With a collection of locomotives dating from Victorian times to the 1960s, there's plenty to discover.
FRIDAY 11 SEPTEMBER
The ‘Ten Year Ticket’
With 6023 “King Edward II” about to steam for the last weekend of her “ten year ticket” (get your tickets here), we look deeper at why steam locomotives once restored have to be taken out of service every ten years . . .
Boilers - there is a lot said about these vital parts of steam locomotive anatomy but the thing that often leads rise to questions about them is “why can you only use them for ten years?” Well, it’s a fairly easy answer - insurance certification. Well, that’s that sorted - see you next week.
That’s not enough?
Ok - pick up your oily rag, mug of tea and follow us once again and we will take another look beyond the workshop doors.
So - the rules say that you cannot operate a steam locomotive without the so called ‘ten year ticket’. Let’s get something straight. There is not in reality anything called a ten year ticket. The boiler inspectors will allow you, once you have overhauled your boiler, to operate your boiler for up to ten annual certificates. But we are getting ahead of ourselves here.
To gain that first year’s ticket, we need to convince the boiler inspector that the boiler is safe to operate. They will be an appointed engineer who inspects the boiler on behalf of the insurance company. In order to do this, we first remove our boiler from the engine, strip it right down so that there are no tubes, fittings and other parts attached and clean it to make inspection as easy as possible. The inspector will look over the condition of the metal, the fastenings (rivets in our case) and the stays (explained below). He will also ask us to commission a set of N.D.T. (Non-Destructive Testing) examinations.
There are certain areas that, despite the removal of all that can be easily removed, are inaccessible. This is mainly the space between the inner copper firebox and the outer steel firebox. This is the big box at the back of the boiler that we put the fire in. I know, right? The two metal skins are held fairly close together by a sort of double ended bolt thing called a stay and there are dozens of these all over the boiler. To inspect the inside of this water space as well as to find out how thick the metal is and if there are any internal or external cracks is done by two different methods.
The first is by ultrasonic testing. This is very similar to the test performed on a pregnant woman and her unborn baby except things are a little bit more powerful! This sends a pulse of ultrasound (sound waves above the usual 20 kilohertz of human hearing) through the metal. It is reflected on the other side and then picked up by a sensor. The trace that comes back on the little oscilloscope type screen can show the thickness of the metal by how far apart the two peaks are. The metal may have begun to lose thickness over the years due to corrosion so if the two peaks are too close, the metal may no longer be strong enough and will need replacing. Additional peaks are not welcome either as these can mean that there are other problems. This could be a defect in the metal or a crack. This also means replacing the metal panel.
The second test method is magnetic particle testing. This uses a fluid with metallic particles that glow under specific wavelengths of light suspended in it. The fluid is painted on and then a strong electromagnet is placed against the metal of the boiler and turned on. The metallic particles are drawn into any cracks and show up when the light is passed over them. Given their findings and those of the NDT exams, a report is drawn up by the inspector and they will point out all the defects that they want to see repaired. We then enter a phase of discussion whereby we agree on the best possible repair methods for each defect. This could be as simple as replacing a rivet or as complex as large sections of metal being replaced.
The repairs are then undertaken and the work is periodically examined as the inspector sees fit. The key thing is that all of the work is properly recorded and that all the materials that we use in them are certificated as being of the required quality. That means that we can trace the history of that material and any parts made from it from it right back to the time the material itself was made. It is of a known standard and therefore can be guaranteed as fit for purpose.
Any welding that is done on the boiler is undertaken by a coded welder. This is a welder that has been trained to and is continually assessed to be able to produce welds of a very high quality. This is mandatory for work on boilers. Technology has moved on as well so that the more expensive copper inner firebox can be welded too. This is dependent upon the grade of copper used but Swindon-built GWR boilers of the 20th century like the majority of ours seem to be compatible.
Once that’s all sorted, the boiler is reassembled. All new drawn tubes (a tube made out from a single piece of metal rather than one having a join down the side) are fitted and any last repairs and sealing using the caulking gun are undertaken. Once the boiler is pressure tight, the first test it undergoes is the hydraulic test. This is where the boiler is pumped up to 1.5 times is maximum working pressure. It then has to hold this pressure for a given time. This is done with cold water rather than steam because, if there is an undetected flaw and something goes wrong you tend to just get wet rather than have high pressure steam loose about the workshop.
