There have been comments forever about how (typically) the front engine of an articulated can slip, and has to be babied (sometimes).
I’ve thought that if there was only one set of valve gear, then a single engine couldn’t slip–it would be both or none. If we assume the rear valve gear is linked to the front piston rod, that would seem to do it. Problem is, getting the movement to a swiveling front end, in an accurate manner, would be an irritation.
But on a duplex drive, that swiveling problem is gone. There’s a rigid frame between the two engines.
Slop and thermal expansion would be the problems to solve in getting the linkage forward.
Overmod mentioned what appears to have been a different approach in another topic. It sounds like a more subtle approach. I wonder if it would have worked on articulateds.
Because there’d only be one set of cylinders, they’d have to be 40% larger diameter (and/or a longer stroke)–as opposed to the “regular” two sets of cylinders.
Rods a bit lighter, I think–same as a duplex. And it does solve that separate-engine-slipping problem.
No. Actually the engines would slip out of time with surprising ease… due to fine differences in wheel diameter or wear, if not via bad rail or too much thrust… and now you’re completely out of time on the engine that isn’t driving the valve gear. Keep in mind that the position of the steam edge even with long-lap long-travel gear at high speed was often measured in increments of 1/64" to 1/128" so even a little bit of out-of-time is serious.
Well. if you have both engines driven off a common piston-with-tailrod, and valve gear, say, driven off the crossheads like Franklin type A, you might get this to work as a form of conjugation. The big problem is that you now have the cylinder dimensions of a plain ol’ big 4-8-4 or whatever, with the same problems in admission and exhaust mass flow, and very little improvement in the rotating dynamics as you can’t do the Withuhn conjugated duplex thing with the engines opposed. What you have is reminiscent of a Russian OR class, now with drive to outside mains, one of which is now the lead driver with all the lateral-motion compliance that implies…
Look at your Wiener. Hagans, for example, addresses this nicely, if a bit mind-bendingly, with pinned rod linkage and levers. But nobody is going to call that a high-speed design. If you are careful with your gearing, you could provide radiating/Klien-Lindner outside axles with the only ‘rods’ being those on the inside two driver pairs, and very good cross-level accommodation as well as suspension, equilization, and damping on what are now the o
Yes. There would be two cylinders, with a piston rod out each end. From each crosshead, a main rod would connect to a driver. Four of them, really.
This, if I am understanding correctly. Envision, for example, a T1. Remove the front cylinders. Connect the main rod (after moving it to the other driver in the pair) to an added crosshead and piston rod at the FRONT of the remaining cylinder. And, of course, fatten the cylinder up to accept the extra steam.
I think it’s a pretty neat idea. Doesn’t mean it would work out, but certainly worth thinking on.
A gripe I have, which may or may not be significant, is that the rods aren’t opposed in motion. So there’d be a bit of yaw. Too much?
MY version is very similar to the Q1, with cylinders at each end of the drivers. What I want is to link the steam admission system so that the main rods WILL be opposed. Always. I believe someone suggested using crank axles and rods internally, to make the connection between the two pairs.
So BaltACD’s engine would just be a 4-8-4 with the cylinders in the middle. Four main rods and four side rods instead of two main rods and six side rods – so maybe more reciprocating mass than the conventional 4-8-4?
Not to mention the rigid wheelbase, even tho the main drivers will be the ones farther from the cylinders, as on the T1.
Playing devil’s advocate for a moment: There is no reason why a locomotive built to Balt’s plan can’t have the two sets of drivers phased 180 degrees apart, as in the Withuhn duplex, preserving the 90-degree quartering on each set. While that replaces the mass of one set of side rods with a heavier main, and furthermore runs that main further outboard than the rod would have been, the reduction of rotating mass is reduced with the Timken thin-section roller rods, and much of the reduction of reciprocating imbalance should apply to this just as it would in Withuhn’s proposal. The cylinders would be ‘necked’ as on the Q2, and driver diameter could easily be held below the 76" that would allow a double Belpaire to be used, so the working rigid wheelbase could easily be kept below a number of established successful rigid-frame designs.
There is the usual issue with long tracting to and from the center-mounted cylinders, but it is little more than that for the rear engine of a T1 or Q2, and there should be room for “one-half an Allegheny” worth of connections.
I prefer the idea of zero overbalance on a duplex with a long enough frame and positive guiding on lead and trailing trucks, and this design would allow it even more readily than a typical duplex. That might help with the problems of having a main as the leading driver pair. And yes, it could use one set of outside RC valve drive to a single set of cams, probably shifting-cam a la Franklin type C.
