Going Loco - March 2021

FRIDAY 26 MARCH

Broad Gauge Banter Part 2 - This Train Sucks!

Dawlish pump house, with the Italianate campanile adopted by Brunel to disguise the chimney of the boilers which fed steam to the pumps

Isambard Kingdom Brunel was undoubtedly a genius. Looking at his achievements, that is beyond doubt. However, you would NOT want to be one of his financial backers. While he strove to break new ground, this was often at enormous cost and he could get himself into a situation whereby either the idea was too far ahead of its time (his magnificent ship the Great Eastern being a prime example) or that he had an idea that was technically sound but the materials of the day let him down. We are going to venture into that second camp this time. The atmospheric railway is an odd concept as the idea is to not use locomotives at all. It relies on differences in air pressure to push (not suck - because physics!) trains along. The first principle of this is that air pressure is trying to be the same, everywhere. This is why wind occurs on our planet. Different areas of hot or cold on the surface means that areas of high and low pressure occur because the air expands with heat and contracts with cold. The pressure tries to equalise and as a result air moves from one place to another. The bigger the difference between two places, the more powerful the wind.

Any reader that has been in a really strong wind* will realise that there is a lot of force involved here. Enough, said the people of the early 19th century, to move some pretty large loads. The first was proposed by a chap called George Meadhurst and was akin to the old systems used for moving documents and money around buildings. A guy called Vallence actually built a person size demonstration version of this that ran in a 6’ (1.8m) cast iron tube. He settled on the bizarre choice of making the seals in his system from bear skin. Much to the relief of bears everywhere(!), his idea failed to find backers. There were a few different systems that were tried subsequently but the majority worked on the following principle. Between the tracks you place a pipe with an open slot in the top. There is a flexible seal in this slot that allows a link between a piston mounted in the tube and the rail vehicle above. Several variations were tried either by increasing the air pressure behind the piston or decreasing it in front, using lineside pumping stations to cause the motive force. This was formalised in a document by one Joseph Samuda which has the wonderfully Victorian title of ‘A Treatise on the Adaptation of Atmospheric Pressure to the Purposes of Locomotion on Railways’ in which, he reasons the advantages are:

• Direct transmission of power to trains from static power stations.**
• The train won't need to carry its fuel, saving weight.
• The power available to the train would be greater so it can ascend steeper gradients. Therefore, building new lines could be done more cheaply with fewer tunnels and bridges, etc.
• No heavy locomotive means the track and associated engineering can be less strong and therefore cheaper.
• No smoke from the loco means tunnels become more pleasant and there is less pollution overall.
• As you can only accommodate one train on each section of the line at a time, the risk of collision is eliminated.
• Samuda claimed that as the piston held the train to the track, derailments due to high speed were unlikely.
• Steam technology of the time was not nearly as safe as it would become. No steam engine boilers near the public reduced the risks...

Isambard Kingdom Brunel saw a system in operation between Dublin and Kingstown (today Dún Laoghaire) and this set him thinking. He had been engaged as the chief engineer of a new railway venture that had just gained parliamentary approval - a line between Exeter and Plymouth - known as the South Devon Railway (S.D.R.). The topography in this area is a little on the lumpy side and forever being the daring sort, Brunel decided that this was a great case for employing atmospheric traction. He engaged Jacob Samuda (his brother having passed away) to help design, operate and maintain the system. The broad gauge line was substantially complete by 1846.

Atmospheric railway station

The history of the S.D.R.'s early atmospheric operations are a bit murky but we do know that the first ‘piston carriage’ (the ‘locomotive’ bit) was delivered on the 25th February 1847 at Exeter. That same day it was taken as far as Turf to clear dirt and water out of the pipe. Passengers had to wait until 13th September to experience the first atmospheric services. It may be that goods services had been operating before that time but we just aren't sure. Teignmouth was the first destination but as time went on, the 4 trains a day slowly increased until all the services to Newton were atmospheric by 2nd March 1848. When it was working well, it was clean, efficient and fast. The top speeds have been reported as being an average of 64mph (103km/h) while pulling a 28 ton load over 4 miles and with a 100 ton load an average of 35mph (56km/h) was achieved. Fast for the day!

