So, outside cylinders were only avoided in Britain because of the loading gauge?
Are there any other advantages of having inside cylinders? I ask as I always feel that locomotives without a connecting rod are missing something ...

I am more used to German types, and especially the northern Germans avoided inside cylinders like the plague (like Robert Garbe of the Prussian State Railways with his P8, when only after his retirement a much needed 3-cylinder P10 could be built), or later Richard Paul Wagner of the Reichsbahn who made trials between 2- and 3-cylinder types (BR 43/44) where the 2-cylinders always won with the only reason of being cheaper to build and run.
Only later when the 2-cylinder BR 43 really needed to show that they could perform just as well and failed miserably, were the BR 44 built for heavy goods trains.

Inside cylinders were avoided because maintenance was more difficult, and the complicated to manufacture "Kropfachsen" (sorry, I didn't find the English term for this) were seen as a weak spot instead of the straight axles for two outside cylinders.

"Kropfachse" of a German BR 44 3-cylinder:


© Armin Schwarz, from https://hellertal.startbilder.de/bild/deutschland~bahnhoefe-in-rheinland-pfalz~betzdorfsieg/374667/treibachse-kropfachse-einer-schweren-gueterzug-dampflokomotive-der.html


In southern Germany (Bavaria, Baden, Württemberg), inside cylinders were more common – but only with 3- and 4-cylinder locomotives. 2-cylinders were also mostly built with outside cylinders.

One reason for the unequal wheelbase in 460s, and 060s, was because of the position of the firebox.

This generally fitted more or less between the middle and trailing wheels, or if sloping firebars, above the trailing and then down to the ashpan.

On a pacific, or anything else with a trailing bogie or pony trick, the firebox was supported above it.

I think...

@Hiawatha

Crank axle.

Not sure why the British continued with inside cylinders for so long. Maybe it was the desire to look tidy, and not have things like pipework and auxiliaries on view. Without going through books, there were a number of accidents caused by the crank axle failing in service.

But simplicity and ease of maintainence became keynotes as labour for keeping locos running became in shorter supply, and presumably also because of time taken to access and oil inside gear. Hence the change to outside cylinders.

It may be the racking forces of outside cylinders which lead to the use of inside. With inside, the piston thrust was close to the centre line of the chassis, but with outside, the thrust was further from the centre line causing frames to flex if not sufficiently braced. The inside cylinder steam chest could be used as part of the bracing at the front, whereas, I think, the outside couldn't.

Martyn

** I've deleted an incorrect reference to the B12s

Martyn

Quote from: Webbo on January 10, 2025, 07:31:39 AMJohn

I've got a question for you that you don't need to answer if it at all derails your thread. In the last photo of the model 4-6-0, we see the centre drivers being closer to the front drivers than the rear ones; that is, they are not quite in the middle. It seems to me that there are many 4-6-0s that share this asymmetry such as the various class 5 locos. Yet, in Pacific wheeled locos, the middle drivers are usually right in the middle.

Webbo

Thank you, Ian and Peter @Hiawatha  for your helpful questions.

And special thanks to @martyn for his splendid answer which leaves me with little to add - my favourite type of discussion! This thread thrives on discussion, and questions and other contributions are warmly welcomed.

The asymmetric placing of axles in six-coupled types is very common.  Standard Derby practice for the wheel centres of six-coupled engines was 8 ft + 8ft 6 in.  ES Cox once wrote that these 'dimensions had become sacred with the passage of time.'

An amazing amount of MR/LMS six-coupled locomotives have these dimensions. Later on, once Sir William Stanier had LMS locomotive matters under control, the dimension no longer was 'sacred' and his 'Black Five' 4-6-0 has 7 ft + 8 ft spacing.

This feature can be seen all over the world, with some choice examples in the USA. The 'Big Goods' or 'Jones Goods', Britain's first 4-6-0 for home rails, had coupled wheel centre spacings of 5 ft 6 in + 7 ft 9 in.

