BR(S) DEMU could they have been developed further.

[D7666]

28 minutes ago, jim.snowdon said:

In some ways, they were developed further - the Blue Pullman sets were essentially the same technology. So, in principle, were the Trans Europ Express train sets.

Also not fully true.

BP are vastly more complex.

The SR DEMU motor coach is fully independant - the engine and motors are all in one car, the other other cars are all trailers.

The BP sets different in that they are distrubuted traction technology. Each half of a BP set has one diesel engine (in the lead car) driving 4 traction motors - but - only 2 of those motors are in the lead car, on the inner bogie; the other two motors are on the adjacent bogie under the adjacent car. The same is mirrored at the opposite end. No SR DEMU is like that.

Further, on a BP an auxiliary diesel engine for train electric power is fitted to one of the other intermediate cars relieving the main engine of some of that load; again no SR DEMU is like that.

[jim.snowdon]

10 minutes ago, D7666 said:

Also not fully true.

BP are vastly more complex.

The SR DEMU motor coach is fully independant - the engine and motors are all in one car, the other other cars are all trailers.

The BP sets different in that they are distrubuted traction technology. Each half of a BP set has one diesel engine (in the lead car) driving 4 traction motors - but - only 2 of those motors are in the lead car, on the inner bogie; the other two motors are on the adjacent bogie under the adjacent car. The same is mirrored at the opposite end. No SR DEMU is like that.

Further, on a BP an auxiliary diesel engine for train electric power is fitted to one of the other intermediate cars relieving the main engine of some of that load; again no SR DEMU is like that.

But, it's all the same technology - a diesel generator set mounted in the car body driving electric traction motors on the bogies. The fact that on the Pullman sets one of the two motor bogies was on the adjacent car has nothing to do with the principles of distributed power, but was the consequence of weight distribution issues with the power cars.

[jim.snowdon]

20 minutes ago, D7666 said:

Sorry

You are wrong

The issue with Mk1 arose after the Cannon Street accident with bodies seperating from frames. That is the underlying issue demanding removal of Mk1. construction - not just actual Mk1 coaches. Swing doors (as they are properly called) and lack of locking is a secondary and more recent issue.

The NIR DEMU are Mk1 construction. It was looked at by one of the leascos to see if they could be used in GB.  Not feasible because they are of Mk1 construction.

 

 

The Cannon Street accident in 1991 did not involve Mk1 stock at all, but SR designed emu stock, where the principal issue was the absence of any effective means of preventing telescoping of the carriages. The earlier 1961 accident involved an SR emu and a BR Hastings demu, the latter being Mk1 stock. There was relatively little damage to both units, apart from some carriages of the Hastings unit being rolled over and body damage, but no reported separation, to one of the carriages in the latter unit.

 

Critically, BR Mk1 stock remains authorised for use on the National network (unlike pre-Nationalisation coaching stock, which is barred because they do not meet crashworthiness standards).

[roythebus1]

How about the Bluebell's Chesham set which I believe has Mansell wooden wheels which was authorised to run from East Grinstead to Kings Cross a few years ago? But that was ECS for a film job.

[phil-b259]

1 hour ago, roythebus1 said:

How about the Bluebell's Chesham set which I believe has Mansell wooden wheels which was authorised to run from East Grinstead to Kings Cross a few years ago? But that was ECS for a film job.

 

The key phrase which is missing is 'in passenger service'!

 

Any coach of any age can (assuming it meets a few basic checks' and being registered correctly) be run of Network Rail Infrastructure - it just cannot do so with passengers on board.

 

In other words it is regarded as a wagon.... not a coach!

[phil-b259]

7 hours ago, jim.snowdon said:

Critically, BR Mk1 stock remains authorised for use on the National network (unlike pre-Nationalisation coaching stock, which is barred because they do not meet crashworthiness standards).

 

For how long though?

 

The ORR have produced several papers where they openly question how long a Mk1, however well maintained can remain in use on the national network. Yes the use of a separate underframe means that body repairs (even the wholesale replacement of sections including crucial elements like end loading piers) are relatively easy to do but at some point those underframes are going to be considered too old to be trusted running round at 75mph.

[jim.snowdon]

11 hours ago, phil-b259 said:

 

For how long though?

 

The ORR have produced several papers where they openly question how long a Mk1, however well maintained can remain in use on the national network. Yes the use of a separate underframe means that body repairs (even the wholesale replacement of sections including crucial elements like end loading piers) are relatively easy to do but at some point those underframes are going to be considered too old to be trusted running round at 75mph.

