A Coarse Guide to the Steam Locomotive for ‘N’ Gauge Modellers

[chrism]

Sounds like you need one of these, Jim 

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 81


Hello Chums

More Than Two Cylinders - 9

Introduction:

There are two main characters in this part - Sir Nigel Gresley and Harold Holcroft.

Most, if not all, all what I'll try to describe occurred before Sir Nigel was knighted in 1936, so, unless the context requires otherwise, I'll refer to him as Mr Gresley.

Harold Holcroft joined the SE&CR in 1914 and spent the latter part of the Great War in the service of the War Office, based at a depot in Purfleet, Essex. He returned to the SE&CR in late January or early February 1919. You might recall that Harold Holcroft's conjugated valve gear had been the subject of patents in 1909, when he was with the GWR at Swindon.

**

In part 79 we met Mr Gresley's first three-cylinder engine - 2-8-0 No. 461 of May 1918. Mr Gresley had obtained a couple of patents for conjugated valve gear in 1916. Construction of a locomotive equipped with conjugated valve gear was delayed by the Great War. No. 461 was fitted with a complicated type of valve motion with rocking levers and the outside cylinders had to be inclined at 1:8, the same as the inside cylinder. The valve gear used had 15 motion pins. That designed by Mr Holcroft had eight.

When an article about the locomotive appeared in The Engineer, there was some criticism of the complexity of her valve gear. Her performance in service convinced Mr Gresley of the superiority of three cylinders and he wanted to build more of the type but knew his valve gear wasn't the optimum solution.

**

Here's an aside. When applying for a patent, fastidious checks are made to ensure what is being proposed is not the subject of a pre-existing patent. However, patents, are specific - unlike in James Watt's day, something he was able to take advantage of. It appears Harold Holcroft thought his idea for operating the valves of a three-cylinder engine from two sets of valve gear was original. It was when applying for his patents that he found out about David Joy's 1884 patent for three-cylinder marine engines.

There is a variation in the interpretation of the evidence here - some, like FAS Brown, Sir Nigel Gresley's biographer,  maintain Mr Gresley was entirely unaware of Mr Holcroft's work and patents.¹ Other suggest his 1916 patents took advantage of the precise nature of the wording of Mr Holcroft's patents in order to apply for his own patents. Here's what Mr Holcroft had to say about his patent application:

'I set to work but, what with the need to make haste and some loss of enthusiasm over the device not being entirely original, and as there was no prospect of a three-cylinder engine being built at Swindon, all possible forms in which the invention could be applied were not fully exploited, with the result that HN Gresley of the GNR found a loophole a few years later on, which a little more thought might have closed.' ²

**

Returning to No. 461, Mr Holcroft joined in the correspondence in The Engineer and was invited subsequently to read a paper, Three Cylinder Locomotives to the Institution of Locomotive Engineers. This was read, in London, just prior to the Armistice and was reprinted in full in The Engineer.

Mr Gresley was especially interested and asked the Leeds Centre of the Institution to arrange for Mr Holcroft to read his paper again, in Leeds, so that engineers from Doncaster could hear it and take part in the discussion. This occurred in mid-December. Unfortunately, Mr Gresley was called away to see his General Manager. He gave his notes to an Assistant to read during the discussion. This is of interest:

'By an entirely different method from that described by Mr Holcroft I devised an arrangement of two levers by which the valve of the middle cylinder could be operated by the valve spindles of the outer cylinder.

It was not until 12 months later that I discovered through the Patent Office that Holcroft had a gear which, whilst differing in its arrangement and application, was based fundamentally on the same principle as mine. I consider therefore that to Mr Holcroft belongs the credit for having first devised the arrangement by which only two valve gears are necessary for three-cylinder locomotives.'³

Gracious and unambiguous.

Mr Gresley invited Mr Holcroft to meet him in his office at King's Cross on 9 January 1919. They had a cordial discussion and Mr Gresley made it clear that Mr Holcroft's simpler conjugated valve gear had given him the key to introduce successfully many more three-cylinder locomotives.
 
After establishing Mr Holcroft was still involved with War work, Mr Gresley said that he could do with him on the Great Northern at Doncaster. Mr Holcroft replied that Mr Maunsell's approval would have to be sought.

A little later, Mr Maunsell saw Mr Holcroft and said:

"By the way, I have seen Gresley and have told him that I propose to construct some three-cylinder engines myself and shall need your assistance here." ⁴

And so the scene was set, Mr Holcroft remained on the SE&CR and, later, Southern where, as we have seen, two locomotives were built with his conjugated valve gear. Mr Maunsell then decided in favour of three independent sets of valve gear.

And, on the Great Northern and, later, the LNER, Mr Gresley introduced lots 'N' lots of three-cylinder engines with their valve gear arranged in accordance with Mr Holcroft's design.




[Great Northern 'H4' 2-6-0 No. 1000 of 1920. The first engine to use Mr Holcroft's conjugated valve gear. Later LNER class 'K3'.]




[The first production 'O2' 2-8-0, No. 477, with conjugated valve gear of Mr Holcroft's arrangement, built by the North British Locomotive Company in 1921.]

**

Interestingly, No. 461 wasn't the first three-cylinder locomotive with its valves operated by two sets of valve gear. That distinction belongs to an experimental 2-8-2T, built by Henschel and tested on Berlin suburban trains in February 1913.

**

Unfortunately, Mr Gresley appears to have fairly quickly decided to stop giving Mr Holcroft credit for the valve gear. In 1925 Mr Gresley read a paper, Three Cylinder High Pressure Locomotives, to the Institution of Mechanical Engineers. He made no mention of Mr Holcroft. Indeed, he included an illustration of the ex-SE&CR 'N1' 2-6-0, No. 822, the caption for which read:

'The centre valve is driven by the author's arrangement of levers, the motion being transferred from the outer gears by the long rods shown.'⁵

In the discussion, James Clayton, Mr Holcroft's senior colleague, raised the matter politely and Mr Gresley's response is interesting:

"Mr Clayton drew attention to the valve gear. He [Gresley] did discover after designing his arrangement that Mr Holcroft  had devised a valve gear for three-cylinder engines, but it had not the the same arrangement of levers. Mr Holcroft had far more levers than he used." ⁶

This is a complete inversion of the facts and one wonders why such an eminent engineer as Mr Gresley took this approach.

