feltonhill wrote:According to my estimates, and that's all they are, the as-built Y6's had valve timings that reflected an adjustment factor of about 74%. The final Y6b's and the improved Y6's were closer to 82%.
dredmann wrote:the Y5/Y6 originally allowed steam admission over, IIRC, 90% of stroke in the HP cylinders and 88% in the LP cylinders ... the new maximum cutoffs were 80% and 75%.
Do those agree?
I'm not ignoring this discussion, just got bogged down on some other stuff today.
The above percentages are correct as stated. However, I use an overall adjustment factor (s) and Jeffries' book uses percent cutoff. Whether they correlate or not, I don't know.
My method uses the standard tractive effort formula for each engine, a boiler pressure of 300 psi and a receiver pressure of 125 psi starting and 84 psi compound. These adjustment factors attempt to take into consideration the pressure losses from boiler to steam chest, and the effect of valve timing on MEP. I use the rated TE as a target value for the two equations and attempt to get a reasonable balance between the HP and LP engines at starting.
Timz, I believe your method uses an estimate of MEP directly?
I have this in a spreadsheet, but it's not possible to post it here. I'll try to summarize it in text format and post it.
feltonhill wrote:I use an overall adjustment factor (s) and Jeffries' book uses percent cutoff. Whether they correlate or not, I don't know.
Reportedly, Jeffries says N&W shortened cutoff on the later Y6s-- you seem to be saying the later Y6 had more starting TE than the early Y6. What's the connection between the two changes?
(I don't see that in the original edition of Jeffries-- it's in the newer edition?)
feltonhill wrote:Timz, I believe your method uses an estimate of MEP directly?
It's not "my" method-- it's the often-used formula for a compound Mallet, which assumes
HP MEP + LP MEP = 85% of boiler pressure
HP TE = LP TE (so HP MEP = LP MEP times the square of (LP cyl bore/HP cyl bore) )
The locomotive engineering section in the first edition of N&WGofS runs from p59 to p83. Cutoff modifications are discussed from p66 to p70. The figures are written out so they're hard to find - original cutoff, p66 first column; modified cutoff, p70 first column.
The modified Y6's had a higher TE and DB pull than the originals. See graphs on pgs 76 and 83.
The N&W timetable rated the A at 12500 tons up the 0.3% to Kingston (Ohio). No idea whether they actually did that-- but if they did, you figure anytime speed dropped below 5 mph on the 0.3% they were doomed to stall?
Normally a loco should be able to start a train of a listed tonnage rating. That's the way it is today and I have no reason to believe things were any different back then. If not, what good would the tonnage rating be in the fist place!
Even though the ruling grade on my district is from 1.6% to 1.64%, there are places that appoach 1.8%. However, they are short and though it may slow you down, it won't normally make you stall. You certainly wouldn't want to stop there with full tonnage or for that matter on top of a rail greaser.
.
re: "Reportedly, Jeffries says N&W shortened cutoff on the later Y6s-- you seem to be saying the later Y6 had more starting TE than the early Y6. What's the connection between the two changes?"
All of the Y6's (and maybe the Y5's) originally were rated for a simple starting TE of about 152,000 lb (yes, even the Y6b's, with the thicker tires and other improvements). Various changes improved HP at speed and other properties, but AFAIK there was only one increase in tractive effort, to a simple starting TE of about 170,000 lb.
As best as I can recall right now (brain gone foggy!), the valve reworking did two (at least somewhat) related things, (1) decreasing the maximum cutoff and (2) increasing the valve efficiency (in a general sense). To speculate on top of a hazy memory, it may well have been that the improved valves allowed a coeficient higher than 0.85, in other words, for more of the stroke, your pressure in (all, in simple) the cylinders more nearly approached the 300 psi boiler pressure. Presumably this more than made up for the lack of additional steam being admitted between 80% and 90% etc.
