Compound Mallet Question

Jamie, the effective control issue is at the heart of the late Chapelon proportioning reservoir. The operating principle is to equalize both the supply and pressure of the steam going to the LP pistons, precisely so that the variation can be minimized to the point you don't need an Ecole Polytechnique degree to run the thing. (Don't be fooled by the way French compounds traditionally required tinkery fiddling to run them! This was different...)

Long and well-established practice proves compounding has advantages with high-pressure steam; advantages with low-pressure steam are there too IF your valve gear doesn't assure long expansion to near-atmospheric pressure in a single cylinder and stroke. Over the full range of operating cutoff and steam mass flow. As you point out, though, it isn't thermodynamic efficiency that rules at the end of the day; it's overall cost per ton-mile, and in-service readiness and reliability.

There are reliable ways to fix a Holcroft/Gresley conjugated v.g. so it works reliably with minimal slop. Neither the Americans nor the British used them. The principal problem with inside-cylinder engines is much more related to cranks and big-end maintenance than it is to valve-gear problems, particularly if you're using cam-activated poppets.

I'm tempted to note that KISS doesn't always produce the lowest cost or the best-operating alternative. Remember that track geometry is part of the cost of running a railroad. There are reasons other than MU and General Motors conspiracies why diesels can make better locomotives... even though more complex and expensive...

I'm tempted to add something: The Dilworth EMD philosophy was to design ONE locomotive, then modify it as little as possible for the railroad situations it had to deal with. The USRA committee chose the minimum number of standard designs that it felt could get the job done nationwide (leaving only truly special situations open). Seems like that's been the successful approach to locomotive building and dieselization. Even attempts to make "locomotives" via combinations of semipermanent drawbars didn't work as well as the 'MU unit' concept...

Cabless units or their contrapositive, the road slugs, are special cases... but how many of their parts are in common with other diesels? Not special incompatible designs customized... and all too often crippled for other purposes, even on the same railroad, in the process.

Overmod -- someday maybe I'll completely understand the late Chapelon system; it did seem to work and produce decent results! Thanks for some clarification! But the older French compounds... !

The advantages of compounding are what drove shipping to triple and quadruple compounding. They are very real, and I think we all agree on that.

And yes, centre cylinder cranks and big end problems were probably the major factor there; three cylinder engines have certain interesting attractive points.

Quite right about KISS not being the only factor -- by any means! But it sure helps... and, one might note, that it is, in a very real way, the philosophy behind Dilworth and EMD's standardization. It was simple and standard.

HA HA Oldtimer, your response is just like I expected from a jealous N&W fan who spends too much time in the trailer park watching Jerry Springer reruns. I doubt those clowns in Roanoke actually designed anything on their own. Inbreds can't think that much. They probably got the designs from Lima or Baldwin by trading moonshine for them.

By the way, as far as eastern locomotives go, the C&O Allegheny was way better than the underpowered crap the N&W had. I bet it just burns you up that the J was no match for a NYC Niagara either. You have spent the last 40 years fuming why nobody likes your hillbilly railroad.

But anyway, have a nice day.

UNION PACIFIC RULES THE RAILROAD WORLD

NORFOLK SOUTHERN "THE INBRED OF TRANSPORTATION"

Quoth Overmod, speaking of the tests of the N&W J on the PRR: "Note that what failed at 115mph on the PRR test plant was the valve drive, and THAT was probably due to unbalanced forces on the valves -- poppets, for example, would have fixed the problem there, even if they introduced other issues elsewhere..."

According to the N&W guy who was on the engine when it failed (the 610), the valve froze in the cage due to lubrication failure. When the engine was hauled back to Roanoke and the cylinders and valve chambers opened up, the liners were colored yellow. It was felt that some component of the PRR boiler water didn't agree with N&W lubricants. But there was no failure of the engine due to design or production problems.

Mr. Big Ol' UP Man: If you would remove your head from your nether aperture, learn to read, and go through the literature you'd find some surprising (to you, anyway) data about the 2-6-6-6 and its comparison to the N&W 2-6-6-4. The data is out there; all you have to do is read it, and I'm not going to trouble this list with repeating it.

I did ask you for some data to compare UP's performance with N&W's, but I see you'd rather blather than do the research - oh, I forgot - you'd have to learn to read.

