4-15. A-1 CHARGING CUTOFF PILOT VALVE (cont)
When a break-in-two occurs, the A-i charging cutoff pilotvalve functions as follows:
Brake pipe pressure drops faster from chamber D than it can from chamber E via the choke. The
resultant pressure differential across the actuating piston causes it and its spool valve to be moved
upward against spring loading.
Main reservoir air is connected through the actuating piston spool valve to chamber C at the outer face
of the cutoff piston and also to port 9 and the power cutoff (PCO) switch and sanding reservoir.
With chamber B beneath the cutoff spool valve normally exhausted, the presence of main reservoir
pressure in chamber C at the outer face of the cutoff piston will cause the piston and its spool valve to
be forced inward to its lowest position, where chamber A beneath the cutoff piston head is exhausted.
Main reservoir air is connected through the cutoff piston spool valve 35 and past the unseated cutoff
check valve to port 53 and to the brake pipe cutoff valve in the 26-C brake valve.
Air pressure in the 90-cubic-inch (1475 cc) volume reservoir, port 11, and chamber E beneath the
actuating chamber continue to reduce to zero through the piston choke and port 1 to brake pipe