Passenger/Freight Trainline Pressures Question...

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#1
It is a fact that passenger trains have higher brake pipe pressures than freight trains (for safety reasons nonetheless). However, I have a few questions:

1) Considering the pressure differential (which is 20 PSI) between freight and passenger trains, how are/were freight locomotives able to run passenger trains on occasion (as I have read about in the past)?

2) With dual-service locomotives, which by default have the "passenger" trainline pressure as the maximum, how are they able to handle freight trains with lower trainline pressure?
 

RCH

Been Nothin' Since Frisco
#2
The pressure setting is adjusted by the regulating valve (aka feed valve). On BNSF it's 90 for freight and 105 for passenger. You simply set the regulating valve to the desired pressure and then charge the train line. Also, the automatic brake valve cutout valve has to be put in Passenger, which allows for the brakes to be released when the brake valve is moved toward release rather than having to move the brake valve all the way to release.
 



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