[lonewolf]

On a train if there is a break in an air line the brakes dynamite and lock on.
When a train leaves a bunch of cars on a siding the air brakes are locked on but also hand brakes are on.
When an engine comes to pick up the cars the first thing that is done is the air line from engine to cars is hooked up,then the hand brakes are released manually and then the engineer pumps up the system to release the air brakes.
The engine needs to pump them up to release them. When the engineer left he would have set the brakes but they bleed off over time ,that's why handbrakes are always applied when a train is going to sit for a while. When I worked for CP putting on handbrakes was just part of the procedure and was always done. As an example ,If we left a bunch of cars on a siding and I didn't put the handbrakes on and later the cars started to move ,no matter how far I would get written up ,fired or worse. Also the person who was to make sure I did it would face the same thing.