My joking reference to "vacuum brakes" in my earlier post has (unbelievably) triggered some questions on how they worked. While I'm not a mechanical engineer, I'm generally familiar with how the systems worked on the U.S. railroads that used them in the 19th century, so I'll confine my answer to these. I would imagine that the more modern version used in Britain works on a similar principle, but I don't know this as a fact.
The simple answer is that air brakes work by blowing, while vacuum brakes suck. This may seem to be a really bad pun (come to think of it, it is a really bad pun) but, if you read on. you'll see it's essentially accurate.
Like the Westinghouse automatic air brake, a vacuum brake used a "train line" running the length of the train But there the similarity ended.
As I mentioned in my earlier post, the Westinghouse brake worked (and still works) by having each car carry its own air supply. It also uses a pressurized "train line" both to supply air to the cars and to signal the cars to apply their brakes. A reduction in the air pressure in the "train line" relative to the pressure in the air tanks causes a control valve on each car (called a "triple valve" in early days) to reduce the pressure in the car's air tank until it equalizes with the reduced train line pressure. The air that's exhausted from a car's air tank during this process "blows" into the car's brake cylinder(s), applying the brakes. But, although the Westinghouse brake works based on pressure differentials, it doesn't create anything approaching a vacuum. For example, assuming the train line is set to carry 70 psi pressure when brakes are released (low by modern standards, but common in the 19th century), a 20 psi reduction in train line pressure will cause a fairly heavy brake application, but won't even come close to creating a vaccum (in my example, there would would still be 50 psi in the train line). And even if the train line is completely exhausted (as in a "pull apart" or an emergency brake application), the train line won't drop below atmospheric pressure.
In a vacuum brake system, the cars didn't carry their own air supply. Rather each car was equipped with a device like a bellows, sometimes called a "pot", which was connected to the train line and the brake rigging. Unlike the Westinghouse system, however, the "train line" in a vacuum brake system wasn't pressurized. Rather, when the brakes were in release, the train line, and the "pots" connected to it, were at atmospheric pressure. When the engineer wanted to apply the brakes, he admitted steam to a device on the locomotive called an "ejector". I don't understand all of the engineering, but the device effectively "sucked" air out of the train line, creating a relative vacuum. This caused the "pots" on each car to collapse proportionately to the amount of air that had been sucked from the train line. As they collapsed, they pulled on the brake rigging, thus applying the brakes. In other words, it's entirely accurate to say that vacuum brakes "suck".
Vacuum braking systems apparently worked tolerably well on short trains (like passenger trains), but didn't work so well on longer freight trains, due to difficulties in maintaining the vacuum over the length of the train. Also, given the way it worked, the 19th century version was probably not "fail safe". In other words, if the train line were broken (like when a train pulled apart), the brakes would become inoperative, since it would be impossible to create the vacuum on either side of the break. With the Westinghouse system, a break in the train line would cause the brakes to apply rather than fail. I would imagine that the modern versions of the vacuum brake system have dealt with this problem in some manner, but I'm not sure how.
Matt -
First, in case no one has mentioned it yet (or I missed it), check out the article on "Dynamic Braking - Power for the (Down) Grade" by Robert S. McGonigal (Date: May 1, 2006) in the Trains ABCs of Railroading section at:
http://www.trains.com/trn/default.aspx?c=a&id=197
Gordon Lightfoot - I heard him perform Canadian Railroad Trilogy in concert about 20 years ago, and bought a tape cassette with it included. A little Internet research in the last few minutes for "Lightfoot" and "Canadian Railroad Trilogy" found many compilations of the lyrics, as well as a Wikipedia article - which says that it has also been performed by John Mellencamp and George Hamilton IV - at: http://en.wikipedia.org/wiki/Canadian_Railroad_Trilogy
That article also says that it is on his 1975 compilation album, "Gord's Gold" - see: http://en.wikipedia.org/wiki/Gord%27s_Gold
It's available as a CD from Amazon (where else, but certainly among others) for under $9 - see:
http://www.amazon.com/Gords-Gold-Gordon-Lightfoot/dp/B000002KCG
Hope this is helpful.
