Thank you Dr Zarkoff for the technical bits of the valves, that makes sense now.



>> Once you'd brought the speed down to a D/B holding speed?

>You either keep trains speed to track speed or stop.

Maybe you guys did, with the luxury of sg equipment.

Not so with 325 max amps D/B rated EMD G-12 and 6SL brake; on 2% the Matamau grade with 530 tons of 4-wheeled 17tonners(often overloaded as well). If you went over the top at 50kmh track speed there you were never going to hold that lot and pull it down to the 30kmh speed restriction on the Piripiri Viaduct(Trestle) even with the 45kmh reverse curves to help on the approach. Those Fert traffic wagons had poor braking and often worn Triples with leaking across the face and thence undesired releasing on that wagon.
Whilst Loco assistant (firing) for various new Drivers on that job, I got a healthy understanding of what "she's all out" meant. :) I also got into the habit of placing Do Not Reload cards on any leakers while the Driver and Guard did the Terminal test before the homebound run.
Only the newer locos(and the Main Trunk Electrics) could hold full loads on grade(which we didn't have there, at the time).

>I don't know of any arrangement like this on a US RR, which should not be taken to mean none ever >existed. However, timed signals are/were quite common on rapid transit operations (NYC, Boston, >Chicago, etc.).


Saluda comes to mind, with the runaway Siding at the base of grade; read about that in a Trains mag. yonks ago.

regards

Chris
in New Zealand