1st gen DMUs and DEMUs

[adamskiodp]

Hi folks,

Hoping you’re all safe and well.

Forgive my ignorance, but I have a few question about 1st gen DMU’s

Why was there a need for so many different types/classes across the country? As a non railway person, some of the differences appear to be just cosmetic.

Was each class more technologically/mechanically advanced than the previous one? Surely it would have been more efficient and less driver/mechanic training needed if fewer types/designs were made?

Sorry if these are simplistic questions.

Kind regards,

 

[Harpers Tate]

I suspect that it was as much a matter of needing a large number fairly quickly and the work being farmed out to various carriage makers, with a specification that was loose enough to allow for the cosmetic variances to which you refer. Whilst there were certain classes that were the exception, the vast majority of those that were still in service in, say, the mid60s to late 70s (by which time many eary units had already gone) were actually mechanically very similar.

There were (are?) three classes of (2nd generation) Pacer for similar reasons.

 

[O L Leigh]

@Harpers Tate pretty much has it. There was a dire need for new trains, so the work was contracted out to anyone who was interested in building them. The coach builders were set the specifications on matters of drivetrain, overall size, control standards and so on and were left to get on with it, so each was able to build in it's own style. Some semblance of order seems to have been imposed a little later on, as the designs started to merge into something a bit more standardised, as exemplified by the Cl108s and the various suburban units from Derby, Gloucester and Pressed Steel. I assume the British Railways Board Design Panel took an interest and imposed some order. I'm sure that part of this was to ensure parts commonality across multiple fleets.

 

[ChiefPlanner]

There were differing "needs" for differing classes / dependant on route requirements . There are a few examples such as : -

Lightweight units for rural lines (Craven 104 sets - East Anglia)

Higher density sets for urban area (but with lower top speeds) -116 sets South Wales Valleys

"Cross Country" sets for lower density , higher quality seating - WR Class 120 for SW Wales to West Midlands etc

"Trans Pennine" sets - as above , but with "proper" buffet cars. (Liverpool to Hull etc)


And so on, of course by the mid 1970's - thanks to falling traffic and line closures , there was a surplus for a few years until scrapping began , ending in units doing sometimes "unsuitable" work......

A very complex history here. The Southern , of course, did their own thing.!

 

[O L Leigh]

Yup. But within each type there were a multitude of different classes from different workshops, all of which were slightly different to each other. To take the lightweights as an example, there were units by Met-Camm, Cravens, Whickham, Derby, Park Royal and BRCW covering TOPS classes from 100 to 113.

 

[Helvellyn]

Railcar.co.uk is a good site for lots of history as to why certain units were built and developments that took place.

Don't forget the BR desire not to beholden to a single supplier. Plus certain classes were built for certain routes, with specific requirements.

• Class 115 suburban units for the services out of Marylebone but also a small batch for Cheshire Lines Committee services in the North West.
• Class 125 suburban units for Lea Valley services out of Liverpool Street. Not really suitable for cascade after electrification due to a unique coupling code (as I recall) so quite a short life.
• Class 127 suburban units for Midland Mainline services out to Bedford from St Pancras.

All built by Derby but with various differences.

But is that any different to say Class 304/305/308 units that were visually similar, or Class 303/311 units in Scotland?

 

[O L Leigh]

Classes 125 and 127 were built with hydraulic rather than mechanical transmissions in order to give them better performance (the Cl125s were built for the Lea Valley lines and were required to work amongst the newly electrified services so needed to be a bit faster). They were built to be compatible with the mechanicals with gear change lights and switchgear but it didn't work so well in practice. If the driver was in the hydraulic he might forget that he still needed to change gears for the mechanical on the back, and so gearboxes were wrecked. The simplest solution was to give them a different multiple working code to prevent units being coupled, even though they were compatible if driven correctly.

Both classes were seen off by electrification (Cl127) and closure of the non-electrified routes for which they were built (Cl125) and not cascaded.

 

[coppercapped]

The designs were driven (sorry!) by the engine power available at the time - bus engines were used. In the early days only some 110/125 bhp per engine was available which meant that the body had to be as light as possible. So the early models were mostly on 57ft underframes.

