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[Anonymous]

QUOTE: Originally posted by dingoix

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.

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.[;)]

[Anonymous]

Thanks for letting me know on the #'s. The IC was too cheap?[:O]

[Anonymous]

QUOTE: Originally posted by dingoix

Thanks for letting me know on the #'s. The IC was too cheap?[:O]

Yes! They were and continue to be.

[Anonymous]

QUOTE: Originally posted by chad thomas

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.

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.

[Anonymous]

QUOTE: Originally posted by nawalins

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 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.

[chad thomas]

Here is a Dynamic brake effort chart from Al Krugs site

[chad thomas]

QUOTE: Originally posted by jg greenwood

QUOTE: Originally posted by chad thomas

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.

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.

Well Ok, Mabee the IC isn't flat. But compared to western grades it is relativly flat.

[Anonymous]

anything that doesn't require helpers is flat.

[Anonymous]

QUOTE: Originally posted by dingoix

anything that doesn't require helpers is flat.

You obviously need to read Krug's site. It all depends on HP, adhesion, and so on. A 0.5% grade can be a relatively steep grade.

[Ham549]

Why the heck have such a complex system? Have break shoes connected to springs that pu***hem on the wheels. Use air pressure to pull the brakes off the wheels. As long as the system has pressure the brake shoes will be held off the wheels but when you start losing pressure the springs start pushing the air brakes back on. You can almost eliminate any possibility of runaways and you can make all the adjustments you want including letting up on the breaks without going into full release.

[chad thomas]

You mean like tractor / trailer parking brakes? That could work with very short trains, but with a long train it wouldn't. Even if you ignore all the leaky air connections, think about the volume of air involved. With the system used there is only a small volume of air needed to pass to the atmosphere to send the controll pressure to the tripple valves. Each car provides it's own air to the brake cylinder for an application (at a ratio of 1:2.5). Plus with a truck style system you could not have an emergency application as all the air would have to pass through the air pipe in the lead unit instead of each car useing it's own air to charge the brake cylinder. With the current system an emergency application travels down the train at 800 feet per second. With a truck style brake it would take way too long to apply the brakes and would not be capable of an emergency application.

[chad thomas]

As far as eliminating runnaways with truck style brakes....
Say you have a 100 car train going down a steep grade and you have insufficient air at the end of the train. Those brakes would try to do more then there share of brakeing. They would overheat and loose there friction against the brakeing surface, That would require more brakeing effort. Reducing the pressure (and applying more brake force) would make the problem worse on the cars that have already overheated there brake shoes and you would have more cars heading in that direction. Basicly you would have a snowball effect that would burn up brakes from the rear forward faster and faster till you have no hope of recovering....RUNNAWAY.

[Anonymous]

QUOTE: A 0.5% grade can be a relatively steep grade

Yes. Even a 0.1% can be steep if the locomotives are fully loaded or overloaded. But I'm quite sure IC used enough engines so the trains don't stall going upgrade.

[emd_SD_60]

QUOTE: Originally posted by jg greenwood

QUOTE: Originally posted by dingoix

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.

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.[;)]

That reminds me, i got a train this afternoon in town with a CN Dash 9 and a 6100-series IC (now in CN colors) as the power. And guess what was leading? The SD40-2.[V] Plus the train was a pretty good long one as well.

[emd_SD_60]

QUOTE: Originally posted by chad thomas

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.

That was also the same principle at MoPac also. Until their 1976 order of SD40-2C's (c for coal), none of the locomotives had them, after that they were equipped with DB.