But I remain,

Your buddy, the Redneck Hickabilly Trailer Trash Old Timer.

Oh, yes - being president of the UP today is like being Emperor of the North Pole. But I guess you don't remember Lee Marvin and Ernest Borgnine, either . . .

Quoth Overmod, speaking of the tests of the N&W J on the PRR: "Note that what failed at 115mph on the PRR test plant was the valve drive, and THAT was probably due to unbalanced forces on the valves -- poppets, for example, would have fixed the problem there, even if they introduced other issues elsewhere..."

According to the N&W guy who was on the engine when it failed (the 610), the valve froze in the cage due to lubrication failure. When the engine was hauled back to Roanoke and the cylinders and valve chambers opened up, the liners were colored yellow. It was felt that some component of the PRR boiler water didn't agree with N&W lubricants. But there was no failure of the engine due to design or production problems.

Mr. Big Ol' UP Man: If you would remove your head from your nether aperture, learn to read, and go through the literature you'd find some surprising (to you, anyway) data about the 2-6-6-6 and its comparison to the N&W 2-6-6-4. The data is out there; all you have to do is read it, and I'm not going to trouble this list with repeating it.

I did ask you for some data to compare UP's performance with N&W's, but I see you'd rather blather than do the research - oh, I forgot - you'd have to learn to read.

But I remain,

Your buddy, the Redneck Hickabilly Trailer Trash Old Timer.

Oh, yes - being president of the UP today is like being Emperor of the North Pole. But I guess you don't remember Lee Marvin and Ernest Borgnine, either . . .

Overmod

Thanks for the very informative reply on back pressure and MU'ing steam. I knew it wouldn't be easy and that someone probably tried it. Regarding drafting and front end design, it's my impression it was often a complex compromise that goes back to the particular fuel used and it's one thing that kept the mechanical departments busy tailoring steam locos to each road. Many of the USRA standard designs ended up as oil burners on the western roads. A telling example from the N.P. book I have is the Timken engine. At 30 mph it produced 3000 drawbar HP on the N.P. compared to 3800 as tested by Alco and some other roads that tried it. It sounds like the range of acceptable draft in the N.P. locos burning Rosebud coal was very narrow. An ideal fire is described as being almost a gaseous cloud. Too little draft would make the fire too cold and too much would pull it out the stack causing unacceptable errosion to the flues and a plugged up front end. Apparently the Q had similar problems with the Sheridan coal they used. I've sen that stuff on the current BNSF coal trains and it's pretty fine an powderey.

I don't share the negative view of the N&W or other eastern roads of another poster. The Eastern coal roads had to go to where the mines were, so sharp curves and stiff grades meant that track speed was a limiting factor. The western transcons were located to find the most advantageous routes. Their steepest most difficult grades were a very small portion of their operation and were often electrified(Milw, GN), dieselized(N.P.), or helper operations(Cajun). On the UP, the rulling grade at places like Sherman Hill was .82% and hauling perishables meant re-icing refers, livestock needed periodic unloading, and ATSF had the shorter route so speed became a major requirement leading to what were really fast freight locos rather than mountain maulers. The Rio Grande and the Missabee Iron Range were 2 western roads more comparable to the N&W and of course the Narrow Gauge roads were an extreme example of going to were the mines were.

GP40 wrote; "Most famous compound was N&W Y6b. Had good low speed tractive effort but was a dog above 30mph"

I hate to knock your d*+# in the dirt, but, the engineers I worked with would run these puppies for all they were worth. One told me that 64 mph was about the fastest you wanted to run one. After that things started getting a little chancy as the rods were really flailing.

So don't ever think a Y6 couldn't get a train over the road in good time. Too bad the western roads didn't aquire the later Y's with the bigger valves and could really breath!