As engine power increased to around 150bhp the bodies could be built longer, so 64ft stock became the norm. However this power level meant that the maximum speed could never exceed 70mph, the train simply ran out of puff.

BR had two design centres for its dmus, Derby for the suburban and local lines designs and Swindon for the cross-country and intercity models. Plus of course all the independent companies. However once the details of the multiple unit control had been sorted out a standard evolved, later known as 'Blue Square' which was painted on the electrical connectors. Under the solebar the arrangments of engines, transmissions and brakes were pretty much standardised in general arrangement whoever built the unit.

 

[Taunton]

It was BR policy, which came down from the government, to give out work to outside contractors, and several of them, at the time, for "new technology" (ie dmus, electric units, etc). This was not only because the Conservative government of the era favoured private enterprise, but was seen (and described as such) as a way of getting the commercial companies into the new technology, and into export markets. The extent to which the "export or die" attitude prevailed then probably cannot be appreciated now.

Because the main rail workshops had made BR reasonably self-sufficient in rolling stock construction (although they had always patronised the private builders to an extent), the latter did traditionally do much of their work for export, where the UK was a world leader up to 1939, but it was slipping as diesel and electrics came along. So the dmus were parcelled out among the major builders, like Met-Cam, Birmingham RCW, Gloucester RCW, etc, and also a few minors as well - Wickham of Ware built only a handful of dmus for BR, but were an established rail export organisation for them.

The same applied to electrics. The first 25Kv locos, or power sets for emus, came from English Electric, Metrovick, GEC, etc, and were built by different workshops. It was felt to be giving a helping hand to all these separate companies with developing their technology. The well-publicised transformer failures on early 25Kv emus in fact only affected one of the several manufacturer's products. If you read the formal accident report into these (one of the explosions caused a fatality) you find it giving repeated emphasis to the need to support the exporting manufacturers, almost at the expense of designs that sometimes went wrong.

It did get a bit extreme. For the railbuses, really for services which were quite unviable and unsuitable for the railway anyway, five different designs and manufacturers for just 22 vehicles, as a trial, was ridiculous. Stewart Joy, Beeching's Chief Economist, says so in his autobiography.

BR had two design centres for its dmus, Derby for the suburban and local lines designs and Swindon for the cross-country and intercity models.

Plus of course Eastleigh, who did their own thing and put diesel-electric power units into emu bodies.

 

[edwin_m]

I guess the DMU programme was similar to what was done with diesel locomotives under the Modernisation Plan, but rather more successful.

Batches were bought from a variety of suppliers to meet essentially the same requirement, but unlike the locos I think very few of the DMU classes were actually failures technically. This is perhaps because diesel engines and drivetrains of that sort of power rating were relatively well proven on similar duties in the bus and truck industry, whereas locomotives needed to borrow from applications such as ships, where the engine tended to run steadily for hours rather than being run up and down constantly. We also had several decades of fleet experience with the GWR railcars, whereas diesel loco experience in 1956 was confined to shunters and a few prototypes.

The early withdrawals were in my view simply a consequence of Beeching eliminating many of the duties the DMUs were built for. The railbuses were obvious casualties, so small that any service that matched their capacity was by definition carrying too few passengers to escape closure. Nearly all the withdrawn DMUs could have run for many more years if there had been a need for them. Not surprisingly when faced with a surplus, BR chose to get rid of some of the oldest and non-standard classes. But unlike locos, they got by without any new DMUs for 20 years afterwards.

 

[adamskiodp]

Some fascinating replies. Thanks to you all for taking the time to respond. Much food for thought and further investigation.

 

[bassmike]

I just wonder why they were all built with the old standard gangways and side-buffers when all other stock at the time had pullman gangways and buckeye couplings. Except of course the swindon types which had a most puzzling array of coupling's ( buckeye--buckeye with no buffing plate--buckeye and drawhook at opposite ends of the same car--- large round buffers etc: the whole thing bordered on the ridiculous. pity the poor guys who had do marshall these throwbacks.

 

[route:oxford]

The designs were driven (sorry!) by the engine power available at the time - bus engines were used. In the early days only some 110/125 bhp per engine was available which meant that the body had to be as light as possible. So the early models were mostly on 57ft underframes.

