Braking Long Trains

There definitely are multiple benefits to removing the need for a brake pipe transmitted signal for apply and release of brakes.

Braking the train, instead of breaking the train, comes to mind, on those really, really long snakes..........

Once the ECP moves to the general interchange fleet, the greatest advantage of ECP will be the fact that the command signals are seperated from the air charging system.

Before, in order to apply the brakes, the trainline had to be reduced in pressure... as has been explained. The catch is that this means the air supply is now less than the car reservoirs. If the engineer needs to make multiple applications due to undulating territory, he then has to release the brakes completely, wait for the trainline to recharge, and also ensure that he has given enough time for the trainline to recharge the reservoirs.

if the territory is really bad, a runaway can occur because the engineer used up all the air in the train without leaving enough time to recharge teh system.

With the ECP, the trainline remains at 90psi, ensuring that the train can recharge that much faster.

Now, I've read conflicting reports of how the ECP in deployment on NS works. Some accounts give the ECP as nothing more then straight electronic control of the existing system, ie you still only have first service, your service zone, suppression and emergency. AND you still have to go to release to get any reduced braking effort.

Other accounts have the system giving the engineer the ability to operate the train's brakes identically to the power's independant system... ie any amount application, any amount reduction, and reapplications.

One thing I don't know about, but would have taken into account for the system, is a load/empty sensor. A 14,000ton freight has forty empties spread throughout the train... I make a full service application for one reason or another, and the entire train equalizes at maximum service pressure in the cylinders. A loaded coal hopper continues to roll, but heavily retarded... an empty flat however locks up.

I'd have designed the system based on "retarding effort"... ie the brakes apply such that the loaded coal hopper decelerates at a given miles per hour/second (roughly) and teh brake cylinder pressure on the flat will create a similar amount of deceleration on that empty flat.

Yes, I realize that this adds a serious complication to the system, however I feel it would have maximized the benefits of teh system. Course, the systems deployed might just be capable of that.

I'd really like the opportunity to drop one of those ECP coal drags down Horseshoe Curve.... just to see exactly how much better the system is.

I dunno how different freight ECP and passenger ECP brakes are gonna be, but Ill explain how it works with the cars I run (NJT)

The brake stand is different - its a 26E or 30ECDW or EPIC (Electro Pnuematic Intergrated Control If I remember correctly). Except for the Arrow 3 MUs cars, the locos and cab cars have Non-Self Lapping Brakes, with a seperate position for EP -

Release
Hold (EP)
Lap
Service
Handle Off
Emergency

Coming into a station - the engineer takes out a bite of air by going to Service. Once the amount of air is taken out that he wants, he goes back to Lap

For example - running 80mph, with 110psi air - takes out a 10psi reduction - brake pipe is 100psi.

The brakes apply faster, almost instantly, because the air is removed from the brake pipe in each car, as the EP signal is sent back electronically. Brake Pipe is reduced, however, in "normal" fashion.

Coming into the station, if the engineer were to make another 5psi reduction, he would be at 95psi.

However, that is slighty too much brake on, so he moves the handle to release for a second and then back to HOLD and releases a little bit of brake cylinder. EP Hold HOLDS the amount of air in the brake cylinders while charging back up the brake pipe. You can keep going back and forth inbetween Release and Hold as many times as you need too, until you have no brake cylinder PSI left. The EP is basically controlling the brake cylinders via magnet valves.

It also saves time in leaving stations, as you don't have to wait for the brake pipe to build to release the brakes - the brake pipe is already maxed out, and you are just releasing the air in the brake cylinders.

If the EP system fails, and doesn't hold, you just make brake applications as if the EP system wasn't there.

Again, I dunno how the freight system works, but im ASSUMING it works on the same general principle.

Even before the NS announcements came out about ECP, I'd run some of the newest Evolution series ES40DC's that were equipped with the ECP controllers. The brake stands aren't any different from a standard electronic 26L on our units.

But again, since the ECP on NS is in assigned service between the mines and the power plant on the Keystone Secondary, I never see the trains. However, I did talk to some guys at Conway who had run them, and they told me that the ECP also uses a special EoT which connects to both the brakepipe and the ECP line.

Thats right, thats another feature that I forgot to mention.

It's called "EP Emergency" (or at least thats what we call it) where basically when there is loco/cab energized, the electrical signal is sent back for the EP Brakes.

If for example, the train is under power, and rolling merrily along, and comes apart, the EP signal is lost to the hind end. If that happens, the back of the train goes into emergency and just like an EOT device, the hind end dumps and it applies the brakes faster, as the brake pipe is now open on both ends (from the location of the break apart and the last car)

On the present brake system, DP trains have a shorter stopping distance. The air is cut in on all consists, lead and slave. The problem is that small bites have to be made each time. If a large application is taken, the middle cars will kick. They will feel a large trainline reduction all at once.

Humm, the problems ive had have been to too little air being set. In the guildlines on running a DPU train says something about remembering in cold weather to make a deep enough set or they'll pop.... something like that. With the ones ive tied down, never had a problem throwing full service to it after seeing that the hand brakes will hold??? Who knows.

a longer train has much more momentum....whats more important is if its loaded or empty, a loaded 130 car coal train weighs about 18,000 tons while the same train empty weighs about 3,000 tons.

UP Engineer, I have not run a dp train since they first became popular about 10 years ago. I remember that there were lots of kickers. I don't know what was discovered to prevent this. I also remember that more trains seemed to kick with early CCB brake valves when the AC locomotives started to replace the SD40s and 60s and -7s with 26 or 30 brake valves.

When you adjust the brakes on a freight car, you must set them to not lock up worst case, when empty [or so I've been told...]. Locked wheels destroy wheels and damage track. So you set them up empty. Once you load the car, you could use a lot more braking before they lock up. But unlike an automobile, there's no driver to sense the wheel status, and modify the pedal pressure to get that.

Once you add ECP to a car, it's not a big reach for the next step. Add anti-lock control to the ECP control box, and each car monitors its wheels, and applies braking up to that point, if needed. You can stop a train in the fraction of the distance.

You can also stage braking; i.e. brake the trailing cars sooner and harder than lead ones, to keep the consist in tension. [I think there's a better RR term, but..] Just have the locomotive brake control computer set up to do so. It should not be too hard to sense the stress on the car [i.e. - is it in tension, slack, or compression? Compression is when you might jack-knife.] & adjust accordingly.

Further, since the head end controller always knows the status of each car's brakes; I'd bet you can skip walking the train before rolling; you'd be able to see the pressures at every car. How much time will that save?

jgallaway81 wrote:
One thing I don't know about, but would have taken into account for the system, is a load/empty sensor.
....
I'd have designed the system based on "retarding effort"... ie the brakes apply such that the loaded coal hopper decelerates at a given miles per hour/second (roughly) and teh brake cylinder pressure on the flat will create a similar amount of deceleration on that empty flat.

This approach will fail for two reasons. First all the cars will decelerate at the same rate. More importantly, it won't help you on your prime objective: keeping the wheels from locking. THAT is a function of loading, requested braking %, and track condition - anything from bone dry to icy to covered with leaves.

The auto industry futzed around for several years with similar attempts of brake proportioning; one approach measured the body to rear axle distance on pickups. (They were notorious for the rear brakes locking up when empty.) The valve reduced rear brake pressure when the distance was high, ergo no load in the bed. First time someone put helper springs on his custom truck and filled it with something heavy; well you can guess....

What *does* work is sensing each wheel's rotation, and if it stops, pulse the brakes off until it spins again. It works so well that I wonder if any new cars sold in the US don't have it.