Now to get back to the original question. For those of you that would like to know how a compound mallet really worked check out the following web site;
http://www.catskillarchive.com/rrextra/mallet.Html

Unless I missed something in this lengthy discussion, only BigJim has made the point that a Y5/Y6 was not limited to 30 mph all the time. Sure, they were at their best at 25 mph flat out upgrade, but once over the top or on relatively level track, they could easily make 40-45 and as much as 50 without tearing themselves up or damaging the track. Agreed, their HP curve dropped off very rapidly after 30 mph or so, but how much HP do you need downhill? In that situation, better counterbalancing rules, and they could definitely get out of their own way. There are many examples of this on video, particularly on the Shenandoah Valley line, where this type of 25-up and 45-down was commonplace. On the east-west main, many videos indicate that after passing Blue Ridge, the A/Y6 combo was not limited to 25 mph on the way to Lynchburg. There's many a scene of the lead A striding along with that big old thousand-legger right behind. Quite a contrast, but it was a many-times-a-day event.

"According to the N&W guy who was on the engine when it failed (the 610), the valve froze in the cage due to lubrication failure. When the engine was hauled back to Roanoke and the cylinders and valve chambers opened up, the liners were colored yellow......" blah,blah,blah

Actually, the N&W guy who was with the engine had no idea why it failed. He was too busy trying to find a sheep to mate with to even care why it failed.

Speaking of sheep, how your mother doing, Oldtimer??

Also, please spew on concerning the mighty H8 vs. the girlyboy A Class. I need a good laugh. Oh, and you didn't address the superior NYC Niagara either.

Mr. Big Ol' UP Guy -

H8 - weighed 778,000 pounds. Cost $230,663 per copy. (First series - 1600-1609.)
A - weighed 570,000 pounds. Cost $123,000 per copy. (First series - 1200-1209.)

Now, Mr. Big Ol' UP Guy - even you, with your obviously limited grasp of mechanical principles, could design an engine that weighed 100 tons more and cost $100,000 more than the one you wanted to beat, and do it. Problem is, that the performance improvement didn't come close to matching the weight differences and cost differences. But you, as a Big Ol' UP guy, obviously don't care about stuff like that.

Now, you'll have to excuse me.

My daddy told me that it wasn't polite to engage in a battle of wits with an unarmed man, and you're obviously as unarmed as they come.

Your friend, the Redneck Hickabilly Trailer Trash Old Timer

Maybe this question has been answered on another thread, but why the fire tube boiler and the relatively low boiler pressure? If marine water tube boilers wouldn't hold up to the bangs and jolts of railroading, how is it that the Schmidt superheater (which is kind of like a bolted-on water tube element) could hold up?

Also, why the steam ejector draft? I know this is the essence of the Stephenson-style steam locomotive, and a lot of work by Champelon and Porta went into making it efficient. But at cylinder exhaust you get a supersonic blast of steam, and I would think some kind of blowdown turbine on the cylinder exhaust would be much more efficient in turning that exhaust energy into mechanical energy -- to power the fire box draft, other accessories, or even contribute to motive power.

The Wright R3350-tc piston engine on the DC-7 and Lockheed constellation prop airliners were turbo compounds where gas engine cylinder exhaust drove turbines connected to the propeller through automotive style fluid couplings -- these piston dinosaurs were like the Pennsy T1s of the aviation world -- refinements of the old technology that got shoved out by the jets.

One more thought on compounding. Obviously a very short cutoff valve gear that allows the maximum expansion will make a simple system efficient, and the automotive world is finally coming around to that with variable valve timing and Atkinson cycle engines on the hybrid cars. But pistons have a lot of friction, so high expansion in a simple piston has diminishing returns. Compounding may help by balancing the friction to the working pressure between HP and LP cylinders.

The other thing that compounding can help with is reduction in heat losses. The HP cylinder runs at higher temps than the LP cylinder and you don't have as much ups and downs of cylinder temps during steam expansion. Also, a big efficiency killer is if steam starts condensing on account of cylinder cold spots because condensing transfer a tremendous amount of heat. I believe that superheat allows you do expand more in a simple system replacing to a degree the need for compounding.

Maybe this question has been answered on another thread, but why the fire tube boiler and the relatively low boiler pressure? If marine water tube boilers wouldn't hold up to the bangs and jolts of railroading, how is it that the Schmidt superheater (which is kind of like a bolted-on water tube element) could hold up?

Also, why the steam ejector draft? I know this is the essence of the Stephenson-style steam locomotive, and a lot of work by Champelon and Porta went into making it efficient. But at cylinder exhaust you get a supersonic blast of steam, and I would think some kind of blowdown turbine on the cylinder exhaust would be much more efficient in turning that exhaust energy into mechanical energy -- to power the fire box draft, other accessories, or even contribute to motive power.

