Thank you Kelly. Refreshing to see how a real RR did this on big engines. It's a whole different breed of dog in America.
I cannot speak for steam technology from around the world because I was dealing with what we had to work with. I've always detected a "look down their nose" attitude from the Euros which I found very annoying. Maybe it's just me, but I think the USA did work with their locomotives that wouldn't even be a gleam in the eye of foreign railroads. Considering that some of their "goods" trains were lighter than a fully loaded UP Centipede tender I remain convinced that ours was the real thing.

This drifting throttle on the C&TS has my attention now.

The idea behind a drifting throttle leading into the steam chest is to keep positive pressure in there with the engine in FORWARD gear. Analogous (but not exactly comparable) to keeping your foot on a car throttle a bit to overcome the effect of 'engine braking' on a downgrade. Just the opposite of compression braking. You can use the drifting throttle at as low a 'pressure' as keeps combustion gas excluded from the exhaust side, and prevents you pulling a partial vacuum due to piston 'suction' on the intake tracting (which would produce 'braking' effort, but at the cost of sucking air and grit into the rod seals...). Technically this could be done with a relatively small mass of steam -- comparable to what an atmospheric pumping engine might use; "just" enough to displace air and to prevent suction.

The water brake depends upon compression -- from the mass and inertia of the locomotive and train. The kind that uses overcritical boiler water depends on a relatively small mass, which flashes to pressure steam readily and then can be superheated at good pressure by subsequent compression.

Meanwhile, the kind that uses air compression (through corner or snifting valves or whatever) can use cooler water. The 'catch' here is that the whole water supply system needs to be freezeproof in service. It can be hard to arrange a reliable source of cold water with dependable metering without some kind of pump; there is also no guarantee that the water feed will always be done 'downhill' from tender to cylinders (i.e. with the locomotive facing 'forward' down the grade). So I think it's usual to find air-compression counterpressure brakes using hot water, too, just using a smaller mass flow and tolerating higher peak temperature than might be the case with cold feed.

I'm not at all surprised to find water brakes not in use any more, at least not on smaller power where maintenance expense is more critical (and perhaps, in the old days toward the end of working steam, maintenance quality is not up to full Class I standards). I would expect it wouldn't take more than one little forgetful moment to run enough water into the cylinder at the wrong time to pop the cylinder head, bend the main rod, etc. etc. etc. Shy of that, easy to flat the drivers with even a few moments' 'excess' braking -- to say nothing of mistaken use of the independent while compression-braking. And wouldn't just one event like those pay for a whole passel of more-worn brakeshoes, crew time spent setting retainers, etc.? It's fun for professionals to use the equipment perfectly, and maintain it in near-perfect (if not perfectly perfect) running condition, and always follow the Right Procedures. That might not have been the case for tired people making a minimum living on the trailing edge of obsolescence...

I have found some more notes on how Trofimov valves (the correct spelling as it turns out) and their predecessors were operated -- PM me if you want the details.

Part of this 1/3 element business is, I think, a question of scale. Nigel Day has been primarily working on smaller engines with comparatively short tubes, probably with no dampers or front-end baffle plates. To get the same net reduction in gastemps to achieve the 300-degree-over-steam differential, his 'shortening' in proportion to original element length will be more, on a percentage basis, than for locomotives with much longer flues. Now, having said that, I remember reading quite a bit about how oil-firing conversions had to shorten element length to avoid burning ... but as I said before, there are so many variables just in the firing arrangements, chamber length, and other aspects influencing the actual combustion-gas temperature and mass flow that you'd want to know those things -- and more particularly, how the gastemp actually falls off as you get deeper into 'populated' flues -- before you could make much more than a general comment.

Here's part of the problem: modern burners are often better at keeping lambent flame going all the way up to the rear tubeplate -- something relatively unlikely with coal firing even in the presence of GPCS. I have seen various figures as to how quickly active luminous combustion persists in tubes and flues after the gas transitions into them. In part this depends on the available oxygen in the flame plume at that point; my understanding is that it's pretty much quenched out within a couple of feet of entry. But my understanding is also that the actual gas temperature at that point, where actual heat transfer acceptance to metal and backing water has not had much time to work, is considerably higher *at peak working* than a coal-fired equivalent. (Naturally, most of the time, you'll fire 'less oil' to get the same amount of enthalpy in the gas for steam generation, just as you'd use less of any other kind of higher-BTU fuel to get the same effect.) It's those times when there's heavy draw on the fire, perhaps in slips, that you'll get the hottest carryover, and then be concerned about any 'thermal flywheel' effect from a few more seconds' worth of gas carried past potentially empty elements...

