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

Trains Magazine Steam & Preservation
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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 co

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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 con

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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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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 o

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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.

[quote]
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

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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 ’

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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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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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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

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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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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-tr

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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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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

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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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I second that sentiment.

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I third it.

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[tup] Glad to see you posting again.

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

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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

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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.