Steamer Identification

[marknewton]

The reason for including the percent cutoff was to calculate starting tractive effort. Obviously, it would be  important to know how heavy a train the locomotive could be expected to start.

Yes, it is. But I'd be astonished if the GN expected their crews to perform this calculation every time they went to start a train, which seems to be what you're suggesting. Most railways simply calculated the average starting TE for a specific class of loco, and published load tables based on that. That information would be much more useful to crews than painting the MEP on the cabside.

Cheers,

Mark.

[timz]

Often the cutoff figure was about 85 percent, but not always, and on some locomotives with a special link in the gear, the cutoff would vary depending on the setting of the reversing lever.

Eh? Surely you didn't mean to write that?

I suspect he was referring to engines that have a slot in the top of the combination lever-- as the cutoff is shortened the front end of the radius rod is somehow slid upward in the slot, thus increasing the lead.

[BDT in Minnesota]

 Feltonhill

Yes, the Great Northern Railroad Historical Society  has Reference Sheet #334, dated June 2006.....

In this reference sheet, they mention that when the percent working pressure was listed, it was common for the number after the decimal point to be a smaller number... ,, as the 85.4 percent on H5 #1355.... other locomotives in this class displayed the 85.4 rating as well, while yet other class H5 locomotives displayed a rating of 85 percent ........

Anouther thing to bear in mind is that these locomotives were  constantly being upgraded, so the ratings could be changed due to an upgrade.

So the 85 percent on the original diagram is a figure that I would not question.   However; on later repairs and upgrades on some locomotives,, that  rating may have been increased to 85.4

 

  

[marknewton]

The reason for including the percent cutoff was to calculate starting tractive effort....This is the "percent cutoff" we hear about. It's existence caused a reduction in the average of cylinder strokes from what one would expect due to the simple calculation of working pressure times cylinder area times stroke divided by wheel diameter....The more technical way to figure starting tractive effort is from the cylinder dimensions, the driver diameter, the working boiler pressure and the percent cutoff built into the valve gear.

But the figure 85.4 is, according to other posters, supposedly the MEP - Mean Effective Pressure - the pressure in the cylinders at maximum cut-off as measured by an engine indicator. It is not a measurement of percentage cut-off.

Showing the maximum cut-off on the cabside is even less useful than showing the MEP, if the intention is to allow the calculation of starting T.E. For one thing, it assumes that a loco will always be starting the train in full fore-gear, which is not always the case.

Starting TE calculations are typically done using the figure of 85% working pressure, not full working pressure, and the formula for that calculation is a little more complicated than what you've stated,and in all the examples I've seen, does not include cut-off.

Often the cutoff figure was about 85 percent, but not always, and on some locomotives with a special link in the gear, the cutoff would vary depending on the setting of the reversing lever.

Eh? Surely you didn't mean to write that? On ANY locomotive, the cut-off is varied by the setting of the reversing lever or screw.

Cheers,

Mark.

[marknewton]

That statement: "something called T.P. was calculated at 85% boiler pressure." that was not my statement, but that of  anouther poster....

Sorry BDT, I got confused about who wrote what. :-)

I agree, the test crew must have been busy; along with the entire steam crew... Some of Great Northern's steamers were rebuilt to the point that I wonder if the bell and whistle were the only original parts left...And then  Great Northern built some of their locomotives from scratch....,,,,They bought new locomotives when needed, so they had a mix.

We share the question  as to WHY the percent working pressure is on the side of the cab, and not boiler pressure.

Well, I'm still not completely convinced that's what the figure actually represents...

And on some locomotives the percent working pressure was left off completely..

As far as inside the cab,, that would be a logical place to place a stamped data panel,  but I would rather confirm that before I said yes.......If not there, there  should be a data plate somewhere on that boiler..

I'll dig a little deeper on this one

If you could, that would be great. I'm quite intrigued by this one.

Cheers,

Mark.

[feltonhill]

I have a copy of the GN locomotive diagrams.  Nothing is mentioned about the numbers stenciled on the locomotive cabs.  Does the GN Historical Society (or equivalent) have some knowledge of this rather significant group of markings on all GN locos?  For the locomotive in question here, the diagram uses exactly 85.0% BP as the factor to compute starting TE, not 85.4%.  

