A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 47


Hello Chums

From Boring to Grosmont

One of the developments which enabled James Watt to make his improvements to the steam engine was boring.  You see, the cylinders for Newcomen engines were made by chaps who were, effectively, blacksmiths and, although skilled craftsmen, they struggled to obtain a suitably smooth finish to the cylinder bore.

Then James Watt became aware of the precision boring techniques for cannon which had been invented by John Wilkinson at his ironworks near Wrexham.  This permitted Mr Watt to have a much more accurate piston/cylinder interface in his engines and represents an important step which allowed for the development of the steam locomotive. 

*

Skipping elegantly over a few matters to which I'll attempt to remember to return, let's have a quick think about a steam locomotive's cylinders.  Remember we mentioned the piston is double-acting?  That means live steam has to be admitted to each end of the cylinder and exhaust steam allowed to escape, also from both ends.  This is done by having holes in the cylinder bore, at each end, called 'ports'.

Time, now, for our visit to Yorkshire, always a pleasure:-




About 1 minute 30 seconds is the bit of special interest to us.  Cylinder boring technology has moved on since James Watt's day, of course.  As one watches the film, the steam ports at the end of the cylinder are obvious.

You will notice, on the part of the bore awaiting machining, there is noticeable scoring.  This is a consequence of wear accumulated over time.  There was, for a while, a notion that wear could be reduced by having a rod at the front of the piston as well.  This passed through a bearing surface on the front cylinder cover and was covered by something a bit like a giant cigar tube.  The LSWR and NER seemed to have been especially disposed to these fitments, called 'tail rods' for a while.

The case in favour is reduced wear of the cylinder bore.  The case against is more weight, increased reciprocating masses and more bearing surfaces to keep steam-tight.  Like so many other gadgets designers tried over the years, tail rods were, eventually, abandoned as British steam locomotive design became more the pursuit of compromise than the pursuit of perfection.

*

If you enjoyed the film, here's another one featuring a '9F', from 45 seconds.  I enjoyed the bit, later in the film, with a keen chap oiling the newly-machined cylinder using a paintbrush.  I use an ever-so-slightly smaller paintbrush when oiling my Union Mills locomotives for the Table-Top Railway.  It's nice to be prototypical:-




There's only so much excitement one can take in a part of this mini-series, so, with special thanks to the Locomotive Department of the North Yorkshire Moors Railway, I'll say:


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-B

John

And as we are still, just, in the festive period, good to see the chap in the  first clip wearing a santa hat.

I am learning so much from this series; really interesting and an ideal amount of information to take in on each post. Thank you!
Cheers

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 48


Hello Chums

An Initial Think about Valves

The previous 47 parts of this mini-series (47 - I originally intended a handful) have taken us to where we have a locomotive with its boiler producing live steam and cylinders - with double acting pistons, remember - all ready to go.  The first stage of getting the steam from the boiler is through the regulator.  This is a handle, big in some locomotive types and smaller in others, which the driver uses, by turning or pulling out (lots of variations exist, of course) to open the regulator valve and allow live steam to make its way to the cylinders.

It is important for the live steam for the regulator valve to be collected where the steam is driest, to avoid admitting water to the cylinders.  You know how many locomotives have a rather attractive feature atop the boiler?  With older locomotives it's usually bigger and in later locomotives it tends to be smaller, as the boiler diameter increased over time but the loading gauge normally didn't.  Once the decorative cover is removed it looks somewhat less attractive.  Its purpose is functional - the hottest steam in the boiler rises into a collector in the dome and is fed to the regulator valve, connected to the regulator handle.




[Not much elegance about this - a steam dome without a fancy cover.]


Some locomotive engineers didn't care for a steam dome and used a perforated pipe instead to collect the live steam.  These types are less common and are called 'domeless boilers'.  Boilers with steam domes are generally called 'boilers'.  Yes, an unforgiveable simplification, but it serves to show what was considered 'standard practice'. 

The Stirling family, Patrick, James and Matthew, and their close associate, Hugh Smellie, were particular enthusiasts for domeless boilers.  Interestingly, when they were succeeded by another engineer, he generally introduced steam domes - often large and elegant.  Messrs Ivatt the Elder on the Great Northern, Manson on the G&SWR and, especially, Wainwright on the SECR are good examples of this.

The GWR was interesting (isn't it always?).  Mr Dean favoured large domes and Mr Churchward's carefully designed and magnificently constructed standard boilers were  were domeless.  But the GWR had a legacy of pre-Churchwardian types, many built after the great man's retirement, with magnificently-domed boilers.  Just think of all these pannier tanks.  Mr Hawksworth eventually introduced pannier tank designs with domeless boilers.




