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

[chrism]

And I would say, yes ... 

On the above mentioned Prussian G8 the superheater enabled the increase of the cylinders compared to their "wet steam" predecessors, the G7.1.
On the G7.1 the cylinders had a bore and stroke of 520x600 mm which was increased to 550x660 for the first few G8s. Within three years the G8 cylinder diameter was enlarged three times to 575, 590 and 600 mm, enabled by the improvements in superheater technology between 1902 and 1906.

But could that not be that the superheater improvements enabled a greater steam delivery rate to the cylinders, allowing larger cylinder to be fitted and, therefore, an increased power output?

According to Wikipedia, as well as the cylinder diameter increase, they also increased the grate area, evaporative surface area and superheater surface area, all of which would help to create more steam to suit the larger cylinders.

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 40


Hello Chums

First things first.  Thank you very much, chums, for all these helpful contributions to the discussion.

*

British locomotive engineers, or, at least, some of them, took an interest in developments overseas and Dr Schmidt's invention attracted attention.  As far as I'm aware, first from the distinctly scientifically-inclined Locomotive Superintendent of the Midland Railway, Richard Deeley, who requested his Board's approval to build forty 4-4-0s fitted with Schmidt superheaters.  This was in April 1904, barely two years after the introduction of the first KPEV 'G8' 0-8-0.  The cost of the superheater apparatus would be about £250 per engine, with an additional royalty fee of £30 for each superheater.

Perhaps Mr Deeley's understanding of the significance of Dr Schmidt's invention made him too enthusiastic and he should have requested permission to equip a couple of engines in the first instance, as a trial.  But the Midland's Board - Successful Northern Men, I like to think - based in the centre of the Railway Universe - Derby - took exception to the cost; especially the royalty fee.

I think it's important to give Mr Deeley acknowledgement for trying.  Credit for succeeding goes to a practical engineer who looked like the member of the Devonian Squirearchy he was.  And to his Board of distinctly aristocratic composition.

In May 1906, Great Western Railway 'Saint' 4-6-0 No. 2901, later named Lady Superior, was the first British locomotive with a fire tube superheater.  And a true Lady Superior she was.

A few months later, that excellent engineer and Chief Mechanical Engineer of the Lancashire & Yorkshire Railway, George Hughes, fitted Schmidt superheaters to a couple of 0-6-0 engines.

What really attracted everyone's attention was the exploits of two LB&SCR 'I3' 4-4-2T engines.  Douglas Earle Marsh, the company's Locomotive Superintendent, had travelled extensively in Europe, observing the latest developments and, by 1907, was considering the use of superheating.  With a lot of assistance from the Schmidt Superheater Company, including Dr Schmidt himself, No. 21 appeared in 1908.  After some further design tinkering, she was followed by Nos 22-26 and then No. 77-81.  At the insistence of the company's Board some of the class were built without superheaters.  In service, the superheated examples were better, much better.

Which brings us to the newly-introduced through train working of the 'Sunny South Express' in November 1909.  LB&SCR and LNWR locomotives worked this train turn about between Rugby and Brighton - a round trip of 264 miles.  Ninety miles between Rugby and East Croydon were run non-stop - no opportunity for the tank engine to take water.

The 'I3' engines used, Nos. 23 and 26, achieved remarkable coal and water consumption figures - 27.4 lbs and 22.4 gals per mile.

The LNWR used one of George Whale's 'Precursor' 4-4-0s, No. 7 Titan, which consumed 41.2 lbs and 36.6 gals per mile.  The 'Precursor' was worked hard and was reputed to have arrived in Brighton on occasions with her smokebox glowing red.

These events caused a stir.  One result of which was the LNWR's new 'George the Fifth' 4-4-0s, designed by Mr Whale's successor, Mr Bowen Cooke, were fitted with Schmidt superheaters.

Other railways were fitting Schmidt superheaters as well and, in some cases, this led to what we might think of as 'backwards progress'.  We have already seen Mr Churchward advocating higher boiler pressures and stating that, if cleverly designed, carefully made and diligently maintained, these did not incur the fearsome maintenance costs many engineers assumed.

Contrariwise, we also saw George Hughes of the L&Y advocating lower boiler pressures and how this resulted in the LMS Hughes/Fowler 2-6-0s having sloping outside cylinders due to their large diameter.

