On Most great western engines they do not have steam brake they only have Vaccum brakes, to create a "Brake" the Large ejetor is operated and draws air out of the system, over time the this needs recharging to bring it back to 25"hg, when shunting
As a fireman i have fired a manor and a 4141, when the loco has clouped up to the train the driver create a brake, thats the large ejector, when the loco is on the move at a 15mph the large ejector is shut off and the mechancal Vacuum pump takes over, before the train comes into the station the large ejector is operated and keeps the 25"hg in the brake system. i thinking thats right if not, please correct me!
as for the locomotives i will find out!