Hello,
Yesterday I went to the Exporail Museum (St-Constant Qc,) and I noticed on old Canadian National Railways steam loco the following marking U-2-g 57% it was located on the cab just under the loco number.
Can anyone explain me the signification of this marking.
Thank You
U-2-g is the class of the locomotive. CN and CP liked to have several sub classes of the main class being slightly different. But in short U (CN 4-8-4) 2 (second incarnation of the wheel arrangement) g (being the 7th variation)
The percentage is a calculation of the of a bunch of factors showing the locomotive’s tractive effort output (correct me if I am incorrect). I’m not sure of the specifics on getting the percentage but all CN steam had their specific percentage shown.
57% indicates the tractive is 57,000 pounds. But I have no idea why CNR chose to use this format, or for that matter, why they even felt it desirable to have stencilled on the locomotive.
The early diesels also carried their tractive effort on the cab side using the same format.
John
This would be the per cent of cutoff which is that part of the piston stroke which has completed when cut off occurs.
In the arrangement of modern steam locomotive valve gear, maximum steam admission can be obtained when the reverse lever is all the way forward (or reverse) and as speed, thus momentum, increases, less steam is required to do the work. Thus the steam supply to each stroke of the piston can be “cut off” and the remaining steam be allowed to expand thus saving vast amounts of steam and in turn water and fuel. As the engine gains speed the engineer will move the reverse gear closer to center, called “hooking-up” in some circles, and this shortens the stroke of the valve which admits less steam to the piston.
Cutoff is part of the expansion phase — one of the four valve events during each cycle or rotation of the driving wheel. Admission, Cutoff, Release and Closure. Of course, 0% cutoff is dead center and no steam is being admitted.
The cutoff is determined this way. Say the maximum stroke of the piston is 28 inches and the cut off occurs when the piston has moved 7 inches. 7 inches is 7/28ths which equals 1/4 or 25%.
Maximum cutoff usually occurs at 85 to 88%. The steam is always cut off before the piston reaches the end of its stroke. You hear the most steam exhausting the stack at maximum cutoff, when the engine is really working, and that’s what we love to hear from trackside.
On the particular locomotive you are asking about the minimum percentage of this cutoff is 57% and is stenciled below the number on the cab. It was relevant to the engineer because, ideally, below 57% the locomotive power would be regulated with the throttle rather than the reverse lever.
Have fun, Ed
Hello Casey and John, thank you for the infos they are greatly appreciated.
Ed, thank you for the well detailled explainations they are also greatly appreciated.
Some more thoughts on the U-2-g and 57% markings.
The U class represents any of the 4-8-X class locomotives owned by CNR in my mind. Meaning any locomotive with 4 leading truck wheels, 8 drivers and a trailing truck. The 4-8-2 Mountains were classed U-1-a through f.
I guess the U-2 class locomotives could be regarded as improved Mountains so the would be the second stage of development. There were also U-3 Northerns and U-4 Northerns. The U-4 class were the streamlined ones.
Both CP and CN used the % symbol to represent 1,000 pounds tractive effort; nothing more. So, the 57% represents 57,000 pounds tractive effort as John states in his reply.
This little USRA Mike is rated at 55,000 pounds tractive effort, almost the same as the U-2? OK, my mistake.
nothing more… I stand corrected?
Ed
So, are we to understand that the 6 paragraphs about valve timing and cut off were just so much conjecture or misinformation? At least the spelling and grammar were good.
Charlie
I appreciate the kudos on the grammar…
Many years ago I had inquired about the “55%” stenciled as shown in the attached photograph. Someone whom I trusted and looked up to for their vast knowledge of steam locomotives gave me the “cutoff” explanation, saying that the 55% was the point where you could run the locomotive with a wide open throttle and regulate speed/power from 55% to near 10% or as close as dead center as the engine would continue in the forward direction. His explanation I took as gospel and never doubted it. I couldn’t understand, though, why CN, CP, GTW, CV were the only roads that cared to supply this information to passers-by (I cannot fathom an engine crew forgetting the tractive effort of the locomotives they ran every day and leaning out the cab window for a peek and a quick reminder??)
There are no markings on a reverse quadrant, let alone knowing exactly where you are with a Baker screw reverse gear (other than the indicator on the Loco Valve Pilot) so I don’t know how an engineer would even know if he was at 55%; 58% or even 63% cutoff. Steam engineers learned how each engine handled, some very differently even in the same class, and they knew from the sound of the exhaust, the anticipation of slipping drivers and just the “feel” of how the locomotive is reacting to throttle, cutoff, train weight and inertia, weather, water (is the boiler steaming freely or is it foaming) the mood and experience of the fireman and his firing technique, quality of coal and condition of the driving gear; are the piston rings leaking by, shoes and wedges so bad that the drivers are out of tram, boiler so plugged with mud and scale that a tea kettle would boil water faster, are flues plugged, superheater tubes leaking, ash screen plugged in the smokebox, staybolts leaking and wetting the fire. Any one of these things can lead to a miserable trip. Tow
While your source was in error, he probably relayed it in good faith. More than once I have found a generally respected expert has wandered slightly out of his specialty and made a superficially logical assumption when asked about some detail. It then gets passed around and becomes “common knowledge”. Sometimes myths originate from a railway employee who gave an answer to an interested fan rather than admit ignorance.
Many early diesels received this stencilling, reflecting the tractive effort. For example, as best I can see from pictures in my collection the CLC H-10-64 seems to be 34%. CN 7700/77 was 36%, and the GP7 was in the 40% range. Meanwhile the aborted order for CLC/Whitcomb 44-tonners were only 22%. Even the electric boxcabs in Montreal had their tractive effort shown as a percentage.
As was said, it is not clear why CN chose to paint the tractive effort on the side of their locomotives. At the risk of starting another myth, perhaps it dates back to the creation of CN from the various predecessors, inheriting a motley collection of locomotives. Its application to non-steam locomotives seems to have been discontinued in the mid 1950s.
John Sutherland
Hello everyone,
thank you so much for your efforts in elucidating these mysterious markings.
One last question if I may, can you elaborate on the term “tractive effort”
Is this the maximum % in weight or pulling force of the engine that the loco can pull?
Thank you
Gidday Serge, to my mind simply put (for Bears with a non mathematical brain), Starting tractive effort is the most important for railroads as it determines the maximum weight of a train that a locomotive can pull from a standing start.
Here’s some links which go into the subject in far more depth…
https://en.wikipedia.org/wiki/Tractive_force
http://www.republiclocomotive.com/tractive_effort_and_power_calculations.html
http://5at.co.uk/index.php/definitions/terrms-and-definitions/tractive-effort.html
Cheers, the Bear.[%-)]
Hello “The Bear”, thank you for the numerous links you provided me.
According to all definitions, “Tractive effort” (TE) is the force applied by a locomotive for moving itself and a train.
So If I go back to the marking of 57% on the cab, does this mean that the locomotive’s maximum pull is 57% ?.
Thank you.
From earlier response:
Hello Chris, thank you for clearing that up for me, I was kind of lost in all the explainations.
Have a nice day.
Back to the first post, railroads generally assigned a letter-number code to each type of locomotive. So on the AB&C Ry., a “B” class engine might be a 2-8-2. The first engines would be “B1” class; if the railroad later bought another group of 2-8-2s but with some improvements, they might be labelled “B2” class. Some railroads added a letter, sometimes for example an “s” would indicate the engine was superheated…“B-2s”.
Each railroad used it’s own system, so a “J” on the Norfolk and Western was a 4-8-4; on the New York Central, it was a 4-6-4. It wasn’t standardized across the industry.