A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 93


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'The Exhausting Problem'

After the live steam has done its work in the cylinders (or cylinder in some of the earliest examples) of a steam locomotive, what can one do with it? Simply letting it escape from the valve chest to atmosphere would be a nuisance, with clouds of steam enveloping the engine. No doubt frightening horses as well. I disapprove strongly of frightening horses.

The earliest locomotives, with their single-flue boilers, had a long chimney to disperse the smoke and create a draught on the fire. Just like factory chimneys - a well-known technology at the time.

Richard Trevithick dealt with the problem of exhaust steam by taking it from the valves of the cylinder/s into the base of the chimney. According to contemporary accounts these pipes were turned through 90^o in the chimney so the exhaust steam travelled straight up and out. This pipe was called an 'exhausting' or 'eduction' pipe. ['Eduction' - what a SuperSpiffing word.]

At the time his Pen-y-darran locomotive was undergoing trials in February 1804, Mr Trevithick was in correspondence with David Giddy, later President of the Royal Society. On 20 February 1804, Mr Trevithick wrote:

'The fire burns much better when the steam goes up the chimney than when the engine is idle.'

And, on 4 March:

'[Steam] makes the draught much stronger by going up the chimney.'

Giving evidence before a Committee of the House of Commons on 'Steam Carriages' in 1831, Mr Trevithick stated that he used a 'forced draught', created by the steam, for the purpose of working on the roads. This meant a high chimney was not required, helpful for a road vehicle.

Mr Trevithick's exhaust system came into general use for the early 'steam dinosaurs'. It gave a gentle exhaust blast, ideal for the single-flue boilers of the time where a sharper exhaust blast would have pulled the fire up the chimney.

'Having a Blast'

There has been much argument over the years regarding who invented the blast pipe. From the 'battle of the blast pipe' in the pages of The Engineer in 1857 right up to BackTrack Volume 38, No. 12, December 2024¹. Incidentally, the 1857 hare was set running by John W Hackworth, Timothy Hackworth's son.

What is known is Mr Trevithick led the exhaust steam into the chimney and then discovered the effect it had on the draught. This, like penicillin over a century later, was an accidental discovery of great significance.

It is not known if any of these early locomotives had the exhausting pipe placed centrally in the chimney. What we can say for certain is a typical locomotive of the time, Lancashire Witch, built in 1828 by Robert Stephenson & Co for the Bolton & Leigh Railway had two upturned exhausting pipes, one for each cylinder, at opposite sides of the chimney. The picturingham shows a plan view of this engine:





The next development was combining the exhaust pipes in a central pipe, coned or tapered to form a contracted orifice. The blast pipe. Credit for this development belongs to Timothy Hackworth who used it on his Royal George of 1827 for the Stockton & Darlington Railway. This locomotive had a 'U'-shaped return-flue boiler, 2ft 2in diameter at the furnace end and reducing to 1ft 6in at the chimney.




[Timothy Hackworth's Royal George]

The Stephensons adopted the coned blast pipe and it permitted the success of Rocket's multi-flue boiler. All these small diameter tubes offer a resistance to the hot gasses resulting from combustion and a much stronger blast is required than for an engine with a single-flue boiler.

Why the fuss? My view is Timothy Hackworth felt hard-done-to by the results of the Rainhill Trials and the subsequent fame of George Stephenson - 'The Father of the Railways'. Robert Stephenson deserved but did not achieve similar recognition as I've mentioned several times in our amazingly brief mini-series.

But, in the public mind, just as James Watt invented the steam engine, Geordie Stephenson invented the steam locomotive. Utter tosh, of course, but who says 'dumbing down' is a new phenomenon.

It was probably a widespread view that the Stephensons 'invented' the coned blastpipe that prompted John W Hackworth to write to The Engineer. My argument is the Stephensons accepted Timothy Hackworth's development of the coned blast pipe and letters from George Stephenson to Timothy Hackworth in 1828 and from Robert Stephenson to Samuel Smiles, George Stephenson's biographer, in 1858 are, in my view, evidence of this.

Commenting on George Stephenson's letter, which the Hackworth family had recently donated to the National Railway Museum, the Railway Magazine of October 2005 stated:

'The letter is controversial for Stephenson has until now been credited with inventing the blast pipe.'

Please contrast this with EH Ahrons writing in his The British Steam Locomotive 1825-1925:

'The credit for coning or tapering the blast pipe to form a constricted orifice is undoubtedly due to Timothy Hackworth in 1827, and was acknowledged by Robert Stephenson himself.'² [My emphasis]

*

The remarkable Rocket/Northumbrian/Planet progression of 1829-1830 saw the multi-tube boiler and coned blast pipe established as fundamental parts of the British steam locomotive and this remained the case until Evening Star was completed at Swindon in 1960.

