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The Most Suitable (non-mallet) Compound for U.S. Use

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The Most Suitable (non-mallet) Compound for U.S. Use
Posted by ShroomZed on Thursday, December 31, 2020 2:52 PM

Hullo, it’s certainly been a while since I’ve  said anything. Crazy crazy year, but I suspect everyone here already knows enough about that. 

Something I’ve been looking at a lot lately are the varieties of compound locomotives used worldwide, including the various late nineteenth century and early twentieth century methods attempted in the United States and with my layman knowledge trying to think about what form of compounding works best in the United States (besides the matter of the mallet of course, think of this as a discussion pertaining exculsively with rigid frame locomotives). 

The main problem with compound locomotives is that while they give the advantage of better thermal efficiency and reduce fuel costs, their arrangements often result in high-maintenance costs from relatively high numbers of components and complicated steam pipe networks, pain-in-the-rear end accessibility for certain arrangements, and in some cases the system was mechanically problematic from the outset (like the four cylinder Vauclain), to the point that either no profit was gained or indeed lost from experiments which were gambles. 

From what I’ve reviewed, the more mechanically sound and efficient the system was, the more complicated it was overall and inaccessibility increased dramatically, along with the chances for something to go wrong. The main examples here would be the four cylinder balanced compounds with inside and outside cylinders, which if properly run (more that could be expected from the average United States driver) could give astounding fuel savings and at the same time were phenomenally smooth runners. The main problem comes from the complexity of the system, with two sets of valve gear inside the frames. Crank axles were required as well which spelled bad news in the U.S.. Problem is crank axle assemblies from what I know simply often did not have the strength to withstand the forces distributed through an American locomotive. These were consequently most popular in continental Europe where operating conditions suited them to a greater extent and had an extremely brief period in the U.S.. 

The United States tried to compromise the advantages of compounding with flexibility and simplicity, which had mixed results at best. The Vauclain outside four cylinders had only two sets of valve gear being actuated by cross heads working from the high-and-low pressure cylinders in harmony. The differential thrust forces from the different pressure cylinders caused torquing effects on the cross head which was a large problem. The tandem four cylinder was even worse, with the asemblies being extremely cumbersome and the differential forces of the cylinders once again causing extreme mechanical strain. The two cylinder compound is the simplest and has the least amount of parts to go wrong, but the uneven size and weight of the cylinders, outside the frame at that, will cause yawing no matter what and that causes extensive damage to the frames of the loco and the rails. 

One of the better systems I‘ve come across is one that was used on the Midland Railway in the late nineteenth century on a few 4-4-0 classes and some neighbouring railways; they were three cylinder compounds with one high pressure cylinder between the frames and the two low pressure on the outside. They were designed in mind with flexibility as one of their strong suits and consequently had a quite ingenious steam admission system which allowed multiple different steam arrangements and automatically switched from simple to compound with a selected pressure by the driver by a series of valves and spindles (in the starting valve, if the optimum pressure is achieved, an opening to that allows steam to go straight to the low pressure cylinders is closed and normal compounding begins). It still is a rather complicated system but did have success in the U.K., which otherwise had little to no true success with compounding designs (the infamous Webb designs for example). 

Essentially the lesson learned is that like with many components of the steam locomotive, a compromise had to be made between mechanical flexibility and robustness and efficiency of the design. The Americans for obvious reasons slid towards simplicity as it suited their operating needs the most, abd complexity was only later increasingly sought as the I.C.C. imposed larger and larger wage restrictions and efficiency was the optimal way to gain a profit as simply and solely enlarging designs wasn’t going to cut it anymore. The superheater, although acceptance was relatively sluggish in the U.S. compared to Europe gave fuel savings comparable to or better than compounding with much more simplicity which quickly won the Americans over and compounding was seen as unesessary and a hassle. The British world follow a similar path although they werent as averse to complicated arrangements (although much of that is likely a response to extremely constrictive loading gauge, large cylinders and heavy Walschaerts valve gear with lateral flexibility arrangements had nowhere to go in nine-foot wide locomotives). 

Even central Europe eventually gave up compounding and France was the main user of compounds up to the end of steam. 

So the question of this topic is let’s say hypothetically the United States wasn’t as willing to drop compounding and at least some tried to advance it, or perhaps compounding was returned to in the thirties or forties, what would be the optimal rigid frame compounding arrangement for United States use, with the knowledge gained towards the end of steam and the massive advancement in assembly and construction? I’m sliding towards a three cylinder arrangement, but I am gravely aware of Baldwin 60000 and the general failure of three cylinder constructions in the U.S. past the 1910s, with the maintenance horror stories of the western 4-10-2s and 4-12-2s. Im curious to see what some of you have to suggest for compounding for ‘modern‘ locomotives in United States operating conditions. 

Discuss away. 

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Posted by Overmod on Thursday, December 31, 2020 3:34 PM

There are some fun answers to this.

Of course, the obvious contender is the extension of the N&W booster-valve system to full proportional IP modulation -- something that even with relay-logic controls of the '50s could be done effectively.  This would produce both equivalent horsepower and full balance out of both engines of a Mallet compound, like a Y-class locomotive, and allow it free running without the usual losses to a speed typical of most North American manifest freight, while maintaining the Rankine-cycle benefits, the enhanced slip recovery, and more importantly the water-rate savings for large power over straight single expansion.  No more steering refinement than that used on, say, the latter AMC locomotives would be required on single-axle lead and trailing trucks, were the suspension to be arranged as on the A-class and the Challengers to take vertical compliance entirely in the equalization.

I am not certain that the maintenance advantages of full roller and needle-bearing rodwork would entirely justify its use on such a locomotive, considering the sizable additional weight over a more conventional floating-bushing setup like that on the UP 800s and appropriate alloy steel to keep rod mass low.  This would be one place that the Chinese experiments into automobile-style pressure lubrication of rod bearings through cross-drilling and seals might be of real worth.

The same modulation approach can easily be applied to a von Borries locomotive, even at higher nominal cyclic than a Mallet.  Since cross-balancing concerns are the principal issue with these, it becomes attractive to have compounding with only two main pins... and with proper Chapelon-style steam jacketing and some other applicable technique, a comparatively simple 'self-starting' locomotive can be provided and worked.  I suspect that an augmented version of the modulation system could substitute for a starting valve in these engines, relieving a considerable amount of constructional and maybe operational complexity in starting arrangements.

