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

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 34


Boiler Water Level - 1

Hello Chums

We've already discussed this, so just a brief re-cap.  The inner firebox, normally made of copper in British practice, is secured to the outer firebox, which is part of the steel boiler shell, by lots 'N' lots of stays.  Feedwater is put into the boiler, almost always by an injector, to replace the water converted to steam and ending up in the atmosphere.

Too much water in the boiler is a bad thing as it can get 'carried over' with the steam - this is called 'priming' and can cause all sorts of problems.  So, do not overfill the boiler.  But not enough water in the boiler can be much, much worse.  Here's why.

The top of the inner firebox is called the crown sheet and it receives the maximum amount of heat from the fire.  More than enough to melt the metal from which it's made.  But the water in the boiler acts to cool the crown sheet - 'cool' here is a relative term, of course - and keep the metal below the point where it softens and loses its strength.

But, if the water level in the boiler falls to such an extent that the crown sheet is not covered, it will overheat, the metal will soften and the crown sheet will fail, usually by bulging inwards and pulling off of a stay.  Then the force of the escaping steam will result in a boiler explosion.  Sometimes the inner firebox will split open, in other instances, the softened metal will be pulled off multiple stays and bulge down. 

Stronger construction, with the eventual elimination of lap joints, resulted in the failure of the boiler barrel becoming much less common.  The last instance in Great Britain, as we have already seen, was in 1921 at Buxton.  Boiler explosions from then on were a consequence of inner firebox failure, normally of the crown sheet.  Not all were due to low water level, there were a couple of instances (both Southern Railway tank engines) caused by the stays becoming weakened and breaking, but low water level was the most common cause.

There was a period of almost nineteen years between the Buxton explosion and the next one in Great Britain, which was at Carstairs in 1940 involving 'Princess Coronation' 4-6-2 No. 6224 Princess Alexandria.

There were three boiler explosions involving the US 2-8-0 locomotives which were used during the War - at Honeybourne, Thurston and South Harrow.  We will discuss the cause of these later.

In 1945, there was an explosion at Hinton Admiral involving 'Lord Nelson' 4-6-0 No. 854 Howard of Effingham. 

Princess Alexandria suffered a second boiler explosion at Lamington, which is not that far from Carstairs, in 1948.

Ex GWR 4-6-0 No. 6859 Yiewsley Grange suffered a boiler explosion near Wrexham in 1952.  The last on BR, and fortunately a mild one, occurred in 1962 near Bletchley, involving 'Princess Coronation' 4-6-2 No. 46238 City of Carlisle.

*

From the above it is clear that it is of supreme importance that the enginemen know the water level in the boiler and think about what is going to happen next in their working.

Early locomotive practice, based on what was used on stationary boilers, was to have three try cocks, set vertically on the boiler faceplate, about three inches apart.  The theory was that water should come out of the bottom c ock when it is opened, steam from the top c ock and a sort of water and steam mixture from the middle c ock.  It's can be difficult to obtain an accurate reading as water flashes into steam when it reaches the air. [My apologies for the oddity of spacing, necessary to prevent our FabulousForum making me look foolish.  Again.]

Something better was required and what we think of as a gauge glass was, I believe, first used by John Rastrick in 1829.  Better known for his later work as a civil engineer, he was one of the judges at the Rainhill Trials and a partner in Foster & Rastrick of Stourbridge, builder of the first steam locomotive to work in the USA, the Stourbridge Lion of 1829.

If you think for a moment of many modern electric kettles that are see-through in some way or another, so that the person about to make a pot of 'Yorkshire Tea' can check there is enough water in the kettle, that what Mr Rastrick achieved.  Please allow me to demonstrate with a milk bottle, not that I'd ever put milk in tea:




[Easy to see the water level when the container is see-through.  Please note, I added some dye to make the water more prominent - our water here, between the Forth and the Tweed, isn't that colour - honest.]




[Some broon tape helps us to imagine the container, like a locomotive's boiler, is not see-through.  I wonder what the water level is.]




[Mr Rastrik's ingenious way of seeing into the boiler can be demonstrated with the handle of the bottle pretending to be a gauge glass.]