- Paul North.
Well its good to have you here, good first question. I am glad the pros here got to answer before I tried, but hopefully you got the info you needed. I was just explaining to a friend the other day why a train can't suddenly stop in a second for something on the tracks. As the air conditioning company says, It's hard to stop a Trane (train in this case).
Hello again all,
A few things I wanted to bring up:
-Thanks again to everyone who took time to write out explanations to my question. I'm now either more knowlegable on the subject than ever before, or so confused I don't know what to ask next (I kid... definately the former).
- Paul, I really enjoyed reading about your working philosophy, and I must say the more I re-read what you wrote, the more I find myself agreeing with you. You had made mention of Gordon Lightfoot's Canadian Railroad Triliogy; any ideas where I could find this?
- Finally, I'd like to second the idea of a discussion on vacuum braking. Coming in, I was vaguely familiar with independant, train and dynamic, but I've never heard of vacuum braking. Any insights would be great!
Thanks again,
Matt
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
Edblysard said, yesterday afternoon:
"Train brakes set up from the head end first, and apply backwards down the train at the speed of sound." [my emphasis]
How can the application travel at the speed of sound? air does not travel that fast. A wave is set up by the reduction in pressure, and the magnitude of the wave is proportional to the amount of reduction. This wave travels at the speed of sound, and its magnitude determines how much air the control valve on each car will admit into the car’s brake cylinders.
Ed also said, "If a train breaks in two, the brakes will set up from the separation, both parts applying away from the separation." And the reduction in pressure when the air hoses part is the same as that when the engineer "big holes it"–from the maximum pressure in the system to atmospheric pressure; the full pressure in the car tanks, within the limits imposed by the system, is applied to the brakes, to stop the train as quickly as possible.
Falcon48, would you be interested in giving a brief discussion of vacuum braking, especially as it is used in Great Britain? On a new thread?
Johnny
bubbajustin Welcome to the fomer forum bro'! The dynamic brakes are used like this. The engineer moves the combined power handle,the throttle, into DNBK. SETUP. He let's it set there for 30 seconds or so then he will push the handle into B1, 2, 3, etc. The dynamic brakes take power from the traction motor's and basiclly turns them into big resistor's , thus the term dynamic brakes. the energy is then exausted out of the side of the locomotive as heat.
Welcome to the fomer forum bro'! The dynamic brakes are used like this. The engineer moves the combined power handle,the throttle, into DNBK. SETUP. He let's it set there for 30 seconds or so then he will push the handle into B1, 2, 3, etc. The dynamic brakes take power from the traction motor's and basiclly turns them into big resistor's , thus the term dynamic brakes. the energy is then exausted out of the side of the locomotive as heat.
A slight correction here, as well.
The traction motors are turned into generators, not resistors. The electricity they generate is then applied to large resistor (more or less heating elements), the heat from which is then discharged from the locomotive by a fan.
You can experience a form of that by turning on your headlights while your car is idling. As you do, you'll hear the engine load down a bit because of the larger load on the alternator.
Those who have used the generators that used to be popular for powering headlights on bicycles should be very familiar with the principal.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Amen trains are of course awesome!!!!!!!!!
This is trucking...
The road to to success is always under construction. _____________________________________________________________________________ When the going gets tough, the tough use duct tape.
bubbajustin Welcome to the fomer forum bro'! The dynamic brakes are used like this. The engineer moves the combined power handle,the throttle, into DNBK. SETUP. He let's it set there for 30 seconds or so then he will push the handle into B1, 2, 3, etc. The dynamic breaks take power from the traction motor's and basiclly turns them into big resistor's , thus the term dynamic breaks. the energy is then exausted out of the side of the locomotive as heat. The train break's are used to supplemen't the dynamic break's sometimes most often though to stop. The air break or automatic break handle in the loco' is moved forward causing air to flow though the air hoses on the entire train then the air enter's the air resivour's pushing the break shoe aginst the wheel thus slowing the train. sometimes you can run out of air. That's bad especially on a grade because you can't apply any form of air break! The locomotive break is basically the same thing and is operated the same way as the train break. But it only work's on the locomotve and it can operate indapendant of the other break's. Hope you will contact me if you have any other queston's about railroading, mackjs01@sbcglobal.net . Enjoy the forum, and enjoy being a railfan buddy!!!
