut and score. Exacerbating this is the inability of the oils in use at the time to withstand high superheat temperatures. They broke down and lost their lubricant properties, further damaging the slide valves. But don't take my word for it, read any of the contemporary trade journals and literature. Also, note the number of different piston valve adapter/conversions used on slide valve engines after they were superheated. If slide valves could be used successfully with superheat, these would have been superfluous.

QUOTE: Um...oil can't burn when surrounded by steam, only in the presence of oxygen molecules, so the steam temperature doesn't really matter as far as the oil burning.

Oh? The oil doesn't need to burn to lose it's effectiveness as a lubricant. The steam temperature matters vitally if it is above that at which thermal degradation occurs in the grade of oil you're using. There was a large body of development work carried out over the years by the oil manufacturers to perfect an oil that could withstand the superheat temperatures of around 800 degrees typical of modern steam locomotives. If steam temperature didn't matter, why did they bother?

QUOTE: Consider these two locomotives: Grizzly Flats Railroad (ex-Nevada Central) no. 2 and Ventura County Railway no. 2. GF no. 2 was built in 1881, Baldwin 5575, has slide valves and is not superheated. Ventura County Railway no. 2 was built in 1922, Baldwin 55415, and has piston vavles and is superheated. They both use Nathan hydrostatic lubricators, both using steam oil...

Yeah, and they would have used - maybe still use, are they currently operable? - differing grades of steam oil in those lubricators when running. Until 2003, I was the travelling fitter responsible for the care and maintenance of a 1915-built saturated engine, and a 1943-built superheated engine, amongst others. I can tell you from experience that the two engines use oils of quite different specification, and that the two were not interchangeable. If you're interested, contact me direct and I'll happily discuss it futher.

All the best,

Mark.

[marknewton]

QUOTE: Originally posted by daveklepper

Can anyone do a good job of explaining the basic differences between the two "conventional" valve grear systems used on North Americqn locomotives, the Walschearts and the Baker?

The significant difference is that Baker uses a bell crank rather than a link to alter cut-off and reverse the loco. It will permit valve travel of up to 9", and has good valve events with constant lead. The advantage over Walschaerts is that all wearing surfaces are pins and bushes, making maintenance cheaper and simpler.

QUOTE: As I remember, nearly all PRR locomotives used Walschearts and nearly all NYC Baker. Why?

I couldn't say, other than to note that Baker valve gear was proprietary, being a product of the Pilliod Company. Perhaps the Pennsy were unwilling to pay royalties and/or a license fee for it's use?

[marknewton]

QUOTE: Originally posted by M636C

The two Pacifics were 3.1249 and 3.1250 which were built as experimental four cylinder compounds with poppet gear, one with Caprotti and one with Dabeg gear (if my memory is correct). The rebuild used the standard cylinders and valve gear from the 2-8-2s, thus making them two cylinder simples. While there were high hopes for these locomotives, they were not regarded as highly as the standard 3.1200 and no more were converted. I think one of these two was displayed at Paris Nord with Gresley's 2001 "**** o' the North" (another locomotive with experimental vave gear) during its period in France.

Well, there you go! I wasn't aware that "**** o' the North" had been in France, either. That would have been something worth seeing. How long was it there?

QUOTE: I think De Caso used the Cossart gear in conjunction with poppet valves on the three cylinder simple 232S class Baltics (or Hudsons, I can't remember which name they had), but this may have been changed later.

Yes, they were the engines I had in mind when replying previously. As far as I 'm aware, they were referred to as "Baltics" - the preserved 232U1 at Mulhouse is labelled as such. Now there's another magnificent loco - I'd happily trade my granny for a day on the footplate of that engine!

All the best,

Mark.

[daveklepper]

Can anyone do a good job of explaining the basic differences between the two "conventional" valve grear systems used on North Americqn locomotives, the Walschearts and the Baker? As I remember, nearly all PRR locomotives used Walschearts and nearly all NYC Baker. Why?

[M636C]

The two Pacifics were 3.1249 and 3.1250 which were built as experimental four cylinder compounds with poppet gear, one with Caprotti and one with Dabeg gear (if my memory is correct). The rebuild used the standard cylinders and valve gear from the 2-8-2s, thus making them two cylinder simples. While there were high hopes for these locomotives, they were not regarded as highly as the standard 3.1200 and no more were converted. I think one of these two was displayed at Paris Nord with Gresley's 2001 "**** o' the North" (another locomotive with experimental vave gear) during its period in France.

I think De Caso used the Cossart gear in conjunction with poppet valves on the three cylinder simple 232S class Baltics (or Hudsons, I can't remember which name they had), but this may have been changed later.

Peter

[marknewton]

QUOTE: Originally posted by M636C

While Cossart Valve Gear was suitable for operating poppet valves, Cossart valves were vertical piston valves operated by camshafts.