In the next part, we'll discuss blastpipes and suchlike in some more detail.


¹ Mike Norman, 'Only in America', BackTrack, Volume 38, No. 12, December 2024, Page 711. This is an interesting but rather strange article. It seems to start from the premise that Timothy Hackworth has been denied his place in history and that the Stephensons were to blame. My view is that, although others might have claimed George Stephenson invented the coned central blastpipe, the Stephensons didn't. I swithered about indulging in correspondence with the magazine, but Andrew McLean, Assistant Director and Head Curator of the National Railway Museum (NRM), fortunately got there first. He made a splendid job of demolishing Mr Norman's argument, quoting from original sources held in the NRM. Please see page 126 of the February 2025 BackTrack. (Vol 39. No. 2) for impressive scholarship from an NRM employee.

Mr Norman responded in the April 2025 BackTrack at page 253. (Vol 39. No. 4) In my view this letter adds nothing of value to the debate and attempts to continue his 'hatchet job' on Robert Stephenson.

² EH Ahrons, The British Steam Locomotive 1825-1925, Locomotive Publishing Company, London, 1927, Page 8.

*

Very many thanks to @martyn for reviewing the draft of this postington and identifying what would have been an embarrassing typo.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-bye

John

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 94


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'Blastpipes - Some Theory-Type Stuff, but with Stories'

The conical blastpipe, pioneered by Timothy Hackworth and taken up by Robert Stephenson was essential to provide sufficient draught to enable a multi-tube boiler to steam well. As the engine worked harder, the exhaust sharpened and increased the draught. Magic!

But, there's a but. Why is there so often a but? Restricting the surface area of the blastpipe will help steaming, at the risk of pulling the fire to bits - we'll have a Saintly little story about this in, probably, the next part - but it causes increased back pressure in the cylinders. Put simply, the constricted blast pipe means exhaust steam will be tempted to linger longer in the cylinders rather than making a sharp exit through the valves and away out to the sky. Increased back pressure causes increased coal consumption. Which meant locomotive engineers had to think carefully about how much to constrict the blastpipe.

Robert Stephenson recognised this and mentioned it in correspondence. His point was sadly misrepresented in the BackTrack article mentioned in Part 93. Let's turn to the invaluable Dr Tuplin for a succinct explanation:

'The ideal was the largest [blastpipe] nozzle that would enable the engine to steam at full power in conditions somewhat inferior to normal ones. If average conditions deteriorated over the years, what was originally satisfactory might cease to be so and should be changed.'¹

Very nicely put, Dr T.

However, in practice, things could be a bit more complicated and the enginemen might end up with a locomotive that was steaming badly. Their traditional answer was to restrict the blastpipe nozzle by means of a home-made (or shed blacksmith-made) device. These had several names - 'Jimmy' and 'razor' being familiar to me. Please feel free to add any other in the discussion. This improved the engine's steaming but it was important not to get caught using one. Authority would not be happy.

But here's a nice little story. When Mr Stanier, later, Sir William, introduced his '5XP' three-cylinder 4-6-0s on the LMS in 1935, they were poor steamers. Possibly even terrible steamers. As a Great Western man, Mr Stanier had no experience of three-cylinder engines. Amongst a series of modifications, guess what they did. Yes, reduced the area of the blastpipe's nozzle. Of course, they used a nice new cap rather than a home-made 'razor' but the effect was the same.




[An LMS '5XP' or 'Jubilee' 4-6-0, made by Rivarossi for Peco. Is this the most influential British 'N' gauge locomotive of all time?]


Then, nearly 20 years later, BR had a steaming problem with its brand new 'Standard' '5MT' 4-6-0s. Whoops! The LMS 'Black Fives, on which the BR design was based, on tended to be good steamers as, of course, were the GWR 'Halls'. Whatever could they do? Yes, they reduced the blastpipe cap from 5 1/8in. to 4 7/8in. Evaporation of water increased from 19,000 lb./hr to 24,000 lb./hr. ES Cox, who had responsibility for the design of the BR 'Standards', helpfully included details of this in an interesting book.² Mr Cox's description is worth reading if you have an interest in such things. He discusses smokebox vacuum and blastpipe pressures which are, I think, beyond the scope of our Coarse Guide. Important stuff, though, and please feel free to mention them in the discussion if you wish.