As for Mr Holcroft, he was especially gracious, writing later:

At first it was referred to as the Gresley-Holcroft arrangement, but, although my part in it was forgotten after a time, I was quite content with the quiet satisfaction of watching its progress over the years.'⁷




[Here is the valve motion as fitted to 'O2' 2-8-0 No. 3487. It is fitted in front of the cylinders in Sir Nigel Gresley's preferred arrangement. The 'D49' 4-4-0 and 'B17' 4-6-0 classes had the derived motion behind the cylinders. Mr Holcroft's preference was for behind the cylinders.]


That, I think, is sufficient discussion of more than two cylinders in the context of simple-expansion engines. In the next part, we'll discuss (mostly British) compound locomotives - how many cylinders do they have?


Postscript.

My special thanks to @Jim Easterbrook for providing intellectual rigour regarding the smoother power delivery of three-cylinder locomotives.


¹ FAS Brown, Nigel Gresley Locomotive Engineer, Ian Allan, London, 1961, ISBN (1975 edition) 07110 0591 5, Page 43.

² Harold Holcroft, Locomotive Adventure, Ian Allan, London, 1964, Page 68.

³ ES Cox, Speaking of Steam, Ian Allan, London, 1971, ISBN 7110 0236 3, Page 80.

⁴ Holcroft, Page 93.

⁵ Cox, Page 81.

⁶ Cox. Page 81.

⁷ Holcroft, Page 93.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Pip-pip

John

[Jim Easterbrook]

My special thanks to @Jim Easterbrook for providing intellectual rigour regarding the smoother power delivery of three-cylinder locomotives.

I think "rigour" is pushing it. More like the unfortunate side effects of interrupted sleep. I'll keep "intellectual" though.

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 82


Hello Chums

Compounding - A Simple Approach - 1

Introduction - Something for Nothing?:

Something for nothing - do you like the look of that?

Invest a £100 at 5% per annum. Take out the fiver interest at the end of the year and we can go down to Wetherspoons. Repeat annually until the end of year 14.

Or leave the interest in and then start to earn interest on the interest. A tad after 14 years and you'll have £200.00. Spend the interest or retain it - £30.00 better off in the long run if it's retained. Money for nothing?

Albert Einstein is alleged to have said:

"Compound interest is the eighth wonder of the world. He who understands it, earns it ... he who doesn't ... pays it."

*

By the way, I used a very conservative example with 5% interest calculated annually, as people that have accrued enormous credit card debt have discovered.

*

I asked a question - 'Money for nothing?'

Certainly you were £30.00 better off by a little after the end of year 14 than if we had spent the interest each year.

But we gave up our annual visits to Wetherspoons. The nearest one to me, here between the Forth and the Tweed, is in Musselburgh. A pint of cask ale costs, normally, £2.00 or so. Your fiver buys us a couple of pints and leaves enough for a token of our appreciation to the nice big gel behind the bar. She rewards us with a winning smile. We sit down, enjoy our fine, foaming ale and talk about toy trains. As we leave, she waves and smiles again. We are happy.

Did you get money for nothing?

No! Fourteen of these agreeable interactions is the cost of your additional money. Is it a price worth paying?

***

Now let's think of a steam engine. We've already discussed valves , cylinders and the like. The exhaust valve opens and the steam goes up the chimney, hopefully by a direct route. As it does so, it provides a draught for the fire, but that's for the next section of this unbelievably short mini-series. There are 'chuffs' from the chimney and, if our locomotive is an LNER 'Pacific', Mr and Mrs @Papyrus have a dance to the music of steam.

But, is it a waste simply [Thank You!] letting the steam go up the chimney without doing any more work. The chuffs tell us there was energy left in the steam - could we not have put it to better use?

Enter, chums, the compound steam engine. The exhaust steam from the first cylinder goes into a second cylinder, so that we can use its remaining expansive force, before it's allowed to escape. We have put it to work.

Something for nothing - a benefit without a cost?

No! There a cost - a sort of steam engine's version of us not enjoying our fine, foaming ale and appreciating the nice big gel's smiles?

Is the cost worth paying? That's the approach I'm going to take in our discussion in this section of the mini-series.

Before we think about any potential costs and whether they are worth paying, we first need to understand what we might gain from using the expansive force of the steam for a second time. Thankfully, the answer is easy, our steam engine will use less fuel and water to do a given amount of work. Let's leave the various oil-burning applications over the years to one side and assume the fuel is coal.

The next part will have a SuperSwift look at the history of compounding and consider briefly a couple of non-railway applications. After that, we'll attempt to negotiate the complex historical Webb of British compound locomotives. Although I might stray slightly from the British part.

I am especially grateful to @martyn for reviewing the drafts for this section of the mini-series and for his advice, ideas and suggestions. Of course, any errors, omissions or episodes of silliness are mine alone. Thank you Martyn.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Tickety-tonk

John

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 83


Hello Chums

Compounding - A Simple Approach - 2

Historical Overview to 1881 or Blame the Prussians:

Like so many other advances with the steam engine, the first buds of what would later burst into flower as the compound engine appeared in Cornwall in the service of its tin mining industry, where, in 1781, Jonathan Hornblower patented a two-cylinder beam engine that used the general principle of compounding.

These early buds were nipped by James Watt whose patents were allowed to have a wider application than one might think. This prevented development of Mr Hornblower's engine. But, like so many ideas it didn't go away, and there followed a period when engineers, various, explored the concept.

What I believe to be a breakthrough occurred in 1833 when a Dutch engineer, Gerhard Moritz Roentgen, modified the steam engine on the steam paddle tug Hercules by adding a low pressure cylinder which was supplied with exhaust steam from her high-pressure cylinders' exhaust.

You might recall that the advantage of the compound engine is it uses less fuel and water for a given amount of work. This was hugely attractive to marine engineers as coal could take up a lot of space onboard ship that could be used for profitable cargo. This was especially important for ocean-going ships.

I believe it's fair to say that the compound steam engine was subject to the most enthusiastic development for marine applications. As well as double-expansion engines, there were triple and even quadruple-expansion marine engines, perfected to extract as much work as possible from each pound of coal.

Water wasn't as much of a problem for ocean-going steamships as @martyn kindly explained to me they used seawater, treated by using waste heat from the engines.

The importance of this little wander off course is twofold. Engineering doesn't occur in a series of little boxes - the various fields of endeavour connect with and inform each other, and compounding was especially important in marine applications because it permitted a worthwhile reduction in the amount of space onboard that was given up to the storage of coal.

