Your basic railroading quest for knowledge from a "newbie"

[trainnut57]

Being relatively new to trainwatching but a long time hobbyist in model railroading, two questions have bothered me for a long time and I'm hoping someone othe there in cyberland can answer them.
1. Why are multiple diesel (power) units hooked up the way they are-generally rear-end to rear end rather than nose of the locomotive to rear of the first unit as in the steam era? I gues the call that "elephant style". Is there some advantage to this practice? and

2. I drove an 18-wheeler for over 25 years. When the air lines separate on a trailer, the brakes lock tight, yet I watch train videos of "switch on the fly" and hump yards, and once the hoses part the cars keep on moving. How do these air brake systems differ?

[Anonymous]

when cars are being humped the brakes are bled so they will roll freely. and during flat yard switching a lot of the time the cars will be bled for kicking.

[BNSFNUT]

One of the advantages of running locomotive back to back is that when the power reaches the end of it's run you do not have to turn them. You just service them and they are ready to go.
As to air brakes on freight cars I will let some one who knows more about them to explain how the work. But railroad cars are designed to set the brakes if a air line parts.
For switching this feature is disbled by bleeding the brakes of or turning angle valves on each end of the car.

[tree68]

All I know about truck brakes is that when you push down on the pedal, they apply (if you have air). The only big trucks I drive are fire trucks, and as volunteers we don't need a CDL to drive them, hence my minimal knowledge. Our mechanic keeps them working...

I'm also no expert on train brakes, but here's some Airbrake 101, to the best of my memory:

The brakes on a railroad car are applied by air pressure stored on the car. Air to charge the reservoirs on each car is received from the engine(s) via the trainline (the pipes and hoses that run the length of the train). The order to apply the brakes is issued by reducing the pressure in the trainline. At first this may seem counterintuitive, until you introduce the triple valve, which works its magic and makes the whole thing happen. You'll have to take my word for it.

The bleeding of the brakes for hump work is somewhat related to a problem the engineer can encounter on downgrades if the brakes are not used wisely. Eventually the reservoirs on the cars are depleted, meaning there is no air with which to apply the brakes, regardless of brake pipe pressure. The conundrum here is that if there is no pressure in the trainline (which should, in principal apply the brakes fully), there is also no air to recharge the reservoirs...

Part of the departure procedure for a train is to ensure that the trainline is intact (a major function of the EOT device) and the individual reservoirs are full.

[csxengineer98]

locomotives are run anyway that the power buro desides to run them..sometimes they are back to back or front to back...what ever the people in charge of motive power deside they want the units to run in.... but in a 2 unit consist.. back to back is better becouse their is no need to turn power to get it faceing in the right direction... and now the air brakes
when the airbrakes are charged up with air....a seporation in the brake pipe (the air hose between the cars for example) will cuse the brakes to apply on the whole train... moving or standing still... now when a train gets into a yard ..and cars from it are going to be switched... they will bleed the air off the cars... (when a train goes into emergancy..the air comes out of the air system on the service side..but still remains in the emergancy side of the air system).... bleeding the cars gets ride of the air on the emergancy side and alows the cars to beable to roll free so they can be kicked or humped.... the only way to put brakes back on cars that are bleed off is the hand brake on each car...or you have to put the air back into the cars and recharge the train with air to make a break aplication or put it into emergancy........
csx engineer

[trainnut57]

Hey, Thanks for the comebacks. Most of the videos I have seen just don't bother to mention bleeding the air tanks to free the wheels. That part is the same as in the trucking industry. I gues running back-to-back makes sense for the arguement of not having to turn the locomotive-never thought of that.

Thanks one and all.

Trainnut57

[Paul Milenkovic]

I have seen Amtrak is in the habit of running their Genesis Diesels elephant-train style, nose to tail, instead of back to back. You would think that back to back would reduce the need for turning, but I am guessing the logic on Amtrak is to recover from an on-the-road failure. If the lead unit fails, you can push it into a siding and leave it there, and then you don't have to turn the back unit -- you can just keep going. If the consist is coupled back-to-back, you will have to turn the back unit to go the rest of the way on one unit.

[Anonymous]

QUOTE: Originally posted by BNSFNUT

One of the advantages of running locomotive back to back is that when the power reaches the end of it's run you do not have to turn them. You just service them and they are ready to go.
As to air brakes on freight cars I will let some one who knows more about them to explain how the work. But railroad cars are designed to set the brakes if a air line parts.
For switching this feature is disbled by bleeding the brakes of or turning angle valves on each end of the car.

Uhhh, no. You can't bottle the air by turning the angle cocks and expect the car to roll free. You need to bleed them off.

Bottling the air can eventually cause the brakes to release on a cut of cars as the pressure held in the train line of the bottled train allows the brakes to slowly release, but this takes time and is not an approved method of releasing brakes for MANY reasons. Just ask the foks in LA and Rochester, NY...

LC