[timz]

The reason for including the percent cutoff ...

So you don't think 85.4 is the MEP divided by boiler pressure either?

...was to calculate starting tractive effort.

Then why not paint the calculated TE on the side of the cab? What's the advantage to painting percent-MEP, or percent of cutoff, and making the roundhouse foreman whip out his slide rule?

Next question: if it is percent of cutoff, is that calculated by a Zeuner diagram or whatever, or is it measured? If the latter, we can't expect it to be the same for the front and back of each cylinder, or for the left and right sides.

[Alan Robinson]

The reason for including the percent cutoff was to calculate starting tractive effort. Obviously, it would be  important to know how heavy a train the locomotive could be expected to start. (Steam locomotives have the characteristic that they could be expected to pull any train they could start.) Some locomotive labels include the starting tractive effort rating explicitly, others with the information required to do the calculation. The second method allowed for any reduction of allowable boiler pressure that might be permitted for that particular locomotive. (As boilers aged, they might have their pressure rating reduced until they were overhauled, repaired or replaced.)

One would think that to calculate starting tractive effort would be an easy thing, but it isn't always so straightforward. One way to make a rough guess is to figure the weight on drivers and take a quarter of that number. This assumes a factor of adhesion of 4 and that the locomotive has the ability to slip the wheels at that factor of adhesion, not always true.

If the locomotive is "overcylindered" for its weight on drivers, it will be very slippery and will be expected to have its tractive effort limited by rail conditions. A skilled engineer will be needed for a smooth ride. Most engineers disliked such locomotives because they were difficult to work, especially in heavy freight service.

If the locomotive is undercylindered, it will rarely slip except under very bad rail conditions. It would be well suited for heavy hauling and would be relatively easy to work. This kind of locomotive would be suited for heavy work on grades, too, where restarting a train on a grade might be required.

The more technical way to figure starting tractive effort is from the cylinder dimensions, the driver diameter, the working boiler pressure and the percent cutoff built into the valve gear. Often the cutoff figure was about 85 percent, but not always, and on some locomotives with a special link in the gear, the cutoff would vary depending on the setting of the reversing lever.

When a steam locomotive started a train, the thrust of the individual piston strokes had to be averaged. The torque for one stroke would be at a maximum when the wheel was at the quarter position. At this point, the peak piston thrust could be calculated as the maximum working pressure times the piston area. Using the ratio of the stroke to the wheel diameter, the peak tractive effort at that point during that stroke could be calculated. It had to be less than the weight on the drivers divided by the factor of adhesion for the existing rail conditions or the wheels would slip. So, for a locomotive with excess thrust, the tendency to slip would be high and starting a heavy train would be a tricky thing made all the more difficult by bad rail conditions. Lots of sand would be needed.

Once the wheel began to turn and the piston thrust left the quarter point, the thrust of the first stroke that we assume occurred at the quarter would begin to diminish even as thrust from the next stroke would begin. But the total of the two strokes is not a straight line. It has "lumps" in it caused by the reduction in effective cylinder pressure due to the percent cutoff of the valve gear.

As the piston neared the end of the stroke, steam was "cut off" from flowing into the cylinder, even if the reversing lever was "in the corner" at the maximum position. This limit conserved steam by allowing for the expansive energy of the steam to be used to some extent before being exhausted. This is the "percent cutoff" we hear about. It's existence caused a reduction in the average of cylinder strokes from what one would expect due to the simple calculation of working pressure times cylinder area times stroke divided by wheel diameter.

The average is less than the peak thrust and the average approximates the starting tractive effort rating of the locomotive. Because of the pulsing nature of these thrust forces, steam locomotives often "took slack" when starting heavy trains, so that the locomotive would be moving at some low speed before all the slack was taken up. This helped get the train moving while slowly building up the tractive effort exerted so that the tendency for wheel slip was minimized.

[timz]

On these locomotives, something called T. P. (40511) was calculated at 85% of boiler pressure. I assume this is "tractive" something.

If by chance the boiler pressure was 210 lb, then the nominal tractive effort ("tractive power" they probably called it) calculated in the usual way (i.e. MEP equal to 85% of boiler pressure) comes out to be 40511 lb.