Going back to our introduction, this is the benefit that was gained. But, please remember our 'no something for nothing' example from the introduction, featuring pints of fine foaming ale and the nice big barmaid's smiles. The benefit came with a significant cost. Obviously, these compound marine steam engines were complex and expensive machines to build and maintain. In the marine context the benefit was worth the cost.

**

Returning, now, to dry land we can discuss the appearance of compounding in railway locomotives. Which means we had better introduce ourselves to some jargon. Two abbreviations:

The rather saucy HP, meaning high-pressure steam, and

LP, meaning low-pressure steam.

These abbreviations are normally found in an adjectival capacity to describe a cylinder - HP cylinder or LP cylinder, that sort of thing.

As far as I have been able to establish, the first locomotive to use anything like compounding was patented in 1850 by James Samuel, engineer of the Eastern Counties Railway. The credit of the invention was given to John Nicholson, an employee in the locomotive department. Two of the railway's locomotives were converted to what was called the 'continuous expansion' system in 1850-52.

This differed from more modern compound engines. There were two inside cylinders, with their associated cranks set at 90^o. Steam was admitted to the HP cylinder and, when it had reached half-stroke, live steam was cut-off and a connecting valve allowed the expanding steam into the LP cylinder as well, which was commencing its piston stroke. I'll not go into more details of the workings of these engines but they were shown to have used less coke per mile than in their unconverted, simple state.

The idea was not pursued by locomotive engineers although Mr Nicholson interested Stewart, a London manufacturer of stationary engines, in the idea and several using the 'continuous expansion' system were built.

*

Credit for the successful compound system for a railway locomotive goes to M. Anatole Mallet, a Swiss engineer. He patented his system in 1874 and, in 1876, introduced a series of two-cylinder compound 0-4-2T locomotives for the Bayonne-Biarritz Railway in France. One of these was shown at the 1878 Paris Exhibition.

British locomotive chaps took a keen interest in this exhibition. Mr Stroudley of the LB&SCR showed his 'A' 0-6-0T No. 40, Brighton. She was awarded a Gold Medal, which was entirely proper as 'Terriers' are lovely engines.

Thus began France's long love affair with the compound steam engine. And, rather like in the case of steamships, there was a good reason.

The Franco-Prussian War was a conflict between the Second French Empire and the North German Confederation which was led by the Kingdom of Prussia. France invaded German territory on 2 August 1870 but soon found itself in serious trouble. After a siege, Paris fell on 28 January 1871, which, effectively, ended the war.

Formal ending of hostilities was achieved with the Treaty of Frankfurt on 10 May 1871. France paid Germany lots 'N' lots of money and handed over most of Alsace and parts of Lorraine. This was especially inconvenient to the French because Alsace-Lorraine had enormous reserves of coal and iron ore. France found itself short of coal for burning in steam locomotives and had to import it, much from Great Britain, at a disagreeable cost. Therefore, the coal-saving benefits of compounding would be especially valuable to the French.

In 1879, FW Webb, Chief Mechanical Engineer of the LNWR since 1871¹, decided to try M. Mallet's compounding system and converted a little 2-2-2 to a two-cylinder compound. The engine worked passenger trains on the Ashby and Nuneaton Joint Railway, showing economies in coal consumption.

We might notice in passing that Mr Webb's Works Manager at Crewe from 1871 until 1881 was Thomas W Worsdell, often called 'TW'. 

**

Let's conclude this part with a quick look at what we can loosely term traction engines. Ranging from ploughing engines to showmen's road locomotives, these had limited space for coal and water. Therefore, anything that would reduce coal or water consumption would be attractive. The first compound traction engine, built by John Fowler & Co, appeared in 1881 and showed savings of up to 30% in use of coal and water. These economies were especially valuable where coal was expensive or water was scarce.





The other traction engine builders attempted to ignore compounding but, after a few years when Fowlers experienced agreeable sales, they started building their own and the type enjoyed great popularity.




[The arrangement of cylinders atop the boiler of a traction engine, in this instance a Foden. HP cylinder on the right and the LP cylinder on the left. The steam passage between the valves for each cylinder is shown. Please note the LP cylinder is noticeably larger in diameter than the HP cylinder. This is an important point.]

Many traction engines had some form of 'simpling valve' which allowed live steam to be admitted to the LP cylinder. Running 'double high' allows for greatly increased power output when required, at the cost of higher coal and water consumption.

In the next part we'll discuss what EL Ahrons called the 'first compound era' from 1882 to 1890.<sup>2


1</sup> Not for the formidable Mr Webb the usual title of the period, Locomotive Superintendent. It took rather a long time for Chief Mechanical Engineer to become the generally preferred term.

² In his indispensable The British Steam Railway Locomotive 1825-1925, Chapter XVIII, Mr Ahrons uses 1882-89. I have chosen to extend this by a year for reasons that will, hopefully, become apparent.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-oo

John

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 84


Hello Chums

Compounding - A Simple Approach - 3

'First Compound Era' from 1882 to 1890 - TW's Compounds:

In Part 83 we noticed M. Mallet two-cylinder compound locomotives and Mr Webb's subsequent conversion of a 2-2-2 to this system. She gave satisfactory service on the Ashby & Nuneaton Joint Railway, which pleased Mr Webb. We recalled that the Crewe Works Manager from from 1871 until 1881 was Thomas W Worsdell, often called 'TW'.

Meanwhile, furth of this island, another engineer was taking a keen interest in M. Mallet's compounding system. Let's introduce the splendidly-named August Friedrich Wilhelm von Borries, who joined the Prussian state railways in 1875, rising to become Chief Mechanical Engineer.

In 1880 Hr von Borries designed the first Prussian compound locomotive, on Mallet two-cylinder principles. The engine was successful and showed significant savings in coal consumption.

*

I suppose most sensible people, attempting to write this, would, at this point in the discussion, head towards Crewe and a discussion of the doings of Mr Webb. 'Sensible' cannot, by any stretch of the imagination include me, so I'll take a different approach. We will go to Crewe, in the year 1881, but just for a fleeting visit because TW is about to depart. You see, he has just been appointed Locomotive Superintendent of the Great Eastern Railway, in succession to Massey Bromley, who had resigned shortly before. I think it might be a jolly jape to ignore the LNWR at present and follow TW to Stratford.




