on Sun Apr 23 03:36:09 2006, in response to Re: SMEE, posted by Jeff H. on Sun Apr 23 02:20:25 2006.
Well, I have problems with nomenclature but my understanding is that the 'straight air' trainline is the supplier of 120-150 compressed air for all pneumatic systems which includes pneumatic suspension. 'Brake Pipe' is trainline pneumatic brake pressure used for service braking. IF straight air pressure drops below 90 PSI dsue to a major air leak (like car seperation) or B3C conductor valve is activated and pressure is evacuated to atmosphere, magnet valve drops on the Pneumatic Operating Unit (Wabco/NY Air/Knorr brake panel) and applies brakes in emergency service. Check your duplex gauge!
On a parked Redbird in FULL SERVICE, the duplex gauge should read 150 PSI straight air and 42 or so PSI brake pipe. Straight air is the pneumatic source and brake pipe is the pressure applied to brake load. I beg to differ........I teach this stuff. In a parked condition connected to shop power, the M7 TOD will read about 147 PSI straight air and 0 PSI brakes...automatic mechanical parking brakes.