Welcome to the fomer forum bro'! The dynamic brakes are used like this. The engineer moves the combined power handle,the throttle, into DNBK. SETUP. He let's it set there for 30 seconds or so then he will push the handle into B1, 2, 3, etc. The dynamic breaks take power from the traction motor's and basiclly turns them into big resistor's , thus the term dynamic breaks. the energy is then exausted out of the side of the locomotive as heat.
The train break's are used to supplemen't the dynamic break's sometimes most often though to stop. The air break or automatic break handle in the loco' is moved forward causing air to flow though the air hoses on the entire train then the air enter's the air resivour's pushing the break shoe aginst the wheel thus slowing the train. sometimes you can run out of air. That's bad especially on a grade because you can't apply any form of air break!
The locomotive break is basically the same thing and is operated the same way as the train break. But it only work's on the locomotve and it can operate indapendant of the other break's. Hope you will contact me if you have any other queston's about railroading, mackjs01@sbcglobal.net . Enjoy the forum, and enjoy being a railfan buddy!!!
So, how does reducing the air pressure in the train line apply the brakes? Here's how it works. Each car on the train has a "control valve" which senses to the resulting pressure differential between the air tank on the car and the reduced pressure in the train line. The valve then exhausts air from the tank into the car's air brake cylinder until the tank pressure equalizes with the reduced train line pressure. The greater the reduction in train line pressure, the greater the brake application (there's a limit to this, but there's no reason to get into it here). To release the brakes, the engineer increases the pressure in the train line. The control valve on each car then senses the pressure inbalance and exhausts the air the brake cylinder to the atmosphere, releasing the brakes.
The way you can run out of air with this system (for example, when descending a heavy grade) is by making multiple brake applications and releases without giving the air tanks in the cars time to fully recharge between applications (the tanks get recharged from the train line). Each brake application in this scenario will have less force. It's kinda like repeately flushing your toilet before the tank has time to fully refill.
This system may seem a little Rube Goldbergish, but is has some important advantages over a system where the locomotive directly applies the train brakes from its own air supply. In the first place, it's relatively "fail safe". If, for example, the train pulls apart, the train line exhausts and the brakes apply. In a system where the brake air comes directly frm the locomotive, the brakes on both segments of the train would fail. Secondly, it doesn't require the locomotive to immediately supply all of the air needed for a brake application, which would make operation of long trains impossible. Instead, small changes in the volume of air in the train line control the air supply carried on the individual cars. I haven't gone into all of the bells and whistles of the system, but these are the basics that railroads have used for over a century.
Railroads are just now begining to deploy "electronic" train brake systems in freight train use, which will eventually supercede the system I've described (although probably not completely during my lifetime). The main difference is that, in an electronic system, the "control valves" on each car are operated electronically by the engineer through a cable or telemetry (cable seems to be preferred), rather than by changes in train line pressure. The "train line" then is relegated to being solely an air supply for the air tanks on the cars. This allows the engineer to operate the brakes more quickly and much more precisely than is possible with the older technology.
Probably more than you wanted to know. But you'll be happy to know that I avoided the urge to describe the workings of vacuum brakes (which, at one time, were considered an alternative to air brakes).
coborn35 CShaveRRI'll resist the urge to put out the Welcome Matt. Welcome, nonetheless! Am I the only one who got that? Haha
CShaveRRI'll resist the urge to put out the Welcome Matt. Welcome, nonetheless!
Am I the only one who got that? Haha
Mechanical Department "No no that's fine shove that 20 pound set all around the yard... those shoes aren't hell and a half to change..."
