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Single valve gear set on a duplex drive locomotive

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Single valve gear set on a duplex drive locomotive
Posted by 7j43k on Monday, May 1, 2023 1:52 PM

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.

 

Ed

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Posted by BaltACD on Monday, May 1, 2023 2:03 PM

Surprised someone didn't design a 'duplex' with the cylinders between the two sets of drivers with main rods coupled to each end of the piston.

I am not that well versed to opine what the benefits of such a layout would be, if any.

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Posted by 7j43k on Monday, May 1, 2023 5:30 PM

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.

 

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Posted by Overmod on Monday, May 1, 2023 5:58 PM

7j43k
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.

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.

If we assume the rear valve gear is linked to the front piston rod, that would seem to do it.

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...

Problem is, getting the movement to a swiveling front end, in an accurate manner, would be an irritation.

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 outer axles, one of which is guiding.  But obviously that is one set of valve gear for one set of valves.

Slop and thermal expansion would be the problems to solve in getting the linkage forward.

Torsion effects alone would make this "inadvisable".  Remember that there was already an operational timing problem with the line-contact wear between the spherical roller followers and the continuous-contour cam when there were a few thousands of miles at the most common 'cruise' settings, which led to the re-introduction of step cams and, ultimately, to that type D with the built-in wiredrawing as a feature, not a bug.

The somewhat better solution is to have each engine with its own precise rotary-cam valve-gear drive, probably on a reasonable implementation of the 'drive arm' geometry, and then conjugate the engines Deem-style with gears and a Ferguson/magnetorheological clutch detented at 135-degree phasing.  That (in theory) allows the engines to accommodate at low relative speed to reach eight events per rotation, for good torque characteristics, while not hard-locking them together to cause rod deflection, weird driver-rim wear, etc.

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Posted by timz on Tuesday, May 2, 2023 6:51 PM

7j43k
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.

Your duplex has two cylinders, but four main rods? Or what?

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Posted by 7j43k on Tuesday, May 2, 2023 8:15 PM

timz

 

 
7j43k
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.

 

Your duplex has two cylinders, but four main rods? Or what?

 

 

 

Not mine, BaltACD's.

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.  

 Both versions would be non-articulated.

 

 

Ed

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Posted by timz on Tuesday, May 2, 2023 8:55 PM

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.

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Posted by Overmod on Wednesday, May 3, 2023 7:50 AM

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.

Would make an interesting model, wouldn't it?

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Posted by BaltACD on Wednesday, May 3, 2023 8:54 AM

Overmod
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.

Would make an interesting model, wouldn't it?

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 pair of drivers.  The Emerson had difficulties making the rear cylinders 'live' considering their proximity to the heat and debris generated by the firebox.

Since above designs had issues, I was just throwing out the central position of the cylinders as a option.  I have never professed to be sufficiently knowledgeable about steam operation and its prefered methods.

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Posted by Overmod on Wednesday, May 3, 2023 9:27 AM

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 that there are eight, rather than four, power impulses per driver revolution, all of them smaller in proportion.  This is something relatively easy to design into a typical rigid-frame four-cylinder locomotive like a British Lord Nelson class, but it is somewhat more subtle on an outside-cylinder duplex: you arrange the conjugation so the mains on one side of the engine are 45 degrees off fully opposed but keep the quartered balancing on each engine as for the British 9F class.

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Posted by timz on Wednesday, May 3, 2023 11:13 AM

Overmod
no reason why a locomotive built to Balt's plan can't have the two sets of drivers phased 180 degrees apart

Far as I can see, his plan has one piston in one cylinder, on each side of the engine. When the piston is at the forward end of the cylinder ...

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Posted by Overmod on Wednesday, May 3, 2023 11:15 AM

timz
Far as I can see, his plan has one piston in one cylinder, on each side of the engine. When the piston is at the forward end of the cylinder ...

You forgot what I said about the two sides of the engine being in quarter, like any other 2-cylinder DA built since the 1820s that worked.

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Posted by timz on Wednesday, May 3, 2023 12:39 PM

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?

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Posted by Overmod on Wednesday, May 3, 2023 12:42 PM

timz
I guess you proposed having the two sets of drivers on the right side of the engine 180 degrees out of phase? 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.