In real life, a gauge glass is a glass tube connected to the boiler by means of shut-off cocks.  It is mounted within a frame and surrounded on three sides by thick glass to offer some protection if the gauge glass bursts, which it can do.  Enginemen carry spares; just in case.  Here's a picturingham:




[A single gauge glass on LNWR 2-4-0 No. 790 Hardwicke.  Typical of mid to late Nineteenth Century practice - the locomotive was built in 1892 as a renewal of an earlier engine.]


The gauge glass is so arranged that, when water is in sight at the bottom of the glass, the firebox crown sheet is covered with water.  Any additional margin of safety allowed was a matter for the designer.

By the eighteen-fifties, the gauge glass was becoming the norm on steam locomotives, with a set of try cocks as back-up.  An important improvement, attributed to the German Professor Reuleaux was the inclusion of a ball valve to shut automatically should the gauge glass break.

Later on, duplicate gauge glasses gradually found favour; the Glasgow & South Western used these as early as 1879, but a single gauge glass with two integral try cocks remained GWR practice and was used on GWR-design locomotives built after nationalisation.

Safe operation of a locomotive requires the gauge glasses to be working properly and to be visible.  Enginemen are expected to test the gauge glasses when taking over a locomotive.  Proper functioning requires the steam and water passages into the boiler to be unobstructed and the shut off cocks to be fully open.

The 1940 Lamington explosion was due to a fitter wrongly assembling the components of one gauge glass and the enginemen believing the other gauge glass was out of use.  Unfortunately, the wrongly-assembled gauge glass caused the water in it to rise well above the actual water level in the boiler.

The 1952 Wrexham explosion was due to a fitter over-tightening the glands at the ends of the gauge glass tube which caused the over-compressed rubber packing to distort and obstruct the flow of steam into the glass, resulting in a false high water level.  You will recall that, like all GWR locomotives, Yiewsley Grange had only a single gauge glass.  Western Region instructions required the enginemen to have confirmed the accuracy of the gauge glass by using the two test cocks - unfortunately, neither of them did so.

As an aside, in the Grouping and BR steam era, from 1923 to 1968, this was the only occasion in which a GWR-designed locomotive suffered a boiler explosion, as far as I'm aware.

The 1962 Bletchley explosion was of interest because one gauge glass was so dirty, the fireman could not see the water level.  He relied on the other gauge glass which appeared to be full every time he looked at it, with the water out of sight in the top fitting.  Unfortunately, it was empty.

Unlike in my colourful demonstration above, water is clear, which means that a full gauge glass and an empty one look the same.  However, by 1962, an ingeniously simple safety feature had been used on LNER-designed locomotives for many years:




[Seen on the twin gauge glasses on Katie are the diagonal-striped back plates.  In a gauge glass empty of water, the stripes go the same way.  Where they are viewed through water, they appear to go in the opposite direction.  Ingenious or what?  Why did BR not adopt this feature on all of its steam locomotives?  Here's another look at it, on the single gauge glass of the replica Sans Pareil.  You can also see one of the try cocks as well.]





What a brilliant idea.  Incidentally, to the best of my knowledge, no locomotive of LNER- design suffered a boiler explosion in the 1923-1968 period.

The next part will discuss another safety feature designed to protect the crown sheet and will again draw on explosions and a violent blow back to inform our discussion of what can happen when things go wrong.

I gladly acknowledge Locomotive Boiler Explosions by the late CH Hewison and The British Transport Commission's Handbook for Railway Steam Locomotive Enginemen as valued sources of information.  Any errors or omissions are, of course, my own.


'N' Gauge is Such Fun.

Many thanks for looking and all best wishes.

Toodle-pip

John

[Bealman]

Wunderful stuff, John.

[Ed]

Wunderful stuff, John.