The Missabe Road: Safety First
Matt--and all others new to the forums--we have a great opportunity to learn quickly from other people who share our interests in railroading. When I became interested in rail transport, I was limited to the encyclopedias at school, and a book given me by an uncle, The Modern Modern Wonder Book of Trains and Railroading, and such passenger timetables that I was able to pick up. The summer before the 10th grade, I planned a trip by rail from Charlotte, N. C., to New Orleans to Chattanooga and back to Charlotte, which my brother who was just older than I and I took. The next spring, I discovered Trains, and my rail horizon was expanded greatly. Since then, I have subscribed to various railroad magazines at one time or another (my subscription to Trains has never been allowed to lapse), and have learned much from them. Also, for twelve years, I had a great deal of interaction with railroad men--agents, trainmen, and enginemen, sometimes even working with them--despite never being employed by a railroad.
The internet has opened a new door on information and, to a certain extent, we are limited only by our knowledge as to where to look for what we want to know.
Matt & Forum-ers ,
As Matt stated in his "first post" this is my first time posting in this forum . As an intro , they call me The Travler . And , I have been around the R.R. all of my life . Learned my numbers and alphabet off the sides of freight cars that ran along THE SOUTHERN RAILWAY . Have been getting PAID to be around the railroad for the past 35 years (6 years 11 months & 28 days till retirement) .
As for your questions Matt , they have been answered pertty well by those on the forum already . The only point that I could possibly add-on to those responses would be that as with anything on the railroad , SKILL in operating the various brakes is what makes the differance . Sort of seperates the "OPERATOR of LOCOMOTIVE" from a "LOCOMOTIVE ENGINEER" .
I am very glad to see a younger person take an interest in RAILROADING , ya'll be safe out there . And if the Master Railroader up there brings US back safely from our run , I'll be back on-line later this week . THINKIN' & BEIN' SAFE The Travler.
The Conrail Kid Hi all, Thanks everyone for the kind words of welcome, and the links to additional information; I'll certainly have some reading material tonight. I'm excited to join the board! Although I don't know very much yet, I'm starting to scratch the surface and it's very exciting to start studying something I've been interested in for so long. There's a mystique about railroading that can't be explained or defined, it has to be lived and experienced and I thank you all for imparting your knowledge and being patient with a newbie.
Thanks everyone for the kind words of welcome, and the links to additional information; I'll certainly have some reading material tonight.
I'm excited to join the board! Although I don't know very much yet, I'm starting to scratch the surface and it's very exciting to start studying something I've been interested in for so long. There's a mystique about railroading that can't be explained or defined, it has to be lived and experienced and I thank you all for imparting your knowledge and being patient with a newbie.
You betcha, Matt.
David P. Morgan - the late, great Editor of trains - once observed that the railroads were the great civilizing and modernizing force in what we would now call the "Third World" - Africa, India, Asia, etc. They introduced mechanical systems , organizations, the Industrial Age, etc. to what were then regarded as primitive peoples.
Someone else on here has as their signature or "tag' line, "If you want to find history, follow the train !" .
For my part, I've been in, seen, or read about just about every aspect of the human condition in, on, or around the railroad, including the arts (except maybe dance). Have you heard Gordon Lightfoot's "Canadian Railroad Trilogy" yet ?
So as a working philosophy, I've come to the conclusion and believe that "It's all on the railroad; and that if it's not there, it's probably not worth much" (at least not to me), and I don't have much use for it otherwise. Some exceptions, sure, but I've found that if I want to know about a place - country or city - start by learning about their railroads (or trolleys, etc. if they don't have any rail lines). If nothing else, it provides a frame of reference for inquiry and study. For example: Did you know that there were - and still is at least 1 ! - railroads on Hawaii ?
Anyhow, welcome again.
Hi all,
Here there Matt...
Independent brake...read as locomotive brake, and only locomotive brake, acts independently of the train brake, is used to apply brakes only on the locomotive, and when kicking or switching cars, and the lag time to recharge the train brake line is a hindrance, or when moving "light" locomotives around.
Works off a separate brake handle from the train brake.
Train brake, just what the name implies, an air brake system on the entire train.
When used, it also sets the independent brake as well as the brakes on the cars...when doing a brake pipe reduction on the train brake, (braking the entire train) you can "bail off" or release the independent brake while still applying the train brake.