[Steam domes come in various sizes.  0-6-0PT No. 5764 has one of what might, politely, be called Jane Russell proportions.]

*

Having got the regulator and steam dome, or absence of one, out of the way.  Let's think what happens to the live steam when the driver cracks open the regular handle.  It flows through pipes towards the cylinders.  Please note, the locomotive in my mind's eye is not superheated.

But here's a thing.  Remember, unlike a typical internal combustion engine, a steam engine is double-acting.  We saw the steam ports at each end of the locomotive cylinders in those splendid films from Grosmont.

Can you see the problem we face?  We have to be able to admit live steam to each end of the cylinder (at different times or we'll be going nowhere!) and we have to allow the exhaust steam to leave the cylinder and make its way to the chimney.  Keeping live steam and exhaust steam separate is essential - we don't want our precious live steam escaping before it does any work.

For many years, from the Stephensons' time until almost the superheater era, (with a few interesting exceptions) this was achieved by using 'slide valves'.  Put simply, a rectangular piece of metal with three square-ish holes cut in it.  Some sort of mechanical contraption - we'll think about these later - moves the valve to-and-fro within the 'valve chest', which also has holes cut in it.  The whole thing is so constructed as to allow the holes in the valves and the valve chest to coincide when we want them to.

This allows live steam into the cylinder, at either end, and the exhaust steam to escape when we want it to - all achieved by making these holes line up at the correct time..  To achieve separation, with slide valves, the two holes at each end of the rectangular valve are normally used for live steam and the hole in the centre for exhaust steam.  The construction of the valve chest then keeps the exhaust steam separate from the live steam.

Typically, a slide valve will have a movement of 3in - 4in, which allows for all the necessary covering and uncovering of the holes to take place.

I hope this made some sort of sense.  The important thing to remember is a double-acting steam engine needs to admit and remove steam from each end of a cylinder.  The slide valves allow this to happen.  For us 'N' gauge modellers, unless interested in particularly unusual prototypes, all this is of academic interest as, due to the aforesaid 'mechanical contraption', which moves the valves, generally being between the frames in the slide valve era, the valve chest is there as well.





Back to the picturingham of the semi-dismantled 0-6-0ST.  That space in the cylinder block, between the cylinders, is the valve chest.  Incidentally, the arrangement of inside cylinders with a common steam chest between them, as seen in the picturingham,  was patented by Robert Stephenson & Co, in 1841.  Although I consider this short mini-series as entertainment, rather than educational, I'd be super chuffed if anyone reading it comes away with a better appreciation of the contribution to the development of the steam locomotive made by that remarkable man, Robert Stephenson.

We met him last on a quayside in Columbia (sounds like the title of a paperback 'thriller') giving a broke Richard Trevithick his fare home.  Now, a few years later, his firm patents what became pretty much the most common cylinder and valve chest arrangement used in Britain for over 50 years.  And, in some cases, longer than that.

Let's restrict ourselves to British standard-gauge mainline railways.  The final class built with slide valves?  I believe this to be our old friend the GWR '9400' class 0-6-0PT, built from 1947-1956.  Another class worth special mention  is the 1949-1951 batch of 'J72' 0-6-0T engines - a NER design going back to 1898. A century after Robert Stephenson's patent, the arrangement was still being used for new construction.

Unless one manages to become intimately involved with steam locomotive maintenance, it's unlikely we'll see much evidence of slide valves in British practice.  However, Linda, on the Ffestiniog Railway, has slide valve chests on top of her outside cylinders.  Her sister, Blanche, is different.  Have a look, if you like, at pictures of the two engines and you'll see what I mean.

Now, I've been a cheeky chappie and suggested slide valves were generally replaced by a different arrangement.  We'll come to this in a later part.

*

A quick question, if I may, for any of the proper enginemen who have endured reading this.  Have you encountered the technique of closing the regulator before moving the reverser on an engine with slide valves?  The idea being to take the pressure off the valve faces.  I'd be keen to know.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-oo

John

Though I'm very familiar with the mechanics of the steam loco, this is a brilliant explanation for a layman to follow.

Well done again, John!

Martyn

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 49


Hello Chums

Some More about Valves and then Back to Cylinders

In part 48 of this brief mini-series we attempted to look at slide valves.  Not an easy thing to do as that great engineer, Robert Stephenson, worked out that the best place to put them on an inside-cylinder locomotive is between the cylinders.