[A BR 'Standard '5MT', No. 73072, with high-sided tender of 9 tons coal and 4725 gallons water capacity.  Built at Derby for the LMR as part of the 1953 Building Programme. Entered service on 11 December 1954, allocated to Chester. Transferred to Polmadie on 22 November 1958 and withdrawn from there on 27 October 1966. Not even a dozen years' service - what a waste!  My late Father-in Law was an engineman at inverness and thought highly of these locomotives. He preferred them to 'Black Fives'. Photograph from my non-collection. I think it's an official BR one.]


But, there we were, in the era of the BR 'Standard' locomotives and we were still working out important design features by trial and error. In the BR example, a 26% increase in evaporation rate (a good metric for 'steaming') was achieved by reducing the blastpipe diameter by 1/4 in. after the class had entered service. By the way, before they went down to 4 7/8 in., they tried 5 in. which gave a water evaporation of 22,000 lb./hr.

This rather supports my contention, made earlier, that this exhausting matter was the last major area of unfinished business at the end of steam locomotive development in Great Britain. A policy decision, made at the start, was that the new BR 'Standards' would have conventional single blastpipes and chimneys. So, why did some locomotives of Class 9 and 4 have double chimneys?³ More of this later.

One last point, a very sharp blast could cause damage to railway infrastructure such as footbridges (Poppingham's now has smoke plates - thank you @icairns) and station canopies.

¹ WA Tuplin, British Steam Since 1900, David & Charles, Newton Abbot, 1969, Page 44

² ES Cox, British Railways Standard Steam Locomotives, Ian Allan. London, 1966, Page 132.

³ As did the '8P' 4-6-2 No 71000, Duke of Gloucester. This engine was not in the original plans for the range of 'Standards'.

Special thanks, once again, to @martyn for reviewing the draft and making helpful comments thereon.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Tickety-tonk.

John

To answer your question about the Peco Jubilee, it is my belief, yes.

Fantastic series, John.  

Quote from: Bealman on October 11, 2025, 11:58:34 PMTo answer your question about the Peco Jubilee, it is my belief, yes.

Fantastic series, John.  

It's amazing how good it still looks, despite the complete absence of the parts of the motion that control the valve travel lead - i.e the drop link, union link and combination lever.

Thanks again, John.

I'll add  a few comments after your next post, as I think they will be more appropriate then.

Martyn

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 95


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'Lang may yer Lum Reek'

Lum, chimney, funnel or smokestack - this is an important part of a locomotive. And not just for aesthetics, although many engineers went to considerable lengths to make the chimney pretty. The view at the time was a chimney is to a locomotive what a hat is to a lady.




[Mr Dean certainly made sure his eponymous goods engine had a pretty chimney.]


As model railway folk, we are interested in what a chimney looks like on the outside. A nicely-shaped one is a delight.

But, for steam locomotive engineers, what goes on inside the chimney is of vital importance to the performance of a locomotive. I don't intend to go into a lot of detail, but here are some basics.

The centrally-mounted restricted-nozzle blastpipe causes the exhaust to form a cone shape. I've been given to understand that the sides of the cone are at around 10^o.  Generally speaking, the lining of the chimney will also be cone-shaped, with the narrowest part called the choke.

You know how we hear so much about the importance of smokebox vacuum? All that stuff about a tightly-fitting smokebox door and the integrity of the wrapper plate, if the smokebox has one (Mr Churchward did us all a favour with his US-inspired round smokebox mounted on a saddle - no wrapper plate rivets to work loose allowing the smokebox to draw air). The 'Royal Scots' in original parallel boiler form needed regular attention to keep maintain the integrity of their smokeboxes.

But this notion of vacuum begs a question - how can one have a vacuum in something that has a big hole cut in top, with a chimney surrounding it? The answer is the exhaust cone , where it leaves the chimney, ought to be the same diameter as the opening of the chimney. That way, when the engine is working, the chimney is effectively sealed to atmosphere by the exhaust.

Getting all this right requires clever design and, often, trial and error. The diameter of the blastpipe and the blastpipe's height in relation to the chimney affect the shape of the exhaust cone. Also, it's worth remembering the chimney isn't simply plonked on top of the smokebox, its lining will likely be continued into the smoke box.

As an aside, and a SuperSpiffing excuse for another picturingham, a few locomotive engineers didn't bother with elegantly-shaped chimneys and the exterior shape followed that of the conical interior. Mr Adams on the GER, then LSWR, was famous for his 'stovepipe' chimney.

The Uries, father at Eastleigh and son at St Rollox, also went in for severe stovepipes as this picturingham of a Drummond 'T9' 4-4-0 shows. Mr Urie, senior, rebuilt the class with superheaters - this made them better engines but, unfortunately, his chimney wasn't an improvement.





