Mk III / Mk IV Compatibility

[Kingfisher200262]

A question... is there anything electrically or mechanically preventing a Mk III coach being coupled to a Mk IV coach?

I'm aware that Mk IIIs have secondary / central door locking and Mk IVs have powered doors, so I'm assuming that some knitting would be required to get them to work together, but other than that, is there anything else?

 

[route:oxford]

I'm aware that Mk IIIs have secondary / central door locking and Mk IVs have powered doors, so I'm assuming that some knitting would be required to get them to work together, but other than that, is there anything else?

If the implementation of central door locking had been devised well, you'd expect it to operate using the same protocols as the MKIVs power doors.

 

[captainbigun]

Mk4s use FDM for the door control. DVTs and Locos are fitted with an FDM rack. This is unique to the Mk4s/89/91 (and some 90s). This is all carried through the UIC connection which the Mk3s don't carry.

 

[WillPS]

I'd expect there must be some major incompatibility, given that when the 91s were introduced they had to be coupled with an HST powercar in order to provide lighting and whatnot to the Mk3s.

 

[Royston Vasey]

I'd expect there must be some major incompatibility, given that when the 91s were introduced they had to be coupled with an HST powercar in order to provide lighting and whatnot to the Mk3s.

91s would be fine with LHCS Mk 3s though, they have even hauled Mk 1s. The issue there was HST Mk 3s' electric train supply. The other reason for the presence of the power cars was of course that they also acted as 125 mph capable DVTs. I recall though that the Mk 3s needed some through wiring mods.

 

[yorkie]

I'd expect there must be some major incompatibility, given that when the 91s were introduced they had to be coupled with an HST powercar in order to provide lighting and whatnot to the Mk3s.

I'm not sure that power issues would be a "major" incompatibility, given that by itself, it doesn't prevent the haulage of the train or coupling up.

Also your post above suggests that the 91s ("they") were themselves coupled to a HST power car, that was not the case. The HST power car was at the opposite end of the train. There is some info here and here and here.

However I don't know what the question is, as it hasn't been defined.

What type of Mk 3 coach? A loco hauled Mk 3 coach or a HST Mk 3 coach?

HST Mk 3 coaches don't have buffers, whereas the loco hauled ones do. They also have different power systems.

And the question first asks just about coupling but then wants a particular detail, ie for the doors to work.

 

[Kingfisher200262]

I'm not sure that power issues would be a "major" incompatibility, given that by itself, it doesn't prevent the haulage of the train or coupling up.

Also your post above suggests that the 91s ("they") were themselves coupled to a HST power car, that was not the case. The HST power car was at the opposite end of the train.

However I don't know what the question is, as it hasn't been defined.

What type of Mk 3 coach? A loco hauled Mk 3 coach or a HST Mk 3 coach?

HST Mk 3 coaches don't have buffers, whereas the loco hauled ones do. They also have different power systems.

And the question first asks just about coupling but then wants a particular detail, ie for the doors to work.

Apologies for the lack of detail in the original question. What I was asking is whether Mk III (LHCS I guess, since as you say, HSTs were designed as DEMUs in reality, with 415 V three phase auxiliaries) coaches and Mk IV coaches could feasibly be formed together with Mk IV coaches and be operated in any kind of service.

The answers given so far are a great help, thanks.

 

[yorkie]

I don't think the HST was designed 'as a DEMU' but they were incorrectly classified as such for a while. Interestingly someone who used to argue with me that HSTs were DEMUs admitted that if GC had changed the locos, rather than the coaches, he would have then had to admit they were locos and stock, as his argument was down to compatibility with other stock. But let's not go there...!

I cannot find a definitive answer, someone will know for sure, but I suspect they probably could be coupled but I doubt the power supplies will be compatible, and the doors wouldn't operate, so I don't think it would work in service.

 

[ralphchadkirk]

I don't think the HST was designed 'as a DEMU' but they were incorrectly classified as such for a while. Interestingly someone who used to argue with me that HSTs were DEMUs

Yes they were, they still are, and no it is not incorrect. But let's not go there.

 

[dubscottie]

The Mk3's (or even the Mk4 as it would prob be easier to modify) would need major alterations to the drawbar and gangways. The centre couplers on a Mk3 can only take tension forces and not compression (hence the use of buffing plate) whereas the Tightlock couplers on a Mk4 take all the forces.

The Mk4's also have sealed gangways which would be incompatible with those on the Mk3.

Did anything come of the plan by Eastcoast in one of its guises to modify a Mk3 Buffet to run in Mk4 sets while they had one of of service for modifications?