So the people who think this particular engine was good for 85.4% figure it could produce 40702 lb rather than 40511? If so, why not paint that on the cab rather than 85.4? The MEP by itself doesn't tell us anything useful-- especially if we don't know the boiler pressure.

MEP obviously varies with speed; did GN measure MEP for all their engines at the same speed? And everyone on the GN who might look at the cabside numerals would know what that speed was? Do we?

[BDT in Minnesota]

It's T.E. - tractive effort.

Sorry  Mark, the Great Northern did not display the tractive effort rating on the side of the cab on their steamers...

I'm not suggesting or stating that they did. I was correcting your statement that:

"something called T. P. was calculated at 85% of boiler pressure."

That "something" is tractive effort - usually abbreviated as T.E, not T.P.

Im intrigued as to why the GN felt the need to display the MEP on it's locos and not include the working or rated pressure of the boiler. Knowing the percentage value of the MEP is not much help if you don't know the boiler pressure. Were the pressure gauges marked, or did the backhead have a data panel or plug?

If each engine displayed an individual figure for MEP, then presumably the GN made an indicator card for each engine. The test department must have been very busy! :-)

Mark.

That statement: "something called T.P. was calculated at 85% boiler pressure." that was not my statement, but that of  anouther poster....

I agree, the test crew must have been busy; along with the entire steam crew... Some of Great Northern's steamers were rebuilt to the point that I wonder if the bell and whistle were the only original parts left...And then  Great Northern built some of their locomotives from scratch....,,,,They bought new locomotives when needed, so they had a mix.

We share the question  as to WHY the percent working pressure is on the side of the cab, and not boiler pressure.

And on some locomotives the percent working pressure was left off completely..

As far as inside the cab,, that would be a logical place to place a stamped data panel,  but I would rather confirm that before I said yes.......If not there, there  should be a data plate somewhere on that boiler..

I'll dig a little deeper on this one

[marknewton]

It's T.E. - tractive effort.

Sorry  Mark, the Great Northern did not display the tractive effort rating on the side of the cab on their steamers...

I'm not suggesting or stating that they did. I was correcting your statement that:

"something called T. P. was calculated at 85% of boiler pressure."

That "something" is tractive effort - usually abbreviated as T.E, not T.P.

Im intrigued as to why the GN felt the need to display the MEP on it's locos and not include the working or rated pressure of the boiler. Knowing the percentage value of the MEP is not much help if you don't know the boiler pressure. Were the pressure gauges marked, or did the backhead have a data panel or plug?

If each engine displayed an individual figure for MEP, then presumably the GN made an indicator card for each engine. The test department must have been very busy! :-)

Mark.

[BDT in Minnesota]

Since the 85 and 4 are different sizes and separated by periods, I don't think it is 85.4.
On these locomotives, something called T. P. (40511) was calculated at 85% of boiler pressure.

It's T.E. - tractive effort.

Mark.

 

Sorry  Mark, the Great Northern did not display the tractive effort rating on the side of the cab on their steamers.....The 85.4 is indeed the percent working pressure.... some of the locomotives were given smaller sized decimal numbers, while others were given full size decimal numbers.... some were given two decimal numbers.... An good example are the class O1 Mikados;; some of them were rated at 87.94    anouther at 65  anouther at 83.7  while some of the O1 Mikados displayed no percent working pressure at all....

As far as the periods placed between the various data elements; some locomotives had the periods and some did not.

Anouther variation was the letter S (second data, after the H5) which stands for superheated... On some locomotives, where the entire class was superheated, this S was not displayed........ 

Anouther noted place where a decimal was used, (but rarely) was on the drivers weight..

[marknewton]

Since the 85 and 4 are different sizes and separated by periods, I don't think it is 85.4.
On these locomotives, something called T. P. (40511) was calculated at 85% of boiler pressure.

It's T.E. - tractive effort.

Mark.

[marknewton]

The obvious question is why? I can understand how the other information would be useful, but MEP? Painted on the side of the cab? As I said, why?

I can't help but wonder whether someone has their wires crossed, so to speak.

Cheers,

Mark.

[BDT in Minnesota]

 85.4-Percentage of cutoff(?)

All but the last, I'm sure of.

