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Posted by tracksionmotor on Sat Apr 22 22:57:11 2006, in response to Re: SMEE, posted by R32 3545 on Sat Apr 22 21:54:44 2006.

One air pipe is trainline...'straight air'...meaning all operational compressors maintain full air pressure for all cars (130 to 150 PSI.)
The other airpipe is 'brakepipe' which is also trainline. While the entire consist depends upon SMEE controls for braking and propulsion control for all cars, trainline brakepipe attempts to insure brake pressure equalisation for all cars. IF a car encountered SMEE brake control failure, common brakepipe trainline would continue to operate that specific cars brakes. Brakepipe is the braking pressure...0 PSI for full release,11 PSI for minimum brake, 42 PSI for maximum brake (full service) and 49 PSI for Brake in Emergency (varies by car specifications.)

Now for an answer for what is not a 'dumb question.' SMEE is electrical control so if all cars had air compressors...two hoses would not be needed BUT SMEE is also a safety redundant system in passenger rail...one hose carrys air pressure and the other controls application of brakes. IF an accident occured where the straight air hose broke or the emergency valve was activated, the air pressure would drop rapidly and trainset would Brake In Emergency powered by air resevoirs...redundant safety system.

FREIGHT is not SMEE...it has two hoses and no electrical connections.
One hose, straight air, provides air pressure. Each car has it's own reserve air resevoir. The other hose is brake pipe...what pressure contained controls all the brakes of all cars. All CARS, whether passenger rail or freight, must maintain at least 90 pounds of air pressure all the time...cut the hose and all cars Brake In Emergency. Getting back to freight, their air brakes are under spring pressure that requires maximum air pressure for no braking and zero pressure for full braking...opposite of SMEE. If a freight car has a major leak or hose cut or accident of straight air pressure, BIE. IF the brake pipe hose is cut in opeation, maximum braking is applied. Freight cars have no redundant system like passenger rail.

Sorry for being too tekky....this is a lot of materiel to cover in a few minutes. To break this down in a nutshell, SMEE cars with independent and compressors and resevoirs have two air pipes for redundancy to be safe. RRCI Peter


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