Martyn has identified the reason for this distinctive feature, seen on many (but not all) six-coupled locomotives - the location of the firebox.  In the typical British 4-4-0 the firebox sits more-or-less between the coupled axles.  The SR 'Schools' class 4-4-0 had a 10 ft spacing for its coupled wheels. Big firebox!

The typical 0-6-0 had its firebox between the rear two coupled axles. As did early examples of the 4-6-0 and 2-6-0.

Unlike for the pioneer 'Jones Goods', in later 4-6-0 types, the larger firebox sits over the rear two coupled axles and various designers had their own ways of achieving this.  Sometimes more successful than others as certain configurations of grate were difficult to fire and maintain steam.  The SR 'Lord Nelsons' were considered to be especially difficult for fireman not used to them.

You might just have been able to make out through the mists of my coarse photography, that the 'B12' 4-6-0, seen in Part 50, has symmetrical spacing of the coupled wheels.  7 ft + 7 ft was the dimension.  This class had its firebox pretty much over the centre coupled axle.  Union Mills caught this feature well in the model.

Although not universal, most British 4-6-0 locomotives have their ashpan sloping forward between the rear coupled axles.  Having the little bit of additional clearance allowed for by asymmetric axle spacing provides for more room at the front of the ashpan.

By the way, asymmetrical wheel spacing was not confined to six-coupled types.  For example, the LMS '8F' 2-8-0 had 5 ft 6 in + 5 ft 6 in + 6 ft 3 in spacing.

I'll return to Peter's question in another postington.

With all good wishes

John

Quote from: Hiawatha on January 10, 2025, 08:29:04 AMSo, outside cylinders were only avoided in Britain because of the loading gauge?
Are there any other advantages of having inside cylinders? I ask as I always feel that locomotives without a connecting rod are missing something ...

Thank you very much, Peter.

And thank you for the excellent picture of the crank axle (Kropfachsen) - I had been looking for one of these to illustrate a future post!

Your question is especially helpful because it addresses something I edited out of an earlier part (I edit out lots!) to get the word count down.  You have given me an opportunity to include it.

Inside cylinders became very common, although not universal in Britain.  But the earliest locomotives had outside cylinders.  Why the change? 

We often think of the first locomotive with inside cylinders as being Robert Stephenson's 2-2-0 Planet, of September 1830 for the Liverpool & Manchester Railway.  However, Edward Bury had built an inside-cylindered 0-4-0, Liverpool, which was tried on the same railway in July 1830. Bury locomotives were distinctive and were important for a while before their innovative designs were overtaken by other developments.  The Furness Railway 0-4-0, No. 3 Coppernob, in the National Collection is a treasured relic of the type.

I have written before about the personal relationship between Robert Stephenson and Richard Trevithick, which provides a nice bit of background about why Planet had inside cylinders.

Robert Stephenson said that Mr Trevithick told him about when he was repairing an old Cornish steam engine which had a bare metal cylinder.  He built a brick casing round the cylinder with a space in which hot gasses from a fire could circulate, keeping the cylinder warm.  The fuel consumption of the engine with the hot-jacketed cylinder was a fifth of what it had been before.

Duly impressed, Mr Stephenson designed Planet with the cylinders jacketed by the smokebox and found a considerable increase in power was obtained compared with the, very slightly, earlier Northumbrian . This set Mr Stephenson firmly on the path of inside cylinders, although the use of the smokebox to provide a hot jacket was phased out over time.

The inside-cylinder type was neat and the forces exerted by the pistons were inside of the wheels and frames.  This reduced the 'rocking couple' effect and made for smooth-running locomotives without the 'punching' from side-to-side action often seen (and felt) with outside cylinders.

Which gives me a good opportunity to include a quotation from the late Derek Cross:

'On a light train from Weymouth to Bristol, composed admittedly of some of the Great Western's more elderly and less creditable stock, a 'Hall' making a spirited attack on the climb to Brewham started with vigour and set up the most alarming fore and aft motion I have ever experienced in a train.'*

Mrs Poppingham and I experienced something a little bit similar on the Torbay & Dartmouth Railway with a large outside-cylinder Great Western 2-8-0T climbing Greenway Bank.