This is quite stressful for the boiler. A cold hydraulic is in some ways the ultimate test. When a boiler is steamed it get hot (obvious or what?!) and the advantage there is that the metal expands and fits together even tighter. Without the heat, you lose this advantage and you then rely on the workmanship of the boilersmiths alone! Having passed that test in the presence and to the satisfaction of the inspector, the boiler will then undergo an out of the frames (not in the engine) steam test. We light a fire in the boiler and bring it up to working pressure. This is particularly important as there is a great deal of the lower firebox that you cannot see when the boiler is mounted on the loco. This will then be witnessed by the inspector and all being well, they pass it for replacement in the frames. The engine is then reassembled and a final ‘in frames’ steam test is witnessed by the inspector. Given a pass here, the boiler is then insured to run for one year.
At the end of that year, the boiler is drained of water, and the boiler inspector will return and have a good look around as much as possible and then the boiler will be refilled and steam tested for the inspector to witness again. All being well, another annual certificate is issued.
And so on up to ten years.
Sometimes, depending upon the condition of the boiler, a short extension might be granted at the end but it’s usually at the ten year mark that the boiler has to come out again and you then go right to the top of this blog post and start all over again.
Currently there are 7 projects on the go within the workshops, so the plan is finish several of those before taking 6023 to pieces to start her next overhaul. Also, as next year is our 60th Anniversary and the restoration of the King is undoubtedly one of the major achievements of the past six decades, we want to keep her on display and an integral part of our celebrations.
Given that we are now starting from the top, I seem to remember that we had a cup of tea with us when we went into the works. Would you put the kettle on please? Lots of work to do...
No, not a discussion about tea. Although, it has to be said that very little would actually get done in the works or in the loco cabs if this vital human lubricant dried up... let’s instead talk about the way we get oil to prevent our historic machines from wearing out. There are two types of oils that we use in our locomotives.* A thinner general lubricating oil and a thicker, gloopy steam oil. We will indulge our sweet tooth while we describe these lubricants. Go into your kitchen and get out (if you have them) a pot of maple syrup and a pot of traditional Golden Syrup. The thinner oil flows pretty much like a maple syrup. Take your golden syrup, open the can, move it about and imagine that the contents is a sort of greenish colour. That’s what the steam oil looks and moves like. It’s really easy to tell the difference and really important NOT to get them mixed up...**
The ‘golden syrup’ steam oil is special and has a very important job to do. The regular ‘maple syrup’ lubricating oil is fine at temperatures and in environments outside those where you encounter live steam. You see this being used for bearings on wheels, motion and the like. In the high heat environment found inside the regulator, valves and cylinders however, the lubricating oil would break down, become much thinner and would provide none of the much needed lubrication in these key areas. What the steam oil does is that in being far thicker to start with, it has much further to go to break down to the point where it becomes useless. In the hostile live steam and even superheated steam, the oil is still doing its job even though it’s not as viscous as it was when it started the day!
There are a huge number of lubricating oil pots on a steam loco and they all distribute their oil in different ways. Some of the oil pots look like you expect. Either a cylindrical or rectilinear shape with a method of filling them at the top. Some have little metal flaps on them but the vast majority are filled up by removing a cork. Take a closer look at the corks. You will find that there is a circle shape on the top. This is a piece of bamboo that goes right through the middle of the cork, top to bottom. Why? This is to slowly let air into the oil pot. If it wasn’t there, the oil would only flow out until a vacuum was created in the top of the pot.
There are other types of oil pot still. There is always a big, solid looking cylindrical one somewhere on a GWR engine. It is most often found on the driver’s side (the left side as you look at the front of a GWR engine) running plate and this one is deliberately sealed as it is the one that lubricates the vacuum pump. Some are built into the part that they serve. The ones in the connecting and coupling rods and the cross heads that support the trailing end of the piston rods are the easiest ones to spot.
Getting the oil to where it is needed can take several different methods. Splash lubrication is where there is a tube sticking up through the middle of the oil pot. Screwed into the end of this is a thing that looks a bit like a broken off tap (the thread creating tool not the method of delivering water!) This is called a restrictor and as the part is moved up and down - such as the side rods - the oil is splashed around in the pot. Only some of it escapes down the tube past the restrictor. The bearing merely sips at the oil rather than swigging it! If the pot is stationary, a worsted trimming is provided. These are little loops of a special wool that are bound together with fine wire. The bit with the wire is pushed into the tube in the middle of the pot and the ‘tails’ of worsted drape down into the oil reservoir. The worsted acts like a sponge, soaking up the oil and delivering it down the tube to get to the bearing surface.