Frankly, IMHO the Jeffries book does a somewhat less than stellar job of explaining and commenting on the sources and realities of the supposed increase in starting TE to around 170,000 lb simple. This is the kind of issue where I would love to hear the views of somebody like Parker Lamb. In fact, let's see whether he can be enticed . . .
you seem to be saying the later Y6 had more starting TE than the early Y6. What's the connection between the two changes?"
BTW, this vast amount of lead was one of the things that the scrapyards bought the retired engines for.
BTW Pt. Deux,I noticed the other day that the subject (Re: ) of this entire post has changed names quite a few times over the now four pages. How does this take place when everything is still under the original title?
BTW Pt. Trois,Not to get this post even more off subject, but, Some of you have obviously read "The Steam Locomotive" by Ralph Johnson of "Baldwin" fame. No doubt that is where some of these formulas are coming from. But, have you noticed in the book the conspicuous absence of anything about a "Compound" locomotive (other than the one or two formulas) ?
Hello everybody,
the change of the topic is not a problem to my eyes, many interesting sub-topics here.
As there are many unknown factors of starting and moving a train, does not some rules of thumbs of calculating train resistance exist? It is hard to believe a yardmaster would do calculations for every single car... or did they have 64bit Abaci?
Sorry for later answering this post,
but would like to verify timz notes on the Columbus route. The N&W used the auxiliary tenders to keep the trains running.
13K to 14K along 100miles looks like tonnage record...
Lars
Lars Loco wrote:Hello everybody,the change of the topic is not a problem to my eyes, many interesting sub-topics here. As there are many unknown factors of starting and moving a train, does not some rules of thumbs of calculating train resistance exist? It is hard to believe a yardmaster would do calculations for every single car... or did they have 64bit Abaci?Lars
North American railways publish a tonnage rating for each class of locomotive each one uses -- its own plus common foreign locomotives -- for each subdivision or segment of subdivision where it matters. For example, on a flat subdivision the rating may be from end to end; for a subdivision with a hill at one end there may be two ratings, one up to the base of the hill and another on the hill itself. The tonnage rating takes into account rolling resistance plus grade resistance, plus characteristics of each locomotive type (4 or 6 axle, A.C. or D.C., Positive Traction Control vs. standard ordinary wheelslip, type of bogie, dynamic brake equipped or not, etc.) The tonnage rating is the maximum tonnage with which that locomotive is expected to just make it over the subdivision without burning up its traction motors or stall. To calculate the tonnage, the trainlist is consulted. The weight of the locomotive itself is already factored into its rating and does not have to be added to the trailing tonnage. Most U.S. railways just use the standard Davis formula for rolling resistance but some railways have modified it slightly. The most common modeling software, Rail Traffic Controller (which is used by the five U.S. Class Is and KCSM, as well as the regionals, but not CN and CP), uses standard Davis formula.
Generally the yardmaster does not assign power or "run trains." That authority rests with the chief dispatcher working with a terminal trainmaster or trainmaster.
Every railroad has slightly different job titles, responsibilities, etc., so, with that caveat, at the last Class I where I worked in the operating department, power was assigned and trains run as follows. The other railways I work with have differences in method but it comes out basically the same. The big differences are that some steps are electronically automated and where the lines of responsibility break between chief and trick dispatcher (or assistant chief), and who does the paperwork.
1. The railroad has a written operating plan it works from. The plan is usually on a weekly basis because carloads tend to be light in the early week and heavy by late week, and because shippers plan their inventory that way. The plan states when a train will be run, what tonnage that train will carry, and what horsepower/ton that train will have. While there is infinite small variation, generally the railroad does the same thing every day or every week. Unit trains which are usually not tied to a day of the week or a week at all, but on an annual tonnage basis or a market basis, are generally on a parallel plan on a 30-day projection.
2. The terminal trainmaster assesses his outbound loads and notifies the chief dispatcher when he thinks he'll have a "schedule" ready, and if that "schedule is over-tonnage or light. If it's over-tonnage a second section may be called, or the overs may be held for the next day's train. If it's light the schedule may be combined with another train and one of the two trains abolished that day.