I was partial to the balanced de Glehn style of compounding (on what were designed as very large 4-8-4s) in my teens; these got around the cranked-axle difficulty with the same solution I proposed for the Withuhn conjugated duplex: tunnel cranks (as in some of the Mercedes locomotive diesels) where the inner race of the bearing also carries the crankpin seat.  Construction and maintenance of these should be no more complicated than the original bearings in the N&W As -- the catch being, as with all inside bearings, that rollers are not particularly easy to implement as they can't be functionally split at reciprocating-steam pressures and duty cycles.  I divided the modulated drive between the leading and second axles, with the LP cylinders in the center as on classical de Glehn-du Bousquet locomotives, but the pressure adjustments were handled automatically rather than using two complete sets of independent gear.  Etc. etc. etc. 

It might have been interesting to see a true North American Garratt with eight-coupled engines, something even Beyer Peacock did not propose.  Theoretically all that would be required within the practical water-rate criteria would be double-sixes, probably with not more than 69"-70" wheels, as things get ridiculously long ridiculously fast, and pivots were not a particular Beyer-Peacock design specialty even with nominally cast engine beds... Whistling

Finally, a perfectly good Meyer can be constructed under a double-Belpaire, either with six- or eight-coupled engines, and with modulated IP that can be a compound exhausting at the 'stack end'.

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Posted by ShroomZed on Thursday, December 31, 2020 5:56 PM

Quite interesting stuff, gives me a good amount to think about. 

First thing is, can you tell me how the von Borries system works? I know there is a two cylinder form and a four cylinder; I’m assuming you’re talking about the four cylinder. Suitable information about it is elusive to me with a lack of suitable images. 

Using a tunnel crank is certainly a distinctive way to actuate the inner axle and is certainly a way to handle the higher forces. Something that catches my eye though is your choice to put the low pressure cylinders within the frame; I have a suspicion that American-size low pressure cylinders wouldn’t be able to fit within the frame, even if we’re talking about pressures of 300 p.s.i. or higher being implemented. There must be simething there I’m missing. 

I‘d appreciate your method of the automatic adjustments on the De Glehn as well; would this be similar in principle to the arrangement used on the Midland compounds or would it be something else? 

I was also wondering what you think of the Maffei four cylinder system (used on Bavarian express engines) and how it compares to other four cylinder systems. 

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Posted by Paul Milenkovic on Thursday, December 31, 2020 6:09 PM

I heard that compound steam didn't live up to its promise of efficiency owing to ghastly condensation by the time steam reached the low-pressure cylinders.

This was how Andre Chapelon got such phenomenal boosts in performance, by figuring out what was going on in the the French de Glehn compound and what the steam conditions were?  

I consider Chapelon's greatest work to be not is high-performance passenger locomotive the 242-A1 (a 4-8-4 by the usual counting of wheels instead of axles).  Rather, it was the 160-A1 6-cylinder and 12-driving-wheel drag-freight locomotive.  The Advanced Steam Traction people in recent years had a technical conference, where one of the papers addressed the experiments done on that locomotive offering cylinder jacketing along with the capability (in the shop) to change whether the HP cylinders are fed superheated steam or the LP cylinders receive reheated steam.  The paper addressed which combination gave the best outcome, which was to feed the HP cylinders with saturated steam and rely on the cylinder jacket to prevent condensation and to supply the LP cylinders with reheated steam, obviating the need for their cylinder jacket.  Don't know if I got this right, but for superheating only the HP feed, there has to be gobs of superheat to make it all the way to the LP exhaust without power and coal-robbing condensation -- what I suggest here may have been the optimal trade between efficiency and valve lubrication problems?

The 160-A1 was said to be remarkable in that its thermal efficiency increased at lower speeds.  Don't know if, count them, 6 cylinders along with superheat to the HP set, reheat to the LP set and cylinder jacketing them all is economically feasible, but the locomotive was a test bed into what it would take to get an efficient hill-climbing freight locomotive instead of those picturesque photos of climbing the ruling grade with sparks and cinders blasting up from the stack like a scale model of Stromboli.

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by Overmod on Thursday, December 31, 2020 11:12 PM

ShroomZed
First thing is, can you tell me how the von Borries system works? I know there is a two cylinder form and a four cylinder; I’m assuming you’re talking about the four cylinder.

No, I'm talking about the 2-cylinder: one HP, one LP.  There is a variety of intercepting valve used at starting to admit a reduced mass flow of steam to give the 'effect' of a two-cylinder simple; the engine then works compound with the HP having an initial expansion between two relatively high pressures, then the LP expanding further to an efficient level of back pressure, but 90 degrees out of phase.  

Key to smooth running with this system is that the LP admission has to be proportioned and timed so that the corresponding piston thrust over the stroke resembles that in the HP.  Historically this was done 'well enough' that some engines, including the original PRR T class with British styling and 84" drivers, could reach considerable speed with a heavy (for the day) consist.  

A modern engine will use a combination of HP exhaust and boiler steam to produce the desired pressure in the LP cylinder matching HP expansion.  It's very similar to one-half a de Glehn-du Bousquet arrangement, giving the same four DA impulses per revolution of a 2-cylinder simple.  No inside cranks or cylinders, no weird rods and bent axles to clear inside mains, cannon boxes and roller bearings no problem.

One principal "reason" is to reduce the effective water rate of what would otherwise be a 2-cylinder locomotive.  It is theoretically possible to perform a reheat pass a la 160 A1 in addition to the modulated steam injection, but careful proportioning and design of the steam circuit is necessary.

Something that catches my eye though is your choice to put the low pressure cylinders within the frame; I have a suspicion that American-size low pressure cylinders wouldn’t be able to fit within the frame, even if we’re talking about pressures of 300 p.s.i. or higher being implemented.

These are not enormous LP cylinders, as they might be on a straight de Glehn-du Bousquet -- think of this as a four-cylinder 135-degree locomotive that uses a proportion of exhaust steam in somewhat larger cylinders to conserve water.  The tunnel cranks allow the inside mains to run close to the inside face of the bearing box, permitting a larger bore than an inside crank would normally allow.