Seconded 


Ed

[Hailstone]

When I was a trainee fireman at Didcot in the early 1980s I was taught by one of the senior drivers how to read test cocks it is quite simple. if there is water at the level of the test 'male chicken' (changed by forum), when opened, steam will immediately condense on the body of the 'male chicken' (changed by forum). if there is steam behind the 'male chicken' (changed by forum), there will be a small gap between the body of the 'male chicken' (changed by forum) and the condensing steam.(remember that steam is colourless until it condenses) Later as a fireman in my own right and later as a driver, I taught the trainee firemen that followed. If the gauge glass was to blow I taught trainees to open the test cocks and start an injector to put water into the boiler until water was observed at the top test 'male chicken' (changed by forum) and the level maintained like this until the gauge glass had been replaced, which all firemen should be capable of doing.

Regards,

Alex

[Firstone18]

Wunderful stuff, John.

Seconded 


Ed

Thirded (is this a correct term?) 

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 35


Boiler Water Level - 2

Hello Chums

Before we start, special thanks to Alex @Hailstone for his expert contribution regarding GWR practice of a single gauge glass and test cocks.

A gauge glass or glasses, with test cocks where appropriate, was the standard British way of advising enginemen of the level of water in the boiler.  BR guidance was to keep the water level in sight in the top half of the glass.

Apart from errors by the enginemen, low boiler water level above the firebox could be caused by cresting a summit, if running chimney first - going over one if tender or bunker first - or braking, as these conditions make water flow away from the firebox.  The firebox crown is at special risk towards the rear of the firebox which is why backward-sloping firebox crowns were introduced; we have already seen Mr Churchward's thoughts on the matter.

Injector (or feed pump) failure is a possibility, there is always a back-up but it's possible both could fail.  An obstruction of the water supply between the water tank/s and the injectors could be a cause.  In pre-Grouping days, it was not uncommon for some enginemen to have a fish in the tender to eat any vegetable matter contaminating the water supply.  But rags and suchlike accidentally dropped in the tank are another matter entirely.

Also, if the engine was struggling for steam, especially on a gradient, the enginemen might be reluctant to put on an injector as the feedwater would cool the boiler and reduce the pressure. 

In later steam days in the USA, some locomotives were fitted with a low water alarm which caused a whistle to sound if the water level was approaching a dangerously low level.

The dreadful boiler explosion, at Hinton West Virginia, which destroyed Chesapeake & Ohio Railroad's 'H-8' 'Allegheny' 2-6-6-6 No. 1642 in 1953 was attributed to crown sheet failure due to low water level. The explosion occurred on straight and level track.  At a point a mile-and-a-half before the explosion, a railwayman saw the locomotive passing.  He believed it to be working on a medium throttle and he heard the low water alarm whistle sounding.

Some time ago, I read the Interstate Commerce Commission's report into the explosion.  It concluded the water level had fallen to seven inches below the firebox crown.  It also noted that the locomotive had a history of repairs requested to the feedwater pump.

Low water alarms are now commonplace in steam plant in Great Britain but, as far as I'm aware, no steam locomotive has been so fitted.

*

The final warning of low water for British enginemen is the fusible plug.  One or more - normally two, sometimes three - of these are screwed into the firebox crown sheet and project about an inch above it into the boiler.  They are made of brass and have a lead core (a bit like graphite in a pencil, seen in cross-section).  Some have a brass button, sort of soldered in place by lead.  Lead has a lower melting point than copper and, if the water level in the boiler drops too low, the fusible plug/s become exposed, the lead melts and allows steam to escape into the firebox.  This, in theory, alerts the enginemen to what is happening.

I think it was Yogi Berra who said, "In theory, theory and practice are always the same.  In practice, they aren't."

With reference to a couple of boiler explosions already mentioned, the enginemen on Yiewsley Grange heard the sound of escaping steam in the firebox and assumed a tube had punctured.  They thought they could get to Wrexham... 

In the Lamington explosion, the enginemen on Princess Alexandria were aware of the sound of escaping steam and stopped at Carstairs, where a foreman and two fitters from the steam shed examined the engine but could not find the source of the leak.  The train then continued on its way...

Fusible plugs are intended as alarms - not as as sometimes stated to allow water into the firebox to extinguish the fire - but steam escaping into a large engine's firebox is difficult to see in the glow of the fire and will be drawn forward towards the tubes by the draught.