Mark 1s are a bit like the DC3 - conservatively engineered. As a steel structure, the only real impediments to life are corrosion and wastage of the structural components, and cracking, particularly at the welds. Essentially, much the same sort of considerations as apply to iron and steel railway bridges, some of which, as well all know are still in use with service lives considerably greater than the Mark 1 carriage. In some ways, the Mark 2 carriage may be a greater long term liability, as the body is part of the structure and is affected by corrosion problems.

 

[D7666]

[1]

1991 Cannon Street accident train - to which I was refering - was more Mk1 then SR.

 

The train was 10EPB formed 4EPB + 4EPB + 2EPB of which the first and last units were BR Mk1 EPB and only the middle unit SR EPB => the train was 60% Mk1. The principal damage was to the 1st 2nd 5th and 6th cars => 50% of the principal damage was to Mk1.

 

It is the end cars that are most vulnerable in an accident.

 

I rechecked the accident report before posting that; the report gives the unit and car numbers so there is no doubt.

 

 

[2]

Cannon Street 1991 followed the 1988 Clapham accident; the latter raised big questions about Mk1 + any other seperate body on underframe crashworthiness, Cannon Street catalysed action.  But aftermath of Clapham focussed on the signalling issues not train destruction.

 

 

[3]

Swing doors (their correct name; slam doors is the popular but technically incorrect name) is a different issue.

 

Up thread i was refering to construction, and construction only, where the body is seperate from the underframe. This applies to all TRUE Mk.1 and includes majority of predecessor designs like the SR EMU rebuilds.

 

 

[4]

The underlying reason for Mk1 elimination was crashworthiness not swing doors nor lack of central locking. 

 

That is why they did the 'cup and cone' anti over ride device experiments, and why the prototype 'networker classic'; the latter still suffered from it being a seperate body on underframe even though it welded not bolted, and was rejected for that reason, it was seperate.

 

"slam doors" is the popularist version if only because doors are tangible and underframes not.

 

 

[5]

Those remaining Mk1 on main line are not permitted to carry passengers when they are the end vehicle. This is due to crashworthiness lack of.  Both ends - of any formation; that is why there either a Mk2 (at least)  if carrying passengers or a utility/generator/out of use coach at either end. The generator coach doubles in this function.

 

 

[6]

The NIR 450s were similar seperate body on underframe; welded or not, they were still seperate which is why, when the leasco that did the investigation, rejected them.

 

Simply welding a few bodyside panels of one type to an underframe of a wholly different type is a production method of fixing the two together, not a method of structural integrity that meets crashworthiness need.

 

 

 

Edited July 7, 2023 by D7666

[jim.snowdon]

2 hours ago, D7666 said:

1991 Cannon Street accident train - to which I was refering - was more Mk1 then SR.

 

The train was 10EPB formed 4EPB + 4EPB + 2EPB of which the first and last units were BR Mk1 EPB and only the middle unit SR EPB => the train was 60% Mk1. The principal damage was to the 1st 2nd 5th and 6th cars => 50% of the principal damage was to Mk1.

 

It is the end cars that are most vulnerable in an accident.

The BR version of the EPB design is not 100% Mk1. The underframe and body construction is derived directly from the Mk1, but the intermediate buffing and drawgear arrangements within the unit are not. They retained the single buffer and chain coupling of earlier SR designs rather than the knuckle coupler and centre buffer/pullman gangway arrangement of the Mk1.  If you refer to the accident report, it was the first and second coaches of the second 4EPB that telescoped due to the inability of the inter-car coupling to resist overriding. Once that happens the relatively weak ends of the non-gangwayed Mk1 body construction have little crashworthiness. Much of the crashworthiness of the full Mk1 carriage comes from the combination of the coupler, gangway and end framing of the car body, the most critical part being to keep the gangways in line and channeling the forces into the body structure.

2 hours ago, D7666 said:

Cannon Street 1991 followed the 1988 Clapham accident; the latter raised big questions about Mk1 + any other seperate body on underframe crashworthiness, Cannon Street catalysed action.  But aftermath of Clapham focussed on the signalling issues not train destruction.

Correctly. The destruction in the Clapham collision was primarily due to the collision of the down train with the laterally displaced stock of the up train, and was confined to those few carriages. The rear 8 cars of the second up train were barely damaged, as were the front cars of the first train. Designing for collisions with already derailed trains is generally beyond the limits of practicality due to the number of variables involved, as the collision at Greatt Heck amply demonstrated, and that was with much more modern stock.

 

2 hours ago, D7666 said:

Up thread i was refering to construction, and construction only, where the body is seperate from the underframe. This applies to all TRUE Mk.1 and includes majority of predecessor designs like the SR EMU rebuilds.