[Thomas W Worsdell 'TW']


His first locomotive design for the GER was the 'G14' class of 20 2-4-0s, built in 1882-83. The arrival of the first engine was eagerly awaited and the incomparable C Hamilton Ellis tells us that local confectioner was selling 'G14 Rock'.¹

The 'G14' class proved to be nothing special. Hamilton Ellis quoted EL Ahrons writing about these engines:

'When it came to fast running there was an indefinable something about them ... they usually seemed to travel after the manner of a stout lady in a hobble skirt.' ² 

It was now, influenced by the work of Hr von Borries, that Mr Worsdell turned to compounding. He had, when at Crewe, known Mr Webb's two-cylinder compound engine and saw in the Mallet/ von Borries system a way to gain thermal efficiency, decrease maximum stresses on working parts and, at the same time, retain simplicity by keeping to the two-cylinder engine without significant changes, apart from the larger-diameter LP cylinder and the addition of a starting valve.

Mr Worsdell's first compound engine, No. 230, appeared in 1884 and ten more, Nos. 700-9, followed in 1885. These were similar to the 'G14' class, but with a bogie instead of a leading radial axle and with the boiler pressure increased from 140 psi to 160 psi. It was reported that the compounds used 14% less coal than the 'G14' class, providing the boiler pressure was maintained.





There are a couple of things which might benefit from elaboration. With a two-cylinder compound engine, it is important to ensure the amount of work done by each cylinder is as equal as possible. Hr von Borris' meticulous calculations showed that, with normal valve gear, the optimum ratio of cylinder diameter, HP:LP, would be 1:2.25. This would result in a LP cylinder of inconvenient size. The solution arrived at by TW and Hr von Borries was to have a smaller LP cylinder diameter and then adjust the valve gear to give a later cut-off in that cylinder.

Starting can be the Achilles' heel of compound engines. If the piston in the HP cylinder was in a 'blind spot' the engine would not start at all. The answer was the starting valve which admitted live steam into the LP cylinder for a short time. An automatic flap valve was fitted so that the locomotive went to compound working once underway.

Clever stuff and the collaboration between TW and Hr von Borries resulted in several patents. We can now bid farewell to Hr von Borries, noting that he left his appointment with the Prussian State Railways in 1902 and commenced a distinguished academic career aa a professor of railway engineering in Berlin.

Meanwhile, well to the north of Stratford, the well-managed North Eastern Railway found itself in something of a disagreeable situation. You see, old Edward Fletcher had retired in 1882. 'Father Fletcher', as he was affectionately known, was something of an institution. As a young man, he had been apprenticed to George Stephenson and he became the Locomotive Superintendent of the the Newcastle & Darlington Junction Railway in 1845. This railway became part of the North Eastern Railway, created by the Great Amalgamation of 1854, and Mr Fletcher became Locomotive Superintendent of the new company.

His successor, appointed in 1883, was Alexander McDonnell, who had been Locomotive Carriage and Wagon Superintendent of the Great Southern & Western Railway since 1864. A clever man, with a university degree, Mr McDonnell attempted to impose his New Thinking upon the NER's Locomotive Department and, in so doing, failed to show sufficient reverence for the work of Edward Fletcher. The men complained about the New Thinking, the new 4-4-0 engines he had designed³ and they complained about him.

This put the NER's Directors in a difficult position, which they resolved deftly by paying Mr McDonnell a year's salary to resign. He wasn't replaced immediately, a committee chaired by Henry Tennant, the NER's General Manager, took over control of the Locomotive Department, with day to day management delegated to the man who had been Assistant Locomotive Superintendent - Wilson Worsdell, TW's younger brother.

The committee was responsible for the introduction of the 2-4-0 'Tennant' locomotives. We all know what committees are like and it was Wilson Worsdell who attended to what needed done. The enginemen loved the 'Tennants', one of which has been preserved, and the NER's locomotive affairs were once again proceeding happily.

In due course, the Directors appointed their new Locomotive Superintendent - TW, who took up the post in 1885. Although only with the GER from 1881 to 1885, TW left a valuable legacy - his 'Y14' simple-expansion 0-6-0 goods engine of 1883. Building of the class, better known to most locomotive enthusiasts by its LNER designation of 'J15', continued under his successors and it was the GER's most numerous locomotive class.

Once at Gateshead, TW commenced equipping the NER with a stud of two-cylinder compound locomotives for both passenger and goods traffic.  His first compound, the 'C' class 0-6-0 goods engine, appeared in 1886. 171 examples were built.

In the same year, his first compound for express passenger work entered service. This was No. 1324, the first of the 'D' class. Perhaps thinking about Mr McDonnell's many troubles resulting from his underpowered 4-4-0, this was a 2-4-0.





Very obvious in the picturingham is the combined splasher, seen also on GER No. 230, and the Worsdell cab, which became standard on the NER and, later, in modified form, on the LNER. This was not altogether new, a vaguely-American style cab had been used on the Stockton & Darlington 4-4-0, No. 160, Brougham, in 1860.

Express passenger 4-4-0s followed in 1887 and, as part of that fascinating reversion to single-drivers that occurred following Francis Holt's invention of steam sanding gear in 1886, two classes of 4-2-2 in 1888-90. Edward Fletcher was one of the first locomotive engineers to abandon the 'single' and none had been built for the NER since 1862.





Incidentally, although the brief 'single' revival was widespread, TW was the only locomotive engineer to build compound 'singles'.  I was fortunate enough to find a fascinating cross-section of one of these engines. Fitting the cylinders between the frames, which were four feet apart, was difficult - the difference in cylinder centres being accommodated by inclining the HP cylinder up towards the driving axle and the LP cylinder down. The valve chests were outside, as can be seen in the picturingham of No. 1517.





Unfortunately, TW hadn't enjoyed the best of heath and he chose to retire at the end of 1890, aged 52. He served the NER as a Consulting Mechanical Engineer for another three years. TW had a long retirement, in the Lake District, dying aged 78 in 1916.


¹ C Hamilton Ellis, Twenty Locomotive Men, Ian Allam, London, 1958, Page 150.

² Hamilton Ellis, Page 150.

³ The 4-4-0s of 1884 were less powerful that the Fletcher 2-4-0s they were intended to replace on the East Coast expresses. The enginemen weren't happy.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-bye

John

[martyn]

Thanks once again, John, for such an interesting postingham.