The Wright R3350-tc piston engine on the DC-7 and Lockheed constellation prop airliners were turbo compounds where gas engine cylinder exhaust drove turbines connected to the propeller through automotive style fluid couplings -- these piston dinosaurs were like the Pennsy T1s of the aviation world -- refinements of the old technology that got shoved out by the jets.

One more thought on compounding. Obviously a very short cutoff valve gear that allows the maximum expansion will make a simple system efficient, and the automotive world is finally coming around to that with variable valve timing and Atkinson cycle engines on the hybrid cars. But pistons have a lot of friction, so high expansion in a simple piston has diminishing returns. Compounding may help by balancing the friction to the working pressure between HP and LP cylinders.

The other thing that compounding can help with is reduction in heat losses. The HP cylinder runs at higher temps than the LP cylinder and you don't have as much ups and downs of cylinder temps during steam expansion. Also, a big efficiency killer is if steam starts condensing on account of cylinder cold spots because condensing transfer a tremendous amount of heat. I believe that superheat allows you do expand more in a simple system replacing to a degree the need for compounding.

Actually, Paul, a water tube boiler was used, at least once -- the Delaware and Hudson had one, on a triple expansion rigid frame compound engine (yeah, the D&H had some pretty far out steam engines at one time!). Worked fine. However, the advantages of water tube boilers really come into play at rather high pressures -- 600 psi or so, perhaps -- and they are considerably more expensive to build than fire tube boilers. Thermodynamically, there isn't much advantage either way; the problem with the fire tube boiler arises in supporting the firebox, crown sheet, and tube sheets, and is a mechanical problem (can you spell 'staybolt'?!).

Why steam ejector draft? It's simple, reliable -- and almost completely self-regulating. And very very efficient; no moving parts and direct conversion of energy. No maintenance. The only real disadvantage is, or can be, inadequate draft at very low speeds (the 3985 had a lot of trouble with that, a few years back, in the famous instance when she was asked to help out a freight with a couple of dead diesels -- she was fine once she was rolling, but I seem to recall that they had some trouble at first at the very low speeds). Turbines are a maintenance bear...

The Wright R3350-TC was a fascinating engine. It and the P&W 4360 Wasp Major were the last gasp of the piston engine in aircraft. The Wright was, in some ways, the more advanced of the two, as it did use turbocompounding to drive the propellor (the Wasp Major was turbocharged, but not compounded). They did get shoved out by jets -- but they didn't take much shoving: in the aircraft world, high horsepower per pound of engine and reliability trump almost anything else, and even the most primitive of the turboprop engines at least tripled both horsepower per pound and reliability... there was a very darn good reason why the DC-7 and the Connies and their kin (and for the Wasp Major, the Stratocruisers) had four engines -- about half of the oceanic flights would see an engine shut down somewhere over the briny, and most pilots don't like to swim. At least not on their working time. And the passengers get fractious. But that's not to take away from those engines -- they were (and the few still flying are!) superb machines.

Quite right about superheat on steam. You move the steam quite some distance away from the saturation point, and can get a lot more efficiency out of the system that way.

Is there any book about m.u. for steam-engines?

QUOTE: Originally posted by jchnhtfd (can you spell 'staybolt'?!).

I can spell staybolt.. Can you spell blower?! A device that uses steam from the boiler to increase the draft at low throttle steeings.

A few quick replies, before more of the other heads chime in: (I tried to post this in the morning, but couldn't get through to the server correctly...)

Compounding works well in marine and stationary engines because of the relative ease of providing the required large 'sink' of cool water to remove the latent heat of condensation. To do this even half-assedly on locomotives has traditionally required a very large radiating surface, for reasons you can e-mail me off list to find out about. American railroads, even in the Southwest, generally found it more 'cost-effective' (i.e. cheaper and more reliable) not to try to build condensing locomotives, even though they might be thermodynamically much more efficient.

