Compound Mallet Question

[daveklepper]

Agree with the assessment of Fred Westing's book. And note the extremely thorough testing of the E-6 before serial production. Compare that with PRR's Metroliners, Amtrak's Acela, the Boeing LRV, and the most recent Breda light rail cars in Boston.

But back to locomotive truck design. Is one reason the various European designs mentioned never were tried in the USA the difference in quality and design of the track structure?

[Anonymous]

For a good writeup on the Reading 4-4-4 see Fred Westing's APEX OF THE ATLANTICS - his history of the Pennsy E6 (one of the greatest locomotive books ever written, BTW).

It seems that neither the leading or trailing trucks of the 4-4-4 were equalized with the drivers. This allowed loss of adhesive weight when the drivers were in low spots, and overloading of the driver axles when they were in high spots. It also contributed to instability at high speeds. The 4-4-4s were all rebuilt into conventional 4-4-2s with the trailer equalized with the drivers.

None were ever equal to the E6, which, interestingly, had the lead truck equalized with the #1 driver and the trailer equalized with the #2; the two drivers were not equalized together.

Old Timer

[Overmod]

Do you have references, preferably to an online-located resource, for E.S. Cox's observations on Cartazzi problems?

My understanding of the Reading 4-4-4 was that it was an "improvement" on the existing Atlantics, which dated back a long way on the Reading -- they had one in the early 1890s with Vauclain compound cylinders and 81" or taller drivers. I had also understood that most of the early Atlantics used an extension of the locomotive's rigid frame to position the trailing axle... but that the axle had substantial lateral motion. Some of the earlier 'built-up' trailing trucks, for example the Cole type that Alco used, were IIRC much more intended as devices for controlled lateral motion than for radial swing from a pivot, were they not? At least in older and presumably slower locomotives, as soon as you have lateral motion, the more significant of your 'rigid-wheelbase' worries do not apply, and some other advantages (such as easier equalization) apply. It's my opinion that only a substantial cast-steel frame makes a Delta-type trailing truck practical...

I think what you're tacitly getting at in the Reading discussion is that the design had a high ... probably much TOO high ... trailing polar moment of inertia, relative to the short driver wheelbase. I can re-create some of the 'logic' behind using a pin-guided truck back there: the lateral spring guiding would inherently provide control of the swing excursion of both front and rear of the locomotive dynamically... and this was known to occur 'correctly' on a wide variety of successful locomotives in practice, on the front, so why shouldn't it do so on the rear...

Now, I don't know whether the Baltic locomotive (of 1912), which essentially used this approach on a six-coupled locomotive, was an inspiration to the P&R for their locomotive. Nor do I know whether the Baltic itself was successful in achieving good guiding -- although it seems memorable enough that Milwaukee thought to apply the name to its earliest true-4-6-4 designs (to this day, a Hudson is a 4-6-4 with a hinged trailing truck, and a Baltic is a 4-6-4 with pin-guided trailing truck). Seems to me you'd get better results with the longer driver wheelbase for a given spring rate and strength in the lateral springs for the bogie pivots.

I also think that the problems with pin-guided trailing trucks can be solved by using weight-actuated outside bearers, or for that matter other forms of bolstering. The principal reason to avoid them is that they interfere with the ashpan, and with any structure under the firebox area, and (imnsho) don't provide any benefits whatever compared to alternative types with proper detail design, in almost all prospective service.

Must say I wi***hat I could have been chasing trains too!

[M636C]

Overmod,

Sorry about that! I've been out chasing trains and I'm too tired. I'm sure I hit the "L" in Helmholtz both times, but didn't notice that it didn't appear. And I did mean the compound sentence about use in the USA to refer to the frames and not the trucks.

The Cartazzi worked well enough in England, but was a complete disaster in India, combined with insufficient initial spring compression in the bogies. E.S.Cox, who accompanied W.A.Stanier to India (basically as a French translator) has described the problem very well.

I think the problem with the 4-4-4 "Reading Type" was that the trailing axles in the Atlantics were virtually rigid (compared to the bogie), and provided a much longer effective wheelbase (much the same problem as the Indian "Pacific" locomotives).
The firebox of the 4-4-4 was shortened by 12" on conversion to Atlantic, which may also have helped by reducing the rear overhang and the mass distribution.

Peter

[Overmod]

Just as a note, Krauss-Helmholtz (note sp) was a reasonable approach to guiding... in Europe. I think you meant that bar frames, not the bogies, were "used widely ... as in the USA" -- I don't know of any successful use of a Krauss-Helmholtz in American practice (lateral-motion devices being used instead). There isn't doubt that they worked nicely in a wide variety of European locomotives, some operating at considerable speed (some Golsdorf locomotives come to mind)

Note what is required for the siderods going to the driver axle in one of these bogies. Even spherical-pivot roller bearings won't be happy with such loadings. I have seen a couple of frankly ingenious arrangements of rods and levers that can, in theory, maintain the rods in quarter for a hinged axle, but again none of these made it to heavy US practice.

