One complaint about steam in relationship to Diesel is not having enough powered axles for lugging a train up a ruling grade. A late steam-era Northern had the peak horsepower as a multiple unit Diesel consist of its day, but it had the same number of powered axles as a single Diesel unit.
Many Superpower steam locomotives were equiped with a booster engine powering a single axle in the trailing truck, often in evidence by an enlarged back axle on a two-axle trailing truck at which was pointed a sanding pipe. The booster engine engaged/disengaged with some kind of clutch so it could contribute an extra axle of traction at low speeds through a gear-reduction drive, and it disengaged so it would not overspeed at high train speeds. A 6-drivered Hudson could have the pulling power (at low speed) of a Northern, a 4-drivered Northern could pull like a 2-10-4 Texas type, the booster-equiped 2-10-4’s on the C&O replaced 2-6-6-2 Mallets, and so on.
Another approach to low-speed lugging power was the Norfolk and Western Y-6 Mallet, a double-engined compound-expansion machine operated long after other roads at given up on Mallets. This locomotive was operated as a compound when moderate tractive effort was required, but for a hard pull, it was operated in simple-expansion mode on both engines or perhaps a “booster” mode where the steam receiver feeding the second engine had its pressure boosted by admission of some extra steam pressure from the superheater header.
If you have a large number of powered axles, you cannot operate at above a brisk walk without running out of steam – the Erie Triplex had this problem. The booster engine idea is that you shut off the booster at speed. The idea used in many compounds is that your “simple” the engines for starting and high traction at low speed, but you operate in compound mode at speed to not use up all your steam.
Has anyone considered the idea of a double-engined locomotive such as a
That is a very interesting idea. I would want to use enough steam to make the extra weight of all that is involved with a extra driver set essentially “neutral”-neither adding or subtracting power. It is interesting you mention the triplex. Could this be used to have say, a 2-8-8-8-2, with the tender drivers not working above a certain speed? As I am not very well versed in steam design, I am looking forward to the answers of others.
I would suppose that this could have worked like the modern V-8 engines in automobiles and trucks where they “shut off” certain cylinders and only run at half horsepower at highway speeds. I doubt that it would have saved steam, though. What really killed steam was the high cost of maintenance, particularly labor costs as wages increased rapidly after the Great depression and World War II. Adding more complexity to steam locomotives would have probably just exacerbated the maintenance costs. As with many varieties of technology, things increase in complexity and then they suddenly disappear and are replaced by something different, i.e. steam and diesel power.
I certainly don’t want to sound anti-German (I am mostly of German descent), but I would think German engineers, if any, would have tried this. Any readers with detailed knowledge of German steam?
I really doubt this would have been worthwhile though. As another post pointed out, the demise of steam was assisted by high maintenance costs. This would have been one more thing requiring attention.
Possible… but would require a number of supporting technologies.
First issue is something most don’t think about and that is lubrication. Standard practice was to atomize the cylinder lubricating oil into the steam flow going into the cylinders and let the steam flow carry it. Once in the cylinders at little bit of that oil condenses or plates out on the cylinder walls and keeps things from seizing. Obviously, in a set of cylinders drifting with throttle totally closed there would be no steam flow → no lubrication – > bad news within a few miles. David Wardale did some (as far as I know) pioneering work in South Africa during the Red Devil rebuild on spraying the cylinder lubricant directly onto the cylinder walls without depending on steam flow to carry the oil into the cylinders.
Other way is to keep all the cylinders working, but avoid draining the boiler by working at extremely short cut-off. Problem here is that working below roughly 25% cut-off with conventional piston valves (regardless of which valve gear) gives poor exhaust events with far too much compression. Beside the rough ride for the engine men, it takes a lot of positive work to overcome the ‘drag’ of compression. If you pinch down the throttle you can run longer (more than 25%) cut-off without draining the boiler, but the thermal efficiency goes down the drain. The fix is separate the intake and the exhaust valve gear and valves so that the you can run 10% or less cut-off with acceptable exhaust events. Both styles of Franklin poppet valve gear can be built to provide this feature, and I seem to recall that some special piston valves gears can do the same.
