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  #1  
Old 16th June 2016, 08:35
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Joanna Joanna is offline  
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Permanently coupled trains

Hi everyone,

I am writing an article about past/present/future of long distance passenger trains.
These trains used to consist of coupled coaches but this solution is being replaced by permanently coupled trains. I guess it is because of (future) implementation of ETCS level 3 (where axle counters won't be needed anymore) but do you have any other ideas why is it happening? What can be benefits of using permanently coupled trains?


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  #2  
Old 16th June 2016, 15:26
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in the past trains were loco hauled which required the loco to be run round the train at the end of a journey,with a fixed formation with a driving cab at each end as used now this is not required.
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Old 17th June 2016, 11:37
ianrail ianrail is offline  
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I can see a disadvantage in that if one carriage develops a fault, the whole train needs to be taken out of service rather than just removing that one carriage. The same would apply if (say) a buffet or restaurant car was being updated.

Similarly, GWR had a programme last year to convert one carriage of its 2+8 HSTs from 1st to Standard class. I remember seeing some trains running in 2+7 formation whilst this work was carried out (or I presume this was the reason for the shorter formation). Again this seems preferable to taking the whole train out of service but perhaps there are members who have more knowledge of operations/engineering who can expand on this?
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  #4  
Old 21st January 2018, 14:13
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Beeyar Wunby Beeyar Wunby is offline  
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Quote:
Originally Posted by Joanna View Post
Hi everyone,

I am writing an article about past/present/future of long distance passenger trains.
These trains used to consist of coupled coaches but this solution is being replaced by permanently coupled trains. I guess it is because of (future) implementation of ETCS level 3 (where axle counters won't be needed anymore) but do you have any other ideas why is it happening? What can be benefits of using permanently coupled trains?
I don't think ETCS (the 'train part' of ERTMS) is the cause for fixed formation trains. In the current issue of Rail magazine (843), Network Rail has stated that ETCS will first be introduced to freight locos in the UK, and of course those are all not permanently coupled. ETCS really only affects the driving cab of a train as it 'supervises' the way the train is driven. All the other vehicles just follow behind.

Quote:
Originally Posted by trophy
in the past trains were loco hauled which required the loco to be run round the train at the end of a journey,with a fixed formation with a driving cab at each end as used now this is not required.
...sums it up pretty well. For passenger operation, being able to 'change ends' saves time and removes the need for run-round loops at terminii.

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Originally Posted by ianrail
I can see a disadvantage in that if one carriage develops a fault, the whole train needs to be taken out of service rather than just removing that one carriage.
Is a good point, but servicing and maintenance is getting smarter. We now have drive-through wheel lathes, where a remote-controlled tug can haul the unpowered train through the lathe and skim the damaged wheels in situ.

Most trains are modular, so sections can be taken out and replaced on an overnight inspection.

Also there is built-in redundancy. Trains now have multiple sets of the vital components. Multiple engines or traction motors strung out along the length of the train. If one or two of them dies, there's enough power to get the train home. There are also duplicates of things like Compressors for air, Converters for traction motors and auxiliaries (110V DC for the battery charging/ 220V for saloon lighting and power sockets).

With mobile phone technology and internet access the train can actually be fixed remotely whilst its going along. Everything is monitored by an onboard computer and this data is relayed continuously to a 'duty fitter' who can not only view all systems on the train on his laptop, but can alter them as well. So when the train comes into a depot on a regular visit there is already a list of things to fix and the components are already ordered.

So with all this you'd expect the trains to run like clockwork wouldn't you ? The trouble is many train faults just come out of the blue. Like when some little s*** flushes all the paper towels down the loo and the resulting flood shorts the power out. Or a late passenger pushes the doors so hard they break the safety sensors. Or a driver presses the Pantograph Up button when there's no overhead wire.

There's always something we didn't see coming.

HTH BW
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  #5  
Old 23rd January 2018, 08:50
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aussiesteve aussiesteve is offline
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G'day,
There is a major advantage of a permanently coupled train, aka solid drawbar, NIL coupler slack.
I have worked and ridden the Down Under Silver Streak, and the coupler slack is terrible.
So much so that you NEVER let the thing bunch up suddenly.
One bloke doing his road trials discovered this fact at Newbridge when he released the train brakes while stationary.
The coupler slack roll in was so severe that one passenger was hurled out of his top bunk and broke his leg.
Yes, tight-lock couplers can also achieve minimal coupler slack, but tight-lock type couplers are expensive.
And, the old buffer and screw-link system also minimizes coupler slack.
But, both tight-lock and screw link can still separate in transit.
Many moons ago, the NSWR screw-linked West Mail came apart a couple of times in transit, leaving us sitting still.
I have also seen a double decker V set interurban divided into two halves, the auto knuckle uncoupling.
Knuckle couplers have one disadvantage, if any height disparity exists and the train goes through a hole in the road, it can uncouple.
The knuckle jaws ride up and over each other.
A second major advantage of solid drawbar system being that electrical jumper couplings cannot be damaged due to accidental separation.
Yes, if a fault occurs with one car, then the entire train must be removed from service.
But, with adequate roll through maintenance, any serious problems should be prevented.
But, naturally nothing is perfect, and even a JR Shinkansen set recently suffered a bogie fracture.
This was thankfully detected in time to prevent a major derailment.
Zooming along at 350 kph may be fun, but hitting the ground at 350 kph wouldn't be so much fun.
A similar bogie fracture having occurred on a Japanese narrow gauge car which did derail.
As BW comments, if you convert your long distance train into an EMU or DMU style, then it also becomes more cost effective.
Plonking a large locomotive up front, and possibly also at the rear can increase operating costs.
PLUS, locomotives are generally much heavier than rolling stock, but possess generally quicker acting straight air brake.
So you had better bail off the straight air when you make a train brake application or have the train run into you.
Yes, EP or Epic ECP brake systems can overcome the old Westinghouse air brake inadequacies.
But, unless the locomotive is specifically designed to operate with such a brake fitted passenger train, it can be expensive to modify.
The Rocket here (XPT), which was based on the UK HST, suffers badly from coupler slack during braking and acceleration.
The individually coupled cars being the meat in the sandwich between the pair of locomotives.
However, ride a permanently coupled emu squirt, and the whole thing takes off and stops in unison.
NO bang crunch whallop due to coupler slack.
Yes, should a derailment occur with a permanently coupled train then the whole shebang can go bush.
But, this can actually be a more preferable result than individual cars uncoupling and spearing into each other.
This is the principle for FRA mandated petroleum tank cars.
They must have knuckle couplers that posses a bottom shelf.
This bottom shelf prevents the coupler jaw from riding up and disengaging.
Yes, the whole train then goes bush, but individual tankers don't uncouple and spear into each other causing a potential fire explosion.
Steve.
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