Railroaders' Nostalgia > Trainline Brake Pipe Pressure 80 psi vs 90 psi stopping distance?

For those technical experts out there:

A hypothetical situations here where a 100 car loaded coal train:

Train 1: ABTH rules require the trainline be charged to 80 psi prior to and during movement

Train 2: ABTH rules reuire the trainline be charged to the "typical" 90 psi prior to and during movement:


The hypothetical locomotive engineer applies the emergency brakes and all other variables equal, which train stops in a shorter distance? If so, by what distance? Finally, is there any academic or technical research/ work on this topic? Does 10 psi make a difference or will the car control valve and railcar main and emergency portions compensate for the difference and make the 80 psi vs 90 psi moot?

Thanks

Burt

A 90 lb. brake pipe fully charged will result in 66 lbs brake cylinder pressure in full service.  An emergency application with the same fully charged 90 lb trainline and reservoirs will result in a 77 lb brake cylinder pressure.

The 90 lb trainline will stop in less distance than an 80 lb, how much I don't know.
The answer is simple, car's brake valves can't make something out of nothing.
The 110 lb brake pipe on passenger trains results in a still shorter stopping distance.
G

The coal train with the 90 pound trainline should stop quicker because of the higher charge in the emergency reservoir.  In 1973 I left a railroad running 80 pound freight trainlines (SCL) to work on a railroad with only 75 pound trainlines (Southern).  Even with that variation, I felt a difference during undesired emergencies.  As for quantified tests, the Southern gave me an outside sourced brake and train handling manual when I came over in 73.  It had those tests using differing trainline settings in the book with accompanying graphs.  It was mostly boring reading, and the book is packed away somewhere.  On my district of the Southern, we had one freight that didn't carry a 75 pound trainline.  It was a 96 car unit coal train of identical high sided aluminum gons.  It ran a 100 pound trainline.  It was a 60 mph Radio train with Locotrol 103 distributed power.  For several months each on a couple of occasions, it was my regular job.  It had a 100 pound trainline because Locotrol 103 perforned better with 100 pounds, and just before the train got to me it had to come down Southern's famous 4.7% grade - Saluda Hill.  Fortunately I only had to "shoot" the air  on that train once.  On that one occasions the train (nicknamed the Silver Bell) "sat down" impressively.  Just my experience and impressions - I thought Southern was too stingy back then with the usual 75 pound feedvalve setting.  It's 90 on the district now.  Factors like tons per operative brake have went up, but still a higher trainline gave you better chances.



Edited 1 time(s). Last edit at 05/19/23 20:00 by Notch7.

I'll agree with Ex SP Conductor. I don't know how much quicker either. Good explanation of equalization pressures. I hadn't thought about them in 45 years. I had forgotten what the exact numbers were.

Sam

Years ago, I was piloting a SSW detour from Newton to Emporia, the engineer had originally been on the Rock Island until they folded. He said The Rock used 80 psi on the brake pipe, but on Santa Fe we used 90. We argued about it for a while, but he said 80 was a better deal than 90, because more leaks showed up at 90, than at 80. And there was less gradient from front to back, meaning more uniform pressure from front to back, and because of that braking might be slight better in the rear portion of the train, than if at 90. I don't know if he was right or not, it made sense to him.

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