The T1 had cylinders at the front of the drivers they powered. the B&O’s George Emerson had the drivers bracketed by the cylinders - ahead of the front pair and behind the rear pair. T1 was reported to be ‘slippery’ especially with the front p
Any locomotive with cylinders at the rear was ultimately a disaster, and I strongly believe the ACE3000 would have been one, too, in the end. PRR was very proud of the arrangement it used on the Q1, which sort of ran up around the side with a snifter-valve diaphragm up there somewhere, but this left vulnerable high-pressure piping right where a shifted load… or another example going the other way at the wrong place (see the J1s!)… would cause trouble.
There are ways to get around the nicked piston rods, gland issues, etc. that forward-facing pistons pose. Espee certainly lived with them.
One interesting detail is that the cylinder maintenance on the design will be less in a couple of respects. First, the piston is supported at both ends a la tailrods, so less wear and improved lubrication. Only one of the cylinder heads needs to be removable, so most of the ‘double maintenance’ woes of the Q2 would not apply. Only one set oif cylinder cocks.
A general consensus was that an ‘unconjugated’ duplex would be inherently slippery, and require careful means of ‘traction control’. The Riley Deem approach to the Q2 was to join the two engines with gearing, so both of them would turn at the same speed and any loss of adhesion would be promptly taken up by the other wheels. This requires both some sprung gear’ action and very good rotational-spring damping in whatever connects the two engines, and it is bad when some of the drivers wear more than others. Note that the Balt design uses the piston rod both as part of the siderod linkage and as slip shock absorption, so the rod, glands, crosshead guides, etc. have to be beefed up to accommodate that. But this isn’t a showstopping issue… just one that has to be done right in the detail design.
One potential way to overcome some of the slipping issues with a four-cylinder conjugated duplex is to set the main-rod angles on the sets of mains so
I guess you proposed having the two sets of drivers on the right side of the engine 180 degrees out of phase with each other? Front crankpin at 3 o’clock when the rear crankpin was at 9 o’clock? But both connected to the single piston, in the single cylinder?
Exactly – just like a Withuhn conjugated duplex’s rods, but ‘turned around’ to the center instead of to four cylinders at the ‘corners’.
Main-rod angularity is likely to be an issue, particularly if shortening driver wheelbase is a priority. But the situation is little worse than for the Withuhn arrangement (or the ACE 3000) and of course the lead and trailing truck design is vastly simpler for Balt’s design.
You’re not thinking. He seems to have proposed an engine with one right-hand cylinder, with one piston inside it, and that piston is connected to a crankpin ahead of it, and to a crankpin behind it. When the piston is at the forward end of the cylinder, both the crankpins are at 3 o’clock.
Dead center, just like any other dead center. If nothing ‘hands’ rotation, it will be deadlocked (which of course is why we call it a ‘dead center’). Just like Francis Webb’s dustbin. But now ‘divided between two main pins’.
Where are the rods on the other side of the engine at this point?
As with any other 2-cylinder DA, these do the whole work of moving the engine off the other side’s dead center (and, not incidentally, determine the direction of rotation). The fact that one main is now pushing, and the other one pulling, doesn’t matter to the overall torque. The piston thrust is divided between the two mains; hence ‘divided drive’.
Burch’s locomotive is critically different: it is an OP with two pistons. The oscillating-port admission and exhaust are facilitated by this, but the two pistons move in opposite directions. I cannot make out whether those loops at the end are crossheads or Scotch yokes; I have never really understood the thrill of Scotch yokes with ‘vibrating’ cylinders… but there you are.
Something I do NOT see is an arrangement of ports to make the pistons double-acting. That might make operation a bit like a slow-beat ship chronometer, no more than 2 impulses per revolution…
IIRC you’re an expert on the Russian OR class, which (equally IIRC) used opposed pistons with some sort of cockamamie lever arrangement to ‘fold’ the drive for reasonable rod angularity. I don’t remember whether the inimitable Mr. Self produced clear diagrams of the operation. It was about as successful as the teploparavoz… which is not saying very much.
I wouldn’t claim expertise in Russian locomotives. However, “OR” stands for “October Revolution”, a name given to the locomotive works at Voroshilovgrad. There were a number of locomotives given “OR” in their classification, the best known being the OR 18, which became the “LV” (which stood for "Voroshilovgrad version of type L) a 2-10-2 which was the last Soviet production steam freight locomotive. In the case of the OR 18, the “18” stood fore the axle load in metric tons. So the OR 23 presumably had an axle load of 23 tons, Since track was never improved to the 23 ton standard, the OR