There are only three types of construction in this respect - separate body and underframe, typical of pre-BR stock, where the carriage body can be lifted off the underframe as a complete unit, combined body and underframe, where the carriage body is built directly on the underframe structure and cannot be separated, as in the Mk1, and integral construction, where there is no underframe as such and the carriage body is the main structural member, as in the Mk2 and subsequent designs. Part of the reason the Mk1 is built the way it is to provide better crashworthiness than the older underframe+body designs, where the bodies had a distinct tendency to part company with the underframes in an accident, notwithstanding the general lack of crashworthiness of their timber framed bodies.

2 hours ago, D7666 said:

"slam doors" is the popularist version if only because doors are tangible and underframes not.

Everyone in the railway industry (and I have been a railway engineer for the last half century) refers to slam door stock, and knows exactly what is meant. The term 'swing doors' is one that I have not come across within the industry.

 

2 hours ago, D7666 said:

Those remaining Mk1 on main line are not permitted to carry passengers when they are the end vehicle.

I do not believe that that is true (and I am not going to comb through videos of steam specials to find out).

 

2 hours ago, D7666 said:

The NIR 450s were similar seperate body on underframe; welded or not, they were still seperate which is why, when the leasco that did the investigation, rejected them.

You have their report?

 

[phil-b259]

9 hours ago, jim.snowdon said:

Mark 1s are a bit like the DC3 - conservatively engineered. As a steel structure, the only real impediments to life are corrosion and wastage of the structural components, and cracking, particularly at the welds. 

 

 

And this is what I think the ORR are highlighting.

 

While its relatively easy to replace parts of the Mk1 bodyshell with new material you will get to a point where the underframe itself has lost so much strength due to 'natural wastage' it can no longer perform as designed.

 

Yes there is nothing to stop a brand new MK1 underfame being built from fresh metal and a existing body put upon it but the costs of such an exercise are not going to be trivial.

 

 

[Wickham Green too]

11 hours ago, phil-b259 said:

... you will get to a point where the underframe itself has lost so much strength due to 'natural wastage' it can no longer perform as designed. ...

... and I suspect we're getting close to the point when all Mk1s are deemed to be so compromised and a blanket ban imposed - so the ORR, HSE or whoever don't have to round actually checking them all.

[bécasse]

It is perhaps interesting to note that many of the injuries incurred by passengers in the second up train involved in the Clapham Junction accident were caused as a result of a traditional feature of railway rolling stock - in this case heavy briefcases falling from luggage racks.

 

Ironically one of those so injured was the man whose attitude to getting jobs done was the primary cause of the accident. It didn't change him though.

[Nick C]

16 hours ago, jim.snowdon said:

The underframe and body construction is derived directly from the Mk1, but the intermediate buffing and drawgear arrangements within the unit are not. They retained the single buffer and chain coupling of earlier SR designs rather than the knuckle coupler and centre buffer/pullman gangway arrangement of the Mk1.  

I've always wondered why they did that with the EPBs, but used knuckle couplers internally on the Hampshire units, which were also non-gangwayed. It can't have been for compatibility with older stock as the units were fixed, and of course had buckeyes on the outer ends - which I don't think the SR ones did.

[keefer]

17 minutes ago, Nick C said:

I've always wondered why they did that with the EPBs, but used knuckle couplers internally on the Hampshire units, which were also non-gangwayed. It can't have been for compatibility with older stock as the units were fixed, and of course had buckeyes on the outer ends - which I don't think the SR ones did.

I read (can't remember where, maybe Colin Marsden's SR EMUs 1898-1948) that using buckeyes within units would mean that 12-car trains would be too long for the longest platforms at Waterloo or Victoria.

I'll try and find the book to confirm.

[45655]

The SR centre buffer and link coupling was a cheap and robust solution where units rarely needed to be split.

 

I think intermediate buckeyes were fitted to the DEMUs to allow units to be reformed more easily, as the power cars were likely to require more down time than the trailers. (Imagine trying to lose a centre trailer at Alton with links and buffers.)

 

Mark 1 loco hauled non corridors were fitted with screw couplings but could presumably have been retrofitted with buckeyes as the apertures are present in the headstocks for buffing plates. Not sure if this applied to Mark 1 type EPBs, etc.

 

Keith

Alton.

[BernardTPM]

The slam part of slam doors really refers to the catch mechanism, closing the door firmly by the angled, sprung catch. Older doors would only shut by turning the handle.