There was an incident on the East Lancashire Railway on 25 May 2009 in which the boiler water level on a locomotive hauling a passenger train became low because of trouble with the injectors.  The enginemen eventually got both injectors working, but during this time, one of the fusible plugs melted.  The enginemen did not realise this had occurred and continued going about the work of the day. It was only after the locomotive had gone on shed for disposal that anyone realised what had happened. I regret I have not been able to identify the locomotive concerned.

Fusible plugs require expert fitting and thorough inspection.  Unfortunately, both of these conditions were not met on the Main Line Steam Trust's railway between Loughborough Central and Rothley (now the Great Central Railway) in 1975/76.  The locomotive concerned was a Norwegian 2-6-0, No. 377 King Haakon 7.  In April 1975, while the locomotive was undergoing boiler repairs, a volunteer had reformed the threads on the fusible plugs and crown sheet incorrectly and one of the two fusible plugs was inserted cross-threaded.  The insurance company's boiler inspector certified the boiler without seeing the fusible plugs removed for his examination.

Eventually, on 7 March 1976, the threads on one of the fusible plugs failed and it blew into the firebox.  The resulting 1 5/8 inch hole in the crown sheet allowed steam at 170 psi to erupt into the firebox causing a massive blow back.

*

The following instances are straying slightly from matters of relevance to 'N' gauge modellers but, perhaps, are of interest, as high pressure steam makes no allowance for well-meaning preservationists.

The Gettysburg Railroad in Pennsylvania was the scene of a catastrophic crown sheet failure on 16 June 16, 1995.  Ex Canadian Pacific 4-6-2, No. 1278 was the locomotive involved.  The National Transportation Safety Board's investigation found multiple failures of locomotive maintenance, and training and supervision of personnel, which led to the engine being in an unsafe state.

Kitson-Meyer 0-4-0+0-4-0 Hawk was hauling a passenger train on the Kirklees Light Railway (now the Whistlestop Valley) on 3 July 2011 when water became low in the boiler, melting the fusible plug. The newly-qualified driver did not drop the fire immediately as he ought to have, the locomotive remained coupled to its train and the passengers were not evacuated.  Some time later, a more experienced person arrived on the scene and the fire was dropped.  There was extensive damage to the firebox but, fortunately, the crown sheet did not fail.

There was speculation that a partially-closed valve was the cause of the low water level but a a careful and thorough investigation by the Rail Accident Investigation Branch established that the driver had simply not used the injectors enough to compensate for the water being used.

Finally, I was glad to read that '2MT' 2-6-0 No. 46464 has returned to steam at the Strathspey Railway, 44 years after she suffered firebox damage there after being lit up, by shed staff, with an empty boiler.  They thought they were filling the boiler from an external source but, due to an improper setting of an injector's valves, they were filling the tender.  When the fireman came on duty he noticed the gauge glasses were empty.  By then the damage was done.

Unlike our train sets, steam locomotives, even preserved ones, are not toys.

*

The next part will be short and will consider the most unfortunate experiences with US 2-8-0s on British railways during the War.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Pip-pip

John

[chrism]

Apart from errors by the enginemen, low boiler water level above the firebox could be caused by cresting a summit, if running chimney first - going over one if tender or bunker first - or braking, as these conditions make water flow away from the firebox. 

In those circumstances the water level can shift quite alarmingly.
I used to work Bulleids and a WD 2-10-0 "over the Alps" on the Watercress Line.

Coming from Alton it's a 1 in 60 up followed by a (IIRC) 1 in 100 down before stopping at Medstead and Four Marks. With such long boilers, if running smokebox first, we had to ensure that the water level before the top of the hill was right up in the top nut of the gauge glasses because by the time we'd stopped in the station it would be bobbing only just above the bottom nut. We'd still need an injector running because shortly after leaving the station the gradient changed again to 1 in 60 down.
It wasn't as bad running to Alton smokebox first because we were stopping on the uphill gradient so had time to get more water in before cresting the summit.

We also had to be careful running tender first. Generally we'd aim to have the water lower than 1/4 up the gauge glass, otherwise when we'd gone over the summit it'd be well above the top nut and we could risk it priming - water being drawn into the cylinders instead of steam, which doesn't do them any good at all.

