Phil,

AB-1B air brakes do not provide for graduated release. The application of the filling piece with incorporated safety valve provides service limiting when the signal line is charged.

EBL

Eric I learn something every time.

Phil

Not trying to take this thread too far afield. I am happy to see an X-29 going to EBT, whether in the Express Car or Freight Boxcar configuration. As a side note on the AB-1B filler piece, they were found on Boxcar Troop Sleepers (and Kitchen Cars) and were generally retained when the cars were converted for Express Service after the war. I have the ones from our troop-sleeper/box express in my shed, when we upgraded from AB to ABD. Eric is correct about their function. By the way, the troop sleepers came with two complete AB brake sets - one for each end of the car.