This prevents the wheels on the locomotive from locking up and sliding because the locomotive is getting "pushed" by the weight of the train behind...it also allows for stretch braking where you use the weight of the cars and their brakes to bring the train to a halt with all the slack "stretched" out.
Train brakes set up from the head end first, and apply backwards down the train at the speed of sound.
If a train breaks in two, the brakes will set up from the separation, both parts applying away from the separation.
Dynamic brakes...a system that switches the DC traction motors from using electricity to generating electricity.
When the dynamic brakes set up, the weight of the train rolling down a grade will spin the wheels of the locomotive, creating an electrical current from the traction motors, which is dissipated through the dynamic brake grid, which is just like heating element in your electric oven or range, only much larger.
Using Back Electromagnetic Force, this creates electromagnetic resistance in the traction motors, making them hard to spin, which in turn retards the speed of the locomotive.
You use this when there is a need for a constant braking force, like taking a train down grade...as was noted, it appears the same as putting your standard shift car in a low gear and using the engine compression as a braking force down hill...again, see Mr. Krug's site for a lot more detailed info.
23 17 46 11
Welcome, Matt. As Paul, Zardoz (if he signed his posts, I’d have said Jim), Carl, and Larry have said, come in, ask questions, share your knowledge. We all enjoy sharing what we know and learning more about the best form of transportation ever.
Matt - welcome aboard. Al Krug's essay on the subject is probably the best you'll find. Once you're through that, come on back and ask away!
One very popular thread a couple years ago was entitled "Stupid Question Thread." It was anything but - a lot of good information was shared there and we're all a little smarter because of it.
Paul_D_North_Jr Hey Matt ! First - welcome to the Forum ! Train brake is for the entire train - including the locomotive(s). Independent brake is for the locomotives only - and as the name implies, can be and is operated independently of the train brakes. The independent can be applied when the train brake is off, and it can also be released ("bailed off" is a common term) while the rest of the train brakes are left applied. EDIT - See Al Krug's page linked below for the more correct answer.
Hey Matt !
First - welcome to the Forum !
Train brake is for the entire train - including the locomotive(s).
Independent brake is for the locomotives only - and as the name implies, can be and is operated independently of the train brakes. The independent can be applied when the train brake is off, and it can also be released ("bailed off" is a common term) while the rest of the train brakes are left applied. EDIT - See Al Krug's page linked below for the more correct answer.
Matt: Welcome!
Paul, the part you crossed out is not incorrect; you just phrased it differently than Krug did.
Dynamic brakes are on the locomotives only, and essentially use the traction motors as brakes - crudely and simply, kind of like slowing a stick-shift car or truck by downshifting it, or maybe with a "JAKE Brake "engine exhaust brake.
For more of the whys and wherefores, wait for the rest of the replies !
In the meantime, I'd highly recommend that you check and and study Al Krug's "Railroad Facts and Figures" webpage at:
http://www.alkrug.vcn.com/rrfacts/rrfacts.htm
Most of your questions are covered at the end of his page named "How RR Air Brakes Work - Part I ", or "Freight Train Air Brakes of North America", at:
http://www.alkrug.vcn.com/rrfacts/brakes.htm#dynamic
Enjoy !
Look forward to seeing you here more often !
Greetings all,
A brief history of me before my first post: My name is Matt, I'm 24 years old, and I live in Columbus, OH (go Bucks!). I've been facisnated with trains my whole life; my earliest memories are watching Conrail trains go by in my cousin's back yard for countless hours.
I don't know much about the details of railroading, but am hungry to learn.
I've been lurking on these forums for a while now, and have finally decided to introduce myself. Though I've never worked in the industry, I've always been a big fan of trains (watching, reading, and yes, even enjoying Extreme Trains). However, as I am just starting to really get into the nitty-gritty of learning of trains and railroads, a number of questions have come up. I've gathered that the vast majority of posts here are well-thought, intelligent insights and would love to contribute to the discussions.
One of the nagging questions I've had: what is the difference between the train brake, independant brake, and dynamic break? In what situation would each of these be used?
Thanks in advance,
P.S - I have looked over the ABC's of railroading on this site (which has been immensely helpful). If you have any other sites to recommend, I'm all ears!
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