RR air brakes article. Where?

[Lithonia Operator]

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?

[tree68]

http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/north-american-freight.html

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.

[Deggesty]

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.

[BaltACD]

Deggesty

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'.

[tree68]

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.

[Falcon48]

"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. 

[SD70Dude]

Falcon48

"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:

1.  Secure train as per applicable rules.

2.  Make a automatic brake application of at least 15 PSI. 

3.  Place DP unit in "set out" status while leaving its brake valve cut in.

4.  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.

[MMLDelete]

Thanks, tree.

[jeffhergert]

SD70Dude

 

 

Falcon48

"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:

1.  Secure train as per applicable rules.

2.  Make a automatic brake application of at least 15 PSI. 

3.  Place DP unit in "set out" status while leaving its brake valve cut in.

4.  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.

 

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.  If it says "out", then we are to let the section being cut away from dynamite as usual.   

Jeff 

[MMLDelete]

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, pssht, pssht" goes rapidly back the train.

 

I thought he pshhhht came from the hose. No? Or from the hose AND the emergency valve?

 

However, with this type of equipment that one leaky car will dump its emergency reservoir air into the brake pipe when it moves to the release position. This action will raise the brake pipe pressure on that car AND THE CARS NEXT TO IT! When the cars next to the leaky one see the brake pipe rise slightly above their service reservoir pressure, their valves interpret this as a release signal AND THEY ALSO MOVE TO RELEASE! Now they also dump their emergency reservoir air into their brake pipes and that triggers the cars next to them to release. Because of that one leaky service reservoir the entire train will release. It is for this reason that it is against the rules to "bottle the air", close the angle cock on the train, when uncoupling the engines.

 

I can’t get my head around this. Can someone explain this more fully? What does the angle cock do?

 

"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.    Quick Reply Reply

 

Okay, you’ve made a service application, so the brake pipe has low pressure in it ...  Please explain from that point on. I don’t get bottling, and why that’s dangerous.

 

So the locomotives had another small reservoir installed called an EQUALISING reservoir. This reservoir is very small compared to the brake pipe volume of a long train and thus its pressure can be reduced almost instantaneously. The engineer's brake valve now reduces the air in the equalising reservoir instead of the brake pipe. He can get the desired reduction (say 10 psi) very quickly and then can take his eyes off the equalising reservoir gauge to look out ahead. An equalising valve is connected between the equalising reservoir and the brake pipe and it is this valve that vents the brake pipe air to atmosphere until it reduces to be equal to the equalising reservoir pressure.

 

So, this gives us an instant pressure drop ON THE ENGINE’S BRAKES? The regular ones not the independent brake? Don’t get how it could affect whole train quickly.

 

[tree68]

Lithonia Operator

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 the locomotive is unable to hold the entire train on the grade, yes.

Lithonia Operator

I thought he pshhhht came from the hose. No? Or from the hose AND the emergency valve?

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.

Lithonia Operator

I can’t get my head around this. Can someone explain this more fully? What does the angle cock do?

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.  

Lithonia Operator

Okay, you’ve made a service application, so the brake pipe has low pressure in it ...  Please explain from that point on. I don’t get bottling, and why that’s dangerous.

The previous paragraph you cited explains that pretty well.  

Lithonia Operator

So, this gives us an instant pressure drop ON THE ENGINE’S BRAKES? The regular ones not the independent brake? Don’t get how it could affect whole train quickly.

Not on the engine brakes (independent).  The equalizing reservoir is like a mini-train.  The time it takes to reduce the pressure in the equalizing reservoir is much less than to reduce the pressure in the brake pipe since there is less volume involved.

When the engineer moves the automatic brake handle into a braking position (say, an intended 6-10 pound reduction), the pressure can be lowered in the equalization reservoir much more quickly than in the entire brake pipe.  

The engineer will see that the pressure in the equalization reservoir has been set to the desired level (80 PSI for a 10 pound reduction).  The equalization valve will then release air from the brake pipe at a suitable rate until the equalization reservoir and brake pipe pressures are the same.

[jeffhergert]

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. 

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, pssht, pssht" goes rapidly back the train.

 

I thought he pshhhht came from the hose. No? Or from the hose AND the emergency valve?