When you get to the bearing, there can be a number of different ways of spreading the oil around. Some just have small holes with grooves cut into the bearing surface radiating away from it, down which the oil flows. Larger bearings or journals (the spinning bit that is in the bearing) can have either a pad of worsted wool - the sprung examples that live under the axle bearings are a particularly impressive example - or felt pads. some of the larger of these felt pads are in the afore mentioned cross heads and wipe oil along the surface of the slide bars they travel up and down.
The steam oil needs something a little more potent to deliver it as it doesn’t flow easily. There are two solutions on the locomotives in the collection at Didcot. The first is the wonderfully titled hydrostatic displacement lubricator. These really deserve a look at in their own blog as they are one of those ‘really clever’ bits of steam locomotive engineering. Suffice to say that they work by floating the oil on water in a big brass container which is in the cab. It uses the water at boiler pressure to force the oil from there all the way along pipes to the front end where it is atomised into the steam flow.
When some of the GWR fleet started to get larger super heaters of 3 or 4 row designs, it was decided to supply oil via a mechanical pump that was driven by the motion. The Kings (like our own No. 6023 King Edward II), Castles that had high superheat boilers fitted (like Vintage Trains’ No. 7027 Clun Castle) and later Modified Halls were fitted with this system as are a few of the non-GWR designed locos in our fleet. This is a large black box on the driver’s side running plate with lots of pipes coming out of it.
So what’s the title about? Clearly we know at least a bit about lubricating steam engines! Well, this is the final thing about oil in steam engines. It’s not like a car that you (hopefully!) check periodically and top up as required. No, a steam engine has to have all of its oil pots filled up at the start of every day that you operate it. This is because the oil will continue to flow no matter what. There isn’t a ‘switch’ as such to turn it on and off. This means that all the oil all leaks out eventually. This is called a ‘total loss’ system. So, every time you see a steam engine running, spare a thought for the driver - oiling up is his responsibility. He clambered all over, through, under and around that morning, making sure his iron horse could easily stretch its mechanical muscles. If it was a big 4 cylinder engine like a King or a Castle, he had over 100 oil pots to fill...
*Us steam engine types have heard tell of some mysterious type of locomotive that actually burns oil in a enclosed box thing with pistons going up and down inside of it, completely out of sight. No coal being burnt at all. We think this unnatural and we don’t think it will catch on.
**It is also of massive importance also not to mistake either lubricating or steam oil for maple or golden syrup. Do not expect the oils to compliment your food or either syrup to be an effective lubricant. You have been warned.
FRIDAY 28 AUGUST
A King-size education for trainspotters
I always had an inkling that trainspotting was good life-training for young lads in the 1950s. The hobby enabled boys to learn social skills by mixing with their fellows on platforms and footbridges, and competitive skills because as a trainspotter you were nothing unless you had seen more locomotives than your peers. Along the way, boys had a wonderful head start in education from the names of the locomotives they saw.
Now that trainspotting has declined as a hobby as a result of decades of derision of spotters as ‘anoraks’, plus trains becoming bland compared with the heroic days of steam, we find that young women outnumber young men at universities and the gender balance is improving at the top of industries. Could the general demise of trainspotting be the cause?
So let us look at the education a trainspotter gained from the names of the locomotives he saw in the 1950s.
King Class No 6023 "King Edward II" survives at Didcot and will be in action for the Bank Holiday Steam Up
First of all are the King class of the Western Region, formerly the Great Western Railway. Thirty locomotives numbered 6000 to 6029, starting with the first No 6000 King George V who was monarch at the time the engine was built in 1927. They went back through the mists of time – the four Hanoverian Georges in the 18th and early 19th centuries. 6007 King William III who deposed the Catholic 6008 King James II; 6009 King Charles II who succeeded his father 6010 King Charles I who had unfortunately had his head chopped off after the Civil War. 6011 King James I, the first King of both England and Scotland who reigned from 1603; then a gap for two Queens, Elizabeth I who ruled over Merrie England and defeated the Spanish Armada, and Mary who persecuted the Protestants and married the King of Spain.
