Pushing vs pulling performance

[bnsf734]

..... And a lot of the push-pull formations on the continent are screw-coupled!

Even the early German ICE sets were screw-coupled including the one that crashed at Enscede. I am not sure about more recent ICE sets.

At least our coaches are coupled together using buck-eye couplers, which are far safer.

 

[delt1c]

..... And a lot of the push-pull formations on the continent are screw-coupled!

Even the early German ICE sets were screw-coupled including the one that crashed at Enscede. I am not sure about more recent ICE sets.

At least our coaches are coupled together using buck-eye couplers, which are far safer.

push pull and screw

 

[ComUtoR]

So you are suggesting that pushing IS more dangerous than pulling and the risk increases as the train gets longer? i.e with a shorter train the risk is acceptable and with a longer one it isn't.

I have never seen this suggested in any literature before and there are some pretty long push-pull formations in use on the continent.

Rob

I watched the program about the Spanish crash. If I remember rightly, there was a discussion about the location of the power cars and how it contributed to the crash and the severity.

 

[delt1c]

I watched the program about the Spanish crash. If I remember rightly, there was a discussion about the location of the power cars and how it contributed to the crash and the severity.

If there was no power cars , then there would be less chance of accidents on the railways. addmitedly trains wouldnot move much , but hey less accidents

 

[edwin_m]

I watched the program about the Spanish crash. If I remember rightly, there was a discussion about the location of the power cars and how it contributed to the crash and the severity.

There was a diesel power car inside the electric power car at each end so similar to the HST type arrangement but wiith more weight. I didn't see any programme on this but I suspect the concern would be more about the high centre of gravity of the diesel rather than the fact it was pushing.

 

[edwin_m]

So you are suggesting that pushing IS more dangerous than pulling and the risk increases as the train gets longer? i.e with a shorter train the risk is acceptable and with a longer one it isn't.

I have never seen this suggested in any literature before and there are some pretty long push-pull formations in use on the continent.

Rob

In the case of certain types of collision the risk is greater when pushing and it does increase as the train gets longer. However this is irrelevant - what is important is when the risk becomes great enough to be unacceptable. I'm not party to the decision process on the APT but it may be that they decided propelling a whole formation was unacceptable while propelling half the formation was OK.

 

[delt1c]

In the case of certain types of collision the risk is greater when pushing and it does increase as the train gets longer. However this is irrelevant - what is important is when the risk becomes great enough to be unacceptable. I'm not party to the decision process on the APT but it may be that they decided propelling a whole formation was unacceptable while propelling half the formation was OK.

how does this equate to the SR 4REP x 2,4TC

 

[robbeech]

Whilst I don't know any documentation specifically, my engineering knowledge reminds me that pushing must be higher risk that pulling under acceleration. That risk is clearly not high otherwise it would not be allowed. The weight of the carriages must play a part in this too. There could be between 15 and 20% increased weight on a full and standing mk4 with luggage comparedto an empty one. An empty coach B must increase the risk if only by a small amount, I doubt it's enough to even consider but starting off on a slight uphill gradient around a fairly tight bend with a locked out of use coach B surely must start to make a difference?

 

[edwin_m]

how does this equate to the SR 4REP x 2,4TC

That's only 4 cars being propelled (I think the end cars of the REP were motored) and only 100mph max so less risk than a 225 set. Were two 4-TCs ever propelled?

 

[edwin_m]

Whilst I don't know any documentation specifically, my engineering knowledge reminds me that pushing must be higher risk that pulling under acceleration. That risk is clearly not high otherwise it would not be allowed. The weight of the carriages must play a part in this too. There could be between 15 and 20% increased weight on a full and standing mk4 with luggage comparedto an empty one. An empty coach B must increase the risk if only by a small amount, I doubt it's enough to even consider but starting off on a slight uphill gradient around a fairly tight bend with a locked out of use coach B surely must start to make a difference?

The worst case in acceleration would be an empty coach next to the loco, where the compressive forces are greatest (isn't this coach M in a 225 set?), but I'm sure this would have been checked and tested before approving them.

There would also be a higher risk in the event of sudden deceleration such as a derailment, and in this case it would be worst near the front of the train. The lighter leading vehicle makes derailment more likely and will suffer more damage than a leading loco. But also, once a derailment happens happens the heavy and underbraked loco still on the rails at the back means there is more compressive force than if it was at the front. An MU set with distributed weight would be intermediate between these. There's really no way of telling if this worsened the Polmont and Great Heck accidents.

 

[robbeech]

It's coach B, which is what I was getting at being next to the loco. A heavy impact will potentially make little difference, either way it would be catastrophic but a light issue like a derailment or hitting a tree whilst still under heavy acceleration could potentially be worse with the DVT leading as the now irregular and asymmetrical nature of the train could cause the pushing locomotive to derail the train further back in addition to the problems at the front. This is essentially what you are saying but for multiple reasons not just the lower weight of the DVT. Put this on a curve (a problem that is more likely due to resticted sight lines as the driver could still be accelerating) and you increase the risk further still.

 

[MotCO]

I may be completely off track () here, but I seem to recall that the Gatwick Express in years gone by were push and pull, but there was an issue which required a loco to be placed at either end.

 

[gimmea50anyday]

I may be completely off track () here, but I seem to recall that the Gatwick Express in years gone by were push and pull, but there was an issue which required a loco to be placed at either end.

GX ran with a 73 at one end supplying 1600hp and a GLV at the other which was effectively a 500hp MLV with a corridoor connection at one end. Marshalled in between were up to 8 mk2d's depending on capacity requirements but 5 or 7 was more usual.

The only time double headed or t+t 73s were used was as a result of shoegear and traction motor fires caused by electrical supply issues to the train when running in series. The combination of the speed of the train and the shoegear interacting with the junctions under certain conditions was causing flashovers in the battersea area. Until the problem was solved leading to the dedicated 73/2 fleet the trains were powered by 2x 73 running on diesel. Wether this was in multiple with the GLV on electric I cannot say, but the bogie fire issue didnt seem to affect the GLV in the same way the 73s were affected

That's only 4 cars being propelled (I think the end cars of the REP were motored) and only 100mph max so less risk than a 225 set. Were two 4-TCs ever propelled?

Yes, and on a regular basis.

 

[furnessvale]

Whilst I don't know any documentation specifically, my engineering knowledge reminds me that pushing must be higher risk that pulling under acceleration. That risk is clearly not high otherwise it would not be allowed. The weight of the carriages must play a part in this too. There could be between 15 and 20% increased weight on a full and standing mk4 with luggage comparedto an empty one. An empty coach B must increase the risk if only by a small amount, I doubt it's enough to even consider but starting off on a slight uphill gradient around a fairly tight bend with a locked out of use coach B surely must start to make a difference?

We only need to look at freight trains in the USA with distributed power to see how little effect pushing v pulling has on a train.

It is possible for the rear helpers to push against quite light freight cars on sharp curves without the whole train jack knifing in front of the pushers (which could number 2-4 x 3000-4000 hp locos.)

 

[axlecounter]

Do you know if each of these locos are pushing at their maximum power or maybe less?
Besides, I doubt that they are using UIC couplings so it can't really be taken as an example.

 

[daikilo]

Do you know if each of these locos are pushing at their maximum power or maybe less?
Besides, I doubt that they are using UIC couplings so it can't really be taken as an example.

Yes, in the US, mid or rear-train locos in general push at maximum power. They are there (rather than at the front) to limit draw-bar loads on the forward part of the train.

The 4-REPs certainly worked with 2x4TC on a daily basis.