Steam-jet drafting is an inexpensive, extremely reliable, and 'automatic' way to provide an appropriate proportional draft in a steam locomotive. All the other ways to do it require expensive machinery that can be difficult to maintain, and that require care if there are ash, cinders, high-vanadium oil residue, etc. in the combustion gas (see the history of the South African 25 condensing class)

There are ways of avoiding shock transitions in the exhaust flow -- multiple nozzles and larger stack cross-sectional area (in part to allow larger nozzle nests) being two general approaches. Again, e-mail me off list for the details ad nauseam.

Bangs and jolts aren't the principal problem with the watertube boiler: temperature transitions with changing load and firing is. That applies not only to the tubes, but also to the enclosure -- which IIRC was the source of much of the trouble with LNER 10000's boiler.

There are also critical difficulties with soot blowing, tube fabrication and replacement, etc. Remember that a major attribute of American steam locomotives in the late 'Golden Age' was that they were CHEAP -- and even some of the more sensible subsystems like feedwater heaters were removed in the '50s as being too expensive to maintain for the returns the railroad saw from them. [As noted, the principal benefits of a water-tube boiler come into play at about 600psi and above -- Jawn Henry country.]

The convection section (the part with the firetubes) of a locomotive boiler is remarkably well-suited to typical locomotive service -- a large reserve of overcritical water to make steam, great strength (the tubes act as longitudinal 'staybolts' between the tube sheets), great ease in cleaning and tube replacement. Particularly significant is that leaking tubes can be easily and cheaply plugged, or even sealed, with the engine in service; a leaking water tube has to be expensively welded before the engine can see service.

The firebox and chamber -- the radiant section of the boiler -- is a different story: here is where the 'success stories' with water tubes can be found (the Emerson box being one example). Even there, however, there were difficulties with getting water tubes to work reliably and in maintaining locomotives in service... you don't see these being adopted even as other approaches, notably Nicholson syphons and systems of arch tubes, gain considerable favor.

Pistons don't have particularly high friction, especially with modern combinations of ring and liner materials. A bit better sealing is required with higher MEPs, but even so it's a very small part of the overall train resistance!

You might be interested in some of the research on piston engines for peaking powerplants, which can be more efficient than turbines if sustained operation at part load or varying loads is required... note that this is characteristic of most locomotive operating regimens 'in the real world'.

You are, of course, correct about the benefits of lower heat drop in each cylinder of a compound, and this has in the past been recognized as an advantage. Some engine designs, notably uniflow designs, have required the cylinder to be bored non-parallel (the Stumpf engines had slightly barrel-shaped cylinders) precisely to accommodate the differential expansion due to 'prevailing' steam temps in operation. One way to solve this is by using saturated-steam or boiler-water jacketing on the cylinders (as Chapelon suggested in late practice); another is to use ceramics and thermal-barrier coatings.

And there is ample evidence in history that superheaters were the 'magic bullet' that killed off the compound frenzy in the very late 1800s and early 1900s. When compounding re-emerged as a hot topic for designers in the 1920s, it was for very different reasons than pure fuel economy...

[Hugh, I don't think you understood jchnhtfd's reference -- it's from a famous American children's show, Mr. Rogers' Neighborhood. One of the things I've always wondered was why blowers seemed to be such noisy, primitive afterthoughts. Perhaps because locomotive designers treated them like annoyances -- necessary but not worthy of extensive attention or investment. (After all, they use boiler steam that hasn't produced useful work...)

Sort of like 'brakes' on classic-era British freight trains... they waste expensively-acquired momentum, so why spend too much time on them... ;-}

Note that any replacement for a 'blower' would almost certainly have to have multiple purposes to justify its cost -- and most of the 'usual suspects' for ancillary systems driven by rotary motors aren't primarily needed with the locomotive at rest (feedwater, generator, etc.). Hard to beat something that uses a single valve and passive nozzles to give the desired effect...]

QUOTE: Originally posted by Modelcar ...PS: Along the same lines of engines....Referirng to similar design [articulated], engines can anyone talk a bit of the type of sealing that was used in the joint where front and rear engine would pivot on a curve and require a pivot in the steam supply line to the cylinders. Was it some sort of ball joint with some kind of seal or perhaps just a tight fitting steel ball and joint....?

I'll take a guess - Gland seals? These are typically found on steam turbine mainshafts. A passage connected to steam pressure allowes steam to fill an anullar bag compressing the packing material in the anullar slot locating the seal.