The King class took up the line of Kings again with 6012 King Edward VI – the short reign of the son of 6013 King Henry VIII who famously had six wives. Then his father 6014 King Henry VII who restored peace and prosperity after the Wars of the Roses but who’s locomotive was nevertheless subjected to an ill-thought out streamlining by the GWR.
The Kings then plunge into the bewildering changes of reign which took place during the Wars of the Roses before emerging at the far side in the Middle Ages. The Kings originally went back to 6029 King Stephen (reigned 1135-1154), who lost his name when King Edward VIII succeeded to the throne in 1936 and Edward’s name was substituted on No 6029. Then a few months later, following the abdication, 6028 was named King George VI and the original name King Henry II removed.
Therefore, in history lessons our 1950s trainspotter had a succinct list of Kings, neatly underlined in his Ian Allan ABC of Locomotives, to help with understanding more than 800 years of monarchy, while his non-trainspotting fellow pupils struggled to learn the names from a standing start.
If the GWR had decided to build ten more King class locomotives, that would have taken us back to 6039 King Ethelred the Unready, which might not have been calculated to reassure passengers that the train would leave on time. Along the way we would have had No 6037 King Canute, who, according to legend, tried unsuccessfully to turn back the tide. The sight of 6037 King Canute battling through waves breaking over the sea wall at Dawlish would be wholly appropriate.
And where do Kings live? They live in Castles and the GWR helpfully provided for trainspotters’ education a Castle class with well over 100 names of castles to improve one’s knowledge of geography. Everybody knew where 4082 Windsor Castle was situated (the building), but some of the others took more than a little initiative to research in those pre-internet days. Most of the actual castles could be found on holidays in the west of England and Wales, but was 5064 Bishop’s Castle a town rather than a castle?
Also 21 Earls had crept into the Castle class list. Well, they often live in castles. Then there were a dozen named after aircraft that had become famous during the second world war. It all adds to knowledge.
After the Castles there were even more than 300 Halls, the next locomotive size down and more scope for lessons in geography. But the GWR had thrown in a few names not related to stately homes, such as concert venues 4983 Albert Hall and 5912 Queen’s Hall. Then there were a few named after halls at the University of Oxford, including 5914 Ripon Hall, 5941 Campion Hall, 5960 Saint Edmund Hall, 7900 Saint Peter’s Hall, and 7911 Lady Margaret Hall.
The next locomotive size down named after important buildings were 80 Granges, followed by 30 Manors. Although a manor might not refer to a building – such as 7808 Cookham Manor which was never a manor house. The National Trust has been Lord of the Manor of Cookham since 1934.
The final geography lesson from Western Region locomotives was the 30 County class, which taught you names of counties in England and Wales.
If a trainspotter strayed into Southern Region territory there were some wonderfully evocative lists of locomotive names with educational possibilities. The Lord Nelsons named after famous admirals taught you about Britannia’s prowess at ruling the waves through the centuries since the buccaneering days of 30851 Sir Francis Drake and 30852 Sir Walter Raleigh. Then the King Arthur class taught you the names of the Knights of the Round Table. 30454 Queen Guinevere and 30455 Sir Launcelot were familiar names even to non-trainspotters. But 30796 Sir Dodinas le Savage? That’s where trainspotters gained the edge.
The Southern Region gave you another geography lesson in the West Country class with evocative names of towns and geographic features in Wiltshire, Dorset, Somerset, Devon and Cornwall. The similar-looking Battle of Britain class taught the names of the RAF squadrons and airfields, and the military and political leaders, who saved Britain from the threat of Nazi invasion during those heroic months in the summer of 1940. The Merchant Navy class was a lesson in the names of commercial shipping companies.
If the trainspotter was to use his knowledge effectively the Schools class listed the elite educational establishments he might aspire to. To fill the list of 40 locomotives which carried the names of public schools the railway had to stray outside Southern territory and add the firmly Western Region 30922 Marlborough, 30923 Bradfield, 30925 Cheltenham, 30927 Clifton, 30929 Malvern and 30930 Radley. Further afield 30920 Rugby and 30926 Repton proved that the midlands were not entirely an educational desert, although the north of England and Scotland might well have been according to those who selected the names of Southern Railway locomotives in the 1930s. Even odder, they chose to ignore the names of girls’ schools such as Roedean, firmly in Southern territory.
