About a week ago, in one of the threads, someone posted a link to an article that is a very lengthy, extensive explanation of how RR air brakes work.
I can’t remember what thread that was in. I ment to go back and read the linked article, but now cannot find that post.
Can someone direct me?
Just remember the name Al Krug… He used to have a number of interesting reads on the 'Net. I don’t know if they’re still out there.
That’s (of course) an excellent article, Larry.
He gives an excellent description of the result of unoupling when one hose is still open to the car’s reservoir–the first place I heard this in a somewhat enclosed area was in the Atlanta Terminal’s train shed, in 1951; it was quite startling. Even in the open air, one will definitely hear the sound of the escaping air.
The pressure contained in the trainline is the reason why you will rarely if ever, see someone try to separate air hoses manually - even if a maximum brake pipe reduction is made and the air is ‘bottled’ within the two air hose at the coupling you are still dealing with a ‘air vessel’ that contains 50 to 70 PSI giving the glad hands some real ‘kick’.
Unless I’m well clear of the glad hands, I usually grab the one in question.
When we do our usual runaround, part of the routine is to open the anglecock on what was the rear of the train. At this point, the locomotive has broken away from the consist on the other end and the pressure in the brake pipe is theoretically zero.
I still grab the glad hand.
If two gladhands are coupled when I put air to them, I still give them as wide a berth as possible.
“Bottling” the air when uncoupling cars from a train refers to the practice of making a service application, shutting off the air line on the cars being uncoupled, and then uncoupling the cars. This is a violation of Federal safety rules, which prohibit “bottling” air on uncoupled cars. The reason is that the brakes on the “bottled” cars can release after the cars are uncoupled (for reasons which would take too long to explain here). The correct procedure is to leave the air line on the cars being uncoupled open so that the brakes go into emergency when the cars are uncoupled.
Believe it or not, there is now an exception to this. If you have a DP unit in the portion of your train being left behind you can tell it to maintain the brake application. CN’s procedure is as follows:
Secure train as per applicable rules.
Make a automatic brake application of at least 15 PSI.
Place DP unit in “set out” status while leaving its brake valve cut in.
Close both angle cocks and uncouple from the tail end portion of the train.
The DP unit will maintain the brake application, and it will also put the train in emergency if it starts to move, if it senses a sharp increase in brake pipe air flow, if it senses a rise in brake pipe pressure, or if the lead unit goes into emergency.
Thanks, tree.
UP has this too. I imagine all DP users have this feature now. If they keep up with the upgrades to DP.
We have to make a 20 lbs set. Watch the DP screen to make sure there is a numeric value in the flow indicator.&
OK. I read that article. It was great but I’m still a bit challenged.
Below are excerpts from the article, and a quote from our own Falcon. They are followerd by questions by me.
If the brake pipe pressure is HIGHER than the reservoir pressure, the triple valve moves to the RELEASE position. In this position it vents any brake CYLINDER air to atmosphere thus releasing the brakes. It also connects the BRAKE PIPE to the RESERVOIR so brake pipe air pressure can begin recharging the reservoir. This is the situation you are in when you are CHARGING the brake system sitting in the yard waiting for a brake test (“pumping up the air”).
So, if the train is level, and the loco’s independent brake is on, the cars won’t move. But on a hill, will you have to set some hand brakes while charging is underway?
If you are standing near a train when the loco uncouples you can hear these emergency valves vent the brake pipe pressure locally on the car you are next to. That car will go “Psssssht”. If you are standing some distance off to the side of the train you can hear each car trigger in succession as the "psssht, psssht, p
If the locomotive is unable to hold the entire train on the grade, yes.
As each car’s brake valve senses an emergency application (very rapid drop in brake pipe pressure), it will also dump the air from the brake pipe, speeding the propogation of the emergency application through the train.
The anglecock is the valve in the brake pipe on each end of the car. If, say, a crew wants to move just one car “on air,” the anglecock for the locomotive end will be open (to take air from the locomotive, see applications, etc) while the anglecock furthest from the locomotive will be closed, lest all the air in the brake pipe leak out of that end.