UP locomotive experts -- do you have any knowledge (or opinion) as to whether the problem with the 4-12-2s was more related to the three-cylinder drive, or to the long wheelbase?

These locomotives came about as the fruits of a dubious era in American steam locomotive design -- different from the 'Super-Power' approach being taken at about the same time. There was a pretty funny cartoon in the December 6, 1931 Railway Gazette that mocked the whole tendency for "higher thermodynamic efficiency numbers as the holy grail of design" -- the locomotive's number, for example, is a parody on the Baldwin 60000 demonstrator.

Offhand I can think of Lackawanna and SP locomotives that were given the three-cylinder divided drive, from about the same era as the 4-12-2s -- were these considered as undesirable by Mr. Acord's counterparts at those roads?

Seems to me that the 'market' for multicylinder power in the United States was won, hands down, by the simple articulated: four cylinders instead of three with less complexity, and better flexibility, and more drivers for less problem with adhesion being a couple of salient benefits. I note that N&W recognized this early on with the class A; IIRC they were going the three-cylinder eight-coupled route but ditched it by the early '30s. (I also note that the D&H went to extreme length to avoid inside cylinders in the triple-expansion 1403 -- about the only weird engineering "solution" that was NOT on that engine!

Where in the USA were there inside-third-cylinder engines that were liked?

jruppert....Thanks for giving the steam seals a shot...

The 4-12-2's were originally delievered starting in 1926 a little before the super-steam era. From what I've read, the biggest problem was the middle cylinder main rods punching holes in the boiler when they broke! The 2nd axle was cranked, automotive style and breakage was a problem there too. The guides also gave much trouble and fixing a lot of this stuff meant finding a hoist! The early ones also had problems with the built-up frames breaking or causing alignment problems and many received cast steel frames and cylinders through the 1st driver. The later ones had 1 piece cast cylinders and frames. Some were rebuilt with double Walshaerts valve gear, but the cost wasn't deemed worth it over the Greesly system. They ran for almost 30 years finishing up on the Nebraska and Kansas divisions, the last was retired in '56. The wheelbase wasn't a problem there or in Wyoming, but they were unsuitable on the Blue Mountain grades on the Oregon line, which led to the development of the Challenger in 1936.

Astoundingly enough, I haven't been able to find a modern reference to the articulated steam joint construction details on later locomotives so far!

The BASIC principle behind the ball joint can be noted here:

http://www.catskillarchive.com/rrextra/blwmal00.Html

about halfway down the page (note the components required) -- a fundamental principle is that there IS a gland (as jruppert indicated) but that it can be tightened without 'gripping the joint'. The ball and socket of the joint are lapped together for final mutual alignment and smooth working. Note that an intermediate SLIDING joint is required in this version of the system in order to accommodate the difference in length as the forward engine articulates; on a Mallet this of course 'sees' a much lower pressure than is the case on a simple articulated!

Some of the details of the improved system used on the Union Pacific Challenger (class CSA-1 rev. A) are visible on the erection diagrams obtainable from Giesler Engineering (800-428-8616); the drawing I could check on short notice is #426CA24900 (dated 8-1-36, revised 5-9-38). Naturally, Steve Lee or other representative of UP's Heritage operations could give you a full and detailed description of these joints (as installed on 3985) and their care and feeding, in detail that should satisfy any reasonable need to know.

Some -- but not all -- the jointing and piping details for high-speed trailing-truck boosters would apply to Mallet joints, and would be easier to find and see on preserved locomotives.

You may be able to access English patent #17,165 (26 July 1907, published 11 June 1908) which is the Garratt locomotive patent. Garratt noted that his initial engineering source for 'spherical joints' was from practice on the Ffestiniog railway. I have no access to this patent & can't verify whether detailed description of the joint is provided there.

A proprietary improved flexible steamline joint was patented by the Bagnall company ("Flextel") in 1936. but I have no access at present to do a search for its drawings.

The "Mason Bogie" (if that's what it is called) at Henry Ford's Greenfield Village (I'd call it a "single Fairlie" but that's because of where I came from) has spherical joints on the exhaust steam pipes from the cylinders to the blast pipe, but I think the live steam was passed through the pivot point (as it was on later Beyer Garratt locomotives).