Some other engineers, good engineers at that, tended more to Mr Hughes' view.  The first Scottish engine with a Schmidt superheater was JF McIntosh's Caledonian Railway 4-4-0,  No. 139 of July 1910, a development of the 'Dunalastair IV' class.  Mr McIntosh took advantage of the superheater to lower her boiler pressure from the 180 psi of the the 'Dunalastair IV' class to 165 psi. Nevertheless, she was an outstanding performer and was used on the prestigious trains.  She showed a coal saving of 16 per cent per ton mile.

Well advanced in design when No. 139 appeared, James Manson's two G&SWR superheated 4-6-0s, Nos. 128 and 129, entered service in 1911.  These were equipped with 21 element Schmidt superheaters which, on test, gave steam temperatures ranging from 600^oF / 315^oC to 650^oF / 343^oC.  These two engines gave sparkling performances; it was calculated they could develop 900 drawbar horsepower (dbhp).  Their predecessors, the '381' class 4-6-0s, built between 1903 and 1911, developed a maximum of 750 dbhp.

Such was the power of superheating (bad pun, sorry).  By the way, Mr Manson reduced the boiler pressure on Nos. 128 and 129, from the 180 psi of the '381' class, to 160 psi.

The royalties required to use Schmidt superheaters made some locomotive engineers file patents for their own fire tube superheaters - these all worked on the basic Schmidt principle - and this accounts for the use of terms like 'Robinson superheater'. Superheaters became fairly widespread in use, led, in numbers, by the GWR, LNWR, NER and Midland.  After the end of the Great War, fire tube superheating was the norm for most express passenger locomotives and many others.  The Furness Railway remained an exception, even on its 4-6-4T engines.

These superheaters generally corresponded reasonably well with Dr Schmidt's recommendation to equalise the free gas area through the flue tubes and boiler tubes - the 50/50 ratio.  The NER experimented with a ratio of about 60/40 on the three-cylinder 'Z' class 'Atlantics' (later, LNER 'C7') from 1913, but this reverted to a more 'normal' ratio in LNER days - the 20 per cent reduction in evaporative heating surface was found to be too much.

Older designs were sometimes reboilered with superheaters, a good example being Mr Urie's reboilering of Dugald Drummond's LSWR 'T9' class.




[I don't think the extended smokebox and Urie chimney help the looks of the 'T9' but they made it a better engine.]


I am conscious that I have been guilty of a 'dog that did not bark in the night-time' approach to Mr Churchward's 'Swindon superheater', patented in 1908, and the subsequent GWR policy that prevailed until 1944.  For me, sitting here, between the Forth and the Tweed, commenting on Great Westernry might be considered presumptuous, at least.

But, unless anyone else cannot resist taking that particular nettle in hand, I'll attempt to cover it in the next part, which will be the last in the boiler and firebox section.  We have got to the point where there is steam ready to do some work and, by the end of the Great War, that is likely to be superheated steam, in the big engines at least, sitting in the superheater header and awaiting our pleasure.  After our Great Western discussion, we will, hopefully, get on to the engine part of the locomotive in Part 42 of this mini-series.

If there is a bit of a hiatus, it's because Mrs Poppingham and I have COVID - four-year-old newsingtons for to-day. Perfik!


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Pip-pip

John

[Ali Smith]

Thank you for another fascinating post. I hope you and Mrs P. get well soon.

All the best,

Ali

[Nbodger]

Hope you both recover quickly and there are no after effects.

Best Wishes and Take care

[Hiawatha]

But could that not be that the superheater improvements enabled a greater steam delivery rate to the cylinders, allowing larger cylinder to be fitted and, therefore, an increased power output?

According to Wikipedia, as well as the cylinder diameter increase, they also increased the grate area, evaporative surface area and superheater surface area, all of which would help to create more steam to suit the larger cylinders.

I have read through my literature about Prussian locomotives, the "bible" Preußen-Report (vol. 2, 5, 6 – express, wet steam goods and superheated goods engines), and right from the beginning a reduction of coal and water consumption was expected as well as an increase in power.
Condensation was considered to be so severe that only 2/3rds of the generated steam would perform work in the cylinders of conventional steam locomotives, with wet-steam compounds doing slightly better at 3/4s. However, at the same time it was expected that the superheated steam would generate more power and thus larger cylinders were fitted as well.
 
