Push Pull

Discussion relating to the operations of MTA MetroNorth Railroad including west of Hudson operations and discussion of CtDOT sponsored rail operations such as Shore Line East and the Springfield to New Haven Hartford Line

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cobra30689
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Re: Push Pull

Post by cobra30689 » Wed Dec 04, 2013 10:17 am

8th Notch wrote:Cab cars do not have ammeters (older ones at least) that indicate if power is being generated by the traction motors so yes if he was in the locomotive he could have verified that when the throttle was placed in idle or reduced, traction power responded correctly. The only other option in the locomotive is using just the engine brakes which wouldn't have made a difference, the control cars have air gauges so if something is wrong with your pressure you should know it.


Not entirely true. The VRE Nippon Sharyo cab cars I run have ammeters (I don't know if the Metra cars have them), but all of our diesels are DC traction....but in the case of MN (Amtrak and NJT as well) with AC traction and their power displays expressed in total tractive effort vs. amps....I don't know how you could display power draw in a cab car.

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amtrakhogger
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Re: Push Pull

Post by amtrakhogger » Wed Dec 04, 2013 10:57 am

cobra30689 wrote:
8th Notch wrote:Cab cars do not have ammeters (older ones at least) that indicate if power is being generated by the traction motors so yes if he was in the locomotive he could have verified that when the throttle was placed in idle or reduced, traction power responded correctly. The only other option in the locomotive is using just the engine brakes which wouldn't have made a difference, the control cars have air gauges so if something is wrong with your pressure you should know it.


Not entirely true. The VRE Nippon Sharyo cab cars I run have ammeters (I don't know if the Metra cars have them), but all of our diesels are DC traction....but in the case of MN (Amtrak and NJT as well) with AC traction and their power displays expressed in total tractive effort vs. amps....I don't know how you could display power draw in a cab car.


The best way to determine if you are taking power in push mode is the "bump" you get when the slack runs in (no sarcasm intended.)
His train? It's MY train! I know what I'm doing, do you?

ACeInTheHole
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Re: Push Pull

Post by ACeInTheHole » Wed Dec 04, 2013 11:07 am

amtrakhogger wrote:
cobra30689 wrote:
8th Notch wrote:Cab cars do not have ammeters (older ones at least) that indicate if power is being generated by the traction motors so yes if he was in the locomotive he could have verified that when the throttle was placed in idle or reduced, traction power responded correctly. The only other option in the locomotive is using just the engine brakes which wouldn't have made a difference, the control cars have air gauges so if something is wrong with your pressure you should know it.


Not entirely true. The VRE Nippon Sharyo cab cars I run have ammeters (I don't know if the Metra cars have them), but all of our diesels are DC traction....but in the case of MN (Amtrak and NJT as well) with AC traction and their power displays expressed in total tractive effort vs. amps....I don't know how you could display power draw in a cab car.


The best way to determine if you are taking power in push mode is the "bump" you get when the slack runs in (no sarcasm intended.)

On NJT, With the loading glitch on the 46As, its more of a hard slam when the slack runs in.. ive gotten minor whiplash from it a couple times.

Patrick Boylan
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Re: Push Pull

Post by Patrick Boylan » Thu Jan 02, 2014 10:11 am

here are a few recent posts in viewtopic.php?f=67&t=153672 turning trains/engines at GCT which I think really belong in either this thread or the Spuyten Duyvil wreck thread
theseaandalifesaver wrote:I don't understand why the push/pull situation keeps getting brought up in every single thread and article I'm reading about this. This is a method that'd been used by railroad for years simply to cut down time and costs of turning a train around to send it back out.

DutchRailnut wrote:And after all had nothing to do with what transpired.

Terrapin Station wrote:How can you say that?

Terrapin Station wrote:Isn't it being brought up because the Shoreliner cab cars don't have the alerters that the locomotives do?


Trainer wrote:
Patrick Boylan wrote:Terrapin Station, I assume you and Dutch are talking about the recent Spuyten Duyvil wreck, which so far nobody has named in this thread. About all I can quibble about Dutch's statement is a bit of hyperbole, the push operation had very little to do with what transpired. Do you doubt that the wreck's immediate cause was engineer's inattention? Other than alerters and other locomotive noises, which might not have helped the engineer pay attention better, what is there about push vs pull that you feel contributed to that wreck?

The reason it keeps coming up is because early media stories reported that the cab alert system that would have been functioning in "pull" mode was not designed to function in "push" mode. I don't know if that is true, but I have not seen that claim refuted here or elsewhere.

If (?) that's true, then push/pull may well have made a difference. Safety systems that only function half the time are idiotic. The notion that an alerter system "might not have helped" if the train was pointed the other way is not a credible argument. It might have helped a lot.


I agree that safety systems that work only half the time are not desirable, and it's hard for me to figure if alerters are a good thing why they don't have them at both of the train's operating ends, but the notion that an alerter system "might not have helped" if the train was pointed the other way is just as credible as arguing that it might have helped a lot. The important word here is "MIGHT". There's no guarantee that the alerter would have actually alerted the engineer. And there's no guarantee that an alerter will have as much impact in a noisy locomotive as it would have in a relatively quieter cab car.

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talltim
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Re: Push Pull

Post by talltim » Fri Jan 03, 2014 6:07 am

When considering the safety of push-pull, other factors come in to play as well as just 'should the loco lead?' If you had to run the loco round the train at each end of the trip, the turnaround time increases, more infrastructure is required. Both put the costs up. This means that a less frequent service can be afforded, and probably ticket prices increase, so the rail option looks less favorable against bus, or car. We all know that rail is far safer statistically than road, so by not having push-pull you actually make people's journeys more dangerous.
Of course, by having distributed power (EMU/DMU) you don't have a heavier vehicle anywhere in the train so you don't get this 'pushing' issue.
Tim David

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