Articulated Steam Locomotives of North America

The Midland 2P says hello

Tom

 

There are various 'high speed' fully enclosed pressure lubricated engines used to drive generators, marine auxiliaries etc but I dont think that the technology transfers to Rail except perhaps in the case of Sentinels

 

Sorry for being a bit thick but can you explain your comment? I am not sure what the OP is getting at with the expression "valve event timing". As Adrian Tester points out in "An Introduction to Large Lap Valves and their use on the LMS" (in a bit of a straw man tactic focusing somewhat narrowly on the angular incidence of the events), the valve events of a typical Midland loco were actually very similar to the large lap SECR E1/D1 and Black Five 44767 for a similar cut-off, the superiority of performance for the latter examples being due to their bigger steam chests / openings / passages.

 

It was really in relation to the OP's original comment: "For others, valve event timing shouldn't be the limiting factor because, with increasing speed, there would be more valve events per unit time."

That can't be true, since there is a limit to the mass-flow rate of steam into the cylinders. At very low speeds, that is irelevant since the valves are open long enough to allow (on the inlet side) the pressure in the cylinder to equilibrate with that in the steam chest - the inlet then closes and expansion takes place. Similarly, at low speed there is no problem in fully exhausting the exhaust in the time available.

As you get quicker, eventually you reach a point at which the valve is open for such as short length of time that, with the available mass-flow rate, the cylinder can't fully charge with steam even if you had a boiler of essentially unlimited steam-generating capacity. At that point, the valves absolutely become a limiting factor. The fact that if you e.g. double the speed you get double the number of cylinder strokes therefore does not lead to double the power, since after a while each stroke is not getting as much steam as it should, and is not exhausting all the old steam by time the stroke finishes.

Referencing the 2P was really a short-hand for an example of a loco commonly held up as having its ability to move quickly hamstrung by the front end design. But actually any loco would do: eventually you get to a point at which the front end cannot fully injest and exhaust steam within the time the valves are open, which therefore sets a limit on power and ultimately speed. You can’t divorce valve events from the speed at which they are happening, hence why (in the shorthand) a 2P piloting a Duchess at 60mph up the WCML was seen as more hinderance than help, yet they were quite well regarded slogging away at 25mph over the Mendips.

Tom

 

OK, thanks. The indicator diagrams become less plump with speed whatever the loco of course. Your point is of the same ilk as that which Tester makes, the valve events are only one element in the steam circuit. I suspect the problem with the 2P was more with getting the steam in than out (in addition to some other steam circuitry ills) but it would be interesting to see some indicator cards.

 

That is certainly true.
Gas Turbine lorries in 1960s US, where fuel was very cheap, were getting about 2 - 3 MPG. And then there came the fuel crisis.
In Britain, Leyland was getting better results, they had claimed up to 98% of trad diesel costs, Ahem!!!!!
Transpired not to be the case I believe. The biggest problem for use in Britain would be noise I might surmise. I have stood next to one of Leyland's Turbine lorries and the noise was impressive to say the least!
In addition the Americans recognised the value of Gas Turbines lay in long distance high speed running, something Britain's infrastructure could not accommodate.

 

Could modern Variable Valve Timing alleviate this problem?

 

I meant when you are reading a book or similar!

 

Given the very direct links between steam and motion, I’m not sure where there’s room for that to work once you’ve got to the point where there’s no time to move the steam.


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Surely that's the point of VVT?
The amount of steam admitted according to the needs by increasing or decreasing the size, and indeed number, of port openings on demand.
In that situation it will be, up to a point, the size of the pipework transmitting the steam to the steam chest, or passages within the steam chest, that will be the limiting factor!

If the book is well researched, and therefore worth reading, the size of the cylinders will be listed!

 

Precisely my point - it’s the other factors that really count, and not so much the valve timing.


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Quite so but my point was made to the question of valve events/sizes made by @Jamessquared regarding their limiting the admission and exhaustion of steam.
Theoretically there is no reason that valve openings could not equal or exceed the CSA of the cylinder and with VVT additional valves could be opened at higher speeds to enable freer breathing.

 

Regarding C&Os Alleghenys, apparently ordered because by 1941 high drivered simple articulated (sic) locos had become a reality. The C&O looked at a 2-12-6, first proposed in 1929. Even with improved cast frames and main rods the curvature of the C&O roads made the proposal a non starter, hence a divided 2-12-6: a 2-6-6-6 with 67inch drivers.

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Just bought William L Withuhn's book. Thanks for the recommendation. Excellent read and dare I say indicates that GB didn't have a monopoly on good locomotive engineers and innovation!

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For clarity this is all based on Withuhn's interviews with Kirchhof and Delano. The actual documents have long since been lost, so whether or not the T1s ever actually exceeded 125mph will probably remain unknown.

 

Not true. If you consult Bill Withuhn's book, you will see that the report was held by the Battelle Memorial Institute in 1981. There's no reason to think that that's not currently the case. They declined to
issue a copy for commercial reasons - this was the time of the ACE 3000 steam locomotive design project.

 

Battelle's report was on a separate subject (the materials used) and did not involve timing locomotives in service. It is not evidence for the 125+mph claims.

 

Yes, that's correct, but Withuhn's interview of Delano and Kirchhof, independently, offered the same story without prompting from the interviewer. Namely, that a "spy" - a Franklin staffer was sent to ride trains anonymously for a month on the Fort Wayne Division and to clock their actual. This was in connection with an investigation into broken valves. There were some instances of speeds up to 140mph. He presented his logs and watch to Kirchhof for verification. Once or twice a week in the recorded month, when a train was ten cars or less in length and running behind schedule, the engineer had made up time by exceeding 125mph. Twice that month, with short trains of six or seven cars, speed had reached 135 to 142mph, as clocked over several miles. Careful inspection of logged entries and watch, as well as the consistency of successive time intervals between mileposts on all the timed runs, attested to the veracity of the logs.

 

Yes, you've just directly quoted Withuhn without attribution there. My opinion remains unchanged.