HST: DMU or LHCS

[najaB]

Wouldn't the 'ultimate' definition be Network Rail's variable usage charges?

Not really, they're an infrastructure operator so they'll classify based the rail/track interface characteristics, not operational ones.

 

[najaB]

As nlogax commented, I can't see any difference in principle between an HST and a topped and tailed loco-hauled set with remote control of the rear loco.

Except that HST power cars are designed to work with HST trailer cars and nothing else. Unlike a 'genuine' loco which will work with anything.

 

[43096]

Except that HST power cars are designed to work with HST trailer cars and nothing else. Unlike a 'genuine' loco which will work with anything.

But there are plenty of combinations of loco that won't work with things. A vac-braked loco won't haul air-braked stock. An HST power car can haul any air-braked stock. You can keep on going and going and going with this debate, and there will always be something that "disproves" it the other way.

HSTs are HSTs is the simplest way of defining it....

 

[najaB]

An HST power car can haul any air-braked stock.

Physically haul, yes. Designed to work with, not really.

I agree that a HST power car by itself is a locomotive but a complete HST is a MU.

 

[sprinterguy]

Thanks for the correction, I'd had a quick look for photos of couplers but I hadn't found any.

No problem, the couplers on the Pendolinos are retractable and hidden behind a sliding panel on the nose in normal service.

Come to think of it, having checked a few photos I'm not sure that the Crossrail class 345s do in fact have more than the mechanical portion of the coupler - the electrical connection box doesn't seem obvious, so you may be right on that one.

 

[43096]

Physically haul, yes. Designed to work with, not really.

But you can have the same debate about any other type. A Class 56, 58 or 60 wasn't designed to work with coaching stock - they were designed for freight work - but can physically haul LHCS. Are they not locos, then?

 

[najaB]

But you can have the same debate about any other type. A Class 56, 58 or 60 wasn't designed to work with coaching stock - they were designed for freight work - but can physically haul LHCS. Are they not locos, then?

As I said, a Class 43 is effectively a locomotive, but they were never intended to work alone or with anything other than fixed rakes of HST-specific Mark 3 coaches. The combination of two Class 43s and coaches is a MU as far as I'm concerned.

 

[43096]

As I said, a Class 43 is effectively a locomotive, but they were never intended to work alone or with anything other than fixed rakes of HST-specific Mark 3 coaches. The combination of two Class 43s and coaches is a MU as far as I'm concerned.

Multiple unit = two or more sets that can work in multiple. Show me two HST sets working in multiple....

You are making my point rather well about people wanting to categorise everything into loco or MU. An HST is different (and superior!) to other traction - it’s an HST.

 

[najaB]

Multiple unit = two or more sets that can work in multiple. Show me two HST sets working in multiple....

As above, show me two 390s working in multiple.

You are making my point rather well about people wanting to categorise everything into loco or MU. An HST is different (and superior!) to other traction - it’s an HST.

No, it's not different to other traction. It's a fixed formation of two power cars working in multiple with a set of carriages between them.

 

[Indigo Soup]

I'd argue that the defining characteristic of a multiple unit train isn't that it can work with other multiple unit trainss, but that it is necessarily comprised of multiple vehicles. A light locomotive can run just fine by itself. A single coach can, in principle, be slipped from a locomotive-hauled train. But a multiple unit must have a driving vehicle on either end, and at least one motor vehicle. This definition is great, of course, up until one encounters things like Class 153s.

Parking that issue, though, a Class 253/254 driving motor vehicle is as much a DMU as a Class 128 parcels multiple unit. Granted, it can handle a bigger tail load, it has less parcels capacity, and the guard really doesn't want to work from it, but both are driving motor vehicles with accommodation for parcels and a guard.

Similarly, the trailer coaches in Classes 253 and 254 are virtually identical to Mark 3 coaching stock. But the trailer coaches in Classes 123, 124 and 309 (and a few others) were virtually identical to contemporary coaching stock, too. They were clearly understood to be part of a DMU.

When the HSTs were classified as DMUs, chopping and changing vehicles between DMU sets wasn't unusual. So, it made sense at the time. The shift to treating them as locomotives and hauled stock, AIUI, is because as far as maintenance is concerned the HST 'motor coaches' closely resemble locomotives, whilst the trailers are virtually identical to hauled stock.

Coming the other way, though... why should an HST be a DEMU whilst an E&G push-pull rake isn't, when they're basically the same thing?

 

[DelW]

But a multiple unit must have a driving vehicle on either end, and at least one motor vehicle.

Which could also encompass GW auto-trains
Haven't there also been cases of FGW/GWR using a pair of HST power cars coupled back to back as an emergency locomotive? Google turned up this discussion:
http://www.rmweb.co.uk/community/in...o-back-hst-power-cars-drag-the-night-sleeper/ though the photo referenced is no longer available.
That wouldn't be possible using a pair of MU driving motor coaches!

 

[birchesgreen]

Back in the 1st generation DMU days they could and did haul other stock on occasions, usually a van but sometimes a non-powered trailer.