[martyn]

Many thanks again, John.

I've amended one of my previous posts about the fusible plug; it wasn't the correct answer!

Looking forward to the next instalment.

Martyn

[Papyrus]

I think it was Yogi Berra who said, "In theory, theory and practice are always the same.  In practice, they aren't."

I hadn't come across that before! I love it and must find a reason to use it.

Great stuff as always, John. Keep it coming.

Cheers,

Chris

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 36


Boiler Water Level - 3: A thread diversion.

Hello Chums

Before I divert the thread, many thanks indeed to Chris @chrism for that fascinating account of the close attention enginemen pay to their boiler water levels going 'Over the Alps'.

The 1940 boiler explosion suffered by No. 6224 Princess Alexandria occurred after cresting Craigenhill Summit and when coasting down towards Carstairs. The enginemen involved did not normally work heavy long distance express trains - this one was 16 coaches - and it was the fireman's first time firing a 'Princess Coronation' 4-6-2.  It appears they were struggling with falling steam pressure climbing the bank and avoided using the injectors.

A combination of Wartime conditions and unfamiliarity with the locomotive type led to this horrid occurrence.

*

A combination of Wartime conditions and unfamiliarity with the locomotive type led to three other horrid occurrences.

These boiler explosions, caused by crown sheet failure, occurred between 17 November 1943 and 30 August 1944 and involved the same class of locomotive.  What on earth was going on?

During the War, the American locomotive builders ALCo, Baldwin and Lima produced over 2,000 'S160' class 2-8-0 engines for US Army service in liberated countries.  As such, they were built to comply with a restricted loading gauge.

Commencing in late 1942, 756 of these locomotives were landed in Britain for eventual use on railway operations in Europe.  398 were loaned to the British railways to augment existing motive power during a time of exceptionally heavy traffic.  All were returned to the US Army by October 1944.  These were good, straightforward and powerful engines which influenced later British design practice - especially Mr Ivatt's '4MT' 2-6-0 class for the LMS.

The explosions were as follows:

Honeybourne (GWR) - 17 November 1943
Thurston (LNER ex GER) 12 January 1944
South Harrow Tunnel (LNER ex GCR) 30 August 1944

The S160 locomotives had one water gauge and three test cocks on the driver's side.  The water gauge was completely different from British practice.  It was called a 'Kinger reflex' gauge and was a vertical case, square in section with three brass sides and the front made of thick glass. The glass had a series of prisms cut into its inner face - this made water appear black and steam silver in colour. 

Unlike a typical British water tube gauge glass, this type was difficult to break in normal service.  Although breakages were unlikely, the shut-off cocks were of the screw valve type, operated remotely from the glass by means of a 2 ft. 6 in. long rod, containing a universal joint, with a handwheel at the end, on the driver's side of the footplate.  The handwheel required a full turn to open or shut the screw valve  Unfortunately, for the water gauge to show a true reading, the valve had to be fully open - even if slightly closed a false high water level would be shown.

The reason for the Honeybourne and Thurston explosions was the steam valve was so stiff (the one involved at Honeybourne had a bent valve spindle) that the driver in each case thought the valve was fully open when it wasn't.

In British practice, providing the everything has been correctly assembled, the simple plug valves, with their restricted range of movement, make it easier to see if they are fully open.  In this picturingham, you can see the valve handles for both gauge glasses on River Irt are vertical and fully open:





The third explosion, at South Harrow Tunnel, was the most severe.  It occurred at night, about half-way through the tunnel.  The screw valves were fully open and the water gauge was in good order.  It was assumed that the enginemen misread the glass in the dark - please remember that water appears black in this type of gauge.

This next picturingham, from a photograph taken for the LNER, shows the buckled crown sheet of the locomotive involved in the Thurston explosion.  The view is looking through the firehole:





The crown sheet was made of 3/8 in. steel plate and was supported by 238 iron stays.  The engine was fairly new as well.

