gregcit would be great to see a reference with numeric data. By my calculations, mean effective pressure is never below 50% and ~98% for 80% cutoff.
Is that calculated with steam tables, or for a 'perfect gas'?
You are correct in thinking that 'much' of the effect of limited cutoff comes at relatively high rod angularity, so the "net" effect on TE for a revolution is limited. If someone can find test-plant measurements of one of the early PRR I1s (which were built with 50% fixed cutoff and no slot/Weiss porting) we could confirm this with data.
I see no reference in the graph you provided for the effect either of wall condensation effects or 'nucleate condensation' in the steam (due to the extraction of work in the cylinder). These are of course the primary things that relatively high superheat is intended to prevent; one reason for keeping cylinder cocks open relatively late is to induce enough flow through the superheaters with draft effectively built up on the fire to produce high early superheat at the cylinders. Somewhere I suspect there are curves that show this for designs comparable to a 24"-cylindered eight-coupled engine.
Overmod You must also take account of the rod angularity and the fact of quartering 'peaking' thrust on one side while the other is near zero. i did. I saw this plot in Semmens. The blue and red curves show the tangential force on the driver at various angles based on a normalized cylinder diameter of 1 unit. The peak is 0.78 (Pi * (dia/2)^2). But when you combine the force from both out of phase cylinders (green curve) and average it over an entire rotation, the effective force become ~1 (128% of peak)
Overmod You must also take account of the rod angularity and the fact of quartering 'peaking' thrust on one side while the other is near zero.
i did. I saw this plot in Semmens. The blue and red curves show the tangential force on the driver at various angles based on a normalized cylinder diameter of 1 unit. The peak is 0.78 (Pi * (dia/2)^2). But when you combine the force from both out of phase cylinders (green curve) and average it over an entire rotation, the effective force become ~1 (128% of peak)
I believe that's just the 'mechanical advantage' of the drive assuming constant piston thrust over the stroke. The graph I remember from Wardale was 'net' of all effects; it might be interesting to superpose the two to see where there are differences. It is not technically difficult to take an indicator diagram for a given cylinder, derive the effective pressure at various points in the stroke (corresponding to, say, the 15 degrees of rotation at each analytic step) and then use this for the wheelrim-torque calculations more directly (without that ballpark "85%" -- I doubt if you'd ever see a Big Boy sag as far as 75%/225psi under most starting circumstances, but you could look for anecdotal accounts of running them).
I see I forgot to account for the ratio of the cylinder stroke and driver diameter 0.41 (28/69), ~31 tons for each pair of cylinders and ~62 tons for all 4. given an adhesive weight of 270 tons, max TE is ~67 tons (1/4 balanced weight on drivers). I think my estimate is in the ballpark assuming there's little purpose in designing an engine that significantly exceeds the max TE.
The thing to remember here is that the engine also has to make relatively good horsepower at high rotational speed, where the admission, cutoff, and torque peak will be very different (and smaller/peakier) than at starting. I don't have access to indicator diagrams for these locomotives during testing (presumably up to the 80mph for which they were balanced) and it would be very nice to see them 'in parallel' over a range of service speeds.
There is a bit of a joker here, that you should probably keep in mind while evaluating these locomotives theoretically: they were designed to burn a weird fuel, almost (if not fully!) subbituminous and comparatively flaky, and they would require a substantial amount of induced draft to produce the necessary levitated combustion at any good road speed. This might well involve a greater mass flow of steam through the (nonvariable) front end than strict thermodynamic analysis of steam use would indicate.
... while these numbers don't account for pressure losses and back pressure, they also don't account for super-heating which while intended to raise steam temperature to minimize condensation in the cylinder may increase steam pressure as well...
If you have a rubber bible (CRC handbook) you can look up the enthalpy of superheated steam. You would certainly not be the first to pin high hopes on the net pressure-generating effect of superheat, or the first to be disappointed when you found out the effective heat was too small to produce torque improvements in step with the numerical pressure increase (and consequent stresses on pressure parts) involved with the superheat. The effect was clearly observed with reference to the ether bottoming experiments (on steamboats) that I mentioned earlier: when there is low specific heat, the expansion from high pressure down to saturation occurs depressingly quickly without much work being done on the piston for All That Initial Pressure. Many folks at SACA tinkering with ORC (look it up!) have regretfully come to similar conclusions.