The answer I got off of the GN Yahoo group was-
85.4 Per cent working pressure, i.e. the ratio of the mean effective
pressure (MEP) to the boiler pressure.

Correct; 85.4 is the percent working pressure....This information is well covered in the June 2006  reference sheet #334, from the Great Northern Railway Society..

This is a great organization to be a member of, especially if you're a Great Northern fan (NUT) like myself.  There are  people in this organization that really go the extra mile to produce some excellent reference sheets and publications...

 

[donbpage]

Since the 85 and 4 are different sizes and separated by periods, I don't think it is 85.4.
On these locomotives, something called T. P. (40511) was calculated at 85% of boiler pressure. I assume this is "tractive" something.
The 4 could be the approximate coefficient of adhesion (TP/wt on drivers was 4.34.)
I don't know why you would want to put this on the side of the cab though.

Don

[marknewton]

Sounds unlikely, doesn't it? How would they calculate that 85.4%, and why would they think such a figure worthy of painting on the cab, when the boiler pressure itself isn't?

But I don't have a better theory. Anybody got pics of the inscriptions on other GN cabs?

85.4% is an empirical figure, presumably based on experience. 

Mean Effective Pressure is not an empirical figure, nor is it based on "experience" - it's measured by using an device known as a steam engine indicator. This produces an indicator card, which can be used to calculate, among other things, the mean effective pressure.

But I agree with Timz on this one. I think it is highly unlikely this number refers to the M.E.P. Perhaps the figure 85 is a Cooper E-rating?

Mark.



EDIT: Nah, scrub that. A quick look at a table of Cooper E-rating figures tells me I'm barking up the wrong tree...

[timz]

Empirical or not, if it were supposed to be the ratio of "MEP" to boiler pressure it would have to come from some sort of measurement, or some sort of calculation-- they didn't get it off a stone tablet. The actual MEP wouldn't be constant to within a tenth of a percent for all the engines in the class, and presumably GN didn't put an indicator on each individual engine.

There are seven dots between those numerals on the cab side, and none of the others are decimal points-- I bet this one isn't either.

[CSSHEGEWISCH]

Sounds unlikely, doesn't it? How would they calculate that 85.4%, and why would they think such a figure worthy of painting on the cab, when the boiler pressure itself isn't?

But I don't have a better theory. Anybody got pics of the inscriptions on other GN cabs?

85.4% is an empirical figure, presumably based on experience. 

[Dakguy201]

After I posted this, I did some internet seaching for pictures of GN locos in everyday service.  I found half a dozen examples -- all of them had something similar, but it wasn't legible in the photos.  On the other hand, Milwaukee 261 and CP 2816 do not have it.   UP 3985 and 844 as well as the Big Boy on display in Omaha (#4023) do contain descriptive lettering.  Here is 844:

I guess each line must have followed its own preference, including exactly what information was displayed.

 

[timz]

Sounds unlikely, doesn't it? How would they calculate that 85.4%, and why would they think such a figure worthy of painting on the cab, when the boiler pressure itself isn't?

But I don't have a better theory. Anybody got pics of the inscriptions on other GN cabs?

[nanaimo73]

 85.4-Percentage of cutoff(?)

All but the last, I'm sure of.

The answer I got off of the GN Yahoo group was-
85.4 Per cent working pressure, i.e. the ratio of the mean effective
pressure (MEP) to the boiler pressure.

[GN-Rick]

H5-Locomotive class

S-Superheated

73-Driver diameter

176-Weight on drivers  (in thousands of pounds)

23 1/2x30-Cylinder bore and stroke

85.4-Percentage of cutoff(?)

All but the last, I'm sure of.

[DanRaitz]

I can decipher some of them.

H5 = Locomotive class

S = ?

73 = Driver size: 73"

176 = ? (Could be Boiler pressure: 176psi)

23-1/2x30 = steam cylinder bore and stroke

85.4. = ?

 

Dan

[Dakguy201]

Can anyone translate the meaning of the line below the numbers?

The picture is GN 1355, recently repainted.  If it helps, it began life as a Baldwin 4-6-0.  In the 1920's the GN reworked it to be a 4-6-2.  As there was a whole class of the reworked engines, why was it necessary for each to carry (what I assume) are some form of specifications?