You went to all that trouble … and missed an important boat.
What you have left out is the most important consideration, as it applies to double-acting steam locomotives. The point is not to overcome the ‘inertia’ effects through stress in the rod and bearings, as it is in IC engines, it’s to control compression to do as much of that job as possible, with the right ‘delta’ at all points in the stroke.
For those who may not know: on a typical locomotive, not “all” the steam in the cylinder is exhausted by the time the valve closes to exhaust. That is often considered to be a ‘bad thing’, as the steam then goes way up in heat and pressure as the piston continues to move to its maximum position at crank dead center, and all this has to be accomplished with ‘work’ from the other expansions taking place or from momentum – neither of which increase thermodynamic efficiency.
On the other hand, while this doesn’t ‘match’ the force profile in the rods and bearings, it does counteract much of the inertial deceleration and need for re-acceleration across the dead center. There is also a potential advantage to having the higher pressure in the cylinder … it equilibrates with pressure (and related temperature) in the dead space. When the valve subsequently opens, the admitted steam does
Glad I struck a nerve with you! - actually, I wasn’t finished writing my post - I don’t know about you but I write it then have to go back and edit it because the posting page on this site is so absolutely crude. I can’t read more than a few lines and the “scroll of the box” is crude.
Anyway, I hope you enjoy some of the changes I was making - but you will have to go back to re-read them!
Also you made a good point on the effects of “steam cushioning” of inertia with regard to “double acting” steam pistons on moving parts! Something distillate fuel engine guys could just dream of having! This effect could have as you pointed out a negative consequence in that “too much cushioning” in effect is “negative work!”
Regarding the use of “drifting valves” - this was steam locomotive improvement - that was not widely seen in the age of American steam in my opinion. It was really fairly advanced piston valve concept appreciated by a few like AT&SF. Widely not understood and quite an intriguing subject as well, important, and hard to learn about. I believe the Europeans who kept steam longer came to use it along with the important “exhaust ejection” technology mostly foreign to Americans.
Regarding “Poppet Valve” steam admission systems - they were tried by American steam builders but the technical on them seems limited as does the understanding of the two existing historic locomotives.
I mean if the Pennsy T-1 project is scratching its head to understand the one remaining C&O 490 hudson and the last US Military “poppet valve” locomotive this speaks worlds to the working knowledge of what remains historically on the subject!
Have gone back for a little revision, too, in light of what you just said and did…
There are reasons why very few double-acting IC engines have been made. One of them is main-bearing thrust. Now, crank thrust in a DA crosshead engine is interesting, because the journal stresses are always acting on the crank the ‘same way’ even though the rod and its bearing surfaces do not. Unfortunately, the stresses on the mains don’t, and the relative torsional stresses in the crank are also likely to be greater. And the valve and lubrication issues on that exposed piston rod are troublesome, particularly if the exhaust gas reacts in any way with the lubricant film. (Steam is bad enough in that regard!)
I don’t see the distillate guys, or anybody else with pistons big enough to need multiple plugs or injectors, going by choice to a DA. (It’s unfortunate enough to see the British getting torque out of both ‘halves’ of an OP engine mechanically ‘in phase’, especially as seen on Doxfords…)
Dr. D (and anyone else who a doctoral dissertation to post), have you considered composing your thesis in a word processor (which probably has the missing Spel Czecher) and copying it to the forum? (I doubt that any has a grammar checker, though.)
This bothers me in a couple of respects. I think you are reasoning by analogy with IC engine induction, and it’s not as good an analogy as you think, for one because the charge in an IC engine is induced either by vacuum (for a NA engine) or with far less kinetic energy in the gas (for forced induction) than is the case with steam.
I would think that the effect of gas kinetics would FAR outweigh “momentum” (based on mass of the gas molecules and direction of their bulk flow) although I do not yet have the math to calculate the two for comparison. I suspect erikem and some others can provide this – say, for 265 to 300 psi steam at a superheated temperature of, say, 750 degrees F? (Use better representative numbers for steam conditions at the ports if you have them at hand!)
There is no question that quicker opening of the ports, larger and better-streamlined ports, less turbulence caused by bridges, etc. increase the effectiveness of an engine at high cyclic rpm. That has been established by Chapelon, Porta, Wardale, etc. for good reasons, and in a different context (valves that go to full opening quickly when actuated) by Corliss and others for mill engines much earlier, although those lessons aren’t as applicable to locomotives.
There are momentum effects in steam flow; one was reported in the PRR Q2 testing. There are some momentum effects in front-end design as described by Jos Koopmans. I wonder, though, if their importance is overshadowed by gas-kinetic effects in significant ways for the ‘normal’ conditions that prevail in a working locomotive.
These were full fledged Conrail locomotives that were delivered in Conrail’s own colors. They simply changed their final SD80MAC order to these models at the request of their suitors so that they would better fit their rosters.
The SD70MAC’s were earmarked for CSX but were delivered in the regular CR number series as CR 4130-4144. The SD70’s were earmarked for NS but were delivered in the NS number series as CR 2557-2570.
Why would they? The Joes were built for the SZD, but never went there, and GE regauged the ones that needed it before delivery (either to MILW or the South Shore). In no case did a railroad have anything to do with their actual construction, which is the requirement here. There are plenty of examples of locomotives built for one road that were not purchased for some reason, and resold to another, but there is nothing particularly unusual about a locomotive builder (or even an equipment trust) doing so.
My understanding was that the thread was limited to a sense of ‘contract manufacturing’, where one railroad’s shops physically built new locomotives (or modified them extensively) for use by a different system.
Thank you, Wiz. That was my intent when I started this thread; with the added condition that the builder of the locomotive and the recipient have no other corporate relationship. Because of their corporate relationships, PRR construction of locomotives for LIRR and WT would not qualify.
I was going to throw in the G-5 and H-10 locos PRR built for LIRR, but you ruled out “parent or subsidiary”. Someone else mentioned the BB-1 electric switchers, but same situation.
Yes, they did, but I don’t think “used locomotives” count here, only those ‘new-built’ (or specially modified) in a railroad’s shops for use on another unrelated system.
A “borderline” case (I don’t think it applies here, but it’s an interesting diversion) might be locomotives built new for a system that never used them but sold them straight to another road – were any of those Chessie 0-8-0s that went to N&W (and were then duplicated a few times in their shops) an example of this? Bet there were tax implications and consequences that would either make this desirable or undesirable at the time…
I wonder whether there were examples of locomotives built during the WPB years by shops, rather than locomotive builders, for service on ‘other railroads’ that needed power built to a ‘standard’ design. (I don’t know of any, but it would be interesting to know if there were any proposed…)
I believe that the gensets in question were probably built under contract for Railpower Technologies to Railpower’s specifications since they did not have their own plant. This would be comparable to the railcars built for Electro-Motive Corporation by Pullman, St. Louis Car, and others.
The C&O switchers did operate for their original owner for a couple of years before being sold to the N&W. The USRA based 0-8-0’s were purchased new from Baldwin, rather than being built in-house as N&W later did when it wanted additional copies of the design.