As engine power increased to around 150bhp the bodies could be built longer, so 64ft stock became the norm. However this power level meant that the maximum speed could never exceed 70mph, the train simply ran out of puff.

Why mechanical or hydraulic transmission rather than diesel electric? Were generators simply not available at that time?

 

[MarlowDonkey]

I just wonder why they were all built with the old standard gangways

Not all sets had gangways between carriages. Those seen as replacements for compartment suburban stock for example. The sets (115 I think) that operated out of Marylebone never had them, whilst the Paddington sets (117s) had gangways fitted in the late 1960s or early 1970s.

 

[Taunton]

The old LMS standard gangways were part of reducing the weight of the original alloy-constructed Derby Lightweight units, along with the short 57' length - typical minimalist LMS approach that still pervaded Derby. Notably the Western Region would have no truck with 57' cars, lightweight bodies or bus seating. It was also felt that few passengers would need to pass between cars. Remember on local services they were usually replacing completely non-corridor compartment stock. The gangway approach then carried forward to all the remaining short frame cars from the independent manufacturers, for interchangeability.

For why the form of transmission, you only have to look at the waste of space on a Southern Region 2-car unit, where virtually half of the body of one car is taken up by the engine-generator set, a huge radiator, etc, and a noise that made people put their fingers in their ears when multi-unit lashups passed. The dmu premise was that the power train was straight from commercial vehicles, both engine and gearbox, all underfloor. The bus industry in the 1950s had just moved from conventional front engine mounting to horizontal underfloor engines, and all the lubrication etc issues with engines mounted "sideways" were addressed. It has a nice weight balance in the car with two engines and transmissions, mirror imaged. The difficulties with the later Cravens cars which only had one larger engine, all cars powered, but unbalanced for weight between the two bogies and significant vibration issues, a classic "it seemed like a good idea at the time", caused their early withdrawal. The railway bus/truck approach came from the pre-war GWR cars, by AEC/Park Royal, and an equivalent LMS set with Leyland engines, which formed prototypes.

 

[Sprinter107]

Not all sets had gangways between carriages. Those seen as replacements for compartment suburban stock for example. The sets (115 I think) that operated out of Marylebone never had them, whilst the Paddington sets (117s) had gangways fitted in the late 1960s or early 1970s.

That's right, none of the suburban sets had gsngways between cars. With the class 116 class 125 and 127 units it was also impossible to move thro the cars either, but was possible on the 117 cars and I believe the class 118 cars, not too sure about the 115s. The 117s, 118s and Cardiff class 116s were gangwayed between cars around about the late 1960s, the Tyseley 116s were non gangwayed throughout the 1970s, even coming back from refurbishment still nkn gangwayed. The only gangwayed class 116s at Tyseley were a few sets from the Western region that were transferred about 1977. the Tyseley sets started being gangwayed between cars during the 1980s. I think the handful of class 116s operating in the Glasgow area may also have remained non gangwayed after refurbishment, not too sure about the few Eastern region sets based at Stratford though.

 

[Bevan Price]

The old LMS standard gangways were part of reducing the weight of the original alloy-constructed Derby Lightweight units, along with the short 57' length - typical minimalist LMS approach that still pervaded Derby. Notably the Western Region would have no truck with 57' cars, lightweight bodies or bus seating. It was also felt that few passengers would need to pass between cars. Remember on local services they were usually replacing completely non-corridor compartment stock. The gangway approach then carried forward to all the remaining short frame cars from the independent manufacturers, for interchangeability.

For why the form of transmission, you only have to look at the waste of space on a Southern Region 2-car unit, where virtually half of the body of one car is taken up by the engine-generator set, a huge radiator, etc, and a noise that made people put their fingers in their ears when multi-unit lashups passed. The dmu premise was that the power train was straight from commercial vehicles, both engine and gearbox, all underfloor. The bus industry in the 1950s had just moved from conventional front engine mounting to horizontal underfloor engines, and all the lubrication etc issues with engines mounted "sideways" were addressed. It has a nice weight balance in the car with two engines and transmissions, mirror imaged. The difficulties with the later Cravens cars which only had one larger engine, all cars powered, but unbalanced for weight between the two bogies and significant vibration issues, a classic "it seemed like a good idea at the time", caused their early withdrawal. The railway bus/truck approach came from the pre-war GWR cars, by AEC/Park Royal, and an equivalent LMS set with Leyland engines, which formed prototypes.