I would note that steam generation would be better, not worse, with 'less' superheater element absorption, as an elementary consideration of heat transfer would indicate. But that's not the whole of the issue -- the elements act partially as Besler tubes, keeping the gases turbulent and closer to the flue walls where they're present, and therefore enhancing effective heat transfer. Now a Besler tube acting correctly is a pure re-radiator; it doesn't 'lose' any of its energy internally to water or steam, but likewise it is not expected to support either pressure or circulation, and therefore can be made refractory enough to stand even the highest gastemps without burned ends. (At least that is the principle, and I've seen nothing practical to the contrary...)

The superheater doesn't make steam, and if you read the Superheater Company reference, you will quickly understand that it greatly decreases efficiency to make even a little 'steam' there (the figure quoted is 17 degrees reduction in superheat for every 1% moisture content in the mass flow through the elements). Wise to keep the two functions in a locomotive boiler separate in your analysis and discussions!

My guess is that the ATSF practice would be just about correct, with the observed reduction from empirical observations being 'just' the amount that balances cost of infrequent burned ends against the working benefits of better heat transfer to the superheated steam. Of course, what we don't know is how the firing equipment and practices might have been changing at the same time. Now we have some very talented people here who know everything important about ATSF von Boden-Ingles burners and so forth, and I cheerfully defer to them right quick. The example I'd use is different (and if anyone can document with facts, PLEASE do) -- the SP Gyro-Jet burner (not to be confused with those wonderful rocket pistols!) that UP also tried, in the early Fifties. I'd expect much longer effective flame travel out of one of these, and therefore some shortening or other thermal protection of the element ends. Who has actual test data or results???


Yeah, I don't care much for perceived European snobbery either. I wouldn't necessarily disparage European technology, though -- they could build pretty effective locomotives even at small size, and some of the approaches would scale nicely to American size (the Chapelon 242 A1 and 2-10-4 being a couple of potential examples size-wise, and Kenneth Cantlie's KFs for China being interesting in other ways). Perhaps the 'happy medium' was something like Chapelon's modifications for the 141R class, which applied to American practice would give all the joy of Lima construction without some of the shortfalls in achievable efficiency. We should keep in mind that French practice valued absolute fuel savings much more highly than American practice did, and did not value speed even in the 80mph range as particularly valuable -- hence the many differences in prioritization. What I've come to wonder is whether much of the 'classical' French approach to detail design is relevant to honest American running conditions (as opposed to some late American design practice that seemed to stress high horsepower at very high speed as an important design consideration -- witness where the PRR Q2 made its best hp relative to what the maximum allowed freight speed on its railroad was, or more familiarly, where any of the Alleghenies were actually used...

Oh yes: Europeans looking down their noses at 1522, or 3751, or any similar American power operating through the best efforts of skilled people, need their heads examined.


RME

Dear Mr. Kelly

A historical point as I understand it. If memory serves me on my discussions with Mr. Knoob, they went to the poor man’s water brake at the same time they upgraded the locomotives to 6ET. I believe maintenance cost on the water brake and train handling issues with pipe trains caused by the alternating pattern of loads and empties were driving factors. If you get the chance watch the compression brake operation it down Cumbres, do it. I saw it in October 2001 on a hospital train move. It is a trip I have never forgotten.

Robby Peartree

Nigel said he likes to keep his posts simple so us Yanks can understand them.

Ye gods, I love it when people lie with statistics.

Page 46 -- exactly where do references for temperature in convective gas passes have anything to do with Schmidt superheaters in locomotives? They're talking about power boilers. I understand it's easy for some people to confuse 'passes' in superheater elements with this, but they aren't the same.

Fry's data: Out of 'A Study of the Locomotive Boiler'? Referenced from location of rear tubeplate. If Nigel gives us his example tube length (and flue, not tube diameter) we can compare directly by distance from the ordinate as to the available gastemp for uptake, but I suspect it is an oversimplification to reason that quench and subsequent uptake occur just the same in 1.75" tubes as in flues of sufficient diameter. Something that is missing from the 'case' given is is precisely a measure of uptake of heat from the gas to the elements (which would include the rate of transfer to the relatively well-insulating steam in them, and involves some double-salience flow), not the percentage of temperature remaining at x distance for purely convective heat transfer to water at 'wall temp' (in case anyone cares this corresponds to around 220psi).