Just a couple of notes; the GER Worsdell G16 compounds were converted to simples by TW's successor, James Holden, when the locos were only about six years old. Holden himself built one of the N31/J14s as a compound on the Worsdell/Von Borries system but this only lasted two years before being 'simpled'. I don't know if the conversion was due to any faults with the locos, or whether Holden (who was ex GWR at Swindon) just didn't like compounds. TW's GER 'Gobbler' 2-4-2 tanks were simples, and it was poor detail design of the valve gear (Joy's) not compounding which was the cause of the high fuel and water consumption.

The NER 'Tennants' became LNER class E5; members of the class  hauled trains in the 'Race to the North' in both the 1888 and the 1895 'races'.

One thing I'm not sure of, but when using two cylinders of different sizes might have been 'racking' of the frames due to an imbalance of work in each cylinder (though presumably this had been calculated for so that each one did equal work), or the imbalance in weight of the different sized pistons not being balanced. I think that I've read that it was so, but I can't recall the source.

Later systems, using multi-cylinder systems, did away with this imbalance.

Over to you again, John!

Martyn
 

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 85


Hello Chums

Compounding - A Simple Approach -

'First Compound Era' from 1882 to 1890 - A Tangled Webb:

In Part 84 we followed Thomas Worsdell, 'TW', from Crewe to Stratford and then Gateshead.  In this part, we go back to Crewe and discuss Mr Webb's early approach to compounding.

We also discussed, in Part 84, a couple of potential problems of the Mallet/von Borries/Worsdell two-cylinder compounds. Great care had to be taken to ensure each cylinder did the same amount of work, otherwise horrid stresses would be imparted to the locomotive's crank axle, bearings and frames. Also, we saw that space between the frames for the two cylinders was not altogether generous. It was easier in continental Europe and the USA, where a large LP cylinder could placed outside of the frames. In Great Britain, it would play Old Harry with the structure gauge, especially our high station platforms.

However, the two-cylinder compounds required little more complication than a two-cylinder simple-expansion engine. A larger LP cylinder and a starting valve was about it. Which means these were, in my view, about as close as compounding in Great Britain came to the 'something for nothing' ideal we discussed in the introduction to this section.

Time, now, to return to the LNWR, Crewe Works and the Chief Mechanical Engineer, FW Webb.





Mr Webb had been Chief Mechanical Engineer of the LNWR since 1871. In his locomotive work, at first, he followed on from the practice of his predecessor, John Ramsbottom. Mr Webb's 'Precedent' and 'Improved Precendent' class 2-4-0s of 1874 and 1887 were excellent engines. Hardwicke, thankfully preserved, maintained an average speed of 67.2 mph from Crewe to Carlisle and Charles Dickens ran a million miles in a bit under 10 years. Likewise, his goods and mixed traffic locomotives, typified by the 'Cauliflower' 0-6-0, were strong reliable engines.

Mr Webb's 1879 conversion of a 2-2-2 to a two-cylinder compound on M. Mallet's system demonstrated savings in coal consumption which encouraged him to experiment further. Also in 1879, M Mallet read a paper to the Institution of Mechanical Engineers regarding his two-cylinder compounding system. Mr Webb was present and contributed to the discussion:

"To get compound engines which would work steadily and economically at high speeds, it would be necessary to go back very much to the form of the engine designed by Robert Stephenson some years ago having three cylinders. But instead of making all the cylinders work with boiler steam, the boiler steam should be taken into the middle cylinder first, and thence into the outside cylinders [...] If that were done there would be no side oscillation and one of the steadiest engines it was possible to produce would be obtained."¹

In early 1882, No. 66 Experiment appeared from Crewe Works. She certainly was an experiment. One difference from what Mr Webb said earlier was there were two outside HP cylinders and one inside LP cylinder. Experiment was the first of Mr Webb's three-cylinder compounds. The two outside HP cylinders of 11 1/1 in diameter, driving the trailing wheels, and a inside LP cylinder of 26 in diameter, driving the leading wheels. Joy valve gear was fitted.

The increased complexity from the Mallet/von Borries/Worsdell two-cylinder is worth noting. Back to that 'never something for nothing' point from our introduction.





At this time, the 2-4-0 was the normal type for passenger working with the 4-4-0 gaining prominence. However, not all locomotive engineers liked coupled wheels, thinking they interfered with smooth running. Patrick Stirling, of the G&SWR and, later, the Great Northern declared famously that a coupled engine was, "Like a laddie running wae his breeks doon." [Anglice available on request.]

Then there was that fascinating return to 'single-wheelers' from 1886 that we touched upon in the previous part. Coupling rod failures were a a problem at the time, as higher running speeds got ahead of the technology to forge the rods and fit them with the required degree of accuracy.

Mr Webb's use of three cylinders, with divided drive, allowed him to dispense with coupling rods and Experiment was a 2-2-2-0, or 'double-single'. She was used for about a year on the Irish Mail between Euston and Crewe. She proved to be a weak starter due to her small diameter HP cylinders, but otherwise performed well. Of course, she had advantages - the best coal, hand-picked and specially-trained enginemen and Mr Webb's keen supervision. Another 29 similar engines, with 13 in diameter HP cylinders, were introduced in 1883 and Experiment was rebuilt to conform. This was the 'Compound' class.

Once in service it became clear that, without the advantages Experiment had enjoyed, their performance on day-to-day main line work was inferior to that of the simple-expansion 'Precedent' class and Mr Webb soon had them relegated to lighter duties.

As the 'Compound' class was coming into service in 1883, Mr Webb was a Vice-President of the Institution of Mechanical Engineers and read a paper regarding Experiment. This passage is instructive:

"The two main objects the author had in mind when designing the Experiment were: firstly to attain a greater economy in the consumption of fuel; and secondly to do away with coupling rods while at the same time obtaining a greater weight for adhesion than would be possible on only one pair of driving wheels without rapid destruction of the road."²

It is interesting that the absence of coupling rods was given almost equal importance to fuel economy. We discussed earlier how, in 1897, Dugald Drummond was also tempted by the 'double-single' concept on the LSWR, with less than encouraging results.

Mr Webb was not to be discouraged by  the performance of the 'Compound' class and 40 'Dreadnought' class engines with larger cylinders and bigger boilers, pressed to 175 psi, were built in 1884-88.

Finally, in 1889-90, arrived the 'Teutonic' class, similar to the 'Dreadnoughts' but with 7 ft 1 in driving wheels. These are generally agreed to have been the best of Mr Webb's three-cylinder compounds. On the same night that Hardwicke made her epic run north of Crewe, Adriatic, according to CJ Bowen Cooke, ran the 158.1 miles from Euston to Crewe in 147.5 minutes. On 1 September 1895, Ionic ran the 299.25 miles from Euston to Carlisle, non-stop, in 353 minutes. Racing days, indeed.