It would be great to get a numerical confirmation (to some extent I have from the someone at 5at.co.uk)
The more important design criterion -- and it is a MAJOR one -- is to assure enough superheat at the valves (and I'd say the exit from the valves into the cylinder ports, which is about the last meaningful place you can actually measure it without lots of instrument-designing fun) to delay nucleate condensation (and make wall condensation in the lubricant film promptly reversible) up to a meaningful degree of expansion. Against this you must remember that ANY effective superheat remaining in the cylinder charge after the moment of first exhaust opening becomes your enemy, as from that point forward anything that tends to increase the volume of steam only chokes the exhaust flow and impedes any practical draft you'll ultimately produce at the nozzle (where the superheat will probably have exhausted itself before producing physical draft for entrainment).
It will be interesting to see the 5AT folks' perspective on this. While you're at it, get their explicit comments on physical cylinder heating (e.g. jacketing or Chapelon's use of admission steam to heat the cylinder block) vs. Wardale's conclusion that good cylinder insulation and proper use of cylinder cocks was adequate to purpose.
Did they swap out the 4014's Type E superheater for a Type A during the restoration? The Type E was known to have caused problems during their service days with more failures and more time down for maintenance, so the last order of Big Boys switched to Type A's.
I do not know. The historical stats for the type E locomotives indicate 2083' of surface, but the official UP page for 4014 indicates 2,486'.
Leo_AmesDid they swap out the 4014's Type E superheater for a Type A during the restoration? The Type E was known to have caused problems during their service days with more failures and more time down for maintenance, so the last order of Big Boys switched to Type A's.
Wasn't the 4014 from the last order of Big Boys?
Never too old to have a happy childhood!
No, she's from the first order.
The last 5 units are from the 1944 order (4020-4024), of which only the 4023 in Kenefick Park still exists.
BigJim I have seen it posted that the replenishment water to the tenders is first run through a water treatment car behind the tenders. Does anyone know anything about this?
I have seen it posted that the replenishment water to the tenders is first run through a water treatment car behind the tenders. Does anyone know anything about this?
Not specifically, BUT anecodotally, I read [possibly TRAINS(?)], a story that referenced problems with 'water quality'; IIRC it was the #488 (?) that suffered some sort of 'failure' while out on the 'road'. It was specifically, related to the failure tio have a water treatment protocol for use of various 'local' water supplied to the locomotive while 'on-tour'(?).
Some of us have seen locomotive's water re-supplied to the locomotive either by a direct line, from a local fire hydrant, or pumped from a local piece of fire apparatus.
I think, I remember reading that #844 was particularly effected by the water quality issue; I am not sure, if #3985 was also affected to some similar degree(?).
For those reasons, I think, I read, that #4014 was put under a water treatment protocol that required some type of chemical (?) treatment for water replinished while on tour?
As to other"Modern additions", The cab have a 'control stand' for operating any f the trailing diesel power provided; IIRC, the rebuilding process of #4014, also included air-mechanical 'system' to keep lubricating oil (?) to a large number of the locomotives bearings, and surfaces.
[Does anyone know if the UP also added any termperature sensors to monitor the bearings; or do they rely on hand=held sensors to check areas where heat /temperature migh be problematic?]
samfp1943I think, I remember reading that #844 was particularly effected by the water quality issue; I am not sure, if #3985 was also affected to some similar degree(?).
Back when Ed Dickens had just 'taken over' the steam shop in place of Steve Lee (which itself led to holy-war-level flame wars) there was an attempt to re-create one of the expen$ive proprietary voodoo water-dosing treatments -- I don't recollect which one -- by going back to the basic chemistry. At least some of the chemicals used apparently were sourced from a pool supply company, and some of the chemistry was not right: there were some truly awful pictures of the result inside 844's boiler, with issues both with encrustation and corrosion. Of course some of the argument went down the "you used POOL CHEMICALS in a modern locomotive boiler???" route and never quite got to what the attempted chemistry was or how it was tested and dosed.