The original 'N15' 4-6-0s on the LSWR, later, after Mr Maunsell's attention, included in the 'King Arthur' class (the 'Urie Arthurs') had a stovepipe of remarkable hideousness. The reason why one sees so many long-lived ex-Caledonian 0-6-0s with plain stovepipes is Mr Urie, junior, used these to replace the more elegant offerings from Messrs Drummond and McIntosh.

For the majority of the time of steam locomotive development in Great Britain, draughting was the subject of ad hoc methods. Some designs had excellent steaming characteristics, others were wanting. Then, just after the War, a clever chap called Sam Ell began a thorough and painstaking analysis of draughting at Swindon, using the stationary test plant and controlled road testing. His work demonstrated that some locomotive types were performing at a fraction of their potential capacity.

His most important insight was that quite minor modifications to the blastpipe, chimney shape or chimney size could produce dramatic results. The GWR 'Manor' class had been something of an enigma. Fitted, due to weight restrictions, with a smaller boiler than other 4-6-0s on the railway, they were uncertain steamers. Most un-GWR-like. Mr Ell and his people got to work and the result was amazing.  Prior to modification, a 'Manor' couldn't sustain more than 10,000 lb. of steam per hour continuously. Not a good figure. After modification, 22,000 lb. of steam per hour could be achieved. Golly gosh - how was that achieved?

By a reduction in the diameter of the blastpipe and a narrowing of the chimney proportions.

The LMS '4MT' 2-6-0s, designed by Mr Ivatt the Younger, ought to have been great engines. But, initially, they were poor steamers. At first this was believed to be due to the double chimney (sorry - I'm getting ahead of myself, we'll discuss double chimneys later in this encouraging brief mini-series) and they were fitted with single chimneys.¹ Better, but there was still something not quite right. An engine was taken to Swindon for the Ell treatment. The single blastpipe and boiler proportions were unchanged, but the maximum continuous steam production was improved by 89%. How?

A reduction in the size of the choke of the chimney from 1ft 2 1/4in. to 1ft 0 3/4in. and a reduction in the amount of taper in the chimney.²

Incidentally, Mr Ell's excellent work had, in my view, a bit of a sting in the tale later. We'll come to that ... later.

Let's finish with a story which might seem far-fetched but it comes from an impeccable source. Effective from 1 November 1932, Mr Ivatt the Younger was appointed Mechanical Engineer, Scotland for the LMS, based at St Rollox Works. JE Anderson had retired and Mr Urie, junior, had been appointed to succeed him as Chief Motive Power Superintendent, causing the vacancy at St. Rollox. Let's now hear from HAV Bulleid, a locomotive engineer and Mr Ivatt's nephew:

'Ivatt also found McIntosh's instruction still in force, that the centre line of the blastpipe should be 1/16in. forward of the chimney centre line, in order to allow for the effect of the engine moving forward! His mind boggled.'³

That's enough, I think, on chimneys. In the next part we'll return to blastpipes.

Once again. thanks to @martyn for reviewing the drafts for this postington.


¹ The first 50 '4MT' 2-6-0s, built from December 1947 to November 1949, were fitted with double chimneys. After trials with 43027, they were all fitted with single chimneys by August 1956. The 112 engines of the class, built between July 1950 and November 1952, had single chimneys from new. 

² Fortunately, Mr Ell wrote up his work and this can be found in the Proceedings of the Institute of Locomotive Engineers, No. 235, 1953.

³ HAV Bulleid, Master Builders of Steam, Ian Allan, London, 1963, Page 174.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-B

John
 

 

So pleased to see you are back and carrying on with this smashing series!
I have, and am learning so much from you - thank you.
Cheers!

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 96


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'Blastpipes Revisited'

In Part 94 of this agreeably brief mini-series, we discussed the dilemma with blastpipes. Make them nice and big and reduce the back pressure in the cylinders and reduce the coal consumption. Or make them smaller and live with the back pressure and, possibly, getting the fire pulled to bits when working with long cut-offs. Finding a happy medium wasn't easy.

Which begs the question - why didn't someone invent a variable blastpipe?

They did! The earliest reference I have been able to find is to Rothwell's version of 1832. Hawthorn fitted a variable blast pipe to some engines built in 1846 for the North British Railway and such a fitment appeared on Sharp-built heavy goods engines of 1848-49. These contraptions were worked from the footplate by a system of levers and rods. They didn't catch on.