I recall they had to experiment with the locomotive to tender coupling on the 'Britannias', when they were new, to attempt to overcome this phenomenon which especially manifests itself in locomotives with two large outside cylinders.

In summary, the idea of inside cylinders, which was not completely new, was adopted for reasons of thermodynamic efficiency and then, giving a nicely-running locomotive, remained in use for years until the time of the coming of the Big Engine, around 1900, brought a reappraisal.

* Mr Cross' introduction to Locomotives Illustrated No. 10 'GWR 'Halls', 'Granges' & 'Manors'', Ian Allan, 1979.

With all good wishes.

John 

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 51


Hello Chums

You Can't Beat Cubes!

Apologies for using an expression from American motor-car and motor-cycle parlance.  The normal American response to a need for more power from an internal combustion engine was simply to make it bigger.  Most of the world measures internal combustion engine displacement in litres or cubic centimetres.  Three-litre Bentley or my 500cc motor-bicycles. The Americans preferred to use cubic inches.  A 750cc Norton is 45 cubic inches. Harley Davidson 'V' twins start at around 74 cubic inches (1200cc) and get bigger and more expensive.

For steam locomotives, the written sources often quote cylinder size but I cannot ever recall seeing cylinder volume used as part of a discussion about British locomotive design.  Perhaps you have - please let me know. I'm going to attempt it and will use cubic inches as a comparative measurement.  Here goes...

*

In Part 50, we discussed the dawn of the era of the Big Engine and ended by mentioning Mr Urie's 'N15' 4-6-0s for the LSWR, later called 'King Arthurs' as part of the Southern Railway's publicity drive.  This class started life with massive 22" x 28" outside cylinders, later reduced on all but one of them.

Two 22" x 28" cylinders provide a volume of 21,286 cubic inches.

The BR 'Britannia' 4-6-2 and '9F' 2-10-0 classes have the same sized cylinders: two - 20" x 28" or 17,593 cubic inches, which is the same volume as a 'B12' 4-6-0 of almost fifty years earlier.

Before we ask what's going on, let's consider an LMS 'Black Five' and an LNER 'B1':

LMS: two - 18 1/2" x 28" = 15,053 cubic inches

LNER: two - 20" x 26" = 16,336 cubic inches

As we have seen, the period from, say, 1900 until round about the Grouping saw a profusion of locomotives with two large cylinders. Do you remember the Horwich Drawing Office having to put high inclined cylinders on the 'Horwich Mogul' 2-6-0 to avoid bashing platforms?

'Mogul': two - 21" x 26" = 18,011 cubic inches

More than a 'Black Five', 'B1', 'Britannia' or '9F'.  Blooming heck!

Why do the later types of locomotive have reduced cylinder volumes?

Are you getting a feeling there might be more to it than, 'Can't beat cubes'?

There is and, in this part, I'm hoping to start to weave some themes together.

*

"When you come to a fork in the road, take it."

[Yogi Berra]


I think British steam locomotive development came to a fork in the road about 1900 or so. New Century. New Monarch. New Approach?

The dawn of the era of the Big Engine.

Also, the introduction of superheating and the widespread use of piston valves.  We'll come back to piston valves in more detail in a later part, but I deliberately introduced them before this part of the short mini-series as they form an important part of the discussion.

For some sort of explanation for the large cylinder volumes in use during the early 20th Century, we ought to look in the direction of the engine's boiler. Locomotive engineers thought (and said) a lot about boilers:

"The modern locomotive problem is principally a question of boiler."

GJ Churchward, Large Locomotive Boilers, a paper read for the Institution of Mechanical Engineers, 1906.


Slide valves had large wearing surfaces which were lubricated by water droplets in saturated steam.  One of the worries about using superheated steam was valve and cylinder lubrication.  Improvements in oil technology and the characteristics of piston valves made superheating a more practicable proposition.

That's not to say one could not have slide valves on a superheated engine.  In fact, Mr Collett made something of a specialty of this with his inside-cylinder locomotives for the Great Western.