Seven of the 'Teutonic' class, built in 1890, featured an interesting development. Something that troubled designers of compound engines was the valve settings for the HP and LP cylinder or cylinders. We have already noted how Hr von Borries and Mr Worsdell used a longer cut-off for the LP cylinder in the NER two-cylinder compounds. Mr Webb's three-cylinder compounds had other complications, having three sets of valve gear, those for the HP and LP cylinders' valves being originally controlled independently but, for the 'Dreadnought' class, by an ingenious arrangement where the HP and LP valve gears could be operated together or independently. Mr Webb was granted a patent for this arrangement.

Then Mr Webb had an insight. Although 'linking-up' the valves for the two HP cylinders was essential for fuel economy, there was no need to be able to link-up the valve for the LP cylinder which could operate at maximum cut-off. In this case the valve gear was only required to operate the valve, without cut-off adjustment, and to allow the engine to work forward or reverse. In such a situation, a straightforward non-adjustable method of operating the valve, by means of a rocking shaft, could be achieved by means of a slip eccentric on the axle - just like on a toy steam engine.

At a stroke, Mr Webb had removed some of the complexities of his three-cylinder system of compounding. Brilliant!

It was all so easy - on starting, the driver opened the regulator and the pistons in the two HP cylinders moved, thus moving the engine forward and causing the slip eccentric driving the valve for the LP cylinder to operate. As their exhaust valves opened, steam was ready to be admitted to the the LP cylinder and engine accelerated away. Perfik. So easy. A compound that a driver can drive like a simple-expansion engine. There was a bypass valve fitted so that the exhaust for the HP cylinders could be diverted to pass directly up the chimney when the engine was starting.

Now for the but. Engines came on to their trains at pretty much the same places on the railway, whether at terminal stations or engine-changing places like Crewe. You'd often see an accumulation of ashes from the engines' ashpans in the four foot.

Now think of the rails where engines are changed. Likely to be greasy from dribbles of oil. A bit dodgy on a dry day and downright slippery on a wet day. Of course, the engine had set back onto the train a bit earlier, so the valve for the LP cylinder would remain in reverse gear until the slip eccentric moved. If the bypass valve, located in the smokebox and operated from the footplate through a rod, pins and levers, stuck closed and the wheels driven by the HP cylinders slipped on the greasy rail, the LP cylinder would then receive steam when still set for reverse.

Which led to the engine going nowhere with its two sets of driving wheels birling merrily in opposite directions. Such fun for the layabout observer [my perfect job title; please send an application form] but seriously annoying for the driver who had to attempt to restart.

This was the main problem with the 'Teutonic' class which, otherwise, could have been very fine engines indeed. Several experts on steam locomotives have said that there were only two things required for the class to be excellent engines - coupling rods!

Notwithstanding these occasional entertainments, Mr Webb's later three-cylinder  compounds (Yes, there are more to come) were all fitted with slip eccentrics and many of the earlier 'Dreadnoughts' were altered to have a similar arrangement.




[In this splendid photograph, taken by Dr Budden,'Teutonic' 2-2-2-0 No. 1304, Jeanie Deans³ is seen at Bushey troughs on an up express. The LNWR was the first railway in the world to use water troughs. The polished cover of the 30 in diameter LP cylinder is prominent below the smokebox.]


That has taken us to 1890 on both the LNWR and the NER. The end of what Mr Ahrons called the 'First Compound Era'. In the next parts we'll discuss what happened next on these lines and have a quick glance at compounding on other railways.


¹ ES Cox, Speaking of Steam, Ian Allan, London, 1971, ISBN 7110 0236 3, Page 21.

² ES Cox, Page 22.

³ Jeanie Deans was the heroine of Sir Walter Scott's 1818 novel The Heart of Midlothian. She was a popular character with the public and many things, from a ship to a rose, were named after her.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerio

John

 

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 86


Hello Chums

Compounding - A Simple Approach -

'Second Compound Era' from 1890 to 1922 - Mr Webb's 'Middle Period' Compounds:

Do you ever wonder about the missing, or especially rare, locomotive wheel arrangements in Great Britain? A good example is the 2-4-2. Found in Continental Europe, New Zealand - I fancy there's a preserved example there - and in the USA, where it was called the 'Columbia' type. The Reading and Burlington railroads made use of it.¹

Where were the British 2-4-2s? There were more 2-4-2T locomotives than we can shake a stick at, especially in Great Eastern territory, but no tender engines.





Please look again - she's not a 2-4-2.

In Part 85, we encountered Mr Webb's 2-2-2-0 'double-single' three-cylinder compounds for the LNWR. Construction of these finished in 1890 and Mr Webb then turned his attention to something a bit bigger. In 1891, a development of the 'Teutonic' class appeared. She had a bigger boiler, but in length not diameter. It is said that, in order to avoid over-long tubes, Mr Webb incorporated a combustion chamber.

What a good idea. Common by the mid-Twentieth century, a combustion chamber is normally thought of as an extension of the firebox into the boiler barrel. This gives additional space for combustion. As an example, we can see fireboxes evolving from the squareness of a '4F' to the more complex forms of a 'Jubilee' or a 'Princess Royal', where the front of the firebox has a backwards slope from top to bottom. This sectioned view of rebuilt 'Merchant Navy' 4-6-2 35029 Ellerman Lines shows how the firebox has been designed with a combustion space in front of the brick arch.




[Photograph courtesy @Bealman ]


Unfortunately, Mr Webb's idea, typical of the man, was rather different. He placed the combustion chamber middle-ish in the boiler. Yes, you read that correctly. The tubes between the firebox and combustion chamber were 5 ft 10 in long and those between the combustion chamber and the smokebox were 10 ft 1 in long. The combustion chamber itself was 2 ft 10 in long.

Here's a couple of quotations from EL Ahrons, who has been a great friend to this astoundingly brief mini-series:

'The combustion chambers were a source of trouble. Whether much combustion took place inside them, after most of the flame had been extinguished during its passage through the first set of tubes, is open to question.'