The 'automatic adjustment' looks at a couple of parameters of thrust from the four cylinders, and tinkers with the modulated admission so the LP matches the HP.  Fine 'tuning' can be made if the system latency is not quick or there are feedback lags; I was using a method of spring actuation of valves 'wound up' by crosshead motion, so some of the fine adjustment could be done with mechanism that did not have to transmit high power.  

As I recall, the Midland Compounds used the same Smith system as Baldwin 60000: the single HP cylinder fed somewhere around 2.3x to 2.7x the volume of 2 LP cylinders phased 120 degrees apart -- the LP volume chosen to be the 'natural' expansion of the volume of steam from the HP event.  This was by far the most successful of the three-cylinder compounds, and with a reasonable degree of initial superheat you could get reasonable expansion out of the LP before wall or nucleate condensation started to bite... and to an extent you could compensate for these with an 'excess' of steam in proportion.  Balance of these things is not the easiest job in the world, though, especially if you intend high sustained horsepower but will run the engine across a wide range of speeds and loads.  Here again a small amount of throttled steam in each of the LP admission ports can smooth out some of the running.  I am ignorant of the specific arrangement on the Midland Compounds for balance across the range of loads -- I'm sure there are people like Bill Hall who have carefully analyzed the arrangement.

I was also wondering what you think of the Maffei four cylinder system (used on Bavarian express engines) and how it compares to other four cylinder systems.

Again, I have not studied German four-cylinder balanced compounds as well as I should; I have always had a preference for divided drive (e.g. not two main pins and two crank throws on one main driver pair) with the possible exception of the Shaw locomotive (which is a four-cylinder engine with the cylinders arranged entirely outboard of the drivers acting on double crank ends, with bearings between the throws; there is no need for any special axle form or clearance between the wheels, and a cannon box with rollers can easily be used, but it is difficult to impossible to forge the main driver shaft in one piece and then press the uncranked wheels on properly).  In theory a Shaw can be compounded like a horizontal Vauclain type 1 with the single cored valve serving both HP and LP cylinders on one side, but the arrangement is already alarmingly wide with simple and relatively small cylinders...

Certainly the Maffei system performed well, I expect on a par with other well-engineered balanced-compound arrangements.  That is something I could NOT say of the Plancher System -- which almost has to be seen to be appreciated.  I confess I still don't quite understand the point of it, but the Italians had cab-forward locomotives using it, so it has to have worked on some level...

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Posted by Overmod on Friday, January 1, 2021 12:19 AM

All a compound does is divide the expansion of steam into more manageable ranges, instead of trying to do it all with (theoretically) modulated admission and early cutoff/long compression and so forth.  It does not 'use steam twice' -- it uses it only once per cylinder but over a different range of pressure.  This becomes significant if you have caught the 'lowest possible backpressure' bug, as so many of us have at one time or another.  An unmodulated compound has a certain design HP back pressure (roughly equivalent to what the admission pressure on a 2-cylinder locm=omotive with the LP cylinder dimensions would be) and to get reasonable expansion thrust over the required stroke, that pressure may be surprisingly high.  It is the differential between high HP admission pressure and lower HP exhaust pressure that determines the thrust from a HP cylinder.

In the case of the 160 A1, the steam admitted to the HP first circulated through jackets surrounding as much of the cylinder as possible, and the mass flow of 'heating' steam was determined by admission.  Presumably a good insulating lagging was supplied outside the steam plenum space.  The steam in the plenum is hotter than that going into the cylinders, and it acts to keep the whole cylinder structure hot 'from the outside' to lessen the cyclic effect of wall condensation.  

It was pointed out to me that a typical road locomotive at 'diameter speed' is seeing the wall temperature fluctuation due to falling steam temperature in only something like .007" of the metal adjacent to the bore.  The higher the temperature of the metal immediately adjacent to this cycling, the less likely the low-temperature end of the cycling will be to induce condensation in the steam contacting it.

The efficacy of steam jacketing on high-pressure steam-engine efficiency was well recognized by 1874; I suspect much more would have been made of this had 'steam carriages' been allowed to flourish in England.  I go so far as to advocate the circulation of overcritical boiler water through tracer lines (with a Lamont-style low relative pressure drop and hence little pumping energy requirement)to keep relative parts of the cylinder structure hot inside the kind of insulation Wardale calls for.  While I suspect the jet pump in a Cunningham circulator can provide adequate flow for this as well as redirecting downcoming convective circulation through the water legs, it may be that a separate pump arrangement for cylinder tracing ought to be used.

I have an issue with "no superheat" in HP admission.  Not all the phase change occurs in steam due to wall effects; there is also a certain amount of 'nucleate condensation' that essentially results from the work being done by the steam, which abstracts heat energy from the mass of steam confined in the cylinder to the point where phase change in the volume of steam, not just at the contact with engine structure, occurs.  The effect on the steam's behavior as a gas, though, is the same in both cases: expansion can produce more pressure drop in the later stages than expected if steam were closer to a perfect gas.  To this end, superheat is added to keep either form of condensation from affecting much of the mass of steam in the cylinder -- and I do think a certain amount, enough to 'make it' past the jacketing space when the cylinders have come to running equilibrium, ought to be added to produce the performance expected of a locomotive given a Schmidt superheater.

It can also be observed that adding superheat is NOT a good way to increase the performance of the heat engine as a prime mover.  Relatively small added heat greatly increases the pressure, and the various stretching and deforming effects to be associated with pressure, but that same relatively small amount of steam extracted as work makes the pressure fall just as dramatically ... not a particularly good tradeoff when the heavy boiler construction, greater need for safety devices, etc. needed for static high pressure is considered.

Now, reheat going to the LP side is much more important in principle, as the phase change to liquid occurs at lower and lower temperature as pressure increases.  So adding heat to preclude this phase change while active thrust is being harvested is generally a good idea, particularly if it can be done in a way that does not greatly impair mass flow or produce long TOF from HP exhaust to LP inlet.  (Chapelon arranged greater-than-usual gas flow to 'belly flues' in the boiler and mounted hairpin exchange elements in them, to help obtain high (but not excessive or runaway) resuperheat with low interference with flow.)

Those familiar with the 'art' of superheater dampers will realize that balancing the added reheat flow complicates things -- perhaps more than saving the initial cost of a HP superheater arrangement will do.

