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Re: SMEE

Posted by Jeff H. on Sat Apr 22 01:13:50 2006, in response to Re: SMEE, posted by Brighton Private on Fri Apr 21 11:33:45 2006.

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So if I understand correctly, it differs from conventional air brake systems in that it uses electronic
signals, rather than variations in the air-line running through the train, to activate the brakes? Or are the
electronic signals used only to equalize braking effort, parallel to the more conventional approach?


To call it "electronic" is stretching it, as there is nothing more
than electromechanical logic involved.

SMEE is an electro-pneumatic overlay system, similar to EP braking
on other rail cars. There are two trainline wires, Apply and Release,
which control service braking. Thers is ALSO a trainline air
pipe called the Straight Air Pipe (SAP). The two signals, electric
and pneumatic, are synchronized. In the event of failure of
either system, the other one will operate without any further
effort on the motorman's part. However, when operating purely
pneumatically, the brakes will apply and release more sluggishly;
it is almost like running a freight train.

Note that "SMEE" deals purely with the braking. It so happens
that all NYC SMEE subway cars also came with dynamic braking,
but it is possible to have a SMEE system with purely friction
braking. Dynamic Braking != Electropneumatic Braking.

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