I remember reading that they had put out a tender for the work.

 

[E&W Lucas]

Simple answer - they are totally incompatible. Mk iii have buckeye couplers, Mk IV have tightlock, and that's without considering door interlocking, etc. Never the twain shall meet!

 

[WillPS]

I'm not sure that power issues would be a "major" incompatibility, given that by itself, it doesn't prevent the haulage of the train or coupling up.

Also your post above suggests that the 91s ("they") were themselves coupled to a HST power car, that was not the case. The HST power car was at the opposite end of the train. There is some info here and here and here.

However I don't know what the question is, as it hasn't been defined.

What type of Mk 3 coach? A loco hauled Mk 3 coach or a HST Mk 3 coach?

HST Mk 3 coaches don't have buffers, whereas the loco hauled ones do. They also have different power systems.

And the question first asks just about coupling but then wants a particular detail, ie for the doors to work.

Sorry for not making that clearer, of course you are correct (although the HST powercars were given buffers at that stage so that the could work in other parts of the train, I believe?).

My understanding of the reason for classifying as DEMU was that the powercars were providing more than just locomotion and auxillary power, but also some other gubbins (above and beyond what you'd normally expect from a LHCS arrangement). I don't know much on this as you can tell, but I'm pretty sure the reason they're now (effectively) classed as loco and stock is more to do with operational ease than a retraction of a mis-numbering.

 

[yorkie]

My understanding of the reason for classifying as DEMU was that the powercars were providing more than just locomotion and auxillary power, but also some other gubbins (above and beyond what you'd normally expect from a LHCS arrangement). I don't know much on this as you can tell, but I'm pretty sure the reason they're now (effectively) classed as loco and stock is more to do with operational ease than a retraction of a mis-numbering.

By "gubbins" I can only guess you mean the ability to communicate with the other power car?

I don't think so, because by that logic the Class 37s that ran in multiple, with the through-wiring could also count as a DEMU

I think it was because of compatibility and the fact they expected them to be in fixed-formation sets. But the same logic applies to a Class 91 and a rake of Mk4s, or the Class 37s with the through wired Mk2 coaches.

An HST isn't a DEMU, it's an HST. If it had to be classified as either loco and stock or a DEMU with no alternative, then it would be loco and stock designed for a specific purpose and incompatible with other stock, I'd say.

The people who claim HSTs are DEMUs don't claim that Mk3 loco hauled coaches are part of a DEMU, so it would be interesting to see what their argument would be if GC had changed the power cars to be compatible with the loco hauled Mk3 coaches. It would also be interesting to know what they would call the 91 + 43 hybrids that ran in the late 1980s.

I didn't want to "go there" but when two or three people claim a HST is a DEMU, I have to respond

 

[ainsworth74]

I didn't want to "go there" but when two or three people claim a HST is a DEMU, I have to respond

Oh yorkie what have you done...

 

[LE Greys]

The people who claim HSTs are DEMUs don't claim that Mk3 loco hauled coaches are part of a DEMU, so it would be interesting to see what their argument would be if GC had changed the power cars to be compatible with the loco hauled Mk3 coaches. It would also be interesting to know what they would call the 91 + 43 hybrids that ran in the late 1980s.

EDMUs

Seriously, you could argue several ways. HST sets change formation sometimes, and power cars swap about fairly regularly. That argues in favour of them being locos working with stock. On the other hand, early DMUs did that sometimes, the unpowered vehicles in Trans-Pennine units (Class 124s) were basically Mk.Is with through-wiring, and the HST is basically a descendent of the Blue Pullman. However, for me, the clinching argument is the inner end of the prototype power cars. Look carefully at the one in the NRM and you see a driver's desk and controls. A powered non-passenger vehicle with two cabs is a locomotive. Production power cars don't have a second cab, but there is plenty of room for one in the old luggage compartment.

Besides, if having a corridor meant that a loco was an MU vehicle, then Mallard would have been part of an SMU for most of her service life. Corridor tender.
--- old post above --- --- new post below ---
Still, to continue the actual debate. If there were enough Mk.IIIa's available, it might just be possible to extend the EC sets to DVT+10 if they were compatible. Unfortunately, they are not. However, there is still the possibility of disbanding three sets and using those coaches to extend the others, then bringing in three Mk.IIIa sets to replace them. Otherwise, we might be looking at Mk.IIIc as a new designation, refurbished Mk.IIIa's with swing-plug doors, new corridor connections and modified electrics to work with Mk.IVs.