You'll here air blowing from the hose if you're close to it.  Farther away it's the noise as each valve goes into emergency and dumps the air at that location.

 

However, with this type of equipment that one leaky car will dump its emergency reservoir air into the brake pipe when it moves to the release position. This action will raise the brake pipe pressure on that car AND THE CARS NEXT TO IT! When the cars next to the leaky one see the brake pipe rise slightly above their service reservoir pressure, their valves interpret this as a release signal AND THEY ALSO MOVE TO RELEASE! Now they also dump their emergency reservoir air into their brake pipes and that triggers the cars next to them to release. Because of that one leaky service reservoir the entire train will release. It is for this reason that it is against the rules to "bottle the air", close the angle cock on the train, when uncoupling the engines.

 

I can’t get my head around this. Can someone explain this more fully? What does the angle cock do?

The angle cock is just a valve that allows air to pass (open) or keeps air from passing (closed).  

 

"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.    Quick Reply Reply

 

Okay, you’ve made a service application, so the brake pipe has low pressure in it ...  Please explain from that point on. I don’t get bottling, and why that’s dangerous.

 

With the air line closed off, it'll maintain whatever pressure was left in the line.  (You might have some leakage either through leaking gaskets between cars or air turbine powered EOTs.)  The air in the train line and reservoirs will equalize, if they hadn't already.  When the air is bottled, say at 70 psi with everything equalized, and a leaky reservoir drops below 70 psi to say 67 psi, the triple valve (while the term is still used by us in the field, technically it is now called the control valve) sees the disparity.  Since the pressure is higner on the brake line side, the triple valve thinks a release of air brakes is in progress.  It goes to release and connects emergency reservoir pressure into the brake line to speed up the release signal.  This locally raises the pressure in the brake line.  The next car sees the increase in brake line pressure and also goes to release, venting some of it's emergency reservoir pressure into the train line.  (I forget how much air the emergency reservoir contributes, but it's enough.)  It continues down the line.  While most freight railroads carry a 90 psi brake line, you don't need to get to 90 psi to get the brakes to release.  A rise of as little as 1.5 psi can be enough for a control valve to think a release is happening.

 

   

 

So the locomotives had another small reservoir installed called an EQUALISING reservoir. This reservoir is very small compared to the brake pipe volume of a long train and thus its pressure can be reduced almost instantaneously. The engineer's brake valve now reduces the air in the equalising reservoir instead of the brake pipe. He can get the desired reduction (say 10 psi) very quickly and then can take his eyes off the equalising reservoir gauge to look out ahead. An equalising valve is connected between the equalising reservoir and the brake pipe and it is this valve that vents the brake pipe air to atmosphere until it reduces to be equal to the equalising reservoir pressure.

 

So, this gives us an instant pressure drop ON THE ENGINE’S BRAKES? The regular ones not the independent brake? Don’t get how it could affect whole train quickly.

The equalizing reservoir leads the brake line.  When the engineer needs to make a brake application, moving the brake handle removes pressure in the equalizing reservoir.  The brake line will "catch up" matching the pressure the equalizing reservoir is at.  On short trains, it catches up fast.  On long trains it might take a minute or so. 

 

The reason it was added is that on the original brake valves, the engineer moved the handle from release to a service position and kept it there until desired pressure was drawn off.  Then he moved the handle to a lap position.  The lap position is where everything, all ports in the valve are closed and air can't move.  With a long train, you would need to keep the handle in the service position, watching the brake line pressure gauge.  The equalizing reservoir makes applying the brakes a lot easier and safer.  The engineer doesn't have to watch the gauge for the entire time the brake line is drawing down.

 

  

 

 

I simplified some things and descriptions.  I used simpler terms, some that are really slang, than I normally would.  I wonder if a sticky thread isn't in order where the working and retired rails (and anybody else, too) could post terms that they use and/or hear. 

Everyone says the old railroad slang is dead, if it ever was in use in the first place.  That may be, but there is still a lot of slang used and it's not always standard.  Some terms I know may be foriegn to Zug, Tree, our Canadian/Canadien brothers and others who stop in at times.  I suppose Trains good put it in a ABC's of Railroading, but how often does one look there?  How often would it be correct one place, but not another?  Just a thought.

Jeff  

[MMLDelete]

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.