Note that perhaps the greatest potential saving is the adoption of the 'asynchronous compound' -- in which there are no piston rings and indeed may be no contact of any kind between the piston periphery and the adjacent bore; these work with the constant equivalent of 'slip' during admission and exhaust pressure and volume are accordingly larger (in proportion to what would be observed if the 'passed' steam were leaking).  The higher-pressure, higher-volume exhaust is handled through an appropriate plenum and admitted to a turbine of complementary design, which completes the stages of compound expansion down to whatever relatively low pressure is deemed most cost-effective.   Much applicable oilless-engine construction can be applied to one of the asynchronous-compound designs, including the use of unlubricated bushings and glands to keep oil of any kind out of the steam path or condensate.  Traditionally this wasn't used much as it had all the expense of a turbine and electric final drive, combined with the maintenance intensiveness (etc.) of a conventionally reciprocating setup.  But for energy recovery, and flexibility of 'boosting', and perhaps adapting a form of turbocompounding, the idea can be attractive.                                                                                                                                                                                                                                                                         

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Posted by ShroomZed on Friday, January 1, 2021 8:38 AM

Overmod

These are not enormous LP cylinders, as they might be on a straight de Glehn-du Bousquet -- think of this as a four-cylinder 135-degree locomotive that uses a proportion of exhaust steam in somewhat larger cylinders to conserve water.  The tunnel cranks allow the inside mains to run close to the inside face of the bearing box, permitting a larger bore than an inside crank would normally allow.

So you're suggesting using a fraction of the exhaust steam from the HP cylinders for further expansion? The steam is still at a lower pressure so it seems that the piston thrusts of the LP cylinders due to reduced size will be much lower than of the HP cylinders either way. 

Is there an inherent disadvantage to applying the LP cylinders on the outside? I know many of the later French four cylinders did this (such as the Chapelon 240P).

There is a Swedish locomotive (the class F I think) with HP inside and LP outside that used two inside steam chests for the sets of cylinders with outside Walscherts, but all the cylinders are in line. 

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Posted by BaltACD on Friday, January 1, 2021 11:16 AM

I am not a steam 'maven'.

It seems to me with each further use of 'exhaust' steam that the pressure and thus the 'speed' of movement of such steam slows down thus slowing down the mechanical operation of the machine down to the speed of the lowest pressure 'engine' is able to operate at.

Annimation of the triple expansion engines of the Titanic.

https://www.youtube.com/watch?v=ptDFqY-0Do8

 

By the time the steam reaches the turbine is it below the boiling temperature of water??????

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Posted by Overmod on Friday, January 1, 2021 11:22 AM

ShroomZed
So you're suggesting using a fraction of the exhaust steam from the HP cylinders for further expansion? The steam is still at a lower pressure so it seems that the piston thrusts of the LP cylinders due to reduced size will be much lower than of the HP cylinders either way.

In a compound, the HP engine valve gear is intentionally kept at longer cutoff to send the desired exhaust mass flow through to the further expansion stages.  For high speed you need to restrict duration of admission (and exhaust) anyway, so the effect is to run the engine a bit more like a simple (with the leakier torque, etc. but with high accepted back pressure instead of going into compression after valve cutoff) and then using whatever modulated steam is appropriate to match the resulting thrust in the LP contribution.

Since it is increasingly difficult to scoop water above 80mph the reduction of water rate becomes more important if sustained high speed is desired ... not a problem actually faced in American practice but surely threatened at a number of times.  I thought this was a reasonable balance (no pun intended) between the running characteristics of a 4-cylinder engine and the lower water rate of a compound.

There is of course applicability of the approach to a conjugated duplex -- the ACE3000 (assuming you could construct the frame and inside rods of a Withuhn conjugated duplex properly, which I do think possible) is an example.  Using Deem-style (geared) conjugation between the engines, the mismatch that has to be accommodated in the conjugation is limited the better the 'load following' on the LP engine can be.  In my opinion at least a proper Deem, while it will be detented to phase to 135-degree alignment when running, would be capable of 'slip' between engines in operation (via the Ferguson clutch) and this would affect how the IP injection would be modulated.

(Incidentally, in general i think a high-speed reciprocating engine needs its valve gear to 'fail safe' at speed, which in part means no purely 'electric' or solenoid-actuated valve gear that might easily lock in a fully-admitting or fully-blocked position at random, possibly at times of greatest stress -- the results with Timken narrow-width rods, in particular, being near-immediately catastrophic.  So all the special high-speed accommodations are made in, say, the follower arrangement in RC poppet gear, or in Wagner throttles at the individual HP inlets (as on the ACE 3000 for a different purpose) or in boosted IP modulation; if they fail the mechanical valves will keep the engine 'in time' to give it a better chance to get down through the critical speeds under control ... or a fighting chance to do so, anyway.  This safety is a primary reason it is unwise to use direct-connected reciprocating locomotives in true high speed.  If you have access to Carpenter's translation of La Licomotive a Vapeur, he included Chapelon's "150mph" design; see if you think safety is adequate at the rod loads involved ... and Chapelon is the one who deduced the required large deflection in Timken rods during high-speed running!

[/quote]Is there an inherent disadvantage to applying the LP cylinders on the outside?[/quote]Augment mass7, and less relevant for North American clearances with inside frame on standard gauge, loading-gage clearances.  This was and is a major factor in general British design.  There is a valid preference for inside connection for high speed (see the Belgian 4-4-2s) and lower augment (Woodard's Central Machinery Support) just as there is for keeping some of the balance weight of heavy rods in bobweights inboard instead of arranged in a driver rim (as in at least one Burlington ten-coupled locomotive circa WWI).  In modern practice the piston mass is important enough that very long stroke (up to 34"!) was preferable to larger bore in achieving low(er) augment.  On that basis alone LP inboard would make better sense; the shorter and more direct passages from exhaust to front end are an additional advantage.  I personally want the jacketed HP cylinders where I can inspect and work on them easily; that would NOT be true of inside cylinders in a cast (or welded composite) engine bed...

 

There is a Swedish locomotive (the class F I think) with HP inside and LP outside that used two inside steam chests for the sets of cylinders with outside Walscherts, but all the cylinders are in line. 

it is not unusual to see arrangements that put the valve gear conveniently and then use simple bell cranks or rockers to translate the movement to valve spindles in 'some other orientation'.  Generations of 'perfected' American 4-4-0s regularly did this in reverse: using four close eccentrics on the main and inside links, then levers to translate the link motion outboard to slide valves with riding cutoff arranged horizontally with 'gravity return' from conpression lifting relief over outside cylinders.  If you look at the Berry Accelerator described on Dr. Leonard's site, or a description of Cossart valve gear, you'll see a different use: to change the phase or direction of valve-gear motion separate from its 'natural' relation to power stroke.