I'd always assumed that these early articulated locomotives would have been fairly "rough and ready" but that certainly isn't the case. I'm pleased that Henry Ford kept one for me to look at. If Greenfield Village is Henry's view of the America his cars were changing, I certainly prefer it to Walt Disney's idea represented by Disneyland.

Peter

So far the discussion has centered on articulated compounds. At the turn of the twentieth century some eastern roads were operating cross compound locomotives. These non articulated two cylinder engines had a small high pressure cylinder on one side and a large low pressure cylinder on the other. Some of them were used in passenger service.

Wasn't there a narrow guage locomotive with a unique cylinder arrangement on the C&S or something? Didn't this locomotive also have some kind of compression braking?

JDQuigg -- von Borries compounds were never extensively used in American practice, perhaps because American builders had other forms of compounding they preferred to use and sell during the time compounds were popular. Certainly the 2-cylinder cross-compounds appear to have worked well in places like Java, where I would expect the engineers' experience, track standards, and locomotive maintenance to be no better than that available in the United States or Canada during the 'compound era.'

I can't speak to C&S experience, but the 'brake' you describe has to be the leChatelier "water brake", which has a distinguished history on D&RGW, including being used... get this, it's on topic, in a sense!... on the simple-articulated 4-6-6-4s. This was a bit akin to a Jacobs brake on a truck diesel, in that it used compression against the pistons to help provide 'counterpressure' braking, but did it in an interesting way. A small amount of hot boiler water was valved into the cylinder on the *return* stroke (opposite the side on which steam was expanding), and the exhaust on this side was given an early cutoff, IIRC by a separate valve. This water already had a propensity to fla***o steam, of course; the extended compression stroke raised the temperature inside the cylinder (much as in a diesel cycle) which essentially completed the flashing of the steam and prevented any chance of hydraulic lock (which is not a pleasant thing on steam locomotives!). It's the counterpressure of this resulting steam that exerts the braking pressure on the piston, or to put it another way, the kinetic and gravitational energy of the locomotive and train running downhill is partially utilized to convert water to steam and then heat the steam. I've always thought it an elegant and effective solution (compared to using typical steam-era air brakes, retainers, etc. for the same general purpose!)

I'd note that using this brake on a Mallet (which by definition is a compound locomotive, usually with large LP pistons on the hinged forward engine) would be more difficult than using it on a simple articulated of modern design, in which the hinge is restricted to one plane and counterpressure produced by the forward engine has lower tendency to induce yaw.

Of course, this brake required a certain amount of skill, judgment and experience to use, and maintenance standards had to be high. Dynamic braking was, and is, probably a better alternative...

This may be a bit off-topic but since 3-cylinder designs have been mentioned, what was the original role for IHB's U-4 0-8-0's, which David P Morgan considered to be "the grandest 0-8-0 of all"? They seem much too large for flat switching, and the lack of pony trucks would seem to restrict them from transfer runs.

Phil O'Keefe said that these big 3-cylinder 0-8-0s *were* used in transfer service. Presumably at slow speeds.

I'd think that Chicago winter conditions might also indicate a bigger locomotive for moving long cuts of cars....

A little more reflection: Is lack of a leading truck THAT unusual for transfer service? Seems to me that an even more extreme example, the Union 0-10-2s (with booster tenders, no less) were used in transfer service. Coal and ore trains don't need to move very fast, and if I remember the Trains description of IHB correctly, there might have been advantages in long, slow trains over faster short ones... it would be justifiable to have as much weight on drivers as possible, and the three cylinders would give 'smoother' power at low speed where a 2-cylinder engine might have trouble.

Didn't Neil Carlson discuss 10-coupled switch and transfer power for Classic Trains? He might have some insights...

I understand the need for trailing axles to support the firebox, but even there, Porta had plans for locomotives (2-10-0) with a really skinny boiler where the boiler and firebox and everything sat above the drivers.

What are the needs on the leading truck? Could a 4-8-4 Northern operated at higher speeds than a 2-8-4 Berkshire? I can see where no leading truck and coupled drivers (0-8-0) restricts you to low speed, but are there speed restrictions on a single leading axle?