3. The chief is working 2-3 days in advance and knows what to expect. The chief has already assigned a crew slot to that train and planned where the crews will be 48-72 hours out, and the power desk has likewise looked ahead to make sure it will have the right kind of locomotives in the right place 48-72 hours out. In the morning conference call each terminal projects where it will be 24-72 hours out and everyone is supposed to listen and plan accordingly.
4. The chief tells the power desk that train #XXX will be ready to be called within a certain time window, the tonnage, and anything unusual, and the power desk assigns the specific locomotives, telling the terminal trainmaster which locomotives to pull from where for that train.
5. The terminal trainmaster instructs the yardmaster to tell the hostler, or tells the hostler directly, which locomotives to put on the train, and the yardmaster projects a call time for the train. If it's a small yard the road crew may have to hostle their own power. The terminal trainmaster calls the trick dispatcher and notifies him of the call time. Usually the terminal trainmaster gives the trick dispatcher an 8-hour advance lineup and then updates if anything changes. Two hours in advance of when the train will be ready the terminal trainmaster calls the trick dispatcher again and tells him the train is ready.
6. The trick dispatcher calls the train by giving a call slip to the crew caller, who calls the crew, pulling the paperwork from customer service to see what work the train has en route, if any, and sets up the train in the trainsheet. He checks the power on the train versus the tonnage shown on the train list to make sure the train has enough power, and looks ahead to see if the train has pickups or setouts in route, and if so if it will still have enough power after the train tonnage changes. The power desk will also often tell the trick dispatcher to perform power swaps en route, or to set out or pick up units en route, or other instructions.
7. The train crew arrives at the terminal, gets the train list and other paperwork, and also confirms it has enough power, and talks with the trick dispatcher to tell them when they're ready and any other issues.
In sum, there is (1) a published tonnage rating, (2) a published hp/ton ratio that is supposed to be adhered to for that train, (3) numerous checks to make sure it's right.
Stalls still occur, however, because tonnage ratings can be optimistic under some conditions or because locomotives are not loading fully or fail en route. For example, we would get a run-through SD45s from a connection that were old and badly maintained. We always discounted their tonnage rating 20-30% below the tables.
RWM
BigJim wrote:The N&W timetable rated the A at 12500 tons up the 0.3% to Kingston (Ohio). No idea whether they actually did that-- but if they did, you figure anytime speed dropped below 5 mph on the 0.3% they were doomed to stall?I think you are making more out of this than is actually there. Wasn't this one of those "momentum" grades, much like the Ohio River Bridge?
BigJim wrote:Normally a loco should be able to start a train of a listed tonnage rating. That's the way it is today and I have no reason to believe things were any different back then. If not, what good would the tonnage rating be in the fist place!
Well, first off, no reason to assume the tonnage rating is any good. The timetable might say an engine can haul X tons from A to B, but who knows whether it's true.
But the point of my quote above was to respond to erikem, who mentioned
"a circa 1920 Baldwin publication that shows the minimum rolling resistance for a passenger train as 4.5 lb/ton at 8 to 10 MPH. The 0 MPH intercept on the graph appears to be 15 lb/ton, 2 MPH looks to be about 10 lb/ton, 5 MPH is about 6 lb/ton."
If that were true-- if it took 15 lb/ton to start a friction-bearing train on the level, and 10 lb/ton to maintain 2 mph-- then an A would have no hope of starting 12500 tons on a 0.3% upgrade, even if it could take slack. And a C&O 2-10-4 would have no hope of restarting 13500 tons on 0.2%. So either the Baldwin booklet is wrong (which I'm guessing it is) or the railroads were known to dispatch engines with tonnage that they couldn't always start.
(One more caveat: the timetable says 12500 tons for an A, but I have no idea whether they were actually assigned such tonnage.)
Got this rating and some others from J.G. Collias BB&Co. A quote to some photos, though these values seem to be reliable.
By the way. TE for "A" is 115000@10mph and 105000@15mph.
timz wrote: BigJim wrote:Normally a loco should be able to start a train of a listed tonnage rating. That's the way it is today and I have no reason to believe things were any different back then. If not, what good would the tonnage rating be in the fist place!Well, first off, no reason to assume the tonnage rating is any good. The timetable might say an engine can haul X tons from A to B, but who knows whether it's true.