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Posted by timz on Wednesday, May 3, 2023 1:00 PM

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.

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Posted by Overmod on Wednesday, May 3, 2023 1:06 PM

.

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Posted by Overmod on Wednesday, May 3, 2023 1:07 PM

timz
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'.

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Posted by M636C on Wednesday, May 3, 2023 7:45 PM

When presented with a concept like this, I always check Douglas Self's site for prior applications.

Balanced Locomotives (douglas-self.com)

Check the first entry. It was never built.

Peter

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Posted by Overmod on Wednesday, May 3, 2023 8:14 PM

M636C
Check the first entry. It was never built.

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.

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Posted by M636C on Thursday, May 4, 2023 8:07 PM

Overmod

 

 
M636C
Check the first entry. It was never built.

 

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 23 never had a chance, even if the complex dive system had worked reliably.

But Douglas Self  has an excellent entry on many of these rather odd Russian locomotives from the Stalin era.

Russian Reforms- Unusual Russian Locomotive Technology. (douglas-self.com)

The OR23 is second, after the AA class. The Diesel-Steam locomotives follow, although the OR 23 was later, built as a simplification of the Diesel-Steam locomotives. The aim was to reduce reciprocating mass and to provide better balance.

I think the simplified diagrams originated in John Westwood's book on Russian Steam Locomotives.

The OR23 arrangement would appear in theory to achieve many of the aims of the single cylinder set duplex, with the advantage of a shorter wheelbase.

Peter

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Posted by Overmod on Friday, May 5, 2023 9:43 AM

I call it the "OR class" by reflex, as the first place I heard about it (and only place for many, many years) was a somewhat cryptic reference in the Ransome-
Wallis Encyclopedia of World Railway Locomotives.

I am delighted to see that the inimitable Mr. Self has gotten around to describing the TP1-1.  That engine is kind of the 'three great tastes in one candy bar' of the locomotive world: rocking levers, jackshafts, and Still-style steam/IC operation all in one package.  (I am tempted to consider this a result of smekalka tempered by killing all the competent engineers in the wrecker trials... but that might be uncharitable.  And I do love me a mechanical complexity (see the avatar).

As a note:  I considered the OR23 to have only two cylinders (not four as he indicates), very long and with multiple ports, each containing the two DA pistons.  This was vaguely reminiscent of the arrangement in the OPOC engine so beloved of Bill Gates near the turn of this century.

I think he is being a bit too hard on the AA20.  Its intended use was in Dona-Cristina-like continuous service on, as I recall, coal trains to industrial facilities in the Donetsk region, on a long virtually straight line built to light and not very certain standards.  It would not have been expected to pass through any switches or crossovers, except perhaps those in a wye (with very long frogs and radius of curvature!) to turn it.  My suspicion is that it was treated much as railway workers were in that era, and expected to handle all sorts of traffic, with everyone being shot when it did not.  The thing I'd like to know is why it was preserved all the way into the decade of the '60s...   

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Posted by M636C on Sunday, May 7, 2023 2:54 AM

Firstly, I should correct my last posting. The simplified valve gear details are from Le Fleming and Price's book, not Westwood's.

There was another locomotive that retained the "OR" classification, the OR21. This was a larger boilered version of the OR 18 / LV class. In fact the LV, OR21 and OR23 were generally similar in overall layout. The high pitched boiler allowed for the opposed piston mechanism to be fitted above the driving wheels on the OR23 without major change in the layout. Clearly the OR21 was midway between the other two in weight. Some additional weight must be expected from the opposed piston mechanism, but maybe not ten tonnes.

The OR21 was intended as a replacement for the FD class, but only three were built as construction changed over to diesel electric locomotives.

The TP1 was summed up by Louis Marre's comment of "What could possibly go wrong?" But it is good that Self has finally added it to his otherwise excellent summary.

I agree that his evaluation of the AA20 is excessively negative. I suspect that it did have track spreading problems but not so great that a place could not be found for it. My work has exposed me to bureacracy in many forms, and I expect that AA20-1 remained for so long because nobody actually gave instructions for it to be disposed of.

Peter

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