I’m not sure were to ask this question, I’ve searched high and low but can’t seem to find anything that properly answers my point. Hopefully there may be someone here who can give a bit of insight, as having looked through previous threads, it looks like there are some users here with fairly in-depth knowledge about steam locomotives.
It appears that the design of powerful steam locomotives particularly benefited from having a larger loading gauge in which to place larger boilers and fire-grates for more steam producing capacity, especially since the maximum pressure that can be practically obtained with a fire tube boiler is ~350 psi (Ralph Johnson, The Steam Locomotive). Specifically, I am interested in just how large steam locomotives could potentially have been made, not being limited by a given track gauge, loading gauge, weight of rail / axle load, tunnel / bridge clearances etc. I am aware that locomotives like the UP Big Boy, C&O H-8 and NP Z-5 were just about the limit of what could be crammed into the allowed loading gauge, but I’m talking beyond standard gauge and its associated limitations.
For example I estimate that a 5.5ft track gauge, with a loading gauge allowance of roughly 19.25 ft height by 12.75ft width would have been sufficient to fit a boiler and firebox large enough to competently provide steam for a simple triplex articulated engine. A hypothetical 4-6-6-6-6, with 3 sets of 6 drivers all under the boiler, rather than have the rear set under the tender like the Erie and Virginian triplexes. Grate area would be 216.7 sq ft (with grate dimensions of ~ 130 inches wide by 240 inches long), firebox direct heating surface of ~
[quote user=“L-105”]
I’m not sure were to ask this question, I’ve searched high and low but can’t seem to find anything that properly answers my point. Hopefully there may be someone here who can give a bit of insight, as having looked through previous threads, it looks like there are some users here with fairly in-depth knowledge about steam locomotives.
It appears that the design of powerful steam locomotives particularly benefited from having a larger loading gauge in which to place larger boilers and fire-grates for more steam producing capacity, especially since the maximum pressure that can be practically obtained with a fire tube boiler is ~350 psi (Ralph Johnson, The Steam Locomotive). Specifically, I am interested in just how large steam locomotives could potentially have been made, not being limited by a given track gauge, loading gauge, weight of rail / axle load, tunnel / bridge clearances etc. I am aware that locomotives like the UP Big Boy, C&O H-8 and NP Z-5 were just about the limit of what could be crammed into the allowed loading gauge, but I’m talking beyond standard gauge and its associated limitations.
For example I estimate that a 5.5ft track gauge, with a loading gauge allowance of roughly 19.25 ft height by 12.75ft width would have been sufficient to fit a boiler and firebox large enough to competently provide steam for a simple triplex articulated engine. A hypothetical 4-6-6-6-6, with 3 sets of 6 drivers all under the boiler, rather than have the rear set under the tender like the Erie and Virginian triplexes. Grate area would be 216.7 sq ft (with grate dimensions of ~ 130 inches wide by 240 inches long), firebox direct
The limit is not so much in the ‘firetube’ portion of the boiler as in the conventional staybolted-plate firebox construction (Johnson in part was referencing Baldwin 60000, which was able to use a nominally higher practical pressure for compound operation, with a watertube firebox, but was limited somewhat by practical considerations of riveted construction and mid-Twenties practical metallurgy.) “Locomotive” boilers in the oilfields routinely ran at 500psi – admittedly these were in stationary applications with reasonably continuous load and no issues with water supply, but here again a “better” firebox design (say, welded Jacobs-Shupert or waterwall) would allow somewhat higher convection-section pressure with proper material thickness and detail design – the critical issue now being staying of the tube/fluesheets if the “boiler” proper is not fully populated with structural tubes. (Most conventional locomotive boilers are not, of which more a bit later)
In practice a large modern locomotive would probably run either with careful Cunningham jet circulation in its firebox water space or explicit forced-circulation Lamont-style waterwall circuits feeding good cyclone/gravity steam separators. These have the watertube-boiler’s inherent resistance to overheating or bursting, but don’t have the prompt consequences of tube failure that make the various Schmidt high-pressure systems so impractical on crewed locomotives.
Not ‘all’ of it appeared precisely at the same time. Some aspects date back to Mikado 8000; some others didn’t really appear until the N&W A (and perhaps arguably the Seaboard R engines) improved on the Baldwin 2-6-6-2 idea for an explicit high-speed simple articulated (which itself was early-Thirties). And a couple of real whoppers in the original Super-Power needed ‘extensive rework’ or replacement before the real promise of, say, 2-8-4s in high-speed service could be achieved.
