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William Dean's Express Tank


MikeOxon

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Being somewhat of a back-water in railway history, the Witney branch via North Leigh became home to many unusual vehicles, rarely seen elsewhere. I have already shown the standard-gauge Tilt Wagon ('Hat Box') but a particular claim to fame for this line was that it became the 'stamping ground' for William Dean's experimental 4-2-4 express tank engine, shown below entering North Leigh station.

 

 

 

 

 

 

 

 

 

 

 

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William Dean's experimental 4-2-4T No.9 at North Leigh

 

My first encounter with this locomotive was many years ago, through the pages of John Gibson's “GW Locomotive Design - A Critical Appreciation”, which portrayed it as such an embarrassing failure that all traces of it had to be expunged from the record, with an order going out that 'this thing never existed'.

 

If that were true, Dean would hardly have provided an article for 'The Engineer, Sept.24th 1886', with a detailed drawing of the unusual outside Stephenson valve gear. Dean explained that this arrangement was intended to get rid of the excessive cramping up of the valve gear, necessary when large cylinders have the valve chests placed between them.

 

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Outside Valve Gear on Re-built GWR No.9 (from 'The Engineer')

 

In fact, Dean had arrived in office knowing that the Broad Gauge was nearing its end and a new type of locomotive would soon be needed, to replace the Gooch singles. Amongst the ideas to be tested was the possibility of using express tank engines, as designed successfully by Pearson, for the Bristol & Exeter railway. E L Ahrons, who arrived at Swindon in 1885, described the original configuration of the engine as having a 30' overall wheelbase, including two carrying bogies of wheelbases 7' 3" and 5' 6" respectively. He also stated that the length of the platform was 36' 5-5/8".

 

Very much later (around 1940), E W Twining produced an outline drawing, purporting to show the layout of the tank engine. A comparison of his sketch with the detailed drawing of the valve gear in 'The Engineer' reveals that it is simply not possible to fit this gear between the front bogie and the driving wheel, if the longer bogie is placed at the front! In my opinion, Twining's chassis seems to bear a very considerable resemblance to the Lehigh Valley inspection saloon, still in existence at that time, even down to the bicycle-style 'mudguards' over the front bogie wheels.

 

My own solution places the shorter bogie at the front and, with this configuration, a well-balanced design results. The front bogie fits neatly under the smokebox, leaving room for the outside valve gear, while the rear 7' 3" bogie fits immediately behind the firebox, within the overall 30' wheelbase. Apart from the reversed bogies, the dimensions conform to Ahrons' description.

 

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My Interpretation of GWR 4-2-4T No.9

 

I have fitted an extended cab roof, similar to those used on other GWR tank engines in the same period, and a rear spectacle plate, appropriate for high-speed reverse running. Other features include cutaways in the tanks, to allow access to the motion, and tanks that extend a short distance in front of the smokebox, both as mentioned by Ahrons. The long (11' 6") boiler, in two rings, was designed to provide similar steaming capacity to the large-diameter boilers of the Gooch singles.

 

My model wears the new livery, introduced in 1881, with Indian red frames and vermilion lining (though at that time the wheels were still green). With this presentation, I believe that the engine is worthy of the description given by David Joy, when he visited Swindon around 1882 "I saw all about a mighty 'single' tank engine ... I saw drawings and all, and she looked a beauty".

 

The real significance of this engine was that, while it showed that the 4-2-4 express tank engine concept was not appropriate for the standard gauge, it addressed an urgent need to re-visit valve-gear design for more powerful engines. The eventual outcome was, of course, the famous Dean Singles, with the same length of boiler and direct-driven valves, mounted below the cylinders. The family relationship can be seen in the following extremely rare photo of these two engines, side-by-side at North Leigh:

 

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Dean 'Single' alongside its 4-2-4T pre-decessor at North Leigh

 

My model currently only has 'cosmetic' outside valve gear, cut from plasticard with my Silhouette cutter. It is powered by a Tenshodo WB28.7 SPUD, contained within the rear bogie, in the same way that my 4-2-2 uses a similar one in its front bogie. The model negotiates my small-radius curves with ease and does not share a tendency for de-railing, which apparently afflicted the prototype!

 

Mike

 

references:

Great Western Locomotive Design, John C Gibson 1984

The British Steam Railway Locomotive 1825 - 1925, E L Ahrons, 1927

Swindon Steam, L A Summers, 2013

Edited by MikeOxon
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  • RMweb Gold

Lots of railways had wierd locos during the early years. There was belief that other designs might be better. There were lots of experiment with Dean and Churchward before the Churchward standards came along. They looked odd to many when first built.Nice model.Don

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Lots of railways had wierd locos during the early years. There was belief that other designs might be better. There were lots of experiment with Dean and Churchward before the Churchward standards came along. They looked odd to many when first built.Nice model.Don

Not just in the early years, either - think Paget, LNER 10000, LMS 'Fury', etc.  Some people are very critical of Dean's experimental designs but forget that Churchward made quite a few mistakes before settling on his 'standard designs' - think 'Kruger' for example.

