Imagine this scenario, I'm driving a class 47 and coaches, or class 40 and tankers down an incline. Perhaps westbound out of Standedge. It's steep enough that I accelerate when coasting, so I need some brake force to stay within the permitted speeds. Would real world driving practice allow using just the locomotive brakes to give a gentle braking performance and hopefully maintain steady speed? As opposed to using the trains brakes which tend to provide too much force, so need to be continually backed-off and re-applied? Is that a valid technique or are loco brakes only intended for when running light?
Yes, at my operator the instruction is train brake only, even when running light. It followed a SPAD when the Driver of a light loco was using the loco brake, and misjudged the braking due to the loco brake having a different feel to it, which he wasn’t used to.
Both loco and train air brakes are friction based, that means that finding a sweet spot of application where it just maintains speed is actually something that you specifically want to avoid at all cost. Because such brakes will quickly overheat and that leads to even complete destruction of the brakes. The correct way to brake freight trains with air on longer descends is saw-tooth braking where you overbrake a lot, and then let the train coast to gain speed again while cooling the brakes in process. Loco brake is primarily meant to hold the train on flat (it releases immediately and you can start moving without waiting for train brake) and when shunting light or with few (2-3) wagons at low speeds.
I have used the loco brake on NTP for fine control of speed as I always find the train brake more aggressive than it ought to be in an initial or slight application. And there is precedent in the real world. Back in the loco hauled days on Waterloo to Exeter, the Class 50’s got through their brake blocks very quickly. This was mainly because the drivers were using the straight air brake rather than the train brake in many instances to “feather” the speed on the many challenging gradients west of Salisbury. It was not unusual for the WR Traction Controller to get a call from his oppo at Waterloo that 50xxx was “one journey” to Exeter for brake blocks. As the locos were diagrammed on a strict in and out basis with around 50 minute turnaround time that presented a huge logistical problem. Exeter Depot became quite adept at reshoeing Class 50’s but even then sometimes they couldn’t, resulting in a 60 MPH DCWA pool Class 50 having to be requisitioned for the Up working to Waterloo!
It was the 4 letter code for the Engineering Class 50 sector pool, common phrase in the Control at the time when something failed around Exeter, “Nick a DCWA”.
It was an artificial speed restriction applied to reduce wear and tear, given the maximum speed of most infrastructure trains was 60 MPH and back then more likely Class 7 at 45 MPH. There is little doubt when they did head off to Waterloo or at least Salisbury from Exeter that sign in the cab was probably treated with a degree of interpretation!
A cynic might suggest that an additional reason for implementing the speed restriction was to discourage the passenger sector from nicking them quite so often.