 

[yorkie]

A powered non-passenger vehicle with two cabs is a locomotive. Production power cars don't have a second cab, but there is plenty of room for one in the old luggage compartment.

In addition a loco only needs to have one cab (Class 20s & steam locos spring to mind) so they can't really moan about that.

Besides, if having a corridor meant that a loco was an MU vehicle, then Mallard would have been part of an SMU for most of her service life. Corridor tender.

Good point, I'll add it to my list

 

[jopsuk]

Surely if Mrk3s were being refurbed (they'd also need 125mph bogies) the "disband, and reform Mrk4s plus additional sets of mrk3s" plan would be better than having an odd coach per set?


Also, isn't the true situation with HSTs that when conceived BR intended to run them as fixed formation MUs, but quickly found maintainence was causing sets to be mixed, so removed the 253/254 numbers and promoted the "43xxx" "coach" numbers to be "loco" numbers?

 

[Kingfisher200262]

Thanks for all the answers. What IS clear is that Mk III and Mk IV coaches could never work together without one or the other (or both) needing substantial modification.

What is NOT clear, is whether an HST is a loco(s) hauled formation or a DEMU. Let's face it, even British Rail struggled with this one, first numbering as a DEMU and then re-numbering as locos and coaches. But we won't go there....

 

[jopsuk]

To be honest, does it truly matter? The classification is surely more for operational reasons than anything else- which is where the 91s + mrk 4s are definitely not MUs, as the locos swap around quite a bit. HSTs are neither "true" MUs nor "traditional" loco and coaches.
Anywhow, BR didn't "renumber" the HSTs as such, the power cars were already "coaches" with 43xxx numbers- it was somewhat a coincidence that in power terms they are type-4 locos.

 

[WillPS]

By "gubbins" I can only guess you mean the ability to communicate with the other power car?

I don't think so, because by that logic the Class 37s that ran in multiple, with the through-wiring could also count as a DEMU

I think it was because of compatibility and the fact they expected them to be in fixed-formation sets. But the same logic applies to a Class 91 and a rake of Mk4s, or the Class 37s with the through wired Mk2 coaches.

An HST isn't a DEMU, it's an HST. If it had to be classified as either loco and stock or a DEMU with no alternative, then it would be loco and stock designed for a specific purpose and incompatible with other stock, I'd say.

The people who claim HSTs are DEMUs don't claim that Mk3 loco hauled coaches are part of a DEMU, so it would be interesting to see what their argument would be if GC had changed the power cars to be compatible with the loco hauled Mk3 coaches. It would also be interesting to know what they would call the 91 + 43 hybrids that ran in the late 1980s.

I didn't want to "go there" but when two or three people claim a HST is a DEMU, I have to respond

By gubbins I mean stuff I don't understand/am not really interested in

I don't think the modern DEMU definition fits at all (a Meridian they aint!) but perhaps it was defined differently in the 60s/70s? Or perhaps the 2xx number range was perhaps originally intended for something other than "DEMU"s?

I don't know

 

[ralphchadkirk]

Thanks for all the answers. What IS clear is that Mk III and Mk IV coaches could never work together without one or the other (or both) needing substantial modification.

What is NOT clear, is whether an HST is a loco(s) hauled formation or a DEMU. Let's face it, even British Rail struggled with this one, first numbering as a DEMU and then re-numbering as locos and coaches. But we won't go there....

So why does the rule book still refer to class 253 and 254? Remembering that 2xx was DEMUs.

 

[sprinterguy]

I don't think the modern DEMU definition fits at all (a Meridian they aint!) but perhaps it was defined differently in the 60s/70s? Or perhaps the 2xx number range was perhaps originally intended for something other than "DEMU"s?

I don't know

Nope, the 2XX series was definitely meant for DEMUs, although you are right in saying that the British DEMUs were a different beast to the modern underfloor units we have today: The thumpers filled the lower numbered class sequences. The Blue Pullman trains were similar to the Thumpers in having a large diesel engine mounted above the frames in power cars at the end of the train with a small passenger saloon at the inner vehicle end (The Blue Pullman trains were classes 251 and 261), and it is widely regarded that the Blue Pullman trains were the precursor to the HSTs, and there are plenty of similarities apparent between the two designs, so it’s understandable as to why a DEMU classification scheme was adopted for complete HST rakes, but the regular splitting of power cars and carriages from formations meant that it never really worked out in practice.