Any modern locomotive needs water treatment if you want the boiler life to be more than what was typical in road service -- a couple of years, perhaps. I wish I still had a linkable version of the early research into McMahon-Porta treatment (which is now commercialized as "Porta Treatment") as it summarized many of the important points: you want very little dissolved oxygen even close to the point of feedwater injection; you want only soluble salts forming with various ions in the feedwater; you want to keep any sludge 'mobile' and not settling out in nooks and crannies or facilitating corrosion at riveted seams and the like, in addition to the usual getting the pH around 11, eliminating organic sediment, etc.
For an older version, see TIA in French practice ("traitement intégral Armand" and NOT transient ischemia!) and what Chapelon and later Porta did in reducing the idea to simple things a normal crew could drop in the cistern while running. For fun, look at the system installed on the N&W TE-1 turbine, which could be thought of as that great railroad's implementation of serious water treatment when needed.
One of the great timeless topics is that some of the agents that reduce or 'soften' buildup also increase tendency to foam or prime -- which is one of the deadliest problems on late modern reciprocating locomotives. The 'best' additive to cure this is an organic antifoaming agent -- which does not last long in the conditions inside a larger modern boiler and has to be carefully and somewhat expensively dosed as you go.
I can't imagine that UP's water treatment regimen on 4014 isn't documented somewhere. I should have thought to ask Mr. Dickens about this when I saw the engine in West Chicago! (But perhaps he might still have been a bit sensitive on the subject, even that late in the triumph... )
samfp1943 As to other"Modern additions", The cab have a 'control stand' for operating any f the trailing diesel power provided;
As to other"Modern additions", The cab have a 'control stand' for operating any f the trailing diesel power provided;
It probably will have a diesel controller by the time it rolls again. However for last year's tours it wasn't so equipped. They ran out of time getting it ready for the tours.
I think I read that they were going to use the controller off the 3985. I've seen pictures of the controllers on 844 and 3985. They are home made and pretty simple to operate.
Jeff
jeffhergert samfp1943 As to other"Modern additions", The cab have a 'control stand' for operating any f the trailing diesel power provided; It probably will have a diesel controller by the time it rolls again. However for last year's tours it wasn't so equipped. They ran out of time getting it ready for the tours. I think I read that they were going to use the controller off the 3985. I've seen pictures of the controllers on 844 and 3985. They are home made and pretty simple to operate. Jeff
So by swapping the controller between the 3985 & 4014 are they in effect stating that they don't intend to ever have both engines operating at the same time - without actually making that statement?
I believe the 3985 was officially retired several months ago. The original plan to restore her to operation was discontinued.
Hopefully she won't get too picked over and will safely stay inside until the day comes that they have a change of heart and decide to give the 844 or 4014 an extended rest in layup.
But with two operating steamers, that's probably all the flexibility they need, so the sad reality is that she's probably just facing a future being stuffed and mounted (Or worse, end up parted out like the 838 where even a cosmetic restoration could be a challenge).
Leo_AmesBut with two operating steamers, that's probably all the flexibility they need, so the sad reality is that she's probably just facing a future being stuffed and mounted (Or worse, end up parted out like the 838 where even a cosmetic restoration could be a challenge).
Only the UP knows what they're going to do with 3985, and that's if even they know. It may come back, it may not, only time (in this case years) will tell.
When you come right down to it a big-time management shake-up could kill the whole steam program entirely. I don't expect that to happen but it wouldn't surprise me if it did.
Leo_Ames Did they swap out the 4014's Type E superheater for a Type A during the restoration? The Type E was known to have caused problems during their service days with more failures and more time down for maintenance, so the last order of Big Boys switched to Type A's.
The 4014 retains the original Type E superheater. Changing to Type A would have required, among other things, a front end throttle assembly configured for Type A. There is only one such part in existence, and it is in the 4023.
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