A number of multicylinder simples, for example post-WWII in Poland or some of the UP Nines, took to using full sets of outside radial valve gear to get around the ... let's call them little idiosyncracies ... of Gresley conjugating levers.  Some of this can be interesting when an inside cylinder was arranged to be actuated from the pilot deck and now has to be remachined or modified for inside access.  In general anything 'inboard' in typical North American capitalist practice involved too much work or special attention to justify its retention; note the king, long history of all those Alco three-cylinder-simple "answers" to increased augment on larger engines before 1928, almost all of which were expensively rebuilt, and the exceptions frequently cursed (see the amusing quote about the SP 4-10-2s that it was like 'having an expensive mistress at every division point')  

In the presence of the post-N&W J and Niagara revolution in lightweight-rod practice (and the UP 800 and now NYC L-3 and L-4 Mohawk practice with lightweight bushed plain-bearing rods) it really makes less sense to retain balanced-compound inside cylinders of either kind if external (e.g. conjugated duplex) is an option.  That is particularly true in a world -- and North American PSR is rapidly returning to one like it in practice -- where peak train speed is 45-50mph.

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Posted by ShroomZed on Sunday, January 3, 2021 7:50 AM

So you're suggesting a system similar to the French PLM 151A which is something I've given some thought myself. I've always been rather impressed with them all things considered. 

Speaking of French locomotives again, can someone explain to me what the heck is going on with the cylinders on these Nord/SNCF decapods? 

 Description of this image, also commented on below

I've never understood why the piston valves are so enormous on these engines. There's also an enormous structure emerging from the top of the steam chests, although I'm guessing those are just huge steam pipes. I've never seen a cylinder arrangement like this on any other engines. 

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Posted by Overmod on Sunday, January 3, 2021 10:44 AM

The 151A still has the inside rods and cranks, and the arrangement of rear cylinders is not that strong.  It certainly succeeds at reducing augment by dividing the drive, but keeping the engines in phase.

In general you want the biggest valve area (port area) you can arrange, subject to minimizing the effective dead space in the port volume between valve and piston and the physical resistance including internal weight of the valve.  In exhaust valves at the end of long expansion you have the need to accommodate large volume, which is where a Willoteaux valve becomes useful.  I do not have a fabrication diagram to show you, but think of a Trick valve made like two piston valves with internal passages arranged in series, made of stamped or formed metal for light weight.  (If I remember correctly the infamous 152P design had these and they show up in the longitudinal section drawings)

https://i2.wp.com/www.advanced-steam.org/wp-content/uploads/2017/05/JD-letter-image-1.jpg?ssl=1

Now I was fooled early into thinking that Willoteaux valves could accelerate port opening dramatically by rotating on their axis as well as sliding, which by careful design of the steam edge in a long-lap valve can give extremely good port opening while maintaining short effective cutoff, something a purely sliding valve would need longer longitudinal lap and longer travel to produce (as the valve would have to acquire considerable speed before crossing the admission edge even with flow-streamlined passages from near-circumferential ports).  I actually designed these, cribbing a bit from Bulleid's Leader, before being apprised that this was not, in fact, what a Willoteaux valve did -- I still don't consider the principle novel as I was 'told' it would be of use somehow or somewhere ...

If you combine double-ported Willoteaux valve travel with long-lap long-travel design precepts -- and the postwar French for travel up above 16" on one de Caso design, as I recall -- you will not be surprised to see the physical valve bore become extended in length.  You would also see passages corresponding to the elongated ports in the liners, and the admission and inlet passages might extend quite far along the elongated valve bore at each end of the cylinder, above it or inboard from it... as I think visible on the 151 shown.

There are parallels, with of course very different physical geometry, for poppets of the different types and for Cossart drop valves, which are like a hybrid of piston and poppet valves actuated at right angles.  In some modes of operation (e.g. flow streamlining becomes more and more critical at higher speeds with shorter events), sometimes what look like exaggeratedly excessive steam space and highly-superheatable volume close to the valves can become important.

If you do not use circulated boiler water through tracer lines, you will need somewhat exaggerated jacket volume, including if you want to try Chapelon's idea from 160 A1 in actual daily North American practice (where, for example, starting losses or freezing are very real concerns).  Wardale famously says that the gains from jackets are not worth the disadvantages over good insulation if you use his approach to valves (articulated heads, multiple diesel-style rings, vastly better supplied tribology, and steam-cooled liners for a start) and I adopted my method in part because other systems on the engine facilitate it, and it can reduce the water rate meaningfully at times, not that it is or isn't more thermodynamically superior in itself.

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Posted by Juniatha on Sunday, January 10, 2021 5:02 PM

On those steam chests ...

Ehm - I tried to post a photo of Aleesha Young - no. Yes

Ok, just take a look here  No

US body builder Aleesha Young

will it stay?

I can't say!

Gee, hey!

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Posted by Juniatha on Sunday, January 10, 2021 5:02 PM

Hi ShroomZed

 

You asked why the piston valves are (must be) so enormous on 

these engines - well, that's about like asking why are the arms

of Aleesha Young so enormous. And the designer of the NORD

railway in France, Marc de Caso, has long been taken from us.

The engine on your picture is preserved at the Musée de Chemin

de Fer in France. She is a four cylinder compound and what you

comment on are the HP cylinders, i.e. you have fresh steam pipes

coming down to the steam chest of the outside cylinders (middle)

then steam is being transferred to the inside LP cylinders and you

want to have capacity in the intermediate receiver in order to keep

steam pressure from fluctuating too hefty with each exhaust HP

and intake LP. These were the outer conducts besides the fresh

steam pipe - and all of it is being covered by one combined cladding.

What exactly Aleesha can do with her arms you might want to ask

herself, but the 150.C locomotives this way could better keep up pulling

force at rising speed due to better steam flow, in other words produce

higher hp outputs.