Memorandum to the agreement for the supply of atmospheric pipes by George Hennet to the South Devon Railway

You may have noted the hint of caution in my words however - WHEN it worked well... The first issues encountered were that the pipes chosen were too small. The original 12” (300mm) pipes were exchanged for 15” (380mm) versions and 22” (560mm) pipes were even installed, but never used, on the hilly sections. This increased the work needed from the pumping engines and resulted in a consequent rise in their fuel bills. The biggest issue was the seal in the top of the pipe. This was made of leather and was at the mercy of the weather. Rain and cold resulted in it becoming stiff. The heat of summer had the same effect. An ineffective air seal was the inevitable result. The Irish system has used a metal weather seal that opened and closed automatically as the train passed but this must have been incredibly noisy and put a great deal of strain on the components involved. The joints between the pipes and the seals on the pistons were leather too. All sorts of varnishes and whale oils*** were used but keeping up with this maintenance was unsustainable.

Exeter pump house on the left and station on the right.

This led to a lot of disagreements between Brunel and Samuda as to who was responsible for the problems and how to tackle them. The only solution was to replace the leather seal on the entire length of the line. This would cost the sum of £32,000. In 1848 this was a terrific sum of money. It's knocking on the door of £4 million in today's money... As he had advised the fitting of the metal weather seal, Samuda understandably refused to go ahead. All for the want of a decent modern elastomer... Needless to say that the last atmospheric train was an up goods arriving at Exeter at 12:30 on Sunday 10th September 1848.

The Totnes Pump house. It had been owned by a dairy since 1934, which started to demolish it in 2008. A successful campaign secured the future of the building, with it being listed Grade II that year

To put into perspective how big an issue this was, the experiment had cost a total of £433,991. Adjusted for inflation, that's over £50 million today! The S.D.R. has to deal with this and also had to face up to the fact that it owned no steam locomotives of its own and had no capital to buy any. The atmospheric system had meant that long lengths of the line were built as single track, when in locomotive operations it really needed to be double track. Not a great place to be. The company soldiered on until it was bought out by the G.W.R. on the 1st February 1876. Standing as mute witness to all this, three of the air pumping station buildings are still there to this day at Starcross, Torquay and Totnes. Amazingly, three full lengths of unused South Devon 22 inch pipe, were found buried in the beach at Goodrington Sands in 1993. They have been displayed next to our branch line since 2000, set up with some genuine pieces of G.W.R. broad gauge rails in as close to the operational set up as is possible. When we reopen - why not have a look for this remarkable survivor? As you do so, speak softly to your wallet or purse, tell it not to be frightened and that you promise to not let Mr Brunel anywhere near it...

The atmospheric pipe at Didcot Railway Centre

P.S.: Amazingly, this technology isn't dead. The Aeromovel Corporation of Brazil developed an automated ‘people mover’ system that is atmospherically powered. It's been in operation at the Porto Alegre Airport in Brazil since 2013. If you are ever out there, have a go!

* 1987 in Kent being a memorable one for your blogger. Opening the front door to see the upper canopy of a large oak tree up close is quite disconcerting...

**Just like electric trains today if you think about it!

***The atmospheric system was an environmentalist's nightmare wasn't it?! A similar system on the London and Croydon Railway used tallow (rendered animal fat) to try to solve the problem. The local rats found this particularly to their liking...

FRIDAY 19 MARCH

Broad Gauge Banter Part 1: Broadening Your Horizons?

Tim Fischer's poster Great World Railway Gauges, topped by Brunel broad gauge, is displayed in the Engine Shed at Didcot

It's time we had a broad discussion with wide ramifications. We need to gauge the feeling of our readers. That's probably enough of the - and let's be fair to them - ‘jokes’(?). Let's make a few definitions. When we talk about gauge here, we refer to the distance between the rails. There are several different gauges that have been used throughout history. The one we refer to today as ‘standard gauge’ is 4’ 8½” (1,435mm) and also goes by the name ‘Stephenson’ Gauge in deference to its populariser. The choice of this size was fairly pragmatic as many of the horse drawn tram systems that came before the advent of steam railways had a gauge very close to this.