For a better illustration of a buckled crown sheet, the final picturingham, from a photograph taken for the Southern Railway, shows the inside of the firebox, looking forward to the tubeplate, of 'Lord Nelson' 4-6-0 No. 854, Howard of Effingham, which was involved in the Hinton Admiral explosion on 23 April 1945:

The heat softened the exposed crown sheet to a plastic state until it pulled off the stays - the holes for which are prominent.  Amazingly, the crown sheet has not split.





*

This diversion has brought us, I think, almost to the end of the part of this series which looks at boilers and fireboxes.  Just one more postington to go.

Once again, I'm glad to acknowledge the late CE Hewison's Locomotive Boiler Explosions, and the British Transport Commission's Handbook for Railway Steam Locomotive Enginemen as valued sources.  Any errors or omissions are, of course, my own.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerio

John

[martyn]

Thanks once again John, for an educating read.

Wikipedia adds that as well as the awkwardly place valve operating wheels, they had to be opened slowly otherwise the check valves fitted at each end would close and trap water, leading to false readings.

The RCTS green bible mentions that, on the LNER, after the difficulties of operating the gauge were known, on some engines the remotely operated valve was painted red,  opened on shed, and a notice to the effect of 'do not operate this valve' was placed on it.

Martyn

[Train Waiting]

Many thanks, @martyn .

The late Mr Hewison, to whom I hope I have given sufficient acknowledgement, was an LNER shedmaster before joining the Railway Inspectorate.  He states in his book that the four main line railway locomotive superintendents were well aware that the US locomotives' water gauges were unfamiliar to British enginemen and placed a notice 'This valve to be always in the open position' beside the steam c ock.  After the Honeybourne explosion this was changed to 'This valve must be fully open'.  Shedmasters where these locomotives were allocated gave instructions and demonstrations to enginemen about the reflex water gauges.

The tragedy at Thurston was that Ipswich shed, where the crew were based, had instructed enginemen regarding it was the driver's duty to establish that both the water gauge and the test cocks were in working order.  Although many enginemen would have been used to duplicate water gauges and would have found test cocks unfamiliar, the old GE was largely a 'single gauge glass' line, with three tests cocks.  Many ex-GER locomotives at Ipswich had this arrangement, so the accident report stated the the driver ought to have been familiar with the need to check the water level showing in the gauge using the test cocks.

The next time I encounter an 'S160' on a preserved railway, I'll have a look and see if the 'Klinger' gauge has been replaced with a 'conventional' British gauge glass... or two of them.

Thanks again and all good wishes.

John

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 37


Hello Chums

I decided at the start to break this little series into three main sections:

Frames and wheels - the rolling chassis
Boiler and firebox - generating the power
Cylinders and motion - the engine: making the power do something useful.

Of course, these three sections are united in a steam locomotive and breaking them into discrete entities was never going to be easy.

Likewise, this approach prevents a strict chronological analysis of development, the result of which is we have being going back and forward through the years.

Let's summarise some of what we have discussed, as far as the Nineteenth Century is concerned.  I think it's fair to say that, give or take at the margins, we can see four eras, each of 25 years:

1801-1825: The Pioneers. Ending, conveniently, with the opening of the Stockton & Darlington Railway.

1826-1850: The Innovators.  A locomotive of 1850, typically a 2-2-2 passenger engine such as Jenny Lind was far removed from Locomotion No. 1.

1851-1875: The Improvers.  2-4-0s for passenger work were well established but 'Singles' were favoured on some railways and, on the 'Brighton Line', Mr Stroudley later preferred the 0-4-2. Outside-cylinder 4-4-0s appeared in the 'sixties, looking slightly like American locomotives and then the classic British inside-cylinder 4-4-0 arrived at the end of the era - Mr Wheatley's design for the North British in 1871 and Jimmy Stirling's elegant G&SWR '6 Class' 'Bogie' of 1873*.  The 0-6-0 was the norm for goods work.

1876-1900: The Developers.  This was the time when the 4-4-0 and 0-6-0 became bigger and, sometimes, better.  Five axle locomotives appeared - 4-6-0s and 4-4-2s and some railways stretched the 0-6-0 into an 0-8-0.  Encouraged by Mr McIntosh's Dunalastair 4-4-0 of 1896, large-diameter boilers, with higher working pressures that could keep the cylinders well-supplied with steam, began to be used.