About the same - yet somewhat more elegantly - can be seen on the

'Little Wolf' the infatigable 141.P engines - Mikados of average

(European) size that in spite of their 65" wheels were used to run

heavy express trains of 16, 18 or more bogie cars at up to 120 km/h

(~75 mph) over ondulating profiles developing up to 4000 ihp (PLM

double exhaust) or 4400 ihp (double Kylchap exhaust) for the later 

series

Well, it takes ample inner volume and careful inner streamlining to

design a compound properly - that's why I don't see how it could

have been adapted to the heavier US steam locomotives without

a hefty boost in live steam pressure and temperature to balance it.

The Norfolk & Western Y-6 gives you an impression where

dimensions would go to - and then create another problem:

how to mechanically and thermally proper handle steam in

and out these enormous cylinders. 

Much more to be written about this ..

generally it can be said that when a compound did not

live up to expectations, it was not the system of double

expansion - it was the lack of quality of design, where simple

'good enough' engineering did not suffice.

More maybe another time, guys!

 

Welcome *) back my friends

to the show that never ends!

Juniatha

(BTW in 1993 I designed a de Glehn four cylinder compound HP outsides)

myself to German profile and axle load specifications as a free lance effort - 

I tell you, I know what I'm talking about ..)

*me)

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Posted by Flintlock76 on Sunday, January 10, 2021 5:20 PM

Look who's back!!!  

Christmas came a little late, but it came just the same!

Welcome back Juniatha!  You were sorely missed!  

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Posted by Paul Milenkovic on Sunday, January 10, 2021 8:56 PM

Flintlock76

Look who's back!!!  

Christmas came a little late, but it came just the same!

Welcome back Juniatha!  You were sorely missed!  

 

I second that sentiment.

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by Overmod on Sunday, January 10, 2021 11:20 PM

Paul Milenkovic
I second that sentiment.

I third it.

 

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Posted by selector on Sunday, January 10, 2021 11:45 PM

Thumbs Up Glad to see you posting again.

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Posted by CSSHEGEWISCH on Monday, January 11, 2021 10:10 AM

I'm not a steam fan by any stretch but it's always good to see the return of a knowledgable contributor.

The daily commute is part of everyday life but I get two rides a day out of it. Paul
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Posted by M636C on Tuesday, January 12, 2021 1:29 AM

Personally, I think this discussion can be likened to the mediaeval theological discussion about the number of angels that could dance on the head of a pin.

However, Overmod's contributuion:

 I do not have a fabrication diagram to show you, but think of a Trick valve made like two piston valves with internal passages arranged in series, made of stamped or formed metal for light weight.  (If I remember correctly the infamous 152P design had these and they show up in the longitudinal section drawings)

https://i2.wp.com/www.advanced-steam.org/wp-content/uploads/2017/05/JD-letter-image-1.jpg?ssl=1

at least caused me to look up the rest of the 152P. It appears as the last folding plate in Carpenter's translation of Chapelon's La Locomotive a Vapeur, plate XIII. This appears to be the same drawing as linked above, just the whole of the locomotive. I note that the centre cylinder drives the third axle while the outside cylinders drive the second. This meant that the second axle had to be joggled to clear the connecting rod, a feature common in Alco three cylinder simples.

But Chapelon had prepared an earlier 2-10-4 design, which I guess we can call the 152A since it preceded nationalisation. The "P" code was used for SNCF standard designs.

This was an enlargement of 160A1 complete with all six cylinders. (What could possibly go wrong?) Looking at this, I noticed that the low pressure cylinders were not all the same size. The LP cylinders are arranged in a line at the front, but the inside LP cylinders are the same diameter as the HP cylinders (ie, the biggest size that will fit between the frames. So I checked 160A1 and it was the same. Not only were they the same diameter but they were the same stroke. So clearly, since the outside LP cylinders were much larger in diameter, there must have been considerable variation in the tractive effort depending on cylinder position during  any rotation cycle.

So when did Chapelon abandon six cylinders?

Clearly when rebuilding the 241-101 as 242 A1....

Now to some extent his hand was forced - 241-101 was a three cylinder simple and converting it to a Smith Compound made sense. Chapelon still inceased the weight by about twenty tonnes (which was the original coupled axleload).

Looking at the drawing linked by Overmod reminded me of something.

On page 21 of O.S. Nock's The Midland Compounds on page 21 there is a cross section of MR 2631 showing a single piston valve under the centre HP cylinder. The outside LP cylinders used slide valves. The layout from January 1902 still worked in the 1940s. 240 Midland Compounds were built over 30 years, the most successful compounds in Britain.

Maybe one of those might have succeeded in the USA? Were Smith compounds ever used in the USA? I think Reading had some three cylinder compounds at one time.

Peter

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Posted by Overmod on Tuesday, January 12, 2021 7:35 AM

M636C
Were Smith compounds ever used in the USA?

I believe Baldwin 60000 was a Smith compound, at a higher HP pressure facilitated by the watertube firebox.  It is my naive observation that several approaches to the idea were tried with various expansion ratios from about 2.3 to 2.7 -- the basic 1:2 with all cylinders equal apparently "leaving some money on the table" with respect to using the expansive energy fully.

 In light of the absence of resuperheat on long expansion of LP causing pressure drop in the latter part of the stroke, this may be less applicable, as in many 3- and 4-cylinder designs.  Again, subject to balance issues, some IP modulation may substitute both for reheat and fiddly adjustment of 2 separate sets of valve gear in getting equivalent thrust over equivalent stroke in all 3 cylinders of a Smith compound.

Since Juniatha is back -- she mentioned to me that the LP arrangement on 160 A1 was actually a 5-cylinder compound with the final LP stage divided into 2 cylinders primarily for clearance and packaging reasons.  She will be a reasonable authority to comment on the 152A.

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Posted by Juniatha on Wednesday, January 13, 2021 10:03 PM

To Quote Overmod:

"Since Juniatha is back -- she mentioned to me that the LP arrangement on 160 A1 was actually a 5-cylinder compound with the final LP stage divided into 2 cylinders primarily for clearance and packaging reasons."

Something got overly babbly-babbled here (no insult intended).

I didn't say (write) that.

There were two inside HP cylinders, working on 90 ° set cranks of #4 coupled axle, then there were four LP cylinders which were altogether arranged as a three cylinder machine: two outside cyls at 120 °, then two smaller inside LP cyls at 180 ° to each other and 120 ° to the outside LP cyls. The two inside LP cyls were together giving the same piston thrust as one outside LP cyl.