Moving to the London Midland Region, our trainspotter’s geography lesson took a worldwide aspect with the Jubilee class listing the countries of the former Empire and Commonwealth. Even with the size of the Empire in the 1930s the names ran out after about 90 locomotives and there followed a mixed bag of naval heroes, battles, ancient Greeks and warships.
There was also the Royal Scot class, faithfully listing nearly 70 regiments. But a knowledge of military history was less useful at school and the names of the famous regiments have now disappeared from the British army, just as the locomotives have been scrapped, except for the two preserved examples.
On to the Eastern Region, and we are even further from the long educational lists of names with a single class theme that trainspotters enjoyed on the Western and Southern Regions. However, the Eastern Region did offer locomotives with sporting names, that the other regions had not exploited. There was a series named after football clubs, and another recurring theme was locomotives named after racehorses. Not much help for trainspotters on the eastern side of the country with their education, but at least they learned which racehorse to bet on!
FRIDAY 21 AUGUST 2020
Prairie Pondering, Part three - Prairies in the Wild.
Just like movies about Tolkien’s Middle Earth - our GWR Prairies come as a trilogy. Geeky enough reference for you? We have had a chat about the two big ones but there is another 2-6-2 to be discovered in the shed at Didcot and this one is a much smaller beast, with a very different mission statement. While the large prairies were mostly main and secondary line machines, the small prairies were destined for the fringes of the GWR network. The halcyon days of the branch line often feature in the mind’s eye of a western fan, either an auto tank (like No. 1466) or a small prairie. They are a natural part of that rural scene.No. 115 was constructed as a smaller version of the previously mentioned prototype large 2-6-2 No.99 (see Prairie Pondering Part One). The weight had been reduced from the 70+ tons of the large version to the 55 tons of this ‘Diet Prairie’ design. It was built in 1904, whilst trials of No. 99 were still ongoing. The trials of No. 115 weren’t completed either when the order was given to build more. This must say something of the confidence that Churchward had in them. As before, there were a great many detail differences between No. 115 and the much later example we have in the collection but the basic blueprint was just right. The idea was for them to take on the myriad duties on the west of England branch lines. At that the time they were the province of a motley collection of fairly aged machines. These prairies were made smaller and lighter as the track, bridges and other structures on these more rural lines tended to not be able to take the higher weights of bigger engines. The curves in the track could be a bit tighter too.
The first ten of the little prairies (not to be confused with Little Houses on Prairies - your author is clearly displaying his vintage here...) were originally conveniently numbered 3101 - 3110. As you may remember from part 1, there were a lot of engines trying to fill the 31XX number series at this time and it can be of no surprise that a renumbering scheme for GWR engines occurred in 1912. These now 44XX Class locos had a slightly higher boiler pressure than No. 115 but really there were only detail differences, with Standard 5 boilers and 4ft 1 1/2in (1.257m) tall driving wheels still being the order of the day.
The next step in their evolution was the 1906 prototype No. 2161. This version had larger driving wheels at 4ft 7 1/2in (1.41m) diameter. The first twenty had the distinction of being the last engines ever built at the GWR’s Wolverhampton Works. Wolverhampton Works is worthy of another blog some other time. We will put it on an ever increasing list... A few of these engines were leased out some of the smaller Welsh railways of the era but they had all returned to the GWR by 1914.
The story of the 45XX Class small prairies (as they were renumbered in 1912) just went on from strength to strength. Boiler pressure went to 200psi and a whole host of other small things were altered but the basics again remained the same. Churchward’s version totalled 75 engines in the end and the last was built 1924. Collett again did his ‘slightly updated’ thing which saw another 100 built beginning in 1927. These engines were numbered from 4575 to 5574 and as part of that last batch completed in February 1929 was our small prairie, No 5572. By the way, that’s 50 engines a year - along with all the other things that were going on at Swindon Works. It was a BIG place!
The small prairies really were the jack of all trades on the branch lines. They pulled both freight and passenger services and spread throughout the GWR, inhabiting many of their Welsh branch lines too. The only place they never really had much of a footing was in the London Division which was almost exclusively the realm of their larger sisters. The wonderful effect of having so many engines all to practically the same design was that things like maintenance and spares supply’s become far easier and in some ways cheaper.