And, as we have seen, British locomotive engineers tended to enjoy inside cylinders.  They especially liked placing the 'mechanical contraption', which moves the valves, between the frames.  Makes it much less accessible for enginemen 'oiling up', fitters fitting and, of course, less disturbing for members of the public of a nervous disposition to see in action. 

*

From early times there was a notion that a different type of valve from the slide valve, more like a mini-piston, or, to be exact, a pair of mini-pistons on a stick, might be a good idea.  The first example of a locomotive fitted with piston valves was earlier than one might think.  1832.  Robert Stephenson & Co built Atlas, an 0-4-0, for the Liverpool & Manchester Railway.  The idea was ahead of its time - piston valves proved more difficult to keep steam-tight and the elegant simplicity of the slide valve won the day.

I'm glad to be a life member of the Vintage Carriages Trust, based at Ingrow (West) on the Keighley & Worth Valley Railway.  The Trust has three locomotives in its collection.  Of these, Bellerophon, an 0-6-0WT, was one of six similar locomotives built for the Haydock Collieries. Bellerophon , completed in 1874, was built by the Haydock Foundry. You might have seen this little brown engine, either on the K&WVR or on the Foxfield Railway.  What might have escaped your notice is he (the Trust uses the masculine pronoun, as will I) has piston valves.  The valve chests are above the outside cylinders - a strikingly modern arrangement.

However, it wasn't until 1887 that piston valves were reintroduced for British main-line railways.  On a railway that is something of a favourite of mine - the NER.  That inventive engineer, WM Smith, Chief Draughtsman of the NER, is credited with making improvements that made piston valves a practical proposition.  We'll hear more of Mr Smith later, I expect*.

I think the exploits of Wilson Worsdell's 'R' class 4-4-0 for the NER, introduced in 1899, really showed the superiority of piston valves.  The first of the class was put onto a double-manned diagram:- Newcastle-Edinburgh-Newcastle-Leeds-Newcastle, Monday to Friday.  That's 455 miles each day.  She had an easier time of it on Saturdays with a diagram of 161 miles.  Boiler wash-out on Sundays.  This is a total of 2,436 miles each week.  At the time, it was considered that this level of performance was made possible due to the class being equipped with Mr Smith's design of piston valves.  I love an excuse to include a picturingham of a Union Mills 'R' class:-





Even allowing for the many deficiencies of my coarse photography, you might be able to discern that the 'R' is an inside-cylinder locomotive.  Yes, some traditional-looking British inside-cylinder locomotives had piston valves, hidden between the frames.  The multitude of MR/LMS '4F' 0-6-0s can certainly be called 'traditional' - here's one of the class being erected:-





One of Mr Smith's clever developments to the piston valve (can we call him SuperSmith?) was to place the valve chests above (or below) the cylinders, as can be seen in the picturingham.  This was a substantial break from the normal practice with slide valves where there was, as we have seen, a common steam chest between the cylinders. Of course, slide valves could also be arranged above or below the cylinders.

Back to Cylinders

The '4F' has 20 inch diameter cylinders.  As the picturingham shows, the space between a locomotive's frames is limited.  We start off with a gauge of 4 ft 8 1/2 in., take off a bit for the width of the frames, then another bit for the clearance between the wheels and the frames. The flange roots of the wheels cannot be hard against the inside face of the rails, so we need to add another bit of clearance to allow for the 'coning' of the wheel tyres to be effective.  All these bits add up and act to restrict the distance between the frames.

Which means the space between the frames is a constraint on the diameter of the cylinders of an inside-cylinder locomotive.  I had an agreeable time looking through some books and the largest diameter of inside cylinders I can find is 20 in., like on the '4F' seen in the picturingham or the powerful GER 0-6-0s later known as class 'J20'.  There are others, but I cannot find an example with cylinders over 20 in diameter.  Do you know of one?

I propose to take a break from valves for a while and return to cylinders in the next part.  There are some matters we might like to consider.  We'll then return to piston valves.

*Incidentally, Mr Smith was on good terms with SW Johnson, Locomotive Superintendent of the Midland Railway.  Mr Johnson was persuaded regarding the benefits of piston valves and, from 1893, fitted them to some of his express passenger locomotives.  Particularly noteworthy was their fitting to the later batches of his SuperSpeedy 4-2-2 'Spinners'.


'N' Gauge is Such Fun

Many thanks for looking and all best wishes.

Tickety-tonk

John

The ex GCR Sir Sam Fay class, LNER B2, initially had 21.5 " inside cylinders, but at least some of the class had them later lined up. If you Google the class, one of the links (LNER encyclopedia) also mentions something also alluded to in this series, poorly designed steam passages.

