Off the Rails - Train Stuff

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Renegadenemo
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Re: Off the Rails - Train Stuff

Post by Renegadenemo » Fri Nov 08, 2019 3:28 pm

Intriguing. I've seen little diddy triple expansion engines in steam tugs and trawlers that would easily fit into a train complete with boiler, condenser the lot. Wonder why they didn't do it that way. Seems like train development stopped and marine stuff carried on.
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Re: Off the Rails - Train Stuff

Post by Jordangbr » Fri Nov 08, 2019 7:18 pm

Probably because carrying a condenser and a way of cooling it would be difficult, bulky and no outside source to cool except fresh air.
Take nuclear subs for example, still driven by steam via turbines and gearboxes but instead of coal, uranium. The nuclear reaction heats the primary circuit to many hundreds of degrees which is also pressurised to prevent it boiling. This is pumped via the heat exchangers and in turn heats the feed water pumped via the condenser hot wells to the feed pumps. This is then heated and turned into steam but must have most of the moisture removed as not to damage your turbine blades on your main engines and turbo generators. After that it’s into the condensers which are in turn cooled by seawater heat exchangers and round it goes again with various chemicals added to the feed water to keep everything happy. 🤓
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Re: Off the Rails - Train Stuff

Post by Renegadenemo » Fri Nov 08, 2019 9:20 pm

That's pretty much where marine steam propulsion had got to when it hung up its pistons and connecting rods and swapped them out for the turbine and a pot of fissioning material. Agreed that getting an effective condenser onto a steam train was always going to be a big problem but what's the reason for not using several expansion stages to at least wring as much as possible out of steam that, without any energy recovery, had a lot invested in it?
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Re: Off the Rails - Train Stuff

Post by mtskull » Sat Nov 09, 2019 8:24 am

Renegadenemo wrote:
Fri Nov 08, 2019 3:28 pm
Seems like train development stopped and marine stuff carried on.
No, steam locomotive development never stopped; just about everything that could have been tried to improve performance and efficiency has been tried at some stage with varying degrees of success. In the end though, it all boils down to one thing and in an era when coal was cheap and nobody cared about the environment, the costs of adopting most of these improvements simply didn’t stack up against the savings. One development that did catch on was superheating, which more or less saw off compounding as a way of improving efficiency, as it gave similar gains with lower cost and less complexity.
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Re: Off the Rails - Train Stuff

Post by Filtertron » Sat Nov 09, 2019 9:32 am

Look up L.D Porta or David Wardale. They virtually revolutionised the front end draughting system on steam locomotives, and quite late in the piece too. They squeezed just about everything they could have out of the simple expansion engine - well worth a look into. Blokes like Nigel Day and Shaun McMahon are continuing on with their work to this day.

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Re: Off the Rails - Train Stuff

Post by Renegadenemo » Sun Nov 10, 2019 2:15 pm

Why was the steam turbine never used in trains, then? It was certainly small enough and more efficient.
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Re: Off the Rails - Train Stuff

Post by thunderer » Sun Nov 10, 2019 7:59 pm

Steam turbines were experimented with on a modified Princess Royal class 4-6-2 Pacific Locomotive of the LMS, built in 1935 which would later be rebuilt to conventional form.

It was rebuilt to conventional form in 1952 using new frames and "Duchess" (Princess Coronation class) cylinders and named "Princess Anne" . Just 2 months later, it was destroyed in the 8 October 1952 Harrow And Wealdstone disaster.

Princess Anne's destruction would lead, in a roundabout way, to the construction of the Class 8P locomotive "Duke of Gloucester" that in and of itself was considered a failure by BR, scrapped by BR minus it's cylinders, purchased by preservationists and rebuilt. To this day, it remains a powerful locomotive thanks to the ongoing efforts of the team behind the salvage, restoration, running and upkeep of it. The "Duke" was at the time and remains now referrred to as "project imposible".

Princess Anne is a documented locomotive, albeit some information has never really been available.
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Re: Off the Rails - Train Stuff

Post by mtskull » Sun Nov 10, 2019 10:11 pm

Renegadenemo wrote:
Sun Nov 10, 2019 2:15 pm
Why was the steam turbine never used in trains, then? It was certainly small enough and more efficient.
The steam turbine was in fact often experimented with in railway locomotives (not “trains” please -a train is the rake of carriages or wagons that a locomotive draws). Issues of cost, complexity and particularly the difficulty in designing an efficient condensing arrangement were never really overcome.
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Re: Off the Rails - Train Stuff

Post by Renegadenemo » Mon Nov 11, 2019 1:17 am

(not “trains” please -a train is the rake of carriages or wagons that a locomotive draws)
Oops - sorry guys. Noted. I'm always the first to get upset if someone calls a compressor a turbine or a turbine a 'hotwheel' (which is almost but not quite as bad as calling Christmas 'Crimbo') So Locomotive it is.

So, moving on from there, and accepting that making condensers work on locomotives is problematic, I still wonder why no one spannered a turbine in there then simply threw away the steam as with the standard reciprocating machinery of the day. It's a topic I honestly know very little about. The turbine is more efficient but is it a case of extracting more energy from a greater volume of steam than reciprocating machinery can manage and therefore you just can't be throwing away all that steam or what is it?
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Re: Off the Rails - Train Stuff

Post by mtskull » Mon Nov 11, 2019 9:58 am

Renegadenemo wrote:
Mon Nov 11, 2019 1:17 am
So, moving on from there, and accepting that making condensers work on locomotives is problematic, I still wonder why no one spannered a turbine in there then simply threw away the steam as with the standard reciprocating machinery of the day.
They did: the LMS “Turbomotive” used a non-condensing turbine where the exhaust steam simply exited via the blastpipe. It was considered reasonably successful too. The locomotive did have its drawbacks, although most of them were surmountable and should be viewed in the context of an experimental locomotive derived from a conventional design.

A class of non-condensing turbine locos was built in Sweden in the early 1930’s; with three built and a service life of over 20 years, IMHO this class of loco is the only truly successful example of the steam turbine applied to rail traction. Even so, they only achieved fuel savings of around 10% compared to conventional locomotives.

The fundamental issue with a steam turbine is that it is only really efficient when running at its optimal speed, which limits its practicality. This can be mitigated by using a flexible transmission such as hydraulic or electric but then you are only adding to the issues of cost and complexity.

Ultimately though, what consigned steam turbine locomotives to a footnote in history was the emergence of the diesel locomotive as a practicable means of traction.

There is some fascinating material on the subject available online; try this site for starters:
http://www.douglas-self.com/MUSEUM/LOCO ... coloco.htm

Here’s a clip of a preserved Swedish turbine loco at work. WARNING: Steam turbine porn!
https://youtu.be/ZsrzUjcHeAs
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