We might also mention the Cartazzi axlebox, which implemented lateral motion via horizontal curves in the boxes and pedestals that matched the 'swing' of the axle on curves while maintaining reasonably tight longitudinal tolerance.

jruppert, you're correct in presuming that the swing at the rear end of some trailing trucks could be extreme. In practice, this didn't matter in most cases, since the bearer connections between truck and locomotive frame at the rear didn't have to be all the way at loading-gauge clearance, and devices (such as toothed rollers) could easily accommodate substantial amounts of swing and still maintain weight transfer. The longer the distance from pivot to leading axle, the greater the 'self-centering' tendency and resistance to instabilities with the engine running nose-forward... and, in some cases, the added length was needed to position the axles correctly under a longer firebox in order to get the axle loadings correct.

[M636C]

Paul, and Overmod,

Most two axle leading trucks used a swing link arrangement to increase the vertical load on the truck proportional to its displacement. This had an inherent problem that the load on each wheel varied with displacement, and this could lead to derailment.

On the British London and North Eastern Railway, a large number of 2-6-2 locomotives of class V2 suffered from problems due to their swing link trucks. When he took over from Nigel Gresley, Edward Thompson rebuilt many of these locomotives with spring centred trucks, using the same centring action as most four wheel bogies. Thompson did substitute a 4-6-2 design, class A2, for new construction however.

In Europe, two designs of truck were developed that coupled a single leading axle with the leading coupled axle, allowing the usual form of leading bogie location and centring to be used.

The older design, the Italian "Zara" truck, used plate frames in what was a conventional two axle truck, except, of course that the wheels in forward and rear wheelsets were greatly different in size. Italian steam locomotives used plate frames, and those on the Zara truck were sufficiently narrower than the main frames to fit inside them, and the main frames had no direct attachment to the leading coupled axle. The most common Italian express locomotive, class 685, was a 2-6-2 with a front Zara truck.

The later design, the German "Krauss-Helmhotz" was a different design more suitable for bar frames, used widely in Germany (as in the USA). The truck had the usual arrangement for the leading axle and the pivot , but at the leading coupled axle the truck was connected to a pivot below the leading coupled axle, which was carried in conventional bearings in the main frames. These allowed additional lateral movement to allow the axle to act as the trailing axle of the bogie.

These Krauss-Helmhotz trucks were used on most German standard locomotives, including the very large number of 2-10-0 War Locomotives of classes 52 and 42, which were not intended to run at high speed. They were also used on 2-6-2 class 23 and 2-8-2 class 41 which were used for passenger traffic.

In this respect, European design was well in advance of British and American designs.

Peter

[Anonymous]

O, I guess in short you are concluding that a two wheeled leading truck can be just as good as a four wheeled leading truck given proper damping.

One advantage that I can see that a four wheeled truck might have over a two wheeled truck, is that any movement or forces transmitted to the frame from the truck is an average of the movement and forces acting at the extremities of the truck.

It seems that trailing trucks have a much longer distance from the axel center to the point of connection to the frame. It seems that would increase lateral movement for a given curve, possibly a bad thing? Or is this distance actually shorter? When compared to a leading truck's distance. It seems in either a leading or a trailing truck, a long reach to the trucks center of movement would increase lateral movement and also increase forces transmitted to the frame for a given curve?

[Overmod]

Might also be mentioned that the British 5AT project, to develop an advanced modern locomotive, will be using a narrow firebox...

But typical American practice used wide, and sometimes long, grates to give the desired combustion area... and most late European practice, especially where coal quality was lower, tended to conform to this. Wide fireboxes are, I think, somewhat easier to fire heavily, as there can be more 'heel' at the back and better loading, shaking, etc. of the grates at sustained hp output. Wide fireboxes generally require a trailing truck for stability -- engines like PRR G5s that put a wide grate above the drivers tend to have decidedly poor riding qualities!

Will Woodard decided, I think correctly, that there would be benefits in articulating a long trailing truck under a BFF (that's a big firebox to those with gentle minds ;-}), but somewhat less correctly he essentially tried to run the locomotive drawbar through the truck frame -- this produced some rather interesting weight-transfer and suspension issues! What got used instead was progressive weight loading (sometimes through actual oval gear-toothed rollers or roller segments!) on the rear of a pivoted trailing-truck frame; to my knowledge, this provided sufficient lateral guiding on the trailing-truck frame for whatever high speeds the engines themselves could reach in service. (I have my doubts that Fabreeka springing would 'live' effectively in trailing trucks due to the heat due to the proximity of the ashpan and grate; a number of roads chose not to use roller bearings on trailing-truck axles for I think this same reason.)