At least some of this is really nit-picking; but still, what we are concerned with is something different from the percentage of temperature drop in the convection section's flues -- it's the effective heat transfer to steam mass in the elements, at or near the region of the return bends, at some nominal rate of steam demand). The magnitude of BTU rate actually experienced at, or within a few inches, of the rear tubeplate is vastly understated in Fry's case as given; I will presume that his 'firebox temperature' also represents that incident temperature (his "T"), and 1935 F at the given gas rate is not particularly high. Put in the right T, and the right M, and the appropriate "weight fo gas" (which I somehow don't think is what Fry called it ;-}) and we might get some more meaningful data in the representation. Meanwhile, your own reference page 46 clearly indicates 'the rate of heat transfer increases rapidly with increases in the velocity of the gases' (and this is true for the 'single pass' represented for a Schmidt-type superheater in a locomotive boiler, as demonstrated in the USGS tests of 1910 or so) -- where's that information in your formula?

A specific piece of data we need to know, that can't be predicted from Fry's simplistic initial conditions for the case quoted, is precisely the falloff in actual gastemp when you have flame impingement on the tubeplate and continued above-transition "combustion" for a certain distance into the flues... because the problem we were discussing, you may recall, is how to proportion the element length so that no part of it overheats due to ITS heat transfer rate with the gas passing it. It's nice to have a lolog function (I learned to call it something different, but cologs, illogs, lologs, and illologs are just fine for those who know what they mean) for heat uptake, but we need to put the right proportions, constants, and dimensions into such a formula if we're to get useful engineering data, rather than score points off non-thermodynamicist audiences.

Where are your data for temperature uptake in superheater elements at different distances in from the return bend? (Preferably as measured by thermocouple at the inner tube wall, or in the actual steam mass) Those data exist, and would be relevant here; in fact, I believe one of the flavors of Locomotive Superheater Company actually took data such as these using proper procedure -- I just don't have 'em (which bothers me greatly). Find that stuff, don't randomly quote the wrong thing out of a promotional book, or misinterpret data from case examples.

Note that I am NOT saying that there's actually a blanket rule that says "lopping one-third off a superheater is always the right proportion" -- you overlay the actual gas temperature in the critical flues, at critical flows, on the element structure and internal steam flow with its attendant heat transfer function, and see... well, you can see one of two things, really. The first is where you want to place the effective return point for the superheater passes to keep the metal temperatures at safe levels in the elements "under worst-case steam flow conditions" -- and this argument is probably going to involve (as it did historically) pretty quick reference to superheater dampers or other gas-flow restrictions if there isn't some means of assuring steam flow, and hence heat transfer, in those elements.

The other of the two things, which hasn't come up yet but perhaps should, is the actual superheated-steam temperature coming from the elements (and through the header, and down the pipes to be measured at the chests or wherever) that is induced by an element under the extreme firing conditions that might lead to 'element shortening' (e.g. on conversion from coal to oil firing, or with new-and-improved burner design, firebox lining, etc.) It was not my impression that most of the Superheater Company designs contained explicit tempering or 'desuperheating' functions (as so many power-boiler designs do) and hence there might be either a perceived or operational reason, or desire, to shorten the elements enough to keep out of lubrication trouble and so forth up front. (I'd tend to concur that Wardale's approach, to steam-cool the liners where the lubrication trouble occurs, is better than crippling the thermodynamics, but that's just a preference on my part; from a pure 'preservation' standpoint, on the other hand, there are likely to be fairly HARD limits on allowable superheat, and therefore on required superheater geometry that 'matches' a given locomotive's prior superheater performance when higher firing levels, sufficient to improve actual steam generation for example, may be used).

Yes, I'd like to see Nigel Day provide a full worked example, with all formulae, of how he would compute the details of superheater construction for one of the locomotives he has worked on. We could proceed from there to see where scientific reconciliation of his approach vs. 'American' style calculations used for our big power will take us -- and I do firmly believe that just such a reconciliation will be possible.

I do further think that this should be done in its own thread; I only answered here to ensure that the wrong impression wasn't left with casual readers.


RME

Being new to engine service on the C&TS, the only time I have seen the drifting throttles used on trains has been to keep the slack stretched on tight curves or sags. In my opinion, using the drifting throttle for a long period would be harmful to the superheaters since you are drafting the fire against a closed throttle. This goes back to part of my original question about when the common practice at some railroads was to completely shut off the throttle while drifting.

I would imagine the two most appropriate times for using a drifting throttle would be for running with a light engine down grade when alternating between using the reverse gear and driver/tender brakes, and perhaps on trains with the older K triple valves and excessive brake pipe leakage which I'm sure was common before the tourist era.