Sorry, I should have made that distinction in my previous post. [:)]

QUOTE: This valve gear was extensively used by the French Nord (Northern) Railway and by the SNCF Northern Region. Two Pacific locomotives were rebuilt with this valve gear, but it was mainly used on a series of 2-8-2 tank locomotives for Paris suburban service.

I wasn't aware of the two 4-6-2s. What were they? I was mainly aware of Cossart valves/gear from accounts of the Algerian passenger Garratts - now there's an engine!

[M636C]

While Cossart Valve Gear was suitable for operating poppet valves, Cossart valves were vertical piston valves operated by camshafts. This valve gear was extensively used by the French Nord (Northern) Railway and by the SNCF Northern Region. Two Pacific locomotives were rebuilt with this valve gear, but it was mainly used on a series of 2-8-2 tank locomotives for Paris suburban service.

The difference is of course, that piston valves admit steam by opening ports in the valve liner, while poppet valves actually close on a seat. Thus the piston valve can remain in continous motion while the poppet valve must stop with some force. The poppet valve can easily provide a larger port area, of course.

The valve gear was adjusted electrically, and the vaves could be set in in open posion for coasting with minimum resistance. Not the simplest solution, but the gear had the distinctive feature of the drive rod having a large mass at the valve gear end, and thus a taper in the reverse direction. This mass allowed the cross balancing of the reciprocating mass of the rods, to some degree.

Peter

[marknewton]

QUOTE: Originally posted by marknewton

QUOTE: Originally posted by tree68

All I know about valve gear is what I read in the Trains article a few years ago. IIRC there is a third type of valves - poppets, roughtly analogous to the valves in an internal combustion engine. I should think that the difference between the timing of the intake and exhaust sides might be a little easier to adjust with them.

Feel free to point out the errors in my assumption.... Always glad to learn more.

You're quite correct - Franklin oscillating cam poppet valve gear allowed for the independent control of admission and exhaust. This valve gear was used on Pennsy T1 #5511, amongst others.

Adding to this, Caprotti (Italy), Cossart and Renaud (France) poppet valve gear, all allowed independent control of admission, exhaust and cut-off.

[daveklepper]

Note that my comment about slipping at high speed and its correction was verified by the Pennsy T-1 thread. From what I understand, both on the T-1 and on certain British 4-6-2's, the management wanted short cut-off for fuel economy, but in certain conditions, engineers found these locomotives were prone to slipping at hight speed, and by reducing throttle and maintaining speed by longer cut-off at the same time, slipping was controlled better. If I am mistaken correct me.

Of course, it is really the reduced throttle setting the reduces slipping, but then the longer cut-off is required to maintain power and thus maintian speed.

Again, if I am not correct, please make the necessary correction.

Otherwise, I appreciate all the comments so far and hope there will be more!

[Anonymous]

Get a copy of THE ARROW, the magazine of the N&W Historical Society, from November/December 2002. The valve gear article therein is an updated and expanded edition of the story that appeared in TRAINS back in 1984. It does not cover poppet valves, but everything the casual railfan needs to know about slide and piston valves and the mechanisms that drive them.

Back issues of THE ARROW are available from the N&WHS website.

Old Timer

[Anonymous]

QUOTE: Originally posted by TomDiehl


Cutoof is controlled by the position of the Johnson Bar or reverser wheel (depending on which the loco has). Cutoff normally is adjustable from 15% to 85% of the stroke.

Steam admitted during the longest part of the stroke will provde the most power, but the same quantity of steam must be exhausted causing back pressure. The back pressure will limit the top speed of the locomotive at the given cutoff setting. A quicker cutoff will admit less steam and give less to exhaust allowing for higher speed.

Another general rule, slide valves won't be used with a superheated engine. The piston valve became more popular, even on saturated steam engines because they were easier to service, repair, and fabricate. All machine shops have at least one lathe.

Just to nitpick, the 85% cutoff figure makes sense, but cutoff can go down to 0% when the reverser is in the center.

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.

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.

QUOTE: Originally posted by marknewton


The main difficulty was in properly lubricating the valves. The temperature of superheated steam was well above the flashpoint of the mineral oils in use at the time.

Um...oil can't burn when surrounded by steam, only in the presence of oxygen molecules, so the steam temperature doesn't really matter as far as the oil burning. Consider these two locomotives: Grizzly Flats Railroad (ex-Nevada Central) no. 2 and Ventura County Railway no. 2. GF no. 2 was built in 1881, Baldwin 5575, has slide valves and is not superheated. Ventura County Railway no. 2 was built in 1922, Baldwin 55415, and has piston vavles and is superheated. They both use Nathan hydrostatic lubricators, both using steam oil, also known as valve oil (as opposed to journal oil).

Sincerely and respectfully,
Daniel Parks

[marknewton]

QUOTE: Originally posted by TomDiehl

Another general rule, slide valves won't be used with a superheated engine.

Generally, no. The main difficulty was in properly lubricating the valves. The temperature of superheated steam was well above the flashpoint of the mineral oils in use at the time.