Showing posts with label Quebec train wreck. Show all posts
Showing posts with label Quebec train wreck. Show all posts

Wednesday, August 20, 2014

Westinghouse automatic air brakes

NPR reported on the Quebec crude oil train wreck of last year.  In that one, the single crewman running the train, pulled into a siding, left the locomotive running, and went off to catch 8 hours sleep at a motel.  While he was sleeping, the train rolled down hill of the siding, into town, derailed, and the crude oil catch fire burning down every building in town. 
   According to NPR,  the locomotive caught fire idling on the siding, the local fire department responded, shut the engine down, releasing the air brakes, which let the train get away. 
   That part is bogus.  Every car on a train has an air cylinder to apply the car brakes, and a tank of compressed air to drive the air cylinder.  Upon a signal from the locomotive, the car brakes go on, and stay on until signaled to release. 
   The signal is air pressure.  There is a long pipe, the trainline, running the length of the train, kept pressurized by an air compressor on the locomotive.  Those rubber hoses coupled between cars  carry the trainline from car to car right to the very end of the train.  The system is fail safe.  Safe means brakes applied.  Fail when talking about pipe means a leak or a blockage.  So the signal to apply the brakes is to lower the pressure in the trainline.  This is especially good in the case of train separation, some coupler fails and the train breaks in two.  In that case, the rubber hoses break, the air rushes out of the trainline and the brakes go on all up and down the length of the train.  That's safe. 
   So, no matter what those firemen did, shut down the locomotive, spray water on it,  what ever,  won't let the brakes off.   NPR got that part wrong.
   More likely, the locomotive engineer failed to set the air brakes before leaving the train to take some crew rest.  He probably wanted to save time in the morning.  It may take the locomotive half an hour to pump up a flat trainline.  A 100 car trainline needs a lot of air, and any cars needing air for their tanks will take it out of the trainline, slowing the pump up process.