Is it safe to say that the second air line that runs between coal cars is to operate the trap doors on the bottom of the cars to unload them?
Yes, but not all hoppers have air-operated doors.
The ones I have seen that do also have electrical contactors to trigger the doors to open. Air supplies the oomph, electricity activates it.
This is not to be confused with cars that are equipped with a straight-air/automatic retainer braking system (like DMIR and CP use/used). These cars also have a second set of hoses.
Greetings from Alberta
-an Articulate Malcontent
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