Which meant, by the time of Queen Victoria's death in 1901, the typical British locomotive had reached a high state of development.  And, usually, they were jolly good looking. I think it's also fair to say they were coming close to the end of the line as regards power and, importantly, efficiency.

The next era, from 1901-1925 can, I believe, be termed 'The Modernisers'.  The next postington will take us firmly into that era and might, with a bit of luck, help link the section on boilers with that on cylinders and motion.

Let's end with a picturingham:-   





The LNWR 'Precedent' class 2-4-0 was introduced in 1874 and is, I think typical of the type of locomotive that was in general use by 1875 - 2-4-0 for passenger work and 0-6-0 for goods.  I believe it is easy to trace its lineage to the typical Stephenson 2-2-2 and before that, Planet of over forty years earlier. Unfortunately, Robert Stephenson died at age 55 in 1859.  I believe, if he had lived to 70, he would have been well aware that this type of locomotive was a development of his work.  Give her a front bogie and a larger boiler with a side-hinged smokebox door and she could still pass muster twenty-odd years later.

The engine in the picturingham is No. 619 Mabel and she was named after George Stephenson's wife - Robert's mother.  Most agreably, Mabel was exhibited at the Stephenson Centenary in Newcastle upon Tyne in 1881.

* Once later designs of 4-4-0 came to the 'Sou West, the '6 Class' became known as the Aul' Bogies. Anglice: Old Bogies.  The last three of the class, rebuilt by James Manson, lasted until 1930.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Pip-pip

John

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 38


Hello Chums

[Warning.  Any physicists who happen to see this postington are advised to hide behind the sofa.  Preferably, a large sofa. In the cause of simplification, liberties, various, will be taken.]

In Part 37 of this mini-series, we saw a picturingham of Mabel, a 2-4-0 locomotive of the LNWR 'Precurser' class introduced in 1874, and I attempted to point out that she was a logical progression of the 'Stephensonian' locomotive going back to Planet of 1830.

I observed that, although boilers got bigger and wheels more plentiful, locomotives to the same basic design concept continued to be built for many years.  Many of these were very good indeed and probably came close to what the power and efficiency that could be obtained from this type of locomotive.

Since the 50 psi pressure required of entrants to the Rainhill Trials in 1829, boiler pressures had risen and pressures of around 175 psi were in widespread use around the start of the 20th Century.  As we have seen, following a thorough examination of overseas practice, Mr Churchward on the GWR was about to adopt 225 psi as a standard for large locomotives.

In order for it to do useful work, the steam which powers a locomotive has to contain as much energy as practicable, bearing in mind the duties it is intended to perform.

*

Now for the fun stuff. Welcome to John's Primary School Science Project.

I enjoyed reading some recent correspondence in a newspaper regarding how tea tastes sub-standard at high altitudes.  The learned correspondents made a point of this being because water boils at a lower temperature than the assumed 100^oC / 212^oF at altitude.  They went on to elaborate that this is due to reduced atmospheric pressure - nominally 14.7 psi at sea level.

Here's an example of my calculation that involves a steam train.  Let's take the train up Yr Wyddfa and walk the final bit to the summit.  Then boil our kettle for a pot of Yorkshire tea.  At 3,560 feet altitude, it will boil at 96.45^oC or 205.6^oF.  As we enjoy (?) our tea we can reflect that the boiling point of water varies with pressure.  The higher the pressure, the higher the boiling point.  As our train makes its way down the mountain, we can confidently assert that the steam in the boiler of the engine is at something over 100^oc / 212^oF.

This is jolly important stuff for locomotive engineers.

From a copy of a nifty table, issued, I believe, by the LMS, I'll give three examples.

Boiler Pressure (psi)  Steam Temperature: (^oc/^oF)

50                  148^oC / 298^oF
175                 192^oC / 377^oF
250                 208^oC / 406^oF

The energy contained in the steam comes from two sources - its pressure and its temperature.  As we have seen, temperature varies with pressure. In the boiler, where steam and water are contained in the same vessel, the maximum pressure and, therefore, the maximum temperature is controlled by the safety valves. Steam in this situation is called 'saturated steam' or, more colloquially, 'wet steam'.