Class 43s are locomotives that usually operate as a DEMU. Not everything in life nearly fits into a tight category.

 

[najaB]

Class 43s are locomotives that usually operate as a DEMU. Not everything in life nearly fits into a tight category.

Well put. And that should be the end of it.

 

[Cowley]

That wouldn't be possible using a pair of MU driving motor coaches!

Although there are these photos taken by Howard Lewsey of two of the power cars from the Hastings DEMU rescuing a class 375 after it hit some cows 2015...

 

[DelW]

Although there are these photos taken by Howard Lewsey of two of the power cars from the Hastings DEMU rescuing a class 375 after it hit some cows 2015...

Good point, I remember that now.

It did occur to me earlier in the discussion that Hastings units were quite similar in layout to an HST. But I wasn't quite sure which side of the discussion that point might support

 

[Cowley]

Good point, I remember that now.

It did occur to me earlier in the discussion that Hastings units were quite similar in layout to an HST. But I wasn't quite sure which side of the discussion that point might support

I guess it doesn’t change anything really, and they had to use an adapter to couple it. Amazing working though.

 

[nlogax]

Which could also encompass GW auto-trains
Haven't there also been cases of FGW/GWR using a pair of HST power cars coupled back to back as an emergency locomotive? Google turned up this discussion:
http://www.rmweb.co.uk/community/in...o-back-hst-power-cars-drag-the-night-sleeper/ though the photo referenced is no longer available.
That wouldn't be possible using a pair of MU driving motor coaches!

Ta-da.

 

[whhistle]

I would always see an HST as a loco + coaches... because that's what it is.
A DMU, for me, involves some engines under the floor of some coaches in a train of carriages put together.

I can't think of any DMU that is more than 2 coaches that has 2 engines (or engine gubbins) or less.

 

[mmh]

I would always see an HST as a loco + coaches... because that's what it is.
A DMU, for me, involves some engines under the floor of some coaches in a train of carriages put together.

I can't think of any DMU that is more than 2 coaches that has 2 engines (or engine gubbins) or less.

There's a picture of one in post #44 - classes 201-207 had 1 above-floor engine per unit. The forthcoming class 755 bi-modes for Greater Anglia will also have above-floor engines.

 

[43096]

There's a picture of one in post #44 - classes 201-207 had 1 above-floor engine per unit. The forthcoming class 755 bi-modes for Greater Anglia will also have above-floor engines.

Classes 201-203 have 2 engines per unit. Class 755 has four engines.

 

[najaB]

Class 755 has four engines.

One engine and four motors, surely?

 

[sprinterguy]

One engine and four motors, surely?

No, 4 x Deutz V8 16 litre engines rated at 478kW (640hp) located in the power unit on the 4-car class 755s, though only 2 will be fitted on the 3-car units.

I'm not sure how many of the axles will be powered.

 

[najaB]

No, 4 x Deutz V8 16 litre engines rated at 478kW (640hp) located in the power unit on the 4-car class 755s, though only 2 will be fitted on the 3-car units.

Right, gotcha. I kinda see that as one engine though or will they throttle independently?

 

[pdeaves]

I can't think of any DMU that is more than 2 coaches that has 2 engines (or engine gubbins) or less.

I refer the honourable member to the class 210.

 

[Indigo Soup]

Right, gotcha. I kinda see that as one engine though or will they throttle independently?

From the sounds of it, they're totally independent to try and keep the working engines in their power band.

 

[43096]

No, 4 x Deutz V8 16 litre engines rated at 478kW (640hp) located in the power unit on the 4-car class 755s, though only 2 will be fitted on the 3-car units.

I'm not sure how many of the axles will be powered.

4 axles powered - the bogies at each of the unit.

 

[The_Engineer]

I refer the honourable member to the class 210.

Yes, a great pair of prototypes. Project shelved for sprinters instead...… A DEMU in the best thumper tradition, similar units were built for Northern Ireland (Class 450?)

 

[DelW]

From the sounds of it, they're totally independent to try and keep the working engines in their power band.

If they work the same way as American genset locos (which also have multiple small* engines), the duty/assist/standby roles are automatically rotated around the engines to even out wear and maintenance schedules.
* - by locomotive standards

 

[delt1c]

when the Edinburgh Glasgow were operated by 27,s was this loco hauled or MU? If MU then what classification for the power cars either end? Likewise are the electrics on ECML loco or MU

 

[61653 HTAFC]

when the Edinburgh Glasgow were operated by 27,s was this loco hauled or MU? If MU then what classification for the power cars either end? Likewise are the electrics on ECML loco or MU

Mk4 sets are generally considered to be LHCS (surely LPCS when heading South?) I think, though operationally they're pretty much fixed-formation sets.

What about the old Gatwick Express 73+Mk2 sets though? AIUI the coaching stock and the DMLVs (if that's the right acronym) each had their own, separate TOPS classifications in the 4xx series.