Push-pull trains: Different characteristics depending on the direction of travel?

[destere]

Apologies if this is a daft question, but here we go:

Take a 225 - if the Class 91 is moving forwards, it's pulling the rake behind it. If the DVT is at the 'front', the 91 is then pushing the rake.

Are there any differences in how the set 'behaves' depending upon the direction in which it travels? Are there differences in acceleration characteristics, operation procedures (including emergency) etc. Or is it simply the same either way?

 

[najaB]

Are there any differences in how the set 'behaves' depending upon the direction in which it travels? Are there differences in acceleration characteristics, operation procedures (including emergency) etc. Or is it simply the same either way?

Possibly not what you are after, but the difference in behaviour during an accident is significant. With the DVT leading a derailment is much more likely in the event of a collision with an object on the track.

This was evidenced during the Polmont and Great Heck accidents.

 

[gimmea50anyday]

Takes time for the loco to compress.all the couplers when pushing so a distinctive "shove" can be felt. When pulling a dead loco (t&t) the rear loco tends to snatch causing it to bump into the rest of the train.

 

[DaveNewcastle]

Try sitting in the so called "quiet coach" of standard class in a MkIV set on a stopping service, coach B, next to the locomotive. Some of them can be far from 'quiet', particularly on departing stations.

 

[AndrewE]

Isn't there an effect of the train polishing the rails so better adhesion and therefore acceleration when propelling? I don't know whether sanding overcomes an adhesion problem to a greater extent when the loco is leading.

I seem to remember it being discussed either at an early stage of APT development or when DVTs were introduced on the WCML.

 

[Bill EWS]

In steam days there were speed restriction when the loco was pushing. 50 mph, if I remember correctly!

 

[Failed Unit]

Takes time for the loco to compress.all the couplers when pushing so a distinctive "shove" can be felt. When pulling a dead loco (t&t) the rear loco tends to snatch causing it to bump into the rest of the train.

You don't notice this as much on the class 91s, I think they have some design features to mitigate this, definately notice it on a class 90 operate service however.

I have heard that it behaves better one way, unfortuantely can't remember which, I have a feeling that it is pushing. I am sure the permanent way crew will give a reason but dewirements seem to be worse northbound (but that could be as simple as the wires get tangled up in the train)

 

[Techniquest]

Following my very rough and jerky ride with 91115 pushing on the 1003 York to London Kings Cross, and numerous journeys with 90s pushing, I would say 91s pushing when in coach B is an experience not to be repeated. I am actively avoiding all journeys with 91s when they're on the rear when possible now. I had some slight jerking with 90s pushing recently, but nothing to the extent of that 91.

Put it this way, there's a reason why I started using the hashtag #IHateClass91s

 

[alexl92]

You don't notice this as much on the class 91s, I think they have some design features to mitigate this, definately notice it on a class 90 operate service however.

Is it to do with a sprung rubbing plate?

Following my very rough and jerky ride with 91115 pushing on the 1003 York to London Kings Cross, and numerous journeys with 90s pushing, I would say 91s pushing when in coach B is an experience not to be repeated. I am actively avoiding all journeys with 91s when they're on the rear when possible now. I had some slight jerking with 90s pushing recently, but nothing to the extent of that 91.

Put it this way, there's a reason why I started using the hashtag #IHateClass91s

So no south-bound journeys at all for you? I've not done it in Coach B but never noticed it when I have travelled on MKIV sets before.

 

[edwin_m]

On the Scotral class 47 push-pull sets, the control from the DBSO end was somewhat cruder, with only a few power notches instead of infinitely variable when driven from the loco itself.

 

[380101]

Possibly not what you are after, but the difference in behaviour during an accident is significant. With the DVT leading a derailment is much more likely in the event of a collision with an object on the track.

This was evidenced during the Polmont and Great Heck accidents.

The lack of a deflector blade on the DVT also played a significant role in the Polmont incident.

 

[najaB]

The lack of a deflector blade on the DVT also played a significant role in the Polmont incident.

Oh, no doubt. That's why they are pretty much standard on newer stock. However the lighter DVT was always going to be more likely to derail than the heavier locomotive had it been leading.

 

[Rick1984]

The class 90 hauled Norwich trains jerk when moving off in either direction. I quite like it!

 

[Techniquest]

I did many 90 hauled, and pushed, journeys the other week and jerking was not part and parcel of any of them. You got some in places, to be expected in leaf fall season, but 90% of my journeys were nice and smooth.

I am avoiding 91 pushage when possible, aiming for HSTs instead of 91s on journeys southbound. Obviously if I *have* to I will get on a 91 pushing, but I'll be well away from the loco end of the train!

 

[DarloRich]

You don't notice this as much on the class 91s, I think they have some design features to mitigate this, definately notice it on a class 90 operate service however.

yes you do! As DaveNewcastle says sit in coach B on a York stopper. It is very much noticable.

 

[47513 Severn]

I wonder how much difference it makes if a propelling loco is attached using a buckeye and rubbing plate or a screw coupling and buffers. The latter would seem to give a lot more potential for 'bounce' between the loco and train.

Chiltern class 68 and DB class 90 locos hired in to VTEC and GA don't have rubbing plates but I don't ride them enough to notice a difference.

What I do find very noticeable is the lurch when a GA class 90 is propelling north away from a stop at Manningtree and reaches the neutral section at the triangle. I guess this is down to the driver accelerating hard to build up momentum for the neutral section and then cutting power abruptly at the last moment. This is then followed by a shunt from the rear when power resumes and then the distinctive mark 3 carriage shudder as the ETH supply is restored and the MA sets kicks in. All in all quite a rough couple of minutes if you happen to be in rearmost coach!