[bécasse]

5 minutes ago, BernardTPM said:

The slam part of slam doors really refers to the catch mechanism, closing the door firmly by the angled, sprung catch. Older doors would only shut by turning the handle.

Not just older doors, Bernard. One post-grouping company stuck to the old style door mechanism right through to the bitter end. I have often wondered whether the fact that one saw so much ex-LMS stock in use on WR local trains in the West Country was because you could slam the doors on them. Even on BR-built Hawksworth stock one had to turn the handle to allow the door to close.

[BernardTPM]

Yes, adoption of it was slower on the GWR, but as far as I know, all BR design stock used it for non-power doors.

[Wickham Green too]

8 hours ago, keefer said:

... using buckeyes within units would mean that 12-car trains would be too long for the longest platforms at Waterloo or Victoria.  ...

Well yes, sort of - but ANY sort of twelve-car train would have been too long for the platforms on suburban routes and ten cars only permissible once the ten-car-scheme had been implemented. Twelve car sets of CEP/BEP/CEP stock and successors were, of course, buckeyed throughout.

[Tom Burnham]

9 hours ago, Nick C said:

I've always wondered why they did that with the EPBs, but used knuckle couplers internally on the Hampshire units, which were also non-gangwayed. It can't have been for compatibility with older stock as the units were fixed, and of course had buckeyes on the outer ends - which I don't think the SR ones did.

All EPB units (SR and BR design) had buckeye couplers and buffing plates at the end of units - so could be coupled to any other EPB/HAP/*EP unit, at least mechanically.  4-SUB units still had screw couplers between units.

[pete_mcfarlane]

10 hours ago, keefer said:

I read (can't remember where, maybe Colin Marsden's SR EMUs 1898-1948) that using buckeyes within units would mean that 12-car trains would be too long for the longest platforms at Waterloo or Victoria.

I'll try and find the book to confirm.

Blood and Custard has more details: https://www.bloodandcustard.com/br-2epb.html

 

 

[jim.snowdon]

10 hours ago, Nick C said:

I've always wondered why they did that with the EPBs, but used knuckle couplers internally on the Hampshire units, which were also non-gangwayed. It can't have been for compatibility with older stock as the units were fixed, and of course had buckeyes on the outer ends - which I don't think the SR ones did.

I've always wonder why Maunsell, having adopted knuckle couplers and pullman gangways on his steam stock, then reverted to screw couplings and side buffers for the Portsmouth electrics.

 

As regards the non-gangwayed BR electric stock, whilst the single buffer and chain was retained for almost all of the stock, I recall that a later batch of the 2HAPs were fitted with knuckle couplers and buffing plates within the unit. The other oddity was that the 1951 3-car sets for the North London Line, which were the first of the BR designed units were equipped with screw couplings and side buffers at the same time as the knuckle coupler had been adopted as normal for the Southern. I'm not certain that they weren't screw coupled within the unit as well.

 

[jim.snowdon]

9 hours ago, bécasse said:

Not just older doors, Bernard. One post-grouping company stuck to the old style door mechanism right through to the bitter end. I have often wondered whether the fact that one saw so much ex-LMS stock in use on WR local trains in the West Country was because you could slam the doors on them. Even on BR-built Hawksworth stock one had to turn the handle to allow the door to close.

Something that has now come to haunt the Severn Valley Railway as an operator of ex-GWR stock. HMRI (aka the ORR) have, I believe now required that they are either taken out of use or fitted with proper slam locks.

[pete_mcfarlane]

11 minutes ago, jim.snowdon said:

I've always wonder why Maunsell, having adopted knuckle couplers and pullman gangways on his steam stock, then reverted to screw couplings and side buffers for the Portsmouth electrics.

There was a problem with the buckeye auto-couplers fitted to one of the first batches of Southern suburban units in the 1920s, which were then removed and replaced with the centre buffer. This experience supposedly put Raworth (who was responsible for the design of EMUs) off using them. 

 

 

[Tom Burnham]

9 hours ago, pete_mcfarlane said:

There was a problem with the buckeye auto-couplers fitted to one of the first batches of Southern suburban units in the 1920s, which were then removed and replaced with the centre buffer. This experience supposedly put Raworth (who was responsible for the design of EMUs) off using them. 

 

 

Indeed there was.  Incidentally the buckeye couplers used within that one batch of suburban units were US MCB couplers rather than the Laycock take on the buckeye coupler used with Pullman gangways (or the buffing plates shaped like the lower part of a Pullman gangway faceplate).  I'll have to look out old photos to see if EPB units had retractable side buffers as on Mark 1 loco hauled corridor carriages.