this is not about steam powered new river trips. I have watched this video about 261 handling the train. 261 wasn't designed to haul 30 cars upgrade at speed. I was told that 765 crew set up the 261's valve gear up to a slightly longer stroke and create 12lbs of back pressure and increase the 261's power to handle the train. the question is was this a common practice back during the steam days? It doesn't sound like it was common back then or now but I could be wrong.

If cyclic is no more than to reach 40 or sp mph, then you could easily increase the travel of the valve, to give the advantages possible with longer travel. These include faster 'unporting' of the exhaust steam edge and quicker opening of the whole port width to steam for exhaust. Whether that would limit back pressure through the front end is not terribly clear to me.

Now, opening up the front end to permit lower back pressure is certainly something that could be done for a little more peak and mean effective pressure. I have to wonder if valve adjustment alone gives the full benefit that would be possible.

I certainly can't answer these very deep questions. However, I have observed on German and Polish locomotives an adjustment on the (piston) valve stems which can be easily accessed by the crew while taking water or making a station stop. While I assumed it was to facilitate keeping them square, it might be used to vary the cutoff.

Mr. King, I think that would only affect the timing to get the engine 'square' -- cutoff would (if I am right) require that the piston heads be moved toward or away from each other. And even then, gains in admission might be balanced by changes in exhaust in a DA cylinder.

Mind you, with a slight modification to Meiningen Trofimov-style valves, the sort of adjustment you mention might actually be possible, if you threaded the internal 'pistons' that Meiningen used to cushion the tinny jingle of the Chinese variant. You would need access ports to look at the steam edges -- which were actually provided on some locomotives! -- through which pins would be inserted to hold the valve heads and internal pistons on the spindle while the valve rod was turned to move the heads in opposite directions. The imternal pistons would then be re-locked to the spindle and serve as the positive location stop for the piston heads when sufficient steam is applied...

Just dropping her down a couple notches increases valve stroke and back pressure. Some locomotives seemed to work well under higher back pressure which is intuitively not obvious..... I recall a TRAINS magazine article about UP 800s (I think) liking high back pressure being exploited by Steve Lee to out accelerate another steam locomotive from another road.

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Think of the reverser quadrant akin to a twenty speed manual transmission. The lower you drop down the reverser, the more steam per stroke you are admitting to the cylinders, and the more power the engine will produce. At the same time, by admitting more steam, the back pressure in the cylinders will rise. The key when running over the road is finding the optimal throttle and reverser positions to keep the engine running at optimum efficiency. The engine will tell you what stroke is correct for the tonnage and terrain.

Obviously, with a "new" engine for the crew, and a heavy consist, it took a bit of testing to see the best settings for that engine on that train on that railroad, as the engine hadn't been worked that hard before. The 261 group gave them some guidance on settings, but they found they needed more back pressure to get optimum performance out of the engine.

I forget the issue, but there is an article by Rich Melvin in Railfan & Railroad from 1995 that goes into all of this comparing the differences between 261 and 765 on that train. There is also a set of articles by Rich and Jack Wheelihan about a year or so before comparing steam and diesel horsepower curves, which goes into a lot more details on the same thing. Very worthwhile reading if you can track them down.

Mr Anderson & Mr Dave, You sure know how to hurt a guy. Of course I know the damn reversor changes cutoff/back pressure/draft. I just didn't speak up because I don't want to give people the wrong idea, like I'm stupid or something, and can't cook up complicated theories. Now who can blame me ??

OK, sorry Sammy...... let's continue the complication by comparing the difference in doing this between Stephenson and any of the constant lead variations of valve gear.

We had a verrrrry long thread in te old steam_tech Yahoo Group on the positive starting benefits of negative lead in Stephenson gear. From what I remember, it would be an advantage on any large 4-8-4 equipped with that gear...

Keep in mind that the back pressure impedes mass flow at the ports in the moments after they open to exhaust. This keeps the pressure in the cylinder high a bit longer, and increases the MEP by that (I think small, but significant) amount. Theoretically at least, it may increase the amount of steam mass retained in the cylinders after axhaust closure, which increases peak compression but also keeps mass transfer at the succeeding reverse admission somewhat 'quicker' as the pressure remains high in the cylinder as the steam edge crosses.

One of the purposes of Jay Carter's reversible compression relief was to modulate the peak compression pressure in the cylinder to optimal level to help balancing, while maintaining the 'hot' mass at the start of the reverse stroke's admission.

What's the BBcode for 'pedantry over'?

So far as I know, trains go forward, backup, and stop.

Unless you are on The Polar Express. (roll eyes).

Depending on the engineer, I've also heard three throttling described as "slack, forward, and reverse". But I wouldn't want to over complicate this thread....

It's really not that complicated. I think what Robert is referring to is the development by Strossell of what he called "nachfahrt" (follow) in his design of the 3 cylinder double conjugated 0-8-2 heavy banking engines for the Sturhmerbahn in 1877.

The Krauts are extremely Clever, they never have a single handle or gadjet or adjustment when half a dozen would do. German is slow reading for me, but if I come across any drawings or references to an adjustable cutoff Trofimov piston valve, I'll be sure and post an update here.

I CAN say that ALL QJs have Trofimov valves, and none that I have seen have any kind of doohickey to allow adjustment of the piston valve steams.

Or has this topic gone completely over my head ?? (No, don't answer that, please...)