“Bottling the air” as stated, is closing the anglecock on the locomotive end of the car.
The previous paragraph you cited explains that pretty well.
[quote user="Lithonia Op
[quote user=“Lithonia Operator”]
OK. I read that article. It was great but I’m still a bit challenged.
Below are excerpts from the article, and a quote from our own Falcon. They are followerd by questions by me.
If the brake pipe pressure is HIGHER than the reservoir pressure, the triple valve moves to the RELEASE position. In this position it vents any brake CYLINDER air to atmosphere thus releasing the brakes. It also connects the BRAKE PIPE to the RESERVOIR so brake pipe air pressure can begin recharging the reservoir. This is the situation you are in when you are CHARGING the brake system sitting in the yard waiting for a brake test (“pumping up the air”).
So, if the train is level, and the loco’s independent brake is on, the cars won’t move. But on a hill, will you have to set some hand brakes while charging is underway?
Maybe. It depends on the how heavy the train is and how heavy the grade is. It’s also possible with AC power to hold the train by using the engines, shoving against the train in notch one. There are places where even this won’t work and then you’ll need to secure the train.
Thanks so much, tree and Jeff. I think I’ve got it now.
It’s interesting. We non-engineers think of the engineer as running the engine. And of course he/she does. But from what I am learning, it seems that braking is the trickiest part. It seems like a real art, with much finesse involve. And the ability to think ahead while multi-tasking is definitely required.
Any idiot can open the throttle and pull. A engineer knows how to operate the various braking and power systems, contolling the slack within his train, and get it across his assigned territory safely in the most efficient amount of time.
When I first sat in the seat, it was the brakes that scared me - aside from some classroom stuff and Krug’s piece, I had no clue.
I do now, and it gets a little better every time I run.
My exposure to, and experience with, older brakes (6, anyone?) has helped a lot.
I just opened a new thread about two books I recently read. Those books really opened my eyes to the challenges of braking and train-handling. A huge responsibility.
When I was an operator (in the dark ages), all I had to make absolutely sure of was that I typed the orders up correctly (and we had a system which virtually assured that), and that I got them strung up and mounted on the post before the train arrived. Nothing else I did, if I screwed up, could have gotten someone killed.
Ran the 6 schedule brakes over at the Boone & Scenic Valley RR before hiring out across town.
Jeff
Now I have a braking system question about “BLENDED BRAKING”. When I used to ride the METRA C&NW commuter trains into Chicago, I would watch an inbound train arriving into Chicago arrive with brakes applied and with power on push into the station. As the train approached the bumping post, the engineer would cut the throttle and the train would stop. But that was befor blended braking which combines air and dynamic braking. I know that synamic drop out at something approaching five mph. And when I operate our diesel at the trolley museum, I can push against the train brakes and bail off the engines brakes. But with the Metra trains in push mode, ie, the engineer is not in the locomotive, how can the engineer “PUSH” against the trains brakes to come to a precise stop? Can this be done with blended brakes?
The ‘answer’ I would give you is that yes, you can make a ‘motored’ stop on a train set up for blended braking, but the locomotive will be in motoring at that point, and not dynamic, so the ‘blended’ system will not have any input from dynamic: it will be all air. On modern power there are computer protections to prevent motoring too hard or too long against a brake set.
Remember that on classical DC-motored power there was a marked falloff of DB effectiveness at slower speeds, so it would not be used during a platform approach. With AC power you can have very effective “dynamic” (I call it ‘countertorque’ to distinguish it from pure dynamic) motoring opposite the direction of wheel rotation even at very low speed, so blended operation would be possible all the way to a stop without need for the vernier ‘push’.
We have several people on here with firsthand experience of this, so I defer any practical discussions to them.
I have zero experience with AC, so I won’t even begin to speculate on that.
Pushing or pulling - there’s no real difference. Just a question of whether the train is stretched or bunched.
Our station is on a slight upgrade, but even on level ground, the technique I learned is the same. Take some air at the appropriate point, under power, and push/drag the train to the stopping point, at which time you crank on more air.
Dropping the power tends to make for a rather abrupt stop in that situation, so I try to avoid it.