But the sizes of cylinders, grates and boiler/superheater were all trial and error on both the express 4-4-0, class S4, and the goods 0-8-0, G8. There were still further enlargements and modifications after the S4 and G8 – but these larger engines were then considered new classes, S6 and G8.1.


I just noticed that there may be a bit of misinformation here. (But then the Prussian tangent is not really that important on this thread.)

After some years of experimentation, initially with smokebox superheaters (please see Part 38 to find out about these), Wilhelm Schmidt designed a practical fire tube superheater.  The first was fitted to a Prussian State Railways' (KPEV) 'G8' 0-8-0 in 1902.

According to the Preußen-Report vol. 6, the first installation of the fire tube superheater was in 1903 on the LAG (Lokalbahn AG Munich) 2-6-0 No. 18.
The G8 was built with the earlier smokebox superheater (which was also a Schmidt design) from 1902 to 1906. Only from the 154th engine in 1906 was the newer fire tube superheater used on the G8.

[Train Waiting]

Thank you very much, Peter.  That came from a normally-reputable source.  But a British source.

At least it acknowledged Dr Schmidt's earlier involvement with smokebox superheaters and gives him full credit as the inventor of a working fire tube superheater.

You might find references to the LB&SCR 4-4-2T which mention the superheater but fail to acknowledge the rest of Dr Schmidt and his company's contribution.  Apparently, he set the valves on the first engine himself.

Thanks again and all good wishes.

John

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 41


Hello Chums

Very special thanks to Peter @Hiawatha for his helpful contribution.

*

Right-oh - fools rush in and all that jazz.  Great Western Railway and superheat.  What's the story.  I'm not an expert on anything, especially the Great Western.  But, we have seen something peculiar going on the pre-Great war period.  Let's see if we can make sense of it together...please contribute.  Even if it's to tell me I'm a half-wit.

We have established the basics of the eituation, I think, as:

Mr Churchward disagreed with many of his contemporaries regardin high boiler pressures - he established 225 psi as a standard for large engines.

Some other engineers saw superheating as, in part, a way to reduce boiler pressures and, they though, cost.

For reasons that we'll examine in the third section, about the engine, GWR locomotives were head and shoulders above those on other railways until the 1920s.  Interrchange trials on the LMS and LNER proved this.  The LMS even asked the GWR to build it some 'Castles'.  This was declined.  Just as well, the private locomotive manufacturers would have gone to court quicker than one can say "Swindon Works" if this had happened.

Great Western engines were optimised to burn Welsh bituminous steam coal mined in the area between the (Newport) Western Valleys and the Aberdare/Rhondda Valleys.  This coal is the stuff of legend and is not anthracite.

Finally, a couple of new points.  Superheating was to a great extent enabled by reliable piston valves - can we please take this 'as read' as it's one for the next section?

Also, by massive improvements in another industry - oil technology.  Mrs Poppingham's Honda 'Jazz' motor car has a performance far in excess of what one would expect fifty years ago.  And, it's an 'old person's car' not a sporty thing.  I can assure you it runs on fairly fancy oil.  My old OHC Norton 'Singles' like 'Castrol R' and I like the smell it makes.  We used to pour a dash of cooking oil into the petrol tank of our 250cc BSAs and suchlike so they smelt like 'Gold Stars'.

Superheating required oil to withstand the higher temperatures being achieved and these were coming on the market at a convenient time.

Let's assume Mr Churchward was Great Britain's second most innovative locomotive engineer and he most certainly knew what he was doing.

Ands, another one for the next section. but I'll mention it on passing so you are aware I know about it.  Mr Churchward favoured long piston strokes.

*

The one thing Mr Churchward was keen to avoid was steam condensing in the cylinders so he set the 'Swindon superheater' to give a temperature to achieve this.  Then built a lot of superheated engines - 750 by 1912; about a quarter of the company's locomotive stock. The LNWR was next with 200.

Why did Mr Churchward stick to the two row superheater giving an approximately 30/70 flues to boiler tubes ratio?


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

John

[chrism]

Why did Mr Churchward stick to the two row superheater giving an approximately 30/70 flues to boiler tubes ratio?

Presumably he found that that ratio gave him the best option for sufficient evaporative surface and superheating.