This is one of the 2-6-2 + 2-6-2 Garratts, formerly of South African Railways, which do such excellent work on the Welsh Highland Railway and weigh in at about 60 tons.

Gauges smaller than this are known as narrow gauge. Examples include The Ffestiniog / Welsh Highland Railways in Snowdonia with a gauge of 1’ 11½” (597mm) and the Talyllyn Railway in Tywyn with a gauge of 2’ 3” (686mm) or the Welshpool and Llanfair Light Railway in Powys which has a gauge of 2’ 6” (762mm). If less than standard gauge is narrow, then greater than standard is known as broad gauge. The first in the U.K. was in Scotland. The Dundee & Arbroath Railway was founded in 1836 and was followed into the broad gauge camp by the Arbroath & Forfar Railway in 1838. They both used a gauge of 5’ 6” (1,676mm) but were soon absorbed into bigger companies and converted to standard gauge to connect with the wider Scottish system. This isolated pair were clearly outliers and the biggest user of broad gauge in the U.K. was the G.W.R. This was the brainchild of our great hero, Isambard Kingdom Brunel. He was the chief engineer of the line and took a very engineer’s decision with regard to the track gauge his line would use. He made it wide - 7’ 0¼” (2,140mm).* When you think about it, that's a very sensible idea. The wider you make the track gauge, the wider you can make your vehicles. This has several benefits.

Bristol & Exeter Railway broad gauge 4-2-4T No 44, built in 1854. This monster had 9ft diameter driving wheels and was capable of 80mph.

For example, wider trains could mean more capacity. As the height of the trains were really no bigger than the standard gauge lines, this put their centre of gravity further down too. The centre of gravity of an object is the point around which the resultant torque caused by gravity vanishes. In layman's terms, if you were to pick up an object from a single hook, if you connected the hook at the centre of gravity, the object would lift up straight and level. The lower an objects centre of gravity, the more stable it is. This is why when you go up a step ladder, the higher you go, the easier it is to tip over. It's also why formula 1 cars are low and wide. If the centre of gravity is low and the wheels are spaced widely apart, then it is far more difficult for the car to roll over when going round a corner at high speed.

The chaos of break of gauge re-created at Didcot Railway Centre in 1986.

Brunel believed this would make for a smoother ride at higher speeds. It definitely did give the benefit of not allowing trains to tip over easily. There are photos of broad gauge engines that have accidentally left the tracks but carried on upright over fairly rough ground! This gave Brunel the confidence to declare the G.W.R. a high speed railway and it was for the time at least! Don't forget that Brunel's G.W.R. were running trains in excess of 60mph in the 1840s! From an engineering point of view, Brunel's gauge decision was entirely correct. Had it been allowed to continue perhaps we could have seen 4 cylinder Castle and King class locomotives with all 4 cylinders between the frames?! It didn't continue though and the decision between standard and broad gauge is thought of as the first ever ‘format war’ This is where two similar technologies have essentially the same function but are totally incompatible. Think of it the same as 8-Track Vs. Compact Cassettes, V.H.S. Vs. Betamax or H.D.D.V.D. Vs. Blu-Ray.**

A South Devon Railway train at Dawlish shows the great width between the rails of the broad gauge and a photograph of Cowley Bridge Junction illustrates the complexity of mixed gauge pointwork.

So if the engineering was on Brunel's side, why did the broad gauge fail? Like so many better formats (Beta-Max being the obvious example) it was outside economic pressures that became its undoing. The first thing was that so much standard gauge track had already been laid that it became the de-facto just by weight of numbers alone. Despite the G.W.R. being a large railway in its own right, it was still smaller than the rest of the railways in the U.K. together which were in the majority standard gauge. This brings up the second issue - the break of gauge. Where the two systems meet, it meant that anything going from one to the other has to be unloaded from the standard gauge trains and reloaded on the broad gauge trains or vice versa. This was a huge expense when you consider that other railways could take wagons and coaches from their neighbours and pull them with their own locomotives. The large black building in the far corner of our site is an original G.W.R. transfer shed. This is one of the buildings where the trans-shipment of goods took place and is unique in still having working 7’ 0¼” gauge track in it!