No. 5572 has a small distinction as she is one of just 15 of her fellow 4575 Class to be fitted with auto working gear that allowed a special coach to be fitted that had a driving cab at one end to remove the need to spend time swapping the loco from one end of the train to the other upon reaching its destination (also on the list for future blogs!). This was made necessary by a fairly large scale rewriting of the timetables of the Welsh Valley lines in the early 1950s. These engines were not heavily loaded for their strength and could often be seen rapidly overtaking the diesel units that eventually replaced them. One last hurrah we guess!
Time ran out for these industrious and feisty little locos. The combination of the march of new technologies and the closure of many of their branch line habitats conspired against them. The 44XXs were all gone by the mid 1950s and the 4575s hung on until the last four were pensioned off in 1964. 3 of the Churchward and no less than 11 of the Collett versions survive to this day. As small, branch line engines, the preserved railways of today - which are almost exclusively ex branch lines - are the perfect place to run them. Nearly all of them (including ours) had the seaside holiday experience at Dia Woodham’s Scrapyard. Many being Welsh engines, delivering them to Barry was easy and cheap!
No. 5572 was withdrawn in 1962 and was liberated from the land of rust in August 1971. She was partially restored at Taunton before finally making her way to her new home at Didcot in 1977. As we hope we have proved, the small prairie definitely deserves its place in the Didcot Collection. They are one of those GWR types that have a charm and personality all of their own. If the good Reverend Awdry hasn’t chose a Pannier and a 14XX* Class as the GWR friends for Thomas the Tank Engine, No. 5572 would have been a great choice. Philbert the Push-Pull Prairie anyone?
*Do we need to point out that these are the characters Duck** and Oliver? Probably not.
**One last little bonus fact for you. Duck is the character’s nickname - his real name is Montague. He’s GWR, we know about these things.
FRIDAY 14 AUGUST 2020
Prairie Pondering, Part Two - The Prairie GTI
Last time we looked at the GWR Prairies we looked at the larger of the two main types and their development. We then went on to have a look at the hard life of our 5101 Class ‘Cinderella’, No. 4144. Didcot is however home to two of the large prairie breed. While the 5101 class is well represented in preservation, our second large Prairie is now unique. Let us delve into the sometimes murky world of the London suburbs... Well, ok - the suburbs at the time were probably made rather more murky by smog than too much in the way of nefarious doings that we might have implied - but it sounded good, right? In 1931, another development of the large prairie design was introduced. Here’s how it came about.
The word commuter itself is part of railway history. In America, during the 1840s (yes - it goes back that far!) the railroads of the day offered a type of ticket that was valid for a set period of time and the price for purchasing it was reduced or commuted when compared to buying the tickets daily. Think of it a bit like a modern season ticket. Henceforth, those travellers that used the ‘commuted fare ticket’ to get to and from work became known as commuters. The industrial revolution caused a huge increase in the size of towns and cities. Before the 1800s, most people would walk no more than an hour between home and work each way. The outward sprawl of large conurbations like London consumed small villages in its wake and turned many of them into mere boroughs of the city. Any new housing to provide homes for the city’s increasing populous had to be built further and further from the city centre and indeed with the invention of the commuter came the notion that you might be able to live in somewhere that was outside the city but work in it during the week.
Suburban traffic in and around Paddington was therefore of prime concern to the GWR. It was a large and growing market. It still is today. The more the market grows, the more trains you need to provide at peak times. Those trains get packed together tighter and tighter in the timetable, requiring locomotives that are powerful enough to accelerate smartly in the short distances between stations. During the late 19th Century, the diminutive 2-4-0 tank locomotives appropriately known as Metro Tanks held sway on the Paddington suburban services but by the start of the 20th Century theses engines were finding the increasingly demanding schedules a little too taxing. G. J. Churchward answered the challenge with a class of 30 4-4-2 or Atlantic Tank engines (Atlantanks?). These engines were based on the 4-4-0 38XX County Class engines and as a result they were known as the 2221 Class ‘County Tanks’. They had 6ft 8 1/2in driving wheels (the same size as the Saints and Castles), so they were capable of a fair turn of speed. As the trains got heavier and the timetable tighter, the County tanks themselves started to be pushed a bit too far. Both the versions of the 4 coupled Counties weren’t the most stable at speed due to a combination of lots of power and a short, tall wheelbase. The short coupled wheelbase (the distance between the first and last driving wheel) also didn’t exactly guarantee a precise start away from the platforms. Slipping being a common occurrence. Either way, C. B. Collett needed a new solution by 1930.