Martyn

Incidentally, the J20s were effectively an 060 version of the B12, with the same cylinders. The GER had done something similar with the J19s using the Claud boiler and cylinders, but in the latter, the boiler pressure was reduced to 160lb: the J20 retained the 180 lb of the B12s.

Martyn

Thank you very much, Martyn.  That is interesting about the 'Sir Sam Fay' class.  I knew these were impressive-looking engines but with disappointing performance. After reading the article you suggested, I can see why.  I noted with interest that the massive inside cylinders resulted in axlebox width being compromised.

Mr Robinson was not alone in having difficulty going from the 4-4-0 to the 4-6-0.

I'm always particularly grateful for contributions like this to the discussion.  And the cylinder diameter mentioned will make for an interesting point of comparison in the next part in the mini-series.

Thanks again and all good wishes.

John

Thank you, John, wonderfully educational and informative as ever. I've often thought that steam locomotives are examples of the way technology advances by gradual development, trial and error until it reaches the limits of what further development can achieve and is then superseded by a different technology altogether. The internal combustion engine appears to be reaching the same point.

Quote from: Train Waiting on January 06, 2025, 10:08:33 PMThe previous 47 parts of this mini-series (47 - I originally intended a handful)

You have obviously taken the idea of Douglas Adams' Hitchhiker's Guide to the Galaxy, a Trilogy in five parts, and expanded it further! Looking forward to the next 48 parts.

Cheers,

Chris

Quote from: Train Waiting on January 08, 2025, 06:16:14 PMBack to Cylinders

The '4F' has 20 inch diameter cylinders.  As the picturingham shows, the space between a locomotive's frames is limited.  We start off with a gauge of 4 ft 8 1/2 in., take off a bit for the width of the frames, then another bit for the clearance between the wheels and the frames. The flange roots of the wheels cannot be hard against the inside face of the rails, so we need to add another bit of clearance to allow for the 'coning' of the wheel tyres to be effective.  All these bits add up and act to restrict the distance between the frames.

Which means the space between the frames is a constraint on the diameter of the cylinders of an inside-cylinder locomotive.  I had an agreeable time looking through some books and the largest diameter of inside cylinders I can find is 20 in., like on the '4F' seen in the picturingham or the powerful GER 0-6-0s later known as class 'J20'.  There are others, but I cannot find an example with cylinders over 20 in diameter.  Do you know of one?

So Brunel was right, and we should have gone with broad gauge?

No-you change to outside cylinders (or multi cylinders), and change the loading gauge!   

Just look at the size of some of the US and Canadian locos.

Martyn

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 50


Hello Chums

Back to Cylinders

'At the end of 1897 there was no British locomotive superintendent designing two-cylinder non-compound engines with outside cylinders, other than small shunting locomotives. In 1898 Ivatt's GNR 'Atlantic' engine appeared and since then the use of outside cylinders has greatly increased.'*

I mentioned earlier that, although the inside-cylinder type became predominant after Robert Stephenson's Planet, outside-cylinder locomotives continued to find favour on certain British railways. You might recall this from part 46 of this brief mini-series:

'And there was one important British main line railway which had a total of five inside-cylinder engines (all tank engines, by the way) in its total locomotive stock until a new Locomotive Superintendent took over in 1896. Then inside-cylinder types began to become common on the line, or, at least, parts of it.  Any idea which railway?'

Profuse apologies for quoting myself - the last refuge of the pub bore.  By the way, the answer is the Highland Railway.

But, by the early 'Nineties, the two cylinder locomotive with outside cylinders appeared to be reaching the end of its time in Great Britain.  Elsewhere, outside cylinders were very much the norm.  Inside-cylinder types could be seen (The Netherlands and Portugal being examples) but they were in a minority world-wide.

Then along came Mr Ivatt the Elder with his first 'Atlantic', No. 990, happily still with us, which was the heaviest locomotive in Great Britain at the time of its introduction in 1898. 





No. 990 was the first British express passenger tender locomotive to run on five axles.  The previous tender engines with 10 wheels, David Jones' 4-6-0 locomotives of 1894 for the Highland Railway and William Dean's experimental Great Western 4-6-0, No. 36, of 1896, were for goods traffic.

The era of the Big Engine had arrived, just in time for the new century and the greatly increased train weights it would bring.  We discussed the increase in size of locomotives and their increasing number of wheels in the first section, so there is no need to repeat that here.  But it helps us to be aware that, to cope with changing operating conditions, locomotives were getting bigger and beginning to 'outgrow' the traditional 4-4-0 and, to a lesser extent, 0-6-0  types.