A train approaching Acton towards the end of the broad gauge. The carriages have narrow bodies so they can be easily converted to standard gauge, and wide running boards to fill the gap from the platform while running on the broad gauge.

A royal commission was set up to investigate the problems. Their findings eventually resulted in the Railway Regulation (Gauge) Act 1846 which stated that“it shall not be lawful after the passing of this Act to alter the Gauge of any Railway used for the Conveyance of Passengers".While the G.W.R. was allowed to build more broad gauge lines in its immediate vicinity, it forbade the building of new broad gauge lines elsewhere. From then on the writing was on the wall. The broad gauge lasted until the 1890s when the last few broad gauge lines were converted over a weekend in 1892.

Yep - you read that correctly - in a WEEKEND! While it signalled a loss in some respects, it did result in one of the greatest and yet little known achievements of railway engineering the world has ever seen. On the 20th May 1892 thousands of workmen stood beside the line between Exeter and Penzance. That's a LONG way! The last broad gauge ‘Cornishman’ express left Paddington at 10:15 on that fateful Friday morning. The train made its way to Penzance, was turned and made the journey back to Paddington. As it moved, the line behind it closed and was relaid from broad to standard gauge. The 10:15 ‘Cornishman’ left Paddington behind a standard gauge locomotive on Monday morning. On time.

The conversion from broad to narrow gauge at Plymouth Millbay on 21 May 1892.

Broad gauge locomotives awaiting scrap at Swindon, 1892.

The remaining broad gauge locomotives, coaches and wagons were gathered at 13 miles of specially laid sidings at Swindon and cut up. Even though they set aside two locomotives - North Star and Lord of the Isles - they too were cut up in the early 20th Century. As a result, the only genuine broad gauge steam locomotive left is with our friends at the South Devon Railway. It's a tiny, vertical boiler shunting engine called, appropriately, Tiny! It's really not representative of what the broad gauge was all about. The best way to think about I heard was if you were to take all the road vehicles in the world and scrap all of them except a Reliant 3 wheeler... The G.W.R. rather guiltily built a replica of North Star in the 1920s. They found that the workers at Swindon had squirreled away quite a few of the original's components which were incorporated into it. This replica now lives with the good people at the Steam Museum in Swindon.

The last remaining original broad gauge locomotive, ‘Tiny’, on a plinth at the new Newton Abbot station on 11 April 1927 and the replica of ‘North Star’ built in 1925.

We thankfully are home to not one but two magnificent replicas of broad gauge locomotives. Iron Duke is part of the National Collection and was built for the G.W.R. 150 celebrations in the 1980s. Fire Fly was the pet project of a number of volunteers in an independent project that eventually moved to Didcot on the basis that we were the only place in the world with a stretch of broad gauge track to run it on! More on Fire Fly later...

‘Fire Fly’ and ‘Iron Duke’ at Didcot Railway Centre.

If you ignore funicular (cliff) railways and their ilk, there was one other public railway in the U.K. that had a larger gauge that the old G.W.R. This was the short lived but amazing Brighton and Rottingdean Seashore Electric Railway. This was a single vehicle that would ride out on rails across the beach even at high tide. It could do this because it was on 23’ (7.0 m) high stilts! The track gauge was no less than 18’ (5,500mm)! It could be argued that, as it ran of 4 rails, not two that it actually only had a gauge of 2’ 8 1/2” (825mm) so the jury is out on that one!

The largest ever proposed gauge was one conceived in Nazi Germany and had the explicit backing of Hitler himself. The first idea for the ‘Breitspurbahn’ was to have a track gauge of 13’ 1½” (4,000mm) but 9’ 10 1/8” (3,000mm) was eventually settled on. It obviously would have had all the same compatibility issues that Brunel’s broad gauge railway had. Like many of the ideas from that horrific ideology, the project ended due to their defeat at the end of WWII. Thank goodness.