The Cravens / Rolls Royce dmus were hopelessly unreliable from their beginning. As soon as the arrived on the Liverpool - St. Helens - Wigan NW services, it was common to see 3 (or 5) coach formations, with one half of a failed unit tacked onto 2 (or 2 x 2) coach formations, whilst the faulty coach was being repaired. Some of them were also prone to self-destruction by fire....
The only improvement over the earlier Cravens units was that they had mostly stopped the "vibrating windows" problems.

 

[Springs Branch]

There were differing "needs" for differing classes / dependant on route requirements

-- snip --

A very complex history here. The Southern , of course, did their own thing.!

I remember reading that for the first decade or so after nationalisation the BR regions continued to act in many ways like independent fiefdoms, adhering to the traditions of each Big Four predecessor.

Perhaps it was lucky that, by the time the majority of the DMU fleet was being specified & built, "Headquarters" had just about imposed enough central control & standardisation that we didn't end up with more variations than we eventually did.

In particular that the Western Region didn't insist on designing and building its own unique family of suburban, local and cross-country DMUs at Swindon - which naturally would be quite different and incompatible with the LMR, ER, NER & ScR fleet. A bit like the WR's diesel-hydraulic locos and different signaling practices.

Only the Southern Region seemed to get away with building its D(E)MUs to be totally different to the rest of the country. Is there any widely agreed explanation of why the Southern ended up with its own very characteristic DMUs, rather than getting some tweaked version of, for example, Classes 115/116/117 ?

 

[Helvellyn]

Only the Southern Region seemed to get away with building its D(E)MUs to be totally different to the rest of the country. Is there any widely agreed explanation of why the Southern ended up with its own very characteristic DMUs, rather than getting some tweaked version of, for example, Classes 115/116/117 ?

I guess a number of reasons. Being DEMUs rather than D(M)MUs meant that the diesel engine was acting as the power source for what, traction motor wise, was effectively an EMU.

Plus it should be remembered that the Southern Region's first DEMUs were the six-car Class 201/202/203 'Hastings' units, which ran as twelve car formations in the peaks. So having two engines per unit as opposed to twelve underfloor engines (two per coach) also made sense. I also think this allowed a higher top speed, which given these were working into London intermixed with EMUs would be important for pathing purposes.

The two-car Class 204 'Hampshire' units might have made more sense to be built as DMUs but by this point the Southern Region had a design concept they liked.

Finally, pure speculation, but given that DEMUs also worked over third rail having an above floor engine possibly made sense from a safety perspective if access were needed.

 

[ChiefPlanner]

I guess a number of reasons. Being DEMUs rather than D(M)MUs meant that the diesel engine was acting as the power source for what, traction motor wise, was effectively an EMU.

Plus it should be remembered that the Southern Region's first DEMUs were the six-car Class 201/202/203 'Hastings' units, which ran as twelve car formations in the peaks. So having two engines per unit as opposed to twelve underfloor engines (two per coach) also made sense. I also think this allowed a higher top speed, which given these were working into London intermixed with EMUs would be important for pathing purposes.

The two-car Class 204 'Hampshire' units might have made more sense to be built as DMUs but by this point the Southern Region had a design concept they liked.

Finally, pure speculation, but given that DEMUs also worked over third rail having an above floor engine possibly made sense from a safety perspective if access were needed.

Good point on the Hastings and other SR D(E)MU ...

The other "factor for consideration" , was that the Southern had a tremendous standardisation ethos in rolling stock terms , whee everything could physically couple mechanically and for braking , and in some cases both diesel and electric units / locomotives could happily work in the same "train" (think 33+TC + 8 VEP out of Waterloo) , - a "bi-mode" in new speak.

Important on such a heavily trafficked system "Coupling adaptors not needed here !" (well - till the 455's came along)

 

[43096]

Important on such a heavily trafficked system "Coupling adaptors not needed here !" (well - till the 455's came along)

Surely the 508s were the break from that tradition: even more so as they lacked air pipes and jumper cables.

 

[ChiefPlanner]

Surely the 508s were the break from that tradition: even more so as they lacked air pipes and jumper cables.