And again:

'Much of the tube heating surface at the front was of small value'²

The length of the boiler on these engines required a set of carrying wheels under the footplate. A total of 10 were built between 1891 and 1894. Mr Webb didn't use his favoured Joy valve gear on these engines, which had inside Stephenson link motion operating the valves for the 15 in diameter outside HP cylinders. The valve for the inside 30 in diameter LP cylinder was operated by a fixed eccentric and rocking shaft, as we saw on the earlier 'Teutonic' class. The 'Greater Britain' class had 7 ft 1 in diameter driving wheels.

Ten similar engines, but with 6 ft 3 in diameter driving wheels for service on the Crewe to Carlisle line, followed in 1894-1898. This was the 'John Hick' class and Mr Ahrons reckoned them to be the worst of Mr Webb's three-cylinder compounds, which was saying something. Fortunately, they were soon put on secondary trains, thus saving them having to try to work the West Coast expresses over Grayrigg and Shap.

Mr Webb also turned his hand to compound goods engines and, from 1893 to 1900, 111 three-cylinder compound class 'A' 0-8-0 engines were built. Mercifully, these engines were spared the combustion chambers. They also had coupling rods and performed fairly well. Incidentally, all three cylinders drove the second axle. Stephenson link motion was used for the outside HP cylinders. The inside LP cylinder's valve was operated by a slip eccentric and rocking shaft. As the slip eccentric was on a driven axle there were no wheels turning in opposite direction problems with these engines.





Just to remind ourselves that Mr Webb was capable of building a good express passenger engine, the picturingham shows Hardwicke relaxing at the NRM's Shildon outstation. Cheap to build and maintain, efficient and simple [Thank you!] She's well looked after - they've even put a Grove headlamp code on her.





This mention of matters royal allows a cunning and subtle segue [good word, segue] to  Queen Victoria's Diamond Jubilee celebrations in 1897. The LNWR, known for its 'blackberry' black locomotive livery, decided to celebrate the occasion in grand style by repainting two of the 'Greater Britain' class locomotives in special liveries.

Greater Britain was painted scarlet, with smokebox and wheel centres blue and white wheel rims. The Royal Arms were carried on one of the splashers and on the tender. Queen Empress was painted in a soft creamy white with lavender edging. OS Nock's Steam Railways of Britain in Colour³ contains attractive illustration of both engines.

I think the idea of a white and lavender locomotive - perfik for Poppingham - is a good place to conclude this part. In the next part, we'll discuss some further LNWR examples which, I think, are evidence of what we mentioned in the introduction about not getting something for nothing.

¹ C Hamilton Ellis, Some Classic Locomotives, George Allen & Urwin, London, 1949, Page 115.

² EL Ahrons, The British Steam Railway Locomotive 1825-1925, Page 291.

³ OS Nock, Steam Railways of Britain in Colour, Blandford Press, 1967, Pages 120 and 121.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John

[martyn]

Thanks again, John.

There are indeed at least three 2-4-2 tender locos in various states of preservation in New Zealand; the Rogers 'K' class of 1887.

https://en.wikipedia.org/wiki/NZR_K_class_(1877)

As for the central combustion chamber locos; don't ask me to go inside to clean or replace the tubes, far too claustrophobic!

If you wanted a rather unusual livery to go with your lavender coloured loco, look no further, here's another. One of the GER Sinclair locos, #284 of class 'W' 2-2-2s was painted cream when it hauled the wedding train of the then Prince and Princess of Wales. There were also garlands draped around various parts of the loco. The only photo I can find is in 'The Great Eastern Railway' by CJ Allen, 1968 edition.


Martyn

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 87


Hello Chums

Compounding - A Simple Approach -

'Second Compound Era' from 1890 to 1922 - Mr Webb's later Compounds:

At the start of this section we discussed the chimera that is obtaining something for nothing in the context of locomotive engineering.  We used an example of you choosing to let your interest compound, rather than taking the fiver interest each year and us each enjoying a pint of fine, foaming ale at my local Wetherspoons. We even got a nice smile and a cheery wave from the fine big gel behind the bar. Very agreeable benefits of you taking annual interest. Forgoing those is the cost of you deciding to allow your interest to compound.

*

The benefit to be gained from compound locomotives was the possibility of savings from lower fuel consumption. The value of this varied - we saw it was especially important for the French after 1870, as the Germans had taken the best coal reserves in Lorraine.

We've discussed Mr Webb's use of three-cylinder compounds. The class 'A' 0-8-0 goods engines were fairly good and the 'Teutonic' 2-2-2-0 engines might have been splendid if only they had coupling rods. However, we saw from Mr Webb's own paper to the 'Mechanicals' that not having coupling rods on the express passenger locomotives was almost as important a consideration for him as fuel economy.

We also noted that the Mallet/von Borries/Worsdell two-cylinder compounds on the North Eastern Railway were about as close to obtaining a benefit from compounding for no cost as was achieved in Great Britain.

Mr Webb had adopted the complication of three cylinders and his 2-2-2-2 engines, complete with a combustion chamber in the middle of their boilers, were inferior to the best of the earlier three-cylinder compound engines - the 'Teutonics'.

What do you think Mr Webb did next?





A sturdy bogie 4-4-0, albeit with outside cylinders - something like David Jones' excellent 'Loch' class of 1896 for the Highland Railway?

Rejoicing across the LNWR from steam shed to the magnificent Euston Boardroom?

Hold on 'alf a mo' - these outside cylinders don't look as big as the 'Loch' class' 19 in x 24 in. cylinders. Just the thing to lift a train up that sharp climb from Carrbridge to the Slochd. They look decidedly smaller. What's going on?

*

We have seen Mr Webb pursue the concept of the three-cylinder compound from 1882 to 1898, with the 2-2-2-0 'Teutonics' being the best and the 2-2-2-2 'John Hick' class the worst. However, before the last of the 'John Hick' class had left Crewe Works, Mr Webb had a remarkable change of approach. In 1897, two 4-4-0 locomotives were built - the first, Iron Duke, was simple expansion and the second, named Black Prince, was a compound.

But a very different type of compound. A 4-4-0, not with the usual bogie but with double radial axles. In a remarkable increase in complexity, Black Prince had four cylinders, two HP on the outside and two LP on the inside. The valves were operated by two sets of inside Joy valve gear. This meant that the cut-off points for the HP and LP cylinders were interdependent. And, in another break with tradition, the locomotive had coupling rods. Truly, a different approach.

Presumably, the idea of building a simple-expansion engine as well was some sort of comparison, but the four 15 in x 24 in cylinders were too demanding for the boiler. In the parlance of the time, Iron Duke was over-cylindered. Mr Webb was careful to ensure the simple-expansion engine had an in-built disadvantage - its boiler pressure was 175 psi, whilst that of the compound was 200 psi.