Juniatha does! We’ll see if she returns soon. Although, I don’t believe that any engine set “drifting” was tested anywhere, but I could be wrong. (Boosters excepted).
This is another advantage to the neutral drivers theory…
What if you were to maintain sufficient steam flow to the “off line” set of cylinders to provide lubrication and to overcome the friction of said unit? You could have that unit set at a long enough valve stroke to overcome back pressure problems and it would be hot and ready to perform when brought on line. The previous sentence is, of course, open for any degenerate comments.
the allies discoverd a german v-8 steam engine after wwll. there is a few photo’s i have found on line. maybe emd/gm killed it with the need 2 sell busese?[8D]
Interesting discussion but the first premise is misleading – the number of driving axles on a steam locomotive does not limit or increase power. The driving wheels of a steam locomotive are there to transmit power and to spread weight, they do not create power. The difference in power between an 0-4-0 switcher and a massive 2-10-4 is not due to the difference in the number of axles. The 2-10-4 is more powerful because of the size of the cylinders, the large boiler and high steam pressure. If you took a 2-10-4 and eliminated all the wheels except two coupled drivers making it an 0-4-0, the modified locomotive would have the same tractive force and horsepower. Of course, without all those wheels the weight concentration would bend the rails but it would have a very high factor of adhesion.
If you want to make a steam locomotive more powerful, whether you measure the power in terms of tractive force or horsepower, you only have to increase the size of the cylinders or raise the boiler pressure. You also need a boiler that can fill those cylinders with a steam output commensurate with the piston speed. However, you are faced with weight limits so as you build a bigger locomotive you need to spread the weight over more drivers – but to repeat, the higher number of driving axles only reflects that your locomotive’s weight is increasing. For example, a lot of railroads liked the “Russian” Decapods (2-10-0) even though they produced a lot less power than a sizable 2-8-0. Why ? Because they spread the weight and were easy on light duty track.
A fundamental reason, though not necessarily the main reason why steam is gone is that the locomotives reached the size that most railroads could accomodate. Boilers had effectively
Railroads in the U.S experimented with similiar reciprocating steam engines prior to WWII but did not find them satisfactory. The best known was the Beler Brothers Steam motor:
It was trialed in a couple of railcar installations and promoted for locomotive use but was very high maintenance compared to conventional steam power…
Interestingly a lightweight Besler motor powered the World’s first (and only,IINM) steam powered airplane:
I believe the purpose of a booster on a steam locomotive WAS to add driving axles for increasing available tractive effort at low speeds. Otherwise deadweight trailing or tender axles become additional “feet” on the rail to get a train rolling and through the hard pulls at low speed. Under such high traction demands, a locomotive’s driver adhesion is at it’s extreme limit and the likelihood of them breaking loose and slipping to a stall are very high. As you mentioned, a locomotives boiler is producing more steam at extremely low speeds, than can be utilized by the cylinders. As speed increases, this steam demand increases and the tractive effort demands diminish. At such time, the booster’s contribution becomes unnecessary, and in fact, the booster steam demand becomes a detraction from the steam available to accelerate the train to line speed. Some engineers I worked with, years ago on the RF&P spoke of firing on booster equipped engines. They said when the engineer cut the booster in, all your carefully laid firing efforts went south, even on northbound trains! The boiler pressure just went down,down,down!
wow that was a long way to say what i am not sure. the john henry turbo proved that more axeles can pull more weight. it was alas too little to stem the tide of internal combustion. or was stea[8D]m the original internal combustion. i.e. a fire in a boiler?
The RF&P had some truly beautiful steam locomotives – wish I had seen them. I experienced Canadian Pacific steam in the 1950’s which in my opinion was among the best for looks.
My previous comment was aimed at getting away from an emphassis on axles or wheels as a way of producing power. Sure axles or wheels are important but their number neither adds nor subtracts power. My comment was directed at the notion that a steam locomotive is better if it has more wheels – that may be the case but not always.