Somewhat later, Macallan's variable blast pipe was introduced. It worked in a different way from the previous examples and was controlled from the footplate. This was the most successful attempt and the Great Eastern Railway, in particular, was quite an enthusiastic user of it. The preserved 'J15', GER No. 264 and BR No. 65462, was built in February 1912 at Stratford Works. It was one of the penultimate batch of ten and had a Macallan's variable blastpipe. I understand that the LNER removed these blastpipes. Hopefully, @martyn will be able to add some more details in the discussion.

I understand that variable blastpipes were popular in other countries but their application in Great Britain is a footnote to locomotive history. Apart from on the GWR.

Yes, the GWR! Only it wasn't called a variable blastpipe.

When the production-series 'Saint' class 4-6-0s were introduced from 1905, everyone concerned with locomotive running on the GWR realised what superb locomotives they were. Mr Churchward had produced a masterpiece. He did that several times. With a high boiler pressure, long stroke cylinders and excellent valve events, they started away from stations with a 'one-two-three-four' of explosive exhaust beats.  Once underway, as the driver linked up the valve gear, the exhaust, whilst still crisp, was less explosive.




['Saint' No. 2922 Saint Gabriel, built in 1907. This series was the first to feature, from new, the 'Holcroft Curves' on the running plate. Earlier engines had straight running plates and looked severe. Mr Churchward was persuaded to prettify the outline and instructed Harold Holcroft to draw something satisfactory. It became part of the overall 'look' of GWR locomotives for as long as they were built.] 

The Locomotive Inspectors noticed that the exhaust was pulling the fire around when the engine was worked at a long cut-off and reported this to Mr Churchward. Many Locomotive Superintendents of the time simply refused to hear any criticism, however mild and well-intentioned. But that wasn't the Churchward way. He thought that reservoirs connecting the exhaust passages would soften and prolong the beats and asked Harold Holcroft, then in Swindon drawing office¹ to find a way to put this in practice. He did and an engine was fitted up and tested. No difference!

Mr Churchward and his people gave the matter more thought and arrived at the 'jumper top' to the blastpipe. This could move up and down and was lifted by the force of the exhaust at cut-offs over 40%. When the jumper top was lifted, it increased the area of the nozzle of the blastpipe. When the engine was linked-up, it resumed the normal lowered position, which gave a smaller blastpipe orifice. That way, drivers could make enthusiast starts without disturbing the fire. All that was required was maintenance to ensure the jumper top could move easily and didn't get jammed by oily carbon deposits. This was an elegant system as it was completely automatic in operation, requiring no input from the enginemen.

As far as I'm aware, apart from an experimental application to some shy-steaming 'A4s' after nationalisation (the answer lay elsewhere and we'll discuss it later), the use of the jumper top was confined to the GWR. I have found no evidence Mr, later Sir William, Stanier used it when he went to the LMS.

Apart from on the GWR, the conundrum about how to balance the competing demands of draught and back pressure remained unsolved as Great Britain moved into the era of the Big Engine. Was there a solution? If so, was it adopted? More on this in the next Part of this astoundingly brief mini-series.

Thank you, as ever, to @martyn for reviewing the draft. 

¹ Mr Holcroft wrote about this, and much more besides, in Locomotive Adventure (Volume 1), Ian Allan, London, undated - I'd suggest around 1960.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerio

John

AARRGHH>>>>>>>>>>>I've written a whole page of response and I've lost it!

Fat finger trouble,

I'll try again soon.

Martyn

Quote from: martyn on Yesterday at 10:34:35 AMAARRGHH>>>>>>>>>>>I've written a whole page of response and I've lost it!

Fat finger trouble,
I'll try again soon.
Martyn

Done that myself more than once, usually by hitting the Back button on the wrong browser tab - if I'm doing a long post I often do it in Notepad first then copy/paste the text into my forum post.

Quote from: martyn on Yesterday at 10:34:35 AMAARRGHH>>>>>>>>>>>I've written a whole page of response and I've lost it!

Fat finger trouble,

I'll try again soon.

Martyn

Oh, no!  Sorry.

That has happened to me a few times although, in my case, it's been due to 'Fat Brain Trouble'. Or, memorably, on a couple of occasions, the 'seven day rule' for saved drafts. I look forward to reading your response in due course.

All the very best.

John

Note to self;

'Use Save draft' button which I've found now its too late.........(and may not work?) I'll try again, and save it as I go, then add to it on the Forum; I'll let you know when its the finished article, otherwise it is 'work in progress'.