[But not on the '56xx' class, as can be seen from the valve chest covers below the smokebox.]


I suspect the traditional GWR low-degree superheat was helpful in this regard.

But, generally, superheated locomotives have piston valves.

I believe, at the time of the widespread use of piston valves and the introduction of superheating, most locomotive designers took the wrong fork in the road, at least for some time.  You see, many saw superheating as a way to avoid increasing boiler pressures or, in some cases, actually reducing them*, convinced that would reduce boiler maintenance costs.  As we saw in an earlier section, Mr Churchward argued that with cleverly designed and carefully constructed boilers higher pressures would not lead to higher costs.  You might recall he went to 225 psi as a standard pressure for his large boilers.

His counterparts were very slow to follow.  George Hughes of the L&Y/LNWR/LMS was especially opposed to high boiler pressures.  This was a shame as he was a good engineer.  Here's what ES Cox, who was in Horwich Drawing Office at the time, wrote about the steeply inclined cylinders of the 'Horwich Mogul' 2-6-0:

'This was necessitated by the 21" diameter cylinders which had to be used due to Hughes' unshakeable determination not to use any boiler-pressure higher than 180 lbs. to the sq. in.'


To obtain the power the designer wanted, with the impediment of a boiler pressure of 180 psi, required these large cylinders.

The Urie 'N15' 'King Arthurs' also had a 180 psi working pressure.  When Mr Maunsell  introduced his improved version in 1925, built to the Southern's composite loading gauge (the 'Scotch Arthurs'), he used a 200 psi working pressure.  His later 'Lord Nelson' 4-6-0 of 1926 and 'Schools' 4-4-0 of 1930 had boilers pressed to 220 psi.

The LMS 'Royal Scot' class of 1927, much of the design of which was undertaken by the North British Locomotive Company, used a 250 psi boiler pressure.

Over on the LNER, Mr (later, Sir Nigel) Gresley's original 'A1' 4-6-2 had a 180 psi boiler pressure. After the interchange trials of 1925, where GWR No. 4079 Pendennis Castle demonstrated superiority over 'A1' No. 2545, subsequently named Diamond Jubilee, on LNER metals, Mr Gresley made modifications to a couple of 'A1s', including raising the working pressure to 220 psi.  This work paved the way for his subsequent class 'A3' 'Super Pacific'.

Mr Churchward's lesson of twenty years earlier was, at last, being learnt.

Yes, I know I have sneaked some locomotives with more than two cylinders in to the discussion, but these  examples help us to understand how gradual was the adoption of higher working pressures that led to smaller cylinder volumes.

As the internal combustion people well knew, cylinder efficiency was a better way to improve performance than simply making the engine bigger.

*

There is a major contributor to cylinder efficiency that we haven't mentioned as yet but our virtual travels are leading us there and the discussion will drop into our laps in due course.

In the meantime - a summary:

1900-1925 (ish!) The era of the Big Engine.  Piston valves made superheating a practicable proposition. Most locomotive engineers saw superheating as a way to keep boiler pressures relatively low. A time of some especially disappointing Big Engines compared with the excellent 4-4-0s they were intended to replace.

But:

On the GWR, Mr Churchward had piston valves, superheating and high boiler pressures as his standard practice when King Edward VII was on the throne.  It took around 20 years for the other railways to catch up.

I hope this part has managed, slightly, to weave these various themes together. We'll discuss piston valves some more in the next part of this brief mini-series, although I might include a supplementary part first.

* JF McIntosh introduced the first British locomotive type with a large- diameter boiler, of 4 ft 8 3/4 in, the Dunalastair 4-4-0 of 1895.  The type was developed over the years until the 'Dunalastair IV' series was introduced in 1904.  These weren't superheated, of course, had slide valves and a boiler pressure of 180 psi.

In July 1910, Mr McIntosh introduced his final development of the type - the superheated 'Dunalastair IV'.  With piston valves and the boiler pressure reduced to 165 psi.