*He originally specified 7’ (2,134mm) but later added the extra 1/4” in order to allow extra clearances after he found the original system a little too tight.

**Pick the format war according to your vintage...

FRIDAY 12 MARCH

The 10 Things Treasure Trail

It looks like we may well be able to welcome you all back to Didcot Railway Centre very soon and in preparation for this I thought I'd send you all on a treasure hunt of interesting things to try and find on some of our vehicles. This has been a group effort so thanks to Phil Morrell (No. 1466's Project Manager), Ali Matthews (one of No. 2999 & No.4079's contractors and boilersmiths) and Leigh Drew (No. 1363's Project Manager and Chairman of the Loco committee) who all chipped in. Cheers chaps! No order of importance or anything - just a bit of fun from the loco team to you!

1) No. 3822 is a life member of the Great Western Society and has the badge to prove it!

That's right, one of our locos is a society member. I don't know if this is unique in preservation but it is in our shed at least! If you look up into the cab of the engine you will see a little framed certificate. This is the engine's life membership to the society. Because, well, why not?

2) No. 5 Shannon is REALLY old.

Most people don't realise when they walk past the diminutive form of this beautiful little 0-4-0 tank loco but it was originally constructed in 1857. She is one of the oldest surviving steam locomotives in the U.K. When she first steamed, the Great Western Railway had been running trains for less than 20 years!

3) No. 6106 has unique A.T.C.* gear.

This has been mentioned previously in both the A.T.C. Blog and the Going Underground series but if you look at the A.T.C. box you will see that it has a brass dial with a little window that says ‘Shoe Catch’. This is to show whether the shoe gear is latched up out of the way so you don't drag it over the live conductor rails of the London Underground lines.

4) No. 6697 wasn't built at Swindon.

The first batch of 100 56XX Class 0-6-2s were built at Swindon between 1924 and 1927. However, the demand for these engines was so great that 50 of the second batch (including No. 6697) were - very unusually for the GWR - built by an outside contractor. If you look on the front splasher (wheel cover) of the engine, you will see her brass works plate that reveals that she was built by Armstrong Whitworth of Newcastle in 1928 and that her first number from the works that built her was No. 985.

5A) No. 1 Bonnie Prince Charlie (B.P.C.) has Port and Starboard brass signs by the windows in his cab.

In the nautical equivalent of putting an ‘L’ and ‘R’ on you shoes(!), B.P.C. has Port over the left and Starboard over the right cab windows. Reason being? B.P.C. spent its whole working life in docks and wharfs. Hence the nautical link.

5B) Bonus fact!

Left and Right are Port and Starboard because very old sailing ships( (Viking, Norman and before) didn't have a rudder to control the direction of the ship. Instead, they had a steering oar or ‘steer-board’. This was always put on the right side of the ship because most people are right handed. When coming into a wharf, you didn't want to put the steer-board between the dock wall and the boat as this would break it. So the left side was always the side that went towards the port. Over the years the Old English word steorboard was eventually changed into the word starboard.

6) No. 5322 has integral gun racks.

Another one mentioned before** but during its service on the Western Front during WW1, improvised gun racks were fitted to the spaces where the roof and side walls in the cab come together. They remained there for the entirety of the engine's working life until withdrawal in 1964. I guess extra places to hang your coat wasn't a bad thing!

7) No. 1338 has a bell.

This is unusual for U.K. steam engines. No. 1338 was originally built by Kitson of Leeds in 1898 for the Cardiff Railway before becoming G.W.R. property in 1923. For a great deal of her working life, she worked on docks, wharves and the like. This occasionally meant that she traversed lines that were like tramways, i.e. integrated into a road. The bell is just another useful way of getting the attention of road users and has the added benefit of not scaring horses so readily as opposed to a steam whistle... No. 1363 was also once so fitted but this was only a temporary arrangement.

