Al--

OTTOMH before going to bed, here's a few features of the K and AB
systems.

Westinghouse "K1/K2 triple" air brake system on STMFC's--No emergency
feature. Brake reservoir, cylinder, and control valve were all in one
assembly. "KD" system separated the brake cylinder and air reservoir
for use on tank cars, hopper cars, etc.

Westinghouse "AB" brake system, introduced circa 1933--STMFC listers
can correct me on exact date. "Release insuring" feature to attempt
to mitigate slack action on long trains, emergency braking feature
increasing brake cylinder pressure by 10-15 pounds. Auxiliary
reservoir, with emergency reservoir attached containing 1.5 times
volume of air of aux. res. to provide extra air to increase brake
cylinder pressure in emergency application. Control valve and brake
cylinder are now separate items mounted on car. Brake cylinder can be
truck mounted ("Wabcopac" system, etc.). Control valve consists of
three discrete items--pipe bracket (that connects control valve to
brake pipe, retainer valve, brake cylinder, and emergency/auxiliary
reservoirs). Service and emergency portions are bolted onto pipe
bracket.

Derivatives of the "AB" system are still on use on freight cars today,
namely the "ABD", "ABDW", and "ABDX" systems.

For more info, you might want to give this a read--

http://www.sdrm.org/faqs/brakes.html

Steve Lucas.