Anyone know why the driver axle loadings on the 4-12-2’s were substantially lower (below 60,000 lbs/axle) than on the 4-6-6-4 Challengers?
I wouldn’t think with the long rigid wheelbase (yes, with lateral motion devices, but still) would be amendable to anything else but main lines with gentle curves? Was the UP using lighter rail on their network into the 1920’s when the 9000-series locomotives were introduced?
I believe Juniatha had a particular interest in the Nines and would be an ideal source for this kind of information on them.
I went looking through the archives here at the “Fortress Flintlock” and all I could find out about the 60,000 pound axle loading was in “Alfred the Bruce’s” [;)] book “The Steam Locomotive In America.” Apparantly the 60,000 pound axle load (and not above that figure) was specified by the Union Pacific, but Bruce doesn’t say why.
Another book I’ve got on American steam development doesn’t say why either.
Maybe it was due to the track it was going to run on. Those 4-12-2’s were smooth-running locomotives though, however due to that long rigid wheelbase they were restricted to mainline runs and trackage with very gentle curves.
I’ll keep looking.
I did. Can’t find nuthin’ else. Sorry.
I had not heard of this wheel arrangement before, so I looked for info on it. I found it was a 3-cyl. engine. Is the 3rd cylinder in the middle? Are the valve-gear and rods exactly the same as those for the other two cylinders?
This is explained in the Wikipedia entry:
Note that the inside cylinder has a stroke one inch less than the outside cylinders.
The outside cylinders drive the third axle while the inside cylinder drives the second axle.
The Gresley gear, in fact developed by Harold Holcroft, had an inherent defect since the inside valve was driven by the mechanism attached to the outside piston valve rods. (I prefer the term pivoted to the description “hinged” used in the Wikipedia entry). But as the outside piston valves and rods expanded due to the heat of the steam, moving relatively forward, the inside valve, fixed at the front. moved relatively backward. This resulted in more work being done by the inside cylinder, which increased the load on the already vulnerable inside big end.
So a number of these had a third set of Walschaerts valve gear fitted on the right side (like Baldwin 60000 and other Baldwin three cylinder locomotives).
I suspect that the original intention was to limit the axle load to reduce the lateral forces on the rail in curves, since the lateral force on the rail is related to the axle load, and high forces might be expected with such a long rigid locomotive, even with lateral motion devices on the end axles.
Peter
If I recall correctly, Holcroft’s gear was originally developed for four-cylinder engines and only incidentally could be extended to three-cylinder ‘line-abreast’ engines with double-pivoted asymmetrical levers; personally, I think Gresley did enough work on the two-lever system and its promotion to qualify the particular variant as ‘his’. Note that the Australian versions that (somewhat imperfectly) tried to implement the ratio with ‘rotating’ rockshafts rather than inertially-challenged levers are not generally referred to as ‘Gresley’ when perhaps he (and by extension Holcroft) should be credited for the geometry and principle. (P.S. – all the Australian designs needed, really, was to use a large-diameter hollow or ‘pipe-based’ shaft to improve the shaft torsional resistance and ‘rate’.)
I’m not sure why on a proper DA 2-cylinder this effect would occur. All that changes with this is the relative timing, and since both ends of the valve conduct both admission and exhaust, it is difficult to see how the ‘net’ result of the differential expansion would have an effect other than transient (e.g. in torsional couples or in rod stresses between crank and outside-driven axles) in ‘work done’…
The explanation I’ve always heard is that the increase in 'work done by the inside cylinder&
Holcroft gear for 4-cylinder locomotives?
The usual 4-cylinder setup has the cylinders on each side working in opposition - much like the “boxer” engine on the rear-engine Porsche and VW Beetle or the front-engine 4wd Subaru. This allows using one valve gear per side, where the inside-cylinder valves are actuated by rocking shafts as on Churchward’s Castle class? I thought the Holcroft gear was “a thing” with 3-cylinder locos as this way for pairs of cylinders to share a valve gear covers the 4-cylinder case, that is, if you don’t mind the 2-cylinder uneven torque curve but want the reduced track pounding.
The British had a Lord Nelson class with one valve gear for each of 4 cylinders where the cylinder strokes were spaced out to give a smoother torque curve than either the “boxer” type 4-cylinder or the 3-cylinder layout. Even though it lacks pistons that balance by moving in opposition, it was said to be so smooth a locomotive that it was hard to fire – the coal shoveled didn’t spread across the grate, and coal didn’t feed itself from the tender from the usual shaking on a steam locomotive.
Was the inner cylinder at the same height from the ground as the side ones? I’ve seen one photo which seems to show that the middle cylinder was up significantly higher, and perhaps angled downward. ?? So I’m wondering if that’s true. If so, was that to make it easier to have the main rod connect to the the second axle without encroaching on the first? I assume that a connecting rod linked the second axle with the first, right?