Similarly, on the the G&SWR, James Manson's original 4-6-0, the '181' class of 1903, had a boiler pressure of 180 psi.  His superheated development, the '128' class of 1911, had the working pressure reduced to 160 psi. 


Endnote

Please be aware I'm not in any way denigrating the locomotive engineers of the day.  They were under pressure [Thank you!] from their Directors to keep maintenance costs to a minimum and boilers were then, as now, expensive to maintain. Their belief that higher working pressures resulted in increased maintenance costs was based on experience. This appears to have made them reluctant to accept Mr Churchward's contention that this was not necessarily the case.

Rather, what I think this whole episode does is demonstrate the brilliance of Mr Churchward.

*

There's quite a lot in this postington and I'm especially grateful to @martyn for reading and commenting on the draft text.  Any errors or omissions are, of course, mine alone.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John

Many thanks, John, for yet another fascinating discourse. This is proving so educational. In all seriousness, I think you really do have the makings of a very good book here and you should consider adapting it for publication when it is all finished.

Incidentally, the title of the thread is becoming divorced from the contents! It certainly isn't a 'coarse guide' any more and it must surely appeal to anybody with an interest in steam railways, N Gauge or not.

Best wishes,

Chris

Yes, hear-hear @Papyrus ! Come on John don't hide your light under a bushel.

All the very best,

Tim

Quote from: Moonglum on January 12, 2025, 05:49:24 PMYes, hear-hear @Papyrus ! Come on John don't hide your light under a bushel.

But, but, but, there is always a but, if he uses his talent to write a book for publishing, he won't have time to write and post any of his amusing posts on the forum, then more to the point, what would we have to read.

Yes agreed @Nbodger , but...

"The needs of the many outweigh the needs of the few", does anyone remember who said that? Sorry no prizes apart from a copy of John's new book.

Tim

I agree with others this is very educational and can easily see this being a book.
keep up the good work.
cheers
Graham

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 51 -Supplement


Hello Chums

Mr Churchward's Long Stroke

As I mentioned in Part 51, this is a Short Supplement (sounds a bit like a Flying Boat) before we revert to discussing piston valves.

If one looks at Mr Churchward's standard classes for the GWR, it is immediately apparent that 18 1/2 in x 30 in cylinders are standard for the big two-cylinder locomotives.  This can be traced to a document prepared at Swindon in January 1901, when Mr Dean was still in charge, nominally at least.  After a prototype 4-6-0, No. 100, built in February 1901, the standard range of locomotives can be traced back to 4-6-0 No. 98 of March 1902 and 2-8-0 No. 97 of June the same year.

I'd be interested to hear of exceptions, but I think the 30 inch piston stroke was only used, in Great Britain, on the Great Western.  Other railways appear to have regarded a 28 inch piston stroke as the maximum.

Certainly, 18 1/2 in x 30 in bore and stroke look like big cylinders.  How do they compare with practice on other railways which, as we have seen, went up to 22 in x 28 in?  This is where the cylinder volume comparisons we introduced in Part 51 might be helpful.

GWR: 2 - 18 1/2" x 30" =  16,128 cubic inches.

Fairly modest for their time and proof that the 'Churchward Magic' was not due to a high cylinder volume.

The early standard locomotives used a boiler pressure of 200 psi, increased to 225 psi with the introduction of the third 4-6-0, No. 171, in December 1903.

The high boiler pressure, for the time and for about another twenty years, enabled Mr Churchward to use lower cylinder volumes than many of his contemporaries.

Many reference works mention the unusually long stroke, but do not provide a reason.  At least, in my library.  If you have a reliable reference that explains this, I'd be very grateful to hear about it.

What we know, because Mr Churchward was open about it, is his standard two-cylindered locomotives were much influenced by contemporary American practice.  In the USA, outside cylinders with inward-inclined steam chests, containing piston valves operated by inside valve gear was common practice.  Not for much longer, though, as external valve gears soon became the norm. 

Also, piston strokes of 30 in or 32 in were in use.

