WW2 locomotive building.

I was wondering more about the attached screenshot containing the witty aperçu from the likes of "Stilton is smelly" about the cheesegrater front end, amongst other bons mots?

Tom

 

Don't know how this happened and attempts to move it have failed. It exaggerates as Stilton is an amateur compared to Livarot or the legendary Maroilles (vieux pouant or "old stinker")

Paul H

 

Its all about where the rockers to transfer the movement between inside and outside go. As far as I can see they can't go behind the outside cylinders because there's a wheel in the way, but if they go in front of the cylinders then expansion of the valve spindles inside the valves will put the inside cylinder timing out.
With inside motion then its not a problem, because the rockers go in front of the outside cylinders with the valve driven from in front, not behind. Its the same problem that caused Holcroft, on his conjugated valve gear for the Southern, to run rods alongside the valve chest to get the movement forward to the conjugating gear. No doubt a similar arrangement could be managed with GWR locomotives, but very easy to get a few extra pin joints doing it, and approaching the point where you may as well, like the Princesses, just have 4 sets of valve gear. We should also note that in the end the Southern seem to have decided the Holcroft setup was too much trouble and replace it with a set of inside gear.

 

That indeed was the situation with the Lizzies; Stanier said he didn't have time to work out a satisfactory way for the outside gear to drive the inside valves so gave them four sets. 6205 was converted to outside gear only in 1938, and had that problem exactly: thermal expansion of the outside valve spindles altered the settings of the inside valves. When 6220 and Co were designed the outside cylinders were moved forward allowing the rocking lever to be behind the valve spindle, so eliminating the problem and allowing outside gear only.

 

I would have thought that, if you were designing a GWR loco to have outside Walschaert's valve gear, you would have started with a fairly clean sheet of paper, not try to make a silk purse out of a pigs ear.
And why use Walschaert's valve gear?

 

Mea culpa. don't know where I got outside from, moral, check everything before posting. But all my references do say inside Stephensons, but none of them are VOR specific books.

 

Unfortunately our gospel Cox has not written something that will guide us.
Some kind of answer can maybe be found in Greece that had both WD engines and S160s.

 

Well, the people you have to ask are long gone.
The Star prototype had a rather different valve gear though, which was a modified walschaerts without eccentrics, and which would have been horrendously complicated if they'd tried to put it outside. There seem to have been a number of issues with that setup, different ones according to which writer you read/believe, but for whatever reason(s), maybe all of them, it wasn't repeated. Converting the design to use inside eccentrics was fairly straightforward. Changing it to use outside Walschaerts would, as far as I can see with my very very limited engineering knowledge, have been a clean sheet of paper job involving some fundamental changes in the whole relationship between cylinders, wheels and motion, and quite possibly added length and weight or compromised other design principles that were considered high priority.

 

C.C. Green's V.O.R. history has all the details. Why they chose Gooch valve gear is uncertain but there seems to have been someone involved who had a "thing" about concealing valve gear (sound familiar?) which led to the adopting of a particularly troublesome arrangement.

PH

 

56XX !! not one of Swindon's better efforts.

 

I'm not sure I agree with this. The advantage of high degree superheat isn't only in how much useful work can be extracted expanding to atmospheric pressure. There's a significant advantage in getting the cylinders above the saturated steam temperature faster or, compared to saturated steam, at all. That eliminates condensation losses in the cylinder, which are particularly aggravating because they get you coming and going; a portion of the incoming steam condenses on the cylinder walls, doing no work, then evaporates again as the cylinder pressure drops on exhaust, putting up the back pressure. Once the cylinder gets above saturation temperature this stops happening.

The thermal mass in a superheater assembly is quite low, compared to a boiler they react quickly; it's the cylinder that takes time to catch up. Therefore high degree superheat is actually particularly appealing on a locomotive making frequent stops - not only does the cylinder get above saturation temperature faster, but because it reaches equilibrium at a higher temperature, it takes longer to cool below the saturation threshold when you stop. Of course, you do need to get the fire genuinely hot for this to work.

Regarding the Great Western/LMS differences on superheat temperature, one of the things spotted on the early Princess trials was that the pressure drop across the small superheater was quite high - pure lost work. The larger superheaters reduced this markedly.

 

There must have been WR enginemen who had experience of both. Gasson says very little, but seems to have quite liked the USAs and loathed the Austerities.

 

Superheating is overvalued.
Have a look at page 17 and page 66 in mr Nocks book of LNWR precursors.(Copyrigth or I would have shown)
Superheating forced much better valve geometry on locomotives.
It is a shame that coal figures for George the fifth(superheated) and Quen Mary(unsuperheated) that was mechanical /valve-wise identical,was not given.
Mr Churchward experimented with different valve timings on a single cylinder stationary test engine.
This was much more future oriented than putting strange looking boilers on simple american 4-6-0 like locomotives.
In germany they knew around 1914 that piston valves shall have 4 or 6 narrow rings on each valve end.
It took a little longer in England.
The ideal new build steam fan locomotive has no superheater as the extra cost will never come back.

 

A strange thing to say. I am aware of at least two present day steam railways that strongly disagree and there will be more. Read Post 111.

PH

 

There will be several NYMR drivers, me included, who have some experience of both; albeit with the 2-10-0 variety of Austerity. Personally, I prefer the S160 although they are both rough and ready types. However, even between the same, there are preferences. 90775 was always preferred over 3672 by me and my memories of 2253 make it a better bet than 6046.

 

Very very interesting.
If both had been balanced the 9F way,that is uniform and simultaneously hammerblow on all driving wheels,what would verdict then have been?

 

Probably no different.

 

I agree with Paul, strange.

The value of a superheater on any new build will depend on future usage, and if main line operation is envisaged, it will certainly be included.

 

Churchward did a very thorough set of like for like tests on the Saints in the early days of superheating, and he was sufficiently convinced that he implemented a very big programme of superheat conversions. By WW1 I would guess the GWR may have had more superheated locomotives than all the other lines put together. By the end of 1912 *every* GWR 4-6-0 and 2-8-0 was superheated and so were the vast majority of 2-6-0s and 4-4-0s: only a handful of examples of the smaller wheeled designs remained to be superheated by the 1920s.

 

Even on branch lines with closely spaced stops (i.e. most tourist lines), the economy of a sensibly sized locomotive with adequate superheat has to be experienced to be believed. However, (LMS2968 will correct me if wrong) as important is the reduction in water consumption which prolongs boiler life. Of course sophisticated water treatment of the reverse osmosis sort will reduce the advantage of this.

Paul H