Yes - quite right (though they were not around too long as I recall !) - bar the odd trailer that survives in "mixed" sets , - anyway , slightly o/topic here.

 

[coppercapped]

I remember reading that for the first decade or so after nationalisation the BR regions continued to act in many ways like independent fiefdoms, adhering to the traditions of each Big Four predecessor.

Perhaps it was lucky that, by the time the majority of the DMU fleet was being specified & built, "Headquarters" had just about imposed enough central control & standardisation that we didn't end up with more variations than we eventually did.

The engineering functions were centralised during the time of the Railway Executive and remained so. The operations and commercial departments still operated a little like the old railway companies and this was supported by the 1953 Transport Act.
The rolling stock designs produced by the main design centres (Derby, Swindon, Eastleigh) reflected the differing commercial thoughts of the regions but these were (mostly) in the fit out of the stock. One can't look at the dmus in isolation - for example the biggest differences in hauled stock - the BR Mark 1 coach - was that the Southern and Western used four aside Third Class compartments and the LMR and Eastern used three abreast. Under the solebar they were the same.
The same is true of the dmus - after the early experiments on different forms of multiple unit control a standard (Blue Square) evolved which was used on all subsequent varieties of dmu until the first of the new generation (Class 150) in 1983/4. The underfloor layout was well standardised - twin pipe vacuum brakes, inter-car cables for the remote control of engines and transmissions, a pair of diesel engine/gearbox and axle drive units, fuel tanks, heaters, exhaust routing and so on were all very similar between classes, even the later ones with bigger engines.

In particular that the Western Region didn't insist on designing and building its own unique family of suburban, local and cross-country DMUs at Swindon - which naturally would be quite different and incompatible with the LMR, ER, NER & ScR fleet. A bit like the WR's diesel-hydraulic locos and different signaling practices.

I don't understand this remark.
The GWR's signalling practice was essentially the same as the signalling practice on all the other railways in the country in that it was route-based and not speed based. (Although the LMS did install some speed based signalling). The visual difference was that the signals were lower quadrant rather then upper quadrant, but the interlocking concepts were identical. Where the GWR was decades ahead of the rest of the country was its use of ATC (now called AWS) and it was all the safer for it.

The diesel-hydraulic locomotives were just as compatible with their trains as any other diesel locomotive - they used side buffers, screw couplings and vacuum brakes. There were as many differences between different flavours of diesel-electric locomotives making them incompatible with each other, for example in driver knowledge, as there were differences between the diesel-hydraulics and the diesel-electrics.

Only the Southern Region seemed to get away with building its D(E)MUs to be totally different to the rest of the country. Is there any widely agreed explanation of why the Southern ended up with its own very characteristic DMUs, rather than getting some tweaked version of, for example, Classes 115/116/117 ?

Yes.

 

[edwin_m]

The GWR's signalling practice was essentially the same as the signalling practice on all the other railways in the country in that it was route-based and not speed based. (Although the LMS did install some speed based signalling). The visual difference was that the signals were lower quadrant rather then upper quadrant, but the interlocking concepts were identical.

That is so for Absolute Block, and the operating rules were essentially the same too. But what power signaling the GWR did was quite different from the three and four aspect signals widely adopted by the LNER and SR (the LMS didn't do much) which I believe was an agreed standard between the companies and later adopted by BR (although behind a façade of similarity the WR did their own thing there too...).

However, getting back on topic, the GWR was way ahead of the others in adopting the DMU, proving before WW2 that they were viable for secondary and branch services and even running some expresses. Perhaps if it hadn't been for WW2 most of their branch lines would have been run by "bananas" of one type or another.

 

[hexagon789]

Only the Southern Region seemed to get away with building its D(E)MUs to be totally different to the rest of the country. Is there any widely agreed explanation of why the Southern ended up with its own very characteristic DMUs, rather than getting some tweaked version of, for example, Classes 115/116/117 ?

Standardisation of parts with their EMU fleet. Their DEMUs being basically an EMU of the period but with power from an engine rather than 3rd rail.

While not done in service, I believe that theoretically a DEMU could've multied with an EMU. The 4-notch power controller of the EMUs would give notches 1, 3, 5 and 7 on the DEMUs.

