Could someone please explain the difference between standard braking and dynamic braking, how they operate, and when is one braking system used over the other?
The Air brake or trainline brake works like most brakes by resistance of the friction between brake pads and the brakeing surface. In the case of railroads it’s usualy the wheel surface itself although many cars in passenger service have disk brakes like your car. The brakes are activated by air pressure from the brake cylinder on each car that are linked to all the brake pads by the rods and levers of the brake linkage. All the cars are hooked up to a common air line that runs the length of the train.
Now the air brake system does not work directly on the air pressure. The air line is hooked to a “triple valve” that reads the air pressure to controll how much air goes to the brake cylinder. It is a complex system with it good points and bad. For a excellent explaination on how they work check out Al Krugs site:
http://www.alkrug.vcn.com/rrfacts/brakes.htm
One of the drawbacks of the air brake system used on almost all freight trains is that you can’t make a partial brake reduction. It’s all or nothing and to release takes time to recover the air. This recovery time can be measured many minuets on a long train and in real cold weather. If you are going downhill and make too big of an application and need to do a release, by the time you recover the air it could be WAY too late and the train will have accelerated to a point of no return and you have a runnaway. Now you can start a release and then make another application before the air recovers, but only once or twice or a few times, depending on how deep the applications. But on most steep grades you only have once or twice to get it right. This is a very simple explaination and you should refer to the above link for a good understandable explaination.
Dynamic brakes are kind of like downshifting your car on a steep downhill grade. It causes drag through the drivetrain. Only in this case it’s an electrical drivetrain and the drag is cause electrically. A deisel-electric loco is an electric loco with an on boa
Thanx for the response! The info you supplied really helpful in understanding how this system functions.
No problem, but be sure to check out Al Krugs site. He has a lot of good explainations of a whole bunch of things that are easy to understand. And his essays are interesting reading too, especialy his one on running steam engine SP&S 700.
One more thing I forgot to mention, Independant brakes. The independant brake is an air brake that works only on the locomotives. These brakes are more like the ones in your car. Yuo can set and release these almost instantly and in graduated amounts. Unlike the train brakes the independants can be partially released. These brakes are used primarily in switching when the cars air lines may not be connected. You can not use the independant brakes while useing the dynamics.
There’s probably a better way to say this. Although you continue with an explanation, a “newby” reading this thread could get the idea that every brake application is an emergency application.
I didn’t mention emergency applications at all. I was trying to keep it simple. For a thourogh brake explaination refer to Al Krugs site
I realize you didn’t mention emergency applications. That’s why I made my point. The fact is that it is NOT all or nothing with air brakes. You CAN make partial applications. A “service application” is a partial application. The point that I think you were trying to make is a valid one: After a reduction it takes time to recover the air. But “all or nothing” in this context sounds like the only choice is to “big hole” the train every time. Al Krug’s terrific site doesn’t suggest anything like that.
HEY! 200 POSTS!
I didn’t say the application was all or nothing. I said the release is all or nothing. Please don’t put words in my mouth that I did not say.
This is what I said:
One of the drawbacks of the air brake system used on almost all freight trains is that you can’t make a partial brake reduction. It’s all or nothing and to release takes time to recover the air.
Sorry. I didn’t meant to come across as jumping to conclusions. But I did not put words in your mouth. The words that still stand out in your quote are these: “you can’t make a partial brake reduction. It’s all or nothing…” Your point about releasing the air is, as I mentioned, a good one. And I assumed that it was what you must’ve meant by “all or nothing.”
I was never trying to belittle you. Whenever my mistakes are pointed out to me (and I make plenty on these threads) I simply edit my post. When that opportunity wasn’t taken I made the point that “You CAN make partial applications. A ‘service application’ is a partial application.” And it is.
Chad, you’re among the top five most knowledgeable resour
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QUOTE: Originally posted by ValorStorm
Sorry. I didn’t meant to come across as jumping to conclusions. But I did not put words in your mouth. The words that still stand out in your quote are these: “you can’t make a partial brake reduction. It’s all or nothing…” Your point about releasing the air is, as I mentioned, a good one. And I assumed that it was what you must’ve meant by “all or nothing.”
I was never trying to belittle you. Whenever my mistakes are pointed out to me (and I make plenty on these threads) I simply edit my post. When that opportunity wasn’t taken I made the point that “You CAN make partial applications. A ‘service application’ is a partial application.” And it is
The first post on this thread was very interesting. I was wondering about Dynamic brakes. but why would they be removed on a loco? IC removed them on some of the SD40-2’s. Seems like air brakes have the drawback because of the recover time. I figured DB was preferred.
Well, Dynamic brakes are an added cost at purchase and add to the maintainance costs of locomotives so equiped. If you have a relativly flat railroad like the IC there is really no need for dynamics, although they would save wear and tear on brake pads.
I guess it does make sense than. Because many of IC’s SD40-2’s were purchased from BN and BN ordered them w/ DB but IC removed the DB on some of them.
A little correction here. You CAN, with limitations, use the independent while using dynamics.
Development of approximately 15-18 psi of independent brake cylinder pressure, dynamic braking will be reduced to that of a standard range dynamic brake or, depending on locomotive brake cylinder pressure switch design, will eliminate all dynamic braking completely.
I really abhor the use of words such as: CAN’T, NEVER, ALWAYS, etc. on these rail forums
They were removed for one simple reason. The IC was far too cheap to perform any necessary maintenance. Even today you’ll climb on a 150-car, 11,000 feet mainfast and the lead unit won’t have dynamics. Buried in the consist will be a unit with dynamics. As a note, all SD-40’s numbered below 6200 does not have dynamcis. Those numbered above 6200 are dynamic brake equiped. Dynamic braking IS the preferred method for slowing your train, on most progressive railroads that is.[;)]
Thanks for letting me know on the #'s. The IC was too cheap?[:O]
Yes! They were and continue to be.
Another common misconception. Take a look at a track profile of the IC from Carbondale, IL. to Fulton, KY. It’s as up and down as any you’ll find in the midwest. In fact, there’s a 28-mile stretch from MP311 to MP339.2 that has a 40-mph. restriction for freight and 45-50 mph. for Amtrak due to the number and degree of curvature.
The two types of dynamic brakes found on locomotives:
Standard Capacity: Can develop 10,000 lbs. of retarding force per axle. Standard range dynamic braking force normally fades below 10 MPH.
High-capacity (extended range) dynamic brakes: Can develop 13,500 lbs. of retarding force per axle. Extended range dynamic brakes maintains a high retarding force down to 6 MPH before fading.