From Wikipedia, Super Power in locomotives first appeared in the 1920s. The first turbine powered ship was Charles Parsons “Turbinia” which was launched in 1894. It still exists in The Discovery Museum in Newcastle, U.K.
Does long boiler tubes become a limiting factor for track grades. Can imagine one of these monsters going down hill uncovering boiler sheet ? How did the SP cab forwards handle the water level problem going up hill calling for max tractive effort ?
The ‘tubes and flues’ are not really the limiting factor as there is an absolute limit on their length no matter how large the diameter of the shell. Just as the firebox only occupies the ‘lower’ portion of the outer wrapper, the tubes and flues only occupy the lower part of the cylindrical shell – that is part of why the superheater-element drop from header to tube entry is so pronounced.
Part of the reason for the ‘taper’ in a wagontop boiler is to accommodate the “tilted” water level in a boiler going up- and downhill. Some railroads went so far as to put a fixed plate on the backhead indicating the ‘correct’ water level to maintain on steep (~2%) grade; careful balancing of the feedwater-heater pump and the injector would be used to keep the water ‘safe’ but no higher … careful balancing.
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Can imagine one of these monsters going down hill uncovering boiler sheet?
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That was often where the problem emerged for the careless – the engine would come up to the top of the grade, under high draft with the fire piled up … and over the top the water runs forward before the fireman can get enough pumped/injected in. With oil firing you can cut back with only thermal cycling a concern, but with coal you need the experience to get the heat you need but not more heat than you can use downhill…
This is one of the ‘problems’ with the turning-the-boiler-around designs: the raked crown that keeps the firebox water level ‘higher’ going uphill now works at cross purpose. I don’t have detailed firing instructions for those locomotives but I suspect they are available, either through SPHTS or a place like CSRM.
I suspected this as much, but wasn’t fully sure until your response. Whats interesting about this is that as a steam locomotive increases in size, it would increasingly deviate from the “traditional” shape that most people would associate with a tender engine, in which the the combined length of the firebox, combustion chamber, barrel and smokebox arrangement more or less matches the wheelbase of the engine. As sizes increase, I’d imagine the engine wheelbase to increase out of proportion to the total length of the whole boiler arrangement, leading to more and more “free space” on top the locomotive frames not taken up by boiler.
Perhaps such intermediate bearing rails would be a pair of rails placed just inside the usual outer rails, with a set of wheels directly behind the outside wheels, somewhat similar to a dual rear wheel arrangement on a truck.
Actually, very quickly upon gauge increase, you start to get into packaging that doesn’t use a Stephensonian layout at all; some of the smaller package-boiler watertube arrangements begin to fit, with ample room for the auxiliary equipment to run them effectively. The same is true for the kind of chain-grate high-pressure boiler on the N&W TE-1, which was tested years ago to be scaled to 6000hp within standard AAR clearance but couldn’t be.
Likewise at some point you can use modular boilers with return. Donlee discovered (back in the 20th Century!) that if you use steam injection to reduce NOx generation from hotter combustion, a long enough pass would let you recuperate the heat of condensation from the water of combustion – this was an interesting savings. Multiple boilers with reasonable turndown could be provided in what would otherwise be ‘excess free space’ on the chassis somewhere, and it becomes very easy to produce the vertically long centrifugal steam separators for a forced-circulation boiler of adequate steam-generation capability.
It certainly does that on a double-Garratt, but to an extent you’ll put some of the Rankine-cycle equipment on those frames, and the ‘transfer mass’ keeps the adhesive weight where it ‘needs’ to be (see the methods used on large Garratts to
The GATX RRollway rail-borne automobile ferry proposal had been depicted in the press as riding on double-track rails. Part of this may have been the model train exhibited to promote the concept, which if my memory serves correctly, rode on double-tracked HO gauge.
I think this was a shortcut taken by a commercial model builders to avoid having to hand-lay track. The concept was always ultra widegauge two-rail. My dad and a GATX colleague are credited with a patent of letting the wheels rotate independently the the manner of what Talgo does, with the patent describing a parallelogram linkage joining the wheels spanning the wide track gauge, and to use rollers gripping one of the rails on one side for positive-force steering rather than relying on cone-tapered wheels connected by a solid axle.
Those steering side wheels raise the question about what to do about track switches? The answer is that RRollway would require a kind of moving frog switch, somewhat akin to the switches used with the Tru Scale milled roadbed for HO scale model trains. You would also need a moving-rail replacement for conventional points. Considerably more complicated than a conventional switch, but a moving frog, I have seen, was used in France for high-speed lines.