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  • RMweb Gold

A lot of the experiments were Dean and Churchward working together. I do think the Kruger wins the prize for the ugliest loco might make an interesting model?Don

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A magnificent beast! The comparison with the Dean Single is most illuminating.

 

Did you built it all from plastikard?

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A magnificent beast! The comparison with the Dean Single is most illuminating.

 

Did you built it all from plastikard?

Only the valve gear is plasticard!!  The body and chassis are brass, using very similar construction techniques to my 'Queen' locomotive.  With the long square tanks it was very simple to cut out the main components from 10 thou (0.25 mm) brass sheet.

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A lot of the experiments were Dean and Churchward working together. I do think the Kruger wins the prize for the ugliest loco might make an interesting model?Don

I agree that the Kruger is so ugly that it becomes attractive as a model concept.

 

Unfortunately, I think that with all those nests of springs, peculiar saddle sandbox, combustion chamber, etc., it would be in the 'too difficult' box for me.  A big attraction of early Armstrong and Dean designs is that they are fundamentally simple :)

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I've got to have me one of these little monsters........ The only difficulty is justifying it on my proposed Great War era layout...

 

Nice model and description, thanks for sharing.

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I could hardly believe this machine, when I first read about it in John Gibson's book.  I built this fairly simple model just to work out how it might have looked.  It may have been a failure but it provided Dean with some important lessons, which led eventually to his famous 'singles'.

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The sad thing is it was the method of attaching the two trucks that was probably a failure and not the locomotive generally (which was sadly untested), however with such a small proportion of the machine's weight available for traction she would have been as slippery as wet grass!

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Yes, William Dean did seem to have some odd ideas about bogies but it all came right in the end!  I think historians have been a little unkind about Dean - we forget how much was unknown when he came to office but he learned a lot from his mistakes and was clearly well-respected by Churchward. (who also learned from his mistakes)

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Interesting about Gibson... while he was undoubtedly there and had the overalls as you might say, it seems to me that he needs to be read with a considerable pinch of salt handy. He definitely has a weakness for these tales of coverups and conspiracies, and one suspects that sometimes it was more of a matter of no-one wanting to talk about errors any more than I like to recall any errors I might have made in my working life. As an example, if you go through his details about the King dimensions, the numbers simply do not add up to what he says they do. The same is also true of some of his "should have builts", again often his concept simply wouldn't have made the weight restrictions.

 

Your analysis re valve gear and wheel spacing appears to me very well observed. I suppose the thinking was that as long as its got 19.5 tons (or whatever Dean's limit was) on the driving wheels it will have the same traction whether its towing a bogie or a tender behind, which is logical enough until the water tanks are nearly empty!

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Thank you for your comments, Jim.  There is nothing like trying to build a model, for finding out what does and doesn't work! 

 

Another amazing thing is that, by all accounts, the Pearson 4-2-4 Tanks did work on the Broad Gauge but, in their case, the width of the gauge left room for well tanks, which would not cause such huge shifts in the centre-of-gravity as they emptied

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Mike - there is something about bogie Singles that 2-2-2s do not have.  "Balance" perhaps.  The NG/SG Lord of the Isles has balance.  My F Moore The Locomotive magazine print from around 1900 shows an elegant machine.   Eric.

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This drawing of No 9 as built was published in The Locomotive magazine, January 1940 edition.

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And as rebuilt.

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Thank you for commenting, @Annie.  I am very sceptical about the Twining drawing, which was produced around 1940.  I suspect he may have been influenced by the bogies on the Lehigh valley 4-2-4T. which was still extant at that time:

 

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The valve gear, as shown in the re-built version of No.9, will not fit between a 7' leading bogie and the driving wheels.  It seems unlikely that they would have gone to the trouble of altering the arrangement during the rebuild, especially as it was re-built again, a little later, to match the layout of the 'Queen' class. 

 

This article referred to by @Miss Prismin the Imaginary Locomotives thread, is incorrect in stating that this engine used Joy's valve gear.  As the 'Engineer' article referred to above clearly states, it was Stephenson gear.  Joy did visit Swindon and saw this engine being built and there was a plan to use Joy's gear on the second, never built, version. 

 

The whole thing was an experiment by Dean to try and find a way of accommodating the valve gear when using larger cylinders.  Eventually, he adopted Stroudley's arrangement, with the valves located below the cylinders.  The real solution, of course, was to use outside cylinders, as Churchward realised.

 

Mike

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Yes I thought the drawing would be controversial Mike, but I thought I'd add it to the comments on this page as a point of interest.  The valve gear certainly doesn't look right as shown in the 1940 drawing. 

 I still much prefer your model as an interpretation of how the original No.9 might have looked when first built.

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