The GER had a precarious financial state, though, roughly coinciding with the appointment of Lord Claud Hamilton as Chairman, and James Holden as Locomotive superintendent, this had stabilised. However, as coal was a major cost, and the GER had no 'native' coal deposits and had to haul all its supplies, economy in its use on locos was a big factor in day to day costs. The GER firebox, and its boilers in general, were 'designed for economy' (RCTS; I don't know details).

As John has said, the GER used the Macallan variable blastpipe. Quoting the RCTS history; 'This apparatus was a standard fitting on most GER locomotives, and consisted of an annular cap on top of the blastpipe which could be raised or lowered by means of a rod-operated crank on the left hand side of the smokebox'. The gear was fitted, without going through the history of all the GER classes, on J65-69, and J14-18 (but see later). Other classes used it, and it can be seen that it was not just on main-line locos. It was supposed to be continually adjusted by the driver as the train was in progress, and assist in altering the blast to suit steam requirements, but it would seem that either the driver set it once in a trip and didn't adjust it, or didn't alter it at all.

The 'Clauds' don't seem to have used the Macallan blastpipe, not surprising on the first ones as they were oil burners, but photos suggest later ones didn't either, however I don't know and stand to be corrected. The B12s, and later the J17/18, used another variation; the Stone's variable blastpipe. This consisted of two concentric blastpipes, the outer of which could be shut off by a driver operated valve. However, these variable exhausts needed cleaning to ensure they were easy to use, and it was found that they became jammed by smokebox ash. The LNER removed all of these fittings fairly quickly after Grouping.

For John's reference, another use of the Churchward jumper cap was on two 'Clauds'; James Holden, the (nominal) designer, was ex GWR and tried a number of GWR fittings including top feed, but none seem to have been widely adopted.

John has mentioned the use of Churchward jumper caps on the A4s as built. They had previously been tried on the C1s and O1s; surprisingly, Doncaster obtained the drawings from Derby and not Swindon! It was found that 'there was an advantage from fitting these caps' on the A4s unlike the other two classes. But due to higher superheat temperatures on the LNER than those found at that time on the GWR,  carbonised cylinder oil was found to jamb them unless kept clean, and steaming troubles could occur. They were clipped down or even removed on shed, and in 1953 -55 removed completely.

The V2s had a number of exhaust arrangements, seemingly five major ones., plus a number where individual engine blast pipes were adjusted by even 1/2" or less. In 1952, a V2 was trialed on Swindon test plant under the supervision of Mr Ells.  Redesigns, including the Swindon findings,  included adjustment of blastpipe height, diameter, and redesign of the blastpipe petticoat in the smokebox (and, one loco, very, very, briefly, a copper capped chimney....until it was seen by senior management).

However, this was still not the full answer, especially as time passed and the quality, in general, of the coal used deteriorated. The poor steaming of most A4s, and V2s, became a heated subject at Doncaster. Mr Cook, the new CME was ex GWR/Swindon, where, as John has suggested, the CME kept a closer eye on running, and could not be wrong. The ER Running Superintendents, including Mr. LP Parker, and Mr. Townsend, pushed for 'something to be done'. Initially, the blastpipe was adjusted to Swindon dimensions; if a 'Dean Goods' blastpipe didn't work, then nothing would.......and perhaps not too surprisingly, it didn't. Doncaster/GNR settings carried over to the LNER weren't so different to Swindon's.

Eventually, after these 'false starts', a solution was found........which I will leave to John to add his thoughts in his excellent series first.  The answer was staring Authority in the face, but the evidence was not accepted, for some reason. Higher Authority, under pressure from the Running Superintendents and Shedmasters, forced Doncaster's hand, and the final set of alterations were carried out.

Note that though I've written about the A4s and V2s in particular, other classes were also monitored and altered/adjusted as required; eg, once again, the 'Clauds'.

I'll just add a final quote from 'Locomotives' by JM Bell, effectively a text book for BR footplatemen;

Quote;

'The blast pipe arranged in the smokebox acts as a powerful inducing apparatus, and can be found in a great variety of forms. The position of the blast orifice relative to the tubes and chimney has been subject to innumerable experiments.

With a much lower position of a nozzle, a "petticoat" pipe, or draught pipe, is usually interposed between the nozzle and the chimney. The proper size of the nozzle for any particular engine is determined more by experience and tests in practice than by any fixed rule; its diameter averages one quarter that of the cylinders.

Methods of varying the diameter of the nozzle to meet different conditions of service, grades of fuel, etc., are very numerous, and much adopted in countries where it is desirable to have a variable blast. Here the tendency is to adhere to a fixed nozzle of a dimension which gives the most general satisfaction, as it has been proved that all movable devices in the smoke box are unreliable in   service, owing to the corrosion, violent expansion, and accumulation of dirt to which they are subject'.