No – but the valve cylinders were (because the Gresley lever arrangement required this) and consequently the location and inclination of the inside cylinder is ‘relative’ to the location of this third valve bore, in order to have comparably short port and passage characteristics with the outside cylinders given the slightly shorter stroke. The third cylinder is to the side of its valve, whereas the two outside cylinders are below, and this will give you a measure both of the elevation and, pointing back at the centerline of the cranked second axle, the angle of inclination.
It was not unusual in these ‘line-abreast’ cylinder arrangements to find the first driver axle ‘cranked’ (sometimes by forging it with an intentional ‘bend’ in the middle relative to quarter) so that the inside rod would clear the axle as it rotated. I believe the Nines handle this without explicitly cranking the first driver axle, by adding to an already long rigid wheelbase by inserting space between the first and second driver axles. The drive is divided: the two outside cylinders have elongated piston rods and crosshead guides, and even so, and with 67" drivers, the outside mains bear on the third driver axle.
You can see the outside connecting rods (which are in the same quarter as the outside mains and other rods) in pictures. They are longer than the other side rods, and you can gauge their mass by looking at the size of the counterweights in the first driver pair.
It has been a while since I have read Kratville’s books on the 4-12-2s, but, I don’t remember him ever mentioning anything about them being “compound”. Can you cite where this was mentioned?
I don’t have any of the relevant Kratville books on the Nines; I’m going by a couple of posts, where a couple of (as I recall, reliable) people mentioned the specific references.
As I recall they were relatively early works, from the era when booboos like this might well enter the ‘enthusiast press’ as easily as Arnold Haas saying both Hudsons and Niagaras regularly exceeded 120mph.
In this photo, you can clearly see the third cylinder.
https://www.facebook.com/photo?fbid=10225035216217807&set=gm.788472115088734
This is the only pic I’ve come across in which it’s visible. Was there generally a panel there that concealed the cylinder?
That’s the third cylinder all right, and just what they looked like, no cover.
Must be right out of the shop, the whole engine’s clean as a whistle!
Well, there is a cover, a shiny passenger-engine cylinder-head cover to match the ones on the outside.
Locomotive cylinders do not have shiny heads only held on with one stud in the middle, you know. [;)]
Note there is even a shiny ‘ring’ cover on the inside valve cylinder, as on the outside. If you need further proof this was considered passenger-grade in its day…
There might have been something over the Gresley levers to protect them from road damage at some point, but I don’t know of any. You will note that if the cylinder has more normal black lagging over the head it would be more difficult to see in the shadow under the smokebox and behind the levers.
What I’d like to see is a clear low ¾ shot of one of the engines modified with the three sets of valve gear, to see how this changed the view into the front deck…
In the other shots I saw, the bright sun and high-contrast light caused deep shadow in that area. I couldn’t see any detail; the area was just dark. I thought maybe there was a black panel to keep grit and debris out.
I just looked at a bunch of Nine pictures, and even on a phone you could make out the angled lagged cylinder end fairly readily. It helps to know you’re looking specifically for a large inclined circle with a dot in the middle.
The center support for the lever has three hoses or lines running over it, and this blocks the view ‘back’ to the cylinder head behind.
Well jeez, if you wanna split hairs! L-O wanted an answer, not a thesis!
It’s cool, love 'ya bro! [swg]
I see the air pumps hung on the front of the smokebox … what is the machienry that interrupts the walkway on the side of the locomotive.
The shiney covers are exactly that - covers for the cylinder head, the cylinder heads themselves would be held down by multiple bolts to withstand the pressures developed during operation.
Remember, auto engines have ‘valve covers’ that are attached to the cylinder heads and are used to contain the lubrication that circulates through the valve train.
I believe that’s the feedwater heater. A Worthington BL type if I’m not mistaken.
[quote user=“Overmod”]
M636C
The Gresley gear, in fact developed by Harold Holcroft…
If I recall correctly, Holcroft’s gear was originally developed for four-cylinder engines and only incidentally could be extended to three-cylinder ‘line-abreast’ engines with double-pivoted asymmetrical levers; personally, I think Gresley did enough work on the two-lever system and its promotion to qualify the particular variant as ‘his’. Note that the Australian versions that (somewhat imperfectly) tried to implement the ratio with ‘rotating’ rockshafts rather than inertially-challenged levers are not generally referred to as ‘Gresley’ when perhaps he (and by extension Holcroft) should be credited for the geometry and principle. (P.S. – all the Australian designs needed, really, was to use a large-diameter hollow or ‘pipe-based’ shaft to improve the shaft torsional resistance and ‘rate’.)
… had an inherent defect since the inside valve was driven by the mechanism attached to the outside piston valve rods. (I prefer the term pivoted to the description “hinged” used in the Wikipedia entry). But as the outside piston valves and rods expanded due to the heat of the steam, moving relatively forward, the inside valve, fixed at the front. moved relatively backward. This resulted in more work being done by the inside cylinder, which increased the load on the already vulnerable inside big end.
I’m not sure why on a proper DA 2-cylinder this effect would occur. All that changes with this is the relative timing