With regard to the long stroke, I was hoping to find something that gave some sort of explanation.  As you know, I like contemporary sources and original sources even more.  I was especially glad to find this quotation from Mr Churchward:

'I think the author is quite right in the statement he makes that the fast piston-speeds give an advantage in the reduction of the condensation or effects thereof [...] This has been done on the Great Western Railway, where a 30-in stroke on a 55-in wheel is used, which gives very much higher piston-speeds than the author contemplates for his engines.'*

As the cylinder proportions were arrived at in 1901, five years before Mr Churchward introduced superheating to Great Britain in May 1906 with 'Saint' 4-6-0 No. 2901, later named  Lady Superior, I suggest we have the answer as to why he used a long stroke.

For any given wheel diameter, the longer the stroke, the faster the piston speed.

It appears Mr Churchward wanted higher piston speeds to reduce condensation in the cylinders.  Superheating, of course, does that but it was in the future at the time the designs were finalised.

Somewhat the opposite of the designers of internal combustion engines moving to shorter strokes with 'square' or 'over-square' cylinder proportions in order to reduce piston speeds and permit higher crankshaft revolutions per minute.





Mr Churchward's use of '55-in wheel' means he had his '2800' 2-8-0 in mind, so it's absolutely fabulous to have @port perran 's SuperSpiffing picturingham of No. 3822, one of Mr Collett's development of the class introduced in 1938.  The biggest difference is the side window cab.  Martin kindly took the photograph for us, to show the cylinder/steam chest/piston stroke features I mentioned.  Thank you, Martin.

* GJ Churchward speaking in the discussion of George Hughes' paper, Compounding and Superheating, read to the Institution of Mechanical Engineers on 7 March 1910.

It is quoted in: HAV Bulleid, Master Builders of Steam, Ian Allan, London, 1963.  Page 124.

Incidentally, Mr Hughes has the credit for the second British application of superheating, to a couple of 0-6-0 engines, also in 1906.

***

Thank you very much, chums for your especially kind comments on the educational value of this brief mini-series.  These are particularly gratifying as I intend it to be primarily for entertainment.  If it occasionally stumbles into education, so much the better.


'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 52


Hello Chums

Steam Passages

As we return to the subject of valves, and piston valves in particular, I think it might be helpful if we spend some time looking at an ancillary matter - the way the live steam gets to the cylinders.  I think I'll leave the exhaust steam for later.

As we mentioned earlier the live steam gets from the regulator valve to the valve chest by way of pipes, often called steam passages.

The traditional Stephensonian slide valves between the inside cylinders were good as they allowed a reasonably direct route to the valve chest.  Once inside cylinders were larger than 18 in diameter, there was insufficient room for the valve chest to be between the cylinders and the valves were normally placed above the cylinders, but, in some cases, were below.

WM Smith's improved design of piston valves allowed them to be placed either above or below the inside cylinders.  Clearly, above offers a much more direct route for the steam.  But some designers put them below, giving tortuous steam passages for the live steam (and the exhaust as well).

The LMS '2P' 4-4-0 class of 1928 was economical and had low maintenance costs.  It also had a performance below what could be reasonably expected in 1928. The similar looking and similarly dimensioned 'D1' and 'E1' 4-4-0 rebuilds on the Eastern Section of the Southern Railway were amazing locomotives with a truly sparkling performance. There were several reasons which contributed to the disparity in performance and I think we'll return to this case study later¹ (so no picturingham of a Union Mills '2P' at present). One of these was Derby Drawing Office decided to put the piston valves of the '2P' below the cylinders.  In 1928! Yes, the Midland had put the valves below the cylinders on some classes years before, but there was no excuse for it now.

As we have seen, the era of the Big Engine saw two outside cylinders becoming increasingly popular.  As superheating became widely accepted, piston valves became the norm and these were usually located in valve chests above the cylinders.

In the earlier designs, including Mr Churchward's, the steam passages went from below the smokebox to the valve chest.

