AWS and DVD brake applications

Starting with a bit of history, a class 47 loco, built dual braked in 1965 had the following specifications:

After an initial delay of 3 to 5 seconds it took a time of 12 to 15 seconds for the ATP to drop to 45 psi - the level of a full service application.

At any time the driver cancelled the AWS (or deadman's treadle?) then control was regained and the brakes could be released.

How does this compare with trains in service today?

Do some trains make an Emergency application rather than a Full Service application?

Do some trains need to stop dead before the AWS or DVD can be reset?

Is this different for AWS and DVD applications?

AWS train will come to a stand . DVD depends on the traction, some the brake can be recovered.
Also in both cases it will be an emergency brake application .
Hope this helps

darwins said:

Do some trains need to stop dead before the AWS or DVD can be reset?

Click to expand...

On some the train has to come to a stand for an emergency brake application. In some cases there us a time delay before it can be released - 321s were 2 mins when new, but reduced to 40 seconds later. On some units, 170s I believe, the emergency brake can be released at 5mph and under, but with such a heavy application the train will usually done to a stand before the brakes fully release.

I think that's what I remember reading in an old thread anyway!

185 wise...

DSD / DVD applies emergency brakes. Once reset brake release is regained without having to come to a stand, and almost immediately.

AWS/TPWS also emergency brake. Takes 60 seconds to reset but putting the brake controller into full service and placing the direction switch to OFF (this puts the emergency brakes on in it's own right but in this case they would already be on) and back into F, N or R will reset the system thus releasing brakes.

It would be very naughty if that was done though!

Units with the latest AWS/TPWS keeps the brakes applied until it has to be manually reset after 60 seconds. 'Keying out' or tripping MCBs will not allow the system to reset in the meantime and coming to a stand will be inevitable.

One does need to be careful on locomotives of 'modern' standards such as the Class 60, where the "Emergency" brake is not what AWS, TPWS and Vigilance act upon, this instead still empties the brake pipe, but via the levelling valves, where as the "Emergency" puts a sodding big hole in the brake pipe, the response times are somewhat different to say the least.