Dear John Hiller

There are several issues that come to mind. First let us consider when a locomotive is stationary and you are building air up in the air brakes the firing rate increases to deal with the increased draft. The superheaters do have steam flowing though them so they do have that heat sink of steam on the other side yet they seem to survive that treatment even in an oil burner. I think the key here is what is temperature and entropy. Temperature being a measure of a materials ability or inability to give up heat energy relative to other materials in its environment. Entropy is defined by the second law of Thermodynamics but for simplicity purposes let us imagine this as a rate of heat flow in and out issue Even though the superheaters do not have a the gas fluid flowing through them there are other sufficient heat sinks from the point of combustion that the superheaters are not affected. Consider a cutting torch, as soon as you light the combustion temperature is sufficiently hot enough to cut. Yet when you point the flame to the area you want to cut you have to wait until there is enough heat absorbed into the metal so that you can begin the cutting process. So by what you describe are they over coming the heat sink with increased fire activity created by the draft, probably not. Given that the Drifting throttles come out of the turrent I think the overall steam flow rate is similar to the air pump at full speed. I believe the intent of the drifting throttle COULD be either not understood or being misused.


Unfortunately the C&TS has seen many turbulent years since my trips in 2001. The fact that any of the operating crew members have stayed as long as they have is a bit of a miracle given the uncertainties since 2001. I am going to suggest talking to Mr. Knoob if he is still in Alamosa or suggesting stopping by Taos, NM and seeing Jeff Stebbings at Jeff’s Joint (it is a BBQ restaurant). Both have operated locomotives over the RR and could give better explanations of your concerns than I. If you go to Jeff’s get a package of ribs to go and he will probably give you reheating instructions for the backhead.

Robby Peartree

John Hillier,

As someone pointed out much earlier in this thread, you have to consider the condition of the fire while drifting. It will be a very low fire and the temperature of the gasses passing through the flues will be much cooler than you would have with the engine working hard. The transition from a hot working fire to a cooler drifting fire takes some time and the flue gasses will be hotter during this period. This can be minimized to some degree by an experienced fireman knowing exactly when to reduce his firing rate and allowing the fire to begin burning down and cooling approaching the point of transition from pulling to drifting.

The technique of using the drifting throttle for pulling in certain places was developed by a couple of the early C&TS engineers to help keep the slack in the train stretched when handling the train over some parts of the railroad, mainly eastbound between Osier and Sublette.

It was not considered good practice to use the drifting throttle with the engine in reverse to augment the train brakes when handling the train down hill. Doing so can cause the slack to bunch on the head portion of the train and give the passengers a rough ride. Not to say that it has not been done with a particularly poor handling train from time to time.

It appears that there may be some confusion about exactly when the superheater units do and do not have steam flowing through them. The narrow gauge engines in question all have type A superheaters with dome throttles. The only time the superheaters are pressurized and have steam flow through them is when the throttle is open. Steam for all other uses comes from the turret which is supplied by its own dry pipe that pulls saturated steam from the steam dome.

Russ

... and little fishes... I get really annoyed with egotistical wannabes that can't do the math, yet slam about engineering concepts attempting to impress the "casual reader".





First off, there is no such thing as "precise" in heat transfer or fluid flow calculation except in a snapshot of time. Second, in a fire tube boiler, all combustion ceases at the tube sheet (remember the bunsen burner flame and the wire mesh screen from 10th grade chemistry?) Furthermore, if combustion is not complete before it hits the tube sheet, there are other serious problems to be dealt with.



Your ivory tower is showing. That is around 220 psi absolute, around 200 psi gauge.



I would like to see Nigel's example too, but since he chooses to keep his work proprietary which is perfectly understandable, YOUR MISSION, should you decide to accept it, is to take a common US locomotive, such as the K-36, and do the calculations based on the steam flow exerting 36,000 lbs TE at 10 miles per hour. The methods of Lawford Fry allow you to do this, (since you obviously googled his book). Please report back to the board, in a new thread your calculations and conclusions.

I have been too busy unwinding this low-watered powerplant these last few months to delve into one-upmanship with a scholastic wannabe.

That's funny, I was just saying much the same thing in the past few posts... ;-}

You should note that I have been very specific not to question your mathematical or professional ability, only a few examples where your scholarship or references have been mistaken. While I've come not to expect common courtesy or gentlemanly behavior from many people on the current incarnation of RyPN, it is still a bit disappointing to see people reverting to ad hominem comments or snarky criticisms of others they do not know.

If you're upset because I caught you out in a few casual remarks on an Internet board, get over it. There are more significant things in life, some of which you're evidently doing in your professional time.