As modellers, we are familiar with what we call outside steam pipes, from the top of the valve chest to the side of the smokebox as seen on this 'Black Five' 4-6-0:-

 



These were a wizard wheeze to allow the live steam to take a more direct route from the smokebox to the valve chest.  What we see on our models are just nice covers, the actual pipes are more work-a-day as can be seen:-




[This picturingham shows the steam pipe going from the smokebox to the top of the valve chest.  Inside the smokebox, the steam pipe is connected to the superheater header. Special thanks to the wonderful people at the Lakeside & Haverthwaite Railway who kindly indulge me as I potter around looking at their lovely locomotives.]


I'm not sure when these outside steam pipes were first used.  Typical Churchward locomotives didn't have these, but the GWR 'retro-fitted' them to a lot of locomotives from the mid-1920s as well as making them standard for new construction.

Mr (later, Sir Nigel) Gresley's 'H2' and the first 20 'H3' 2-6-0s² for the GNR did not have outside steam pipes. These appeared from No. 1660, built in 1918, onwards and then became standard for both classes.

An earlier application of outside steam pipes can be seen in James Manson's two superheated 4-6-0s of 1911 for the G&SWR, Nos 128 and 129:-




[This old photograph clearly shows the outside steam pipes on LMS No. 14973 (formerly No. 128).  She is in black livery and towards the end of her life.  Withdrawal came in December 1933.  Note no smokebox numberplate, Caledonian 'semaphore' route indicator, and the typical G&SWR water column.]


Please let me know if you can think of an earlier use of outside steam pipes.  This is an important point as it is visible evidence of locomotive engineers becoming aware of the importance of straight and wide steam passages.  To be fair, Mr Churchward had a good appreciation of this.  In later years, improvements to the 'steam circuit' would assume great importance.  I think we are likely to return to this topic later and we might even meet a jolly clever French chappie.

In the next part we'll get the piston valves out of the steam chest and have a look at them.  Or, to be more accurate, we'll watch a couple of fine fellows doing the heavy lifting on our behalf.  I enjoy hard work - I could watch it all day.

¹ Almost certainly I'll use the '2P'/'D1'/'E1' comparison again - I have a nice quotation from ES Cox that I'd like you to see.

² Later, LNER 'K1' and 'K2' - the 10 'K1s' were rebuilt as 'K2s' between 1921 and 1937.  Class 'K1' was later re-used for Mr Peppercorn's good-looking 'Moguls'.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Tickety-tonk

John

John
I really think your wonderful series should eventually be available as a book! So easy to follow and understand compared to some I've read regarding the way steam engines work!
Perhaps some clever person on this forum could create a pdf type document for you from all your wonderful posts?
I look forward to the next one.
Cheers 

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 53


Hello Chums

Piston Valves

You might recall that the cylinders of a steam locomotive have double-acting pistons.  That is to say, they move under steam power in both directions.  Unlike an internal combustion engine which almost always has single-acting pistons.  In most cases nowadays, these are powered in one stroke out of four.

In order to achieve this, as we have seen, the cylinder has steam ports at each end to let the live steam in and the exhaust steam out.  This letting in and out is done by valves. We are discussing piston valves in more detail because they are easier for us to see as, on a modern two-cylinder locomotive, they are mounted on top of the cylinders.  In what tends to look a bit like another cylinder, longer and narrower than the main one.  If you squint through the fog of my coarse photography, you might just be able to discern what I have attempted to describe:-





Mr Ivatt the Younger's '4MT' 2-6-0 is a good example of a thoroughly modern two cylinder locomotive. The high running plate gives us a SuperSpiffing view of her large piston valves atop the cylinders, with nice straight steam pipes leading to the sides of the smokebox.

I suppose, for us 'N' gauge modellers, that's all we really need to know.  This ultra-brief mini-series attempts to go slightly (and 'slightly' is important here) beyond what we really need to know, so that we have some idea of what causes our lovely little locomotives to look the way they do.