Swindon’s eyes turned to the 5101 Class large prairie. They were doing sterling work on the suburban services in the Birmingham area. A plan was formed. While a standard large Prairie was capable of performing the task in Britain’s second city very well, Collett wanted to ‘future proof’ the design for London. The answer to this was the 61XX Class. The plan with these was to use what was essentially a 5101 class engine but run it at a higher boiler pressure. 225psi as opposed to the earlier 200. An increase in boiler pressure means an increase in tractive effort. Think of them as a Large Prairie GTI model! The idea here was that the increase in tractive effort meant that they could pull more and accelerate faster.
And it worked - really well.
This boosted the tractive effort* from the 24,300 lbs of the 5101 class to 27,340 lbs on the 61XXs. They were another instant hit being able to take on all the difficult schedules could throw their way. The crews found them very easy to handle in the difficult circumstances in which they operated. The only complaint regularly levelled against them (and all the large prairies) was the poor ergonomic design of the cab. The already cramped space was further hindered with the water tanks intruding into it, the big reverser lever that got in the way of the driver and the handbrake column got in the way of the fireman. Other than that, the 61XXs pretty much ruled the roost on the London suburban services for nearly 30 years. These engines were almost exclusively London based and had homes at Old Oak Common, Southall, Slough, Reading and Aylesbury sheds to name a few. Typically they never strayed far from Paddington where their full capabilities could be put to best use. After the diesels began to replace them in 1960, they hung on here and there in increasingly menial tasks until withdrawn.
Our example, No. 6106, was completed in May 1931 and did its duty keeping London workers moving for 34 years, finally ceasing operation in 1965 and being preserved directly from British Rail service. Southall shed was where the 4 founder members of the Great Western Society (GWS) would do their train spotting. It was therefore very apt that an engine that once was housed there, came into the collection. She was first moved to the then recently disused goods shed at Taplow where one of the earliest ever GWS public events was held. The other starring engine? None other than Pendennis Castle - although it was to be a full 33 years and a journey to Australia and back before No. 4079 was to become part of the Didcot Collection.
Taplow was also the scene of a rather bizarre occurrence when No. 6106 took part in filming of the movie ‘The Bliss of Miss Blossom’. The film stared such luminaries as Richard Attenborough and Shirley MacLaine but for us of course, the real star was No. 6106. The locomotive spent quite a while in makeup and the end result was a positively psychedelic paint scheme. The engine was filmed in full view of the drivers on the GWR main line. To make it better, it was done in the middle of a fake snowstorm. Because, er, why not? It was the ‘60s you know...
No. 6106 made her way to Didcot in October 1967 and was in fairly regular use up until close to the turn of the century. Like No. 4144, she has been a very popular engine and went out to preserved lines as well as putting in her turns at Didcot. Although she has been still and quiet for quite a while now, she serves for the time being at least as one of the engines that welcomes our visitors to her cab, to see exactly how cramped it is and to allow them to guess what part of the fireman’s anatomy was constantly obstructed by the handbrake. The increased boiler pressure gained by No. 4144 during her last overhaul gives you an almost complete 61XX Class Large Prairie experience. Just the number plates give the game away...
*Think of tractive effort as the amount of force that steam engines can apply to pull or push a load. It’s a bit more complicated than that but to put the 61XX in context, the Castle has a rated tractive effort of 31,625lbs, and a King (nearly the most powerful passenger steam engine built in the UK) has 40,300 lbs tractive effort.
FRIDAY 7 AUGUST 2020
Prairie Pondering, Part 1 - Primary Prairies
While it sounds like something that should be introduced from horseback by someone wearing a Stetson, armed with a six-shooter that says ‘y’all’ a lot, the GWR Prairie is quintessentially English. The word Prairie here does not refer to the setting of a movie staring John Wayne / Clint Eastwood / Kevin Costner (delete as applicable to suit your vintage!), but to the 2-6-2 wheel arrangement.
There are two main varieties of GWR Prairie type locomotives - small and large and we will begin the first of our 3 part prairie series with a look at the history of the large ones. The story is quite complex but it starts, as most twentieth century GWR types do, with George Jackson Churchward in the early 1900s. The series of prototypes that he experimented with at that time included a 2-6-2 tank engine, completed in 1903. No. 99 had an extended trial period to really perfect the design - a common occurrence for Churchward’s experiments. This was a reasonably large tank engine - by U.K. standards at least. It was 41 ft (12.5m) long and was fitted with the latest in water boiling technology of the time - the Standard 2 Boiler. It weighed just over 72 tons fully loaded. It also had quite large driving wheels for a tank engine at 5 ft 8 in (1.72m)in diameter. All this enabled it to attain a good mix of reasonable speed, acceleration and power.