Wardale in “The Red Devil” writes about a Double Garratt proposal for the Argentinian 2-foot narrow gauge coal hauling line.
One of the problems with ultra-large steam locomotives is that you don’t have the modular flexibility as with MU connection of diesel “units.” Yeah, yeah, when EMD’s single-engine units were limited to 1500 HP, the MU capability was more to make up for the limited horsepower, and with 6000 HP out of a 2-cylinder 4-8-4 (OK, it was the rare Northern having even that much indicated HP, but the 1500 HP out of an F unit involving 16 cylinders and electric drive didn’t wasn’t HP at the drawbar, either).
My question/concern is using steam, hydraulic fluid (the Lewty booster) or anything other than electricity to convey power to multiple trucks (bogies). The advantages of electric drive led to the C&O turbines and Jawn Henry on the N&W, which had problems with coal dust flashing over the traction motors it was said.
So how does a “steam traction motor” work out, with the booster engine, the front engine on a Mallet-style articulated, along with the drive system on Bulleid’s Leader and Turf Burner locomotives? With the 2-cylinder (or even 3-cylinder or 4-cylinder arrangements driving crank axles, all placed near the smoke box), you have short, direct steam passages for admission and exhaust.
As Wardale points on in his “would have been” if his project would have been to enhance the G/MAM Garratt class instead of the 4-8-4 25 class, a Garratt introduces serious pressure drops along the long steam pipes needed. He claims that this could have been surmounted by “drilling holes in the boiler cradle” and running more pipes in parallel, but I don’t know if he had analyzed this more than in the most superficial sense.
As to the Lewty booster, isn’t this a hydrostatic drive akin to a garden tractor or a light-utility farm tract
I’ll get back to RRollway in another post, as that idea is still dear to my heart and I think at some point it should be tried.
That is just the opposite of the situation here. You physically can’t get meaningful TE for ‘South African consist density’ on 2’ gauge with only two engines that even with radiating axles would go around the curves. So a double-Garratt (as in the original Beyer-Peacock drawn proposals) makes eminent sense there. Even if what you get is a reversion to the original Mallet chassis, with only four axles to the whole combination locomotive… [:O][D)]
There is no need to make excuses for modularity; as I keep discussing with Tom Blasingame and a few others, there is a minimum horsepower for any conventional modern steam locomotive – essentially set by the need to provide and package sufficient Rankine-cycle auxiliaries and low-efficiency expanders to make the capital and maintenance ‘worth’ the putative fuel saving – and for one with an externally-fired boiler that works out to somewhere larger than a couple of 4400hp units.
Some of the Besler and Doble powerplants inherently ‘scale’ appropriately between small and large power, as of course do some of the Sentinel locomotives with exotic boilers. The Oxford Catalysts system inherently scales in a remarkably small and light form factor while retaining astounding effective turndown … what a pity there are ‘certain inherent issues’ with its practical adoption!
The good news is that from a variety of approaches we converge on two things: (1) t
It does seem that using multiple tracks is the optimum solution and perhaps the only realistically viable and effective solution when it comes to supporting potentially huge broad gauge locomotives and rolling stock. The ability to still run conventional “single track trains” is a particularly good point as it allows more scalability of operations depending on demand.
Even a double track standard gauge arrangement would allow for extremely generous proportions. To a give a rough estimate, in “double track mode” the effective gauge would be something on the order of 19’ with a maximum loading gauge width of ~25’ (depending the loading gauge width of single track trains and track spacing). Perhaps any railroad intending to operate primarily double track trains may wish to comprise it of two narrower gauge tracks (although not so narrow to the point were it constrains the usefulness of single track locomotives). To give an example, a double track arrangemnt comprised of two 3.5’ gauge tracks, with each individual track having a loading gauge on the order of 8’ width x 12.25’ height. Spacing between the tracks (from the centerline of each track) would be 10.5’. For double track trains this would give an effective gauge of 14’ and a loading gauge
The mention of using a double track reminded me of a TV program in the seventies or eighties; it featured a luxurious (complete with a swimming pool on board) passenger train that ran out of Grand Central on a double track. I do not remember any episode, but I do remember that near the start of one. there was an announcement that the Silver Meteor was arriving in the station.
From these pictures, it is apparent NBC and the Fred Silverman production company didn’t understand that the loading gauge could be larger than the track gauge.
http://nbc_supertrain.tripod.com/
It did not appear to run on a double track, merely an ultra-widegauge dual-rail.