As I said previously, adding superheater flues reduces the number of small tubes that can be fitted and, thus, the overall evaporative surface. If the boiler can't make sufficient steam in the first place there's no point in superheating it.

[martyn]

One thing not mentioned in the once again excellent posts are snifting valves.

AFAIK, these were not fitted to saturated engines, but were on superheated ones to allow air to circulate with regulator closed.

It was appreciated by locomotive engineers that when the regulator was closed when running, the cylinders would act like a vacuum pump drawing smoke box ashes back into them; also, with the regulator closed and hence no steam flow through the superheater tubes, these tubes would be 'dry' and prone to overheating. The answer was to fit a valve-frequently in pairs, so that when the regulator was closed, outside air would be drawn into the superheater tubes to keep them 'cool'.

There were variations in design; a common one looked like the 'pepperpot', another like a mushroom. these were usually in pairs (one for each cylinder?) with one each side of the smokebox top and behind the chimney.

Mr Gresley's design was was usually, at least in multi cylindered locos, a single circular perforated unit placed just behind the chimney.

Some CMEs officially required the regulator to be left just open and allow a minimum steam flow through the superheater and cylinders when coasting, but observations suggested that this was not always what happened 'on the road'. When the snifter valves worked, they chattered as air was drawn in, and of course, were one way so that steam could not escape back to atmosphere when the regulator was opened.

Thanks again, John, and I hope I haven't jumped the gun on this one.

Martyn

[martyn]

Regarding the later LNER pacific boiler policy, amongst other facts, the RCTS book says;

(Peppercorn A2); the boilers of the A1 and A2 had a smaller [tube} heating surface...but a larger firebox heating surface. This meant a more rapid evaporation only resulted in wet steam carried over.....where the superheater was inadequate to raise the temperature sufficiently. .......this highlighted the fact that Doncaster's policy with [later pacific] boilers was wrong, as each new variety of high pressure [250psi] boiler had an identical tubing arrangement whether the barrel was 16' or 19' long. Deficiencies were masked by employing as large a firegrate as possible....and ignore subsequent higher coal consumption'.

To be added to.

Martyn

[Train Waiting]

I'm so sorry, chums.  In my Covid befuddled state last evening, I managed to press 'post' rather than 'save draft'.  Hence the curt ending which I've tried to ameliorate to-day.

I'll continue with the postington (possibly with another one) but it won't be to-day.

Sorry for the mess-up.

Covid is such fun!

With all good wishes

John   

[Bealman]

No worries, mate. All will be well. 

[martyn]

A final (I hope!) tail lamp to the later Doncaster Pacific boiler designs.

The RCTS again;

Class A2/3 on trials against V2;

'it was noted that whereas the surface heating figures were identical.....the temperature of the smokebox gases in the A2/3 were higher, ie more heat was lost through the chimney.....this was assumed to be due to an imbalance in the size of firebox and boiler barrel. ......although the temperature of the superheated steam was higher in the A2, it was not sufficiently so to benefit from the higher boiler pressure. '


However, both the Thompson and Peppercorn types could generate 2000hp+, which was of use handling the heaviest trains.

It goes on to say what I have posted before, that the larger firebox was later deemed wasteful of coal, water, and power, and could only be used to advantage on the heaviest trains. This latter is repeated in the chapter about the Peppercorn Pacifics, which were developments from the Thompson designs. They were less economical than the A4s on similar duties; it is to be remembered that the A4 boilers were a development of the A1/A3 boiler, which was itself scaled from the Pennsy K4 which had been extensively tested before entering service, and has been mentioned in the thread before. The later Pacific boilers had lost the relationship between firebox, small tubes, and superheater that had been evolved for the other classes.

Hope at least some of you are still interested! It does shown what a complicated relationship there was/is between the various parts of a steam loco.

Martyn

[Papyrus]

Blimey! My head is definitely beginning to hurt. So much I don't know...

Thanks all!

Cheers,

Chris

[maridunian]

Blimey! My head is definitely beginning to hurt. So much I don't know...

Thanks all!

Cheers,

Chris

Do you remember a few years ago when a bunch of British plane spotters were arrested near a Greek military airfield? They were locked up for days. Unfortunately for them, their interrogation began with the question, "Tell us everything you know ...."

Mike