I had myself also experimented - in theory - with divided inside cyls on what was otherwise a three cyl simple - just to balance the inner drive. However, while this brings about a very balanced inner drive it leaves the outside drives now even less balanced. My idea back then was to balance out the outer drives each individually rather than seek an overall self-balaning in an engine where the outer cranks are some 80 ins apart - thus inevitably a major degree of self-balaning would only result in a twisting motion of the overall engine - non desired by me. What stayed was the less sturdy coupled axle with those counteracting cranks, making a long centre interconnecting lever. If used in a common axle drive, the outer cylinder will subject this axle to distortions by mass forces at speed - undesireable! If used as a first coupled axle drive the lesser stiff axe against a single throw axle in a three cyl engine is also less than desireable with flange / rail contact lateral forces.

Thus in the end I dismissed the type and threw away the double throw design.

On the 160.A.1 it would have been difficult to arrange the LP cyls like a four cyl engine and all with the same dxs dimensions because of general restrictions to cyls inside the frame - while on the outside possible volume would been lost. It was André Chapelon's major aim to give the twelve coupled engine an ample amount of cylinder volume to work on economic cut off rates up-hill at low speed. This he achieved by this rather unconventional design concept - and the six cylinder engine had a 3/4 rythm of exhaust beats. You may ask why not use but one instead of two smaller cylinders inside: well, that - to my view - was just due to the very short connecting rods on this inside drive to the second coupled axle: with two cyls arranged at 180 ° the piston force each was smaller and the drive was balanced. 

In general my suggestion would be never to use more cyls than can be arranged in one group aside each other, thus banning staggered arrangements in general. 

This may in a certain instance involve even fife cylinders side by sides - 

but that is another story ..

Juniatha

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Posted by SD70Dude on Thursday, January 14, 2021 1:42 AM

Great to have you back, I'm really enjoying reading this thread, keep it up!

Greetings from Alberta

-an Articulate Malcontent

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Posted by M636C on Thursday, January 14, 2021 9:44 PM
I believe Baldwin 60000 was a Smith compound, at a higher HP pressure facilitated by the watertube firebox.  It is my naive observation that several approaches to the idea were tried with various expansion ratios from about 2.3 to 2.7 -- the basic 1:2 with all cylinders equal apparently "leaving some money on the table" with respect to using the expansive energy fully. (Overmod)
 
I agree that 60000 is a Smith Compound, but I was thinking of locomotives more contemporary with the Midland Compounds or Smith's own single conversion.
In his Steam Locomotives of the Reading, Wiswesser provides rather confusing details of the class P6 Camelback Atlantics. He first indicates that the four units, 300 to 303, built by the P&R in 1909 to 1911 were three cylinder compounds with cranks set at 120 degrees. However, it seems that they had second thoughts during the build, and 301 and 302 were completed as two cylinder simples, all four using saturated steam,
300 had three cylinders 19"x24" and 303 had three at 18.5"x24" while the two simples had 22"x26" cylinders. The compounds were converted to simple by 1918 and all four were superheated in 1924.
Apparently there was one 3 cylinder simple, class P5 number 344 with three cylinders 19"x24", so the same as the compound 300. It had piston vavles driven by Walschearts gear (outside) and Joy gear (inside). It too became a two cylinder in 1917.
O.S, Nock indicates that Smith Compounds had the low pressure cylinders 90 dehrees apart with the high pressure at 135 degrees to the other two. Was this the case with 60 000?
But the topic of the thread concerns the use of compounds in the USA.
It should be remembered that in France, coal was relatively expensive and crews were rewardedby additional payment for saving fuel. They were also paid additional amounts for making up lost time.
In this environment, the forces that directed Chapelon's work can be seen more clearly. His locomotives were built for economy, but with the ability to provide additional power when required to make up time, even if being "thrashed" by other standards. 
In the USA, fuel and water economy were not taken as seriously.
Baldwin 60 000 was tested by the ATSF in normal service against four of their standard 3800 series 2-10-2s in March and April 1927, outlined in Santa Fe Locomotive Development by Brasher..
60 000 did the work in 11.5% less time than the 3800
60 000 hauled, on average 3.5% greater loads.
60 000 used, on average 24.5% less coal per 1000 ton miles.
60 000 used on average 27% less water per 1000 ton miles.
In France, that would have assured 60 000 of a rosy future. In the USA, this was regarded much less important than the penalty imposed by the more complex mechanism.
 
In these condtions, 160A1 would not have even been tested...
 
There were two inside HP cylinders, working on 90 ° set cranks of #4 coupled axle, then there were four LP cylinders which were altogether arranged as a three cylinder machine: two outside cyls at 120 °, then two smaller inside LP cyls at 180 ° to each other and 120 ° to the outside LP cyls. The two inside LP cyls were together giving the same piston thrust as one outside LP cyl.-(Juniatha)

I recommend checking out Chapelon's own drawings of 160A1 in Capenter's translation of La Locomotive a Vapeur .  For a start, there are only 12 fire tubes in the boiler, the remainder being flues with Houlet elements in the approximately one third of the flues devoted to high pressure steam, and conventional Schmidt elements in the two thirds of the flues devoted to intermediate pressure steam. This of course requires three separate superheater headers, the high pressure at the top in the usual place, and one further each side for the intermediate steam. The smokebox is forced into a triangular shape, visible in side on photos just behind the smoke deflectors.

As Juniatha has indicated, the inside low pressure cylinders are at 180 degrees to eachother and 120 degrees from the outside low pressure cylinders. This allows the two inside cylinders to provide an even turning moment with the two outside LP cylinders.

However, this is similar to the Gresley arrangement of three simple cylinders and requires a conjugating gear to derive the action of the inside poppet valves from the outside Walchearts gear driving the outside LP poppet valves. Fortunately, the Henschel design was used rather than Gresley's.

Of course the locomotive is driven on the second, third and fourth axles with two sets of Walschearts gear driven by separate return cranks on the third axle.

What could possibly go wrong?

Peter

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Posted by Overmod on Thursday, January 14, 2021 10:17 PM

Overmod
Since Juniatha is back -- she mentioned to me that the LP arrangement on 160 A1 was actually a 5-cylinder compound with the final LP stage divided into 2 cylinders primarily for clearance and packaging reasons.