It's possible (as on the 5AT proposal) to use a modified Franklin radial buffer to snug the tender up against the locomotive, which essentially uses the first tender truck as if it were a trailing truck to control and guide the motion of the frame and drivers of the locomotive. This should dramatically relieve problems like those encountered on the G5s.

Paul, the question about the leading truck requires a somewhat more detailed answer, and a bit of 'what-if' imagineering.

Traditionally, the pin-guided four-wheel truck has been used on high-speed power, and the 'Bissel'-style two-wheel truck on freight power. The reasons have to do with geometry. The Bissel truck is inherently dynamically unstable in yaw ... the further it deflects, the greater the deflecting force on it, as opposed to the inherent restoring force on the same geometry when the axle is behind the pivot, as in a Delta trailing truck. That means that without lateral compensation the 2-wheel truck will develop high forces and perhaps sudden oscillations or instabilities without warning at higher speed... and most traditional 2-wheel leading trucks only used some variant of weight or friction to control their lateral movement. In the pin-guided truck, thrusts from the leading and trailing wheels 'balance out' to keep the truck frame aligned with the track, and the lateral motion of the pin relative to the locomotive frame (which does the actual guiding of the locomotive proper in curves) is not explicitly tied to yaw moment. However, this geometry is NOT what you want under the end of the locomotive behind the drivers, as there's no inherent means of damping oscillations or hunting of the pin-guided truck when constrained to follow the frames... the Germans tried this approach with some of their 'bidirectional' express locomotives and had to limit top speed to about the equivalent of 81mph as a result of rather substantial oscillation and other problems that even their engineering couldn't cure...

The Reading had a couple of sad failures that point up both these tendencies. A progressive engineer thought a good cure for Bissel instability would be to mount a pair of heavy lateral springs to keep the truck aligned with the frame by default -- good thinking, as far as it went: the springs would provide the desired kind of restoring force, but would be comparatively neutral for small-arc truck movements. Unfortunately, nobody seems to have recognized that with no damping other than friction, the springs would build up oscillations -- the 2-10-0s with these devices became notorious for hard riding, and apparently one guy got so fed up that he welded the spring gear up so it didn't "cushion" -- wow, instant improvement, I wonder why...

Meanwhile, at about this time, the Reading built a 4-4-4 with symmetrical pin-guided trucks under both front and rear... a nice improvement in capacity for big Wootten fireboxes over what an Atlantic's single axle could support at reasonable track-saving axle loading. It did not take them long to remove it, and the history I've been able to find is mercifully silent on their experience convincing them to do so.

The correct approach was at least tried by N&W, which was to use composite springs, similar to those used on pedestal tenders, on the leading-truck axle. These "Fabreeka" springs are sandwiches of rubber blocks and metal sheets, similar to the 'chevron' springs seen in some of the high-speed trucks of a quarter-century ago, and have very good lateral restoring force coupled with very high inherent damping. On pedestal tenders, they are used to locate the (otherwise laterally floating) tender axles, to give fully flexible lateral motion on curves and during equalizing, while providing a fixed location for the actual vertical suspension to bear upon. In the two-wheel leading truck, they allow a degree of highly-damped lateral motion, and consequent good guiding, for small lateral movement, and also damp any oscillations that may develop on curve entry and negotiation. Further angle of the truck in curves can be accommodated by a progressive weight-transfer system, or by variable-wound or other variable-rate springs accompanied by dashpots or other appropriate forms of damping. There is no theoretical reason why such a truck wouldn't be capable of equal or better stability compared to a 'typical' pin-guided lead truck (which normally doesn't have anything other than accidental friction and, to an extent, viscous damping about its axis of rotation)

Hope this is helpful and relevant to what you were asking!

[Anonymous]

Mark -

You state that UP's financial results were difficult to break out of all the intricate corporate structure and that's true. But the statistics such as GTM/TH and operating ratio wouldn't have anything to do with the oil and coal operations, and would provide some comparisons.

Paul Milenkovic - Baldwin beat Porta to the skinny-boilered 2-10-0 concept by about eighty years. They were selling light-axle-loading Decks to short lines beginning in the late 1920s. Strasburg 90 is a living, breathing example and several that were owned by the Gainesville Midland in Georgia still exist, although none operate. The old Russian Decapods were even earlier examples of the concept, and the IRM at Union, Ill. has one of those that has operated in the recent past if it's not running right now.

Old Timer

[Paul Milenkovic]

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?

[Overmod]

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...

[Overmod]

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....

[CSSHEGEWISCH]

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.

[Overmod]

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...

[Anonymous]

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?

[Anonymous]

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.

[M636C]

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

[Overmod]

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.

[Anonymous]

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.

[Modelcar]

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

[Overmod]

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?

[Anonymous]

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.

[Overmod]

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...]

[Hugh Jampton]

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.

[martin.knoepfel]

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

[jchnhtfd]

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.

[Paul Milenkovic]

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.

[Paul Milenkovic]

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.

[Anonymous]

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