Can a Brake Van or Coach stop a runaway train?

[DiveController]

I was prompted to start a new thread arising from a comment on another thread regarding how effective a brake van might be in stopping a runaway train

 

A 20 or 30t van would not have had snowballs chance in hell of stopping a heavy train once the coupling broke and the train started to roll back down the 1:70? gullet.

 

Hopefully the brake van slowed it enough to limit the damage. How effective was a van in stopping a goods train?

Most locos would be 80-100 tons? So less weight on the brake van be it 10T, 20T or 30T. Did they work effectively on the flat and what was the stopping distance for a branch line goods versus a maximally loaded train, either in absolute terms or as some percentage of the stopping distance if stopped by the locomotive?

 

Gradients; I suspect that even a slight gradient would probably have increased the stopping distance significantly. So could the van stop the train at all beyond a certain gradient?

Were there gradients such as the gullet and longer gradients such as on the Derry road where a train would not have stopped at all with the brake van brakes fully applied until it hit the flat sections again?

[Mayner]

Don't ask me to do the math, but there are several stories of couplings breaking and loose coupled trains running away in McArnolds "Golden Years of the GNR" and David Smiths "Tales of the G&SWR (Scotland) & the Little Railways of South West Scotland. The usual cause was a coupler breaking as the loco suddenly took in the slack while climbing out of a dip at the bottom of a long grade. One of the guards main jobs was to apply the handbrake on the van to keep the couplers stretched out while going downhill and avoid this happening.

 

The usual procedure when this happened seems to have been for the loco crew to put on steam to get as far ahead of the runaway as possible in the hope the train would come to rest in the bottom of a dip.

 

On CIE there are well documented stories of brakes failing on Woolwich including the Cahir Disaster and a near miss on the Midland between Clonsilla& Liffey Junction a distance of 5 miles where the crew managed to stop the train using the tender and van hand brakes short of the Junction for the Liffey Branch otherwise it was next stop Holyhead! as they would have no chance of bringing a train under control on the Liffey Branch or Broadstone lines

Edited July 7, 2017 by Mayner

[Garfield]

Was the purpose of brake vans not so much to stop runaways as to keep tension in loose couplings to avoid any working loose and splitting the train?

[DiveController]

Was the purpose of brake vans not so much to stop runaways as to keep tension in loose couplings to avoid any working loose and splitting the train?

I think you're correct as John alludes to this above also. I had also forgotten that the tender had brake which is the only other braking mechanism that the crew effectively had any access to.