WTB Clippard MJQC-B4B4

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Re: WTB Clippard MJQC-B4B4

Post by NP317 » Wed Nov 14, 2018 11:18 pm

This is a very interesting discussion on brake application delay.

When I was engineering tourist steam trains at Snoqualmie, WA and at Mt. Rainier Scenic RR in Elbe, WA,
our normal practice was to to make a 5 psi reduction on the 70 psi train line brakes when approaching a road crossing.
This preset the brakes on the passenger train (heavy weight vintage) so that any necessary application at the crossing would happen faster, with little delay.
A little brake drag while approaching roads was a safety practice.
I had several experiences where this prevented collisions with cars driven by stupid drivers.

I practice this on my own 1/8th scale steam trains with vacuum brakes. An old operating habit.
Food for thought.

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Re: WTB Clippard MJQC-B4B4

Post by BigDumbDinosaur » Thu Nov 15, 2018 12:44 am

ccvstmr wrote:
Wed Nov 14, 2018 10:48 pm
Straight air brakes are pretty much direct acting when using an air reservoir to store pressure.
Pretty much. None of our trains is long enough to see significant brake pipe propagation time, which is about 1.1 milliseconds per foot in standard atmospheric conditions (20° C at sea level). Restriction in the brake pipe and fittings will cause some lag in pressure rise toward the hind end of the train, producing some run-in. However, none of this should pose any kind of safety threat.
I'm an old guy. What's your excuse? ☻

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