Often the tonnage ratings are not good. At the last Class I that I worked at, our tonnage tables claimed a single SD70MAC or AC4400CW would easily take 135 empty aluminum coal gons up 1.5%. (That's 2835 trailing tons, or 85,050 lbs. tractive effort required for grade alone). Well, a MAC or AC would not do that, if the rail was wet (and it was always wet), probably because of the curve resistance. Rail profile may have been none to good either. That stunt was only tried once and the train stalled right about where I figured it would.
Hey railwayman, thank you for explanation!
You give a nice view train-perparing!
But in practical terms, only weighted train-load (and Factor of expirience, of course) plays a role, then. From slow and heavy to light(er) and fast.
Trainmaster: "Got 5430t of that PFE-Stuff"... Hostler: "Oh man, they need a helper again, 'n today my day off!"...
dredmann wrote:As best as I can recall right now (brain gone foggy!), the valve reworking did two (at least somewhat) related things, (1) decreasing the maximum cutoff and (2) increasing the valve efficiency (in a general sense).
But when you're starting-- when the engine is stationary-- the valve doesn't have any efficiency. It's either open or closed. They reduced the maximum cutoff to improve the valves' efficiency at running speeds.
dredmann wrote:... your pressure in (all, in simple) the cylinders more nearly approached the 300 psi boiler pressure.
Just to clarify-- if you did actually admit 300 psi steam to the Y6's low-pressure cylinders, the TE from them alone would be 200,000+ lb-- so don't forget to gear that engine to the rail before you try it.
As I recall Jeffries explains about the reducing valve, but he doesn't say what pressure it allowed into the LP cylinders.
Lars Loco wrote:Hey railwayman, thank you for explanation!You give a nice view train-perparing! But in practical terms, then only weighted train-load (and Factor of expirience, of course) plays a practical role. From slow and heavy to light(er) and fast.Trainmaster: "Got 5430t of that PFE-Stuff"... Hostler: "Oh man, they need a helper again, 'n today my day off!"...
But in practical terms, then only weighted train-load (and Factor of expirience, of course) plays a practical role. From slow and heavy to light(er) and fast.
Naw. The hostler would say, "Looks like I'm not going to get the early quit, so might as well pork it for the overtime."
RailwayMan,
you ran an AC4400? What capacity it had, at say, around15mph?
I've "run" one but only with a real engineman telling me what to do. I've never worked in train service, only in other roles in the operating department and other departments.
I envy you, but in positive way,
never 've been on a real running locomotive...
a single SD70MAC or AC4400CW would easily take 135 empty aluminum coal gons up 1.5%. (That's 2835 trailing tons, or 85,050 lbs. tractive effort required for grade alone). Well, a MAC or AC would not do that, if the rail was wet (and it was always wet),
BigJim wrote:If you don't believe what is published in the employee timetable, then who are you going to believe? As I said before, todays tonnage ratings are very accurate and I have no reason to believe things were any different before.
I'll get an example for you from home. You could reasonably ask: why put impossible or unlikely ratings into the timetable? A friend of mine came up with a plausible explanation-- it's just to make life easier for RR officialdom. When the conductor complains the train has too much tonnage, whip out the TT and rub his nose in it. Then when the train stalls, no one's to blame.
BigJim wrote:I was just wondering what causes it to happen.
Any time you reply, the "subject" is up at the top of the form and can be changed to reflect your reply's subject.
I can't find the source right now, but somewhere I got the figure of 125 psi LP receiver pipe when starting, 84 psi in compound operation for the Y6. This is not the same as MEP.
The "booster" valve raised the pressure in the receiver while still in compound operation to somewhere between 100 and 110 psi. According to notes in the spreadsheet I'm working on, this was from Class Power 3A (USRA 2-8-8-2's) by King and Dressler, p135. I've been using 105 psi as an average, also not MEP.