If you think about it, the valves for a steam engine's cylinder have four things to do for every two strokes of the piston, or one revolution of the driving wheels:

1. Let live steam in the front cylinder port;

2. Let exhaust steam out the rear cylinder port;

3. Let live steam in the rear cylinder port;

4. Let exhaust steam out the front cylinder port.

And repeat until one arrives safely at Canon Street (other termini are available).

A four-stroke petrol engine will typically have an inlet and exhaust valve (of the poppet valve type*) for each cylinder.  Nowadays, some might have two of each (not a new idea, the magnificent 500cc Rudge 'Ulster' had a four-valve cylinder head before the War).

In the interests of completeness, three-valves per cylinder have also been used on occasion.

Which begs the question - how many valves does each cylinder of our two-cylinder steam locomotive, equipped with piston valves, require to permit the four things - let's call them 'events' as it looks posher than 'things' - described above to occur?
 
Answers on the back of a Ten Bob note, please. Addressed to:

Mr Hill,
Landlord,
'The Crown',
The Square,
Poppingham,
Poppyshire

Please endorse the bank note with 'Bertie Poppingham's account'.  Ta muchly.

**

In the next part I'm planning to use Poppingham - A Table Top Railway in British 'N' Gauge to help us understand a little bit more about piston valves.  "Madness!", you say.  Probably - please wish me luck. 

* Please, let's ignore all efforts at sleeve valves.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-B

John

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 54


Hello Chums

More About Piston Valves

The answer to the question posed in Part 53...

'How many valves does each cylinder of our two-cylinder steam locomotive, equipped with piston valves, require to permit the four events to occur?'

...is one.  But the valve has two parts, each of which looks like a piston.  Which is why they are called piston valves.

The two pistons are mounted some distance from each other on a rod and the whole assembly can move to-and-fro within the cylinder-shaped valve chest.

The two pistons, mounted on a rod and moving within a cylinder-shaped valve chest, means that there are three distinct and separate spaces:-

The space in front of the leading piston;

The space between the two pistons,

And, the space behind the rear piston.

One valve, two pistons and three distinct and separate spaces.  Will we be able to convince ourselves that this arrangement can permit the four events we listed in Part 53 to occur?

Let's have a look at an agreeably heavy piston valve as two fine fellows at Grosmont Motive Power Depot remove one from 'Black Five' No. 44806.  The part of the video of interest, at present, is from 1:28. Although I expect to return to other scenes later.


Hopefully, the piston valve assembly looks something like my attempted description.

As the hardy chaps extract the piston valve, you can see some steam ports inside the cylindrical valve chest.

***

And now we'll divert ourselves as I attempt an analogy.





The picturingham is of Poppingham, my semi-scenic, train-setty layout in the old-fashioned style.

A double track oval with, frequently, two trains going round - Such Fun!

I wish it was clockwork like the Sherwood Section but it's worked by electricity at 12 volts DC.  I know electricity can be a tad difficult to understand for the likes of me, but each of the ovals has a positive or negative wire attached to one or other of the rails.  I'm bang-up-to-date - no third rail for me - it's two-rail electrification. Like Tri-ang Railways of the 1950s - do you remember the power connecting clip?  If the track was on the shag pile, it became a power disconnecting clip.

The controller is a Gaugemaster 'Series D' twin-track controller. It has two knobs - one for each of the tracks, known, in railwaylike terminology, as the Up Line and the Down Line.

Our electrician is a lovely chap called Gordon and he is a first-rate tradesman.  He was enchanted with Poppingham when he saw it and thoroughly enjoyed playing trains. As one might expect, he was interested in the electrical aspects and I told him it was my favoured system with three wires from the controller to the layout.  What I call Three Wire Control.  He gave me a thoroughly quizzical look which I understood - two separate circuits (in both senses of the term) but controlled by only three wires? 

I explained that it is, effectively, the earth return system used on motor-bicycles and motor-cars, although us toy train enthusiasts call it 'common return'.

Gordon looked at me for a couple of seconds, then smiled and said, "Of course" and carried on playing trains.

You might struggle to believe me, but the 'common return' concept is a way of helping to understand how a piston valve, with three distinct and separate spaces, can control four events.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John