8) No. 2999 Lady of Legend has been signed.

The eagle eyed among you might spot the word ‘Letterknight’ under the driver's side tender handrail. This is the company owned and operated by signwriter John Leeson. John was the guy responsible for the fantastic lining and lettering on No. 2999.

9) No. 08604 Phantom has a large platform step so you can ride on the front of it.

The Class 08 0-6-0DE shunters like Phantom ;were built, well, as shunting engines! No, really... As a result the steps at the front of the loco are actually quite large. This enables the shunter (the person that couples and uncouples the vehicles and not the engine - confusing isn't it?!) to stand on the front of the loco so they don't have to walk everywhere. If you think about how long trains are, you can end up walking a seriously long distance while shunting. This step enables to train to take at least part of the strain.***

10) No. 6998 Burton Agnes Hall has been quite the traveller!

While she has been out of traffic for quite a while, No. 6998 has been quite a pivotal locomotive for preservation. Like No. 3822, she also has the badges to prove it. If you look at the cab steps on the loco you will see that she has two plaques (a different one on each side). The first one shows that she took part in the 25th Anniversary celebrations of the East Lancashire Railway in 1993. On the other is the commemoration of her playing her part in the return to steam on Network South East track (something banned for a long time) in 1991/1992. When you also consider she also hauled the Western Region's last steam hauled service in January 1966, you realise the significance of this machine...

We hope we get to see you all at Didcot when it is safe for us all to meet again and when you do, enjoy the treasure hunt! I know it’s all been for the very best of reasons but I also know that I feel weird not having had my regular dose of coal smoke, oil and grease...

*See my blog Actually, Totally Cool! and the Going Underground two-parter for more details.

**See my blog No. 5322 - The Iron Warhorse for more details.

***To paraphrase an old British Railways advertising campaign. Remember that one?

FRIDAY 5 MARCH

Deeper Underground?* Part 2

So, we found out about the origins of western end of Crossrail last time but we didn't get to the raw meat. Again, with assistance from Harry Pettit, let's take a second look at the G.W.R. Womble Trains.**

A train of white-painted MICAs headed for Smithfield and approaching Paddington station in the 1930s.

The passenger services weren't the only part of the GWR's involvement with things under London. There was a freight service that required the special attentions of the both the Carriage & Wagon and the Locomotive Department. This was the service that linked Acton freight yard to the Smithfield Meat Market.

A plan of the GWR depot at Smithfield.

MICA van 105860 at Didcot Railway Centre in the 1980s.

This service lead to the development of the MICA range of 4 wheeled refrigerated freight vans. Originally, fresh meat was transported in ordinary ventilated vans with the obvious drawback of ventilation not being the same as refrigeration. In order to preserve the product better, in 1897 the first of the refrigerated vans with their characteristic ice boxes on each end and white paint scheme with red lettering was built in the X diagram.

The MICA van is in the carriage shed for a complete overhaul with new timber purchased by owners, the 813 Fund. The project will re-commence when volunteers are allowed back on site after the current lockdown.

We have one of these vehicles, a diagram X8, owned by our friends in the 813 Fund. No. 105860 was built towards the end of the MICA building period in 1925 and is currently being restored with all new woodwork by our Carriage & Wagon Department. We also have the fabulous model of TOAD No. 56985 in 7¼ in scale in the museum. If you look at this Diagram AA7 vehicle, you will see that it is much shorter than the standard TOAD designs. This is to facilitate it working the confined space of the Smithfield Branch.

The 7¼ in scale model of the Toad in the Museum and Archive at Didcot.

The issue the services presented for the Locomotive Department - as it was with all underground steam workings - was the tendency of steam engines to produce a lot of steam and smoke. No, really, they do! This tends to fill up tunnels pretty fast and make the environment basically a bit anti-breathing.

