[N&W] Train Air Brakes

[nw-mailing-list at nwhs.org]

I'd like to commend Gordon Hamilton for his excellent article on train air 
brakes in the latest edition of "The Arrow".  I was definitely a 
"preschooler" and now feel as if I've graduated to "lower elementary".  I'd 
recommend the article to every one.  I do have some questions which will 
either show my understanding or lack there of.

First question-If a great drop in the trainline pressure will cause an 
emergency application of brakes, what prevents this from happening when a 
car is purposely cut loose from the train?  EG-humping?

Second question-Am I correct in thinking that with no air pressure in an 
individual car's brake system there will be no brakes unless the hand brake 
is set?  EG-a single car sitting in a yard for an extended period of time 
that has lost all pressure.  I am comparing this to  truck air brakes which 
will engage if air pressure is below a certain level.

Thanks in advance and please go easy on me. I've not yet graduated to the 
"higher level of learning" when it comes to train air brakes;)

Dave Moorehead
Milford, OH