A consequence of this enlargement of the steam locomotive was the potential constraint placed upon the designer by inside cylinders.  I was grateful @martyn drew our attention to the 21 1/2 inch diameter inside cylinders of the Great Central's 'Sir Sam Fay' class.  These managed to fit between the frames although there mustn't have been much space left, but the proximity to the frames of the cranks led to insufficient bearing surfaces on the driving axleboxes.

However, 20 inch diameter inside cylinders were used on several very satisfactory classes, including the 'B12' 4-6-0, with its 20 inch bore by 28 inch stroke cylinders.  Incidentally, I'm not aware of any locomotives having inside cylinders with a stroke longer than 28 inches.  Can you think of any?




[A 'B12' 4-6-0, this example is of the LNER rebuild as 'B12/3'.  I think it is fair to say this was the most successful 4-6-0 class with inside cylinders. An attractive engine as well.]

*

There then began a gradual - but so very gradual - move away from inside cylinders.  The various two cylinder 'Altlantic' designs following Mr Ivatt's No. 990 had, with the exception of Mr (later, Sir John) Aspinall's 'Highflyers' for the L&YR,  outside cylinders.  The final North British 'Atlantics' had 21" x 28" outside cylinders.

Although all but one of the locomotive engineers, who tried the type, settled for outside-cylinder 'Atlantics', the situation regarding 4-6-0s was more complicated, with a variety of inside-cylinder and outside-cylinder types being introduced, sometimes on the same railway.

Between 1902 and 1921, JG Robinson designed nine, yes nine, 4-6-0 types for the Great Central.  Two were four-cylinder engines and are not for our notice at present. Of the remaining seven types, five had their cylinders outside and two inside.

On the Caledonian, between 1902 and 1922, Mr McIntosh introduced five types of 4-6-0 with inside cylinders of up to 21" x 26" size and his successor, W Pickersgill produced two types of 4-6-0 with outside cylinders.  And a three-cylinder 4-6-0 class of extraordinary incompetence.

For smaller locomotives, two outside cylinders were unusual for designs introduced after 1900 - the GWR 'County' 4-4-0s, and the Highland Railway's Snaigow and Durn being interesting examples.

* 

At this point the problem of the British loading gauge presents itself.  There are several aspects to this, but the one of relevance here is that caused by the British love of station platforms.  Platform clearance is critical for locomotives with outside cylinders and, of course, each of the pre-Grouping companies set its own standard.

21 inch diameter outside cylinders can be found on other classes, such as the LSWR 'H15' class 4-6-0 (21" x 28") and the LBSCR 'K' class 2-6-0 (21" x 26").  Especially, they can be seen on the LMS 'Horwich Mogul' 2-6-0 class (21" x 26"), but set high and at a sharp angle in order to provide platform clearance on the 'tighter' parts of the LMS system. This class demonstrated it was more difficult for the 'Big Four' companies, or, at least, three of them, as they had to contend with the differing loading gauge dimensions of their constituents.  Easier, of course, for the GWR.




[In order to prevent the 21 inch diameter cylinders bashing into station platforms, Horwich Drawing Office raised them high, which then required a sharp angle to get the connecting rod to meet the crankpin.  I've always thought these 'Horwich Moguls' were attractive engines.  Good performers too - they could steam, had plenty of power and good brakes.  Sir Henry Fowler got his hands on the design after Mr Hughes retired and 'Midlandised' some of their details, including equipping the class with that ridiculously narrow Midland tender.]


I think the largest diameter outside cylinders used in Great Britain were on a couple of Mr Urie's designs for the LSWR - the 'N15' 4-6-0, later called the 'King Arthur' class, with 22" x 28" cylinders and the LSWR 'G16' class 4-8-0T shunting engines, also with 22' x 28" cylinders.  Mr Maunsell arranged for all but one of the 'N15s' to have their cylinders linered down to 20 1/2" in the course of general repairs during 1927-1929.  No. 755, The Red Knight, continued to run with 22 inch cylinders until withdrawal in 1957.  Apparently, there was no appreciable performance advantage to No. 755's larger cylinders.

*

In the next part, I'm hoping to draw some of the threads together and I'm going to attempt an approach that I've never seen before.  Of course, it will have been done, but I've not seen it.

* EL Ahrons, The British Steam Locomotive 1825-1925, Locomotive Publishing Company, London, 1927, Page 311.


'N' Gauge is Such Fun

Many thanks for looking and all best wishes.

Cheerio

John

John

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

@Webbo I think this was done to get even weight distribution on the three driving axles while on Pacifics this could be achieved by the distance of the trailing axle.