As we have already seen, higher pressures require more careful boiler construction, potentially more weight and increased maintenance.  We have noted that the maximum boiler pressure used in normal railway service in Great Britain settled at 250psi.

All of which leads to the conclusion that the maximum temperature of saturated steam in the context of British railways would be 208^oC / 406^oF.  A problem with saturated steam at (relatively) low temperatures is, whenever it leaves the boiler it suffers from heat loss, leading to potential condensation (returning to liquid state) in the cylinders.

To obtain maximum power, it is important to minimise heat loss.  The latest developments in steam locomotives make great use of lagging.  Interestingly, it is believed what made Robert Stephenson decide on inside cylinders for Planet (with the consequent complexity of a crank axle) was Richard Trevithick telling him about the extraordinary increase in efficiency he had obtained in an old beam engine by fitting a jacket around the cylinder to minimise loss of heat by radiation.  In Planet, Robert Stephenson enclosed the cylinders with the smokebox.  We'll discuss another advantage of inside cylinders later, in the next section.

*

Hopefully, my science project gives an idea of the situation facing locomotive engineers.  What was needed was wizard wheeze to increase the temperature of the steam other than by increasing boiler pressures to a point beyond that achievable by the technology, materials and techniques of the time.

In other words, they were looking for ways to 'superheat' the steam.  Superheated steam (quick reversion to my science project) can be defined as steam at a temperature higher than its vaporisation point at a given pressure.

As far as I can establish, James McConnell on the Southern Division of the LNWR was first to experiment with superheating, in 1852, but the first really successful application in Great Britain was in JAF Aspinall's twentieth 'Atlantic' 4-4-2 for the Lancashire & Yorkshire Railway, No. 737 of 1899. 

Mr Aspinall's superheater was a  3 ft. 6 in. long drum fitting inside the smokebox.  The drum had a series of tubes and the hot gasses from the fire, having passed through the boiler tubes, then passed through the drum's tubes, further heating the steam inside. It was accepted that, being located at the coolest end of the flow of hot gasses, the additional heat imparted to the steam was modest, around 35^oC / 95^oF above the steam temperature generated by the boiler which was pressed to 180 psi.  The term for this type of device is a 'smokebox superheater'. Five similar locomotives were fitted with these in 1902.

Twelve years afterwards, Mr Aspinall (later, Sir John) mentioned that these smokebox superheaters were more like steam driers than true superheaters.  In fact the Drummond brothers, Dugald and Peter, on the L&SWR and G&SWR respectively, put a couple of short cast steel boxes in the smokeboxes of some of their later designs.  The steam was led through these boxes which were heated by the hot gasses in the smokebox.  I don't think it was worth the bother as the increase in steam temperature was in the region of 6.5^oC / 20^oF.




[G&SWR 0-6-0 No. 300 of Peter Drummond's '279' class of 1913.  The heaviest British 0-6-0 until the introduction of the LNER 'J38' class in 1926.  Festooned with Drummond gadgetry, including a steam drier in the smokebox, these were thoroughly disappointing engines.  Coal consumption was half as much again as the locomotives they replaced and an official G&SWR report described their oil consumption as enormous.  The enginemen petitioned for a bonus for working on these engines.  They were successful.] 


A much more elaborate smokebox superheater, the Phoenix, was marketed in the 1908-1914 period by the New Superheater Company.  The Furness and Hull & Barnsley both used it on several locomotives and other companies tried it on one.  Although reasonably effective, one fitted to a LB&SCR 'B4' 4-4-0 allegedly raised the steam temperature from 193^oC / 380F to 277^oC / 530^oF, it made tube cleaning and maintenance difficult.

The smokebox superheater or steam drier was an evolutionary dead end.  The way forward lay in a foreign invention by, titter ye not, 'Hot Steam Willy', as we will, hopefully, see in the next part.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-oo

John

PS Please do let me know if you see any dodgy figures.  I never trust my calculations.

[Bealman]

This ex-physics teacher awards you 10/10, and you get an early lunch mark too