End quote.

Martyn

That's your lot-for this post!

Note that, unlike John/Trainwaiting, my research is based on ex LNER locos, as just about all my references are for that Company. I'm sure something similar happened on most railways.

I'm so very pleased to see the return/continuation of this "micro mini-series" on the workings of the steam locomotive. Having been trained as an artist, my mechanical/technical knowledge boils down to "if it moves, grease it; if it's not meant to move, bang it in harder!" Thus this series is a wonderful revelation to me. Yes, I have read many of the books/articles by O.S.Nock, H.Holcroft, and the like, but "Train Waiting" has put the works of such as these afore-mentioned gentlemen into much greater clarity.
Surely there's a book lurking within Train Waiting's erudite work on this Forum...

Some notes from the RCTS book on BR Standard Pacifics, partly in paraphrase so as to not just quote the entire part.

Until Mr Ell stared his work at Swindon, it wasn't realised how much a small adjustment in dimensions could produce a large difference in steaming rates. His work showed that 'rule of thumb' or calculations often did not result in best performance. John @Train Waiting has mentioned the 'Manor' class, and Ivatt cl4 where adjustment of dimensions vastly increased the outputs.

Mr Ell showed that the 'Britannias' and 'Clans' were best built with single, rather than the proposed double, chimney. Dimensions were drawn which included Ell's work, though, once again, some improvements were found after initial building when the locos were tested on stationary (Swindon, and the new one at Rugby) plants, or on the road.

The book doesn't include details of these alterations, but mentions that they are available in BR test result archives. With experience in service, the 'Clans' had the blastpipe narrowed by 1/2" after trials with a Std Cl 5; this small modification increased the draft.

Finally, 71000.

It had been proposed to fit a Kylchap system (sorry, John), but actually a double chimney was designed, based on the work by Swindon; with 'the actual design based on  that of the GWR Dean Goods built prior to the turn of the century'!

Perhaps Mr Cook at Doncaster was 'on the right lines' all along with the A4s and V2s (but actually, a better solution for these classes was found).

Martyn

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 97


Hello Chums

The Final, Exhausting Section of Our Gloriously Brief Mini-Series

'Doubling Up - 1'

We've identified the blastpipe conundrum: big reduces back pressure but limits the draught. Will the enginemen resort to using a 'Jimmy'?  Small gives a good draught at the expense of increased back pressure and resulting coal consumption. It might also pull the fire to bits when the engine works at long cut-offs.

And, by the time of the Grouping, we were entering the era of the truly Big Engine and the chances are it will have more than two cylinders, with a resulting higher swept volume. That's more exhaust to get out to the sky, probably requiring a larger blastpipe orifice area. But at the expense of steaming? A good example of this is the LMS three-cylinder '5XP' or 'Jubilee' class 4-6-0s. Introduced in 1934 and unsatisfactory steamers from the start. A solution was found which, amongst other things, involved reducing the diameter of the blast pipe. But, was there a better solution?

As far as I'm aware, the ultimate answer first appeared in Great Britain on the LNWR as early as 1897.

The Conventional Double Chimney

An answer to the conundrum was to have two blastpipes, giving a greater combined orifice area, whilst keeping each individual blastpipe to a reasonable size.

From 1897, Mr Webb fitted a few engines, including his first two four-cylinder compounds and the sole four-cylinder simple, No. 1501, with double chimneys, arranged in a single casing. The smokebox had a horizontal partition and the blast pipes were arranged so that one drew the exhaust gasses from the lower rows of boiler tunes and the other from the upper rows. The arrangement was that the exhaust from two cylinders passed into one chimney and from the other two into the second chimney.

The idea wasn't new - a few engines in Chile had a similar arrangement. Mr Webb's application was ingenious - too ingenious for its own good - and, after a couple of years, Mr Webb abandoned it. I'm glad that I've found a not very good photograph of one of these rarities - the picturingham is from that photograph:-





Which brings us to the Grouping era. As far as I'm aware the Southern and LNER didn't use conventional double chimneys. [Please note my emphasis - we'll come back to this point in a later part.] Nor did the Great Western until the introduction of the 'County' two-cylinder 4-6-0s in 1945.