Consider boosters again. As a general matter, boosters are cylindered to produce in the neighborhood of 12,000 lbs. of tractive force at starting. Suppose I have a 2-8-2 that I think would benefit from some additional TF at starting. I could add booster cylinders to the trailing axle and the 50,000 or more weight the Mikado carries on that axle would provide enough adhesion. But suppose I have an 0-8-0 that could use some additional power pushing a long cut up a hump. The only place to add the booster would be to one or two of the tender trucks. Let’s say my tender weighs about 100,000 lbs. when carrying a quarter load of coal and water, or in other words about 25,000 lbs. on each of its four axles. I can’t power only one axle because the weight on only one axle will not provide sufficient adhesion for my 12,000 TF booster. So what do I do – I add coupling rods to the truck wheels and now have a 0-4-0 with 50,000 lbs of weight on the drivers. That is enough weight for adhesion even when my water and coal are fairly low. This is to say, the power I added with boosters to my two locomotives is the
You’ve made your point very nicely. I think the confusion began to arise when a larger locomotive was built so as to produce more power, it generally required more axles to keep the axle loading within limits. The casual and not-so-casual observer is led to believe that more axles means more power. I’m sure designers would gladly have given a 4-4-0 the ability to generate the power of a 4-8-4 if they could have done so without crushing rails, ties, ballast, and bridges…
This is all getting away from the original point of the thread.
Max practical TE developed by any locomotive is a function of the number of axles and the applied axle load (and hence factor of adhesion). The ideal is to have all the carrying axles powered just up to their practical adhesion limit (and the history of the Duplexes and early diesels with limited slip control will give you additional detail on what ‘practical adhesion limit’ implies…)
Diesels (and the Jawn Henry TE-1) are horsepower-limited in a way a reciprocating locomotive is not: the engine horsepower limits the rail horsepower, and that in turn can limit the top speed regardless of what the starting TE of the locomotive might be raised up to.
What the original post involved was not using boosters on carrying axles to use ‘a bit more’ of the locomotive’s total weight for adhesion, it was to use a group of DRIVING axles less intensively at higher speed after starting, to save fuel and perhaps wear once the train reaches speed, is on a net downgrade, etc. In other words, it is converting some percentage of the driving axles into carrying axles on demand.
Taking the example of a 2-8-8-4 – we aren’t concerned whether there is a Franklin booster on the trailing truck, or a Bethlehem auxiliary locomotive on the tender. We’re concerned with reducing the power to four of the eight axles, perhaps all the way down to zero, relying on the other four’s power to handle the train plus the engine mass when only four axles can do the required job.
(I don’t believe the subject of a counterpressure brake on the four ‘idled’ axles exclusively during net-downgrade running has been discussed, and its use is somewhat more limited than the diesel-electric alternative (dynamic braking) – but it is a potential feature of the approach, whereas it is not practical to do this with a production Franklin booster, and very unlikely with an auxiliary locomotive…
Personally, I don’t think many railroads would buy a large, heavy locomotive with two full sets of reciprocating running gear, just so one set could be left substantially idle at speed. That’s based on my assumption that operating profiles with long enough ruling-grade sections justifying articulated power, but long enough ‘easier’ sections to make meaningful gains in part-load running economy exist, and that the capital and basic maintenance charges on the larger locomotive would be less than the fuel/water and marginal-maintenance savings resulting from operation of the system. (I’m presuming these locomotives are equipped to operate across multiple divisions without engine change, and have adequate support in place to make that achievement seem ordinary, as it was in fact ordinary even for first-generation diesels…)
It’s just the opposite of the logic of the booster (and to a different extent the asynchronous compound) where the additional power is provided via the auxiliary engine(s) only at slow speed, when needed.
Having said that, I’ll promptly make what looks like a flip-flop and note that a comparatively simple set of control changes would enable a simple articulated to operate in the manner Paul describes – and having that flexibility easily at hand, backed up by the proper training and support to use the features effectively, might easily demonstrate substantial benefit to operations. I do have to confess I’m not smart or sensitive enough to be able to fire one of these things effectively for maximum efficiency, especially with solid fuel… but I can make a very good start on quasi-artificially-intelligent aids to simplify the job.