Interestingly, Mr Webb didn't publish details of the comparison. He merely provided an overall average coal consumption for the two engines of 40.3 lbs/mile. Iron Duke was converted to a compound in 1898 and renamed Jubilee.

A total of 40 'Black Prince' class, sometimes called the 'Jubilee' class, locomotives were built to the end of 1900. Another 40, slightly enlarged engines, the Alfred the Great class, entered service between 1901 and 1903. No. 1952 was provided with independent sets of valve gear for her HP and LP cylinders. Tests were arranged in September 1903 which showed an indicated horsepower (IHP) of 835 for the interdependent cut-off and 949 IHP for the independent cut-off. The rest of the 'Alfred the Great' class was converted to this arrangement. The 'Black Prince' engines remained as-built.




['Alfred the Great' four-cylinder compound 4-4-0, No. 1942 King Edward VII. Of interest is the rebuilt 'Lady of the Lake' class 2-2-2, No. 827 Victoria. The 'Ladies' saw much use piloting the various compound locomotives. She was scrapped in March 1907.]

With regard to performance, the smaller 'Black Prince' class weren't especially good. Their boilers were of similar dimensions to those of the 'Dreadnought' and 'Teutonic' classes of ten years earlier. The 'Alfred the Great' class had a larger diameter boiler, pressed to 200 psi, and were much better engines.

in 1903, two 'Alfred the Greats', Charles H Mason and Commonwealth ran a special train to Glasgow non-stop from Euston to Carlisle in 5 hours 58 minutes. Both engines carried a relief fireman.

One important point to note is Mr Webb's three-cylinder compounds had a LP/HP cylinder ratio of 2:1. The 'Alfred the Greats', with 16 x 24 HP cylinders, had the ratio reduced to 2:1.64. This is noticeably less than the ideal and the HP cylinders were reduced later to 15 in diameter. This reduction from the theoretical ideal ratio demonstrates that, notwithstanding their complexity, the four-cylinder compounds were unable to achieve the maximum possible benefits from compounding. 

One hundred and seventy four-cylinder compound 0-8-0 goods engines were built between 1901 and 1904.





There were also the 30 four-cylinder compound 4-6-0 engines of the '1400' class for express goods service, commonly known as 'Bill Baileys'. These were never satisfactory and Mr Bowen Cooke had them all broken up after 10 to 15 years' service.




By the way, the locomotive in the first picturingham is 'Alfred the Great' four-cylinder compound 4-4-0, No. 1950 Victorious.


*

In the next part, we'll have a quick look at what happened to Mr Webb's compounds, then discuss a couple of applications on other railways. After that we'll return to what occurred on the North Eastern Railway after TW Worsdell was suceeded in office by his younger brother, Wilson Worsdell.


'N' Gauge is Such Fun!

Many thanks and all best wishes.

Pip-pip

John

[Papyrus]

For someone who was reluctant to write about compounding, you are doing an excellent job, John. I am, as always, learning a huge amount. In the process, your recent episodes have made several references to coupling rods. This has set me thinking, which is an activity which never ends well, but out of my brain has popped a question to which there must be an answer...

We are all familiar with locos with cylinders either outside the frames, or inside or, in some cases, both. As you described, some CMEs tried to do away with coupling rods altogether. But why were the coupling rods always outside the frames, attached to the wheels? Why did nobody ever build a locomotive with the cylinders outside and the coupling rods inside? I say rods, but you would only actually need one, on a crank on each axle. There must be a good reason why no one ever tried this.

Over to you John @Train Waiting and @martyn !

Cheers,

Chris

[Train Waiting]

That is an interesting question, Chris.

We have discussed why the British favoured inside cylinders for most of the 19th Century, and, in some cases, afterwards. One or two locomotive engineers generally preferred outside cylinders, Messrs Adams and Jones being good examples.

Stephenson link motion was almost always between the frames in British practice. US as well.

Outside coupling rods were easy to fit and to remove as required. As such, they were used right back in the days of the 'steam dinosaurs'. Locomotion and Sans Pareil being good examples. Outside coupling rods could be taken off easily and did not require a pit, sheer legs or a wheel drop.

The cranks on the outside of the wheels were easy to engineer.

A two-cylinder engine would have the eccentrics for the valve gear and the cranks - either outside the wheels or on a crank axle - on one axle. Normally - we discussed 'Fletcher's Patent' Dolgoch.

The other axle/s would be plain axles. Much easier and cheaper to make.

If the coupling rods were inside, a humble two-cylinder 0-6-0 goods engine would require three crank axles, rather than one. The oiling-up of the coupling rods would have to be done below the engine.

If only one coupling rod was used, it would be best, to equalise forces, centred between the frames - exactly where the eccentrics for Stephenson link motion are.

Sufficient clearance would require to be found for the inside cranks to swing round without bashing anything. Often the ashpan would between two axles - a coupling rod swinging around would make this an interesting proposition.

We have already seen that the distance between the inside faces of the frames - say, four feet in British practice, was tight enough already when there were axlebox bearings, big ends and eccentrics involved. Imagine trying to add an inside coupling rod to this. 

For a locomotive with more than four coupled wheels, can you imagine the complexities of the coupling rod's bearings and jointed sections to enable it to be taken down for examination and repair?

What is a straightforward job with outside coupling rods and fine, stout fellows would be a nightmare. Please see this film at 13.30.

I think I've rambled on enough for now but will, of course, be glad to discuss further.

Thank you for your kind comments about the compounding section. @martyn kindly agreed to check every part in this section prior to posting. That will have saved me from countless embarrassments. Any errors or omissions are, of course, mine.

With all good wishes.

John

[martyn]

As well as John's excellent answer, there was often frame strengthening cross members between the axles. I think that with inside valve gear, the cross members were used as anchor points for the pivoting parts.

But, I'd think, the difficulty and cost of making multiple cranked axles and ease of access were probably the main reasons.

Martyn

[chrism]

As well as John's excellent answer, there was often frame strengthening cross members between the axles. I think that with inside valve gear, the cross members were used as anchor points for the pivoting parts.

And as locations for the sliding parts - the rear valve guides and the back ends of the slidebars were usually firmly fitted to a stout frame stretcher - the front ends of the slide bars usually fitted on the back of the cylinder block or rear cylinder covers in much the same way as with outside cylinders.