The solution to this is to have a valve in the smokebox that can direct the exhaust from the chimney and put it in a container. In a steam engine, the obvious container is the water tank and this is kind of a good news, bad news situation. The good news is that not only do we get far less steam and smoke filling the tunnel, we also get a lot of the steam condensed back into water thereby extending the range of the locomotive. The bad news is that it makes the water hot and if you read my previous post on injectors, you will find that they generally don't work well on hot water. The solution is to have one Giffard type injector and one steam powered pump. The steam pump is less efficient but will work when the water gets hot. You can then use the more efficient Giffard injector when not in the tunnels.

633 class 0-6-0T No 642, built in 1872, fitted with condensing apparatus.

633 class 0-6-0T No 643, built in 1872, photographed by Dr Ian C Allen at Clapham Junction in October 1929. This locomotive retained the condensing apparatus for the rest of its life, being withdrawn in February 1934 having run more than a million miles.

The first of these ‘condensing’ locos built by the GWR. were two of the 633 Class 0-6-0 tank engines. These were standard gauge and the first was built in 1871. At first, only Nos. 643 and 644 were fitted with condensing gear but as time went on a number of them were retro fitted. The 633 Class were also known as ‘Get Wets’, due to having no cab roof...

No 9701 built in September 1933, one of the 11 condensing locomotives derived from the 57XX class 0-6-0 pannier tanks. This photograph shows the water feed pump mounted on the side of the smokebox.

In 1933, a condensing version of the ubiquitous 57XX 0-6-0 pannier tank locomotive was developed to replace the 633s. Nos. 9700 was used as the test bed and consequently Nos. 9701 to 9710 were built as condensers from new. No. 9700 was originally No. 8700 and had the old style cab, with porthole style windows but the others in the ‘class’ had the later style taller cab with large windows which is the same as Didcot's resident panniers, Nos. 3650 & 3738. They were easily identified as their ‘pannier’ tanks partly stretched down to the running plate (really making them side tanks) and the smokebox was exposed. On the driver's side of the smokebox was the water pump and there was a conglomeration of pipes over the top of the boiler and tanks which fed the exhaust smoke and steam into the water tanks. Sadly, none were preserved but they lasted until the end of the steam era. Just two classes in all that time goes to prove that they don't build ‘em like they used to...

Condensing locomotive No 9702.

The G.W.R. locos used on the shared underground lines also threw up a few issues. Firstly, the signalling system on the underground uses pieces of equipment called trip cocks. These are small valves under the locomotive that are opened by a piece of equipment at the side of the track if the train goes through a signal at danger. The valve lets the air out or in - depending upon if you have a vacuum or air based brake system - and stops the train. It was simple job to fit these to an existing steam loco. Another more serious problem was the conductor rails. The A.T.C. (Automatic Train Control) shoe mounted under the engines sits in the middle of the loco with the shoe dangling down. On the G.W.R. lines, this made contact with the ramps near the signals*** Unfortunately, this is where the underground lines saw fit to place one of their conductor rails. This has -210v DC running through it. When connected to the positive outside conductor rail (at +420v DC) it gives a combined voltage of 630v DC. Enough to really ruin your day if mishandled.

Condensing locomotive No 9703, photographed in 1962 by Mike Peart and still displaying GWR initials.

The locos that used the L.T. tracks were fitted with self-raising A.T.C. shoes. The sole surviving 61XX class loco, our very own No. 6106 is still fitted with all this gear as it was used on the passenger services described last time. As a result the access to the platforms that were equipped with the conductor rails was restricted to those classes fitted with the retractable A.T.C. gear. It didn't mean to say however that the wrong sort of engines didn't get sent to platforms 13 to 16. It is said that a King class locomotive was sent there in error once. The results were quite literally and figuratively shocking (!) as the centre rail was directly connected to earth through the loco frames, wheels and track. In a flash, a fairly large chunk of the L.T. system was shut down.

One imagines that there was some fairly extensive explaining to do after that...

A train from Smithfield emerging into the open air at Paddington behind one of the 9700 class locomotives.

*With sincere apologies to Jamiroquai this time round.

**Underground, Overground - just like the theme music. You lot know what I'm on about. Sing along now...

***See my blog on the A.T.C. system for more details.

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