I've done some of that stuff. One afternoon, I shoved a freight
train over Newcastle with my 'hopper' without cutting off, or 'cutting
in'. Like you say, it could have been messy, but wasn't, he really
didn't take much shoving. I've had the Belle Ayr helps cut off on the
fly with the crew on the waycar, and no air cut in. Sometimes they weren't
even coupled, just pushing against closed knuckles.
If you helped another train on the road, it paid time or miles, whichever
was greater, with a minimum of two hours (25 miles). The time started
when you were notified by the Dispatcher that you would have to cut off to
shove them, and ended when your train was moving again. The miles were
counted from where you cut off to where you cut off the train you were
shoving, and back again.
In reference to the original question, I've
always read that with steam helpers, the helper would try to start the train
first, then the road engine would start pulling, though Karl would probably be
in a better position to comment on that. The principle was that the
Helper was 'bunching' up the slack, so that the Road engine didn't have to
start the whole train at once. The two Engineers would communicate by
whistle signals. The helper had the automatic brake valve cut out, with
what was commonly called the 'double heading cock'.....though the instructors
at BNU in St. Paul would loudly inform you that it was properly known as the
'brake pipe cut out cock' :>)
Mike