Now whether thats true I'm not really sure, I can't remember where I read that anyway!

 

[Taunton]

In particular that the Western Region didn't insist on designing and building its own unique family of suburban, local and cross-country DMUs at Swindon - which naturally would be quite different and incompatible with the LMR, ER, NER & ScR fleet.

Well actually they did. The WR turned its back on the short frame, bus-seated, alloy-bodied cars that the other regions (SR excepted) all took as their mainstream fleets. Instead they built far better equipped Cross-Country cars, long frame, proper seats, steel. The Scottish Region, only, also had a range of these built, by Swindon, but they were fundamentally a WR type, although well received when transferred around later. For some reason the ScR required a unique non-standard, non-Blue Square control arrangement, which the WR did not put on their own cars.

The WR also had Suburban high-density units built for the rest of their units; others took some of these for some specific high density routes, but the WR used them for general purposes right across the Region. Again, they seemed popular when transferred around later. They got used on some lengthy services for which they were not the best.

Another WR feature was the way they had cars built by contractors, which were entirely to their own designs rather than letting the builder design them. Apart from the Swindon Cross Country units themselves, with their distinctive 2-window front ends, they always stipulated the Derby Suburban front, on all of the Gloucester RCW-built Cross-Country units (built to the same drawings as the Swindon-built ones), and the Pressed Steel and Birmingham RCW-built Suburban units (built to the Derby Suburban drawings). Both Gloucester and Birmingham had been allowed to do their own designs for other regions, but not for the WR. That was the Swindon way - they did just the same with the North British Warships, which looked identical to the Swindon ones because Swindon had given NBL the drawings to use.

Gloucester RCW had a long tradition of being a subcontractor to Swindon when they needed more capacity, they had actually built the GWR railcars numbers 19-38 in 1940, which were effectively a prototype for BR underfloor bus-engined, bus-gearbox dmus, along with other GWR work. They also did quite a lot of Mk 1 hauled stock and wagons for the WR as well. It was common for the more specialist components to be issued by the Swindon stores to Gloucester RCW for incorporation in the build.

 

[delt1c]

Standardisation of parts with their EMU fleet. Their DEMUs being basically an EMU of the period but with power from an engine rather than 3rd rail.

While not done in service, I believe that theoretically a DEMU could've multied with an EMU. The 4-notch power controller of the EMUs would give notches 1, 3, 5 and 7 on the DEMUs.

Now whether thats true I'm not really sure, I can't remember where I read that anyway!

A 205 was configured on refurbishment to work with EMU’ s. Think it was 205 111. Don’t know if it ever worked in service multipled to an EMU though. Back to 1st gen DMU’s below the sole bar they were all basically the same regardless of whether a suburban or longer distance cross country units. Due to line closures many were used on services completely unsuited to there designed use, for example suburban units used on services of over 2 hours. Whilst Cravens were used on services from Kings Cross. 8 cars made up of 4x2 car units resulting in 8 driving cabs and 4 brake vans in each , completely wasted space.

 

[hexagon789]

For some reason the ScR required a unique non-standard, non-Blue Square control arrangement, which the WR did not put on their own cars.

The Scottish Region XC sets (TOPS Class 120) were Blue Square. Only the older Swindon InterCity (79xxx and TOPS Class 126) were not Blue Square.

 

[Bevan Price]

For anyone interested, the book "DMU and EMU Recognition Guide" by Colin J Marsden includes photos and some technical details of all DMU & EMU types - including pre-BR designs up to its date of publication in 2013. It includes summary of numbering series (but not lists of every single coach number).
Published by Ian Allan, ISBN 978-0-7110-3740-3.

(Probably out of print, but several copies advertised on ebay at time of posting)

 

[matchmaker]

The Scottish Region XC sets (TOPS Class 120) were Blue Square. Only the older Swindon InterCity (79xxx and TOPS Class 126) were not Blue Square.

White Circle on the 79xxx and 126. Another difference was that the Class 120 had screw couplings and scissors gangways, the 79xxx and 126 buckeyes and Pullman gangways.

The unique feature of the Scottish 120s that I remember best is that they were fitted with Mansons automatic token exchange apparatus operated by the guard, principally for use between Aberdeen & Inverness.