O/T: Sorry. A Train question.

[Toolguy]

Fourth is spelled forth in the 5th paragraph.

[andywander]

Wow .. that must have been written a while back. Everything is pretty much spot on except where he is
talking about applying the brakes by releasing air from the brake pipe and then going to lap to lock that in.
There may be a couple of yard switchers around that have that brake valve, but they haven't been used on
the road in decades.

Now they use a brake valve that you just set/reduce the air by pulling the brake handle and it laps so to speak
automatically and the air compressor does not disengage because it has to maintain that reduced pressure in
the brake pipe. If this new reduced pressure in the brake pipe is not maintained, it will leak down and the
brakes will continue to set harder.

Back in Pennsylvania coming down the horseshoe curve in Altoona, it was a pretty steep grade like 10 or 20 miles
long (can't remember). Anyways .. when we came out of the tunnel at the top and started down the hill you had
to set just the right amount of air. It was a matter of the train running away, or you having to have it in notch 8
(full throttle) to pull it down the hill.

Man .. the stories I could tell you.

What id the term "lap" in this context?

[Mike Amick]

On the old brake valves, When you moved the brake handle from its released position to the braking position, it takes
air out of the brake pipe triggering a valve on the cars to apply the brakes.

If you left the handle is this braking position, it would just drain all the air out of the brake pipe, so to prevent that,
you moved the handle to a position that was nether release nor application. It was just a spot that stopped the
reduction without releasing the brakes. This spot was the lap.

As I said in the earlier post ... the new brakes just automatically lap. You move the handle to put the brakes on
and the distance you move the handle determines how much air is removed from the brake pipe. On the other
system .. its how long you leave the handle in braking that determines the amount of air.