Something got worse than babbly-babbled in that sentence.  But she subsequently explained how the thing is actually constructed, so there is no lasting harm.

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Posted by Paul Milenkovic on Friday, January 15, 2021 9:34 AM

Bill Withhun's recent postumously published book suggests that the problem with Baldwin 60000 was the watertube firebox.  Withhun himself counted many more washout plugs than a conventional locomotive, suggesting that even the mandated-to-be-at-least monthly washout and scale removal would be costly in labor hours.

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by Paul Milenkovic on Friday, January 15, 2021 9:45 AM

I just "hit" me.

I suppose the reason for the 90-deg 135-deg arrangement of a 3-cylinder compound is that it works better than the more even-torque 120-deg spacing when the HP and LP are not perfectly balanced?

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
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Posted by Overmod on Friday, January 15, 2021 10:23 AM

Paul Milenkovic
I suppose the reason for the 90-deg 135-deg arrangement of a 3-cylinder compound is that it works better than the more even-torque 120-deg spacing when the HP and LP are not perfectly balanced?

Think of the steam flow, too.

I had always thought the reason for the 90-degree quartering of the outside mains was to give the best 'continuous' thrust on the outer pair... as with conventional 2-cylinder DA.  The HP 'four pulses per revolution' is phased to fill in the 'low spots' in the resulting torque curve... 

As far as I've modeled it, a similar phasing arrangement ought to work if IP injection is in use to 'normalize' all three cylinder contributions.  Remember that unless you have a Leader-style engine, a typical three-cylinder locomotive is NOT augment-balanced; the outer cranks are only at 240 degrees to each other -- not as in a Swiss drive where the 120-degree throws are inherently balanced.  This is complicated, again in a way I haven't bothered to calculate, so I don't know how slightly, if the center cylinder is angled to clear the forward driver axle and the crank throw and counterweights are slightly rotated to keep the effective phasing at 120 degrees.

I've always been a proponent of balanced four-cylinder drive, even if it does mean smaller cylinders.  Note how many of the balanced compounds put the four cylinders 'abreast' as Juniatha indicated, even when the leading driver axle has to be 'cranked' for inside-main clearance.  The problem there is that it becomes complicated to provide and maintain roller bearings (of '30s construction and tribology) in a cranked axle of appropriate geometry and strength.

The use of proper Deem conjugation on a more-or-less conventional duplex (with the engines each quartered with zero overbalance, and the two engines detent-phased at 135 degrees) still represents an attractive proposition.  It is not as easy to implement Voyce Glaze's balancing (although there is less piston thrust in the vertical plane to compensate, there is less potential to shift overbalance to the other drivers -- which is another reason to use zero overbalance) but the fixed phasing provides a better torque curve at very short cutoff -- an important issue even on a conjugated duplex -- and active predictive suspension can do a better job of controlling both vertical travel and effective momentum damping (in addition to magnetorheological damping).

The critical high-speed consideration, in my opinion, is emergence of resonance at critical frequencies, which is a far more significant concern than 'how fast the steam can run the engine' or other relatively naive consideration.  I found it particularly interesting that an Eastern European design team identified one such likely harmonic in the class 05 design at right around the equivalent of 122.5mph, without noting that this might have been an emergent reason no German run to 'outdo Mallard' was undertaken. 

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Posted by M636C on Friday, January 15, 2021 4:00 PM

Paul Milenkovic

Bill Withhun's recent postumously published book suggests that the problem with Baldwin 60000 was the watertube firebox.  Withhun himself counted many more washout plugs than a conventional locomotive, suggesting that even the mandated-to-be-at-least monthly washout and scale removal would be costly in labor hours.

 

As well as the figures noted in my post above Brasher quotes:

The equivalent evaporation pounds of water per pound of coal for the boiler was 7.9% less and for the boiler and superheater 10.5% less for locomotive 60 000 than for locomotives of the 3800 class.

This suggests that the water tube firebox is significantly inferior to a conventional staybolted firebox (which is not unexpected) but indicates the relative efficiency of the compound cylinders was even better than was observed from the test results given the poorer performance of the firebox.

Peter

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Posted by M636C on Friday, January 15, 2021 4:14 PM

The critical high-speed consideration, in my opinion, is emergence of resonance at critical frequencies, which is a far more significant concern than 'how fast the steam can run the engine' or other relatively naive consideration.  I found it particularly interesting that an Eastern European design team identified one such likely harmonic in the class 05 design at right around the equivalent of 122.5mph, without noting that this might have been an emergent reason no German run to 'outdo Mallard' was undertaken. (Overmod)

I'm not sure how significant this is, but an interview with a crew member on 05 002 on the day of the record run included the remark that, unlike previous runs, "everything was was working perfectly" and the locomotive was running more smoothly than usual, and this continued as the speed increased. As everything was going so well, they just let the speed increase until they passed 200km/h and then shut off, slowed down and stopped to do a running check.

It is possible that the track in question was particularly well aligned and the temperature range was conducive to optimum perforformance.

Peter

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Posted by Overmod on Friday, January 15, 2021 11:06 PM

M636C
It is possible that the track in question was particularly well aligned and the temperature range was conducive to optimum performance.

It is also possible that the Eastern European analysis was wrong about the critical speed or the prospective intensity of the resonance in question.  My real concern is only that the power involved in critical resonance at the speeds in question is dramatically greater as you get into this high speed range, and the consequences less easy to 'damp out' by closing the throttle, or centering the reverse, or applying the brakes in time to avoid difficulties.

There are a number of accounts where engineers encounter severe 'rough riding' in a particular speed range -- ISTR the 6000-series Garratts have one around 50-55mph, might be give or take a few mph, and engineers learn to 'ride it out' if going faster and then 'ride it down' to get out of the critical range.  At much higher force or rapidly-amplifying resonance, riding it out might not be possible or prudent to engage in.

I have little question that the 05 design was capable of well over 125mph but I continue to find it strange that no attempt to reach even Gresley's acknowledged top speed was at least undertaken.  Perhaps the contemporary 'rail emphasis' was indeed on Diesels, and the magic 'double metric ton' was enough to establish credentials for steam.

It is my opinion that the documented complaints of 'hard riding at 135mph' for T1s, if genuine, are the result of a resonant effect.  This is one of the specific things that the multiphysics modeling (and perhaps later testing) of replica 5550 is intended to develop.

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