[BaltACD]

Lithonia Operator

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.

[tree68]

BaltACD

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.  

[MMLDelete]

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.

[jeffhergert]

tree68

 

 

BaltACD

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.  

 

Ran the 6 schedule brakes over at the Boone & Scenic Valley RR before hiring out across town.

Jeff

[Electroliner 1935]

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?

[Overmod]

Electroliner 1935

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 before blended braking which combines air and dynamic braking. I know that dynamics 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.

 

[tree68]

Electroliner 1935

...how can the engineer "PUSH" against the trains brakes to come to a precise stop?

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.  

[Overmod]

tree68

Dropping the power tends to make for a rather abrupt stop in that situation, so I try to avoid it.  

While I can't tell you how to do it, the 'theory' is to have just enough set that power reduction between low notches (rather than to an 'idle' notch) causes the final deceleration.  Had this demonstrated to me both on PRR MP54s (with AC motors) and New York IRT subway cars (with DC).

There's a corollary for both, which came as a great insight to a 12-year-old.  These cars had very few notches in their controllers, which resulted in a more or less hellacious jerk when even the first 'notch' was selected.  Most motormen on NYCTA just knocked the train into motion at stations, but one day I noticed smooth starts and went up to the front to see why.  The technique was to apply that first notch while the brakes were still releasing from the set, timing it to minimize any locked-rotor heating while preventing the starting jerk.  This appeared to be fairly quickly haptically learned for a given train, once you knew the secret woid.

I would give many dollars to be able to ask R.J.Russell, who ran the BP-20s in suburban service, how he handled stretch braking with units that would run nearly 30mph in the first notch if you let them.

[daveklepper]

Overmod.  Note that the AC motors on the classic PRR MP-54s were not the slant-bar squiral-cage AC motors on modern diesel-electrics and electrics and modern light rail and commuter and subway mu cars.  They were basically dc motors (with brushes and commutators) with specific compensating coils to compensate for hysterirses effects of switching polarity 50 times a second (25 Cycle AC power).  They can run on AC, as did the New Haven's regularly.  But try to run them on 50 or 60 Cycle (OK, Hz), and they will simply sit and hum and eventually burn up.  I am referring to the motors only, the control equipment on MP54s, like GG1s ran all power through transformers, which do not of course pass dc power.  The New Haven's equipmenet that ran into GCT basically had two control system for each mu car and locomotive.

[Overmod]

daveklepper

Note that the AC motors on the classic PRR MP-54s were not the slant-bar squirrel-cage AC motors on modern diesel-electrics and electrics and modern light rail and commuter and subway MU cars.

Oh no, these were the same 'Universal' motors as in the pioneering 11kV 25-cycle (no Hz back then!) electrification to Paoli.  You have carefully defined how these motors worked in a couple of prior posts (I believe both the motors used in the GG1s and the later 'improved model' 428As run on the same principles).

Did not mean to imply that the controllers were like the 2-speed devices used to select poles on 3-phase locomotives, for 'high' and 'low' synchronous lock-in.  Although I suspect if you had such a thing on MU cars, the careful use of the brake release would soften the start a bit, and perhaps an intermediate set before the 'speed change' would help at that time, too.

It is notable of course that the first testing of Ignitron rectifiers on PRR was on an MP54, and very successful it was, too.

As a side note: the 'few notch' controllers on the MP54s would not have been provided for even a vacuum-tube version of motor control, as relatively stepless control of gate turn-on or turn-off could have been made with little more than a potentiometer.  I think this would still be a bit jerky at low speed as the gated on time necessary to produce motion would be much less than full-wave, but certainly better than the alternative as fitted!  Of course getting equipment so modified to MU with 'standards' would be interesting at best (!) and if you can figure out a way to do it with 1940s technology I'd be fascinated to hear how you'd do it.

[tree68]

Overmod

While I can't tell you how to do it, the 'theory' is to have just enough set that power reduction between low notches (rather than to an 'idle' notch) causes the final deceleration.

I do this as well.  Platform is 5 MPH, so creeping in anyhow.  First service about a car or so out, and if it comes down too much, add power.  Every day is different.  

Of course, that's our "local" four cars.  In the fall, with Polar and 12 cars, a first service brings you down to zero really fast.  And the "landings" there have to be spot on.