 

[ChrisCooper]

Surely if Mrk3s were being refurbed (they'd also need 125mph bogies) the "disband, and reform Mrk4s plus additional sets of mrk3s" plan would be better than having an odd coach per set?


Also, isn't the true situation with HSTs that when conceived BR intended to run them as fixed formation MUs, but quickly found maintainence was causing sets to be mixed, so removed the 253/254 numbers and promoted the "43xxx" "coach" numbers to be "loco" numbers?

The Mk3 hauled coaches already have 125mph bogies, they are exactly the same as on the HST trailers. You might be thinking of the DVTs which are only rated at 110mph (but should be capable of 125mph).

The only way an unmodified Mk3 could couple to an unmodified Mk4 would be at the Mk4 TSOE which has a standard buckeye coupler. Train supply, coupling and braking are all compatable, but as has been said door control is not. Push pull would also not be available as the Mk3s and Mk4s use different wiring and connectors for their TDM. A 91 could haul an unmodified Mk3 set though, and work push pull with a Mk3 DVT.

 

[dubscottie]

Looking back at an old "Modern Railways" Mag it says that all the Mk4's are capable of being fitted with buffers at there ends..

So in theory a Mk4 could be modified easily to work with other LHCS. (don't know how they would get round gangways though..).

Going slightly off topic, which class of multiple unit is (although a different shape) a Mk4??

Also would Eurostar Power Cars be Loco's as well?

 

[Daimler]

So why does the rule book still refer to class 253 and 254? Remembering that 2xx was DEMUs.

Equally, if you look at the information panel on the rear of a FGW HST powercar, the vehicle is clearly defined as a 'Class 43', which would suggest that First Great Western are in no doubt as to their classification...

 

[Royston Vasey]

Going slightly off topic, which class of multiple unit is (although a different shape) a Mk4??

Also would Eurostar Power Cars be Loco's as well?

Well Mk 4s can of course be hauled by anything, and the Class 91 was always designed to be a separate locomotive.

Of course nobody calls Eurostar power cars locomotives, because they aren't, but in terms of relative compatibility to their coaching stock, their function and arrangement in the train, they are identical to the HST power car.

This amuses me, the reason this debate won't ever go anywhere is that many enthusiasts class the HST as their favourite train and see loco haulage as good and DMUs as bad. I think the reasons for this debate are more emotive than based on fact and history.

 

[Daimler]

Of course nobody calls Eurostar power cars locomotives, because they aren't, but in terms of relative compatibility to their coaching stock, their function and arrangement in the train, they are identical to the HST power car.

Not really - on a Eurostar, the bogies nearest the locomotive in the first and last vehicles are powered, so there clearly is distributed traction, unlike the HST, where a variable number of unpowered carriages are coupled to two distinct 'power cars' at each end of the train.

This amuses me, the reason this debate won't ever go anywhere is that many enthusiasts class the HST as their favourite train and see loco haulage as good and DMUs as bad. I think the reasons for this debate are more emotive than based on fact and history.

Again, not really. I think the TGV is pretty much unbeatable as a train, but, like the Eurostar, it has distributed traction. That doesn't bother me - but like many others, I believe that the HST is formed of two engines and a series of coaches! It's pure pedantry, of course (as it is for anyone arguing that it's a unit! ), but that's how I see it - it's got nothing to do with liking the HST or otherwise.

 

[Sir_Clagalot]

going slightly off topic, which class of multiple unit is (although a different shape) a mk4??

158/9

 

[Royston Vasey]

Not really - on a Eurostar, the bogies nearest the locomotive in the first and last vehicles are powered, so there clearly is distributed traction, unlike the HST, where a variable number of unpowered carriages are coupled to two distinct 'power cars' at each end of the train.

Again, not really. I think the TGV is pretty much unbeatable as a train, but, like the Eurostar, it has distributed traction. That doesn't bother me - but like many others, I believe that the HST is formed of two engines and a series of coaches! It's pure pedantry, of course (as it is for anyone arguing that it's a unit! ), but that's how I see it - it's got nothing to do with liking the HST or otherwise.

Not sure Eurostar's traction is really distributed in the true sense, merely reflecting the power car being a actully power car and a bit, but you are right that the HST does vary in that sense.

Pedantry indeed, I do enjoy the passion on both sides, while not giving two hoots myself!

 

[ralphchadkirk]

Equally, if you look at the information panel on the rear of a FGW HST powercar, the vehicle is clearly defined as a 'Class 43', which would suggest that First Great Western are in no doubt as to their classification...

So why do LHCS rules not apply to a HST?