In 1933, Mr Stanier introduced his first two prototype 'Pacifics', Nos 6200 The Princess Royal and 6201 Princess Elizabeth. These had a short-firebox boiler with low superheat in the Swindon tradition. Their performance wasn't as good as hoped for and No. 6201 was fitted with an experimental double exhaust system. The exhaust of the inside and outside cylinders was taken separately to one or other of the blastpipes, instead of being combined in the usual way. Sort of shades of Mr Webb. As you might imagine, the experiment wasn't a success and the engine swiftly reverted to a single chimney arrangement. The eventual answer was a higher superheat and a firebox with a combustion chamber. The remaining 10 'Princess Royals' were delivered in 1935 with the new boiler.





[LMS No. 6201 Princess Elizabeth with the short-lived experimental double chimney. LMS Official Photograph.]


The next development on the LMS was the 'Princess Coronation' class 'Pacifics' introduced in 1937. These represented a great improvement on the 'Princess Royals'. Some examples, including the first ten, were streamlined, others commencing with a batch built in 1938, weren't. It was one of these non-streamlined locomotives which achieved immortality in February 1939 - No. 6234 Duchess of Abercorn. The LMS had arranged some tests, ostensibly to establish whether certain trains could be combined over the Northern Banks. No. 6234's first test result, although not published, was understood to be disappointing.

The second test, on February 26, 1939 saw her achieve a drawbar horsepower of around 3,300. A British record and, possibly, a world record for a hand-fired simple-expansion locomotive. What was the reason for the remarkable difference in performance? She had received a double chimney. Later construction of the class had this from new and the single-chimney locomotives all received double chimneys.

This was not lost on Mr Stanier and his team and, in 1940, it was decided to resolve the still-at-times disappointing performance of the 'Jubilees' by rebuilding the class with larger boilers. The War slowed progress and it was a considerable achievement that, in early 1942, Nos 5735 Comet and 5736 Phoenix entered service rebuilt with the 2A boiler, which featured a double chimney. And what engines they were - in 1943 they were reclassified from '5XP' to '6P', the same as a Royal Scot. LMS '6P' became '7P' in BR days. The LMS announced the rest of the 'Jubilees' would receive the same treatment but, in the event, that didn't happen. There was a more pressing need.

The 'Royal Scots' had been in front-line service for around 15 years and the earlier examples were becoming due for new boilers and cylinders. In addition, there was trouble from leaky smokeboxes, a problem alluded to earlier. In December 1942, authority was given for the 20 most needing 'Royal Scots' to be rebuilt, chosen by the state of their frames or cylinders. Although extensive rebuilds, these were known officially as 'Converted Royal Scots'. No. 6103 Royal Scots Fusilier was the first, in June 1944. The process took a while with the last to be converted, No. 46137 The Prince of Wales Volunteers (South Lancashire), not appearing until 1955. As part of the 'Conversion', the 'Royal Scots' were fitted with the 2A boiler and double chimney. These were magnificent locomotives and were, with the Bulleid 'Pacifics', the heroes of the 1948 Locomotive Exchanges.*




[Converted 'Royal Scot' 4-6-0 No 46115 Scots Guardsman at Carlisle Citadel on 18 August 2021. She gave us a splendid run over the Settle & Carlisle in both directions.]


Sir William Stanier had been seconded to Government service in 1943, resigning from the LMS in 1944. CE Fairburn, who joined the LMS as Electrical Engineer in 1934, was appointed Deputy Chief Mechanical Engineer and Electrical Engineer in 1937 and became Chief Mechanical and Electrical Engineer on Sir William's departure. Mr Fairburn concentrated primarily on diesel and electrical traction, leaving steam locomotive matters largely in the especially capable hands of Mr Ivatt the Younger. Mr Fairburn was in poor health and died at the end of 1945. He was succeeded by Mr Ivatt who was something of an enthusiast for double chimneys, as we'll discuss in the next part.

I haven't forgotten about No. 6170 British Legion, rebuilt in 1935 from the unfortunate high-pressure locomotive Fury. She will appear in a later part.

* Here's Cecil J Allen on the performance of the 'Royal Scots' during the 1948 Locomotive Exchanges:

But for steam-raising it was the relatively small boiler of the 'Royal Scot', with the small firegrate [31.3 sq. ft.] already mentioned and the superheating surface of no more than 357 sq. ft., that was to provide the greatest surprises, for many of the exploits of these most ably handled 4-6-0s practically equalled, and in some cases beat, those of the 'Pacifics' in full test conditions'.

Cecil J Allen The Locomotive Exchanges, Ian Allan, London, 1948, Page 69. I have the late Dr Tuplin's copy of the book and is is full of pencil annotations. Many are uncomplimentary - such as 'Rubbish'.

Once again, my thanks to @martyn for reviewing the draft text.


'N' Gauge is Such Fun

Many thanks for looking and all best wishes.

Toodle-oo

John