Edward Thompson: Wartime C.M.E. Discussion

Thompson, Peppercorn, Stanier and Bulleid all had Pacific designs whose smokeboxes that were longer than those of the 1930s and 20s. I honestly don't think it's that big a leap from the locomotives before - and it was in maintenance, steam circuit and self cleaning apparatus that they all had advantages over the older locomotive stock.

 

Using a shorter boiler barrel also saves weight. The front end of the boiler tubes contributes very little to the steam raising capacity of a boiler.

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Which would surely result in different weight distribution, when compared with a more 'conventional' arrangement, affecting ride quality (for better or for worse?). No?

 

The more you depend on forced draught, the more gasflow matters, I suspect the bigger the smokebox the more even the vacuum caused by the blast is. Theoretically, I wonder it it's possible to get it so wrong you get a pressure pulse in the tubes that really impedes gasflow (qv an expansion chamber on a two-stroke internal combustion engine)?

 

The boiler design does affect weight distribution, but for a new design that is something being calculated anyway. For example, a Bulleid pacific boiler has a large firebox and combustion chamber volume, a short barrel, and a long smokebox, and thereby works out quite light.

If you read A.F.Cook's book on LMS boiler design, it is an eye-opener into just how many things there were to consider when designing a boiler - weight distribution being one of them - and also how irritatingly frequent it was that optimising one parameter invariably had an adverse impact on another!

(It might be more of an issue when reboilering existing locos with a. different design boiler, but then generally there wasn't much scope other than to put on a boiler that was dimensionally similar to the original).

Tom

 

If you don't like long smoke-boxes, there are other design options.

https://en.wikipedia.org/wiki/Belgian_State_Railways_Type_10

 

Where's a decent photo of the Turf Burner's boiler when you want one?

 

I do not think that the weight on the bogie will affect the riding as long as there is sufficient to allow the side control to work without the wheels lifting off the track. The weight on the bogies of large locos can vary over quite a range. From weight diagrams a LNER A3 bogie carried less than 16 tons and the SR Lord Nelson with the round top firebox had 23 tons on the bogie.

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So, yet another belgian locomotive where one is left wondering what on earth the designer was thinking

 

Separate designers for the boiler and chassis?

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I dunno, yes it looks weird, but they appear to have had a long and successful career, and I can't spot any aspect of the design that doesn't seem to have a rational basis. Maybe the designer had heard that M. Churchward's Pacific in England was having trouble with steam temperature due to over long boiler tubes?

 

Separate tape measures I think ...

Tom

 

Its just looks like someone rummaged in the parts bin. Drummond smokebox, Gresley boiler, chassis off a Princess Coronation and cab by Emmett Brown. Its all about familiarity, I suppose, but the best european steam locomotives get is "not too ugly". YMYD...

 

Surely the Thompson long smokebox was just a consequence of the chassis layout, and if it had any advantages they were incidental, though knowing the amount of plumbing inside many smokeboxes a bit more space would have eased assembly and maintenance.

Having thought a lot about the Thompson Pacifics while reading this thread, I think what he did was logical. If there were crank axle breakages with the Gresley designs, then that had to be dealt with as a safety issue. Divided drive provided an answer. What surprises me is that the additional front-end length and weight of the Thompson design was thought acceptable. Adhesive weight was lower and I think this has been discussed, but route availability and turntable length come to mind.

 

Perhaps that is what happened when they built the Blackburn Beverley aircraft. It looked like the horizontal and vertical scales did not match.

My apologies for the thread drift.

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Not (quite) always true ..... The FC deMallorca employed some charming 3'-0" gauge 4-4-0t locos. Originally developed from a trio of small Nasmyth Wilson machines from 1877, successive batches were rebuilt by the workshops at Palma, into a well proportioned (and somewhat larger) version, of which the best looking (IMHO) and final iteration saw the original stovepipe chimney replaced with a very fetching copper cap. They just made it into the 1960s. I must admit, I find the larger 4-6-0t version from the same source, with their oddly proportioned wheelbase and cylinders hidden behind sheet metal, downright ugly!

 

Presumably a Flemish one and a Walloon one?
They were highly successful. The boiler was actually designed for a 2-10-0 version, on which it looked rather more in proportion
The latter was so good that Hughes nearly built some for the L&Y.
https://en.wikipedia.org/wiki/L&YR_2-10-0_(Hughes)?wprov=sfla1
Although odd looking at first glance, I think they have a certain je ne sais quoi.
One of the Pacifics is preserved.

(Edited to make sense!)

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Exhaust pipe run and inside cylinder get at ability was good compared to some GWR locomotives.
The were designed very early in the superheating age(1910).
Being able to get at valves and valve gear was important

WP_20200331_001[1] by Hermod posted Mar 31, 2020 at 9:32 AM

 

Next project for @Corbs's model railway?! (For those who don't know it's the Island of Sodor but if it was a real system. It's well worth checking out)

 

The exhaust looks quite smooth (apart from the one bend, but I can't see where the live steam passage is. Where I'd expect it to run seems to be full of exhaust passages