my understanding is the the nominal brake ration (NBR) defines the maximum brake force for rolling stock as 10% of the car weight (yes, it would be different for empty and loaded)
is 10% correct as the maximum brake force of the independent brake on the locomotive?
greg - Philadelphia & Reading / Reading
Are you inquiring about the applied force at the shoe against the wheel tread?
I have several pages of foundation brake gear in this album:
https://www.flickr.com/photos/gmpullman/albums/72157708812136901/with/50146849412/
Westinghouse_foundation_0003 by Edmund, on Flickr
Or are you interested in including the wheel-to-rail friction? Addressed here (and additional pages found in the album):
Westinghouse_foundation_0006 by Edmund, on Flickr
Westinghouse_foundation_0007 by Edmund, on Flickr
The example above results in a 20% coefficient of friction. The coefficient of adhesion is addressed here: (below)
Westinghouse_foundation_0009 by Edmund, on Flickr
Many of the variables have to be taken into consideration.
A locomotive will pretty much act like a loaded freight car. Weather the brake cylinder pressure is applied using the independent or automatic brake application has no bearing. Brake cylinder pressure will result in the same force.
"Generally" the locomotive brakes will be "bailed off" to prevent wheel slip and flat spots as the train brakes are applied.
More here.
Good Luck, Ed
thanks once again, Ed
i'll look thru the material you posted
as i tried to explain, i'm trying to figure out if there is a typical value for the max brake force as a % of loco weight, like it is for rolling stock, the NBR
Things may have changed in the days since I worked, but...
For engines with cast iron brake shoes (generally 2 brake shoes per wheel), independent cylinder pressure was 45lbs.
For engines with composition shoes (1 brake shoe per wheel), 72lbs.
The engines with cast iron shoes just about always had better brakes, particularly for switching.
Some of those engines with composition shoes could barely stop themselves.
I never had any trouble with composition shoes when there were two shoes per wheel. The locomotives with only one shoe per wheel did not stop well.
Mark Vinski
Here's the thing: the figures for cars already presuppose solid wheels. I suspect much of the discussion regarding diesel locomotives (and newer electrics) would involve the same. You can brake these until they turn bright blue and expect reasonable safety.
That's not at all the case for steam locomotives or power with separate tires. The effect is amplified if heating due to driver brakes is limited and more dependence is placed on leading and trailing trucks.
A great deal of the braking effort to slow down the great mass of, say, a modern 4-8-4 has to be provided by a trailing consist. There are videos of 3751 on test that show rakes of spine flats or other lightweight intermodal equipment used for this purpose.
Although I still can't find a shred of evidence that it was 'legal' in the ETTs, when test speeds of GG1s in Metroliner service began exceeding 110mph it became very clear that Amfleet consists could not and did not do their fair share of decelerating those heavy locomotives... and the required tread braking started driver tires coming loose. I assure you this is NEVER a good thing operationally, and a much larger factor of safety than that provided for one-piece forged or cast wheels, including multiwear down on the wear limit, ought to be provided for any such power...