"Precisely" in that sentence doesn't mean precise numbers, as you well know; it means 'focusing in on that particular aspect of gas behavior'. I'd be happy to discuss some aspects of semantics and rhetoric in English usage if you want, but it really isn't germane here.



No, it doesn't. If you had been listening in your 10th-grade chemistry, you might remember the explanation of why wire flame arrestors work as they do. That's not the case at tube entry. "Combustion" (defined more precisely as oxidation reactions still going forward above transition temp and liberating heat) can and often does continue in the early part of the tubes; the issue here is that a dogmatic statement that it 'ceases' is just -- flat -- not -- correct. My apologies if this damages your ego.



One of them soot buildup; another likely to be excessive smoke. Yes, there are others. By all means mention the ones you consider most significant. Everyone (who is still reading this thread) will benefit from the explanations.

I thoroughly concur that a *properly-operated* locomotive should not have active combustion at the rear tubeplate (whether or not combustion of the fuel is reasonably 'complete'). I am not entirely sure how the original discussion got from the subject of heat damage to empty superheaters during drifting to overheat damage to return bends, which doesn't have nearly as much, if anything, to do with drifting ('thermal flywheel' or otherwise...). But it was my understanding that we were talking about situations where the return bends were suffering 'burning' as a result of excessive gas temperature, and no longer about elements that were suffering thermal damage from having been drifted empty with 'normal' gas temperatures under drifting conditions.




My value corresponded to what the equations' context would be using: temperature in Rankine, pressures in psi absolute. If you think it needs 'correction' take it up with the people producing the steam tables. Are you telling me you do these calculations in psig? (And surely you meant 'around 205 psi gauge' if you were going to do a proper correction?)




Actually, his reason for keeping his work 'proprietary' is indeed understandable, it's to avoid the whole kerfuffle of discussion and insult on here. Perhaps he will actually choose to give some hard details, which (I repeat) I consider him fully qualified to do. Heaven knows this thread hasn't given him much incentive to do so...



Be glad to when I have time. Are you saying that you want me to use his 1924 methods and formulae to arrive at the 'conclusions'? (I will state the assumptions used, in the usual way.) I take it you're wanting a curve for the gas-temperature falloff in superheater flues under 'balancing' conditions for the given steam demand, right?

(PM me if you don't see anything in a reasonable time -- I will need a correct copy of Fry if you want me to use it, as 'googling' it, which I did to check your reference, doesn't produce a legal online-readable version, and I don't use that book as a primary reference.)



Only you seem to be doing any one-upsmanship. I apologize if you perceive things a different way.

I saw those elements the first time you posted them -- pity this isn't a technical board, because I'd like to hear details of the incident that got 'em in that condition...


RME

May I take just a minute to point out that we here at Wasatch Railroad Contractors, with the full support of the Durango and Silverton have done the most extensive field testing work on a steam locomotive this side of the past ten years. In fact, we believe that our work surpassed that done for the ACE project of the early 1980's.....simply because we used better/more advanced technology.

Our project manager at the time was in close communication with Mr. Day, who has been credited for his work on the project as well. All of that said, I have a simple request of the parties included in the debate;

At this stage, unless you have more compelling information than we have, I doubt that you are in an actual position to debate the matter. I wish to end the debate by simply saying; We have the hands on study of this project and as kindly as I can say it.....a few of you "know it alls" simply.....well.....do not!

Mr. Day is to be credited for the "simple" approach to the debate contained here-in and as is par for the course, others wish to denigrate the debate with personal attacks. Sparing any name calling, there are clearly two people included in the debate that wish to denigrate each other, not produce a productive debate. This is sad to see..... specifically when the information you want is out there to be had. (at least good portions of it.)

I will remain at bay on the issue as I see that the debate of "facts" is not a significant part of the discussion.

We plan to start a new discussion about superheaters on Monday.

Kindly submitted,

You know, we are PRETTY FAR from Mr. Hillier's original question and are getting rather heated (superheated??). Can those of you who are interested in the thermodynamic vagaries of superheaters take your discussion to a new thread so we can get back to the discussion about drifting techniques?

Thanks!

Drifting techniques? Oh yeah, that's what the thread was about wasn't it?
I'm looking forward to seeing John's real world results on superheaters. I've always enjoyed results and facts as opposed to theory.
Frankly I wish I had kept my nose out of this one and my mouth shut.

Just a bump to connect this thread with the C&O Mallet low-pressure cylinder thread.

viewtopic.php?f=1&t=43668