The intended duties for the design was as a mixed traffic locomotive for trains not requiring very high speeds. They however ended up proving themselves suitable for a wide range of duties in service. This early locomotive looks a little different visually to the 2 examples we have at Didcot but under the skin, a solid foundation had been laid. This is where the twisting and turning starts - in the production machines. There was a dizzying range of building, modifying and rebuilding going on, renumbering them to try and keep up with the changes too* There ended up being the original 31XX Class which became the 51XX Class, some of those eventually became rebuilt to become the 81XX Class. The 3150 Class was an updated version of the old 31XX Class with larger boilers and some of those got rebuilt and renumbered to become a new 31XX class... It makes the whole thing a bit of a pain to wade through frankly. However we have done the wading so you don’t have to!
All you really need to know is that Churchward’s successor, C. B. Collett (as he so often did) thought “that’s working very well - let’s update it all a bit.” With it’s new features including increased coal and water capacity and even a new, sleek looking lowered roof (do we sound too much like a stereotypical dodgy car salesmen?), it was just what the railway wanted. So successful was the new 5101 Class that it was built in various batches from 1929, until 1949. There were 140 of these engines built and they used the 51XX numbers that were not already in use and Nos. 4100 - 4179.**
Our survivor from the class is No. 4144 and she is of 1946 vintage. She has a fairly humble history, her most interesting duty being as a banking and pilot locomotive to help heavy trains get through the Severn Tunnel. The tunnel takes a relatively steep dive and then a matching climb the other side to get far enough down to get under the river. It can be challenging for both crews and their locomotives. This is why at each end of the tunnel, help was provided. On freight trains the extra locomotive would simply push from the rear of the train which was known as banking. On passenger trains, the assisting engines were usually put on the front and coupled up and these were known as the pilot. As you can imagine, steaming back and forth though what is essentially a tube, did not do much to promote cleanliness on the outside of the locomotive. It probably didn’t do much for the health of the crew either...
She was withdrawn in 1965 but was fortunate enough to have been purchased by a Mr Dai Woodham and sent for a little seaside holiday at Barry Scrapyard. She languished here until rescue in the form of the GWS materialised in 1974. The restoration to traffic was completed in 1997. She made a foray out to London Transport tracks in 1998 as part of the Steam on the Met gala and showed her colours, keeping pace with the rigours of the timetable of the electric trains she shared the tracks with.
A second overhaul in preservation commenced in 2010 and was finished in 2015. During this overhaul it was realised that the boiler No. 4144 was preserved with was one that had been used on a locomotive that used it operating at the higher pressure of 225 psi rather than the 200 psi she had in service. As there is no reason why the locomotive cannot handle it (more of this next time) and the boiler inspector was happy to support it, we opted to certify her boiler at this pressure. It gives her a little more strength and faster acceleration capability from a standing start which is always useful in preservation. You don’t need the top end speed it offers, but when she goes out on a run to other railways, that extra 25psi margin has been warmly welcomed by her crews. She went to the Severn Valley last year for the season and was allowed to stretch her legs a bit for once. A process much enjoyed by all.
At the time of writing, No 4144 is taking a rather more luxurious holiday than the Welsh one(!) courtesy of our friends at the Kent & East Sussex Railway although, being 2020, the amount of use she is getting has been somewhat curtailed... It’s quite pleasant to note that a locomotive that spent so much time doing hard graft in dirty conditions and generally being out of the limelight (and the sunlight for that matter), has found a role and gained popularity in preservation. She perhaps truly is the closest thing we have in the shed to a mechanical Cinderella...
*No. 99 herself was extensively rebuilt over the years and renumbered 3 times It was known as No. 3100, No. 5100 and lastly No. 8100. Sadly, she was scrapped as late as 1962 - even in her much rebuilt form, a genuine Churchward prototype would have been most welcome in today’s preservation collection. You can’t have everything...
**Why didn’t they go straight to 61XX I hear you cry? Well, there was already a class of 70 engines carrying those numbers. Tune in to further posts to hear about them...