BigJim: The formula for grade resistance is:
Grade resistance (in pounds of tractive effort per ton of weight being lifted) = 20 x percent of grade.
In this particular case:
20 x 1.5% = 30
30 x 2835 tons = 85,050 lbs. tractive force needed just to overcome gravity. Additional tractive force is needed for rolling resistance, curve resistance, and inertia effects if any.
This formula uses Newtonian physics and trignonometry; there is no "measured value" embedded in this formula like there is with horsepower calculations.
A difficulty arises in knowing what the percent of grade is. Do you measure the average grade from top to bottom? The average grade on which the train happens to be at any instant in time? A momentum grade assuming such-and-such train length, tonnage, and speed? And do you compensate for curvature, and if so how much?
Often the track charts on which the tonnage tables are based are wrong. They have math errors, or construction changes were made in the field and no one updated the chart, or there were assumptions made, or bad survey done, or the engineering department has softened curves, raised sags, leveled off crests, and never updated the charts, and it can add up to big errors. Some railroads have better track charts than others. When we do track engineering for line changes, 2nd track, siding extensions, etc., we use the track chart as a conceptual reference, then we hire an experienced surveyor that specializes in railroad work and see what's REALLY out there.
A dispatcher friend a few months ago told me about a controlled siding that has had the same published length in the timetable for 50 years. One day he had a train of almost exactly that length that he tried to fit in the siding, and it hung out by 400'! This created a jackpot with lots of embarassment all around, so the engineering department went out and measured the siding, and lo, it really was 400' shorter than what the timetable, track charts, val maps, and engineering drawings in the file drawer said it was.
So, yes, I take the tonnage tables with a grain of salt. I expect them not to underestimate what a locomotive will do, but I don't feel like testing those numbers with real trains, either.
feltonhill wrote:I can't find the source right now, but somewhere I got the figure of 125 psi LP receiver pipe when starting, 84 psi in compound operation for the Y6. This is not the same as MEP.The "booster" valve raised the pressure in the receiver while still in compound operation to somewhere between 100 and 110 psi.
The "booster" valve raised the pressure in the receiver while still in compound operation to somewhere between 100 and 110 psi.
As I recall, the diagrams in Jeffries' book suggest that receiver pressure is the same in booster and in simple. The same reducing valve is admitting semi-high-pressure steam in either case.
If that's true, LP TE would be the same in booster and in simple-- it's just the HP TE that increased when you shifted from booster-compound to simple.
BigJim wrote:todays tonnage ratings are very accurate and I have no reason to believe things were any different before.
The wackiest ratings I've seen were on the SP eastward out of El Paso, where the 1% grade is miles long (as I recall it's around 1.1%, and 10+ miles long). For years in the 60s/70s the timetable showed 3355 tons for a GP35 (and the corresponding 6710 tons for a DD35B) and 4835 tons for SD45s. Those are the only ratings I've seen that are definitely hopeless, but lots of RRs have had ratings that look doubtful (and that rarely if ever get tested, the dispatchers knowing better).
The wackiest ratings I've seen were on the SP eastward out of El Paso, .... the only ratings I've seen that are definitely hopeless, but lots of RRs have had ratings that look doubtful (and that rarely if ever get tested, the dispatchers knowing better).
I can't speak for what other RR's do. All that I can do is give accounts of my own personal first hand experiences. If you choose to believe them, fine.
If the pressure in the receiver pipe were only 84 psi when starting, the Y6 could never develop more than 126,000 lbs TE, the same as its rating when operating in compound mode. I believe that's where the 1.2 x compound TE adjustment factor comes in.
The so-called emergency valve on the original compounds (ALCO system), or the simpling valve on the modified Y6's accomplished the same purpose - letting the engineer hold the Y6 in simple "gear" until he decided to switch to compound.
Big Jim is more expert on this subject than I am.
So, the values in the TE-table for Y6(refined) are reliable, or not? Has somebody checked it at locofonic?
For me, would not take care about an unknown factor of -/+ 5%.
lars
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